ChE 350 Problem Set 8

When the ceiling surface temperature in the PSU Ice Pavilion drops below the dew point of the air in the

ice rink, water condensing on the ceiling will drip onto the ice surface, causing bumps to form. Your

assignment is to examine the effect of the emissivity of the ice rink ceiling on the propensity for

condensation; specifically, is it best to make the ceiling have a high or low emissivity? The ice rink can be

modeled as a large rectangular building with a 60 m x 20 m floor space and a 10.0 m high ceiling. You

may consider the ceiling to be a diffuse gray surface, the walls (all 4 of them) to be blackbodies at 10°C,

and the ice to be a blackbody maintained at -7°C. The air in the rink is maintained at 15°C with a relative

humidity of 70%. The convection heat transfer coefficient between the air and the ceiling, ice surface, and

walls is 5.0 W/m²K. The ceiling is separated from -5°C external air by a 0.30 m-thick layer of insulation

(-0.045 Wm ¹K¹), and the external convective resistance is negligible.

a. Draw a resistance network for a 3-surface enclosure that represents the radiation heat transfer between

the ceiling, ice, and side walls. Label the nodes and resistances, and calculate the value of each

resistance. The ice-ceiling view factor may be calculated using the result for aligned parallel rectangles

shown below. Other view factors can be determined using the summation and reciprocity rules.

b. Consider a flat ceiling with highly reflective panels (-0.05) or painted panels (-0.95). Calculate

the ceiling temperature in each case to determine if condensation would occur on the ceiling. The

dewpoint for the specified air temperature and relative humidity can be estimated using the Antoine

equation.

c. For each ceiling type, plot the ceiling temperature as a function of the insulation thickness (in the range

0.1-1.0 m) to identify conditions for which condensation would occur on the ceiling.

d. Plot the ceiling surface temperature as a function of the emissivity of the ceiling. What range of

emissivity values will prevent condensation on the ceiling? Should ice rink ceilings be designed with

high or low emissivity?

e. Plot the refrigeration load on the ice rink (i.e., the total rate of heat transfer to the ice) as a function of

the emissivity of the ceiling.