Development of a methodology for determining heat transfer coefficients under the existence of various boiling modes on a finned wall

Vladimir Marinenko,Boris Davydenko

doi:10.15587/2706-5448.2020.213453

Abstract

The object of research is the computational-experimental method of determining and identifying the heat transfer coefficients on the finned wall under the conditions of coexistence of different modes of boiling water that is forced to move. The peculiarity of cooling finned surfaces during boiling is that boiling is carried out on a non-isothermal surface. In this regard, the surface elements – «fin-wall», in the General case, can simultaneously coexist convective heat transfer, bubble, transient and film boiling. One of the problems that needs to be solved is the substantiation and development of a new method for determining the distribution of heat transfer coefficients on the surface of the fin during the coexistence of different boiling regimes on the finned wall.Most methods of calculating heat transfer on finned surfaces are based on the assumption that the heat transfer coefficient at a given point of the non-isothermal surface is a function of only the temperature pressure between the surface and the liquid at this point. Experimental studies of heat transfer on the finned wall were carried out to test the method of calculation of heat transfer coefficients. The calculation part of the proposed method is based on the numerical method of determining the temperature field in the system «fin-wall» with a constant supply of heat from the smooth wall. Transferring, from both sides, to heat the heat flow – permanently, with given geometric dimensions, cooling, and efficiency of heat conduction material – fins to rotate the heat transfer.The main stages of realization of computational-experimental technique are given in the work. Unlike most of the known methods for solving inverse problems, the proposed method, based on the use of three-diagonal matrix algorithm, makes it possible not to apply an iterative process to determine the heat transfer coefficients on the surfaces of the fins, which provides a quick result with a higher accuracy

Highlights

In technology, the ribbing of surfaces is increasingly used, cooled by a boiling liquid
In the course of the work, a new method was developed for determining the distribution of heat transfer coefficients over the surface of a fin during boiling of water on a finned wall and an algorithm for solving the inverse problem of heat conduction
This algorithm is based on using the finite difference method and matrix sweep to solve a system of finite difference equations. This can be used to determine the distribution of heat transfer coefficients over the surface of the fin according to experimental data on the temperature distribution along the axis of the fin

Summary

Introduction

In technology, the ribbing of surfaces is increasingly used, cooled by a boiling liquid. The density of the heat flux supplied can significantly exceed the first critical density of the heat flux during boiling on isothermal surfaces This circumstance makes the method of cooling finned surfaces with a boiling liquid promising in many branches of technology. Methods for solving problems of heat conductivity for a fin under conditions of liquid boiling in a large volume in a one-dimensional formulation are presented in [2,3,4]. Most of the methods for thermal design of finned surfaces are based on the assumption that the heat transfer coefficient α at a given point on a non-isothermal surface is only a function of the difference between the temperature of the fin surface tw and the saturation temperature tsut.

Methods of research

Research results and discussion

Conclusions