GB1254931A - Treating materials with microwave energy - Google Patents

Abstract

1,254,931. Drying apparatus. N. H. WILLIAMS, and H. W. SCHUETTE. 30 Jan., 1969 [30 Jan., 1968], No. 5267/69. Heading F4G. [Also in Division H5] Material to be dried is subjected to microwave energy at spaced points, a high velocity gas flow impinges on the material at locations at least between some of the points and the gas is removed from the vicinity of the material at said locations. A microwave source 54 delivers 10 kW of power at 915 Mc to a serpentine rectangular waveguide 41, the dominant mode being TE, such that the electric field extends between the walls 45, 50. The parallel straight sections 42 of the waveguide 41 have slots (46, 47) through which the material to be dried e.g. wooden boards are transported by rollers 32 driven by sprockets and link chains from motor 34. On passing through the slotted waveguide the moisture in the material is driven to the surface. A centrifugal pump (71) delivers air at a high pressure to the jets 62 located between the parallel section of waveguide above the material by means of ducts 73 communicating with supply chamber 72, and to jets (67) below the material by means of a further duct 74. There are jets below the material only at those locations where there is no roller 32. The jets 62, 67 are disposed such that the spaces between the jets at one location are aligned along the path of the material with the jets at the preceding and succeeding locations. A high velocity gas flow (8000<SP>1</SP> feet/min.) of heated air (100-250‹ F.) having a relative humidity of less than 90% issues from the jets and impinges normally on to the material removing the moisture and is exhausted through openings at the opposite side to the supply chamber 72, into an exhaust chamber 103 which is maintained at a negative pressure by means of a centrifugal pump (104), The entrance and exit slots for the material are closed by walls 99, 102 to the supply and exhaust ducts. For drying material which cannot stand high stresses, e.g. lighter wood, paper and textile materials, the forces on each side of the material are equalized by providing jets 62 above and nozzles 67 below at each moisture removing location. In this case the rollers 32 would be replaced by jets (67) and the material transported by a take-up roller mounted at the end of the drier.