Abstract
This paper reports the results of heat transfer during refrigerant flow in rectangular mini-channels at stationary conditions. The impacts of selected parameters on boiling are discussed, i.e., thermal and flow parameters, dimensions and orientation of the channels. Four refrigerants (FC-72, HFE-649, HFE-7000 and HFE-7100) were used as the working fluid. Research was carried out on the experimental set-up with the test section with a single rectangular mini-channel of 180 mm long and with a group of five parallel mini-channels, each 32 mm long. The temperature of the mini-channel’s heated wall was measured by infrared thermography. Local values of the heat transfer coefficient at the contact surface between the fluid and the plate were calculated using the 1D mathematical method. The results are presented as the relationship between the heat transfer coefficient and the distance along the mini-channel length and boiling curves. Two-phase flow patterns are shown. Moreover, the results concerning various refrigerants and the use of modified heater surfaces are discussed. The main factors influencing the heat transfer process were: mini-channel inclination to the horizontal pane (the highest heat transfer coefficient at 270° and 0°), using modified heater surfaces (especially electroerosion texturing and vibration-assisted laser No. 2 texturing) and working fluids (FC-72 and HFE-7000).
Highlights
The progressive development of miniaturization and the rapid growth in the areas of technology application have resulted in the need to dissipate increasing amounts of heat from ever smaller surfaces, and it becomes necessary to look for new ways of heat dissipation
The influence of various parameters on flow boiling heat transfer has been widely discussed for over a dozen years, the results relate to different geometries and spatial orientations of the mini-gaps, and various fluids are still investigated
As in most scientific works, the results of heat transfer are presented in the form of temperature graphs, Heat transfer coefficient (HTC), flow structures and boiling curves
Summary
The progressive development of miniaturization and the rapid growth in the areas of technology application have resulted in the need to dissipate increasing amounts of heat from ever smaller surfaces, and it becomes necessary to look for new ways of heat dissipation. At Kielce University of Technology, previous investigations on boiling heat transfer during cooling liquids’ flow [19,20,21] along rectangular mini-channels of changeable spatial orientation, with smooth or modified heater surfaces, were discussed in [20,22,23]. This work provides a summary of the results collected during experimental work in a laboratory setup, in which an essential element was a model mini-channel heat exchanger with a singular long mini-channel or a set of short parallel mini-channels It aims to deliver a summary of observations and comments concerning boiling heat transfer during refrigerant flow in rectangular mini-channels of different dimensions (depth, length and width), with changeable inclination to the horizontal plane and asymmetrically heated—. Previous studies were carried out using a singular mini-channel, which are summarized here, with many additional parameters of the experiment being tested
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