Document rwOENDjOo50OM2xKnGrN31Ee

470 CHAPTER 32 Table 4 .... External Surface per Linear Foot of Copper Tubing Ovtiido diemotur K in. preafer (ban nominal size Tube Siz* Surface Area Tube Size Surface Area Tube Six* Surface Area (inches) (SqR) (Indies) (Sq Ft) (inches) (Sqft) H 0.164 2 0.556 5 1.342 X 0.229 2K 0.687 6 1.604 1 0.295 3 0.818 8 2.128 IK 0.360 3K 0.949 IK 0.426 4 1.080 1960 Guide . k-U 9 , r* r, r. log. -- r. log, - + (2) where n -- outer radius of second layer of insulation, inches. r, " outer radius of last layer of insulation, inches. Hie method of solving Equation 2, which is the most diffi cult of the two, is given in Example 3. Example 3: Compute the heat loss per linear foot of pipe sur face per hour from a 6-in. pipe, insulated with a 3-in. tht/rlme^ of 1600 F diatomaceous earth, and a nominal 2-in. thiclrnnes of 85 percent magnesia. The pipe is operating at a temperature of 1200 F and is exposed to a room temperature of 80 F. Solution: In figuring the heat lass from Equation 2, it is neoesary to first make an assumption for the outer surface tem perature U and the temperature between the diatomaceous earth and 85-percent magnesia insulation, so that the mean tempera ture of each material can be obtained and the thermal conduc tivity corresponding to the mean temperature of each material substituted in the equation. First assume an outer surface tem perature of 135 F and a temperature of 570 F between the two materials corresponding to a mean temperature of (1200 + 570) -j- 2 or 885 F for the diatomaceous earth and (570 + 135) -f2 or 3525 F for the 85 percent magnesia insulation. The conduc tivities of these two materials at mean temperatures of 885 and 3525 F, interpolated from Table 1, are 0.677 and 0.466 Btu, re spectively. Fig. 1 .... Heat Loss through 1 In. Thick Pipe Insulation (Use <rrffi foUt 6 for Various laudations] Table 5 .... Area of Flanged Fittings, Square Feet* NoeuacJ Pipe Size (Iacbes) Ranged Coupling Standard Extra Hoary 90 Dog BJ long Radius Bl Tee Crass Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy ! 0.320 0.438 0.795 1.015 0.892 1.083 1.235 1.575 1.622 2.07 IK 0.383 0.510 0.957 1.098 1.084 1.340 1.481 1.925 1.943 2.53 IK 0.477 0.727 1.174 1.332 1.337 1.874 1.815 2.68 2.38 3.54 2 0.672 0.848 1.65 2.01 1.84 2.16 2.54 3.09 3.32 4.06 2K 0.841 1.107 2.09 2.57 2.32 2.76 3.21 4.05 4.19 5.17 3 3K 4 4K 5 6 8 10 12 0.945 1.122 1.344 1.474 1.622 1.82 2.41 3.43 4.41 1.484 1.644 1.914 2.04 2.18 2.78 3.77 5.20 6.71 2.38 2.98 3.53 3.95 4.44 5.13 6.98 10.18 13.08 3.49 3.96 4.64 5.02 5.47 6.99 9.76 13.58 17.73 2.68 3.28 3.96 4.43 5.00 5.99 8.56 12.35 16-35 3.74 4.28 4.99 5.46 6.02 7.76 11.09 15.60 18.76 3.66 4.48 5.41 6.07 6.81 7.84 10.55 15.41 19.67 5.33 6.04 7.07 7.72 8.52 10.64 14.74 20.41 26.65 4.77 5.83 7.03 7.87 8.82 10.08 13.44 19.58 24.87 6.95 7.89 9.24 10.07 10.97 13.75 18.97 26.26 34.11 * Including trees at teooaipanirisg boltad to tbe fitting. Industrial Insulation 471 Fig. 2 .... Heat Loss through In. Thick Pipe Insolation (Use with Tobin 0 for Various Anataboos) These values are substituted in Equation 2 and a trial calcula tion made. The actual thir-knega of diatomaceous earth covering is 3.095 in. and that of the 85 percent magnesia is 2.125 in. For a nominal 6-in. steel pipe: -- 3512, r* = 6.407, and r -- 8532. Then, fig. 3 .... Heat Loss through 2 In. Thick Pipe Insulation (Use with Table 6 for Various laudations) The mean temperatures of the two insulations corresponding to the new asumptions are (1200 + 545) -* 2 -- 8725, and (545 + 129) 2 ~ 337, and the interpolated conductivities correspond ing to the new mean temperatures are 0675 and 0.461 for the diatomaceous earth and 85 percent magnesia, respectively. By substituting in Equation 2 1200 - 129 1071 9* 5.63 2.44 " 854 + 5.30 785 Btu. 0.675 + 0.461 Again referring to Fig. 5, it is seen that the temperature drop from the outer surface of the insulation to the surrounding air 6.407 8532 853 + 554 The temperature drop from the outer surface of the insulation to tbe surrounding air tor a heat loss of 785 Btu is found from Fig. 5 to be 495 deg for a 17-in. OD cylindrical surface, or 495 + 80 F room temperature -- 1295 F surface temperature. Since a surface temperature of 135 F was assumed, it is evident that a temperature closer to 1295 F, or, for instance, 129 F should be used for recalculation: 1200 - 129 9. 853 + 554 785 Btu. Since the temperature drop through each material is equal to the heat Sow times the actual resistance of each material, the temperature drop through the diatomaceous earth is 785 X 853 = 657 F, or the temperature between the two insulating materials is (1200 -- 657) = 543 F. Since a temperature of 570 F between the two materials was asumed, it is obvious that a temperature closer to 543, or for instance 545 F may be selected. fig. 4 .... Heat Loss through Insulation on Hat Vertical Surface (Os* wrfh Table 6 for Various laudation^