An experimental study of turbulent heat transfer separation external in an annular passage

Abstract

Experimental investigation was carried out to study the effect of step height on the heat transfer process to a radially expanded outward air flow in a concentric annular passage. The separation, reattached and redeveloped air flow occurs in a test section subjection outer tube only to a constant heat flux boundary condition . The experimental investigation conducted to investigate the effect of separation intensity on the local and average convection heat transfer The experimental setup having a concentric tube an annular passage with a sudden reduction in passage cross section created by the variation of outer tube diameter of the annular entrance section (D) that will change the separation intensity as the result of changing the step height prior to test section heated surface. For all cases , the results show an increase in the local heat transfer coefficient values as the heat flux and Reynolds number increases. The effect of step variation is clear in the separation region on the heat transfer process increases as the step height increases and it shows a little effect on the redevelopment region . In separation region , the local heat transfer coefficient increases until reaches maximum value at reattachment point and then decreases gradually in the redevelopment region . The point of reattached point along the heated surface is more effect with step height and shows very little effect with Re number. The results has been correlated and compared with pure force convection in a concentric annular passage and result shows an improvement to 18% within the step height been tested (Smax = 18.5 mm) comparison with the pervious work shows a good agreement and with the trends.