1914] on Surface Combustion 49 



supply of gaseous mixture is controlled by one lever which operates 

 in a single movement the gas and air cocks. The ignition is effected 

 automatically by means of a small pilot light. Each boiler does 

 10 to 12 heats per diem, each lasting twenty minutes, and some of the 

 diaphragms have been in continuous daily use for about a year. I 

 saw in the factory a battery of thirteen such boiling pans, all in 

 •constant use, and was informed that the gas consumption was not 

 more than half what it formerly used to be when the pans were 

 heated over ordinary atmospheric flame burners. The secret of this 

 higher efficiency lies in the fact that gas flames are a very unsatisfac- 

 tory means for boiling liquids in metallic vessels, owing to the non- 

 conducting layer of relatively cool gas which forms between the flame 

 and the undersurface of the pan ; but with a diaphragm the large 

 percentage of radiant heat is quickly absorbed by the vessel and 

 transferred to the liquid with high efficiency. 



Moreover, in evaporating liquids it is possible to use an overhead 

 diaphragm, directing the radiation downward on to the surface of the 

 liquid, thus eliminating altogether the influence of the containing 

 vessel. In this way only the upper layers of the liquid are actually 

 heated up to the working temperature, whilst the evaporation is 

 extraordinarily rapid and efficient. Given a sufficiently cheap high- 

 grade gas there would appear to be endless possibilities for diaphragm 

 heating in the industrial field. 



Incandescent Surface Combustion in a Bed of Refractory 

 Granular Material. 



The second process is applicable to all kinds of gaseous or vapor- 

 ized fuels ; it consists essentially in injecting, through a suitable 

 orifice at a speed greater than the velocity of back-firing, an explosive 

 mixture of gas (or vapour) and air in their combining proportions 

 into a bed of incandescent granular refi'actory material which is 

 disposed around or in proximity to the body to be heated. 



I can perhaps best describe the process by the aid of two diagrams 

 showing its applications to the heating of crucible and muffie furnaces. 

 Fig. 5 shows the process as applied to a crucible furnace. The crucible 

 is surrounded by a bed of refractory incandescent granular material. 

 The mixture of gas and air is injected at a high velocity through a 

 narrow orifice in the base of the furnace, and as it im23inges upon the 

 incandescent bed, combustion is instantaneously completed without 

 flame. 



The seat of this active surface combustion is in the lowest part of 

 the bed ; the burnt gases, rising through the upper layers, rapidly 

 impart their heat to the bed, maintaining it in a high degree of in- 

 candescence. Fig. 6 shows a similar arrangement for the heating of 

 a muffle furnace which needs no further explanation. 



Vol. XXL (No. 108) e 



