an integrated test which incorporates four fundamental parameters of TPV direct energy conversion. These are: (1) the TPV devices, (2) spectral control, (3) a radiatiodphoton source, and (4) closed cavity geometry affects. The overall efficiency of the TPV device is controlled by the TPV cell performance, the spectral control characteristics, the radiator temperature and the geometric arrangement. Controlled efficiency measurements and predictions provide valuable feedback on all four. This paper describes and compares two computer codes developed to model 16,l cm2 TPV cells (in a 4x4 configuration) in a cavity geometry. The first code, subdivides the infrared spectrum into several bands and then numerically integrates over the spectrum to provide absorbed heat flux and cell performance predictions (assuming infinite parallel plates). The second, utiliies a Monte Carlo Ray-Tracing code that tracks photons, from birth at the radiation source, until they either escape or are absorbed. Absorption depends upon energy dependent reflection probabilities assigned to every geometrical surface within the cavity The model also has the capability of tallying above and below bandgap absorptions (as a function of location) and can support various radiator temperature profiles. The arrays are fabricated using 0.55 eV InGaAs cells with Si/SiO interference filters for spectral control and at steady state conditions, array efficiency was calculated as the ratio of the load matched power to its absorbed heat flux. Preliiary experimental results are also compared with predictions.

An emissometer was designed and constructed to measure the normal, spectral emittance of opaque solids over the spectral range from 1 to 8 /Jtm for temperatures ranging from 500 to 1500°C using an integral blackbody technique. The emissometer is gas-tight so that the gas environments surrounding the sample can be controlled and emittance data can be collected as a function of exposure time to a specific environment at a particular temperature. An FT-IR spectrometer collects the blackbody and sample infrared signals, which are ratioed to calculate the material's emittance. A computer code was developed to check the validity of the assumptions associated with the measurement technique. The emittance of silicon carbide in the form of a-SiC (Hexoloy SA) and TiB 2 -toughened SiC (Hexoloy ST) was collected over the spectral and temperature ranges given above. The emittance for Hexoloy SA was measured in the as-received condition and after sample exposure at 1300°C to carburizing, oxidizing, and low-pressure nitrogen environments. Emittance data for Hexoloy ST were collected for samples in the as-received condition and for samples exposed to oxidizing environments. The surface morphology and composition of the samples were characterized using SEM, EDX, and X-ray diffraction techniques. NomenclatureCi, C 2 , C 3 = correction factors for systematic errors, -d = layer thickness, imm E = emissive power, W/m 2 FJ_J = view factor, from A t to Aj H = irradiation, W/m 2 / = radiation intensity, W/m 2 sr n = index of refraction, -S = signal strength, mV § -unit direction vector, -T = temperature, K e -emittance 0 = polar angle, rad A = wavelength, /jum = azimuthal angle, rad Subscripts b = blackbody bg = background / = incident ra = measured s = sample ss = stainless steel drop tube A = spectral value, per unit wavelength

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