INFRARED ENERGY-TRANSFER MECHANISM IN CONSTANT AND FALLING RATE PERIODS OF PAPER DRYING AND ITS CORRELATION TO DRYING EFFICIENCY

A medium intensity, medium frequency infrared system has been develope d by converting the heat of combustion of natural gas to infrared flux using a series of ceramic emitters. A region of operation has been fo und where this system produces a surprising improvement in drying effi ciency of newsprint grade paper on the paper machine brought about by prolongation of the constant drying rate period to a relatively low mo isture content. The fact that the drying rate remains relatively const ant even in a partially dry porous paper surface leads to analysis of diffusion processes near a solid surface. A modification of a previous ly proposed model includes the experimental observation that a partial ly wetted paper can yield practically the same drying rate as that of the completely wetted paper under certain conditions encountered in dr ying. The validation of the model considers the infrared spectrum divi ded into small intervals. The IR energy flux generated by natural-gas combustion was calculated and its efficiency was determined separately for IR internal absorption, IR energy generation, and total heat of c ombustion using a numerical illustration.