Solar Absorber Plates: Design and Application to Microgravity Capillary-Pumped-Loop Experiments

Abstract

An absorber plate is proposed to collect solar energy to be supplied to experiments in space. Its performance depends on the geometry of the satellite, on the incident environmental heat loads (solar, albedo, and Earth infrared radiation), and on the temperature level of the plate, which is usually an outcome of the microgravity experiment. A steady-state mathematical model is proposed to estimate the temperature distribution along the plate. Finite difference numerical models are developed for the steady-state and transient conditions and compared with the analytical model. Average temperatures and the net heat absorbed are determined. An experimental setup is developed to generate data to be compared with the theoretical models. A good agreement is observed among the experimental data, the analytical, and the numerical results. The procedure is applied to the small-scale capillarypumped-loop experiment, which will y aboard the French Brazilian Microsatellite. This experiment is described. Solar absorbers can be considered as a reliable alternative to improve the available heat power for experiments in space. Nomenclaturea = half the length of the capillary pump, m B = bias error b = half the length of the border of the plate, x direction, m C n , CC n = integration constant (n variable) C p = speci c heat, constant pressure, kW/kg¢ K c = half the length of the border of the plate, y direction, m d f = degrees of freedom h r = radiative heat transfer coef cient, W/m 2 ¢ K k = thermal conductivity, W/m¢ K; time-iteration counting variable m, n = node numbering (x and y directions, respectively) N = maximum number of series terms, number of elements P = electrical power, W q = thermal power, W/m 2 R = electrical resistance, X S = environmental total heat load, W/m 2 ; standard deviation T = temperature, K T f = uid temperature, K T s = space temperature, K t = thickness of the plate, m; time, s; Student t multiplying factor U = uncertainty interval V = voltage, V x, y, z = orthogonal directions, Cartesian system a = absorptivity ² = emissivity h , H , U , W = temperature difference, (T ¡ T f ) k , l = eigenvalue q = density, kg/m 3 r = Stefan-Boltzmann constant, 5.67 £ 10 ¡ 8 W/m 2 ¢ K 4