Document ExYnBOxw030LN0o7YN591Yb64

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 The radiation under black-body conditions, or for an emissivity of 1.0, is given in Table 1 for cold surfaces as low as -- 39 F to warmer surfaces as high as 139 F. The emissivities of a number of surfaces ordinarily encountered in engineering practice are shown in Table 21. For horizontal cylinders, the value of C = 1.016 has been well estab lished by various investigations. For vertical plates, the value of C = Table 1. Heat Transmission by Radiation for Black-Body Conditions* Expressed in Btu per square foot per hour Temp. Deg F -30 -20 -10 0 0 59.3 65.2 71.4 78.0 -1 58.7 64.7 70.8 77.4 -2 58.2 64.1 70.1 76.7 -3 57.7 63.5 69.5 76.0 -4 57.2 62.9 68.9 75.4 -5 56.7 62.3 68.3 74.7 -6 56.2 61.7 67.7 74.0 -7 55.7 61.1 67.1 73.4 -8 55.2 60.5 66.4 72.7 -9 54.7 59.9 65.8 72.1 0 + 1 +2 +3 +4 +5 +6 +7 +8 +9 0 78.0 78.7 79.4 80.1 10 85.0 85.7 86.5 97.2 20 92.4 93.3 94.0 94.8 30 100 101 102 103 40 109 110 111 112 50 118 119 120 121 60 127 128 129 130 70 137 138 139 140 80 148 149 150 151 90 159 160 161 162 100 170 171 173 174 110 183 184 185 187 120 196 197 199 200 130 211 212 214 215 80.8 88.0 95.6 104 112 122 131 142 152 163 175 188 201 217 81.5 88.7 96.4 105 113 123 132 143 153 164 176 189 203 218 82.2 89.4 97.2 105 114 123 133 144 154 166 178 191 204 220 82.9 90.2 98.0 106 115 124 134 145 155 167 179 192 206 221 83.6 90.9 98.8 107 116 125 135 146 156 168 180 193 207 222 84.3 91.7 99.6 108 117 126 136 147 157 169 182 195 209 224 n *Example: Radiation from walls of room at 32 F to surface at -- 25 F for effective emissivity of 0.95 = (102 -- 62.3) 0.95 = 37.7 Btu per square foot per hour. Table 2. Emissivity Values for Various Surfaces Surface 100 0.14 0.53 0.07 0.43 0.06 0.28 0.79 0.90 0.87 0.76 0.88 0.88 Temperature, Dbg F 200 0.15 0.53 0.07 0.44 0.06 0.28 0.79 0.90 0.89 0.76 0.89 0.88 300 0.16 0.53 0.07 0.46 0.07 0.28 0.79 - 400 0.17 0.53 0.11 0.48 0.79 0.90 0.90 0.89 *Heat Insulation in Air Conditioning, by R. H. Heilman (Industrial and Engineering Chemistry, Vo\. 28, July 1936, p. 782). 728 CHAPTER 42. PIPE AND DUCT INSULATION 1.394 has been fairly well established. A value of C = 1.79 for horizontal plates warmer than the surrounding air facing upward and 0.89 for horizontal plates warmer than air facing downward is indicated by recent investigations2. The heat transmission by free convection from vertical walls 24 in. or more in height is given in Table 3 as calculated from Equation 2 for ambient air temperature of 80 F. The values in Table 3 will not be changed appreciably by a considerable change in air temperature for a given temperature excess. For instance, a change in air temperature from 80 to 40 F will increase the heat transmission given in Table 3 by only 1.3 per cent. Table 3. Heat Transmission by Free Convection for Large Vertical Surfaces Expressed in Btu per square foot per hour Dec F Temperature Difference between Body and Surrounding Still Air at 80 F 0 10 20 30 40 50 60 70 80 90 100 110 120 130 0 0 4.4 10.4 17.4 25.0 33.2 41.8 50.6 59.9 69.4 79.4 89.2 99.4 109.8 1 0.3 4.9 11.1 18.1 25.8 34.1 42.6 51.5 60.8 70.3 80.4 90.2 100.4 110.9 2 0.6 5.5 11.8 18.9 26.7 34.9 43.5 52.4 61.8 71.3 81.4 91.2 101.5 112.0 3 1.0 6.0 12.5 19.7 27.5 35.7 44.3 53.4 62.7 72.3 82.4 92.2 102.6 113.0 4 1.4 6.6 13.2 20.5 28.3 36.6 45.2 54.3 63.7 73.3 83.3 93.3 103.6 114.1 5 1.8 7.3 13.9 21.2 29.2 37.4 46.1 55.2 64.6 74.3 84.2 94.3 104.7 115.2 6 2.3 7.9 14.6 22.0 30.0 38.3 47.0 56.1 65.6 75.3 85.2 95.3 105.7 116.3 7 2.8 8.5 15.3 22.7 30.8 39.1 47.8 57.1 66.5 76.3 86.2 96.3 106.7 117.3 8 3.3 9.1 16.0 23.5 31.6 40.0 48.7 58.0 67.5 77.4 87.2 97.4 107.8 118.4 9 3.8 9.7 16.7 24.3 32.4 40.9 49.7 59.0 68.4 78.4 88.2 98.4 108.8 119.5 Table 4. Free Convection Factors for Various Shapes Shapes Horizontal cylinders 24 in. in diam. or over IaOng vertical cylinders 24 in. in diam. or over Vertical plates 24 in. in height or over..... Horizontal plates warmer than air facing upward Horizontal plates warmer than air facing downward Horizontal plates cooler than air facing upward Horizontal plates cooler than air facing downward Factor 0.73 0.88 1.00 1.28 0 64 064 1.28 Table 5. Free Convection Factors for Various Diameter Pipes or Various Height Plates Actual o. d., or height, in........ i 2 3 4 5 6 7 - 8 Factor....................................... 1.88 1.64 1.52 1.43 1.37 1.32 1.28 1.25 Actual o. d. or height, in.. 9 10 12 14 16 18 20 22- Factor 1.22 1.19 1.15 1.11 1.09 1.06 1.04 1.02 *The Transmission of Heat by-Radiation and Convection, by Griffith and Davis {Special Report No. 9. 1922, Department of Scientific and Industrial Research, His Majesty's Stationery Office. London, England)! 729 1