Patent Publication Number: US-2009236088-A1

Title: Heat Exchanger with Multiple Internal Diverters

Description:
TECHNICAL FIELD 
     The present application relates to heat exchangers and more particularly relates to heat exchangers with multiple internal diverters for controlling flow rates of the cooling medium through the heat exchanger. 
     BACKGROUND OF THE INVENTION 
     Generally described, the rate of flow of the cooling medium through a heat exchanger has both a minimum level and a maximum level. The minimum level is determined by the amount of flow required to perform the heat exchanging function of the heat exchanger, and the maximum level is determined by the fluid velocity limits of the heat exchanger. In practice, the amount of fluid that is actually delivered to a heat exchanger may be greater than the minimum amount of fluid that is required to run the exchanger. 
     A variety of methods currently exist for controlling the rate of flow through heat exchangers. One method involves installing bypass piping outside of the heat exchanger between the fluid inlet piping and the fluid outlet piping. Unfortunately, this fixed design is only effective over a limited range of flow rates, and increases the weight and footprint of the heat exchanger unit. Another method involves installing an external control valve on the fluid piping and using digital controllers to adjust continuously the valve so as to control the flow rate. Although this method may be able to control the rate of flow, the control valves, controllers, and pressure sensors may be prohibitively expensive. 
     What is desired, therefore, is a heat exchanger that can provide a more consistent rate of flow through the heat exchanger over a wide variety of total fluid flow rates. The heat exchanger may be relatively inexpensive, and may allow for a relatively small heat exchanger footprint. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present application thus provides a heat exchanger that controls the rate of flow through the heat exchanger and a method for exchanging heat. The heat exchanger may include an inlet coolant box, and an outlet coolant box, wherein the inlet coolant box and the outlet coolant box are separated by a partition, wherein the partition comprises a first diverting device and a second diverting device, and wherein the range of flow rates over which the first diverting device diverts fluid is different then the range of flow rates over which the second diverting device diverts fluid. The method may include providing a heat exchanger comprising an inlet coolant box and an outlet coolant box, wherein the inlet coolant box and the outlet coolant box are separated by a partition; feeding a fluid into the inlet coolant box at a total rate of flow, wherein the total rate of flow varies over time between a minimum and a maximum; diverting a first portion of the fluid across the partition and into the outlet coolant box during periods of time when the total rate of flow is above a first rate of flow between the minimum and the maximum; and diverting a second portion of the fluid across the partition and into the outlet coolant box during periods of time when the total rate of flow is above a second rate of flow between the minimum and the maximum. 
     These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional side view of a prior art steam condenser heat exchanger. 
         FIG. 2  is a cross sectional side view of one embodiment of a heat exchanger coolant box. 
         FIG. 3  is a partial cross sectional side view of the heat exchanger coolant box of  FIG. 2 . 
         FIG. 4  is a raised perspective view of the heat exchanger coolant box of  FIG. 2  with the end cover removed. 
         FIG. 5  is a lowered perspective view of the heal exchanger coolant box of  FIG. 2  with the end cover removed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present application provides an improved heat exchanger and improved methods for exchanging heat. 
     I. General Heat Exchanger Structure 
     Referring now to the drawings,  FIG. 1  shows a cross sectional side view of a prior art steam condenser heat exchanger  100 . The heat exchanger  100  may be used to convert steam into condensate (water). 
     The heat exchanger  100  may include a tube side  102  and a shell side  104 . The tube side  102  may include an inlet coolant box  106 , an outlet coolant box  108 , and an intermediate coolant box  110 . The Inlet coolant box  106  and the outlet coolant box  108  may be separated by a partition  112 . The shell side  104  may include one or more baffles  114 . The baffles  114  may direct the flow of fluid through the shell side  104 . 
     A cooling fluid, typically water, may enter the inlet coolant box  106  through a cooling fluid inlet  116 . The cooling fluid may then flow from the inlet coolant box  106  into a first bundle of tubes  118 . After passing through the first bundle of tubes  118 , the cooling fluid may enter the intermediate coolant box  110 , pass through a second bundle of tubes  120 , and enter the outlet coolant box  108 . The cooling fluid may then exit the heat exchanger  100  through a cooling fluid outlet  122 , 
     A hot fluid, typically steam, may enter the shell side  104  through a hot fluid inlet  124 . The hot fluid may then pass around the baffles  114  and over the tubes  118  and  120  so as to exchange heat with the cooling fluid and condense. The condensed steam (water) may exit the heat exchanger  100  through a condensate outlet  126 , and air and any remaining steam and may exit the heat exchanger  100  through a vapor outlet  128 . Similar designs are known. 
     II. Heat Exchanger With Multiple Internal Diverters 
     Referring again to the drawings,  FIG. 2  shows a partial cross-sectional side-view of one embodiment of a heat exchanger with multiple internal diverters  200  as described herein. 
     The heat exchanger  200  may include an inlet coolant box  202  and an outlet coolant box  204 . The inlet coolant box  202  and the outlet coolant box  204  may be separated by a partition  206 . The heat exchanger  200  also may have an end cover  208  for allowing access into the heat exchanger  200 . 
     A cooling fluid, typically water, may enter the inlet coolant box  202  through a cooling fluid inlet  210 . The cooling fluid may then flow from the inlet coolant box  202  through one or more bundles of tubes (not shown). After passing through the tubes, the cooling fluid may enter the outlet coolant box  204 . The cooling fluid may then exit the heat exchanger  200  through a cooling fluid outlet  212 . 
     The partition  206  may contain multiple internal diverting devices that divert flow within the heat exchanger. The diverting devices may comprise essentially any type of diverting device known in the art. Importantly, the range of flow rates over which each of the diverting devices operates is different then the range of flow rates over which the other diverting devices operate. Non-limiting examples of suitable diverting devices include flow control orifices, lift valves, and “flapper” style valves, in one embodiment, the diverting devices comprise “flapper” style valves that utilize a spring. The spring may counteract the pressure of the cooling fluid at low flow rates so as to keep the flapper closed, and my allow the flapper to open at high at high flow rates. 
     In a particular embodiment, the diverting devices may comprise a first lift valve  302  and a second lift valve  304 . Details of the first lift valve  302  and the second lift valve  304  are illustrated in  FIG. 3 , which shows a partial cross sectional side view of the heat exchanger coolant box of  FIG. 2 . The first lift valve  302  may include a first lift disk  306 , and the second lift valve  304  may include a second lift disk  308 . The lift disks  306  and  308  may be positioned respectively over a first opening  310  and a second opening  312  in the partition  206 . 
     Over a first lower range of flow rates, the first lift disk  306  may cover the first opening  310  so as to block the flow of fluid through the partition  206 . Over a first high range of flow rates, the first lift disk  306  may move up a first guide rod  314  so as to allow fluid through the first opening  310  in the partition  206 . Similarly, over a second lower range of flow rates, the second lift disk  308  may cover the second opening  312  so as to block the flow of fluid through the partition  206 . Over a second high range of flow rates, the second lift disk  308  may move up a second guide rod  316  so as to allow fluid through the second opening  312  in the partition  206 . 
     The range of flow rates over which the first lift valve  302  operates and the second lift valve  304  operates may differ due to the design of the lift valves. In a particular embodiment, the first lift disk  306  has a mass that is different than the mass of the second lift disk  308  so that the first lift disk  306  moves up the first guide rod  314  at ranges of flow that are different than the ranges of flow at which the second lift disk  308  moves up the second guide rod  316 . In another embodiment, the first opening  310  has an area that is different than the area of the second opening  312  so that the first lift disk  306  moves up the first guide rod  314  at ranges of flow that are different than the ranges of flow at which the second lift disk  308  moves up the second guide rod  316 . In yet another embodiment, the first lift disk  306  has a mass that is different than the mass of the second lift disk  308  and the first opening  310  has an area that is different than the area of the second opening  312  so that the first lift disk  306  moves up the first guide rod  314  at ranges of flow that are different than the ranges of flow at which the second lift disk  308  moves up the second guide rod  316 . 
     The use of diverting devices that operate over different ranges of flow rates can provide significant advantages as compared to the use of diverting devices that operate over the same range of flow rates. For example, diverting devices that operate around the low end of the total range of flow rates may be completely open around the high end of the total range, resulting in uncontrolled flow rates through the heat exchanger at high levels of total flow rates. Likewise, diverting devices that operate around the high end of the total range of flow rates may be completely closed around the low end of the total range, resulting in uncontrolled flow rates through the heat exchanger at low levels of total flow rates. By using diverting devices that operate over different ranges of total flow rates, the amount of flow through the heat exchanger may be effectively controlled at the lower end of the total range by one diverting device, and the amount of flow through the heat exchanger may be effectively controlled at the upper end of the total range by a second diverting device, so that the rate of flow through the heat exchanger may be effectively controlled over a broad range of total flow rates. 
     The heat exchanger  200  may he used to exchange heat between a cooling fluid, typically water, and a hot fluid, typically steam. The method of exchanging heat may include feeding a cooling fluid into the cooling fluid inlet  210  of the inlet coolant box  202  at a total rate of flow, wherein the total rate of flow varies over time between a minimum and a maximum; diverting a first portion of the fluid with the first diverting device across the partition  206  and into the outlet coolant box  204  during periods of time when the total rate of flow is above a first rate of flow between the minimum and the maximum; diverting a second portion of the fluid with the second diverting device across the partition  206  and into the outlet coolant box  204  during periods of time when the total rate of flow is above a second rate of flow between the minimum and the maximum; passing a third portion of the fluid through the tubes (not shown) of heat exchanger  200  and into the outlet coolant box  204 ; and feeding the first portion, the second portion, and the third portion of the fluid through the cooling fluid outlet  212  of the outlet coolant box  204 , wherein the first rate of flow is different than the second rate of flow. As a result, the first diverting device may divert fluid when the total rate of flow is above the first flow rate, the second diverting device may divert fluid when the total rate of flow is above the second flow rate, and both the first diverting device and the second diverting device may divert fluid when the total rate of flow is above the first flow rate and the second flow rate. 
     In those embodiments in which the first diverting device includes the first lift valve  302  and the second diverting device includes the second lift valve  304 , the step of diverting the first portion of the fluid may include opening the first lift valve  302 , and the step of diverting the second portion of the fluid may include opening the second lift valve  304 . Furthermore, in those embodiments in which the first lift valve  302  includes the first lift disk  306  positioned over the first opening  310  in the partition  206  and the second lift valve  304  includes the second lift disk  308  positioned over the second opening  312  in the partition  206 , the step of opening the first lift valve  302  may include lifting the first lift disk  306  off the first opening  310  in the partition  206 , and the step of opening the second lift valve  304  may include lifting the second lift disk  308  off the second opening  312  in the partition  206 . 
     It should be understood that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.