ROSE-HULMAN Institute of Technology

Department of Mechanical Engineering


ME462

Thermal Design

Homework 4

Problem 1

A two-layered furnace wall made of common brick and fire clay brick is to reduce the heat loss through the furnace wall to 1000 W/m2. The common brick layer is 8 in. thick and is exposed to the inside of the furnace. The inside surface temperature of the common brick is 1500°F. If the outside temperature of the fire clay brick is not to exceed 100°F,

  1. find the required thickness of the fire clay brick, and
  2. the temperature of the interface between the brick layers.

Problem 2

Finish Convection Concepts Review handed out in class.

Problem 3

A pipe has the dimensions given in the figure. On the outside, a gas with the following properties is flowing:

h = 5 Btu/ft2-hr-°F k = 0.0140 Btu/hr-ft-°F
ρ = 0.81 lbm/ft3 Pr = 0.72
cp = 0.24 Btu/lbm-°F T = 32 °F
μ = 1.165 x 10-5 lbm/ft-s  

On the inside, a liquid has the following properties:

V (average velocity) = 5 ft/s k = 0.394 Btu/hr-ft-°F
ρ = 60.1 lbm/ft3 Pr = 1.89
c = 1.0 Btu/lbm-°F Tin = 200 °F
μ = 0.205 x 10-3 lbm/ft-s Pipe is made of copper.
ν = 0.341 x 10-5 ft2/s k = 226 Btu/hr-ft-°F

Compute the pipe length required to cool the liquid to 180°F

HW4_3.GIFID = 2.5"
OD = 3.0"

Problem 4

Comment on the length for Problem 3. Make a practical suggestion for reducing this length and explain how this would change your analysis. You don't need to crunch numbers here, but you should be specific.