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Politecnico di Milano – A.Y. 2025–2026 Master Programme in Energy/Nuclear Engineering Heat and Mass Transfer Examination – 01 July 2026 Surname: Name: Student ID number: Grade 1 -. . . . . . . . . /15 2 -. . . . . . . . . /15 Total . . . . . . . . . /30 The time available is 3 hours . Only the material provided as Supplementary Material may be used. No textbooks, notes, or electronic devices are allowed. The maximum score is 30/30. At the end of the exam, this text must be submitted with the numerical results written next to each question , and no more than two protocol sheets (eight written pages) containing the detailed solution must be handed in. Problem 1 (15 points) In a paper-mill drying process, a thin sheet of paper slurry (water–fiber mixture) leaves a roll and moves with a constant velocityus = 5.0 m/s. Radiant heaters maintain the sheet surface atTs = 310 K while evaporation occurs from both the upper and lower surfaces of the sheet. The surrounding air is atT∞ = 290 Kand p = 1 atm, with relative humidityϕ∞ = 0.30. The analysis refers to a sheet segment of lengthL = 1.0 min the direction of motion. The radiant heaters may be modeled as blackbodies atTH = 1000 K. They are two identical black strips, one above and one below the sheet. Each strip is parallel to the sheet, very long in the transverse direction, located at a distanceH = 0.50 mfrom the corresponding sheet surface and centered with respect to the sheet segment. The slurry surface is diffuse and opaque and has the following spectral reflectivity: ρλ =    0, λ < 5 µm, 0.50, 5 µm ≤ λ < 9 µm, 0.90, λ ≥ 9 µm. The surface exchanges radiation with large surroundings atT0 = T∞. The air properties can be assumed equal to those of dry air, while the slurry is assumed to have water properties. Find:…