Date of Award
Master of Science in Chemical Engineering - (M.S.)
Robert M. Casciano
John E. McCormick
The effects of heat and mass transfer across a frosted heat exchanger operating in the absence of air was evaluated. It is felt that this work could be applied to processes such as desalination of water or the purification of materials by reverse sublimation.
The system consisted of a single 1/2” O.D. stainless steel tube mounted within a 3" O.D. plexiglas tube with the ends suitably flanged. A vacuum was maintained in the annular space. Refrigerated ethylene glycol passed through the inner tube in laminar flow. A series of runs with substantially air-free water vapor added to the annular space deposited an ice film on the metal tube. Small, finegrained droplike sites of ice were observed at the start of each run. These soon joined together and formed a continuous layer of ice. The experiments, carried out at reduced pressures, for a 2 1/2 to 4 hour period developed sufficient ice which could be measured, removed from the metal tube and weighed.
Five runs were made under vacuums of 1.3 mm. to 4.0 mm. Hg and 1 run at atmospheric pressure. From the concept of resistances in series, overall coefficients of heat transfer were calculated and compared to values found in the literature from frosted heat exchanger experiments. The present experiments showed that improvement in heat transfer rates can be expected when air is evacuated from the system. For example, at 1.5 mm., the , heat transfer coefficient was 6.72 compared to 0.662 at atmospheric pressure.
Wilson plots were also used to evaluate the surface coefficients. With this method it is possible to obtain an overall resistance of the system at infinite ethylene glycol velocity. From this is subtracted the know resistances of the metal and ice film. The remainder is the surface film resistance. This method gave good agreement with surface coefficients as calculated above.
Howley, James Joseph, "Heat and mass transfer in the absence of air" (1967). Theses. 2086.