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A thermodynamic model is developed to analyze the thermal performance of two-phase solar collectors. The well-known equilibrium homogeneous theory is used to model the two-phase flow in the solar collectors. The resultant set of coupled ordinary differential equations for saturated pressure and quality of working fluid in the collector tubes are solved by an iterative procedure using a fourth-order Runge-Kutta method. The results are then applied to determine the thermal performance of a solar assisted heat pump which uses two-phase flow collectors as the evaporator. The results indicate that even with the use of less expensive bare solar collectors as evaporator for the heat pump, the heating coefficient of performance (COPH) as high as 6 can be obtained under realistic ambient conditions provided a proper matching exists between the collector’s evaporative capacity and the compressor’s pumping capacity.

An infrared imaging system was used to detect the thermal signature of boundary-layer flow regimes on a NACA 0012 airfoil from zero angle of attack up to separation. The boundary-layer transition from laminar to turbulent flow and the onset of separation could be seen on the airfoil thermograms. The findings were compared against the behavior of aluminum foil tufts observable both visually and with the infrared imaging system. This arrangement offers the option of using the infrared imaging system both for flow regime detection through surface thermograph} and flow visualization by the aluminum foil tufts. Ultimately the surface temperature changes due to variation in the angle of attack of a lifting surface provide a means for interpretation of the boundary-layer flow regimes.

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A new theoretical analysis has been made of turbulent heat transfer in the region of simultaneously developing hydrodynamic and thermal boundary layers in annular flow. A boundary layer-potential stream model has been used to describe the flow, heat transfer being predicted through the use of a modified Reynolds analogy. Skin friction data for the inner heated wall have been obtained from correlations pertaining to boundary layers on immersed bodies. Experiments have been made with air in the entry region of internally heated annuli with radius ratios 2·1 and 4·0. Satisfactory agreement between theory and experiment has been achieved.