Performance of divergent-chimney solar power plants

Simulations of divergent-chimney solar power plants (DSPPs) are conducted, and the DSPP performance studied by changing chimney outlet-to-inlet area ratios (COAR, representing the degree of divergence) over a wide range of values. Study method involves the use of total pressure potential (TPP) which consists of buoyancy and static pressure recovery in which an effective pressure potential recovery coefficient (EPPRC) is employed. Results show when the COAR is large enough, the boundary layer separation (BLS), flow stall and backflow will occur, vortex be formed, and a part of flow area be blocked. Due to the backflow from the ambient cool air, the temperature greatly decreases above the BLS point, possibly causing the reduction of buoyancy of the divergent chimney. With COAR increasing, the TPP initially increases and reaches a maximum for COAR = 8.7 then decreases. The mass flow rate and the power output have the same variational trend, while the collector temperature rise has the inverse variational trend. A maximum power of 231.7 kW is attained at COAR = 8.7, which is 11.9 times as high as that for COAR = 1. Before the occurrence of flow stall, the EPPRC decreases slowly due to the gently thickening of boundary layer and is higher than 0.91. While after the occurrence of flow stall, mainly due to the vortex and backflow the EPPRC greatly decreases and is found to decrease gradually with COAR. The effective ground heat flux increases the power output, but has little influence on the characteristics of the flow stall in the chimney, specifically the EPPRC.