Document jmy2Km93y8BbgqnRm580npwmk

B.t.u.prSq.Ft. p ir Hr. ptr Dg.Fntir.Tempwotur.Diffirtnc* ,, ^ . , p ,, ,.F.p, r H , ^ ^ . F k,Tmptrot1I, 0,i American Society of Heating and Ventilating Engineers Guide, 1930 '* ^ Heat Loss through 1 in. thick. Covering *fenpTofuTt Oifftrtnt^Deg. Fahr., Pipe fe Room Fig. 4. Heat Loss through 1J4 in. thick. Covering 410 Chapter 24--Insulation for Pipes and Surfaces practically the same as for canvas surfaces so that the curves given may be followed with no alteration on account of the surfaces commonly,used. (See discussion of surface transfer of heat in Chapter 2, page 18). To determine the thickness of insulation necessary to prevent sweating for coverings having conductivity values differing from the value of 0.3 used in computing the curves, increase or decrease the values taken from Table 4. Values of k Corresponding to Commonly Used Coverings k Per Cent Variation from k = 0.3 0.246 0.27 0.36 0.27 0.30 0.35 -18% -10% +20% -10% 0% +17% Table 5. Pipe-Covering Factors Ttps or Covering TncFZ&ATirB* Djttebencb, Pipe to Air, Deg. Fahr. 100 200 300 400 500 600 700 85% Magnesia.......................................... Laminated Asbestos Type. Approx. 20 laminations per inch-----------------Laminated Asbestos Type. Approx. 30 to 40 laminations per inch___ :..... High Temperature................................... Felted Brown Asbestos Fibre.-'............ Rock Wool...... ................. :....................... Corrugated Asbestos, 8 plies per inch Corrugated Asbestos, 4 plies per inch 1.234 1.515 1.022 1.438 1.665 1.058 1.349 1.520 1.184 1.474 1.019 1.358 1.577 1.045 1.340 1.550 1.148 1.441 1.016 1.292 1.505 1.035 1.333 1.580 l.in 1.409 1.013 1.233 1.436 1.022 1.323 1.605 1.082 1.383 1.010 1.190 1.387 1.020 1.051 1.360 1.007 1.147 1.340 1.014 1.025 1.345 1.005 1.109 1.300 1_.0_1_0 -- Table 6. Thicknesses of Insulation Ordinarily Used Steam Pressures (Lb. Gacb) Steam Temperatures (Dkg. Fahr.) Thickness op Insulation Pipe larger Pipes Pipes than 4 in. 2 in. to 4 in. Hin to lHin. 0 to 25 25 to 100 100 to 200 Higher Pressure or Superheat Higher Pressure or Superheat 212 to 267 267 to 338 338 to 388 388 to 500 500 to 600 1 ' in. 1H in. 2 in. 2M in. 3 in. 1 in. 1 in. 1J^ in. 2 in. 2}4 in. 1 in. 1 in. 1 in. in. 2 in. Example:' Determine the heat flow in B.t.u. per hour per square foot of pipe-surface through a magnesia covering 1 in. thick on a 4 in. pipe. Solution: The temperature of the pipe is 270 deg. fahr. and the room temperature, 70 deg. fahr. The loss through a covering 1 in. thick-on a 4 in. pipe at 200 deg. tem perature difference from Fig. 5 = 0.395; the factor for magnesia at 200 deg. temperature difference from Tabie"5 = 1.184; then the heat loss through the magnesia covering = 0.395 X 1.184 X 200 = 93.5 B.t.u. per square toot of pipe surface per hour. 411