DE9102118U1 - Device for heat transfer in the thermoelectric heat transport system - Google Patents

Description

M:LA0765B

Device for heat transfer in thermoelectric heat

metransportsystem

In the course of the discussion about the environmental compatibility of the refrigerants used in compression refrigeration circuits, other, already known heat transport systems are becoming increasingly important.

One of these systems are so-called Peltier elements, in which heat is transported between two semiconductor bridges by means of electrode current, stimulated by electric current (Ref.1+2).

As with any other known refrigeration device, the amount of energy Q required to dissipate a certain cooling capacity Qo depends primarily on the temperature difference between To (cooling temperature) and Tc (recooling temperature). The greater this temperature difference is chosen at the design point, the higher the investment costs, and the greater the average temperature difference during operation, the higher the operating costs. Peltier elements are very expensive and, even under the same boundary conditions (To, Tc), do not achieve the cooling performance factor ^k (Q°/Q ^k ) of a compression refrigeration machine under comparable boundary conditions. However, this is the only noticeable disadvantage, which can be reduced to a minimum, in particular by the inventive claim, and opens up new application perspectives for this environmentally friendly technology.

The dependence of the efficiency of a Peltier element will be illustrated using an example. We will consider a Peltier element of size 40*40mm, with a cooling temperature of +5 ⁰ C.

M:LA0765B

To ^0C Tc ^0C Qo P ,5W U k QcQo spec .Qc spec ^{0C 0C} W W/ ^m2 W/ ^m2 +5 ^0C 35 ^0C 38W 65 ,5W (11V) 0.58 103.5W 23850 64375 +5 ^0C 55 ^0C 25W 78 ,5W (13V) 0.32 103,OW 15625 64375 -5 35 36W 127 (15V) 0.28 163.5W 22500 102200 35 29W 65 (11V) 0.44 94.5W 18125 59600

-5°C 35°C 10W 22,IW (6,5V) 0,45 32,IW 6250 20100

Tab.l

Lit.l Textbook of Refrigeration Technology,

S23,172,235

Lit. 2 Energy Fricke/Borst, p.122, 143

H.L.von

Melcor, one of the most important manufacturers of Peltier elements, writes in its brochure:

"In most cases, the temperature of the cold side (Tc) is specified as the task. Tc is usually, if there is good thermal contact and material with good thermal conductivity is used, directly set as the surface temperature of the TE. When using intermediate media (gas, liquid), the heat transfer resistance to the TE surface must be taken into account. Tc must then be set a few degrees lower."

It is obviously assumed that there is usually a direct connection between the body to be cooled and the Peltier element.

When transferring to a liquid or gaseous heat transfer medium, the heat transfer coefficient α (W/m ^z K) otherwise has a decisive influence on the number of Peltier elements to be installed and their operating costs.

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For optimal transfer to a flowing medium at 1 K temperature, the heat transfer coefficients must be realized in accordance with the heat flow densities shown in Table 1. However, air with free convection has maximum values of approx. 30 W/m^K, and with forced flow of approx. 115 W/m^K. With water as the heat transfer medium, heat transfer coefficients of approx. 2500 W/m K can be realized on smooth surfaces.

A significant disadvantage of known Peltier elements is that the heat flow density in the limiting electrical insulation layer intended for heat dissipation is significantly higher than the heat transfer coefficients that can be achieved on a smooth wall structure of usual fluids suitable for heat transport.

From the available figures it is clear that Peltier elements, which are intended to be used to supply heat transfer circuits, are operated with great difficulty. As a result, the deterioration in efficiency leads to a significant increase in both operating and installation costs.

The problem is solved by a thermoelectric Peltier module or a thermoelectric heating or cooling device according to claim 1.

In the Peltier module according to the invention, the ceramic plates enclosing the Peltier element are designed in the form of a porous, permeable sinter matrix or a sinter matrix is combined with a conventional ceramic plate to provide good thermal conductivity. Such a sinter matrix, especially if it consists of a highly conductive material such as copper or aluminum granulate, is able to handle extraordinarily high heat flow densities in relation to the boundary wall area, which are

M:LA0765B ' 4

Order of magnitude of the heat flow density of the Peltier element. All other components of the Peltier module according to the invention are designed like conventional Peltier modules, so that a detailed description is not necessary.

The Peltier module according to the invention preferably consists of a plurality of conductor elements made of semiconductor material that are connected thermally in parallel and electrically in series, with successive conductor elements being alternately n- or p-doped (Fig. 1).

The contact area between the Peltier module and the sinter matrix will generally be as large as the effective heat transfer area of the Peltier module, so that the heat exchanger area defined by the inner surface of the sinter matrix can be varied by adjusting the dimension "H" (Fig. 2) as required.

Any side of the matrix form can serve as an inflow or outflow surface, and any of these sides can be tightly sealed in any combination so that the most sensible flow direction of the fluid can be selected.

In Fig. 3, a data sheet of an exemplary embodiment of the invention is given.

Claims (5)

M:LA0765A Protection claims 1. Thermoelectric cooling or heating device with two conductor elements (1, 2) which have different electrical conductivity, which are electrically connected to one another at two ends by means of a contact bridge (9) and which have electrical connections (13, 14) at the other two ends, a heat absorption device (15) having a first electrically insulating cover (16) covering the contact bridge (9), and a heat dissipation device (17) having a second electrically insulating cover (18) covering the electrical connections (13, 14), characterized in that at least the heat absorption device (15) or the heat emission device (17) have a porous, permeable sinter matrix (20, 21). 25 2. Device according to claim 1, characterized in that the electrically insulating cover of the heat absorption device and/or the heat emission device is designed as a porous, permeable sinter matrix . 3. Device according to at least one of the preceding claims, characterized in that the two conductor elements consist of differently doped semiconductor materials, e.g. n- and p-doped bismuth telluride material. M:LA0765A 4. Device according to at least one of the preceding claims, characterized in that a plurality of pairs of conductor elements are provided, which have a common heat-emitting device and a common heat-absorbing device, and wherein the individual conductor elements are thermally connected in parallel and electrically connected in series. 5. Device according to at least one of the preceding claims, characterized in that the sinter matrix consists of material that conducts heat well, such as copper or aluminum granulate.