Document K6KzdmQ556KpBaavBgbNXX1ox

650 CHAPTER 28 1955 Guide Magnesia Insulation Manufacturer's Association. The new simplified nominal inch thicknesses for these insulations are 1, 1)4, 2, 2)4, 3, 3)4, 4, 4)4 and 5 for most pipe sizes )4 to 33 in. Most of these new nominal thicknesses are slightly greater than the actual thickness. Revision of 1.3 pipe and Industrial Insulation 651 with a 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 tem perature ranges encountered. In calculating the heat loss through such a combination the mean temperature of each layer must be determined along with the thickness of each. This is readily done in three or four calculations performed as a series of approximations, in which assumptions 0.| 40 I I M 1 J. I 1.1 1,1 II IJ 80 120 160 200 240 280 TEMP OIFF FROM PIPE TO ROOM. F DEG Fig. 1. Heat Loss Through 1 In. Thick 85 percent Magnesia Type Covering the heat loss charts, Figs. 1, 2 and 3, will be made, but for the present these charts may be used with the factors given in Table 7 for all of the insula tions shown in Table 6 without serious error. Pipes operating at high temperatures are frequently insulated to the best advantage by combining a high temperature insulation near the P'Pe Fig. 2. Heat Loss Through 1)4 In. Thick 85 percent Magnesia Type Covering of thickness and mean temperature are adjusted as indicated in the dis cussion 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: where k(t, - t,) g ------------------ Tt ilog, --rT,l (1) -- Btu per (hour) (square foot of outer surface of insulation). ri = outer radius of nipe or inner radius of insulation, inches.