HTTA 2019 01 17 Solutions

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Heat T ransfer and Thermal Analysis - A.Y. 2017/18 - Date 17/01/2019 Surname: Name: ID number: Signature: (“matricola” or person code) Part A 1. Write the general conduction equation for a domain with constant conductivity. 2. Write the finite different approximations of the first derivative of temperature with respect to a space direction using: a) the backward form, b) the forward form, c) the centered form. 3. Place the following materials in ascending order of conductivity: rubber, air, iron, stainless steel, copper. 4. Write the expression of the net radiative transfer between two parallel planes having constant and uniform temperature. 5. Draw the temperature profiles T (x) for the two fluids in a co-current heat exchanger in which ˙CH→∞ . 6. Write the general expressions of temperature and heat flux as a function of the radius in a hollow sphere in steady-state conditions and with heat source, before application of any b.c.. 7. Write the Biot dimensionless group, stating its physical meaning. Heat T ransfer and Thermal Analysis - A.Y. 2017/18 - Date 17/01/2019 - Part B INSTRUCTIONS - Read them very carefully! • test duration is 1 h 45’. After 35’ part A will be collected. If you finish part A in a shorter time, you can immediately move to part B; • you must answer to part A questions in the spaces provided after the questions themselves; remember also to fill in all the fields (surname, name, progressive number, ...) on the part A paper; • for part B, you can use only one foolscap paper for the final copy (additional papers will not be collected). On top-left of the first page of the foolscap paper you have to write (in a large and well-readable way): – progressive number (this is the progressive alphabetical order number the teacher will give you in each test, not your…