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ABSTRACT
Experimental results of flow boiling characteristics and flow patterns with acetone in two different microchannel heat sinks are presented in this paper. A semi-open microchannel heat sink and a straight microchannel heat sink with 19 parallel microchannels each were designed and tested. The semi-open microchannels have a channel width of 0.8 mm, fin width of 0.4 mm, and pedestal height of 0.2 mm and the straight microchannels have a rectangular cross section of 0.8 mm × 1 mm. The experimental heat fluxes ranged from 0 to 90 kW/m2, vapor quality ranged from 0.05 to 0.5, mass fluxes ranged from 4.34 to 15.62 kg/m2·s and the inlet temperatures were 20 and 30°C, respectively. Compared to those in the straight microchannels, flow boiling heat transfer coefficients can be improved by up to 36.2%. Furthermore, flow patterns were observed with a speed video camera. The flow boiling heat transfer mechanisms are analyzed according to the observed flow patterns.
Nomenclature
| Ach | = | total heat area of microchannels, m2 |
| cp | = | specific heat of acetone, J/kgK |
| CHF | = | critical heat flux, W/m2 |
| G | = | mass flux, kg/m2s |
| hfg | = | latent heat of vaporization, kJ/kg |
| htp | = | local two-phase heat transfer coefficient, kW/m2K |
| H | = | height, m |
| I | = | the voltage and current, A |
| k | = | thermal conductivity, W/m·k |
| L | = | length of heat sink, mm |
| Li | = | distance from the inlet to thermocouple location in the downstream direction, m |
| m | = | fin parameter |
| = | the mass flow rate, kg/s | |
| N | = | number of electrical cartridge heaters |
| ONB | = | onset of nucleation boiling |
| Pin | = | pressure of inlet, Pa |
| Pout | = | pressure of outlet, Pa |
| qin | = | total power input, W |
| qeff | = | effective absorbed heat,W |
| q″eff | = | effective heat flux based on platform area, kW/m2 |
| R | = | thermal resistance, °C /W |
| Ttci | = | thermocouple reading, °C |
| Tin | = | inlet fluid temperature, °C |
| Tout | = | outlet fluid temperature, °C |
| Tw, tci | = | channel bottom wall temperature at thermocouple location, °C |
| ΔTsct,tci | = | wall superheat, °C |
| Tsat,tci | = | local saturation temperature of thermocouple location, °C |
| Tin | = | inlet fluid temperature, °C |
| U | = | voltage, V |
| W | = | width, m |
| wc | = | width of channel, m |
| x | = | thermodynamic vapor quality |
| Greek symbols | ||
| δ | = | width of fin, m |
| η | = | fin efficiency |
| λ | = | thermal conductivity, W/mK |
| ϕ | = | the heat transfer ratio |
| Subscripts | ||
| Cu | = | copper |
| cell | = | unit cell of channel |
| cp | = | cover plate |
| fin | = | fin |
| tci | = | thermocouple location |
| in | = | inlet |
| out | = | outlet |
| sat | = | saturation |
| tp | = | two-phase |
| c | = | channel |
| l1 | = | channel length of closed section |
| l2 | = | channel length of open section |
Additional information
Funding
Notes on contributors
Guodong Xia
Guodong Xia is a leading professor in Thermal Energy Engineering at Beijing University of Technology, China. He received his Ph.D. in Thermal Energy Engineering at the State Key Laboratory of Multiphase Flow at Xi'an Jiaotong University, China in 1996. He was a visiting professor in the Institute of Process Engineering at the University of Hanover, Germany in 2000–2001. His research interests include fundamentals and applications of microscale heat transfer, multiphase flow and heat transfer, waste energy recovery, thermal energy system, heat exchanger design and enhanced heat transfer. He is a member of the multiphase flow committee of the Chinese Society of Engineering Thermophysics and a member of the multiphase flow committee of the Chinese Society of Theoretical and Applied Mechanics. He has published more than 100 papers in journals and conferences.
Yue Cheng
Yue Cheng is currently working on a postgraduate program at the College of Environmental and Energy Engineering, Beijing University of Technology, Chaoyang, Beijing, China. He is working in flow pattern, pressure drop, and boiling heat transfer in microchannel. He obtained his B.E. in 2014 from Beijing University of Technology, China.
Lixin Cheng
Lixin Cheng is a principal lecturer at Sheffield Hallam University, UK. He obtained his Ph.D. in Thermal Energy Engineering at the State Key Laboratory of Multiphase Flow at Xi'an Jiaotong University, China in 1998. He has extensive international working and collaboration experience as associate professor, senior lecturer, lecturer, and research fellow at Aarhus University, University of Portsmouth, University of Aberdeen, Swiss Federal Institute of Technology (EPFL), Leibniz University of Hannover, London South Bank University, and Eindhoven University of Technology for 18 years. He was awarded an Alexander von Humboldt Research Fellowship in 2004–2006. His research interests include multiphase flow and heat transfer, nanofluid two-phase flow and heat transfer, and compact and micro-heat exchangers. He has published more than 100 papers in journals and conferences, 10 book chapters, and edited 10 books. He has been an associate editor of Heat Transfer Engineering since 2016.
Yifan Li
Yifan Li is currently a Ph.D. candidate at the College of Environmental and Energy Engineering, Beijing University of Technology, Chaoyang, Beijing, China. She is mainly engaged in the fields of microelectronic cooling, fluid flow, and heat transfer in micro-scale, especially for the complicated microchannels.