A finned tube heat exchanger coupled to parabolic trough solar collector for drying application

This paper presents the design and performance analysis of a finned tube heat exchanger used to transfer thermal energy from a 20 kW parabolic trough solar loop to a rotary dryer. This heat exchanger is designed to absorb the energy provided by the solar system and transfer it to an air stream. A detailed thermal modeling for the finned tube heat exchanger based on logarithmic mean temperature difference method (LMTD) was carried out. Using the Engineering Equation Solver (EES) software, a simulation code was developed to study the effect of HTF fluid velocity and fluid type on the heat transfer surface area and pumping power. These two parameters were selected as they significantly affect the operating and the investment costs. The simulation code accept changes in the number of longitudinal and transversal tubes, as well as their size, to account for any space limitation in the heat exchanger installation. Four different geometries were simulated, leading to varying results for the heat exchanger configuration. Geometry C1, while having the smallest heat transfer area, provides the best performances when compared to the others. This can be explained by the high compactness of Geometry C1 which promote a better energy transfer to the airside. The choice of HTF fluids also affects the heat exchanger design. Simulation results show that the use of Therminol VP1 and Syltherm XLT yield respectively the minimum surface area and minimum pumping power. An optimal fluid velocity inside the exchanger tubes was found to be in the 0.43 – 0.57 m/s range for the studied heat exchanger geometries.