Heat Transfer Engineering, Vol.33, No.8, 682-692, 2012
Experimental Investigation of Thermal Performance in a Tube With Detached Circular Ring Turbulators
This article deals with the experimental investigation of thermal performance of detached circular ring turbulators in turbulent flow regime. The experiments were conducted by four different circular rings. Two different pitch ratios (1 and 2) and two different distances (1 mm and 2 mm) at which the circular rings were detached from the tube wall were considered in the experiments. Uniform heat flux was applied to the external surface of the tube and Reynolds number was varied from 4350 to 24,920. The tube with circular ring turbulators introduced both higher heat transfer and higher pressure drop than the smooth tube, depending on pitch ratio and distance. According to the experimental results, the Nusselt number and friction factor increased with decreasing of pitch ratio and distance. Therefore, the circular ring turbulator with a pitch ratio of 1 and distance of 1 mm offered the highest heat transfer rate accompanied by the highest pressure drop. The highest thermal performance efficiency of 26% was also achieved for this case at a Reynolds number of 4421. Evidently, the experimental results revealed that the best operating regime of all circular ring turbulators was found at low Reynolds number, leading to a more compact heat exchanger.