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History of laptops
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Alan Kay with his 1972 "Dynabook" prototype (photo: 5 November 2008 in Mountain View, California)
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The history of laptops describes the efforts in the 1970s and 1980s to build small, portable personal computers that combine the components, inputs, outputs and capabilities of a desktop computer in a small chassis. Before laptop/notebook computers were technically feasible, similar ideas had been proposed, most notably Alan Kay's Dynabook concept, developed at Xerox PARC in the early 1970s. One of the first reasonably portable computers was the Xerox NoteTaker, again developed at Xerox PARC, in 1976. However, only 10 prototypes were built.
Contents
1 Portal R2E CCMC
2 Osborne 1
3 Bondwell 2
4 Compaq Portable
5 Epson HX-20
6 Grid Compass
7 Dulmont Magnum/Kookaburra
8 Ampere
9 Tandy Model 100
10 Sharp and Gavilan
11 Kyotronic 85
12 Commodore SX-64
13 Kaypro 2000
14 IBM PC Convertible
15 Toshiba T1100, T1000, and T1200
16 US Air Force
17 Hewlett-Packard Vectra Portable CS
18 Cambridge Z88
19 Compaq SLT/286
20 NEC UltraLite
21 Apple
21.1 Macintosh Portable
21.2 Powerbook
22 IBM RS/6000 N40
23 Windows 95 operating system
24 Intel Pentium processor
25 Improved technology
26 Netbooks
27 Smartbooks
28 See also
29 References
30 External links
31 Further reading
Portal R2E CCMC[edit]
R2E CCMC Portal laptop
The portable micro computer the “Portal" of the French company R2E Micral CCMC officially appeared in September 1980 at the Sicob show in Paris. The Portal was a portable microcomputer designed and marketed by the studies and developments department of the French firm R2E Micral in 1980 at the request of the company CCMC specializing in payroll and accounting. It was based on an Intel 8085 processor, 8-bit, clocked at 2 MHz. It was equipped with a central 64K byte Ram, a keyboard with 58 alpha numeric keys and 11 numeric keys (separate blocks), a 32-character screen, a floppy disk: capacity = 140 000 characters, of a thermal printer: speed = 28 characters / second, an asynchronous channel, a synchronous channel, a 220 V power supply. Designed for an operating temperature of 15–35 ° C, it weighed 12 kg and its dimensions were 45 × 45 × 15 cm. It provided total mobility. Its operating system was Prologue.
Osborne 1[edit]
An opened Osborne 1 computer, ready for use. The keyboard sits on the inside of the lid.
The Osborne 1 is considered the first true mobile computer by most historians. Adam Osborne founded Osborne Computer and formed the Osborne 1 in 1981. The Osborne 1 had a five-inch screen, incorporating a modem port, two 5 1/4 floppy drives, a big collection of bundled software applications, and a battery pack. The computer company was a failure and did not last for very long. Although it was large and heavy compared to today's laptops, with a tiny 5" CRT monitor, it had a near-revolutionary impact on business, as professionals were able to take their computer and data with them for the first time. This and other "luggables" were inspired by what was probably the first portable computer, the Xerox NoteTaker. The Osborne was about the size of a portable sewing machine, and could be carried on commercial aircraft. The Osborne 1 weighed close to 11 kg and was priced at $1795.
Bondwell 2[edit]
Although it wasn't released until 1985, well after the decline of CP/M as a major operating system, the Bondwell 2 is one of only a handful of CP/M laptops. It used a Z-80 CPU running at 4 MHz, had 64 KBs of RAM, and a 3.5" floppy disk drive built in, which was unusual for CP/M laptops. The flip-up LCD display's resolution was 640x200 pixels. Bondwell 2 also included MicroPro's complete line of CP/M software, including WordStar. The Bondwell 2 was capable of displaying bitmapped graphics. The price of the Bondwell 2 was listed at $995.
Compaq Portable[edit]
The Compaq Portable was the first portable computer created in 1982 which one of the first 100% IBM PC compatible systems. The first shipment was in March 1983 and was priced at $2,995. The Compaq Portable folded up into a luggable case the size of a portable sewing machine. The third model of this development, Compaq Portable II, featured high resolution graphics on its tube display. It was the first portable computer ready to be used on the shop floor, and for CAD and diagram display. It established Compaq as a major brand on the market.
Epson HX-20[edit]
Epson HX-20 (1981)
Epson L3s (~1990?)
Another significant machine announced in 1981, although first sold widely in 1983, was the Epson HX-20. A simple handheld computer, it featured a full-transit 68-key keyboard, rechargeable nickel-cadmium batteries, a small (120×32-pixel) dot-matrix LCD with 4 lines of text, 20 characters per line text mode, a 24 column dot matrix printer, a Microsoft BASIC interpreter, and 16 KB of RAM (expandable to 32 KB). Through at least the late 1980s Epson continued to release laptops such as the L3s.
Grid Compass[edit]
Main article: Grid Compass
The first laptop in the modern form was the Grid Compass 1101, designed by Bill Moggridge in 1979–80, and released in 1983. Enclosed in a magnesium case, it introduced the now familiar clamshell design, in which the flat display folded shut against the keyboard. The computer could be run from batteries, and was equipped with a 320×200-pixel electroluminescent display and 384 kilobyte bubble memory. It was not IBM-compatible, and its high price (US$8,000–10,000) limited it to specialized applications. However, it was used heavily by the U.S. military, and by NASA on the Space Shuttle during the 1980s. The GRiD's manufacturer subsequently earned significant returns on its patent rights as its innovations became commonplace. GRiD Systems Corp. was later bought by the Tandy (now RadioShack) Corporation.
Dulmont Magnum/Kookaburra[edit]
Main article: Dulmont Magnum
Another contender for the first true laptop was the Dulmont Magnum, designed Barry Wilkinson and Terry Crews Engineering Manager at Dulmison in 1982 and released in Australia in 1983 It included an 80×8 display in a lid that closed against the keyboard. It was based on the MS-DOS operating system and applications stored in ROM (A:) and also supported removable modules in expansion slots (B: and C:) that could be custom programmed EPROM or standard word processing and spreadsheet applications. However, the Magnum had no nonvolatile memory, but could suspend and retain memory in RAM, including a RAM Disk (D:). A separate expansion box provided dual 5.25-inch floppy or 10 MB hard disk storage. Dulmont was eventually taken over by Time Office Computers, who marketed the Magnum internationally in 16 and 25 line LCD versions, and also introduced the brandname Kookaburra to emphasize its Australian origins.
Ampere[edit]
The Ampere,[1] a laptop with a sleek clamshell design by Ryu Oosake, was made in 1983. It offered a MC68008 microprocessor dedicated to running an APL interpreter residing in ROM. It was released as the Ampere WS-1.[2]
Tandy Model 100[edit]
The TRS-80 Model 100 was an early portable computer introduced in 1983. It was one of the first notebook-style computers, featuring a keyboard and LCD, battery-powered, in a package roughly the size and shape of a notepad or a large book.
It was made by Kyocera, and originally sold in Japan as the Kyotronic 85. Although a slow seller for Kyocera, the rights to the machine were purchased by Tandy Corporation, and the computer was sold through Radio Shack stores in the United States and Canada as well as affiliated dealers in other countries, becoming one of the company's most popular models, with over 6,000,000 units sold worldwide. The Olivetti M-10 and the NEC PC-8201 and PC-8300 were also built on the same Kyocera platform.
Sharp and Gavilan[edit]
Two other noteworthy early laptops were the Sharp PC-5000 and the Gavilan SC, announced in 1983 but first sold in 1984. The Gavilan was notably the first computer to be marketed as a "laptop". It was also equipped with a pioneering touchpad-like pointing device, installed on a panel above the keyboard. Like the GRiD Compass, the Gavilan and the Sharp were housed in clamshell cases, but they were partly IBM-compatible, although primarily running their own system software. Both had LCDs, and could connect to optional external printers. The Dulmont Magnum, launched internationally in 1984, was an Australian portable similar in layout to the Gavilan, which used the Intel 80186 processor.[3]
Kyotronic 85[edit]
The year 1983 also saw the launch of what was probably the biggest-selling early laptop, the Kyocera Kyotronic 85. Owing much to the design of the previous Epson HX-20, and although at first a slow seller in Japan, it was quickly licensed by Tandy Corporation, Olivetti, and NEC, who recognised its potential and marketed it respectively as the TRS-80 Model 100 line (or Tandy 100), Olivetti M-10, and NEC PC-8201.[4] The machines ran on standard AA batteries. The Tandy's built-in programs, including a BASIC interpreter, a text editor, and a terminal program, were supplied by Microsoft, and was written in part by Bill Gates himself. The computer was not a clamshell, but provided a tiltable 8 line × 40-character LCD screen above a full-travel keyboard. With its internal modem, it was a highly portable communications terminal. Due to its portability, good battery life (and ease of replacement), reliability (it had no moving parts), and low price (as little as US$300), the model was highly regarded, becoming a favorite among journalists. It weighed less than 2 kg with dimensions of 30×21.5×4.5 centimeters (12×8½×1¾ in). Initial specifications included 8 kilobytes of RAM (expandable to 24 KB) and a 3 MHz processor. The machine was in fact about the size of a paper notebook, but the term had yet to come into use and it was generally described as a "portable" computer.
Commodore SX-64[edit]
The Commodore SX-64, also known as the Executive 64, or VIC-64 in Europe, was a portable, briefcase or suitcase-size "luggable" version of the popular Commodore 64 home computer, and was the first full-color portable computer.[5]
The SX-64 featured a built-in five-inch composite monitor and a built-in 1541 floppy drive. It weighed 20 pounds. The machine was carried by its sturdy handle, which doubled as an adjustable stand. It was announced in January 1983 and released a year later, at $995 USD.[6]
Kaypro 2000[edit]
Possibly the first commercial IBM-compatible laptop was the Kaypro 2000, introduced in 1985. With its brushed aluminum clamshell case, it was remarkably similar in design to modern laptops. It featured a 25 line by 80 character LCD, a detachable keyboard, and a pop-up 90 mm (3.5-inch) floppy drive.
IBM PC Convertible[edit]
Also among the first commercial IBM-compatible laptops was the IBM PC Convertible, introduced in 1986. It had a CGA-compatible LCD and 2 floppy drives. It weighed 13 pounds (5.9 kg).
Toshiba T1100, T1000, and T1200[edit]
Toshiba launched the Toshiba T1100 in 1985, and has subsequently described it as "the world's first mass-market laptop computer".[7] It did not have a hard drive, and ran entirely from floppy disks. The CPU was a 4.77 MHz Intel 80C88, a variation of the popular Intel 8088, and the display was a monochrome, text-only 640x200 LCD. It was followed in 1987 by the T1000 and T1200. Although limited floppy-based DOS machines, with the operating system stored in ROM, the Toshiba models were small and light enough to be carried in a backpack, and could be run from lead-acid batteries. They also introduced the now-standard "resume" feature to DOS-based machines: the computer could be paused between sessions without having to be restarted each time.
US Air Force[edit]
The first laptops successful on a large scale came in large part due to a Request For Proposal (RFP) by the U.S. Air Force in 1987. This contract would eventually lead to the purchase of over 200,000 laptops. Competition to supply this contract was fiercely contested and the major PC companies of the time; IBM Corporation, To shins, Compaq, NEC, and Zenith Data Systems (ZDS), rushed to develop laptops in an attempt to win this deal. ZDS, which had earlier won a landmark deal with the IRS for its Z-171, was awarded this contract for its SupersPort series. The SupersPort series was originally launched with an Intel 8086 processor, dual floppy disk drives, a backlit, blue and white STN LCD screen, and a NiCd battery pack. Later models featured an Intel 80286 processor and a 20 MB hard disk drive. On the strength of this deal, ZDS became the world's largest laptop supplier in 1987 and 1988. ZDS partnered with Tottori Sanyo in the design and manufacturing of these laptops. This relationship is notable because it was the first deal between a major brand and an Asian original equipment manufacturer.
Hewlett-Packard Vectra Portable CS[edit]
In 1987, HP released a portable version of their Vectra CS computer.[8] It had the classic laptop configuration (keyboard and monitor closes up clam-shell style in order to carry), however, it was very heavy and fairly large. It had a full-size keyboard (with separate numeric keypad) and a large amber LCD screen. While it was offered with dual 3.5-inch floppy disk drives, the most common configuration was a 20 MB hard drive and a single floppy drive. It was one of the first machines with a 1.44 MB density 3.5-inch disk drive.
Cambridge Z88[edit]
Another notable computer was the Cambridge Z88, designed by Clive Sinclair, introduced in 1988. About the size of an A4 sheet of paper as well, it ran on standard batteries, and contained basic spreadsheet, word processing, and communications programs. It anticipated the future miniaturization of the portable computer, and as a ROM-based machine with a small display, can – like the TRS-80 Model 100 – also be seen as a forerunner of the personal digital assistant.
Compaq SLT/286[edit]
By the end of the 1980s, laptop computers were becoming popular among business people. The COMPAQ SLT/286 debuted in October 1988, being the first battery-powered laptop to support an internal hard disk drive and a VGA compatible LCD screen. It weighed 14 lbs.[9]
NEC UltraLite[edit]
Main article: NEC UltraLite
The NEC UltraLite, released in mid-1989, was perhaps the first "notebook" computer, weighing just 2 kg (4.4 lbs). In lieu of a floppy or hard drive, it contained a 2 megabyte RAM drive, but this reduced its utility as well as its size. Although portable computers with clamshell LCD screens already existed before it, the Ultralite was the first computer in a notebook form-factor. It was significantly smaller than all portable computers that came before it. People can actually carry-it like a notebook and fold its clamshell LCD like a book cover over the rest of its body.
Apple[edit]
Macintosh Portable[edit]
The Macintosh Portable, Apple's first attempt at a battery-powered computer
The first Apple Computer machine designed to be used on the go was the 1989 Macintosh Portable (although an LCD screen had been an option for the transportable Apple IIc in 1984). Unlike the Compaq LTE laptop released earlier in the year the Macintosh Portable was actually a "luggable" not a laptop, but the Mac Portable was praised for its clear active matrix display and long battery life, but was a poor seller due to its bulk. In the absence of a true Apple laptop, several compatible machines such as the Outbound Laptop were available for Mac users; however, for copyright reasons, the user had to supply a set of Mac ROMs, which usually meant having to buy a new or used Macintosh as well.
Powerbook[edit]
The Apple PowerBook series, introduced in October 1991, pioneered changes that are now de facto standards on laptops, such as room for a palm rest, and the inclusion of a pointing device (a trackball). The following year, IBM released its ThinkPad 700C, featuring a similar design (though with a distinctive red TrackPoint pointing device).
Later PowerBooks featured optional color displays (PowerBook 165c, 1993), and first true touchpad (PowerBook 500 series, 1994), first 16-bit stereo audio, and first built-in Ethernet network adapter (PowerBook 500, 1994).
IBM RS/6000 N40[edit]
In 1994, IBM released the RS/6000 N40 laptop based on a PowerPC microprocessor running the AIX operating system, a variant of UNIX. It was manufactured by Tadpole Technology (now Tadpole Computer), who also manufactured laptops based on SPARC and Alpha microprocessors, the SPARCbook and ALPHAbook lines, respectively.
Windows 95 operating system[edit]
The summer of 1995 was a significant turning point in the history of notebook computing. In August of that year Microsoft introduced Windows 95. It was the first time that Microsoft had implemented the advanced power management specification with control in the operating system. Prior to this point each brand used custom BIOS, drivers and in some cases, ASICs, to optimize the battery life of its machines. This move by Microsoft was controversial in the eyes of notebook designers because it greatly reduced their ability to innovate; however, it did serve its role in simplifying and stabilizing certain aspects of notebook design.
Intel Pentium processor[edit]
Windows 95 also ushered in the importance of the CD-ROM drive in mobile computing, and initiated the shift to the Intel Pentium processor as the base platform for notebooks. The Gateway Solo was the first notebook introduced with a Pentium processor and a CD-ROM. Also featuring a removable hard disk drive and floppy drive, the Solo was the first three-spindle (optical, floppy, and hard disk drive) notebook computer, and was extremely successful within the consumer segment of the market. In roughly the same time period the Dell Latitude, Toshiba Satellite, and IBM ThinkPad were reaching great success with Pentium-based two-spindle (hard disk and floppy disk drive) systems directed toward the corporate market.
Improved technology[edit]
A 1997 Micron laptop
Early laptop displays were so primitive that PC Magazine in 1986 published an article discussing them with the headline "Is It On Yet?". It said of the accompanying montage of nine portable computers, "Pictured at the right are two screens and seven elongated smudges". The article stated that "LCD screens still look to many observers like Etch-a-Sketch toys, or gray chalk on a dirty blackboard", and predicted that until displays improved, "laptops will continue to be a niche rather than a mainstream direction".[10] As technology improved during the 1990s, the usefulness and popularity of laptops increased. Correspondingly prices went down. Several developments specific to laptops were quickly implemented, improving usability and performance. Among them were:
Improved battery technology. The heavy lead-acid batteries were replaced with lighter and more efficient technologies, first nickel cadmium or NiCd, then nickel metal hydride (NiMH) and then Lithium-ion battery and lithium polymer.
Power-saving processors. While laptops in 1991 were limited to the 80286 processor because of the energy demands of the more powerful 80386, the introduction of the Intel 386SL processor, designed for the specific power needs of laptops, marked the point at which laptop needs were included in CPU design. The 386SL integrated a 386SX core with a memory controller and this was paired with an I/O chip to create the SL chipset. It was more integrated than any previous solution although its cost was higher. It was heavily adopted by the major notebook brands of the time. Intel followed this with the 486SL chipset which used the same architecture. However, Intel had to abandon this design approach as it introduced its Pentium series. Early versions of the mobile Pentium required TAB mounting (also used in LCD manufacturing) and this initially limited the number of companies capable of supplying notebooks. However, Intel did eventually migrate to more standard chip packaging. One limitation of notebooks has always been the difficulty in upgrading the processor which is a common attribute of desktops. Intel did try to solve this problem with the introduction of the MMC for mobile computing. The MMC was a standard module upon which the CPU and external cache memory could sit. It gave the notebook buyer the potential to upgrade his CPU at a later date, eased the manufacturing process somewhat, and was also used in some cases to skirt U.S. import duties as the CPU could be added to the chassis after it arrived in the U.S. Intel stuck with MMC for a few generations but ultimately could not maintain the appropriate speed and data integrity to the memory subsystem through the MMC connector. A more specialized power saving CPU variant for laptops is the PowerPC 603 family.[11] Derived from IBM's 601 series for laptops (while the 604 branch was for desktops), it found itself used on many low end Apple desktops before it was wildly used in laptops, starting with PowerBook models 5300, 2400, 500 upgrades. What started out as a laptop processor was eventually used across all platforms in its follow up, the PowerPC 750 AKA G3.
Improved Liquid-crystal displays, in particular active-matrix TFT (Thin-film transistor) LCD technology. Early laptop screens were black and white, blue and white, or grayscale, STN (Super Twist Nematic) passive-matrix LCDs prone to heavy shadows, ghosting and blurry movement (some portable computer screens were sharper monochrome plasma displays, but these drew too much current to be powered by batteries). Color STN screens were used for some time although their viewing quality was poor. By about 1991, two new color LCD technologies hit the mainstream market in a big way; Dual STN and TFT. The Dual STN screens solved many of the viewing problems of STN at a very affordable price and the TFT screens offered excellent viewing quality although initially at a steep price. DSTN continued to offer a significant cost advantage over TFT until the mid-90s before the cost delta dropped to the point that DSTN was no longer used in notebooks. Improvements in production technology meant displays became larger, sharper, had higher native resolutions, faster response time and could display color with great accuracy, making them an acceptable substitute for a traditional CRT monitor.
OLPC XO-1 laptop in Ebook-Mode.
Improved storage technology. Early laptops and portables had only floppy disk drives. As thin, high-capacity hard disk drives with higher reliability and shock resistance and lower power consumption became available, users could store their work on laptop computers and take it with them. The 3.5" HDD was created initially as a response to the needs of notebook designers that needed smaller, lower power consumption products. With continuing pressure to shrink the notebook size even further, the 2.5" HDD was introduced. One Laptop Per Child (OLPC) and other new laptops use Flash RAM (non volatile, non mechanical memory device) instead of the mechanical hard disk.
Improved connectivity. Internal modems and standard serial, parallel, and PS/2 ports on IBM PC-compatible laptops made it easier to work away from home; the addition of network adapters and, from 1997, USB, as well as, from 1999, Wi-Fi, made laptops as easy to use with peripherals as a desktop computer. Many newer laptops are also available with built-in 3G Broadband wireless modems.
Other peripherals may include:
an integrated video camera for video communication
a fingerprint sensor for implementing a restriction of access to a sensitive data or the computer itself.
Netbooks[edit]
Main article: Netbook
In June 2007, Asus announced the Eee PC 701 to be released in October, a small lightweight x86 Celeron-M ULV 353 powered laptop with 4 GB SDHC disk and a 7-inch screen.[12] Despite previous attempts to launch small lightweight computers such as ultra-portable PC, the Eee was the first success story largely due to its low cost, small size, low weight and versatility. The term 'Netbook' was later dubbed by Intel. Asus then extended the Eee line with models with features such as a 9-inch screen and other brands, including Acer, MSI and Dell followed suit with similar devices, often built on the fledgling low-power Intel Atom processor architecture.
Smartbooks[edit]
Main article: Smartbook
In 2009, Qualcomm introduced a new term "smartbook", which stands for a hybrid device between smartphone and laptop.[13]
See also[edit]
Timeline of portable computers
Portal laptop computer
References[edit]
Jump up ^ Bob Armstrong, http://cosy.com/language/cosyhard/cosyhard.htm
Jump up ^ Japanese PCs (1984) (13:13), Computer Chronicles
Jump up ^ "OLD-COMPUTERS.COM : The Museum". Retrieved 11 August 2015.
Jump up ^ See TRS-80 Model 100 / 102 at old-computers.com
Jump up ^ "Commodore SX-64 Portable". Retrieved 11 August 2015.
Jump up ^ "Commodore SX-64 portable computer". Retrieved 11 August 2015.
Jump up ^ "World's First Laptop PC". Toshiba Science Museum. Retrieved 21 May 2017.
Jump up ^ "Business Desktops/Calcs". HP Computer Museum. Retrieved 7 April 2014.
Jump up ^ Lewis, Peter H. (23 October 1988). "THE EXECUTIVE COMPUTER; Compaq Finally Makes a Laptop". The New York Times.
Jump up ^ Somerson, Paul (July 1986). "Is It On Yet?". PC. pp. 122–123. Retrieved 9 January 2015.
Jump up ^ "IBM Power Systems archived white papers". Retrieved 11 August 2015.
Jump up ^ Paul Miller. "Asus' new Eee PC 701 joins the laptop-lite fray with a bang". Engadget. AOL. Retrieved 11 August 2015.
Jump up ^ Hachman, Mark (1 June 2009). "Qualcomm Shows Off Snapdragon Smartbooks". PC Magazine.
External links[edit]
"Laptops, 360 degree models", Russian Vintage Laptop Museum (museum)
Further reading[edit]
Wilson, James E. (2006). Vintage Laptop Computers: First Decade: 1980–89. Outskirts Press. p. 132. ISBN 978-1-59800-489-2.
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Heat transfer
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Simulation of thermal convection in the Earth's mantle. Colors span from red and green to blue with decreasing temperatures. A hot, less-dense lower boundary layer sends plumes of hot material upwards, and cold material from the top moves downwards.
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.
Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.
Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means.
Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.[1]
Contents
[hide]
1 Overview
2 Mechanisms
2.1 Advection
2.2 Conduction
2.3 Convection
2.3.1 Convection-cooling
2.4 Convection vs. conduction
2.5 Radiation
3 Phase transition
3.1 Boiling
3.2 Condensation
3.3 Melting
4 Modeling approaches
4.1 Climate models
4.2 Heat equation
4.3 Lumped system analysis
5 Engineering
5.1 Insulation, radiance and resistance
5.2 Devices
5.2.1 Heat exchangers
6 Applications
6.1 Architecture
6.2 Climate engineering
6.3 Greenhouse effect
6.4 Heat transfer in the human body
6.5 Cooling techniques
6.5.1 Evaporative cooling
6.5.2 Laser cooling
6.5.3 Magnetic cooling
6.5.4 Radiative cooling
6.6 Thermal energy storage
7 See also
8 References
9 External links
Overview[edit]
See also: Heat transfer physics
Earth's long wave thermal radiation intensity, from clouds, atmosphere and surface.
Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system. The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential, designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V). Joule is a unit to quantify energy, work, or the amount of heat.
Heat transfer is a process function (or path function), as opposed to functions of state; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process.
Thermodynamic and mechanical heat transfer is calculated with the heat transfer coefficient, the proportionality between the heat flux and the thermodynamic driving force for the flow of heat. Heat flux is a quantitative, vectorial representation of heat-flow through a surface.[2]
In engineering contexts, the term heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (Caloric) that can be transferred by various causes,[3] and that is also common in the language of laymen and everyday life.
The transport equations for thermal energy (Fourier's law), mechanical momentum (Newton's law for fluids), and mass transfer (Fick's laws of diffusion) are similar,[4][5] and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.[5]
Thermal engineering concerns the generation, use, conversion, and exchange of heat transfer. As such, heat transfer is involved in almost every sector of the economy.[6] Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
Mechanisms[edit]
The fundamental modes of heat transfer are:
Advection
Advection is the transport mechanism of a fluid from one location to another, and is dependent on motion and momentum of that fluid.
Conduction or diffusion
The transfer of energy between objects that are in physical contact. Thermal conductivity is the property of a material to conduct heat and evaluated primarily in terms of Fourier's Law for heat conduction.
Convection
The transfer of energy between an object and its environment, due to fluid motion. The average temperature is a reference for evaluating properties related to convective heat transfer.
Radiation
The transfer of energy by the emission of electromagnetic radiation.
Advection[edit]
By transferring matter, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another.[7] This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics.[citation needed] This can be described by the formula:
Q = v ρ c p Δ T {\displaystyle Q=v\rho c_{p}\Delta T}
where Q is heat flux (W/m²), ρ is density (kg/m³), c p {\displaystyle c_{p}} is heat capacity at constant pressure (J/kg·K), ΔT is the change in temperature (K), v {\displaystyle v} is velocity (m/s).
Conduction[edit]
Main article: Thermal conduction
On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact.[8] The process of heat transfer from one place to another place without the movement of particles is called conduction. Example: Heat transfer through Metal rods.[clarification needed] Steady state conduction (see Fourier's law) is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further.[9] In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out.[8]
Transient conduction (see Heat equation) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.[8]
Convection[edit]
Main article: Convection
The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by using a pump, fan or other mechanical means.
Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid.[10] Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming.[11] The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction.
Free, or natural, convection occurs when bulk fluid motions (streams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.[12]
Convection-cooling[edit]
See also: Nusselt number
Convective cooling is sometimes described as Newton's law of cooling:
The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings.
However, by definition, the validity of Newton's law of Cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients, and in some cases is strongly nonlinear. In these cases, Newton's law does not apply.
Convection vs. conduction[edit]
In a body of fluid that is heated from underneath its container, conduction and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy, while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On the other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong.
The Rayleigh number ( R a {\displaystyle Ra} ) is the product of the Grashof and Prandtl numbers. It is a measure which determines the relative strength of conduction and convection.[13]
R a = G r P r = g Δ ρ L 3 μ α = g β Δ T L 3 ν α {\displaystyle Ra=GrPr={\frac {g\Delta \rho L^{3}}{\mu \alpha }}={\frac {g\beta \Delta TL^{3}}{\nu \alpha }}}
where
g is acceleration due to gravity,
ρ is the density with Δ ρ {\displaystyle \Delta \rho } being the density difference between the lower and upper ends,
μ is the dynamic viscosity,
α is the Thermal diffusivity,
β is the volume thermal expansivity (sometimes denoted α elsewhere),
T is the temperature,
ν is the kinematic viscosity, and
L is characteristic length.
The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system.
The buoyancy force driving the convection is roughly g Δ ρ L 3 {\displaystyle g\Delta \rho L^{3}} , so the corresponding pressure is roughly g Δ ρ L {\displaystyle g\Delta \rho L} . In steady state, this is canceled by the shear stress due to viscosity, and therefore roughly equals μ V / L = μ / T c o n v {\displaystyle \mu V/L=\mu /T_{conv}} , where V is the typical fluid velocity due to convection and T c o n v {\displaystyle T_{conv}} the order of its timescale.[citation needed] The conduction timescale, on the other hand, is of the order of T c o n d = L 2 / α {\displaystyle T_{cond}=L^{2}/\alpha } .
Convection occurs when the Rayleigh number is above 1,000–2,000.
Radiation[edit]
Red-hot iron object, transferring heat to the surrounding environment through thermal radiation
Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.[1]
Thermal radiation is energy emitted by matter as electromagnetic waves, due to the pool of thermal energy in all matter with a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.[14]
Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface.
The Stefan-Boltzmann equation, which describes the rate of transfer of radiant energy, is as follows for an object in a vacuum :
Q = ϵ σ T 4 . {\displaystyle Q=\epsilon \sigma T^{4}.}
For radiative transfer between two objects, the equation is as follows:
Q = ϵ σ ( T a 4 − T b 4 ) , {\displaystyle Q=\epsilon \sigma (T_{a}^{4}-T_{b}^{4}),}
where Q is the heat flux, ε is the emissivity (unity for a black body), σ is the Stefan–Boltzmann constant, and T is the absolute temperature (in kelvins or degrees Rankine). Radiation is typically only important for very hot objects, or for objects with a large temperature difference.
Radiation from the sun, or solar radiation, can be harvested for heat and power.[15] Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation.[16] For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F).[citation needed]
Phase transition[edit]
Lightning is a highly visible form of energy transfer and is an example of plasma present at Earth's surface. Typically, lightning discharges 30,000 amperes at up to 100 million volts, and emits light, radio waves, X-rays and even gamma rays.[17] Plasma temperatures in lightning can approach 28,000 kelvins (27,726.85 °C) (49,940.33 °F) and electron densities may exceed 1024 m−3.
Phase transition or phase change, takes place in a thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water. The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation.
Phase transitions involve the four fundamental states of matter:
Solid – Deposition, freezing and solid to solid transformation.
Gas – Boiling / evaporation, recombination / deionization, and sublimation.
Liquid – Condensation and melting / fusion.
Plasma – Ionization.
Boiling[edit]
Nucleate boiling of water.
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid[18][19] and the liquid evaporates resulting in an abrupt change in vapor volume.
Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition.
At standard atmospheric pressure and low temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling, and is a very efficient heat transfer mechanism. At high bubble generation rates, the bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling, or DNB).
At similar standard atmospheric pressure and high temperatures, the hydrodynamically-quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low, but rise slowly with temperature. Any contact between fluid and the surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation"). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux, or CHF).
The Leidenfrost Effect demonstrates how nucleate boiling slows heat transfer due to gas bubbles on the heater's surface. As mentioned, gas-phase thermal conductivity is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier".
Condensation[edit]
Condensation occurs when a vapor is cooled and changes its phase to a liquid. During condensation, the latent heat of vaporization must be released. The amount of the heat is the same as that absorbed during vaporization at the same fluid pressure.[20]
There are several types of condensation:
Homogeneous condensation, as during a formation of fog.
Condensation in direct contact with subcooled liquid.
Condensation on direct contact with a cooling wall of a heat exchanger: This is the most common mode used in industry:
Filmwise condensation is when a liquid film is formed on the subcooled surface, and usually occurs when the liquid wets the surface.
Dropwise condensation is when liquid drops are formed on the subcooled surface, and usually occurs when the liquid does not wet the surface.
Dropwise condensation is difficult to sustain reliably; therefore, industrial equipment is normally designed to operate in filmwise condensation mode.
Melting[edit]
Ice melting
Melting is a thermal process that results in the phase transition of a substance from a solid to a liquid. The internal energy of a substance is increased, typically with heat or pressure, resulting in a rise of its temperature to the melting point, at which the ordering of ionic or molecular entities in the solid breaks down to a less ordered state and the solid liquefies. Molten substances generally have reduced viscosity with elevated temperature; an exception to this maxim is the element sulfur, whose viscosity increases to a point due to polymerization and then decreases with higher temperatures in its molten state.[21]
Modeling approaches[edit]
Heat transfer can be modeled in the following ways.
Climate models[edit]
Climate models study the radiant heat transfer by using quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.
Heat equation[edit]
The heat equation is an important partial differential equation that describes the distribution of heat (or variation in temperature) in a given region over time. In some cases, exact solutions of the equation are available;[22] in other cases the equation must be solved numerically using computational methods.
Lumped system analysis[edit]
Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newton's law of cooling.
System analysis by the lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady state system. That is, the method assumes that the temperature within the object is completely uniform, although its value may be changing in time.
In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the object's boundary, known as the Biot number, is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into the object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object.[23]
Engineering[edit]
Heat exposure as part of a fire test for firestop products
Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances.[citation needed] Heat transfer methods are used in numerous disciplines, such as automotive engineering, thermal management of electronic devices and systems, climate control, insulation, materials processing, and power station engineering.
Insulation, radiance and resistance[edit]
Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both. Thermal resistance is a heat property and the measurement by which an object or material resists to heat flow (heat per time unit or thermal resistance) to temperature difference.
Radiance or spectral radiance are measures of the quantity of radiation that passes through or is emitted. Radiant barriers are materials that reflect radiation, and therefore reduce the flow of heat from radiation sources. Good insulators are not necessarily good radiant barriers, and vice versa. Metal, for instance, is an excellent reflector and a poor insulator.
The effectiveness of a radiant barrier is indicated by its reflectivity, which is the fraction of radiation reflected. A material with a high reflectivity (at a given wavelength) has a low emissivity (at that same wavelength), and vice versa. At any specific wavelength, reflectivity=1 - emissivity. An ideal radiant barrier would have a reflectivity of 1, and would therefore reflect 100 percent of incoming radiation. Vacuum flasks, or Dewars, are silvered to approach this ideal. In the vacuum of space, satellites use multi-layer insulation, which consists of many layers of aluminized (shiny) Mylar to greatly reduce radiation heat transfer and control satellite temperature.[citation needed]
Devices[edit]
Schematic flow of energy in a heat engine.
A heat engine is a system that performs the conversion of a flow of thermal energy (heat) to mechanical energy to perform mechanical work.[24][25]
A thermocouple is a temperature-measuring device and widely used type of temperature sensor for measurement and control, and can also be used to convert heat into electric power.
A thermoelectric cooler is a solid state electronic device that pumps (transfers) heat from one side of the device to the other when electric current is passed through it. It is based on the Peltier effect.
A thermal diode or thermal rectifier is a device that causes heat to flow preferentially in one direction.
Heat exchangers[edit]
A heat exchanger is used for more efficient heat transfer or to dissipate heat. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface.[citation needed]
Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions; and in cross flow, the fluids move at right angles to each other. Common constructions for heat exchanger include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate.[further explanation needed]
A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems or the radiator in a car. A heat pipe is another heat-transfer device that combines thermal conductivity and phase transition to efficiently transfer heat between two solid interfaces.
Applications[edit]
Architecture[edit]
Efficient energy use is the goal to reduce the amount of energy required in heating or cooling. In architecture, condensation and air currents can cause cosmetic or structural damage. An energy audit can help to assess the implementation of recommended corrective procedures. For instance, insulation improvements, air sealing of structural leaks or the addition of energy-efficient windows and doors.[26]
Smart meter is a device that records electric energy consumption in intervals.
Thermal transmittance is the rate of transfer of heat through a structure divided by the difference in temperature across the structure. It is expressed in watts per square meter per kelvin, or W/(m²K). Well-insulated parts of a building have a low thermal transmittance, whereas poorly-insulated parts of a building have a high thermal transmittance.
Thermostat is a device to monitor and control temperature.
Climate engineering[edit]
See also: Anthropogenic heat
An example application in climate engineering includes the creation of Biochar through the pyrolysis process. Thus, storing greenhouse gases in carbon reduces the radiative forcing capacity in the atmosphere, causing more long-wave (infrared) radiation out to Space.
Climate engineering consists of carbon dioxide removal and solar radiation management. Since the amount of carbon dioxide determines the radiative balance of Earth atmosphere, carbon dioxide removal techniques can be applied to reduce the radiative forcing. Solar radiation management is the attempt to absorb less solar radiation to offset the effects of greenhouse gases.
Greenhouse effect[edit]
A representation of the exchanges of energy between the source (the Sun), the Earth's surface, the Earth's atmosphere, and the ultimate sink outer space. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect.
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.
Heat transfer in the human body[edit]
See also: Wet-bulb temperature
The principles of heat transfer in engineering systems can be applied to the human body in order to determine how the body transfers heat. Heat is produced in the body by the continuous metabolism of nutrients which provides energy for the systems of the body.[27] The human body must maintain a consistent internal temperature in order to maintain healthy bodily functions. Therefore, excess heat must be dissipated from the body to keep it from overheating. When a person engages in elevated levels of physical activity, the body requires additional fuel which increases the metabolic rate and the rate of heat production. The body must then use additional methods to remove the additional heat produced in order to keep the internal temperature at a healthy level.
Heat transfer by convection is driven by the movement of fluids over the surface of the body. This convective fluid can be either a liquid or a gas. For heat transfer from the outer surface of the body, the convection mechanism is dependent on the surface area of the body, the velocity of the air, and the temperature gradient between the surface of the skin and the ambient air.[28] The normal temperature of the body is approximately 37 °C. Heat transfer occurs more readily when the temperature of the surroundings is significantly less than the normal body temperature. This concept explains why a person feels “cold” when not enough covering is worn when exposed to a cold environment. Clothing can be considered an insulator which provides thermal resistance to heat flow over the covered portion of the body.[29] This thermal resistance causes the temperature on the surface of the clothing to be less than the temperature on the surface of the skin. This smaller temperature gradient between the surface temperature and the ambient temperature will cause a lower rate of heat transfer than if the skin were not covered.
In order to ensure that one portion of the body is not significantly hotter than another portion, heat must be distributed evenly through the bodily tissues. Blood flowing through blood vessels acts as a convective fluid and helps to prevent any buildup of excess heat inside the tissues of the body. This flow of blood through the vessels can be modeled as pipe flow in an engineering system. The heat carried by the blood is determined by the temperature of the surrounding tissue, the diameter of the blood vessel, the thickness of the fluid, velocity of the flow, and the heat transfer coefficient of the blood. The velocity, blood vessel diameter, and the fluid thickness can all be related with the Reynolds Number, a dimensionless number used in fluid mechanics to characterize the flow of fluids.
Latent heat loss, also known as evaporative heat loss, accounts for a large fraction of heat loss from the body. When the core temperature of the body increases, the body triggers sweat glands in the skin to bring additional moisture to the surface of the skin. The liquid is then transformed into vapor which removes heat from the surface of the body.[30] The rate of evaporation heat loss is directly related to the vapor pressure at the skin surface and the amount of moisture present on the skin.[28] Therefore, the maximum of heat transfer will occur when the skin is completely wet. The body continuously loses water by evaporation but the most significant amount of heat loss occurs during periods of increased physical activity.
Cooling techniques[edit]
Evaporative cooling[edit]
A traditional air cooler in Mirzapur, Uttar Pradesh, India
Evaporative cooling happens when water vapor is added to the surrounding air. The energy needed to evaporate the water is taken from the air in the form of sensible heat and converted into latent heat, while the air remains at a constant enthalpy. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect.
Laser cooling[edit]
In quantum physics, laser cooling is used to achieve temperatures of near absolute zero (−273.15 °C, −459.67 °F) of atomic and molecular samples to observe unique quantum effects that can only occur at this heat level.
Doppler cooling is the most common method of laser cooling.
Sympathetic cooling is a process in which particles of one type cool particles of another type. Typically, atomic ions that can be directly laser-cooled are used to cool nearby ions or atoms. This technique allows cooling of ions and atoms that cannot be laser cooled directly.[citation needed]
Magnetic cooling[edit]
Main articles: Magnetic refrigeration and Magnetic evaporative cooling
Magnetic evaporative cooling is a process for lowering the temperature of a group of atoms, after pre-cooled by methods such as laser cooling. Magnetic refrigeration cools below 0.3K, by making use of the magnetocaloric effect.
Radiative cooling[edit]
Radiative cooling is the process by which a body loses heat by radiation. Outgoing energy is an important effect in the Earth's energy budget. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere.
Thermal energy storage[edit]
Thermal energy storage includes technologies for collecting and storing energy for later use. It may be employed to balance energy demand between day and nighttime. The thermal reservoir may be maintained at a temperature above or below that of the ambient environment. Applications include space heating, domestic or process hot water systems, or generating electricity.
See also[edit]
Combined forced and natural convection
Heat capacity
Heat transfer physics
Stefan–Boltzmann law
Thermal contact conductance
Thermal physics
Thermal resistance in electronics
Thermal science
Heat transfer enhancement
References[edit]
^ Jump up to: a b Geankoplis, Christie John (2003). Transport Processes and Separation Principles (4th ed.). Prentice Hall. ISBN 0-13-101367-X.
Jump up ^ "B.S. Chemical Engineering". New Jersey Institute of Technology, Chemical Engineering Departement. Archived from the original on 10 December 2010. Retrieved 9 April 2011.
Jump up ^ Lienhard, John H. IV; Lienhard, John H. V (2008). A Heat Transfer Textbook (3rd ed.). Cambridge, Massachusetts: Phlogiston Press. ISBN 978-0-9713835-3-1. OCLC 230956959.
Jump up ^ Welty, James R.; Wicks, Charles E.; Wilson, Robert Elliott (1976). Fundamentals of momentum, heat, and mass transfer (2nd ed.). New York: Wiley. ISBN 978-0-471-93354-0. OCLC 2213384.
^ Jump up to: a b Faghri, Amir; Zhang, Yuwen; Howell, John (2010). Advanced Heat and Mass Transfer. Columbia, MO: Global Digital Press. ISBN 978-0-9842760-0-4.
Jump up ^ Taylor, R. A. (2012). "Socioeconomic impacts of heat transfer research". International Communications in Heat and Mass Transfer. 39 (10): 1467–1473. doi:10.1016/j.icheatmasstransfer.2012.09.007.
Jump up ^ "Mass transfer". Thermal-FluidsPedia. Thermal Fluids Central.
^ Jump up to: a b c Abbott, J.M.; Smith, H.C.; Van Ness, M.M. (2005). Introduction to Chemical Engineering Thermodynamics (7th ed.). Boston, Montreal: McGraw-Hill. ISBN 0-07-310445-0.
Jump up ^ "Heat conduction". Thermal-FluidsPedia. Thermal Fluids Central.
Jump up ^ Çengel, Yunus (2003). Heat Transfer: A practical approach (2nd ed.). Boston: McGraw-Hill. ISBN 978-0-07-245893-0.
Jump up ^ "Convective heat transfer". Thermal-FluidsPedia. Thermal Fluids Central.
Jump up ^ "Convection — Heat Transfer". Engineers Edge. Retrieved 2009-04-20.
Jump up ^ Incropera, Frank P.; et al. (2012). Fundamentals of heat and mass transfer (7th ed.). Wiley. p. 603. ISBN 978-0-470-64615-1.
Jump up ^ "Radiation". Thermal-FluidsPedia. Thermal Fluids Central.
Jump up ^ Mojiri, A (2013). "Spectral beam splitting for efficient conversion of solar energy—A review". Renewable and Sustainable Energy Reviews. 28: 654–663. doi:10.1016/j.rser.2013.08.026.
Jump up ^ Taylor, Robert A.; Phelan, Patrick E.; Otanicar, Todd P.; Walker, Chad A.; Nguyen, Monica; Trimble, Steven; Prasher, Ravi (March 2011). "Applicability of nanofluids in high flux solar collectors". Journal of Renewable and Sustainable Energy. 3 (2): 023104. doi:10.1063/1.3571565.
Jump up ^ See Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning
Jump up ^ David.E. Goldberg (1988). 3,000 Solved Problems in Chemistry (1st ed.). McGraw-Hill. Section 17.43, page 321. ISBN 0-07-023684-4.
Jump up ^ Louis Theodore, R. Ryan Dupont and Kumar Ganesan (Editors) (1999). Pollution Prevention: The Waste Management Approach to the 21st Century. CRC Press. Section 27, page 15. ISBN 1-56670-495-2. CS1 maint: Extra text: authors list (link)
Jump up ^ Tro, Nivaldo (2008). Chemistry: A Molecular Approach. Upper Saddle River, New Jersey: Prentice Hall. p. 479. When a substance condenses from a gas to a liquid, the same amount of heat is involved, but the heat is emitted rather than absorbed.
Jump up ^ C. Michael Hogan (2011) Sulfur, Encyclopedia of Earth, eds. A. Jorgensen and C. J. Cleveland, National Council for Science and the environment, Washington DC
Jump up ^ Wendl, M. C. (2012). Theoretical Foundations of Conduction and Convection Heat Transfer. Wendl Foundation.
Jump up ^ "How to simplify for small Biot numbers". Retrieved December 21, 2016.
Jump up ^ Fundamentals of Classical Thermodynamics, 3rd ed. p. 159, (1985) by G. J. Van Wylen and R. E. Sonntag: "A heat engine may be defined as a device that operates in a thermodynamic cycle and does a certain amount of net positive work as a result of heat transfer from a high-temperature body and to a low-temperature body. Often the term heat engine is used in a broader sense to include all devices that produce work, either through heat transfer or combustion, even though the device does not operate in a thermodynamic cycle. The internal-combustion engine and the gas turbine are examples of such devices, and calling these heat engines is an acceptable use of the term."
Jump up ^ Mechanical efficiency of heat engines, p. 1 (2007) by James R. Senf: "Heat engines are made to provide mechanical energy from thermal energy."
Jump up ^ "EnergySavers: Tips on Saving Money & Energy at Home" (PDF). U.S. Department of Energy. Retrieved March 2, 2012.
Jump up ^ Hartman, Carl; Bibb, Lewis. (1913). "The Human Body and Its Enemies". World Book Co., p. 232.
^ Jump up to: a b Cengel, Yunus A. and Ghajar, Afshin J. "Heat and Mass Transfer: Fundamentals and Applications", McGraw-Hill, 4th Edition, 2010.
Jump up ^ Tao, Xiaoming. "Smart fibres, fabrics, and clothing", Woodhead Publishing, 2001
Jump up ^ Wilmore, Jack H.; Costill, David L.; Kenney, Larry (2008). Physiology of Sport and Exercise (6th ed.). Human Kinetics. p. 256. ISBN 9781450477673.
External links[edit]
A Heat Transfer Textbook - (free download).
Thermal-FluidsPedia - An online thermal fluids encyclopedia.
Hyperphysics Article on Heat Transfer - Overview
Interseasonal Heat Transfer - a practical example of how heat transfer is used to heat buildings without burning fossil fuels.
Aspects of Heat Transfer, Cambridge University
Thermal-Fluids Central
Energy2D: Interactive Heat Transfer Simulations for Everyone
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