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Mass/heat transfer analogy method in the research of convective fluid flow through channels with a specific geometry

Grosicki Sebastian, Wilk Joanna

Archives of Thermodynamics

2023

Vol. 44, no 4

427--446

The present work contains the results of the comparative analysis of the literature data and the own investigations on mass and heat transfer coefficients occurring under conditions of the convective fluid flow through channels characterised by a specific geometry. The authors focused on the available experimental investigations on mass transfer. The considered experiments were carried out using the electrochemical method named limiting current technique. Two channel geometries were discussed: the annular channel of the conventional size and the long minichannel with a square cross-section area. Taking into consideration dimensionless numbers: Schmidt and Nusselt – analogical for mass and heat transfer – the formulas describing the phenomena under consideration were included. In the case of the annular channel the laminar and turbulent range of Reynolds numbers was studied. For the square minichannel – the laminar flow is considered. The analogy between mass and heat transfer introduced by Chilton and Colburn was applied in the analysis. An equivalent boundary condition is included in considerations concerning the mass and heat transfer. It is the Dirichlet boundary condition characterised by constant temperature of the wall which corresponds to the situation of constant ion concentration at the cathode surface in the limiting current technique. The main purpose of the present work was to verify the method for the determination of heat transfer coefficients using the analogy between mass and heat transfer processes in the case of convective fluid flow through the annular and square channels. The problem discussed in the present work is important and actual due to the possibility of the elimination of temperature measurements in the investigations of heat transfer processes occurring in channels characterised by a specific geometry. It should be noted that sometimes temperature measurement may be difficult or even impossible. This situation also causes high uncertainty of the obtained results. Due to this problem, the presented analysis was performed also with the use of thermal results based on the analytical solution. The verification of the use of mass/heat transfer analogy method in specific cases gives the extended knowledge of correct application of the limiting current technique in heat transfer research. The main objective of the work was achieved by conducting a comparative analysis of the adequate mass and heat transfer results. The existing literature data do not provide an answer to the question about the correctness of using the limiting current technique in the case of discussed annular channels or long square minichannels. The received results make us be critical of applying the mass/heat transfer analogy method in some heat transfer cases.

Research methods in the study of heat transfer coefficient during flow in minichannels

Tychanicz-Kwiecień Maria, Grosicki Sebastian

Journal of Mechanical and Energy Engineering

2021

Vol. 5, No 1

59--67

The paper presents the specification of research methods commonly encountered in the studies of heat transfer processes in minichannels. In particular the following methods have been emphasized: electrochemical limiting current method as well as the thermal balance method. In thermal balance method the mean heat transfer coefficient is determined by the set of experimental thermal measurements of the investigated heat exchanger. In turn, limiting current method is based on heat and mass transfer analogy. The discussed research methods have been implemented on two specially designed and constructed test facilities with compact minichannel heat exchangers, which have been presented and described in details. In order to validate the designed setup, the preliminary experimental measurements of two minichannel heat exchangers with hydraulic diameter of 2 mm and rectangular cross sections during single-phase liquid flows have been carried out. In further perspective it is planned to extend the experimental studies of minichannel heat exchangers and to compare the results obtained by both methods described.