THE ARTIFICIAL SEASONING OF TIMBER 



395 



In America, thermal circulation has received most favour, and apart 

 from the progressive kilns of the American Blower Company, numerous 

 companies are selling compartment kilns all working on the thermal 

 principle, and differing only in small details and accessories. The 

 general basis of all these is a bank of steam pipe radiators under the floor 

 of each compartment. The air is renewed by chimney draught, some- 

 times assisted by steam pipes or steam jets, and steam vapour is 

 admitted under the timber to provide the humidity required when starting 

 a charge, and generally to restrain the action of the heat. 



Apart from the two leading types of dryers, progressive and compart- 

 ment, the only variant is the condensing kiln, which can be applied to 

 either type. This was first fitted to fan-operated dryers, secondly to 

 thermal kilns, and finally to kilns where thermal ventilation is assisted 

 by the cooling and ejector action of water sprayers. The fan-operated 

 condensing kiln (known as the Common-sense Dryer) could be either 



COMDENSER HEATER FAN 



of the progressive or compartment variety. This had a closed circuit, 

 and constantly re-circulated the same air. The wet air from the kiln 

 passed over cold-water pipe coils which condensed the excess moisture. 

 The air then passed to the heater, and thence back to the dryer. From 

 a salesman's point of view this could be made very attractive, as it was 

 possible to show a dryer at work with wet timber going in, dry timber 

 coming out, and the extracted water trickling away from the condenser. 

 However, as this system had no real advantage, after a brief period of 

 popularity it ceased to be used. 



The thermal circulation condensing kiln was devised by the Andrews 

 Company. In this the hot-water pipes are, as in most cases, under the 

 floor, the cold pipes of the condenser being in a side chamber. The 

 direction of the circulation is upwards through the timber, and down- 

 wards in the side flue. Excess moisture is condensed from the wet air, 

 which then passes to the radiator pipes and re-circulates. 



The third variety of condensing kiln is that invented by Mr. H. D. 

 Tieman, M.E., M.F., of the U.S.A. Forest Service. This is a development 

 of the Andrews kiln, but instead of cold-water coils in the side flue. 



