Abstract
The aim of the paper is to estimate effect of the heating surface enhancement on FC-72 flow boiling heat transfer for a vertical minichannel 1.7 mm deep, 24 mm wide and 360 mm long. Two types of enhanced heating surfaces were used: one with minicavities distributed unevenly, and the other with capillary metal fibrous structure. It was to measure temperature field on the plain side of the heating surface by means of the infrared thermography and to observe the two-phase flow patterns on the enhanced foil side. The paper analyses mainly the impact of the microstructured heating surface on the heat transfer coefficient. The results are presented as heat transfer coefficient dependences on the distance along the minichannel length. The data obtained using two types of enhanced heating surfaces in experiments was compared with the data when smooth foil as the heating surface was used. The highest local values of heat transfer coefficient were obtained using enhanced foil with minicavities - in comparison to other cases. Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil. Probably this porous structure caused local flow disturbances.
Highlights
There is a worldwide interest in compact heat exchangers with minichannels
The results are presented as heat transfer coefficient dependences on the distance along the minichannel length
Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil
Summary
There is a worldwide interest in compact heat exchangers with minichannels. They are characterized by many advantages such as higher efficiency and reduced size. The results may be used for the designing of cooling systems with minichannels to improve their efficiency and thermal stability. Experimental investigations show that the average heat transfer coefficient in compact heat exchangers with minichannels is higher [1]. It is possible that compact heat exchangers with enhanced walls will have better thermal parameters. If the surface of the heating element is enhanced too much, i.e. it is too porous, the flow of the refrigerant and, the whole boiling process in the minichannel, may be periodically disturbed [2]. Investigations often deals with frictional pressure drop in minichannels [3]
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