Heat/mass transfer analogy in the case of convective fluid flow through minichannels

Abstract

The main objective of the study was to present the Chilton-Colburn analogy in relation to mass and heat transfer processes occurring in minichannels. Because of the so-called scaling effects being in channels of small geometry the validation of the analogy between transfer processes in the case of convective fluid flow through the mninichannels seems to be necessary. The paper provides an overview of the experimental results of mass and heat transfer measurements performed under analogical conditions. The investigations concerned transfer processes in minichannels of different geometry. Channels with circular and rectangular cross section of small hydraulic diameter have been discussed. The ratio of minichannel length to the hydraulic diameter has been taken into account in the considerations. The analysis has been provided on the basis of the available literature results and the own author's investigations on mass transfer in short circular minichannels and preliminary results of mass transfer in long square channels of the mini heat exchanger. In order to validate the Chilton-Colburn analogy between mass and heat transfer the cases of transfer processes in minichannels which best meet the conditions of geometrical similarity have been discussed. The considered cases of heat transfer were experimentally studied with the use of thermal balance method while the mass transfer processes were investigated using the limiting current technique. On the basis of the analysis performed no definite answer was found on confirm Chilton-Colburn analogy applied in minichannels. Both convergence and divergence of results were noted. The discrepancy between thermal results and the results received from Chilton-Colburn analogy may be due to various reasons. One of them is a difference in the geometry of tested channels. Further research in conditions of full similarity of the channels geometry is expected. Another problem concerns thermophysical properties of the fluids used in investigations. The application of gases and liquids in thermal and mass experiments respectively, may cause a deviation from the mass/heat transfer analogy in minichannels. Measurement uncertainty also plays an important role in the discussion on the analogy between mass and heat transfer processes during the fluid flow through the channels of small characteristic dimensions. The total validation of mass/heat transfer analogy in minichannels in the form of Chilton-Colburn formula requires further experimental research.