"The cooling of a gas-vapor mixture or a mixture of several vapors, in the general case, results in condensation (phase-change) of one or more of the vapors when their respective dew-points are reached. This results in a mass transfer of the vapor to the cooling surface accompanied by energy transfer as the vapor gives up its latent heat of vaporization to the surface and becomes a liquid. The liquid accumulation adds a resistance to the further transfer of mass and energy unless some means is provided for its removal from the surface, such as gravity action.
In this paper we are concerned particularly with a mixture of air and water vapor at atmospheric pressure coming into contact with a surface whose temperature is below the freezing point of water. The freezing of water onto a surface is a somewhat different process from condensation in that the layer of frost or snow will build up with time resulting in an increasing resistance to the flow of heat and mass. Condensation of a vapor onto a cool surface results in a liquid build-up to a certain thickness which then flows off if the cooling surface is sloped enough to allow this to happen. Frost, on the other hand, builds up in crystal form and has the ability to adhere to a smooth surface until the shear effect becomes too great and a portion of the formation slides off. Usually, considerable time has elapsed before this occurs (on the order of an hour or greater).
This paper presents a method of transient heat transfer analysis using graphical means for the determination of the heat transfer rate and corresponding liquid boil-off rate of liquid oxygen from a thin aluminum tank. The effects of wind, dry bulb temperature, relative humidity, thermal radiation, and increasing frost build-up were considered in this problem.
The author became interested in attempting a theoretical determination of the effects of frost formation while conducting tests comparing the boil-off rates of liquid nitrogen contained in a tank constructed of aluminum with one built of fiberglas laminate. These tests were carried out in the spring of 1955 while employed as a development engineer at Redstone Arsenal, Alabama.
This subject is of interest in liquid rocket missile work in being able to predict the magnitude of liquid oxygen losses which would result from exposure to widely varying atmospheric conditions.
In general, the problem of frost formation and its attendant reduction in heat transfer is of interest in refrigeration work in connection with the frosting up of evaporator coils. A familiar example of this is the household refrigerator where it is observed that frost gradually builds up on the freezing unit, making it necessary to "de-frost" the refrigerator after a certain time period in order to restore the effectiveness of the freezing unit.
The author has noted that considerable deviation exists in the published data for the thermal conductivity and apparent density of frost and the variation of frost conductivity with temperature. It is believed that further experimental work on these fundamental data would be of much utility to engineers engaged in refrigeration and low temperature heat transfer design work"--Introduction, pages 1-3.
Miles, Aaron J.
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
Missouri School of Mines and Metallurgy
iv, 54 pages
© 1958 Jack Lewis Loper, All rights reserved.
Thesis - Open Access
Library of Congress Subject Headings
Heat -- Transmission -- Mathematical models
Heat -- Transmission -- Graphic methods
Frost -- Thermal conductivity
Print OCLC #
Electronic OCLC #
Link to Catalog Recordhttp://laurel.lso.missouri.edu/record=b2614107~S5
Loper, Jack Lewis, "Frost formation and its influence upon heat transfer" (1958). Masters Theses. 2173.