Steam boiler engineering; a treatise on steam boilers and the design and operation of boiler plants

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ... material plus one surface resistance is not double that of the 1 in. of material plus one surface resistance, and heat transmission is inversely proportional to total resistance. Thickness, Inches Fig. 181. Effect on Heat Transmission from a Pipe Surface of Various Thicknesses of Insulating Material. Fig. 181 shows the effect of the thickness on heat transmission for pipe surfaces. The loss through material 2-in. thick is even more above one-half of that through the 1-in. thickness, than it was for the flat surfaces. In addition to the surface resistance effect, the second inch of insulation is applied over a larger area than the first inch, so that it does not offer as much resistance to heat flow. Pipe Size and Heat Transmission. Fig. 182 shows how the rate of heat transmission through a given thickness of insulation varies with pipe size. By comparing this chart with Fig. 180, the losses through different thicknesses on pipes are found to be greater than through the same thickness of the same insulation on flat surfaces; also, as shown in Fig. 183, the losses are greater on small than on large pipes, other factors being the same. Nominal Diameter of Pipe.lnches Fig. 182. Comparison of Heat Loss from Various Sizes of Pipe. In flat surface insulation all the heat flows straight through in parallel lines, but in pipe insulation the heat has a continually widening path into which to spread as it flows outward. Consequently more heat will flow from a given area of pipe surface than from the same area of flat surface. The smaller the pipe the more rapidly the path for heat flow spreads out; therefore the greater is the rate of heat loss for a given pipe area and thickness of insulation. Air Currents and Surface Finish. Air currents greatly decrease the surfac...