Numerical study of heat transfer enhancement in the receiver tube of direct steam generation with parabolic trough by inserting metal foams

The present numerical simulation investigates the effect of inserting metal foams in receiver tube of parabolic trough collector on heat transfer. The effects of layout (top/bottom), geometrical parameter (H), and porosity (phi) of metal foams on the flow resistant, heat transfer and thermo-hydraulic performance are analyzed. Optimum thermo-hydraulic performance considering the flow resistance increase is obtained when H = 0.25 (bottom), Nu increases about 5-10 times with the increase of f 10-20 times and the PEC range from 1.4 to 3.2. Optimum thermal performance is obtained when H = 0.75 (top), Nu increases about 10-12 times with the increase of f 400-700 times and the PEC range from 1.1 to 1.5. The maximum circumferential temperature difference on the out surface of receiver tube decreases about 45% which will greatly reduce the thermal stress. The result shows that for constant layout and phi, the H effects on the thermal performance greatly, but for constant layout and H, the phi effects on the thermal performance slightly. Moreover, the layout in view of no-uniform heat flux boundary affects the heat transfer significantly. These methods and results can be extended to the heat transfer enhancement of all the solar concentrated receivers. (c) 2012 Elsevier Ltd. All rights reserved.