Solar collectors for low and intermediate temperature applications

Abstract

.4,, = area of aperture. .4, = receiver surface area. C = .4,, .4, = concentration. % = specific heat of the heal transfer fluid. F' = collector efficiency factor. F~ = heat removal factor. G = flow rate per unit surface area of collector. h = convective heat transfer coefficient. Hh = insolation on a horizontal surface. 1 = insolation. 1~ = beam insolation. I< = HhR = insolation of collector. 1~ = diffuse insolation. I, = total insolation. k = thermal conductivity. n = number of reflections, or index of refraction. ( n ) = average number of reflections. q~ .... = rate of heat transfer from the absorber plate to the environment. R = ratio of the insolation of the plane of the tilted collector to the insolation on the horizontal surface. To = ambient air temperature. Ts.,, = fluid inlet temperature. 7).,,,, = fluid outlet temperature. Tt, = collector plate temperature. L:~ = back loss conductance. U< = collector heat loss conductance, also called U-value. r = air velocity. :~ = absorptance. /7 = collector tilt from equatorial plane. & = angular half-width of sun ~ 4.7 mrad ~ 1 4 °. ¢: = emittance. ~h = collector efficiency. ~h = fin efficiency. ~I,, = optical efficiency. ~ = rim angle of concentrating collector. ¢)~ = angular half-width of source t=acceptance halfangle of ideal concentratorl. 0,,, = angle of incidence. p = 1 z~ = reflectance. a = Stephan-Boltzmann constant. : = transmittance of cover.