Patent Description:
The NEDO and TherMAT National Project has developed a thermoelectric conversion module for cogeneration that can improve power efficiency by <NUM>% (for example, output of <NUM> kW/m<NUM> in the cogeneration of 35kW class) from exhaust heat (from <NUM> to <NUM>) of cogeneration. In the cogeneration, while <NUM>% of total fuel energy is wasted as heat, there is a demand to increase electricity even by <NUM>%. An improvement of about <NUM>% in a gas engine installed in the cogeneration is possible by improving the engine, but further improvement requires other improvement technologies.

In general, a thermoelectric conversion module is configured by combining a p-type thermoelectric conversion material and an n-type thermoelectric conversion material. Thus, in order to obtain high thermoelectric conversion characteristics in the thermoelectric conversion module, it is obviously desired to obtain a high performance index ZT for both p-type and n-type thermoelectric conversion materials. Furthermore, performance can be maximized by optimizing the structure in accordance with element characteristics peculiar to the materials used.

In this regard, for example, in Patent Literature <NUM>, a cross-sectional area ratio of the p-type element and the n-type element for maximizing the characteristics is specified as p-type: n-type = t: <NUM> - t, where <NUM> ≤ t ≤ <NUM> (see paragraph [<NUM>] of Patent Literature <NUM>). This is an optimum structure for thermoelectric elements based on an Fe-Ti-Si ternary system.

Further, for example, in Patent Literature <NUM>, although a material system of the thermoelectric element is not shown, the cross-sectional area ratio t is defined as <NUM> ≤ t ≤ <NUM>.

<CIT> refers to a thermoelectric conversion module and thermoelectric conversion device. <CIT> discloses a manufacturing method of thermoelectric converter.

In a n-type module that combines a p-type element and an n-type element of ZT = <NUM> class, a power generation output changes depending on a module structure (element area and element thickness) and a heat source surface area which is a factor of a heat transfer capacity of the heat exchange part.

However, in the conventional art represented by Patent Literatures <NUM> and <NUM>, structural factors of the thermoelectric conversion module have not been optimized, and a maximum power output has not yet been obtained.

In view of such circumstances, the present disclosure provides a thermoelectric conversion module that further improves power efficiency from exhaust heat of cogeneration.

In order to solve the above problem, the subject matter of claim <NUM> is provided. The present disclosure proposes, for example, a thermoelectric assembly comprising a thermoelectric conversion module and heat supply units, wherein the thermoelectric conversion module comprises a p-type thermoelectric conversion material and an n-type thermoelectric conversion material, each of which is a silicide material based on a binary system, wherein the thermoelectric assembly includes multiple thermoelectric conversion modules, wherein the heat supply units are disposed on an upper surface and a lower surface in a thickness direction of the thermoelectric conversion module,are configured to impart a temperature difference to the thermoelectric conversion module, and are configured to supply heat for power generation by Seebeck effect of the p-type and n-type thermoelectric conversion materials and cooling source discharging heat, wherein the p-type and n-type thermoelectric conversion materials have a cross-sectional area ratio t satisfying:.

More features of the present disclosure will be apparent from the description of the present specification and the accompanying drawings. The aspects of the present disclosure are achieved and implemented by the elements, combinations of various elements, the following detailed description, and the aspects of the appended claims.

The technology of the present disclosure can achieve a thermoelectric conversion module having a maximum power output exceeding <NUM> kW/m<NUM> (equivalent to a conversion efficiency of <NUM>%).

The embodiment of the present disclosure is based on our binary silicide material (which is distinctively different from Patent Literatures <NUM> and <NUM>). Further, in the present embodiment, the structure is optimized in consideration of heat transfer regarding an outlet of a heat flow (which is different from Patent Literature <NUM>).

In the present embodiment, the cross-sectional area ratio of the p-type thermoelectric conversion element and the n-type thermoelectric conversion element manufactured from a silicide material based on the binary system configuring the thermoelectric conversion module is optimized and the cross-sectional area of the electrodes at the outlet of the heat flow is optimized, thereby achieving a maximum power output (the power output of the thermoelectric conversion module using a silicide material based on the binary system is maximized). Hereinafter, examples according to the present embodiment will be described. In the examples, the description is given in sufficient detail for those skilled in the art to implement the technology of the present disclosure. However, other implementations and forms are also possible, and it is to be understood that a configuration or structure can be changed and various elements can be replaced without departing from the scope of the technical idea of the present disclosure. Therefore, the following description is not to be construed solely by the examples.

<FIG> is a diagram showing a configuration example of a single-pair thermoelectric conversion module <NUM>. <FIG> is a diagram showing a configuration example of an electrical equivalent circuit of the single-pair thermoelectric conversion module <NUM>.

Performance of the single-pair thermoelectric conversion module <NUM> is derived from the electrical equivalent circuit shown in <FIG>. Using the symbols in <FIG>, Equation (<NUM>) is established for voltage. <NUM>] <MAT>.

From equation (<NUM>), output Pout can be obtained as in Equation (<NUM>). <NUM>] <MAT>.

The maximum power output Pmax of the thermoelectric conversion module is represented as in Equation (<NUM>). <NUM>]
In the case of R = rp + rn : <MAT>.

Here, an internal resistances rp and rn can be obtained from Equation (<NUM>). <NUM>] <MAT>.

Here, ρp and ρn are electrical resistivities in a length direction of the p-type and n-type thermoelectric conversion elements, respectively. Furthermore, generated voltages Vp and Vn can be obtained from a temperature integration of Seebeck coefficients (Sp and Sn) as in Equation (<NUM>). <NUM>] <MAT>.

A temperature difference is smaller than an environmental temperature difference ΔT = TH-TC. This is because a thermal resistance is generated due to the heat transfer coefficient at an interface and thermal conductivity of the thermoelectric conversion element. As a result, the temperature difference generated at both ends of the element is represented as in Equation (<NUM>). <NUM>] <MAT>.

Here, hp is the heat transfer coefficient at the interface between a high temperature electrode and the p-type thermoelectric conversion element, hp* is the effective heat transfer coefficient of a low temperature electrode, and hn and hn* are defined similarly. The effective heat transfer coefficient is defined as in Equation (<NUM>). <NUM>] <MAT>.

Here, d is a thickness of the electrode and κ is the thermal conductivity of the electrode. Considering that the electrodes are thin and have high thermal conductivity and that the heat transfer coefficient is smaller at a water-cooling interface than at an element interface, Equation (<NUM>) can be approximately represented by the following Equation (<NUM>). <NUM>] <MAT>.

Here, h' is the heat transfer coefficient of water cooling, Ap and An are the cross-sectional areas of the element, and Ap' and An' are surface areas of a water cooling part. According to the experimental data, temperature characteristics can be approximated linearly. From Equation (<NUM>) using the symbol <> indicating an average, the internal resistance and the generated voltage are represented as in Equation (<NUM>). <NUM>] <MAT>
[Math. <NUM>] <MAT>.

Using Equations (<NUM>) and (<NUM>), the maximum power output Pmax of power generation is represented as in Equation (<NUM>), and the maximum power output per unit area is represented as in Equation (<NUM>). <NUM>] <MAT> [Math. <NUM>] <MAT>.

Here, α is a filling factor and is defined as in Equation (<NUM>). <NUM>] <MAT>.

Here, an area A is represented as in Equation (<NUM>), and each Ap and An can be represented as in Equation (<NUM>) by using the cross-sectional area ratio t. <NUM>] <MAT> [Math. <NUM>] <MAT>.

<FIG> is a diagram schematically showing a state of the cross-sectional areas Ap and An. In <FIG>, a shape of the cross-sectional area is represented by a square; however, according to a theoretical formula, the result is irrelevant to the shape of the cross-sectional area and a circular, elliptical, or polygonal shape is also possible. For relaxing distortion, a circular shape is considered to be preferable.

<FIG> is a diagram showing a state of cross-sectional areas in a multiple-pair module. In the multiple-pair module, as shown in <FIG>, the filling factor α is obtained by (a sum of the cross-sectional areas of the p-type element and the n-type element) ÷ (a total bottom area of the module). Using the above, g(t) and v(L) are defined as in Equations (<NUM>) and (<NUM>), respectively. <NUM>] <MAT> [Math. <NUM>] <MAT>.

Here, fp (L) and fn (L) are defined by Equation (<NUM>). <NUM>] <MAT>.

In order to maximize the power generation output per unit area Pmax/Atot, it is only necessary to minimize (t) and maximize v(L). First, g(t) is minimized in a state as shown in Equation (<NUM>). <NUM>] <MAT>.

This means that the cross-sectional area ratio is determined only from the electrical resistivity as shown in Equation (<NUM>). <NUM>] <MAT>.

Then, a minimum value of g(t) is represented as in Equation (<NUM>). <NUM>] <MAT>.

Next, for maximizing v(L), a numerical calculation was performed to avoid a complicated equation.

Thermoelectric performance of the silicide material based on the binary system (p-type thermoelectric element MnSi<NUM> and n-type thermoelectric element Mg<NUM>Si) was calculated. Assuming that a high temperature part is at <NUM> and a low temperature part is at <NUM>, the following physical property values were used.

Sp = <NUM> to <NUM>µV/K, kp = <NUM> to <NUM> W/Km, ρp = <NUM> to <NUM>µΩm, Sn = -<NUM> to -<NUM>µV/K, kn = <NUM> to <NUM> W/Km, and ρn = <NUM> to <NUM>µΩm.

<FIG> is a graph showing the calculation results of the maximum power output per unit area Pmax/Atot with respect to the cross-sectional area ratio t. <FIG> shows that the maximum output per unit area Pmax/Atot is the largest at around t = <NUM>. The value at t = <NUM> is determined only by the electrical resistivity. Note that <FIG> shows the results in a case where the effective heat transfer coefficient is <NUM>,<NUM> W/m<NUM>K, which matches a condition that the maximum power output is exactly <NUM> kW/m<NUM>. In this case, <FIG> shows that a maximum performance can be obtained where <NUM> < t <<NUM>.

<FIG> is a graph showing the calculation result of the maximum power output per unit area Pmax/Atot with respect to the length L of an element, using the effective heat transfer coefficient h* as a parameter. The graph shows that <NUM> kW/m<NUM> (equivalent to a conversion efficiency of <NUM>%) can be achieved when the effective heat transfer coefficient is h* > <NUM>,<NUM> W/m<NUM>K. The Microelectronics Package Handbook (p. <NUM>, Nikkei Business Publications, Inc. ) describes that the heat transfer coefficient of forced water cooling is represented as h'= <NUM>,<NUM> to <NUM>,<NUM> W/m<NUM>K. This indicates that even when h' = <NUM>,<NUM> W/m<NUM>K, where the heat transfer coefficient is worst, the maximum power output of <NUM> kW/m<NUM> can be achieved if Equation (<NUM>) is satisfied for the cross-sectional area ratio. <NUM>] <MAT>.

Experiments were conducted on a single-pair module and a nine-pair module actually manufactured, and the following results were obtained for the single-pair module.

A difference between Module-<NUM> and Module-<NUM> is the cross-sectional area ratio, which corresponds to t = <NUM> for Module-<NUM> and t = <NUM> for Module-<NUM>. As predicted by the calculation of cross-sectional area ratio optimization, the output was slightly higher at t = <NUM> as an asymmetric area ratio.

Claim 1:
A thermoelectric assembly, comprising a thermoelectric conversion module and heat supply units,
wherein the thermoelectric conversion module (<NUM>) comprises a p-type thermoelectric conversion material (<NUM>) and an n-type thermoelectric conversion material (<NUM>), each of which is a silicide material based on a binary system;
wherein the thermoelectric assembly includes multiple thermoelectric conversion modules,
wherein the heat supply units are disposed on an upper surface and a lower surface in a thickness direction of the thermoelectric conversion module (<NUM>), are configured to impart a temperature difference to the thermoelectric conversion module (<NUM>), and are configured to supply heat for power generation by Seebeck effect of the p-type and n-type thermoelectric conversion materials (<NUM>, <NUM>) and cooling source discharging heat,
wherein the p-type and n-type thermoelectric conversion materials (<NUM>, <NUM>) have a cross-sectional area ratio t satisfying:
the p-type thermoelectric conversion material (<NUM>) :
the n-type thermoelectric conversion material (<NUM>) =
t:(<NUM>-t),
characterized in that <NUM> < t < <NUM>, and a length L of a thermoelectric element satisfying L ≤ <NUM>,
wherein, when cross-sectional areas where electrodes (<NUM>) for discharging the heat from the p-type thermoelectric conversion material (<NUM>) having a cross-sectional area Ap and the n-type thermoelectric conversion material (<NUM>) having a cross-sectional area An are in contact with the cooling source are Ap' and An', respectively, the thermoelectric conversion module (<NUM>) has an area ratio of Ap'/Ap ≥ <NUM> and An'/An ≥ <NUM>.