HEAT TRANSFER IN COIL HEAT EXCHANGERS WITH VARYING GEOMETRIC CHARACTERISTICS

Abstract

Coil-type heat exchangers are widely used in power industry and medical and electronic technology due to the relatively simple design of their basic elements, low operating costs, reliability and long service life. The process of designing the devices with coil heat exchangers requires choosing the tube surface configuration and taking into consideration the specific operating conditions, as well as thermophysical properties and parameters of the working fluid. One of the important factors that hinder the wider use of coil heat exchangers is the lack of reliable engineering techniques for calculating the heat transfer and aerodynamic drag.

This study aimed to improve the technique of calculating the heat transfer and aerodynamics of coil heat exchangers by modifying the dependences that take into consideration the specific operating conditions and allow determining the design characteristics of one-layer recuperative coil heat exchangers mounted in annular channels under the conditions of partially twisted working fluid flow. In order to do that, the authors conducted a physical experiment using a test setup, both of which are described in the article in detail.

The analysis of the experimental results on heat transfer in a coil heat exchanger under forced gas convection and laminar flow of the working fluid helped to establish the dependence of the heat transfer coefficient on the main geometric parameters of the heat exchanger and to determine the allowances taking into consideration the extent to which the heat transfer intensity is impacted by the step characteristics of the tube bundle and the gap between the tube bundle and the heat exchanger housing, thus making it possible to optimize the geometric characteristics of the coil heat exchangers mounted in annular channels for specific operating conditions.