Thermal performance assessment of internal longitudinal fins with sinusoidal lateral surfaces in parabolic trough receiver tubes

In this study, the effect of the internal longitudinal fins with the flat and sinusoidal lateral surface on the thermal performance of the parabolic trough receiver tube was investigated. Nusselt number (Nu), friction coefficient (f), thermal enhancement factor (psi) and circumferential temperature difference (Delta T-max) were evaluated by the numerical analyzes. Analyzes were carried out using the different amplitude (a) and periodic length (p) values of the sinusoidal geometry for the different Reynolds numbers (Re). It was observed that the most important factors affecting the heat transfer were the fluid inlet temperature (T-in) and the a value. The highest enhancement in the Nu was found to be 25% and 78% for the flat and sinusoidal fin, respectively. The Delta T-max with the sinusoidal lateral surface geometry decreased in the range of 66-164 K. With the increase in the Re, the psi remained approximately constant for the flat fin geometry (psi approximate to 1,43). For the sinusoidal lateral surfaces, the psi fell below 1 in high amplitude and Re values. For the T-in in the range of 300-600 K, the psi value in the range of 0.85-2.32 were obtained. The results of the analysis revealed that the sinusoidal lateral surface geometry contributes to the heat transfer enhancement. (C) 2019 Elsevier Ltd. All rights reserved.