Investigation of thermal energy exchange potential of a gravitational water vortex

Abstract The conversion of hydel energy of the water vortex formed under gravity is well known in the form of gravitational water vortex turbines; however, the thermal energy exchange potential of the gravitational water vortex flow (GWVF) is yet to be explored. Heat transfer investigation of GWVF is important because the natural gravity being the sole driving force can considerably reduce the pumping power requirement. The present study is the first of its kind to investigate hydro-thermal characteristics of the gravitational water vortex heat exchanger (GWVHE) using an in-house developed experimental test rig. The proposed heat exchanger involves a spiral channel of rectangular cross-section constructed around a cylindrical basin generating a GWVF. For various inlet mass flow rates and temperature combinations, energy balance between the two water streams as well as Nusselt number correlations are determined. Experimentally, a reasonable energy agreement has been achieved with a maximum loss of 30% among the two different inlet temperature tested conditions. Moreover, maximum rise in cold side temperature for the tested conditions was 6K, whereas for the hot side the measure in temperature drop was 8K. A numerical simulation has also been conducted to virtually predict the performance of the designed heat exchanger. The simulation process has shown an increased energy balance with a maximum loss of 10%. A comparison of the experimental and numerical results shows that a GWVF has the potential to effectively exchange the heat between the two fluid streams moving under gravity. The performance of the proposed GWVHE with a pipe in pipe heat exchanger (PPHE) with parallel flow configuration (without vortex) has also been modeled and compared. For the same conditions, the maximum difference in temperature drop and gain between GWVHE and PPHE is 5K and 2.5K, respectively. The present study may act as a benchmark for the new class of GWVF based heat exchangers.