Document KRJLaZEDRqqNkNeJyqgxwyjGX

\r American Society of Heating and Ventilating Engineers Guide Table 3. Areas of Flanged Fittings, Square Feet ji I93t| tions are the average values from a number of tests on each type of] material, also that all variables due to differences in thickness, differentj pipe sizes, and different air conditions are eliminated. * The heat losses through any of the insulations shown in Fig, 4 for<i various thicknesses of covering and for any temperatures generally used in engineering practice can be obtained from Table 7 and Figs. 5,6 and 7. In these curves the unit loss through 1, 1J4 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. Table 7 gives the factor by which the loss from the curves shown in Figs. 5 to 7 must be multiplied to give the loss through any of the cover ings whose conductivity values are given in Fig. 4. Table 4. Emissivity Values (e) for Various Surfaces ------------- .--------------- ------ j------------- >-------------------------- Subacb TmmuTrao, DEGREES FiBMsaitT Polished silver--............ Lampblack..................... Asbestos paper.............. Rough steel plate....... ....... . Aluminum-surfaced roofing Polished brass................ ' Flat black lacquer-------Black lacquer............ -.... White lacquer................. 0.0221 0.945 0.930 0.945 0.216. 0.096 0.96 0.80 0.80 00 700 0.945 0.929 0.969 0.0308 0.0312 0.945 0.945 0.938 0.943 0.975 \ 0.975 0.096 334 Chafter 22--Coverings for Pipes and Hot Surfaces insulation for cold surfaces maintained at a low temperature should be insulated so as *wLthe flow of heat from the outside into the low temperature area nt the formation of condensation and of frost if the tempera[few enough, as well as to prevent corrosion, induced by the gg^of condensed moisture on metal surfaces. . are available commercially to meet varying temperature Kiir^ts' For example: The thickness of insulation for ice water is ^'^eD'mately VA m- t^ie temperature in the line is not lower than aporoxi r thickness of insulation for brine is approximately 2J/ in., 1---- - A l/1O^ Fjrj>j> fxeAl (9/h "c /I 8 >PA Tt j*! il-p*L Jmasspit IM/NATcD ASBESTOS TYPE 1 'JO fa 4-0Lam/ncr+ionsperIn ch 'Rock Wool LJ-- 200 300 400 500 600 Mean Temperature, Deg. Fahr. between Inner'and Outer Surfaces [R. H. Heilman, hitch. Eng.. Vol. 46 (1924). p. 693) Fig. 4. Thermal Conductivity 100 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. Fig. 8 may be used for the determination of thick ness of any material of known conductivity which should be used to prevent sweating on pipes and flat metallic surfaces. The curves in Jpg. 8 have been calculated on the basis of using an insulating material which has a thermal conductivity of 0.3 B.t.u. per hour per. square foot pgr degree fahrenheit per inch of thickness. The surface resistance used 335