Numerical investigation of pitch value on thermal performance of solar receiver for solar powered Brayton cycle application

Small scale open solar thermal Brayton cycle with Concentrated Solar Power (CSP) system can provide an efficient, clean, sustainable and low cost energy conversion system to produce different forms of energy such as electricity. The current paper investigates various configurations of open cavity solar receivers including cylindrical, conical and spherical with an aperture of 0.02835 m2 and average irradiance values of 2.5 kW/m2. Advanced ray tracing (OptisWorks®12), as this is the latest available version) and computational fluid dynamic (CFD, ANSYS® 15) simulations are used to reduce optical and thermal losses and maximize the exit temperature of the working fluid. The received irradiance on the external surface of the helical coils inside these receiver geometries was used to predict the heat transfer fluid temperature through CFD analysis. Investigations were carried out to discover the effects of coil pitch and tube diameter on the working fluid's exit temperature. The results showed that for a pitch value of 3 mm and a tube diameter of 10 mm, the exit temperature is 401.3 K, 405.7 K and 409.4 K for each of the spherical, cylindrical and conical geometries respectively; indicating that the conical shaped receiver is more efficient than the other geometries. Moreover, the best pitch value, when the higher outlet temperature was achieved, depends on both the tube diameter and the cavity configuration. The effect of some other factors such as the ambient temperature and the pressure losses on the receiver's performance have also been investigated in this study.