Heat Transfer Enhancement in an Electrically Heated Horizontal Pipe Due to Flow Pulsation

Abstract

The concept of applying a periodic pulse to a fluid flow has been widely used in industrial applications for many years. One would expect flow pulsation to have a significantly positive effect on the efficiency of heat transfer. However, several decades of research into this type of flow (mainly for a gas such as air flowing in a pipe) has brought conflicting conclusions as to the advantages or disadvantages of pulsation on heat transfer. In order to study the published evidence in a more objective manner, this research project was initiated. The approach used was experimental, involving laboratory experiments with water flowing in a heated horizontal pipe. For this purpose, a special experimental apparatus was designed and built, and a large number of experiments were performed for different values of pulsation frequency and amplitude, superimposed over a varying main flow rate through the pipe. For the range of variables considered in this study (ie, 5,000 < Re < 23,000, 0.1 Hz ≤ f ≤ 1.0 Hz and various pulsation amplitudes), it was found that (a) increasing pulsation frequency improved the heat transfer by as much as 15%, (b) increasing pulsation amplitude reduced the heat transfer by as much as 25% and (c) up to 50% heat transfer enhancement was obtained for pulsatile flows with flow reversal.