Experimental study of the thermal-frictional behavior of a horizontal straight tube equipped with a vibrating string turbulators: A novel active method

Abstract

The active methods are recently considered to increase the heat transfer rate. Compared to the passive methods, the active ones experience less pressure drop. Some inherent disadvantages, such as inefficiency in terms of energy consumption or the necessity of specific properties for the working fluid can limit using active methods. In this study, a novel idea is experimentally studied to explore the changes in the rate of heat carried by the fluid passing through a heated tube. To this end, a stretched string is implemented coaxially inside the tube and excited to vibrate at its natural frequency in the presence of an adjustable frequency AC magnetic field. This new approach to vibrating a starched oscillator remotely is called electro-magnetic vibration method (EMV). The vibration of a string inside the tube is predicted to cause severe turbulence and strong radial flow. The impacts of the changing diameter of the vibrating string turbulator (VST) and the position of the exciter on the heat transfer rate are studied at different mass flow rates. The thermal enhancement factor (TEF) is calculated to choose the best diameter and excitation location. The results showed that in the best scenario, TEF could reach up to 1.47, which indicates that the EMV method is an effective way to generate harsh radial flow to increase heat exchanger's thermal performance.