Temperature difference between surface and

AT, At Temperature difference Atj, Ato, and At temperature difference across bodies 1, 2, and 3 or at points 1, 2, and 3 AT, , At, , for overall temperature difference Ati, for temperature difference between surface and boihng hquid K ... 

This is the rate of heat transfer from a surface to the surrounding air (or fluid) due to conduction convection and radiation. It is generally used only in still-air conditions and when the temperature difference between surface and ambient is of the order of 30 K. It is obtained by dividing the thermal transmission per unit area in watts per square meter by the temperature difference between the surface and the surrounding air. It is expressed as W/nf K. 

For a 12 mm insulating board with a thermal conductivity of about 0.38 kcal/m,h,°C (equal to 0.044 W/m°C) perpendicular to the sheet, the temperature difference between surface and thickness center under the conditions used was measured to be 10°C at a mean temperature of 190°C. For a hardboard with nearly three times this thermal conductivity it is negligible. For example, for a 3.2 mm hardboard it varies from 1 to 3°C over the 185° to 230°C range. 

Waste incineration requires sophisticated scrubbers to contain corrosive volatiles which are in contact with the scrubber wall at elevated temperatures reaching 220°C. " Glass mat reinforced novolac epoxy vinyl ester resins have good performance in this application except that they are subjected to thermal stress due to the temperature difference between surface and wall, and they frequently crack. In order to improve performance, a two layer laminate was produced. The base layer is composed of resin reinforced with glass mat. The resin contains 15-20% graphite filler. The surface layer contains 100 g/m" of carbon fiber. The presence of these two fillers helps to distribute heat more evenly throughout the layer of laminate and prevents cracking even under extreme conditions. "... 

A natural question is how long the soil can sustain the heat flux to the gas cloud. Nielsen and Ott (1999) studied the problem of linear heat diffusion in a homogeneous semisolid coupled with forced convection from the surface setting the surface flux proportional to the temperature difference between surface and gas layer. The temperature difference and surface flux after sudden exposure to a gas cloud of constant temperature was found to be... 

P = coefficient of expansion AT = temperature difference between surface and fluid p = density... 

---