Ukraine, Kyiv, ¹National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”; ²ISEE SSU.

Decrease in mass and dimensional characteristics of semiconductor devices with simultaneous increase in allocated power dissipation creates conditions of heat-loaded operation of the most critical elements of radio-electronic equipment. Such growth of heat flows requires effective small-size systems for maintaining safe temperature conditions of electronic equipment and its reliable functioning. The use of miniature heat pipes (MHP) commensurate in size with the microchip crystals can significantly reduce their temperature level of operation. The paper presents the experimental results of investigation of thermal resistance and maximum heat fluxes of miniature heat pipes with diameters from 3 to 6 mm and lengths from 150 to 300 mm with metal-fiber capillary structure. The porosity of the capillary structure varied from 70% to 88%. Water and ethanol were used as coolants. The study was carried out at different orientations of MHPs in space: vertical by gravity forces, horizontal, and vertical against gravity forces (+90°, 0°, -90°). It is shown that the heat transfer characteristics of the MHPs are affected by both geometric and mode factors. It is determined that the minimum thermal resistance and maximum heat flux significantly depend on the diameter of the vapor channel, porosity of the capillary structure and thermal physical properties of the heat transfer medium. The data on the heat transfer intensity in the heating zone depending on the size of the vapor channel are given. It is shown that decreasing the diameter of the vapor space of MHPs worsens their heat transfer characteristics.

Keywords: miniature heat pipe, maximum heat flux, thermal resistance, capillary structure, boiling, heat carrier, space orientation.

1. Cotter T.P. Principles and prospects of micro heat pipes. Proc. 5th Int. Heat Pipe Conf. Tsukuba, Japan. 1984. pp.328-335.
2. Peterson G.P. Investigation of micro heat pipes fabricated as an integral part of silicon wafers. 8th International heat pipe conference. Bejing, China, 1992, pp. 1-11.
3. Faghri A. Advances and challenges in micro/miniature heat pipes. 11th Int. Heat Pipe Conf. Musashinoshi, 1999, Tokyo, Japan, vol. 3, pp. 1-18.
4. Mantelli M.B.H. Thermosyphon and heat pipes: Theory and applications. Switzerland, Springer, 2021, 420 p.
5. Chen H., Groll H., Rosler S. Micro heat pipes: experimental investigation and theoretical modelling. 8th Int. Heat Pipe Conf. Bejing, China, 1992, pp. 1-5.
6. Reay D., Kew P., Mcglen R. Heat pipes theory, design and applications. USA, Elsevier Ltd, 2014, 251 p.
7. Wang W., Cai Y., Wang L. et al. Thermo-hydrodynamic analytical model, numerical solution and experimental validation of a radial heat pipe with internally finned condenser applied for building heat recovery units. Energy Conversion and Management, 2020, vol. 219, pp.113041. https://doi.org/10.1016/j.enconman.2020.113041
8. Kravets V., Alekseik Ye., Alekseik O. et al. Heat pipes with variable thermal conductance property developed for space applications. Journal of Mechanical Science and Technology, 2017, vol. 31, pp. 2613-2620. https://doi.org/10.1007/s12206-017-0503-8
9. Liu D., Tang G., Zhao Fu., Wang H. Modeling and experimental investigation of looped separate heat pipe as waste heat recovery facility. Applied Thermal Engineering, 2006, vol. 26, iss. 17-18, pp. 2433-2441. https://doi.org/10.1016/j.applthermaleng.2006.02.012
10. Velardo J., Singh R., Ahamed M. Sh. et al. Thin thermal management modules using flattened heat pipes and piezoelectric fans for electronic devices. Frontiers in Heat and Mass Transfer (FHMT), 2021, vol. 17 - 1, 11 р. https://doi.org/10.5098/hmt.17.1
11. Han X., Wang Y., Liang Q. Investigation of the thermal performance of a novel flat heat pipe sink with multiple heat sources. International Communications in Heat and Mass Transfer, 2018, vol. 94, pp. 71-76. https://doi.org/10.1016/j.icheatmasstransfer.2018.03.017
12. Koito, Y. Numerical analyses on vapor pressure drop in a centered-wick ultra-thin heat pipe. Frontiers in Heat and Mass Transfer (FHMT), 2019, vol. 13 - 26, 6 p. http://dx.doi.org/10.5098/hmt.13.26
13. Mochizuki M., Nguyen T. Review of various thin heat spreader vapor chamber designs, performance, lifetime reliability and application. Frontiers in Heat and Mass Transfer (FHMT), 2019, vol. 13 - 12, 6 p. http://dx.doi.org/10.5098/hmt.13.12
14. Li J., Lv L., Zhou G., Li X. Mechanism of a microscale flat plate heat pipe with extremely high nominal thermal conductivity for cooling high-end smartphone chips. Energy Convers Manage, 2019, vol. 201, 112202. https://doi.org/10.1016/j.enconman.2019.112202
15. Kravetsʹ V.Yu. Protsesy teploobminu u miniatyurnykh vyparno-kondensatsiynykh systemakh okholodzhennya [Heat exchange processes in miniature evaporative-condensation cooling systems]. Kharkiv, FOP Brovin O.V., 2018, 288 p.
16. Semena M.G, Gershuni A.N., Zaripov V.K. Teplovyye truby s metallovoloknistymi kapillyarnymi strukturami [Heat pipes with metal fiber capillary structures]. Kyiv, Vishcha shkola, 1984, 215 p.