Gnielinski’s correlation and a modern temperature-oscillation method for measuring heat transfer coefficients

Abstract

The heat transfer coeffcient is one of the most important parameters in the design of apparatuses in which convective heat transport takes place. Classical direct methods based on determining basic thermal quantities can be used for measuring heat transfer coeffcients. Another option is to measure concentrations, electric current or other quantities that can be transformed to thermal quantities using the analogy between heat and mass transport. The temperature-oscillation method is less frequently used, although the theoretical basis of the method dates back to 1997, and although the method has the major advantage that the heat transfer coeffcients can be measured without making any contact with the heat transfer surface. In the temperatureoscillation method, the heat transfer surface is exposed to an oscillating heat flux, and the temperature response on this surface can be measured by a contactless method (e.g. infra-red thermography). The heat transfercoeffcients can be determined on the basis of mathematical relations between the oscillating heat flux and the temperature response. However, the method depends on an appropriate method for processing the measured data when it is necessary to correct some conditions that are not included in the mathematical model. This paper evaluates the impact of processing the experimental data on the resulting heat transfer coeffcients in one of the basic geometrical configurations – the flow of a liquid in a pipe with a circular cross section. In this paper, we present the results of a comparison of real experiments based on the temperature oscillation method and numerical modeling of the heat transfer in this geometry, using the ANSYS CFD commercial system.