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The sweat control provided by cold pipe/sheet insulation depends on the surface temperature, the dew point of air and the thermal and surface characteris tics of the insulation. The objective of the present research is to observe and better understand how surface sweating on closed cell foam insulation occurs at different relative humidities and air temperatures. An apparatus was built to measure the sur face temperature of foam insulation on a cold plate at various air temperatures and relative humidities. From the analysis of the experimental data, it can be concluded that the surface of an insulation would visibly sweat only if adverse conditions of air temperature and relative humidity are sustained for rather long periods of time. The reasons are a strong dependence of surface sweating on surface temperature, an increase in the convective heat transfer coefficient with relative humidity at constant air tempera ture, and a possible condensation of a thin invisible layer of water on the surface.

A balance has to be struck between the complexity of the models used to represent the heat transfer mechanisms and the amount of experimental information and the associated accuracy of information needed to verify these models. The solid, gas and radiation contributions can be treated as uncoupled, yet such a treatment can reasonably represent the heat transfer through foams. The solid contribution is a strong function of how the polymer is distributed between struts and cell walls, and the density of the foam. The radiation heat transfer through foams can be represented by diffusion approximation, and it is mostly absorption dominated. Therefore, measurement of the extinction coefficient is sufficient for adequate representation. The higher the extinction coefficient, the lower is the radiation contribution.

Wide usage of cellular foam as low temperature thermal insulating material warrants good understanding of its thermal and water vapor transmission behavior. An attempt has been made to experimentally observe the effect of cell shape on heat and mass transfer characteristics of cellular foams. The foam samples used in this study were derived from elastomeric foam The thermal conductivity and water vapor transmission data were taken on foams with three different cell shapes. one having spherical cells and two having elliptical cells, with varied degree of elongation.The thermal conductivity measurements on the samples described above were obtained using Thin-Heater thermal conductivity apparatus, otherwise known as the ASTM C-1114 test. The thermal measurements were performed in the temperature range of 35 to 153°F. The experimental data indicated no significant effect of the cell elongation on thermal conductivity of foam. This could be attributed to the following : a) the densities of the foam were roughly the same, and therefore conduction heat transfer was not significantly changed; b) the possible decrease in the radiation component of thermal conductivity because of elongated cells was nullified by the increase in transmission of heat attributable to relatively thinner walls resulting from the stretching of the foams during sample preparation. Additionally, the change in the shape of cells could have changed the radiation heat transfer characteristic of the samples.Water vapor permeabilities of the foams with elongated cells were measured with Permatran® and compared to that of the foam with uniform cells. It was found that the foams with elongated cells had almost twice the permeability as the foams with uniform cells Also, the two foams with elongated cells had about the same perme-

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