162 



THE INDIA RUBBER WORLD 



December 1, 1920 



Fluid Heat Transmission 



Bv Alexander B. McKechnie* 



THE ADVANTAGES of transmitting heat liy means (if a high 

 boiling point fluid have been known lor many years and 

 several independent systems have been built and operated 

 with more or less success. These systems consisted merely of 

 a pipe coil or similar heater, a pump and some kind of a iiuid. 

 High flash point oil being easily obtainable was naturally the 

 fluid chosen. These early systems operated for a short time, but 

 soon commenced to give trouble and those that were used for 

 the high temperature field were particularly short-lived, due 

 principally to the carbonization of the circulating oil. 



Heat transmission by hot oil embodies the desirable features 

 and elimmates the objections of other methods for obtaining 

 high temperatures. The quantity of heat delivered is under con- 

 trol at all times, and temperatures up to 550 degrees F. are 

 reached without difficulty. 



The pressure on the entire system is practically negligible, thus 

 making it particularly adaptable to vessels with cast integral 

 jackets usually built to withstand pressures of about 100 pounds 

 and to the jackets of glass enamelled steel tanks designed only 

 for pressures up to 75 pounds. This point is readily appreciated 

 when we consider that the temperature of 100 pounds of steam 

 represents only 338 degrees F. The distribution of heat is uni- 

 form over the entire surface of the vessel and its contents are 

 treated instantly and uniformly without damaging the product. 



The temperature can be controlled within close limits, either 

 manually or by thermostatic devices. This is of vilal importance 



mcnt, and should condit;on.s make it nece-sary the entire heating 

 plant can be installed in a separate building. 

 DESIGN OF SYSTEM 



There arc five main factors in a system of this kind. They are 

 as follows: Design of heater or absorber; type of circulating 

 pump ; type of system ; quality of circulating oil ; construction of 

 pipe lines. 



HEATER OR ABSORBER 



The absorber, like any other heat cxclianger, must be designed 

 lor maximum efliciency, con.'iistent with long life and freedom 

 from trouble. It must be readily accessible for inspection or 

 repair. The furnace must be built to withstand the high tem- 

 peratures met in work of this kind and be thoroughly insulated 

 to prevent undue radiation losses. Such points as the length and 

 size of tubes, the velocity of the circulating oil and pro.ximity of 

 the fire to the tubes, all require careful study. 

 CIRCULATING PUMP 



The circulating pump should be of the positive displacement 

 rotary type to insure known and non-pulsating flow. The necessity 

 for these features is apparent, because the temperature drop in 

 the circulating oil is inversely proportional to the flow and a 

 varying discharge pressure, particularly when starting a cold 

 system, would produce excessive vibration. 

 TYPE OF SYSTEM 



Experience has taught the superiority of the closed system 

 shown in the illustration. By a closed system is meant one in 



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I'arf-st. 



in reactions where temperature variations in the heating medium 

 are not permissible. Charts from recording thermometers sliow 

 a temperature difference of from about 3 degrees F. to 7 degrees 

 F. in the circulating oil when it is thermostatically controlled. 

 The fire hazard is entirely removed, as there is no flame in 

 contact with the vessels. The absorber furnace, the only place 

 where flame exists, is isolated from the manufacturing equip- 



"Engineer. Parks-Cramer Co., Ronton, Massachusetts, 



Typical Merrill Process System 



Shown Connected 'Q a Large Jacketed Kettle, Absorber, and Furnace in Cko's Section 



which the hot oil does not come in contact with the atmosphere. 

 This point is vital, as the oil would rapidly oxidize and soon be- 

 come too viscous to pump freely, resulting in a decreased flow 

 and the absorber tubes burning out, due to carbon deposit. Pro- 

 vision must be made, however, for expansion of the oil. The 

 circulating oils generally used have a coefficient of expansion of 

 about .000486, which means approximately a 25 per cent volumet- 

 ric increase in 500 degrees F. rise. .\n expansion tank is placed 



