Thermohydraulic characteristics of transitional flow in a circular tube with inlet disturbances

Abstract

The influence of a triangular prism at the inlet of a circular tube on the thermohydraulic characteristics in the laminar, transitional and turbulent flow regimes is investigated experimentally. The effects on transition, i.e. the transition shift, due to the presence of triangular prism for three different clearance ratios (CR) are studied in this present work. The tube had an inner diameter of 20 mm, and length of 3.5 m (heated portion). Air was used as the working fluid. The test were conducted at two different heat fluxes of 2 and 4 kW/m2 for Reynolds numbers between 1 000 and 6 500, to ensure that all the three flow regimes were covered. The position of the triangular prism is at a distance (x) of 1.85 m from the inlet plane. The length of the pipe is 5.5 m, after 2 m from the inlet plane the pipe is heated with constant heat flux. The results show a good agreement with the available correlations. The effect on transition behavior due to the presence of triangular prism is reported in terms of Nusselt number, friction factor, j-factor and thermal performance factor (η). However, the heat transfer coefficient for this arrangement is showing more promising result as compared with the plain tube.