Document kOJY9zEMvOEGzKG0GNXL8jm0

American Society of Heating and Ventilating Engineers Guide, 1930 material, also that all variables due to differences in thickness, different pipe sizes, and different air conditions are eliminated. The heat losses through any of the insulations shown in Fig. 2 for various thicknesses of covering and for any temperatures generally used in engineering practice can be obtained from Table 5 and Figs. 3, 4 and 5. In these curves the unit loss through 1, \x/i and 2 in. thick covering is given for temperature differences up to 700 deg. fahr. The loss through other thicknesses of covering can be obtained from the curves by inter polation. MeanTemperature,Deg.Fahr. between Inner'and Outer Surfaces (R. H. Heilman. Mcch. Eng.. Vol. 46 [1924J. p. 593) Fig. 2. Thermal Conductivity Table 5 gives the factor by which the loss from the curves shown in Figs. 3 to 5 must be multiplied to give the loss through any of the cover ings whose conductivity values are given in Fig. 2. INSULATION FOR COLD SURFACES Surfaces maintained at a low temperature should be insulated so as to retard the flow of heat from the outside into the low temperature area and to prevent the formation of condensation and of frost if the tempera tures are low enough, as well as to prevent corrosion, induced by the presence of condensed moisture on metal surfaces. Coverings are available commercially to meet varying temperature gradients. For example: The thickness of insulation for ice water is approximately in. if the temperature in the line is not lower than 408 1 Chapter 24--Insulation for Pipes and Surfaces Table 2. Radiating Surface per Linear Foot of Pipe Pips Size In. V % i m m Surface Sq. Ft. 0.22 0.275 0.344 0.435 0.498 Pipe Size In. 2 2H 3 3V 4 Surface Sq. Ft. 0.622 0.753 0.917 1.047 1.178 Pipe Size In. 5 6 8 10 12 Surface Sq. Ft. 1.456 1.734 2.257 2.817 3.338 25 deg. fahr.; the thickness of insulation for brine is approximately 234 in., where the temperature ranges from 0 deg. to 25 deg. fahr.; and the thick ness of insulation where the brine temperature ranges from --30 to 0 deg. fahr. is approximately 4 in. The thermal conductivities of the materials commonly used for low temperature insulation for pipes and surfaces are given in Table 4. In some cases, the prevention of condensation rather than the con servation of heat is the governing factor in determining the thickness of insulation required. Figs. 6 and 7 may be used for the determination of thickness of any material of known conductivity which should be used to prevent sweating on pipes and flat metallic surfaces. The curves in Fig. 7 have been calculated bn the basis of using an insulating material which has a thermal conductivity of 0.3 B.t.u. per hour per square foot per degree fahrenheit per inch of thickness. The surface resistance used is based on results obtained on canvas covered surfaces. However, it - c-- --mA refiner surfaces is Table 3. Areas of Flanged Fittings, Square Feet _----------- Nominal Pifb Size I.D. r w l V" 2" IV" 3" 3V" 4" 4V" 5" 6" 7" 8' 9" 10' 12' 14' 0. D. 15' O. D. 16' 0. D. Flanged Coupling 90 Dbg. Ell Long Radius Ell Teb Cb08S Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy Standard Extea Heavy 0.320 0.383 0.477 0.672 0.841 0.945 1.122 1.344 1.474 1.622 1.82 2.17 2.41 3.00 3.43 4.41 5.39 6.18 6.69 0.438 0.510 0.727 0.848 1.107 1.484 1.644 1.914 2.04 2.18 2.78 3.46 3.77 4.44 5.20 6.71 8.30 9.52 10.05 0.795 0.957 1.174 1.65 2.09 2.38 2.98 3.53 3.95 4.44 5.13 6.17 6.98 8.71 10.18 13.08 16.38 18.50 20.17 1.015 1.098 I.332 2.01 2.57 3.49 3.96 4.64 5.02 5.47 6.99 8.62 9.76 II.44 13.58 17.73 22131 25.28 27.18 0.892 1.084 1.337 1.84 2.32 2.68 3.28 3.96 4.43 5.00 5.99 7.38 8.56 10.57 12.35 16.35 20.17 22.92 25.41 1.083 1.340 I.874 2.16 2.76 3.74 4.28 4.99 5.46 6.02 7.76 9.73 II.09 13.17 15.60 18.76 25:70 29.34 31.73 1.235 1.481 1.815 2.54 3.21 3.66 4.48 5.41 6.07 6.81 7.84 9.37 10.55 13.18 15.41 19.67 24.81 27.91 30.32 1.575 1.925 2.68 3.09 4.05 5.33 6.04 7.07 7.72 8.52 10.64 12.33 14.74 17.23 20.41 26.65 33.63 38.04 40.94 1.622 2.07 1.943 2.53 2.38 3.54 3.32 4.06 4.19 5.17 4.77 6.95 5.83 7.89 7.03 9.24 7.87 10.07 8.82 10.97 10.08 13.75 12.00 16.83 13.44 18.97 16.78 '22.10 19.58 26.26 24.87 34.11 31.48 43.15 35.48 48.79 38.34 52.35 409