This voltage Vo , known as the Seebeck emf, can be expressed as:. If a voltage Vin is applied to terminals Tl and T2 an electrical current I will flow in the circuit. As a result of the current flow, a slight cooling effect Qc will occur at thermocouple junction A where heat is absorbed and a heating effect Qh will occur at junction B where heat is expelled. Note that this effect may be reversed whereby a change in the direction of electric current flow will reverse the direction of heat flow.
The Peltier effect can be expressed mathematically as:. Joule heating, having a magnitude of I x R where R is the electrical resistance , also occurs in the conductors as a result of current flow. This Joule heating effect acts in opposition to the Peltier effect and causes a net reduction of the available cooling. Whether heat is absorbed or expelled depends upon the direction of both the electric current and temperature gradient.
This phenomenon, known as the Thomson Effect, is of interest in respect to the principles involved but plays a negligible role in the operation of practical thermoelectric modules. For this reason, it is ignored. Power Semiconductor Substrate. Process Tool Parts Cleaning. In devices with long thermoelements, the COP is high, and the contact resistances have a little effect on the cooling capacity, while in devices with short thermoelements, the contact resistances have an increased influence on the cooling capacity; in particular, starting from a long thermoelement and reducing its length, the cooling capacity increases up to a maximum value; then it decreases sharply [ 20 ].
As mentioned above, the thermal performance of a TEC depends on the thermoelectric material properties which change with the TEC operating temperature. Some manufacturers use the maximum design parameters and the performance chart [ 43 ]. A key aspect of the use of the TEC performance chart is that the module parameters are considered to be known and unchanged for different devices, while actually these parameters change because of the outcomes of the manufacturing process.
The design procedure illustrated in [ 43 ] is simplified by considering the thermal resistance of the heat sink as one of the key parameters, avoiding the heat transfer analysis of the heat sink.
Thermal design involves the determination of the heat sink geometry considering the thermal resistances and the optimization of the heat sink characteristic. The heat sink located on the hot side is useful to dissipate heat from the TEC system to the environment and is considered an important factor affecting the TEC performance. Therefore, to enhance the TEC performance, the heat sink must have a low thermal resistance to be minimized.
Important TEC efficiency improvements are obtained by optimization of the different types of heat exchangers at the hot side water-air system with a cold plate, pump and fan coil, finned heat sink with fan, heat pipe with fan [ 44 ].
A normal heat sink uses fins to increase heat transfer surface. When the thermal resistance of the heat sink is computed, it is necessary to take into account an additional heat thermal resistance of the thermal grease applied to provide a good thermal contact between TEC and heat sink [ 45 ]. The design of the heat sinks is presented in [ 4 ], where some aspects useful to find the optimal heat sink geometry fin thickness and position are detailed.
Sometimes at the hot side of TEC, thermal storage using phase change materials PCMs or a heat pipe heat exchanger may take the place of a heat sink with fins in order to reduce the temperature T c of the TEC. For thermal storage , the heat sink is designed to have a high storage capacity to keep the sink temperature less than the junction temperature.
In this case, PCMs are useful to improve the performance of the thermoelectric refrigerator. These high-energy-density materials have the advantage that the heat is transferred at constant temperature.
Furthermore, PCMs operate in a wide range of phase change temperatures, providing different alternatives to be used at the hot side and at the cold side of the TEC [ 46 ]. Refrigerators based on PCMs exhibit useful storage capacity behaviour in case of blackout, as they are able to limit the temperature variation during a blackout much more than other materials. The heat pipes are heat exchangers with very high thermal conductivity using ethanol or methanol as refrigerant water.
They are used on the both sides of the TEC to dissipate both the cooling and waste heat to the heat sinks. If heat pipes with a thermosiphon are used at the hot side of the TEC, the waste heat is rejected to the environment by natural or forced convection.
These systems have a low thermal resistance, leading to reduction of the temperature differential between the hot side temperature of the TEC and the environmental temperature. The heat pipes are used at the cold side of TEC to keep T c constant during peak and off-electricity times [ 46 , 47 ]. Two prototypes of thermoelectric refrigerator are described in [ 48 ], one with finned heat sink and the other one with a finned heat sink integrated in an aluminum thermosiphon in which phase change occurs.
The thermosiphon depends on the specific latent heat at the phase change from vapour state to liquid state, useful to disperse the heat efficiently to the environment. The results of the experimental heat sink optimization demonstrated that the thermal resistance between the hot side of the TEC and the environment reduced with about The operating conditions of a thermoelectric refrigerator depend on parameters as environment temperature, humidity, lower setpoint of the internal temperature and difference between higher and lower setpoints of the internal temperature [ 49 ].
This represents a drawback for these refrigerators compared with the thermoelectric refrigerators in which there are no start and stop cycles and the supply voltage gradually increases. However, overall the thermoelectric refrigerators are not competitive with vapour-compression refrigerators in terms of COP [ 10 , 11 , 48 ].
This control is critical in the period in which the TEC is switched off, because in this period, the heat stored in the heat sink connected to the hot terminal returns into the refrigerator compartment; in this way, the power consumption of the refrigerator increases and the COP decreases [ 11 ].
To optimize the system, a thermal bridge aluminium slab was used between the freezer compartment and the thermoelectric compartment.
The power consumption in these environmental conditions for each compartment was 0. The results demonstrated that the total electric power consumption reduced from If the environmental conditions are modified e. In addition, in [ 49 ] a reduction of electric power consumption was obtained by experimental optimization of the temperature controller for a thermoelectric refrigerator in stationary state.
More efficient temperature control systems applied by the manufacturers to increase the performance of the thermoelectric refrigerator include the use of different voltage supply levels for the modules or the exploitation of proportional-integral-differential control systems. In spite of their relatively low efficiency with respect to other refrigeration technologies, the TEC technologies are experiencing a period of development, with subsequent efficiency improvement and reduction of the manufacturing costs [ 52 ].
One of the drivers that have increased the interest in the development and use of TECs as refrigerators is the absence of environmental pollution in the TEC operation, in particular, the absence of chlorofluorocarbon CFC issues. The current trends towards replacement of CFCs consider good solutions with low global warming potential GWP using natural refrigerants like CO 2 used at pressures much higher than traditional refrigerants [ 6 , 53 ].
Further drivers to increase the TEC applications depend on positive aspects of the TECs such as low noise, possibility of operation in different positions, absence of mechanical vibrations, ease of transportation and possibility to obtain accurate temperature control. Today, thermoelectric refrigerators are the most significant applications at the commercial level [ 17 , 40 ].
In addition to domestic refrigerators [ 10 , 54 , 60 ], other applications have been developed for food-related services, such as portable refrigerators [ 55 , 56 , 57 ], food expositors, refrigerators mounted on vehicles for perishable food transportation as well as low-power refrigerators for minibar, hotel room, offices, boats and aircraft services [ 8 ].
Further applications are available for the medical sector vaccine transportation and instruments for blood coagulators, dew point sensors and others , for the military sector and for scientific devices subject to precise temperature control [ 58 ]. In addition, thermoelectric systems are found in the automobile industry for air conditioning or car-seat coolers [ 59 ] and in different applications to the microelectronics sector [ 60 , 61 ].
Besides the applications mentioned above, the present trend towards the use of green energy raises the attention on the possibility of supplying the thermoelectric refrigerator through energy produced from renewable sources.
The refrigerators powered by renewable sources may work in stand-alone of off-grid connection. To connect a thermoelectric refrigerator to the PV module in off-grid mode, the possibilities are [ 8 ]: the refrigerator is directly powered by the PV panel the main components are the PV panel, the battery bank, the battery charge controller and the refrigerator ; and.
Solar-driven thermoelectric refrigerators are of two types, namely, PV-battery thermoelectric systems and PV-PCM thermoelectric systems. The performance of the PV-battery thermoelectric systems depends on the intensity of solar radiation and temperature difference at the hot and cold sides of the TEC.
Thermal storages have generally restricted capacity, and to improve this in some applications, the thermoelectric units use PCM integrated with thermal diodes [ 62 ].
Table 1 presents the technical characteristics of some selected thermoelectric refrigeration units with data available from the literature. The selected cases represent various applications with different capacities from a few litres for medicine transportation to some hundreds of litres for food storage , temperature difference, type of heat sink, AC or DC voltage input, powering from electrical grid connection or PV and electrical power input.
The performance of these units is indicated with cooling capacity and COP. Thermoelectric refrigeration solutions are gaining relevance because of a number of positive aspects, such as long duration, noiseless operation, limited maintenance needs, absence of flammable or toxic refrigerants, possibility of being used in different positions and in movable solutions as well as flexibility of usage through optimized control. This chapter has summarized the principles of thermoelectric refrigeration, by presenting the analytical formulations determining the heat flow rate, cooling capacity and COP of a TEC, illustrating the methods to enhance the TEC performance and indicating the current applications of thermoelectric refrigeration.
The future improvement of the TEC performance, together with the operational flexibility of the TEC driven by appropriate control systems, will increase the variety of the applications of thermoelectric refrigeration in different contexts, from single units to their inclusion into integrated energy systems.
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Downloaded: Abstract This chapter recalls the general principles and main formulations useful in the study of thermoelectric coolers. Keywords refrigeration thermoelectric unit energy indicators cooling capacity coefficient of performance temperature control renewable sources. Introduction The thermoelectric effect represents direct conversion of the temperature difference into voltage and vice versa and refers to phenomena with which the current flows through the thermoelements or legs of a thermoelectric module.
Steady-state and transient approaches 2. The limits of steady-state analysis Steady-state analysis for a TEC is typically carried out by resorting to a set of approximations. Transient analysis Thermoelectric refrigerators are controlled devices that operate in transient conditions. But when summer rolls around and the mercury rises, your cooling capacity rises with it. On a degree day, the cooler will only be able to hover around 65 degrees. This may not be a problem indoors if you have central heating and air conditioning to limit extremes, but the temperature difference can be a big deal in RVs or camping applications.
While thermoelectric cooling does offer fine temperature control, it's crucial to understand that this is only within the range allowed by the outside temperature on any given day. Thermoelectric coolers also don't dehumidify the air around them.
The ceramic plates simply transfer heat away from one area and into another, leaving the moisture content of the air intact. This is very different from compressor cooling, in which cold evaporators on the inside of the machine lower the dew point of the air and cause moisture to condense.
These water droplets are carried outside and left to drip away in a compressor air conditioner, effectively lowering the moisture content of the air in your home. It should be noted that dehumidifying may or may not be a virtue depending on the application; for example, cigar humidors should stay quite moist as they cool, while a refrigerator for food should be dry to help keep rot at bay.
Most people don't build their own electronics, so thermoelectric cooling typically comes into play in small refrigerators or portable coolers for food and drink. So which is better when it comes to choosing a dedicated wine fridge or beverage fridge? Thermoelectric cooling is a fascinating technology, and it definitely has its place when it comes to wine coolers and humidors.
Be sure to carefully compare your options as you shop and keep in mind the features you personally find most important to select the perfect appliance for your home. One application where a thermoelectric cooler is always a good choice? A high-performance cigar humidor. This is because the Peltier effect doesn't have any influence over the humidity levels in your humidor, making it much easier to keep humidity levels where you like them — without having to constantly add moisture to keep up with a compressor's dehumidification.
If you live in a cold climate, a thermoelectric cooler can also be run in reverse, which will allow it to operate as a heater to maintain the perfect temperatures for your cigars all year round. Vote for Your Champion Game Pick. Rookie the Froster is set to win the Championship Game. The new home appliance is pretty much built for March Madness festivities. But its quick Read More.
If you plan to store your cigars for longer than a day or two, you'll need a humidor. How to Set Up and Maintain a Humidor. Learn how Read More. Cigar humidors may look simple, but they're actually highly specialized devices designed to create and maintain a controlled environment for your cigars.
A crucial part Read More. What's the origin of decanting, and how is it done? Learn about decanting your wine. For centuries, people from around the world have been decanting Read More.
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