Effect of the heating surface enhancement on the heat transfer coefficient for a vertical minichannel

Abstract

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.

Impact of Fe powder sintering and soldering in production of porous heating surface on flow boiling heat transfer in minichannels

“…15÷80 µm (with an average being 40÷65 µm); the density of the solder paste -2990 kg/m 3 , the thickness of the soldered layer -approx. 100 µm and the maximum height of the soldered layer -200 µm [27]. …”

“…Finally, the formation of vapour bubbles can be responsible for the reduction in heat transfer efficiency [27]. In the case of the surface formed by iron powder soldering, thermal resistance additionally occurs at the contact zones between the substrate and solder and between the solder and Fe powder grains.…”

Enhanced Surfaces Used in Research on Flow Boiling Heat Transfer in Minichannels

“…One of the methods of heat transfer enhancement involves heat transfer surface modification. The modification causes the increase of heat transfer coefficient values through increasing the number of active nucleation sites during flow boiling [1][2][3][4][5][6][7][8][9][10] or pool boiling [10][11][12]. Modified surfaces exhibit reduced surface superheating and improve heat dissipation by increasing the area of heat removal.…”

“…In their previous articles, the authors of this paper reported their findings concerning various enhanced heat transfer surfaces with the flow of various working fluids through rectangular heat exchangers with minichannels. The surfaces studied included laser-textured surfaces with regular recesses [2,7], vibration-assisted laser-textured surfaces [3,4,6], surfaces with irregular recesses obtained in the process of spark erosion [1,2,5,6,10,11], surface with capillary-fibrous structure [1] and powder surfaces produced by sintering or soldering [8,9]. Based on the research results for flow boiling in minichannels, this article discusses the enhanced surfaces used, along with their production methods and effects on heat transfer processes.…”