project in applied heattransfer

ETME321 Project 1 – Heated Box

DUE (upload to D2L dropbox) by 5 pm FRIDAY FEB 23, 2018.

The objective of this problem is to design a heated box (incubator) with an interior air

temperature of 65C. The interior dimensions of the box are to be 0.8 m  0.8 m  0.8m (note

that the box has 5 air exposed sides to consider). The outside surface of the box will be exposed

to ambient air at 20C with a convection heat transfer coefficient of 5 W/m2-K. The average

temperature of the surroundings (e.g., walls, floor, ceiling, etc.) is also 20C. The box will sit on

a flat surface that is well-insulated. An electric resistance heater is placed inside the box that

dissipates 100 W. The box also contains an electric fan that mixes the air, yielding an average

heat transfer coefficient of 15 W/m2-K along the interior surface. The fan dissipates an additional

20 W of heat.

Your job is to select the wall material(s) needed to maintain a steady-state air temperature of

65C inside the box. You should specify the material composition(s) and calculate the required

thickness(es). You may use more than one type of material for the wall but keep each wall

section identical for construction simplicity. The outside of the box should be structurally rigid.

Refer to Appendix Tables A.1, A.2, A.3, and A.11 in the textbook for different materials and

their properties.

You may assume that i) all material properties are constant, ii) conduction through each wall

section (top plus four sides) is identical, iii) conduction is one-dimensional as long as the total

wall thickness does not exceed 0.08 m, iv) steady-state conditions prevail, v) the surroundings

are large compared to the box, vi) the given heat transfer coefficient (15 W/m2-K) inside the box

accounts for any internal radiation effects, and vii) the box is air-tight.

PART 1:

Provide an analysis of the box heat transfer with all property values clearly specified and

referenced for the material(s) that you have chosen. Put the following information in a table as a

summary:

 Wall material composition(s)

 Wall material thickness(es)

 Inside wall temperature

 Outside wall temperature

PART 2:

A mini-incubator has been suggested as a prototype. The interior dimensions of the box are

to be 0.35 m  0..35 m  0.35m with the same conditions above ie a goal of keeping the interior

air temperature of 65C. Could the same heater be used: what would you recommend?

Present your findings in a brief report (less than 10 pages) with calculations included (as an

appendix) and upload as a .pdf file in D2L dropbox for Project 1. DUE by 5 pm Feb 20.