# Discussion on the solar concentrating thermoelectric generation using micro-channel heat pipe array

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## Abstract

Heat pipe is a high efficient tool in solar energy applications. In this paper, a novel solar concentrating thermoelectric generation using micro-channel heat pipe array (STEG-MCHP) was presented. The flat-plate micro-channel heat pipe array not only has a higher heat transfer performance than the common heat pipe, but also can be placed on the surface of TEG closely, which can further reduce the thermal resistance between the heat pipe and the TEG. A preliminary comparison experiment was also conducted to indicate the advantages of the STEG-MCHP. The optimization based on the model verified by the experiment was demonstrated, and the concentration ratio and selective absorbing coating area were also discussed. In addition, the cost analysis was also performed to compare between the STEG-MCHP and the common solar concentrating TEGs in series. The outcome showed that the solar concentrating thermoelectric generation using micro-channel heat pipe array has the higher electrical efficiency and lower cost, which may provide a suitable way for solar TEG applications.

## List of symbols

- A
Area of selective absorbing coating

- \(a_{teg}\)
Cross-sectional area of a P or N leg m

^{2}- \(C\)
Concentration ratio

- \(C_{fx}\)
Local friction coefficient

- \(C_{p}\)
Specific heat of air kJ/(kg K)

- \(E_{con}\)
Heat flux via conduction W

- \(E_{\text{cov}}\)
Heat flux via convection W

- \(E_{in}\)
Solar energy absorbed by selective absorbing coating W

- \(E_{rad}\)
Heat flux via radiation W

- \(G\)
Solar radiation W/m

^{2}- \(h_{\text{cov}}\)
Coefficient of convection heat transfer W/(m

^{2}K)- \(h_{rad}\)
Coefficient of radiation heat transfer W/(m

^{2}K)- \(I\)
Current A

- \(K\)
Thermal conductivity of heat pipe W m

^{−1}k^{−1}- \(k_{air}\)
Thermal conductivity of air W m

^{−1}k^{−1}- \(k_{teg}\)
Thermal conductivity of TEG W m

^{−1}k^{−1}- L
Length of the heat sink m

- \(L_{hp}\)
Length of heat pipe m

- \(l_{teg}\)
Height of TEG m

- \(n_{teg}\)
Numbers of PN junction

- \(Nu\)
Nuselt number

- \(\Pr\)
Prandtl number

- \(Q_{tegh}\)
Energy that passed in hot side of the TEG W

- \(Q_{tegl}\)
Energy that passed out of cold side of the TEG W

- \(R_{conf}\)
Resistance of the heat conduction in heat sink KW

^{−1}- \(R_{{\text{cov} f}}\)
Thermal resistance of convection Heat transfer between heat sink and ambient air KW

^{−1}- \(R_{ct1}\)
Thermal contact resistance between selective absorbing coating and heat pipe KW

^{−1}- \(R_{ct2}\)
Thermal contact resistance between heat pipe and the TEG KW

^{−1}- \({\text{R}}_{ct3}\)
Thermal contact resistance between TEG and heat sink KW

^{−1}- \(R_{fin}\)
Thermal resistance of the heat sink KW

^{−1}- \(r_{teg}\)
Electrical resistivity of P or N junction Ω m

- \(\text{Re}\)
Reynolds number

- \(St\)
Stanton number

- \(S_{1}\)
Cross section area of the heat sink m

^{2}- \(S_{2}\)
Total area of the heat sink m

^{2}- \(T_{a}\)
Temperature of ambient air K

- \(T_{h}\)
Temperature of the evaporating side of the heat pipe K

- \(T_{tegl}\)
The temperature of cold side of TEG K

- \(T_{tegh}\)
Temperature of the hot side of TEG K

- \(T_{1}\)
Temperature of the condensate side of the heat pipe K

- \(T_{p}\)
Temperature of absorbing coating K

- \(T_{sky}\)
Temperature of sky K

- \(u\)
Wind speed m/s

## Greek letters

- \(\alpha\)
Heat diffusivity m

^{2}/s- \(\alpha_{b}\)
Absorptivity of absorbing coating

- \(\alpha_{teg}\)
Seebeck coefficient VK

^{−1}- \(\delta\)
Stefan–Boltzmann constant Wm

^{−2}K^{−4}- \(\varepsilon\)
Reflectivity of absorbing coating

- \(\mu\)
Viscosity (dynamic)2, N.s/m

^{2}- \(\nu\)
Kinematic viscosity, \({{{\text{m}}^{2} } \mathord{\left/ {\vphantom {{{\text{m}}^{2} } {\text{s}}}} \right. \kern-0pt} {\text{s}}}\)

- \(\rho\)
Density of air kg/m

^{3}

## Notes

### Acknowledgements

The study was sponsored by the National Science Foundation of China (Grant Nos. 51408578, 51611130195), Anhui Provincial Natural Science Foundation (1508085QE96).

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