Document VGQkrnLMNMn0R0g5JpOY2okGN

fi For low rates of heat transfer by free convection the exponent decreases towards JjjfiS 1 ratesi, iinnccrreesasseesst-o--w---a--rds 0.33. The above equations employing an exponent equal to 0.25 are applicable in to | intermediate range indicated. NOMENCLATURE AND DIMENSIONS FOR TABLE 2 cp = heat capacity at constant pressure, Btu per (pound) (Fahrenheit degree). * D = cylinder diameter, feet. / = subscript denoting film. ' Heat Transfer 95 a = body force per unit mass, feet per hour per hour. (For static system on earth, g = 32.2 X 36001 feet per hour per hour.) G = 3600 uj -- mass flow per unit cross-sectional area normal to flow, pounds No. per (hour) (square foot of flow cross-section). = Grashof modulus, dimensionless {No, = D'p'fiCttg/iP). A. = average unit thermal convective conductance from the leading edge of surface to the position x, Btu per (hour) (square foot) (Fahrenheit degree). tx ' local unit thermal convective conductance, at the position x from the leading edge of surface, Btu per (hour) (square foot) (Fahrenheit degree). k = thermal conductivity, Btu per (hour) (square foot) (Fahrenheit degree per foot thickness). l = a dimension of the system, feet. m = a subscript denoting mean. P = pressure, atmospheres. Po = pressure (atmospheric) atmospheres. t = temperature, Fahrenheit. T = temperature, Fahrenheit, absolute. u = fluid velocity, feet per second. V = volume, cubic feet. x = a dimension of the system, feet. e coefficient of cubical expansion (fi = ^1 (d^V)p); for perfect gases fi = 1/T. hi difference between wall and fluid temperatures, Fahrenheit degrees, n fluid viscosity, pounds per (hour) (foot), p density, pounds per cubic foot.. infinity, referring the quantity to a point not directly affected by the phenomenon in question. 3.Table Radiation Factors ob Emissivities, t* For the determination of factor Fe in Equation S Clash ____________ Surfaces Fraction or Black-Boot Radiation At 60-100 F At 1000 F Absohptiviti ron Solas Radiation 1 A small hole in a large box, sphere, furnace, or enclosure.............. BiacJc non-metallie surfaces such as asphalt, carbon, slate, paint, naner Ked brick ana tile, concrete and stone, rusty steel 0.90 to 0.98 0.80 to 0.98 0.97 to 0.99 0.85,to 0.98 4 and iron, dark paints (red, brown, green, etc.).. 0.85 to 0.95 0.75 to 0.90 fellow and buff brick and stone, firebrick, fire 0.65 to 0.80 clay.............................................. White or light-cream brick, tile, paint or paper 0.50 to 0.70 8 plaster, whitewash............. Window trlncro ringht aluminum paint; gilt or bronze paint.... 0.85 to 0.95 0.90 to 0.95 0.40 to 0.60 uuil brass, copper, or aluminum; galvanized 0.30 to 0.50 steel; polished iron.................. 0.20 to 0.30 10 polished brass, copper, monel metal.. 0.02 to 0.05 0.05 to 0.15 polished aluminum, tin plate, nickel chromium 0.02 to 0.04 0.05 to 0.10 0.10 to 0.40 * Emissivities of other materials may be found in Reference 4. * Reflects about 8 percent. fourth powers of the absolute surface temperatures (TV -- Tj4). The pro portionality factor (oFaFe) may be conveniently separated into three parts (excepting in some problems involving interreflections, where it not possible to divide the product (FaFe) into separate terms): IS v = t/he S---t-e---fran-Bol.t.z..m...a..n..n. ,roaudiitatUtioyUn ccuoinissitaannit == i1/o73u0 XX 10-'* Bif1t,u11 pnperr f(hhnonurr)l hrr f,0t^ (Fahrenheit degree absolute temperature to the fourth power), for tgh Ttncal f,act?riwhich dimensionless and 5 1. This factor accounts ,, . . . cuuuuuies. countTfoiV*by factor twhich is also dimensionless and S 1. This factor acunis lor the absorption and emission characteristics of the surfaces for the