Journal
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
Volume 194, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijheatmasstransfer.2022.123066
Keywords
Flat plate pulsating heat pipe; Ethanol-water mixtures; Thermal resistance; Slug-plug oscillations; Droplet oscillations
Categories
Funding
- Research and Innovation Center - Defence Research and Development Organisation, IIT Madras Research Park [SP/2021/0532/ME/DRDO/008440]
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The thermal performance and internal flow regimes of a closed-loop flat plate pulsating heat pipe (FPPHP) are experimentally investigated using ethanol-water mixtures as working fluids. The results show that the mixtures with increased ethanol content perform better in terms of thermal resistance and slug-plug flow oscillations. The effect of different condenser cooling modes on the thermal performance is also reported.
The thermal performance and the internal flow regimes of a closed-loop flat plate pulsating heat pipe (FPPHP) are experimentally investigated. Reports on the FPPHP using the ethanol-water mixtures as working fluids are scarce in the literature. The binary mixtures with different boiling point components are suitable for a wide range of heat fluxes. Therefore, the results are reported for the ethanol-water mixtures of ratios 3:1, 1:1, and 1:3, and the corresponding pure liquids filled in the range of [40-80] % with power inputs given from 40 to 200 W. The effect of different condenser cooling modes, such as forced convective water cooling, forced convective air cooling, and natural convective air cooling on the thermal performance of the FPPHP, is also reported. With the increase in the power input, the observed flow characteristics in the FPPHP channels are: no oscillations, slug-plug oscillations, droplet oscillations, and the evaporator dry out. The binary mixtures with increased ethanol content give better slug-plug flow oscillations with smaller thermal resistances and fewer evaporator drying out instances than the pure working fluids. For power inputs of less than 120 W, the ethanol:water mixture ratio of 3:1 at all filling ratios gives a larger slug departure frequency in the evaporator. The smallest thermal resistance measured is 0.1 K/W, a decrease of 27% over pure ethanol. For power inputs greater than 120 W, the mixture ratio of 1:1 at all filling ratios performs better with continuous droplet oscillations. The smallest thermal resistance measured at the 80% filling ratio is 0.12 K/W, a decrease of 22% over pure ethanol. When the condenser cooling mode is changed to air cooling, the evaporator temperatures reach around 100 degrees C for power inputs greater than 40 W and 80 W for natural and forced air convection. Thus, the FPPHP filled with ethanol-water mixtures with the water-cooled condenser gives a stable flow regime and better thermal performance for a long-range of power inputs. (C) 2022 Elsevier Ltd. All rights reserved.
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