Document YjOgRK8L08bgpGwOzB1g3ayo8

128 Am. Soc. of Heat.-Vent. Engineers Guide, 1922 The late John R. Allen, while Director of the Society's Research Laboratory, submitted a paper as a report (see A. S. H. V. E. Journal, January, 1920), which in addition to the treatise on the heat emitted by various types of radiation, from which the above tables were calculated gives other data from which the following is taken. EFFECT OF HUMIDITY Figure No. S shows the effect of increasing the humidity upon the heat transmission. It will be rioted that with extreme change of humidity there is a slight change in the heat transmission, the heat transmission reducing slightly as the humidity increases. Humidity can have very little, if any effect upon radiation, and the effect of humidity must there fore change the convected heat lost by the radiator. This change of convected heat js probably due to the change in the density of the air passing over the radiator. FIG. 5- EFFECT OF HUMIDITY ON HEAT TRANSMISSION EFFECT OF AIR CIRCULATION . The amount of heat given off by a radiator may also be increased by increasing .the velocity of the air over the surface of the radiator. This, increase in velocity will increase the amount of heat carriedoff by con vection. No exact data are available on the effects that may be introduced by increasing these velocities over radiator surfaces, but in rooms with moving. machinery the heat transmission is increased approximately 10 per cent. EFFECT OF PAINTING The effect of painting was originally determined by experiments made with a cast iron rectangle, and in applying these to radiators of standard type, corrections must be made to allow for the difference between the area' of the radiating and convecting surfaces. The effect of painting Am. Soc. of Heat.-Vent. Engineers Guide. 1922 129. is to change the radiation constant of the radiating surface and has practi cally no effect upon the heat lost by convection. It is, therefore, a surface effect and it makes no difference what paints, are placed on the radiator as a priming coat, the results are always dependent upon the last coat of paint put upon the radiator. In radiators having a large proportion of radiating surface such as pipe coils or wall coils, the effect of painting will be more marked than in four-column radiators having a comparatively small radiating surface in proportion to convecting surface. All finely, ground materials have about the same radiation constant. Therefore all paints having finely ground pigments will give about the same effect. Metals have a poor radiating, effect so that any paint involving flake' metal, such as the bronze, will have a low radiating constant. The fol lowing Table shows the heat loss from a two-column 38 in. radiator, 10 sections long, when painted with different kinds of paints: Effect of Painting on Two-Column 38 in. Radiator, Steam Temferature 215 Dre. Room Temperature 70 Deg. Fahr. Condition of Surface Per Cent. Cast iron bare......................... .......................... 240 Painted with aluminum bronze....,___ 200 " " gold bronze............. ............... 205 " `` white enamel......... ................. 242 " " maroon japan..................... ;.. 240 " " white zinc paint........................... 242 " " no-lustre green enaniel............. 230 WARMING THE RADIATOR It is often very important to know the maximum condensation that occurs in a radiator when steam is turned on. Fig. 6 shows the condensa tion rate in pounds per hour for the time elapsing after steam is turned, into the radiator. It will be noticed that the maximum condensation, occurs 10 min. after steam is turned on, and in that case it amounts tqabout 3)4 times normal condensation. After the end of 25 min. the radiator had reached a normal rate of condensation. This curve was made from observations at intervals of 10 min. so that the intermediate points between the 10 min. points are not known, and the form of the curve is not exact. It shows, however, that in starting a plant, the demand made upon the boiler may be very much higher than the normal demand. Time elapsing after Steam is turned into Radiator (n Minutes) Fig. 6