HTTA 2015 07 10 Solutions

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Heat T ransfer and Thermal Analysis - A.Y. 2014/15 - Date 2014/07/10 Surname: Name: ID number: Signature: Part A 1. Draw (qualitatively but with physical accuracy) the steady-state temperature profiles in a passive flat plate having fixed temperatures on the external surfaces and: 1) constant conductivity, 2) conductivity increasing with temperature, 3) conductivity decreasing with temperature 2. Put the following materials/substances in correct ascending order of Prandtl number values: air, very viscous mineral oil, water, mercury 3. Sketch the Nukiyama curve stating the different stages during pool boiling 4. Write the Richardson number and the criterion to distinguish between forced, natural and mixed convection 5. Write the Laplace-Young equation, stating the meaning of the involved terms 6. Write the Wien law and its meaning 7. Write the reciprocity rule for two gray surfaces enclosing a cavity Heat T ransfer and Thermal Analysis - A.Y. 2014/15 - Date 2014/07/10 - Part B Question 1 (up to 10 points) Commenting the hypotheses and assumptions you make, derive the general conduction equation from the First and Second Principles of Thermodynamics, then derive from it the general (before application of the b.c.s) expressions of the steady-state, 1D temperature and heat flux profiles in a hollow cylinder having constant conductivity and constant and uniform heat source. Exercise 1 (up to 10 points) In a radiator (cross-flow, both fluids unmixed) a mass flow rate ˙Mw = 2 kg/s of water is flowing within N = 100 tubes (Di = 5 mm, L = 1 m, negligible thickness) while the external air (atmospheric pressure, mass flow rate ˙Ma = 6.25 kg/s) is flowing between the flat plates of the radiator, that have a total surface area which is 20 times the total internal surface area of the ducts. The…