Numerical simulation of convective heat losses in a helical tube of a cylindrical solar receiver

Abstract

In this paper, natural convection heat losses in a cylindrical solar receiver areinvestigated numerically. The study is conducted using three helical tube diameters: 12mm,16mm and 25mm. The diameter of the receiver is 0.3 m with an aspect ratio equal to one andthree aperture ratios of 1, 0.75 and 0.5. In each case, the receiver tube inside the cylindricalcavity is modelled by a helical spiral similar to those of real systems. The simulations areperformed for three inlet temperatures (of 50, 75 and 100°C) and four receiver tilt angles (of 0,30, 60 and 900) with a constant mass flow rate of 0.0885 kg/s. The effects of some parameterssuch as receiver size, boundary conditions, tube diameter, receiver tilt, inlet temperature andopening ratio on convective heat losses and outlet temperature are presented in form of graphs.It has been found that the convective heat losses are reduced by using the adiabatic boundarycondition imposed on the half-circumference of the tube. Thus, increasing the helical tubediameter causes an increasing in the convective heat losses. The increasing of the fluidtemperature and the opening ratio are found proportional to the increasing of convective heatlosses.