A Numerical Analysis of Heat Transfer Enhancement by Turbulence Generated From Swirl Flow by Twisted Tape

Heat exchangers are widely used in heating and cooling devices. The primary challenge is to improve the efficiency of the heat transfer equipment. Researchers have utilized various techniques to achieve this goal. Using twisted tapes could significantly increase the heat transfer rate from a circular surface due to turbulence generated from swirl flow. To enhance the heat transfer rate by twisted tape, two types of arrangements namely: (i) plain twisted tape and (ii) altered twisted tape geometries are used. These arrangements result in swirl flows. For improving heat transfer through swirl flow, some important parameters such as Reynolds number, external surface temperature, friction factor, inlet pressure, and surface heat flux are also considered. To identify the aftereffect of the velocity of inlet water, several parameters namely: (i) external surface temperature, (ii) inlet pressure, (iii) external surface heat flux and (iv) twist ratio are varied. A numerical modelling using k-ε method is performed to evaluate the effects of turbulence from the twisted tape on the heat transfer rate. The objective is to analyze the improvement of heat transfer effectiveness due to the swirl flow. The change in the values of the resulting Reynolds number by changing the inlet fluid velocity from 0.1 ms⁻¹ to 0.7 ms⁻¹ and rotational speed from 200 rpm to 600 rpm is studied. It is observed that for such changes heat transfer increases by 17 percent. It is also observed that heat transfer is directly proportional to inlet pressure and inversely proportional to the increment of twist ratio. The rate of heat transfer increased from 17 percent to 19 percent when the angular velocity of the twisted tape is changed from the 0 rpm to 600 rpm while the velocity of the water inside the pipe is held constant at 0.7 ms⁻¹. Higher heat transfer rate is observed with high inlet pressure. Likewise, higher value of the Nusselt number is observed with higher rotational speed of the twisted tape and higher velocity at the pipe inlet. In addition, it is also observed that when the twist ratio is changed from 4 to 6, the rate of heat transfer is diminished by 6 percent.