ESTP exam 2024 02 09

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Engineering of Solar Thermal Processes 09.02.2024 LAST NAME ___________________________ FIRST NAME _____________________________ Write last name and first name on each sheet. Hand in also your rough draft and this text. The approximate time to elaborate the answers is: 1.a) 30 min., 1.b) 15 min, 2) 15 min. 1. Collector physics a. Derive the expression for the global heat loss factor UL and the involved radiative heat transfer coefficients with reference to the illuminated absorber area of the vacuum tube collector shown in Figure 1. The collector is made of a single tube and is so well insulated from the ground that conductive losses can be neglected. Assume to know convective heat transfer coefficient between glass tube and air; emittances of surfaces; temperatures of surfaces, ambient air, ground and sky. Clearly state the hypotheses underlying the thermal model. NOTE Absorber width is W, glass pipe diameter D, and tubes diameter d << D. b. With reference to the vacuum tube collector shown in Figure 1, heat is removed from the absorber plate through a U-shaped tube, represented by the tubes of diameter d in the figure. Explain how to apply the efficiency factors F and F’, used in the derivation of the collector heat removal factor (FR), to the geometry of this collector. Figure 1 – Schematics of vacuum tube collector. 2. Solar cooling a. Draw the schematic of a water-LiBr single effect absorption chiller. b. Explain how to calculate, with the aid of the P-T-X diagram, the minimum temperature of the heat source that is sufficient to drive the cycle using the following input parameters: evaporation temperature, condensation temperature, solution temperature at pump inlet, circulation ratio.