RU2087054C1 - Thermoelectric multiple-stage cooler - Google Patents

Abstract

FIELD: radio and space engineering and other industries. SUBSTANCE: introduced in elementary N-stage cell are (N-1) stage circuits of same polarity of conductivity with one to (N-1) stages electrically connected to three-dimensional passive superconducting circuits using branched circuit of current distribution among stages. Number of passive circuits is same as that of active circuits and they are inclined to the latter. EFFECT: improved design, enlarged functional capabilities. 3 dwg

Description

The invention relates to thermoelectric devices for cooling, in particular to cascade chillers operating at low (50 ^o C150 K) temperatures, and can be used in electronics, space technology and other fields.

 Known cascade thermoelectric coolers containing semiconductor branches of II- and p-type conductivity, connected according to the scheme with parallel (branched) power supply of cascades [1] that allows you to supply current only to the “hottest” junctions and does not require electrical insulating heat transfers that introduce thermal resistance between cascades.

 However, at low temperatures (below 150K), the thermoelectric efficiency of such coolers is low, since there are currently no highly efficient p-type branches for this temperature range. (Type II branches - BiSb).

To increase the efficiency of the cooler, instead of p-type semiconductor branches, superconducting branches are installed, which, although they do not have thermoelectric properties, do not emit Joule heat [2]
It is possible to use non-superconducting passive branches of thermocouples.

 A simple replacement in the known cascade cooler with n-branches from BiSb of p-type semiconductor branches by superconducting branches does not realize all the possibilities of such a replacement. There is a loss of temperature difference due to the mutual arrangement of the passive (superconducting) and active (semiconductor) branches of the thermocouple, when the active (Peltier-generating heat) branch of the first (colder) cascade is located on the passive (not absorbing heat) branch of the second cascade, etc. . Temperature imbalances in the contact plates also aggravate the main drawback of the considered circuit, the difficulty of implementing the maximum economy mode due to the equality of voltage drops on thermocouples of all cascades.

These disadvantages are mainly eliminated in the well-known cascade thermoelectric cooler [3]
In this cooler (prototype), the active (semiconductor) branches are located one above the other, forming one N-cascade active branch in an elementary N-cascade cell. Between the active branches (cascades), electrical insulating plates and metal plates are installed.

 The location of the passive (superconducting) branches is such that it is possible both independently allowing the implementation of an economical mode and parallel (when combining unipolar outputs) power supply. (In the latter case, the voltage drops in the cascades are the same).

 The specified cascade cooler has several disadvantages.

In an elementary 2-cascade cell, two active branches have three passive branches. This complicates the design and reduces the thermoelectric figure of merit (temperature drop for a given heat load or cooling capacity for a given temperature drop) due to heat inflows through an additional passive branch. (The current cross section of a superconducting branch, usually made of ceramic, cannot be infinitesimal, because it is determined by the requirements of strength and critical current density.)
When building cascades for each subsequent active branch, two passive branches are required, one of which (additional) is directly connected to the power source, i.e. with the environment (the hottest junctions of the cooler).

 In the general case, N active branches require (2N 1) passive branches, of which N-1 are additional (from the power source to the corresponding active branch).

 The ratio of thermocouples in cascades is 1 1, which complicates the coordination of cascades and reduces the supply voltage of the unit cell and the cooler as a whole.

 With parallel cascade power supply (unipolar leads are combined), it is impossible to refuse insulating heat transfers that reduce the overall temperature difference (thermoelectric figure of merit), in contrast to the classic cascade cooler with parallel (branched) cascade power supply (see analog).

 The aim of the invention is to eliminate these drawbacks and increase thermoelectric figure of merit by reducing heat losses, as well as improving the matching conditions of cascades, increasing the supply voltage.

 To achieve this goal, in addition to the main N-cascade active branch, from one-to (N 1) -cascade active branches, electrically connected to passive branches according to the scheme with branching of currents in cascades, the number of passive branches is equal to the number of active, and voluminous passive branches are inclined to the active.

 The decrease in the number of passive branches per active branch and their gradual cooling due to additional active branches minimizes the heat influx to the heat-absorbing junctions of the active branches along the passive branches, which increases the thermoelectric efficiency of the cooler.

 A decrease in the heat influx along the passive branches occurs due to the fact that the inclined passive branches have a longer current length than the active branches.

 Additional active branches increase the supply voltage of the elementary N-cascade cell and the cooler as a whole.

 Despite the branched (parallel) power supply, voltage drops in cascades of the main H-cascade branch are generally different and can be easily optimized.

 Thus, the matching conditions of cascades in the H-cascade branch are improved.

 In FIG. 1 and 2 schematically depict two and three-stage unit cells of a cooler; in FIG. 3 electrical diagram of the connection of the branches of thermocouples.

The cooler contains active semiconductor branches 1, for example, from n-type BiSb and passive superconducting branches 2, for example, from Y, Ba ₂ Cu ₃ O ₇ ceramics with a temperature of transition to the superconducting state T _with 92 ^° C95K or thallium ceramics with T _with 120K, interconnected with a highly conductive metal 3 (copper, solder, etc.) with the formation of junctions.

 Active branches of thermocouples installed one on top of another form cascading active branches.

 The unitary two-stage cooler cell contains a two- and single-stage active branch, and the three-stage unit cell of a three-, two-, and single-stage active branch.

 The active branches in each cascaded active branch can be of the same current section and different current heights (Fig. 1), different current sections and the same current heights (Fig. 2), or different current sections and current heights.

 The current section of the active branches is approximately an order of magnitude larger than the minimum possible current section of the passive branches.

 Passive branches, the number of which is equal to the number of active, can be combined into common plates (Fig. 1).

 The cooler operates as follows.

 At an ambient temperature equal to the transition temperature of the passive branches from the superconducting state, the cooler is ready for operation.

 DC electric current distributed in accordance with the circuit shown in FIG. 3, causes the Peltier effect.

 Next, we consider the work on the example of a three-stage cooler (Fig. 2) and, first of all, the main three-stage active branch.

The heat Q _o generated by the cooling object and the heat supplied by the thermal conductivity of the passive branch 1 of the cascade are absorbed at the working junction of the active branch 1 of the cascade.

 At the opposite junction of the active branch 1 of the cascade, this heat plus heat corresponding to the energy consumed by the active branch 1 of the cascade is released. Heat also flows here through the passive branch of the second cascade.

 The active branches of the II and III cascades work in a similar way, only heat from the fuel junction of the active branch of the III cascade is transferred to the environment.

After reaching the junction mode, temperatures T ₀ <T ₁ <T ₂ <T are set.

 Two-stage and single-stage active branches of a three-stage cooler cool passive branches, reducing heat inflows on junctions of the main three-stage branch, which increases thermoelectric figure of merit. This is also facilitated by the fact that passive branches of superconducting ceramics (volume branches) located obliquely have a slightly longer length than active branches.

 The proposed device helps to solve the problem of cooling electronic components in the temperature range below 150K, in which traditional thermoelectric coolers based on bismuth and antimony chalcogenides produced by industry are ineffective. Its technical and economic advantages over the prototype are determined by a decrease in the loss of thermoelectric efficiency when using passive superconducting branches due to the reduction of heat gain through them.

Claims (1)

 A cascade thermoelectric cooler containing active semiconductor branches of one type of conductivity, mounted one on top of the other and forming one active N-cascade branch in a unit N-cascade cell, and bulk passive superconducting branches electrically connected to active semiconductor branches, characterized in that in elementary N-cascade cell introduced (N 1) -cascade branches of the same type of conductivity, with the number of cascades from one to (N 1), electrically connected to bulk passive superconducting and branches according to the scheme of parallel cascade supply, moreover, volumetric passive superconducting branches are inclined to the active ones and their number is equal to the number of active ones.

Images