Author : Vinous M. Hameed and Aliaa H. Akhbala

The augmentation of convective heat transfer in a single-phase turbulent flow by using corrugated tubes type has been experimentally investigated. The effect of pitch (15, 7.5 and 3.75 mm) of corrugated tube and the volumetric flow rate on the heat transfer coefficient are examined. Cold and hot water are used as working fluids in the shell and tube side, respectively. Experiments are performed under conditions of mass flow rates 0.1075 kg/s for cold water and from 0.016 to 0.065 kg/s for hot water, respectively. The inlet cold and hot water temperatures are 40oC and 70oC, respectively. The results obtained from the outside corrugated tubes type are compared with the smooth tubes heat exchanger. It is found that the corrugated tubes have a significant effect on the heat transfer augmentations. The more efficient heat transfer rate is obtained at pitch length 3.75mm which is equal to 30.25% . While, for pitch 7.5 and 15mm will be 23.25 % and 15.8 % respectively. A correlation for coagulated type aluminum tube with enhancement depth 0.5mm are derived. The proposed correlation related the effect of pitch dimensions with the required outlet temperature of the water, it can calculate the heat transfer coefficient and it compared with sixteen experimental data points and very good agreement is obtained. The proposed correlations can predict the experimental data with average relative error of 7 %when compared with the experimental heat transfer coefficient. Simplification is made on the proposed correlation which make it more easy to apply with very reasonable accuracy when compared with experimental data point which is reduced to 9% only. The proposed correlation is derived based on four experimental data points but it applied on sixteen data point with very good accuracy. Another approach for calculating the heat transfer coefficient for enhanced tube heat exchanger was tried. The equation for calculating Nu is modified to suite the condition of enhanced tube type heat exchanger. The modified relation related to pitch dimensions data which gives very good agreement with average relative error of 17.23 % when compared with the experimental data. Another improvement on heat transfer rate in a single-phase turbulent flow by adding helical baffles in the shell side around the tube at 3.75mm enhancement since this enhancement gives the more efficient heat exchange between the shell and tube side. The introduction of helical baffles in the shell side (case 5) increase the heat transfer rate. The results show that increment in heat transfer by using a helical baffle over the smooth tube heat exchanger )case 1) is about 39% and 13% higher than the (case 4) of without using the helical baffles.

Keywords: Corrugated tube; heat transfer coefficient; pitch dimension; enhanced heat exchanger

Article published in International Journal of Current Engineering and Technology, Vol.5, No.3 (June-2015)