On the influence of wind on cavity receivers for solar power towers: an experimental analysis

Kurzfassung

The influence of wind on the convective losses of cavity receivers for solar power towers was analyzed experimentally in a cryogenic wind tunnel. At an ambient temperature of -173 °C a Grashof number of Gr=3.9E10 can be reached. Six different wind directions ranging from head-on to rearward flow, five wind speeds up to Re=5.2E5 and four inclination angles of the cavity in the range of phi=0°...90° were analyzed. With a similarity approach the results can be transferred to a receiver in normal ambient conditions with an inner diameter of 2.4 m and a wall temperature of approximately 730 °C. The methodology and its restrictions are discussed in detail. The experiments show that the influence of wind on large horizontal receivers is small. However, with increasing inclination angle the receiver becomes more susceptible to wind, although the convective losses never exceed those of the horizontal cavity. In some cases a reduction of the convective losses under the level of natural convection was observed if wind is present. Additionally, local information about the heat losses of different heater sections are presented, which are used to analyze the heat loss mechanisms inside the cavity. A shrinking of the stagnant zone is found to be the main reason for the increasing losses.