HTTA 2016 07 05 Solutions

Pagina 1

Heat T ransfer and Thermal Analysis - A.Y. 2015/16 - Date 2016/07/05 Surname: Name: ID number: Signature: Part A 1. Write the relation between the absorption, reflection and transmission coefficients for a diffuse emitter, both in total and spectral versions. 2. Draw (qualitatively but with physical accuracy) the steady-state temperature profiles in a passive flat plate having fixed temperatures on the external surfaces and: A) constant conductivity, B) conductivity increasing with temperature, C) conductivity decreasing with temperature. 3. Write a suitable correlation to estimate the local convective coefficient h for laminar flow of air over a flat plate having constant and uniform temperature. 4. Write the general form of the Laplace-Young equation, stating the meaning of the involved terms. 5. Put the following flows in correct ascending order of values of the Reynolds number: A) water flowing in a circular duct at the transition between laminar and turbulent flow; B) air flowing over a flat plate at the transition between laminar and turbulent flow; C) water flowing at T = 15◦with Peclet number Pe = 5000. 6. Write the finite difference approximations for the first and second derivatives of temperature with respect to space using the basic centered form. 7. Write the general expressions of the temperature and heat flux profiles in a hollow cylinder, having constant conductivity and with uniform heat source, before application of any b.c. Heat T ransfer and Thermal Analysis - A.Y. 2015/16 - Date 2016/07/05 - Part B Exercise 1 (up to 15 points) A mass flow rate ˙Mr = 20 kg/s of a corrosive liquid (having ρr= 1200 kg/m 3, cP r = 1400 J/kgK, µr = 2.0 ·10−4 Pas, λr = 0.15 W/mK) is flowing within the N = 100 tubes of a shell-and-tube counter-current heat exchanger. Shell-side, water is flowing…