Numerical and Experimental Investigation of Heat Transfer Augmentation in Double Pipe Heat Exchanger with Helical and Twisted Tape Inserts

Nowadays, heat exchangers with twisted-tape inserts have widely been applied for enhancing the convective heat transfer in various industries such as thermal power plants, chemical processing plants, air conditioning equipment, refrigerators, petrochemical, biomedical and food processing plants. In general, twisted tape insert introduces swirl into the bulk flow which consequently disrupts a thermal boundary layer on the tube surface. A 3-D numerical model has been developed to study the performance of (i) bare tube-in-tube heat exchanger, (ii) tube in tube with twisted tape insert and (iii) helical insert at annulus and twisted tape insert inside the inner tube of the heat exchanger. Numerical results have been compared with the available analytical solution. It has been observed that there is a good agreement between these two results: within ±19.78 percentage error limit for Nusselt number measurement and ±25 percentage error for friction factor. The numerical simulation for twisted tape insert with twist ratio (y) 5 has been performed using different turbulent models by varying Reynolds number ranging from 2000 to 10000. SST k-ω turbulent model has been selected as better turbulent model for further simulation. Experiments on double pipe heat exchanger with twisted tape inserts with twist ratios y= 4.167, 5.556, 6.944 and helical tape insert in annulus has been performed with Reynolds number ranging from 4000 to 20000. These experimental results have been compared with the numerical results. From the results, it has been found that, by using twisted and helical tape inserts the heat transfer enhancement takes place in the expense of pressure drop. Keywords—Double pipe heat exchanger, Heat transfer augmentation techniques, Twisted tape insert, Helical tape insert, Twist ratio, Numerical and Experimental investigation, Computational fluid dynamics, Turbulence modelling, Friction factor, Nusselt number, Friction factor ratio, Nusselt number ratio.