Patent Publication Number: US-6210268-B1

Title: Air mixer for static mixing of two air streams

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an air mixer, located in the flow direction of a heated air stream for example in a flow channel upstream of a heat treatment chamber, for example for drying textile goods or tissue webs, and provided for the static mixing of two air streams of different temperature or quality flowing into one another, for which purpose the air mixer is provided with air mixing parts. Such previously known mixing parts are generally only deflectors that deflect the second air stream. 
     A dynamic air mixer is know for example from U.S. Pat. No. 4,495,858. In that patent, a fan is provided in a tube that is open to the exterior or to which in any case air is supplied from outside, by which fan a second air stream accelerated by the fan is introduced into the first air stream. The housing of the fan in the flow channel of the first air stream and also the mounts of the fan impede the flow of the first air stream and a low-loss mixing of the two air streams is not possible. For this reason, an additional fan is provided as well. 
     SUMMARY OF THE INVENTION 
     The goal of the invention is to permit two airflows to be fed into one another without additional expenditure of energy in such fashion that they automatically mix uniformly on contact. 
     Taking its departure from the device of the species recited at the outset, to achieve this stated goal, the invention provides that a hollow body is provided in the flow cross section of the first air stream to receive and guide the second air flow. A plurality of hollow bodies is distributed uniformly over the cross section of the flow channel of the first air stream so that simply because of this fact alone a distributed air supply of the second air stream into the cross section of the first air stream takes place. If, in another embodiment of the air mixer, the hollow body narrows toward its outlet end internally and possibly also externally to form a nozzle-shaped air outlet area, the second air stream flows into the first air stream at a higher speed because of this narrowing of the cross section alone, producing vortices that result in the desired mixing. 
     One special advantage of the device according to the invention is the extremely short mixing paths that result in only a small pressure loss. As a result of the radiating effect of the nozzle at the outlet from the hollow body, the pressure of the gas flowing through is even partially recovered. Advantageously, therefore, the air streams to be mixed have different pressure drops. This is the case for example in the mixing of a gas subject to a vacuum, for example after the air has been drawn out of a screen drum dryer and an added hot gas from another energy source, whose flow has a higher density, higher temperature, and possibly also a higher pressure. 
     Advantageously, therefore, flowrate differences between the two air streams are advantageous. These air streams can be further influenced without supplying energy, with the second air stream flowing at a higher pressure into the hollow bodies. This can easily be accomplished or intensified by including a diffuser, directly in front of the hollow body for example. As a result, the flowrate of the second air stream is reduced upstream from the hollow body but the hydraulic pressure is increased, so that when the air flows out of the nozzle the desired higher air flow is obtained. This can even be so high that the fan located downstream is driven. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several advanced details are also provided on the air mixer. A device of the type according to the invention is shown as an example in the drawing. 
     FIG. 1 shows a screen drum dryer in cross section in a schematic representation and on a reduced scale, whose drum interior is subjected to a vacuum with a piping system for renewed acceleration and heating of the circulated air; 
     FIG. 2 shows a section perpendicular to the one in FIG. 4 with one of the hollow bodies in an end view; 
     FIG. 3 is a section through the tube of the second air stream in the vicinity of the air mixer with the nozzles as seen from below, and 
     FIG. 4 is a section through the tube of the first air stream in the vicinity of the static air mixer along line IV—IV according to FIG. 3 with the supply nozzles of the second air stream, likewise in cross section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A screen drum dryer consists of the rotatably mounted screen drum  1 , which has the web of goods to be dried wrapped around its exterior. In the area that is not covered by the goods, the screen drum is covered on the inside by an interior covering  3  against air leakage. On the outside, screen drum  1  is surrounded by the air supply housing  4  in the drying area, to which housing the heated drying air  5  is supplied through a pipe  6 . The air enriched with moisture from goods  2  is drawn by fan  8  out of the interior of screen drum  1  and recycled to air supply housing  4  heated in a circuit. Previously, a portion  9  of the moist drying air is drawn off through a channel and this part is returned along with dry ambient air from tube  10  to the first air stream  11 . Regulation is accomplished by exhaust air flaps, not shown. 
     The cooled and dry first air stream is heated again in the flow path upstream of fan  8 . For this purpose, in the embodiment a hot second air stream  12  is used that possible flows as exhaust air from another energy assembly, not shown, with increased pressure and speed to a mixer  13 . The two air streams therefore encounter one another at right angles but this can also take place at any desired angle. 
     Air mixer  13  is shown in FIGS. 2-4 in individual cross sections. This is a static air mixer, in other words an air mixer in which the mixing of the two air streams is intended to take place as completely as possible due to its intrinsic flow energy. For this purpose, the first flow channel  14  is provided through which the first air stream  11  flows. This air stream is subject to a vacuum because it is drawn in by fan  8 . The second hot air stream  12  is drawn in at higher speed through flow channel  15  and strikes the first air stream  11  in the air mixer  13 . 
     For deliberate mixing of the two air streams, hollow bodies  16  open endwise according to FIGS. 3 and 4 with a space between them are located in the air mixer in the direction of the incoming second air stream  12  so that the first air stream  11  can flow between hollow bodies  16 . Hollow bodies  16  are made round facing the flow direction of the first air stream  11  so that the air can flow without losses around hollow bodies  16 . At the opposite end, the elongate hollow bodies  16  have air outlet nozzles. These air outlet nozzles consist of a main nozzle  17  located centrally in each case, said nozzle being made slit-shaped at the end of the hollow body  16  that narrows to form a nozzle. Two side nozzles  18  are provided on each hollow body  16 , said side nozzles being formed where the conical narrowing of nozzle  17  begins and are open at that point. 
     As stated above, hollow bodies  16  are made open endwise in the direction of the incoming second air stream  12 . The remaining area of channel  15  is closed over its cross section by walls  21  so that the hot air can flow in only in the direction of arrows  19  into the vicinity of air mixer  13 . The escape of the hot air is permitted only through nozzle openings  17  and  18 . Because of this fact, intensive mixing of the two air streams is ensured without additional dynamic vorticization assembly. 
     An increase in this effect is produced by the diffuser  20  as well which is provided immediately upstream from air mixer  13  in flow channel  15  of second air stream  12 . The higher speed of the second air stream is converted by this diffuser into a higher pressure, so that the hot air emerges at even higher speed from the nozzles into the first air stream  11  that is flowing with a vacuum. The resultant vortices produce intensive mixing of the streams.