Document YGpzdBQnnw9yERVExdDQZYZMk

,702 CHAPTER 27 . 1957,-Guide The heat losses through 1, 1H, and 2-in. thick block, blanket, or cement insulation when applied to a flat vertical surface is given in Fig. 4. ,The losses through any of the insulations given in Table 1 can be obtained by. multiplying the losses obtained from Figs. 1, 2, 3, or 4 by the factors given in Table 6. Pipes operating at high temperatures are frequently insulated to the best advantage by combining a high-temperature insulation near the pipe with a Pipe and Industrial Insulation 703 and mean temperature are adjusted as indicated in the discussion which follows. In the case of a single thickness of pipe covering, the quantity of heat transferred per, square foot of outer surface of the insulation is given by the equation: k(ti -- fj) log. -n (1) Fig. 2. Heat Loss through 1)4 In. Thick Pipe Insulation (Use with Table 6 for Various Insulations) moderate or low-temperature insulation around it as an outer layer. By this method an efficient material may be used for each of the two temp ^ ture ranges encountered. In calculating the heat loss through sue*! combination the mean temperature of each layer must be determined al* with the thickness of each. This is readily done in two or three calculati performed; as a series of approximations, in which assumptions of thickn Fig. 3. Heat Loss through 2 In. Thick Pipe Insulation (Use with Table S for Various Insulations) where ?o = Btu per (hour) (square foot of outer surface of insulation). ri = outer radius of pipe or inner radius of insulation, inches, n = outer radius of insulation, inches. = thermal conductivity of insulation, Btu per (hour) (square foot) (Fahren( heit degree per inch). 1 -- temperature of inner surface of insulation, Fahrenheit degrees. - temperature of outer surface of insulation, Fahrenheit degrees. the*i 'S C0J*ven'ent to work from the outer surface of the insulation, since oss through the covering must be determined from the outer surface