Abstract
The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT). The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.
Highlights
Boiling is an extremely efficient heat transfer process used in power generation, chemical industry and nuclear engineering
The paper presents the results of boiling heat transfer research during FC-72 through a minichannel of 1 mm depth with an enhanced heating surface, positioned vertically and horizontally
In the twodimensional approach both the inverse problem in heating foil and the direct problem in glass barrier were solved by means the finite element method with Trefftz functions as shape functions (FEMT)
Summary
Boiling is an extremely efficient heat transfer process used in power generation, chemical industry and nuclear engineering. Owing to the change of state, which accompanies flow boiling in minichannels, it is possible to meet contradictory demands simultaneously, i.e. to obtain a heat flux as large as possible at small temperature difference between the heating surface and the saturated liquid and, at the same time, retain small dimensions of heat transfer systems. It leads to the conclusion that much has been written recently on flow boiling heat transfer in minichannels, the observations related to the effects of various factors on boiling heat transfer in minichannels are diverse and frequently conflicting. They are usually verified experimentally for channel systems heated by smooth heating surfaces
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