• Energy Research
• Closed Access close
• CN close
• IN close
• SA close
• Solar Energy close

Abstract It is cost effective to manufacture a reflective surface of a solar parabolic trough concentrator in a parabolic cylinder shape by pure bending of a flat sheet. However, the surface manufactured by such an elastic bucking is only a coarse approximation of a parabola, which is not precise enough for meeting the demand of a high quality concentrator. A novel design concept was proposed to remove this error by applying an external force on both edge of a sheet, together with two additional forces: the edge torsion force and the pressing force. The optimal position and magnitude of two additional forces were figured out among various conditions, thereby a theoretically maximal concentration ratio up to 115 was found. Prototypes and engineering realizations of this method were also presented. This method provides a very attractive approach for low cost and high efficiency solar energy solutions.

Abstract It is cost effective to manufacture a reflective surface of a solar parabolic trough concentrator in a parabolic cylinder shape by pure bending of a flat sheet. However, the surface manufactured by such an elastic bucking is only a coarse approximation of a parabola, which is not precise enough for meeting the demand of a high quality concentrator. A novel design concept was proposed to remove this error by applying an external force on both edge of a sheet, together with two additional forces: the edge torsion force and the pressing force. The optimal position and magnitude of two additional forces were figured out among various conditions, thereby a theoretically maximal concentration ratio up to 115 was found. Prototypes and engineering realizations of this method were also presented. This method provides a very attractive approach for low cost and high efficiency solar energy solutions.

Abstract 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.

Abstract 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.

Abstract An experimental investigation has been carried out to study flow and heat transfer in solar air heater for inline holes inserted between absorber and back plate. The analysis has been carried out for cross flow conditions. The effect of flow and geometrical parameters, especially jet diameter and hydraulic diameter has been studied. Mass flow rate for the study is varied corresponding to the Reynolds number range of 4600–12,000. The jet diameter, streamwise pitch, and spanwise pitch, each normalized by hydraulic diameter, i.e. Dj/Dh, X/Dh, and Y/Dh, are in the range: 0.053–0.084, 0.53–0.63, and 0.53–0.63 respectively. Performance is studied in terms of Temperature Rise Parameter (TRP), collector efficiency, and Nusselt number. Hourly variations of solar intensity have also been shown. Collector efficiency increases and Temperature Rise Parameter decreases with increase in mass flow rate for all geometrical configurations. All the above-listed performance parameters are found to be maximum at jet diameter to hydraulic diameter ratio of 0.07. A correlation for Nusselt number in terms of Reynolds number, jet diameter, and hydraulic diameter has also been developed.