|Fluid Dynamics & Materials Processing|
A Systematic Review of Thermoelectric Peltier Devices: Applications and Limitations
1Department of Computer Science and Engineering, NMAM Institute of Technology, Udupi, 574110, India
2Department of Electrical and Electronics Engineering, NMAM Institute of Technology, Udupi, 574110, India
3Department of Engineering Management, College of Engineering, Prince Sultan University, Riyadh, 11586, Saudi Arabia
4Department of Mechanical Engineering, NMAM Institute of Technology, Udupi, Karnataka, 574110, India
*Corresponding Author: Abdul Aabid. Email: email@example.com
Received: 18 November 2021; Accepted: 18 April 2022
Abstract: Conventional refrigeration processes release ammonia and freon into the atmosphere, which results in global warming. These problems may be overcome by using thermoelectric modules because of the absence of coolants or refrigerants in these systems. However, the cooling performances of such modules are relatively small in comparison to those of conventional refrigerators. In this paper, the working principles of thermoelectric modules are discussed together with a review of different relevant aspects, namely: the thermoelectric materials, and their mechanical properties used to build thermoelectric devices, different types of thermoelectric devices available on the market, mathematical modeling of thermoelectric materials, and various applications of thermoelectric materials in different fields.
Keywords: TEG; peltier module; seebeck effect; refrigerator; CoP; TEC
The world’s demand for energy is uninterruptedly increasing each day and over utilization of non-renewable energy sources have cause various ecological issues such as dangerous atmospheric temperature deviation, corrosive downpour, ozone layer consumption, and environmental change . Greenhouse gases are radiated into the air because of the abundant utilization of fridge, heating, and air-conditioning systems. Such disasters can be reduced by the consumption of conventional energy resources and the use of renewable sources or technologies. However, the world is shifting toward a renewable resource economy. Green technologies, such as wind turbines, hydrogenation, solar photovoltaic, and biomass are attaining significance in tackling energy and environmental issues [2–4]. This move towards clean power generation is an effort to decrease the carbon footprint and the amount of carbon dioxide emissions in the future. Thermoelectric devices are used as one of the technologies to achieve this goal.
The initial innovation linked to thermoelectricity occurred in 1821 by Thomas Seebeck, who established that an electric current could flow during an electric circuit fabricated from two completely different metals only if the connections of the metals were sustained at two different temperatures. The Peltier effect was discovered in 1834 by Jean Charles Athanase Peltier. He demonstrated that the utilization of current at the outskirts of two different materials results in the centralization of hotness and release of hotness at the subatomic level, which is frequently conducted with different vitality levels of materials, particularly N and P-type materials [5,6]. Thermoelectric devices are solid-state devices that transform heat into electricity. The merits of thermoelectric (TE) are that it does not have any moving parts, compact, eco-friendly, has no chemical reaction, wide operating temperature range, maintenance-free, and has a long life span . Various studies have also been performed to improve the heat transfer in heat exchangers [8–15].
This review work provides a detailed study about thermoelectric Peltier devices with application and limitations. Following section elaborates the thermoelectric modules with the existing contribution in recent investigation with research gap. The section three illustrates mathematical modelling of the Peltier devices. Section four lists some of the important applications of thermoelectric modules and section five is the critical analysis of the literature with discussion and limitations. Finally, a conclusion has been provided based on the current existing work.
A Thermoelectric module (TEC) is a device arranged by thermoelectric couples (N and P-type semiconductor pellets) that are electrically arranged and thermally equal as shown in Fig. 1. The semiconductors were inserted between the ceramic plates. Thermoelectric semiconductor materials generally used in thermoelectric coolers are alloys of Bismuth Telluride. More thermoelectric materials are accessible according to necessary applications such as Lead Telluride (PbTe), Silicon Germanium (SiGe), and Bismuth-Antimony (Bi-Sb) alloys [16,17]. The most commonly used semiconductor material is Bismuth Telluride (Bi2Te3) which has a dissimilar electron density. A typical thermoelectric module contains an arrangement of Bi2Te3 semiconductor pellets that transmit the majority of current. Couples of P and N semiconductors are arranged so that they are coupled electrically in series, but thermally in parallel . The ceramic plates exhibit mechanical integrity and also act as electrical insulators for cooled and heated surfaces. The plates also deliver great thermal conductance for heat transfer with nominal hindrance. Aluminum Oxide (Al2O3) ceramics are commonly used because of their low cost, and performance ratio. Other ceramics such as Aluminum Nitride (AlN) and Beryllium Oxide (BeO) can also be employed . When an input is established at the free ends of two conductors, a temperature change is generated through the intersections of semiconductors owing to the flow of current. One aspect of the connections is identified using low temperature (heat absorbed) and another side of intersections by high temperature (heat released).
The Peltier module works on the Peltier Effect. This indicates that when voltage is applied between two completely different terminals of a conductor, which is coupled by a semiconductor material that generates an adjustment in the temperature that causes the material to draw out from the warm facet to the cold facet as shown in Fig. 2 . When the current begins to flow from one side to another side of the junction, the outside layer can be warmed or chilled according to the need. When electrical energy is applied to the module, the positive and negative charge carriers absorb and release energy respectively. One side of the plate absorbs heat energy from one material surface and releases it to the other side . Reversing the supply terminals results in reversed hot and cold sides.
Thermoelectric materials are employed for both refrigeration and power. The structure comprises N and P-type semiconductors. The application of hotness on one facet and a cooling heat sink on another facet generates electrical power and vice versa. The efficiency is low by 10% when it is used as a power generator; however, it is advantageous because of its high electrical conductivity, high Seebeck effect, and low thermal conductivity. Usually, Bi2Te3 is used because of its high figure of merit. The mechanical properties of some thermoelectric materials are given in Table 1 [23,24] and the figure of merit (zT) characteristics for P and N-type thermoelectric materials has been studied in .
Depending on the industrial applications different types of thermoelectric modules are available with various dimensions and different electrical input configurations . These thermoelectric modules are used in various industrial applications such as electronic equipment cooling, temperature baths, medical equipment, food industry, measurement equipment, and transport.
The process for the Peltier cooler device can be characterized accurately by modelling and the device working is evaluated through a personal computer (PC) . The semiconductor material used in the module depends on numerous temperature-dependent properties that should be considered while modelling. For the selection of the thermoelectric module cooling purpose, parametric studies must be performed [27–29]. This can be performed theoretically and can be validated experimentally on a PC. An extensive investigation of numerous Peltier cooler modules over a wide range of temperatures has been carried out . This study has resulted in the advancement of mathematical models that are used to consistently forecast module efficiency for different functional surroundings. Numerous parameters related to thermoelectric materials or modules should be considered to develop a mathematical model. The essential parameters for modelling thermoelectric devices include the module’s Electrical Resistance (RM), Seebeck Coefficient (SM), and Thermal Conductance (KM) .
3.1 Effective Seebeck Coefficient
When a temperature gradient is sustained along with the thermoelectric device, a voltage can be generated that is sensed at the input terminus. The amount of the output voltage is called the Seebeck electromotive force, which can be compared to the amount of change in temperature which is calculated using the Eqs. (1) and (2),
SM-Module’s Seebeck coefficient in V/°K.
-Module’s Seebeck coefficient at Th.
-Module’s Seebeck coefficient at Tc.
T–Average temperature in °K.
and S4 are the variables, whose values are given below:
The electric resistance of the thermoelectric module in terms of the temperature function is calculated using Eqs. (3) and (4),
RM-The electrical resistance of module in Ω.
-Electrical resistance of module in Ω at Th °K.
-Electrical resistance of module in Ω at Tc °K.
T-Average temperature in °K.
r1, r2, r3and r4 are the variables whose values are given below:
Thermal conductance of the thermoelectric module in terms of temperature is calculated using Eqs. (5) and (6),
KM–The thermal conductance of module in W/°K.
–Thermal conductance of module at Th °K.
-Thermal conductance of module at Tc °K.
T–Average temperature in °K.
k1, k2, k2 and k3 are the variables whose values are given below:
The above parameters were calculated for 71 couples and 6 A Peltier device. For a novel or diverse thermo-molecular arrangement to be modelled, the correction factor has to be used which is given in Eqs. (7) to (9),
Snew-The novel Seebeck coefficient of the new module.
Rnew-The novel electrical resistance of the new module.
Knew-The novel thermal conductance of the new module.
Nnew-The amount of couples in the new module.
Inew is the optimal current in the new module.
The figure of merit could be an amount of the performance of a thermoelectric device or material which is given in Eq. (10),
Usually, the TEC manufacturer mentions the maximum temperature gradient and specification, but the figure of merit of TEC is not disclosed; hence this can be calculated theoretically and can be validated by connecting the TEC to the PC. The MATLAB/Simulink model can be used to determine the parameters of the thermoelectric cooler and generator .
3.4 Coefficient of Performance
The coefficient of performance (CoP) may be defined as the ratio of the cooling capacity of the module to the power consumed by the module. The operation of a thermoelectric cooler device can be estimated theoretically by identifying the maximum temperature gradient (ΔTmax) and cold facet heat pumping rate (QC) [30–32]. This can be calculated by using Eqs. (11)–(14),
Heat rejected by the Peltier module on the hot side
Total energy supply
Hence the CoP of the TEC is given as
Generally, the value of CoP for the TEC is less than one when compared to a commercial cooling refrigerator whose CoP is greater than one. Hence it is necessary to increase the value of the CoP for TEC for effective and fast cooling purposes. Many researchers are trying to improve the CoP of TEC; hence in the future, the CoP for the TEC may increase.
4 Applications of Thermoelectric Module
A thermoelectric generator (TEG) is a solid-state device that transforms heat energy directly into electrical energy through the phenomenon of the Seebeck effect. They function as heat engines but their efficiency is low and the cost of the TEG is high . Generally, this TEG can be used in power plants to convert waste heat energy into electrical energy and can also be used in automobiles as automobile TEGs to increase fuel efficiency . Automobiles transform unused warmth present in the dissipated gases unswervingly into electrical energy by employing TEG. The pump delivers cooled water from the side to the cooling water circulation paths. A variety of stacks are connected with thermoelectric elements that are associated with the exhaust pipe and the cooling water pipe consecutively in a path from the upward to downstream of the exhaust gas . The downstream stack has an increased temperature difference between the cooling pipe and exhaust which reduces the stack output and increases the total power output. The temperature difference between the hot and cold sides of the TEG increases as the motor speed increases, which generates the yield voltage level specified by the Seebeck impact. The TEG was employed on the top side of the duct . The duct is linked with the exhaust manifold, to covert the energy from the TEG. When the TEG was connected in series, the performance increased. For maximum performance, the duct is completely insulated and a temperature difference is generated which increases as the motor RPM is increased [37,38]. Thermoelectric generators can be employed in various applications such as radioisotope TEGs which are applied in space probes. The TEG has high reliability and less maintenance; hence a long-time service TEG can be constructed. Various studies have been proposed to improve the performance of TEGs [39,40].
Automobiles have many systems such as locomotives, gearboxes, cooling systems, and exhaust systems which yield high temperatures throughout the ride, which can be recovered using the TEG . In general, vehicular heating, ventilation, and air conditioning (HVAC) system consist of mechanical refrigeration and absorption systems. It includes moving parts with noisy operations and refrigerants. However, the efficiency of the thermoelectric refrigerator is less than the mechanical refrigerator, but it can maintain its efficiency and works silently with no moving parts and requires less maintenance.
Most of the automobile industries such as GM, Jaguar, Hyundai, and Renault have technologically advanced their methods towards the recuperation of exhaust heat via thermoelectric generators, which keeps the seat of automotive cold or warm . The installation cost of the thermoelectric cooler is considerably lower than that of conventional mechanical refrigeration . The current cooling system in automobiles consumes up to 3500–4000 W for cooling compared to 700 W of consumption by the cooling system with TEG .
With the progress in electronic engineering, the heat dissipation of electronic devices has increased which poses a serious problem to the processing speed and the life of electronic devices. Heat dissipation can be reduced by passive cooling using fins and cooling fans; however, at their full load it fails to manage heat dissipation; hence TEC can be employed to decrease heat dissipation . Generally, water-cooled TEC is utilized to decrease the temperature which has achieved better cooling than the air-cooling TEC. The heat exchanger is placed between the heating component, when the TEC is activated, it provides cooled air; hence the water inside the heat exchanger carries heat from the thermally isolated material . This reduces the heat dissipation which increases the processor speed. The Peltier system incorporated with the gravity assistant heat pipe (GAHP) is arranged just as built up, which was intended for cooling the electrical gadgets as shown in Fig. 3 . The heat pipe transfers the hotness with a minor change in temperature because of the stage progress. A heat sink can be incorporated on the cooling side to increase the concentration of heat on the thermoelectric plate. The GAHP through a uniform and even vaporization exterior is fixed on the heating side of the thermoelectric unit and to the build-up zone of the GAHP to blow the hot air. When the DC is passed to the TEC, the Peltier unit absorbs the temperature from the heating surface and dissipates warmness to the warm facet of the TEC. Fig. 4 shows a variation in the two TEC systems. The deployment of GAHP improved the cooling capability by almost 73.54%, linking with the TEC with the heat sink and the electrical energy intake was decreased by 42.20% to generate an equal quantity of cooling . The chilling capability of the TEC with heat sink improved and was later reduced by methods for aggregating the surrounding air temperature, which influenced the working effectiveness of the electrical framework.
4.4 Thermoelectric Refrigerators
Refrigeration is a process in which heat is removed to maintain the required temperature [49–51]. Generally, refrigerators are used to preserve food, beverages, fruits, and vegetables. However, a commercial refrigerator uses a vapor compressor cycle where it uses refrigerant for cooling purposes [52–55]. This refrigerant leads to a greenhouse effect; hence this can be reduced by using a thermoelectric refrigerator. In TEC there is no moving part and it has no refrigerant; hence it is eco-friendly . The thermoelectric refrigerator is portable  and can be carried anywhere and can be used to preserve food and cold drinks . The thermoelectric refrigerator uses electricity to cool the space, charging the TEC can be done through batteries and the solar cells may be used to charge the batteries [3,25,59,60]. The main components of thermoelectric refrigerators consist of thermoelectric modules, aluminum water blocks, heat sinks, and cooler fans [61–64]. The schematic diagram of the thermoelectric refrigerator is shown in Fig. 5. The CoP of a thermoelectric refrigerator usually ranges between 0.3–0.7 which is less than that of a vapor-compressed refrigerator [65,66]. Experimental results show that the effectiveness of solar cell integrated thermo-electric refrigerators remains highly dependent on the concentration of solar insulation and the temperature of the thermoelectric module [67–70].
Thermoelectric cooling is broadly used in numerous areas of science and technology, specifically in medicine. It is very important to preserve the vaccines and other medicinal syringes at a very low temperature so that they do not lose their potency [71,72]. To reach low temperatures, liquid nitrogen is being usually preserved at low temperatures, which significantly limits its usage in hospitals [73–75]. In most circumstances such devices are massive, and proper temperature control could cause damage . The use of thermoelectric cooling can resolve this problem because it has several benefits when correlated with conventional thermal effects . Thermoelectric cooling can be used in practical applications , such areas of medicine as cryosurgery, cryotherapy, neurosurgery, urology, plastic surgery, and dermatology. In dermatology thermoelectric devices can be implemented for the smoothening of wrinkles, strengthening parts of the human body, and other medical procedures. Homeostasis is a unique function of the human body for temperature control in the body. Patients with spinal cord injury (SCI) lose the ability to adjust their body temperature . Hence TEC can be employed to maintain the body temperature using artificial means of cooling which offers patients thermoregulatory ability lost due to SCI . The development and improvement of thermoelectric medical devices for skin disease treatment are becoming more important.
4.6 Miscellaneous Applications
There are various additional applications of the thermoelectric module which can be improved because of its compactness in size, transferability, and non-rotational part. Numerous uses of TEC such as wearable Solar e-uniform meant for soldiers who maintain the required temperature by increasing the temperature in cold and decreasing the temperature in extremely hot weather conditions . TEC is also employed in the umbrella to provide cold air to people with high deviations in temperature and abundant sunlight . A Peltier device transforms heat energy into electrical energy using a collection of thermocouples. Using these thermocouples integrated with a TEC battery can be recharged by the thermoelectric generator principle which can be used to charge mobile phones or cell phones [83,84]. A thermoelectric cooler can also be employed to improve the lifetime of the battery. This module can also be employed in a thermoelectric lunch box to preserve food at the necessary temperature . The moisture content present in the soil and drying of the wet soil can be completed using a thermoelectric device with infrared light . TEC is also used in the measurement of the thermal characteristics of low-cost MEMS IMU sensors . It is also used for cooling and humidity control over engineering surfaces [88,89]. Similarly, there are various applications of thermoelectric devices depending on the application.
Over the last 5 years, the number of works has been reported in the literature. When it has been compared the selected application of this review it has been found the thermoelectric module was used in electronic devices with the highest range up to 43% following to thermoelectric generator 30% and then medical application 17% (Fig. 6). When observed thermoelectric refrigerators and automobile cooler only 7% and 3% used were found respectively and this range compared to other types of application is small. It discloses that in the recent studies and investigation Peltier devices was highly used for electronic and medical application additionally to the thermoelectric generator.
5 Critical Analysis of the Literature
The output power and thermoelectric conversion efficiency of segmented TEG components with changed length proportions under two different thermal boundary conditions are studied in . The increasing and decreasing patterns in the output power and efficiency of the thermoelectric materials with an increase in the length ratio. It is observed that the maximum efficiency and the maximum output power of the tentatively acquired segmented thermoelectric devices are very close and equivalent to the calculated value. The error obtained was less than 4%. Zhang et al.  studied the Seebeck potential, Ohmic potential, and internal resistance of the segmented TEG units for various length ratios. The maximum output power of a segmented TEG depends on both the Seebeck potential and the internal resistance. Table 2 shows the different designs of heat exchangers in TEGs.
A higher Seebeck potential and lower internal resistance lead to higher output power. Because there was an increasing and decreasing trend as shown in, the ideal length proportion is required to achieve good efficiency . The GAHP is integrated into the Peltier device for electronic cooling application, Fig. 7 shows the performance of the Peltier plate with heat sink and with GAHP, it is observed that when the surrounding temperature was 30°C, 35°C, and 40°C the accumulation of the heat was reduced by the heat sink whereas the GAHP did not increase the performance .
However, when the surrounding temperature was increased to 45°C and 50°C, the heat removal rate of the heat sink with Peltier was not effectively related to that of GAHP as shown in Figs. 7d and 6e, which remarkably reduced the heat accumulation on the heating side of the Peltier device which increased the efficiency of the system.
The thermoelectric cooler system was set inside the vehicle and the analysis was directed for various natural conditions, for example, in the morning, afternoon, and at night and it was noticed that the cooling at night was more positive than on different occasions . The thermoelectric refrigerator was investigated by varying the input power. The cool side of the heat sink temperature and cooler box temperature with a variety of input powers (50.5, 72.72, and 113.64 W) for 2 h, respectively .
The rate of input power rate influences the temperature of the cooling device. The results show that the temperature at the cool side of the heat sink and cooler box decreases with the increase in the input power that is provided to the system, owing to the higher heat absorption on the cool side of the TEC modules. Thus, a lower temperature is acquired at the cool side of the heat sink and cooler box. The hot side of the heat sink temperature with the surrounding temperature and CoP of the cooler box with a variety of input powers [109,110]. The measure of input power likewise influences the temperature on the hot side of the heat sink. The results show that the hot side temperature of the heat sink increases with an increase in the input power, and because of the greater heat absorption on the cool side of the TEC, the more heat dissipated in the hot side of TEC so the temperature of the hot sink will rise. CoP decreases when the input power is increased to decrease the temperature rapidly. Table 3 shows the different designs of heat sinks in thermoelectric refrigerators. Additionally, some study has been found on energy observations in a turbine blade to resist the thermal effects [111,112] and few others study was in [113–115].
6 Conclusion and Recommendations
This paper is focused on a review of thermoelectric (Peltier devices). Due to the peculiarity and straightforwardness of the thermoelectric guideline, the conversion of vitality makes it progressively advantageous for various applications. It has decent future opportunities due to natural concerns and innovation advancement. The main disadvantage of the thermoelectric module is that it has got less efficiency. The CoP of the thermoelectric module is less than 1 usually in the range of 0.3–0.7 hence the CoP of TEC should be increased in the future. Thermoelectric generators assume an essential job in a few fields, for example, power plants, electrical powerhouses, heaters to deliver power from squandering heat recuperation. There are different odds of immediate and incorporated utilization of the thermoelectric component for cooling if the unit dimensions are increased or familiarize with stage change constituents. A compact cooler is suggested by analysts in their examination. In electronic gadgets cooling and execution improvement, TEC shows an exceptionally basic job because of its compacted dimensions, working system. The standard of thermoelectric vitality has adaptable applications for cars as talked about.
In the clinical field, thermoelectric has an exceptionally broad assortment of uses, for example, surgery tools, sensors, medical procedure apparatuses. The benefits of long-life expectancy, no moving parts, and calm activity of thermoelectricity are appropriate for little and medium purpose, yet it has got low proficiency. It could turn into creative signiﬁcant environmentally friendly power vitality goals when the examination endeavors are progressed, and appropriate material improvement may build effectiveness later on. The fuse of thermoelectric with present frameworks would assume a significant job in the expansion of their exhibition.
Acknowledgement: This research is supported by the Structures and Materials (S&M) Research Lab of Prince Sultan University.
Funding Statement: The authors received no specific funding for this study.
Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.
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