Radiation coefficient

FIG. 5-7 Radiation coefficients of heat transfer h,.. To convert British thermal units per hoiir-sqiiare foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply by 5,6783 = ( F — 32)/l,8,... 

Equation (12-47) assumes that all heat sources are at the same temperature and that the convection coefficients to the evaporating surface and to the unwetted portions of the tray are equal. When radiation occurs from a source at a different temperature, the radiation coefficient can be corrected to the same basis by multiplying by the ratio (t — f()/(U i ), where t, t, and t are the diying-gas, evaporating-surface, and radiator temperatures respectively. 

Combined convection and radiation coefficients, hc + hr, for horizontal steel or insulated pipes in a room at 80°F... 

The reactor for radiation chemical synthesis with an agitator (about 200 rotations per minute) is located in the operation chamber. Inside the reactor there is a cavity for introducing sources of y-radiation. The role of the radiation source is played by 60Co in airproof stainless steel ampules the activity of 60Co radiation is about 3000 eq Ra. The consumption degree of the energy of radiation when the sources are placed in the cavity, or the radiation coefficient of efficiency, varies from 17 to 19%. The equipment is encased in a special box made of stainless steel and plexiglass the box has intensive ventilation. 

Obviously, the radiation coefficient is a very strong function of temperature. 

A solid surface at 1100 K is radiating to a second surface at 330 K. What temperature of the hot surface would be required if it were desired to double tbe number of joules transmitted per hour, the sink temperature and botb emissivities remaining constant What will be the percentage increase of the radiation coefficient hr under the changed conditions ... 

In these relations, qo i specified heat flux in W/m h is Ihe convection cocfficieiii, /i(ombin d Combined convection and radiation coefficient, T is the temperature of the surrounding medium, T un [Pg.315]

Where (r) is thermal radiation flux received at a distance from target r is atmospheric transmission rate rj is thermal radiation coefficient nds mass flow rate of the fuel is combustion heat ... 

Radiation coefficient from gas blanket between pieces 14 17.3... 

Perry and Green (P3, p. 10-14) give a convenient table of natural convection plus radiation coefficients (h + h ) from single horizontal oxidized steel pipes as a function of the outside diameter and temperature difference. The coefficients for insulated pipes are about the same as those for a bare pipe (except that lower surface temperatures are involved for the insulated pipes), since the emissivity of cloth insulation wrapping is about that of oxidized steel, approximately 0.8. A more detailed discussion of radiation will be given in Section 4.11. 

Equation (18-7) applies to any conventional arrangement of the convection section. However, the coefflcient he is the pure convection coefficient and it does not include radiation from the flame, from the hot gas, or from the walls. Monrad has made a study of these factors. The first of these is designated as hr or the coefficient of heat transfer from the gas by radiation. As an approximation, the value of the gas radiation coefficient may be found by the following relation ... 

The second factor, the wall effect, usually ranges in magnitude between 6 and 15 per cent of the sum of the pure convection and the radiation coefficients. 

During the selection of the proper materials to be used for protection, several characteristics of each material would be rated to help narrow the decision. The minimum characteristics that should be evaluated for these materials are ability to withstand environmental and plant produced radiation, coefficient of thermal expansion, density, electrical resistivity and conductance to control electrostatic discharge, material chemistry ar d composition, operational temperature range, resilience, specific heat, strength, stiffness, thermal conductivity, thermal radiation absorptivity, thermal radiation emissivity, the ability to fasten the material to the support structure and/or the components themselves, and the compatibility between the protecting material and material to which it would be fastened... 

---