Results from thermal studies performed for an annular solar receiver assembly to be used with the Sandia Laboratories 2-m, 90-deg parabolic collector trough are presented. The receiver configuration modeled consists of a 2.54-cm o.d. steel tube with a black-chrome selective surface and an enclosing concentric Pyrex glass envelope. One- and two-dimensional thermal models have now been developed to provide receiver assembly temperatures, heat losses, and working fluid energy extraction data with the Therminol-66 (T-66) bulk temperature maintained at 315/sup 0/C. Parameters varied in the work include wind velocity, ambient air temperature, annulus gas pressure, and T-66 flow condition (Reynolds number). Heat loss and energy extraction results are tabulated and temperature distributions from two-dimensional thermal modeling are graphically presented in the Appendices. The thermal studies indicate excessive temperatures (greater than or equal to 340/sup 0/C) for the receiver tube surfaces when the operating Reynolds number is low (30000). Such temperature levels can result in T-66 and black-chrome degradation. Therefore, it is recommended that the Reynolds number be maintained above 50000. The studies also show the importance of receiver assembly alignment. Misalignments, particularly an upward misalignment, can greatly increase the peak temperature experienced by the T-66 fluid and black-chrome selective coating. Further,more » since one-dimensional and two-dimensional heat loss and energy extraction results are comparable, one-dimensional thermal modeling is recommended so long as receiver temperature distributions are not needed. Increasing wind velocity and decreasing ambient air temperatures have been found to increase receiver heat loss. These increased losses are minimized if the annular space of the receiver assembly is evacuated.« less