Thermal fluid modelling of a titanium fluted tube condenser

Abstract

Heat exchangers form a vital component in numerous energy conversion processes, ranging over multiple industries; such as mining, food, automotive and aerospace. With the continuous population growth and a drive towards more efficient energy consumption, there exists a persistent need to improve heat exchangers. Over the past decade research focused on improving the internal convective heat transfer of tubes by means of spiral flutes or grooves. Fluted tubes gained popularity in the industry as the spiral flutes increase the heat transfer by disrupting the boundary layer at the tube surface. Spiral fluted condensers are used in water heating heat pumps which are widely applied in the industry to reduce the overall electricity consumption of a facility. Due to a fluted tube's complex geometry and manufacturing challenges, additive manufacturing may be a solution for improving on conventional methods. This study investigates the effect of altering the flute pitch and flute depth on the thermal performance of a titanium helically coiled fluted tube heat exchanger, focusing on the internal fluid. In attaining the latter, computational fluid dynamic software STAR-CCM+ is utilised to simulate the enhancements of the heat exchanger. For the mesh selection, a grid verification index is performed, and the physics model utilises the K-Epsilon approach with segregated flow. Sixteen different configurations were modelled where each comprise a different depth and pitch combination. The flute pitch and depth vary from 9mm to 12mm, and 4.59mm to 7.17mm respectively. The results indicate, that with an increase in flute depth, the thermal performance and the pressure drop both increases. Increasing the flute pitch, results in a decrease in pressure drop and thermal performance. It is concluded that flute depth and pitch have a significant effect on the thermal performance of the internal fluid. The enhancement comprising a flute depth and pitch of 7.17mm and 9mm respectively resulted in the highest Nusselt number. Finally, the effect of altering from pure titanium to Titanium-6 Aluminium-4 Vanadium additively manufactured material was investigated and compared against the enhancement with the highest thermal performance. This led to a decrease in 8.97% in Nusselt number when compared to pure titanium.