A review on thermoelectric cooling technology and its applications

Controlling devices thermally is an important issue to increase the span of any equipment that converts energy and nowadays available latest automation like LED, computer processers and electric battery. Thermoelectric Cooling Technology (TCT) is best option because it has high reliability and also its usage of energy is low for the cooling of devices, which are working on the basis of Peltier effect. TCT have features such as it is not big in size, very light in weight. Also it has no mechanical moving part which results in no or less noise, eco friendly and it does not has any working fluid. This paper presents a comprehensive review of TCT to understand the state of art in the cooling techniques and its applications on heat pipe cooling, sensible air cool warm fan and solar still productivity enhancements. The challenges and opportunities for future research are also highlighted.


Introduction
In nowadays, almost every day some new product is coming in market, there is also a need of thermal control for them. There are many examples of electronic products around us like even our fan, light, gaming consoles, diodes and other types of electronic gadgets. One of the possiblewaystoovercome the problem of thermal control is thermoelectric devices. The later have also been used in many types ofindustries, medical,space and terrestrial applications and are used in generating electricity. There are various cooling technologies that are used to maintain their temperature below the temperature where they are operated. Automatic industry has its own share of use which is thermal battery management system. There is also a need of converting of electrical power to thermal power. TECs help in the problem of current heat dissipation. There is always rapid development in thermoelectric materials.TEC's which is also a cooling technique uses thermoelectric modules.
There are various advantages of these modules such as they are notdynamic,because no part of them moves, so they automatically become reliable .Also they are quiet appealing in many ways. They operate for a longer time and need less or no maintenance. Module has stack of TEUnicouples which are connected in series which also increases the severance and sustainability. They have complex applications. Peltier effect is the basis of the working of thermoelectric coolers. The former was discovered in 1834. In this temperature dissimilarity is created by flowing current across two different materials. It is one of three famous methods invented for thermoelectric cooling, the other one are There are various factors which decide the working of thermoelectric cooling like thermoelectric modules whichare α,k and σ.α is regarded as seebeck coefficient,thermal conductivity is symbolised by k and σ represents electrical conductivity.ZT is a dimensionless figure which is used to symbolise the influence of properties of materials on performance of thermoelectric system. That figure of merit is also defined as: Where, Th, is the hot sideand Tc is the cold side temperature of TEC. IfZT increases then COPmax will increase. Interest has to be increased in improvement of value of ZT which is highly dependent on the need of well organised thermoelectric materials which are further used for refrigeration and generation of power. It should have high value of seebeck coefficient α,increased amount of σ and decreased level of k for higherlevel of ZT. Voltage at which it is operated, temperature suitable for its working temperature its typical applications like condensation of the risk coupling which is done with a PV system. Lie et al [5] thermo electric cooling module Seebeck coefficient Thermal resistance Symbolising of TECT applied in electric cooling.
Luoet al [6] Air duct aidedwith system which is photovoltaic in nature for cooling the space.
Photovoltaic panel and Thermoelectric module optimum temperature difference, cooling capacity, COP, which also provides reliability and is free from Freon*.
Irshadet al [7] Also, common thermoelectric cooling system depends on limits like the current, thermal conductance present in extreme temperature sides of heat disposable area and temperature. Example is the smallest shallow temperature of devices. Increase in power input results in development of presentation of cooling of electronic devices, which in return primes to higher consumption of power of cooler. Significant techniques have been applied to increase the performance of system and it decreases consumption of energy.
Liu et al. [2] deliberate a active model for composite systems as thermoelectric ventilator system to give warmth in winter and concurrently heat to attain inclusive use of solar radiations. Numerous researches have been done and are going on to smear the thermoelectric present in different types of cooling systems.In this paper we are going to present somepreciseclaims of thermoelectric cooling technology like heat pipe coolingin more intricatefacts.Sensible air cool warm fan is alteration of conservative fan system by the usage of thermoelectric module. Refrigeration system can be utilised in numerous fields. With assistance of coupling heat pipe the cooling performance of refrigeration system will get amplified.

ThermoelectricCooling
This phenomenon was initially discovered by Alessandro Volta in 1794,in which difference in the temperature ranges resulted in thermo, electro and motive forces. 1821 resulted in Seebeck experimentally investigating a pattern and re-examined the Volta theory and later on in 1834Peltier discovered the Peltier effect. This entire discovery helps in the quick expansion of thermoelectric technology.

2.1.Parametric Review
The physical conditions of materials are most important issues,validating the working of TCs. it is cumbersome to gain active, precise limits by experimental amount because of interaction between heat sink and TEC. Various researches are going on experimental size and simplification of limits of TCs which have been described in numerous publications .if its physical conditions are confined to the logical model of TCs and could be solved by sequence of limitations. Typically, there are different procedures, like technique of thermal confrontation system and technique of number of transmission units, were applied on TCs for resolution of refining presentation. This cooler, from ages is commercialised for higher flow. One connection of which will be airconditioned and other when directly heated when current is passed through it. As a consequence thermoelectric cooler is a cooling technology by using thermoelectric unit.

Fabrication of Thermoelectric Module
The thermoelectric component encompasses numerous couples (p-n type) of portions, connectors which are metallic and insulating ceramic plates. Theplateswhich are existing on both the sides of thermoelectricmodule acts as insulation in electrical appliances. Excess of electrons are present in n type semiconductor while p type has deficit of electrons. They together comprise a Unicouple. Inside thermoelectric module,these types of semiconductors are electrically joined in particular manner and also temperature wise they are arranged in parallel, which together comprise of numerous Unicouples. Electrons start moving from one type of semiconductor to another, the electrons jump from a higher energy state dissipating thermal energy. On going through, the lattice,the electron start moving through n-side to the p-side, that is to a lower energy level dissipating energy again in that case current flows from one type of element to another which is given below in figure 1.  (TAC).It utilises thermoelectric cooler to take away heat directly. In various cooling applications, TAC aids in preserving the devices at a condition of temperature which we need.As shown in figure 2, the specific system should be apprehended by giving it a TEC.  (TSC).In this electricity is generated from generatorfrom difference in ranges of temperatureforsupply of power to water pump or fan. The devices gives some amount of heat ,reason being casual application and there is a need for its temperature to decrease if we want to prevent its overheating .As shown in the figure 3, TEG which is connected to devices can use that heat which is produced by that electricity forheat sink in which heat goes and then we use that heat which is depicted in given system accurately. Now what we have to choose between TACsystems or thermoelectric self cooing depends on the difference in temperature ranges between the surface and environment of electronic devices with an aim to improve cooling efficiency.

2.4.Thermoelectric Material
TECT is also one of the also technology used for the transfer of heat in all types of electronic devices which do cooling.Reason beingits advantages which are its not very difficult structures and it is not dynamic in nature. Also, this technology is one of the important technologies for energy that can be used again in applications by the application of solar radiations and energy of low range, also these types of production of materials of thermoelectric nature .The inorganic materials (e.g.PbTe,Bi2Te3) are used in research studies on thermoelectric which have great commercial application.These inorganic materialsare the predictable thermoelectric material with ZT about 1.Various disadvantages are there like they not being eco friendly. They have less stability at ranges of temperature which are higher .This helps to use thermal energy which is otherwise hardly usable into productive applications as efficiently as possible.

Application ofcooling which are thermoelectric in nature
Lots of usages of thermoelectric devices are there which help in the recovery of waste heat specially in automotive industry .It is also used to generate electric power .Some specific application are discussed in this paper.

3.1.Sensible air cool warm fan
An experiment on the applications of these types of moduleswhich are thermoelectric in nature and is done for checking out the air supply which can either be heated or cooled of the predictable systems .It comprises of six plates which are thermoelectric in nature which contains boxes which are cold in nature of water and one box of hot water. The module which is thermoelectric in nature comprises of plates which are thermoelectric in nature,hot and boxes of water which are cold in nature.Resultswhich we get from thelevel of heating of the fan system, the details of which arepresent and thoroughly matched with those atrocities from the old fan system that is one without these types of modules which are thermoelectric in nature. It also founded thatextreme temperature of water which we get from the module which is thermoelectric in natureat70 and 12 degree, respectively. Also because of the varying temperatures that is cold in its respective weather and hot in its.Because of which older type of systems here has no use. So there is a need of temperatures to be hot and cold at their respective sides of the thermoelectric and then used judicially.

3.1.1.Fabrication of sensible air cool warm fan.
One of the newest study which is conducted byS.Wiriyasaratet al. [8] in which fan(with module which is thermoelectric in nature )is studied. Results obtained from the same arethen compared with the ones from the old fan system .Results got are expected,that they will guide the developmentof fan(with module which is thermoelectric in nature). Also it has high thermal performance. In summer, this type of modified fan is used in which water is taken by the help of water pump from water tank, which then flow into the coil which is cooled and itcools the supply of natural air.It then 3rd International Conference on Advances in Mechanical Engineering (ICAME 2020) IOP Conf. Series: Materials Science and Engineering 912 (2020) 042004 IOP Publishing doi:10.1088/1757-899X/912/4/042004 7 moveinto the boxes of box which is cold and contains water of these types of modules .coolant moves through same module into two hot boxes of water which is hot and flow into the mechanical device which help to regulate temperature and dissipate high temperature in the atmosphere which then comes into the hot water and absorbs warmth through hotterside of plate. Temperaturesin different portions of water which is cold and in the form of loop are calculated, by T -thermocouple, which gives precision of 0.1percentages For winter, weather is maintained at normal temperature by the application of modified fan system. Hot water is then water tank, which then it goes into the coil and heats upthe air supply (fan system. After that it flowsin the heating module, which then absorbs heat from the hot water box. It comes back water tank in which hot water is present as depicted in figure 4. At the same time, coolant moves box of cold water of the module. It moves through the tank which contains water and is used for cooling and finally moves in boxof water which is cold in nature.

Cooling system which is thermoelectric in nature and coupled with heat pipe
Refrigeration system, as we all know can be used in various types of fields.Dual functions, one is of refrigeration and other is of heating and which makes it prominent in all types of applications in engineering sector.Dryer of clothes was invented by Liu et al [9] used the heating model of the system which is thermoelectric in nature and heated. . Refrigeration system has advantage of not causing any type of mechanical noise .It is also environmental friendly, havesmallsize and also show sensitivity to temperature.  [10].It's base is presented by transfer of heat which is a dimensional. It also gives a platform for small systems which are thermoelectric in nature and are coupled with pipe which is heated. A spoiler duct is made by it which is helpful in increasing the working of the system which is cooled.
Themathematical model is presented on the basis of refrigeration cycle which is ideal in nature. Simplified calculation can be done for the same. Model ispresumed that symmetric structure can be built. It can be used in analysis.

Solar still
Solar distillation still system is economically feasible in desalination of saline water. It is simple process as well as cost effective. It is non-polluting and free of cost. In this process, by the help of sun rays, water is evaporated which then falls on a condenser where it is cooled and desalinated.

Opportunities for advancements
Thermoelectric materials result in the formation of TEMs. It is one of the main parts of thermoelectric cooler which is used for cooling. To increase its performance, we have to decrease its thermal conductivity. Also we have to increase its conductivity which is electrical in nature and also its seebeck coefficient which will help in getting higher figures of merit (ZT) value. The mixture of polymers which are organic with some materials which are inorganic is used to make films which are thin, in turn present the material as non isotropic. Designing this high thermal performance materials are cumber some due to lack of theoretical basis .We have to improve it. Developments are going on and newer concepts are being developed like super lattice, plasma treatment etc. which is then used to higher the amount of ZT. To increase it above 4 is still difficult.Already researches aregoing on so that material becomes environment friendly and affordable.There is always scope of future development.

Conclusion
This work reviews the present researches which are done technology which is cooler and thermoelectric in nature. It gives us some idea of its usage in various cooling methodologies. It has a mode for cooling for different types of material. The observations are as follows: This TECT system can be divided into two types i.e. TSC and TAC. Itsperformance is highly influenced by the materials which are thermoelectric in nature.These types of materials can be considered as valuable as bio thermal batteries. It is also present in solid state thermoelectric cooling and optoelectronic devices, space and automotive power generator. Higher the ZT value, better will the thermoelectric materialnumerous efforts has been done to improve the value of ZT.In the type of module which is thermoelectric in nature, a voltage, dc in nature is moved through the meeting point which is connected for the module, whose side is cooled and the other side is also heated. The results which we get from this type of fan system with module which is thermoelectric in nature .System are compared with those from the old fan system. The results which we get are expected to provide details that will help us to continue this development and designing the fan system with module which is thermoelectric in nature with performance of a higher notch. Solar still, invented in 1872 is thermoelectrically active device which will help people in simplifying their day to day activities like desalination of water in an easy and cheaper way.