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Heat Transfer and Thermal Analysis - A.A. 2013/14 - Date 2014/??/?? (Example) Surname: Name: ID number: Signature: Part A (exact answer 1.5 pts, no answer 0 pts, wrong answer −0.5 pts. Part A sufficient if ≥ 16) NOTE: THIS IS A REDUCED EXAMPLE, REAL PART A IS MADE BY 20 QUESTIONS For a double-pipe heat exchanger in which no fluid undergoes a phase change, the energy balance allows to state that the heat transfer rate between the fluid is given by: ⨂ ˙QH→C = ˙MHcP H(THu−THi) ⃝ ˙QH→C =hHu−hHi ⃝ ˙QH→C = ˙MHTH(sHu−sHi) ⃝ ˙QH→C =UHu−UHi In steady-state conditions, the general temperature profileT(r) in a hollow cylinder of infinite length in which a heat source is present reads as: ⨂T(r) =−˙U ′′′ r2/(4λ) +C1ln(r) +C2 ⃝T(r) =C1ln(1/r2) +C2 ⃝T(r) =−˙U ′′′ /(2λ) +C1ln(1/r) +C2 ⃝T(x) =−2C1 ˙U ′′′ r2/λ+C2ln(r) The most general form of the conduction equation for homogeneous, isotropic media with conductivity varying with temperature is: ⃝λ∇2T + ˙U ′′′ =ρc∂T/∂τ ⃝∇2T + ˙U ′′′ /(ρc) =−λ∂T/∂τ ⨂∇(λ∇T) + ˙U ′′′ =ρc∂T/∂τ ⃝∇2T = 0 Two gray planes (T1 = 50◦C,ε1 = 0.5; T2 = 150 ◦C,ε2 = 0.25) are immersed in the vacuum and parallel to each other. The heat flux between the two in steady state conditions is? ⃝ ˙Q ′′ = 1350 W/m2 ⃝ ˙Q ′′ = 1200 W/m2 ⃝it cannot be calculated as some data are missing ⨂ ˙Q ′′ = 240 W/m2 In case of natural convection, the correlation for the evaluation of the convective coefficient may read as: ⃝Nu =ARenPrm ⃝Nu =ARenBim ⨂Nu =AGrnPrm ⃝Nu =AGrnStm In terms of heat removal rate, dropwise condensation is: ⨂ more effective than film condensation because the vapour is always in contact with the surface ⃝ more effective than film condensation because the pre- sence of drops positively affects the vapour convective coefficient ⃝ less effective than film condensation because the liquid does…