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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.

Badania jakościowe wpływu stanu powierzchni katody na wyniki pomiarów współczynników wymiany masy techniką elektrolityczną

Wilk J., Grosicki S.

Wiadomości Chemiczne

2017

[Z] 71, 5-6

403--413

The paper presents the results of qualitative investigations on the effect of the cathode surface state on mass transfer coefficients during the electrochemical process. Electrochemical methods have wide applications [1]. One of these method is the limiting current technique which is used in model studies on mass and heat transfer. Exemplary applications of the limiting current technique in heat transfer research with the use of mass/heat transfer analogy can be found in [2–7]. In the present paper the authors focused on measuring the mass transfer coefficients at the flat nickel cathode under free convection conditions. A schematic diagram of the measuring system is shown in Fig.1. The obtained voltammograms with clear visible flat segments representing limiting current values are presented in Fig. 2–4. In turn, Table 2 and 3 include the results of mass transfer coefficients calculation on the basis of limiting current values obtained for different condition of cathode surface. The surface of cathode was prepared before the experiment. It was polished using 400- , 600- and 800-grade SiC paper. Next, the cathode was polished by the special abrasive compound. Necessary for mass transfer coefficient calculations the ion concentration was measured using iodometric titration method. The experimental results confirmed the importance of keeping the measurement conditions. The cathode surface smoothing increases the mass transfer coefficients. The results are consistent with those received by the other researchers [9].