Abstract:
A heat exchanger employs a variable number of repositionable baffles in its headers to permit changing the number of passes made by the fluid processed therein.

Description:
BACKGROUND OF THE INVENTION 
     Sometimes the optimum flow conditions for a fluid passing through a heat exchanger can not be determined until after the heat exchanger is put into operation. For example, when concentrating radioactive waste liquors which have a predominant scaling tendency, it is advantageous to heat such liquors at as high a velocity as is practical. But the optimum velocity for minimum power consumption consistent with maintaining scale-free operation is often unknown. In addition, future operations may include crystallization of salts from the concentrated liquors, and it may be impossible to predetermine the optimum velocity for minimizing erosion and extending tube life when operating as a crystallizer. Thus it is desirable to be able to change the velocity of the fluid flowing through the heat exchanger after the exchanger has been installed and operated. This can most easily be accomplished by changing the number of passes the fluid being heated makes through the tubes of the exchanger. Such flexibility was not easily attained with prior art apparatus in that extensive and costly modification of the equipment or excessive down time was required. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is an object of this invention to provide an improved heat exchanger. 
     Another object is to provide a heat exchanger in which the velocity of the fluid being heated can be readily varied 
     Another object is to provide a variable pass heat exchanger in which the number of passes made by the fluid being heated can be changed without requiring basic structural modification of the exchanger. 
     Another object is to provide a heat exchanger in which the number of passes can be doubled or halved. 
     Another object is to provide a heat exchanger for processing radioactive waste in which the time needed to change flow characteristics is minimized thereby reducing exposure of personnel to radioactivity. 
     Another object is to provide a variable pass heat exchanger that is relatively efficient, durable, simple to adjust and maintain, and which does not possess defects found in similar prior art apparatus. 
     Other objects and advantages of the invention will be revealed in the specification and claims, and the scope of the invention will be set forth in the claims. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is a partially broken-away, cross sectional, side view of a heat exchanger in accord with this invention. 
     FIG. 2 is a cross sectional view taken along the line 2--2 of FIG. 1. 
     FIG. 3 is a cross sectional view taken along the line 3--3 in FIG. 1. 
     FIG. 4 is a cross sectional view corresponding to FIG. 2, but showing a different number of baffles. 
     FIG. 5 is a cross sectional view corresponding to FIG. 3, but showing a different number of baffles. 
     FIG. 6 is a cross sectional view corresponding to FIGS. 2 and 4, but showing a different number of baffles. 
    
    
     DESCRIPTION OF THE INVENTION 
     The drawing shows a heat exchanger 10 in which the number of times the fluid being heated passes therethrough can be quickly and easily varied. A heat exchange fluid, such as steam, enters cylindrical container 11 through an inlet 12 and exits through an outlet 13. A plurality of longitudinally extending hollow heat exchange tubes 14 are divided into groups and essentially evenly spaced throughout container 11. The upper end 16 of each tube is anchored in a first tube sheet 17, and the lower end 18 of each tube is anchored in a second tube sheet 19. A cylindrical header 21 at the top of container 11 is defined in part by tube sheet 17, and a cylindrical header 22 at the bottom of container 11 is defined in part by tube sheet 19. Header 21 has an inlet 23 and an outlet 24 for the fluid being treated (e.g., radioactive waste liquid). A removable head 26 is affixed to flange 27 of container 11 by suitable means such as nuts and bolts (not shown) so as to seal against conventional gasket means 28, and in an identical way, gasket means 29 is sealed between a removable head 30 and flange 31. 
     Tubes 14 are arranged in a predetermined number of separated groups (e.g., eight as shown in the drawing) which establishes the maximum number of times the fluid being heated can be made to pass through container 11. The number of passes made by such fluid can be varied by changing the number and/or positions of removable flat baffle plates 35 in headers 21 and 22. Baffle plates 35 are identical in size and shape and are slidably received in channels 36, each of which is defined by a pair of longitudinally extending support bars 37 attached to the inside of a header. Plates 35 are also slidably received in slots 38 running the length of a pair of longitudinally extending cylindrical posts 39 and 40. One end 41 of post 39 is anchored to the center of tube sheet 17, and one end 42 of post 40 is anchored to the center of tube sheet 19. The other ends 44 and 45 of posts 39 and 40 are received in circular recesses 47 and 48 in the center of heads 26 and 30. One end of each plate 35 seats in a radially extending groove 49 in one of the tube sheets, and the other end of each plate 35 is held in a corresponding aligned groove 50 in the mating head. The grooves 50 in head 26 are at mirror image positions to grooves 49 in tube sheet 17, and the same is true of grooves 50 and 49 in head 30 and tube sheet 19. Each set of aligned grooves 49 and 50 and the associated channel 36 and aligned slot 38 capable of receiving the same plate 35 are in the same longitudinal plane. Such planes must be unobstructed by any tubes 14, and such planes should be spaced at equal radial cross sectional intervals (e.g., 45° ). 
     FIGS. 2 - 6 show how the number of passes the liquid makes through exchanger 10 can be quickly and easily doubled or halved. The plane including the slot 49 in the nine o&#39;clock radial position will be designated 0°, the plane in the twelve o&#39;clock radial position will be designated 90°, and so on proceeding clockwise around the cross section of headers 21 and 22. With baffle plates 35 occupying the 45°, 135° and 315° positions, shown in FIG. 2 and the 45° and 225° positions shown in FIG. 3, the liquid would make four passes through exchanger 10. Inlet 23 would be between the plates 35 in the 45° and 315° positions, and outlet 24 would be between the plates 35 in the 45° and 135° positions. The liquid wound enter header 21 through inlet 23 and then flow downwardly into header 22 through the tubes 14 occupying the quadrant between 315° and 45°; the liquid would then flow upwardly into header 21 through the tubes 14 occupying the quadrant between 315° and 225°. The liquid would then flow downwardly into header 22 through the tubes 14 occupying the quadrant between 225° and 135°, and finally the liquid would flow upwardly into header 21 through the tubes 14 occupying the quadrant between 135° and 45°, and then would exit through outlet 24. 
     To double the number of passes the liquid would make through exchanger 10 to eight, heads 26 and 30 should be removed and plates 35 should be added and repositioned in the locations shown in FIGS. 4 and 5. In header 21, plates 35 would occupy the 0°, 45°, 90°, 180° and 270° positions shown in FIG. 4, and in header 22 plates 35 would occupy the 45°, 135°, 225° and 315° positions shown in FIG. 5. Inlet 23 would be between the plates 35 occupying the 0° and 45° positions, and outlet 24 would be between the plates 35 occupying the 45° and 90° positions. The liquid would enter header 21 through inlet 23 and flow downwardly into header 22 through the pipes 14 in the sector between 0° and 45°, and then would flow upwardly into header 21 through the pipes 14 in the sector between 0° and 315°. The liquid would then flow downwardly into header 22 through the pipes 14 in the sector between 315° and 270°, and then upwardly into header 21 through the pipes 14 in the sector between 270° and 225°. The liquid would then flow downwardly through the pipes 14 in the sector between 225° and 180°, then upwardly through those in the sector between 180° and 135°, then downwardly between those in the sector between 135° and 90°, and finally, upwardly into header 21 through those in the sector between 90° and 45°, and then exit through outlet 24. 
     To reduce the number of passes the liquid would make through exchanger 10 to two, heads 26 and 30 should be removed and all plates 35 should be taken out of header 22, and plates 35 should be placed in only the 45° and 225° positions shown in FIG. 6. The liquid would enter header 21 through inlet 23 and flow downwardly into header 22 through the pipes 14 in the semi-circle between 45° and 225°, and then upwardly into header 21 through the pipes 14 in the remaining semi-circle, and then exit through outlet 24. 
     It has thus been shown that by the practice of this invention the number of times a fluid passes through the tubes of a heat exchanger can be easily changed without requiring structural modification of the exchanger. Such changes can be accomplished quickly in the field after the exchanger has been placed into operation. These advantages result from the simple way in which longitudinally slidable identical baffle plates 35 are held in place in sets of aligned grooves 49 and 50, channels 36 and slots 38. 
     While the present invention has been described with references to a particular embodiment, it is not intended to illustrate or describe herein all of the equivalent forms or ramifications thereof. Also, the words used are words of description rather than limitation, and various changes may be made without departing from the spirit or scope of the invention disclosed herein. It is intended that the appended claims cover all such changes as fall within the true spirit and scope of the invention.