THERMAL INSULATION'
G
REAT progress has been made during
- the past 50 years in the development of
heat-insulating materials and of scientific information pertaining to the rate of heat transfer from bare and insulated surfaces. Tests conducted by Charles Emery in 1881 and reported before the American Society of Mechanical Engineers show that many crude admixtures were in use a t that time. One very popular covering consisted of 4 parts of coal ashes, 1 part of plaster of Paris, 1 part of sour flour, and a small portion of hair to act as a binder. The covering or cement was compounded by wetting the ashes with water, putting in the hair, and mixing to a mortar; the plaster and flour were then mixed together. This mixture was worked into the hair and ashes and the resulting composition was applied to the pipes with a trowel. The sour flour in its fermentation generated considerable gas, which caused the covering to become very porous. Because many of the coverings used consisted mainly of organic materials, a great many disastrous fires resulted. In fact, the situation became so alarming that the Boston Manufacturers' Mutual Fire Insurance Company requested John M. Ordway to conduct a series of tests to determine the danger of combustion as well as to measure the economic efficiency of the coverings. The results of about 200 tests on a great variety of combinations from dead air spaces to coal ashes were reported by Professor Ordway in 1883 and 1884. Since that time there has been a steady development in the art, and probably there is more research and development work in progress in this field today than a t any time during the past. The continuous development of heated equipment of all kinds necessitates this. While heat insulation was used principally on steam pipes in Professor Ordway's time, today it is used on practically every known type of heated and cooled equipment where the escape of heat is to be prevented.
Courtesy, P h i l i p Carey Cornpanu
INSULATED TOWER OF HANCOCK OIL Co., LONGBEACH,CALIF.
I T h e group of papers on pages 821 to 838 was presented before the Division of Industiial and Engineering Chemistry at the 97th Meeting of the American Chemical Society, Baltimore, hld.
820
INDUSTRIAL AND ENGINEERING CHEMISTRY
It would be impossible to evaluate the savings to industry through the use of modern heat insulation or to describe the vast array of equipment in which heat insulation is a contributing factor to efficient operation. Such industries as chemical, steel, oil, ceramic, glass, cement, etc., require various types of heat insulation. I n many plants the operating temperatures range from subzero up to 2500" to 3000" F.; obviously, this vast range in temperature requires the use of different types of insulation. There are many instances where the use of the correct type and thickness of insulation has resulted in a saving which has repaid the original cost in a period of less than one month. Besides the monetary saving, insulation is often required in order to operate a process, for fire protection, to protect operators from burns, etc. In industrial furnaces and many processes the use of insulation results in more uniform products. In the modern residence, heat insulation helps to stabilize inside temperatures, thus increasing the comfort and improving the health of the occupants, and insulation makes possible the use of the increasingly popular air-conditioning systems. Owing to the continuous development of new insulating materials and the improvement of the older types, it is necessary to check and recheck the thermal conductivity of many insulating materials. It is also necessary to test several samples of a given material in order to obtain its average conductivity. Although there is practically no information available on the conductivity of insulation a t subzero temperatures, it is
VOL. 31, NO. 7
possible to obtain fairly accurate conductivities under operating conditions by the surface loss method. When this method is used, it is imperative to keep the surface of the insulation above the dew point temperature or correct for the greater rate of heat transmission to the surface. The effect of moisture on the thermal conductivity of lowtemperature insulating materials has been studied by several investigators. Owing to the extreme difficulty encountered in these determinations, further information on this item is very desirable. The high-temperature field also presents serious obstacles in the determination of thermal conductivity. During the past few years investigators have directed a concerted effort to devise means whereby these obstacles may be overcome. Considerable progress has been made, but the problem is still a long way from being solved. There is also need for additional data on the rate of heat transfer by free and forced convection from large flat plates, especially by free convection from plates in various positions and of various characteristic dimensions. Additional data are desirable on the rate of heat transfer by free convection across air spaces of various thicknesses, for different values of breadth and height, and in various positions. It is believed that the papers which follow will add materially to our ever-increasing fund of knowledge on heatinsulating materials and on heat transfer in general.
R. H. HEILMAN
Courtesy, P h i l i p C a r e y C o m p a n y
INSELATION OF SPRINGFIELD STATEHOSPITAL, SYKEBVILLE, MD.
