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.
Wine Coolers vs. Regular Refrigerators. When should you use a wine cooler instead of a regular refrigerator? When you're a wine connoisseur, you may one day wish to convert your Read More.
Dual Zone Wine Fridges. Black Stainless Steel Fridges. Freestanding Fridges. Outdoor Beverage Fridges. Schematic of Peltier effect and Thomson effect in a thermocouple. Its expression is given by. If a current density J exists through a homogeneous conductor, the heat production per unit volume or volumetric heat generation is. The Seebeck effect converts temperature to current and occurs like the Peltier effect, but the direction of the electric current is reversed. The Seebeck effect appears when a temperature gradient along a conductor provides a voltage increment.
The Seebeck voltage appearing at the circuit junctions is. The Seebeck coefficient or thermoelectric power is a very important parameter for the thermoelectric materials, determining the performance of Peltier elements. For a good thermoelectric material, the Seebeck coefficient has to be high in order to obtain the desired voltage more easily, the electrical conductivity has to be high, and the thermal conductivity has to be small to reduce the thermal losses in the junctions of the thermocouple [ 4 ].
The sign of the Seebeck coefficient depends on the hole and electron flow: A negative Seebeck coefficient is obtained in semiconductors negatively doped e. N-type semiconductors. A positive Seebeck coefficient is obtained in semiconductors positively doped e. P-type semiconductors. There is interdependence between the Peltier coefficient and the Seebeck coefficient, as well as between the Seebeck coefficient and the Thomson coefficient, given by the following relationships [ 5 , 6 ]:.
A thermoelectric cooler TEC is a semiconductor composed of an electronic component which transforms electrical energy into a temperature gradient. The TEC consists of one or more thermoelectric couples.
The thermoelectric couples are connected in such a way that when the current flows through the device, both the P-type holes and the N-type electrons move towards the same side of the device.
The two legs are made of two different thermoelectric materials. A thermoelectric material is defined as an alloy of materials that generates thermoelectric properties thermal conductivity, electric conductivity and Seebeck coefficient. The quality as a semiconductor material to be cooled strictly depends on the transport properties of the material Seebeck voltage, electrical resistivity and thermal conductivity as well as the operational temperature field between the cold and hot ends [ 5 ].
Considering that the input voltage of a single thermoelectric couple is reduced, many thermoelectric couples are connected to each other by junctions and are sandwiched between two ceramic substrates to form a thermoelectric module TEM. These ceramic substrates act as insulator from electrical point of view but allow the thermoelectric couples to be thermally in parallel.
The number of thermoelectric couples is influenced by the needed cooling capacity and the maximum electric current [ 5 ]. When a low voltage DC power source is applied to the free end of the TEM, the heat flow rate is transferred from one side to other side of the device through the N- and P-semiconductor legs and junctions.
In this case, one side of the TEM is cooled, and the other side is heated [ 7 ]. In the cooling mode, the sense of the electrical current is from the N-type semiconductor to the P-type semiconductor Figure 2. The Seebeck voltage is generated in the device when there is a temperature difference between the junctions of the thermoelements [ 8 ].
Schematic of a thermoelectric module TEM operating in cooling mode. The direction of the current is then essential to establish the functionality of the device.
If the direction of the electrical current is reversed, the compartment would be heated instead of being cooled. At the top of every junction, the temperature is the same T c , and at the bottom of every junction, the temperature is the same T h.
Through the cold junction, the electrons are transported from a low energy level inside the P-type semiconductor legs to a high energy level inside the N-type semiconductor legs.
This heat is dissipated at the heat sink a passive heat exchanger that cools a device by dissipating heat into the environment , and the free electrons flow to an inferior energy level in the P-type semiconductor. The main components of a refrigeration unit Figure 3 are [ 7 , 9 , 10 ]: the insulated refrigerator cabinet with thermoelectric technology having variable dimensions e. The TEC can operate in a definite operating range of its temperature difference.
To keep this temperature difference inside the specific operating range, a TEC is compulsory to have a heat sink at the hot end to dissipate heat from the TEC to environment.
Sometimes, another heat sink with fins is fixed inside the compartment to improve the heat transfer from the insulated volume which is cooled fluid, solid to the cold side of the TEC. In this case, the heat sink is cooled at a temperature lower than the insulated volume, and the heat flowing between the fins is collected by means of a fan [ 11 , 12 , 13 ];.
Schematic of a TEM used for the refrigeration unit. The continuity equation is. The general heat diffusion equation for transient state [ 14 ] is.
Substituting Eq. Steady-state analysis for a TEC is typically carried out by resorting to a set of approximations. In these conditions, there is no heat transfer from or to the external environment, so that the heat flows occur only between the source and the sink.
On these assumptions, Eq. By replacing in Eq. Let us consider the boundary conditions between the following limits Figure 4 :. Schematic of a TEC geometric elements and material properties. Then, Eq. However, this model can be used only at first approximation for the selection of thermocouple materials [ 9 ].
In practice, the semiconductor properties depend on temperature, the contact resistances cannot be avoided, and the Thomson effect cannot be neglected. Moreover, in the steady-state model, the temperatures T h and T c are input values that have to be determined accurately. If the object to be cooled is directly in contact with the TEC cold surface, the object temperature has the same value as the temperature of the TEC cold surface T c. However, if the object to be cooled is not directly in contact with the TEC cold surface, e.
In this case, the cold surface of the TEC has to be some degrees colder than the desired temperature in the refrigerator compartment, and the temperature T c is unknown. With a similar reasoning, if a heat exchanger is placed at the hot side, the known value is the ambient temperature, and the temperature T h is unknown. The temperature distribution of a complex system refrigerator with TEC is depicted in Figure 5.
Schematic of temperature profile in a thermoelectric refrigeration system. Therefore, in practical applications in which the TEC is connected to other components e. Thereby, the temperatures at the TEC terminals can be determined by using a dedicated model of the interconnected components. These temperatures are calculated from the solution of the overall system equations, in which all the temperature-dependent thermoelectric effects Peltier, Seebeck, Thomson and Joule are taken into account [ 17 ].
Thermoelectric refrigerators are controlled devices that operate in transient conditions. Thereby, it is important to formulate a detailed model taking into account all the thermoelectric effects and the dependence of the model parameters on temperature.
The solution of this equation has been obtained in [ 18 ] by constructing an electrothermal equivalent model with resistances and capacities in which the thermoelectric modules are represented through a multi-node structure and the other components are represented by a single node. The implicit finite difference method has been used to solve the equations. In this model, the input data are the number of modules, the geometric parameters lengths and cross areas , the structural characteristics of the components, the heat flow rate produced by the heat source, the voltage supply from the electrical system and the environment temperature.
The structural characteristics can be given as constant values density, specific heat, surface electrical resistivity of the thermoelectric elements or can be expressed as functions of the temperatures Seebeck coefficient, electrical resistivity and thermal conductivity.
Since the model is non-linear, the solution requires an iterative process, so that the initialization of the temperatures at each node of the model has to be provided as well. The outputs of the method with their evolutions in time are the temperatures at all the nodes, the heat flow rates in each component, the power produced by the modules and consumed by the fan and the efficiencies of the modules and of the system. This formulation is consistent with an experimental application, such as the one presented in [ 17 ].
The energy indicators useful for the design and the performance of TEC are the cooling capacity, the rate of heat rejection, the input electrical power, the dimensionless figure of merit ZT and the coefficient of performance COP. The input electrical power P el or electrical power consumption [ 19 ] is. An important physical property of the TEM is the figure of merit Z.
The valence band is occupied by the electrons with the highest energy level of those which are still attached to their parent atoms, these are the outer most or valence electrons. The conduction band is occupied by electrons which are free from their parent atoms.
These electrons are free to move through the material. When a voltage is applied these electrons will drift to produce an electrical current. In semiconductors there is an gap between the valence and conduction bands. Semiconductors are mainly classified into two categories: Intrinsic and Extrinsic. An intrinsic semiconductor material is chemically very pure and possesses poor conductivity.
It has equal numbers of negative carriers electrons and positive carriers holes. Where as an extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor and improves its conductivity.
Introducing impurities into the semiconductor materials doping process can control their conductivity. Doping process produces two groups of semiconductors: the negative charge conductor n-type and the positive charge conductor p-type.
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