Experimental investigation of thermosyphons with horizontal evaporator for low heat flux applications

Srivastava, A and Kumar, P and Ambirajan, A and Dutta, P and Varghese, Z and Rohith, BL and Subrahmanya, P (2024) Experimental investigation of thermosyphons with horizontal evaporator for low heat flux applications. In: Applied Thermal Engineering, 257 .

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Abstract

Thermosyphons that operate with low evaporator heat fluxes and exhibit a small temperature difference between the evaporator and condenser have significant potential for thermal management of buildings or other spaces when used in conjunction with radiative sky cooling. In such applications, thermosyphons may be used to transfer heat from the evaporator, located in the space to be cooled, to the condenser which may be in contact with a radiator covered with spectrally selective radiative sky cooling coating. To ensure adequate cooling of the space, the temperature difference between the evaporator and condenser in such a thermosyphon should be as small as possible and the thermosyphon should startup under these conditions. For such applications, this paper presents an experimental investigation of a tubular thermosyphon with a horizontal evaporator and inclined condenser. For a given external geometry of the thermosyphon, this study presents an experimental investigation of five copper thermosyphons with a variety of working fluids, fill ratios and evaporator inner threading. Of these thermosyphons, one contains methanol with an evaporator fill ratio of 50 and the other four contained R134a. Two of the R134a thermosyphons had a fill ratio of 25 and the other two had a fill ratio of 50. For each fill ratio, one of the thermosyphons had a smooth inner surface of the evaporator, whereas the other was circumferential threaded on the inside. The goal of the threading was to enhance wetting of the periphery of the evaporators since they were partially filled. The thermosyphons were tested in both evaporator and condenser-controlled modes to examine their start-up performance, thermal resistance, and cool-down capability. In the former, heat flux was varied at the evaporator end and the condenser was cooled, whereas, in the latter mode, the condenser temperature was varied, and the evaporator was dipped in a water tank (that acted as a thermal storage medium). In the evaporator-controlled mode, observations from experiments showed that the R134a thermosyphons required lower super-heat for startup and had significantly lower thermal resistance than methanol. Further, the threading of the inner surface of the evaporators significantly improved startup and further reduced the thermal resistance. During the condenser-controlled mode, the cool-down time of the thermal storage medium was shorter with the threaded R134a thermosyphons. The evaporator fill-ratios considered in this study did not appear to significantly affect the performance of the thermosyphon. © 2024 Elsevier Ltd

Item Type:	Journal Article
Publication:	Applied Thermal Engineering
Publisher:	Elsevier Ltd
Additional Information:	The copyright for this article belongs to the publisher.
Keywords:	Condensers (liquefiers); Thermosyphons; Wetting, Condition; Evaporator and condensers; Experimental investigations; Fill ratios; Inner surfaces; Storage medium; Temperature differences; Thermal; Thermal storage; Tubulars, Radiative Cooling
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	20 Sep 2024 09:22
Last Modified:	20 Sep 2024 09:22
URI:	http://eprints.iisc.ac.in/id/eprint/86106

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