Abstract:
The invention relates to a method for cleaning a heat exchanger. The heat exchanger comprises a plurality of tubes extending between a first header and a second header, and further comprises an insertion unit for introducing a plurality of projectiles thereinto. A first step of the method comprises pumping a fluid into the first header. A second step comprises inserting the plurality of projectiles into the fluid, such that the plurality of projectiles are distributed within the fluid. A third step comprises flowing the fluid and the projectiles through the tubes, such that the projectiles abrades at least one tube. A fourth step comprises discharging the fluid and the projectiles out of the second header. Among the plurality of projectiles, at least one projectile has a different specific gravity, relative to the fluid, from at least one of the remaining projectiles.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for cleaning a heat exchanger. 
       BACKGROUND OF THE INVENTION 
       [0002]    Heat exchange systems are used in various industries for a myriad of applications. Common applications of the heat exchange systems include heating ventilation and air-conditioning (HVAC) installations. In such installations, fluid is circulated through the heat exchange system for heat exchange to occur at a bundle of tubes making up a portion of the heat exchange system. Heat exchange efficiency at the bundle of tubes requires debris and fouling deposits accumulated therewithin to be substantially removed. Taking the heat exchange system off-line for physical flushing is not only ineffective but also disallow use of the heat exchange system for the duration it remains off-line. 
         [0003]    Current cleaning systems for use in conjunction with the heat exchange systems uses sponge balls transported by fluid to be fed and circulated in the heat exchange system. When the balls passage through the bundle of tubes during circulation in the heat exchange system, any debris or fouling deposits in the bundle of tubes are pushed out. 
         [0004]    It is known in the art that some of such cleaning systems utilize sponge balls that are larger than the internal diameter of the tubes of the heat exchanger. The sponge balls are highly compressible such that when the balls squeeze into the tubes, they tend to expand back to their initial uncompressed state, thereby generating a frictional force along the inner surface of the tube as the balls move through. The sponge balls can thus only be transported singularly through the tube. It is this frictional force along the internal surface of the tubes that scrubs deposits and dirt off the surface. However, if the sponge ball encounters a large deposit, the force of the fluid may not be sufficient to push the sponge ball through and the sponge ball becomes stuck within the tube. 
         [0005]    Sponge balls are designed to be used for heat exchanger tubes with smooth internal surfaces. For tubes with rifling grains, also known as enhanced tubes, the scrubbing action of the compressed sponge balls cannot reach the grooves of enhanced tubes; they can only clean the landings of the enhanced tubes. It is in these grooves where dirt accumulates and need cleaning most. 
         [0006]    In addition, in heat exchangers with multiple horizontal tubes arranged in stacks, the sponge balls cannot be efficiently distributed to all the tubes in the stacks. The sponge balls are all of the same weight and will generally float or sink to the same portion of the stack. This leaves the other tubes in the stack with little sponge balls to for proper cleaning thereof. 
         [0007]    Therefore, there is an apparent need for an improved method of cleaning a heat exchanger in order to address the foregoing problems. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a method for cleaning a heat exchanger. The heat exchanger comprises a plurality of tubes extending between a first header and a second header of the heat exchanger. The heat exchanger further comprises an insertion unit for introducing a plurality of projectiles into the heat exchanger. A first step of the method comprises pumping a fluid into the first header. A second step comprises inserting the plurality of projectiles into the fluid, such that the plurality of projectiles are distributed within the fluid. A third step comprises flowing the fluid and the plurality of projectiles through the plurality of tubes, such that the plurality of projectiles abrades at least one tube. A fourth step of the method comprises discharging the fluid and the plurality of projectiles out of the second header. In the method for cleaning the heat exchanger, among the plurality of projectiles, at least one projectile has a different specific gravity, relative to the fluid, from at least one of the remaining projectiles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  to  FIG. 9  shows multiple cross-sectional views of a heat exchanger with the plurality of tubes arranged in various configurations. 
           [0010]      FIG. 10  to  FIG. 12  shows different variations of the plurality of projectiles. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0011]    Reference will now be made in detail to an exemplary embodiment of the present invention. While the invention will be described in conjunction with the embodiment, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments of the present invention. 
         [0012]    For purposes of brevity and clarity, descriptions of an embodiment of the present invention are limited hereinafter to a method for cleaning a heat exchanger  10 , in accordance with the drawings in  FIG. 1  to  FIG. 9 . This however does not preclude embodiments of the invention where fundamental principles prevalent among the various embodiments of the invention such as operational, functional or performance characteristics are required. 
         [0013]    In an exemplary embodiment of the present invention, a method for cleaning a heat exchanger  10  or heat exchange system is described hereafter. The heat exchanger  10  comprises a plurality of tubes  12 . The plurality of tubes  12  is, for example, an evaporator or a condenser of heating, ventilation, and air-conditioning (HVAC) systems or the like heat-exchange systems. For such heat exchange systems, heat transfer occurs at one or more segments containing the plurality of tubes  12 . The plurality of tubes  12  are typically clustered as a module with an intake at a first header of the heat exchanger  10 , wherethrough a fluid is introduced, and an exhaust at a second header of the heat exchanger  10 , wherefrom the fluid passaging through the plurality of tubes  12  is subsequently discharged. 
         [0014]    There is a displacement pump for circulating the fluid, which may be in a liquid or gaseous state, or a combination thereof, through the heat exchange system, specifically through the plurality of tubes  12 . The displacement pump is used to pump the fluid into the intake at the first header for passaging through the plurality of tubes  12 . The method of cleaning the heat exchanger  10  may be used in conjunction with the operation of the heat exchanger  10 , i.e. when the displacement pump is circulating the fluid through the plurality of tubes  12 . 
         [0015]    The heat exchange system comprises an insertion unit, having a plurality of projectiles  20  stored therein. The insertion unit functions to introduce or insert the plurality of projectiles  20  into the heat exchanger  10 . In conjunction with the operation of the heat exchanger  10 , the plurality of projectiles  20  is inserted into the fluid, such that the projectiles are distributed within the fluid. When the fluid is passaging through the plurality of tubes  12 , the projectiles  20  flow together with the fluid through the tubes  12 . As the flow progresses, the plurality of projectiles  20  abrade the inner surface of at least one tube  12 , thereby encountering and removing particles along the inner surfaces of the tubes  12 . The fluid, together with the plurality of projectiles  20 , is discharged out the exhaust at the second header. Among the plurality of projectiles  20 , at least one projectile  20  has a different specific gravity, relative to the fluid, from at least one of the remaining projectiles  20 . 
         [0016]    The specific gravity relative to the fluid is defined as the ratio of the density of the projectile  20  to the density of the fluid. For example, a projectile  20  with a higher density than that of the fluid will have a ratio of more than one; and a projectile  20  with a lower density than that of the fluid will have a ratio of less than one. In this embodiment, the plurality of tubes  12  are arranged horizontally such that the plurality of tubes  12  may be separated into three distinct portions top  12 , middle  14 , and bottom  16 . As the fluid containing the projectiles  20  is pumped into the plurality, of tubes  12  via the intake at the first header, the projectiles  20  will distribute themselves among the top  14 , middle  16 , and bottom  18  portions of the plurality of tubes  12 , depending on the specific gravity of each projectile  20 . Projectiles  20  with a specific gravity equal to unity will stay buoyant within the fluid, such that the projectiles  20  suspend in the fluid around a middle portion  16  of the plurality of tubes  12 . Projectiles  20  with a specific gravity of less than unity will float in the fluid around a top portion  14  of the plurality of tubes  12 . Projectiles  20  with a specific gravity of more than unity will sink in the fluid around a bottom portion  18  of the plurality of tubes  12 . 
         [0017]    The advantage of having projectiles  20  with different specific gravities is that with such control of the specific gravities, the user is able to determine what portion of the projectiles  20  goes to which portion of the plurality of tubes  12 . For example, in some heat exchangers  10 , the plurality of tubes  12  may not be evenly distributed in the top  14 , middle  16 , and bottom  18  portions. Some heat exchangers may have more tubes  12  in the top portion  14  and lesser tubes  12  in the bottom portion  18 . Some examples of such arrangements and configurations can be seen in  FIG. 1  to  FIG. 9 . Hence, by way of example and not limitation, by having more projectiles  20  with lower specific gravities and lesser projectiles  20  with higher specific gravities, there will be more projectiles  20  going to the top portion  14  of the plurality of tubes  12  and lesser projectiles  20  going to the bottom portion  18  of the plurality of tubes  12 . This leads to a more even distribution of the plurality of projectiles  20  within the plurality of tubes  12 . The user thus has the advantage of controlling the portion of projectiles  20  going to whichever portion of the plurality of tubes  12 . In contrast, if projectiles  20  of the same specific gravity are used, the projectiles  20  will float or sink to the portion of the plurality of tubes  12  where their buoyancy allows them to be. In some cases, some of the tubes  12  will not receive any projectiles  20 , because their buoyancy does not allow them to reach those tubes  12 , and those tubes  12  will not be cleaned as there will not be any projectiles  20  passaging therethrough. 
         [0018]    The projectiles  20  may also be known as cleaning balls or elastomeric balls. The projectiles  20  may also be made of other types of resilient materials. Unlike large sponge balls used in prior art systems, the elastomeric projectiles are highly resilient and not as compressible as the sponge balls. The elastomeric projectiles are not designed for compression while they squeeze through the tubes. Instead, the elastomeric projectiles are designed to be smaller than the internal diameter of the tubes for bouncing inside the tubes. The resilient material of the elastomeric projectiles allows them to sustain continued wear and tear as they bounce and move through the tubes for cleaning thereof 
         [0019]    As the plurality of projectiles  20  are introduced into the first header, the projectiles  20  travel through the plurality of tubes  12  for cleaning thereof. The projectiles  20  are thus dimensioned to be smaller than the internal diameter of the plurality of tubes  12 , i.e. the largest width of each projectile  20  is smaller than the largest internal diameter of each tube  12 . For example, each projectile  20  may have a largest width of 11 to 12 millimeters, while the largest internal diameter of each tube  12  is 15 to 16 millimeters. Preferably, the ratio between the largest width of the projectile  20  and the largest internal diameter of the tube  12  is between 0.75 and 0.85. The tolerance of 3 to 5 millimeters between the projectiles  20  and the inner surface of the tube  12  allows the projectiles  20  to have some degree of freedom of movement within the tube  12 . Thus, the projectiles  20  can bounce or ricochet off the inner surface of the plurality of tubes  12  while passaging therethrough for dislodging of debris and deposit therefrom and cleaning thereof. In addition, by having the projectiles  20  smaller than the internal diameter of the tube  12 , the projectiles  20  will not be trapped while being carried therethrough, as in the case of a prior art system in which the projectile  20  is larger than the internal diameter of the tube  12  and is being forced through the tube  12  to scrape deposits off the inner surface thereof. 
         [0020]    Subsequent to the passaging of the plurality of projectiles  20  through the plurality of tubes  12  and the cleaning thereof, the projectiles  20  have to be retrieved for storage and/or future usage. Preferably, the heat exchanger  10  comprises a configuration means, as commonly known in the art, which selectively impedes the passage of the projectiles  20  through the tubes  12 . By way of example and not limitation, the heat exchanger  10  may comprise a flow diverting system coupled to the exhaust and a trap disposed proximal thereto. The flow diverting system and the trap is configurable for collecting the projectiles  20  that are discharged out of the tubes  12 , thus preventing further transport of the projectiles  20  through the rest of the heat exchange system  10 . Alternatively, the flow diverting system and trap may be configured such that the projectiles  20  are not collected thereby, but instead are transported through the rest of the heat exchanger  10  and back to the intake for another cycle of cleaning of the tubes  12 . Other configuration means known to the person having ordinary skill in the art may also be implemented in the heat exchanger  10 . 
         [0021]    With reference to  FIG. 10  to  FIG. 12 , each of the projectiles  20  has a centre of mass that may be at any location or point within the body  22  of the projectile  20 . Using an example of a single, uniform, spherical projectile  20 , its centre of mass is positioned at its geometric centre. The position of the centre of mass in the projectile  20 , i.e. the offset of the centre of mass away from the geometric centre, affects the lateral bouncing of the projectile  20  when passaging through a tube  12 . The greater the offset is towards the surface  24  of the projectile  20 , the greater will be the lateral bouncing of the projectile  20 . This leads to increased randomness of the bouncing of the projectiles  20  when passaging through the tubes  12 . 
         [0022]    The offset and the specific gravity of each projectile  20  may be varied through different means. The following describes some non-limiting examples of such means. 
         [0023]    Each projectile  20  has a geometric centre within its body  22  and an outer surface  24 , and the centre of mass may be positioned anywhere within the body  22 , between the geometric centre and the outer surface  24 , inclusive. A projectile  20  with a uniform material composition will have the centre of mass at the geometric centre, while a projectile  20  with non-uniform material composition, such as through a combination of two structural portions  26  and  28  with different material compositions, will have the centre of mass positioned away from the geometric centre. 
         [0024]    The projectile  20  may include a hollow portion  30  within the projectile  20 , thereby shifting the centre of mass away from the hollow portion  30 . Alternatively or additionally, a ball bearing made of metal and/or other material, may be placed in the hollow portion  30 . A recess  32  may also be created on the surface  24  of the projectile  20 . The recess  32  may be shallow through a small portion under the surface  24 , or the recess  32  may be deep through till near or through the opposite side of the surface  24 . The recess  32  may be a straight or tapered bore to provide greater variation to the location of the centre of mass. The projectile  20  may also comprise of multiple structural portions, for example  26  and  28 , combined together. 
         [0025]    Each portion may have a material that is different from the other portions. The non-uniformity of the material composite of the projectile  20  provides varying degrees of the offset of the centre of mass from the geometric centre. Other methods of varying the position of the centre of mass, known to the skilled person, are also possible. 
         [0026]    Preferably, at least one projectile  20  comprises bristles  34  extending outwards from the surface  24  of the projectile  20 . The bristles  34  may be disposed all around the surface  24  of the projectile  20 , or only on a portion of the surface  24 . The bristles  34  advantageously assist in the abrading and scraping of deposits from the inner surface of the plurality of tubes  12  when the projectiles  20  are passaging therethrough. Moreover, the inner surface of the tubes  12  may not be entirely smooth and may comprise a rifling grain, such as enhanced tubes. The bristles  34  thus assist in removing deposits from the grooves of the inner surface of the tubes  12 . Alternatively or additionally, where the projectile has its surface partially covered with the bristles, the bristled portion will scrub against the grooves of the enhanced tubes, while the non-bristled portion will scrub against the landings of the enhanced tubes, thereby providing a more uniform scrubbing action against the insides of the enhanced tubes. 
         [0027]    In cleaning the heat exchanger  10 , the fluid is pumped through the plurality of tubes  12 , with the plurality of projectiles  20  transported within the fluid. Preferably, the rate of flow of the fluid through the tubes  12  is controllable by a system and/or device implemented in the heat exchange system. By controlling the rate of flow of the fluid through the tubes  12 , the speed of the projectiles  20  through the tubes  12  can thus be controlled. For example, a projectile  20  travelling at a higher speed will be subjected to greater bounce and higher frictional forces. Therefore, the projectile  20  will bounce more within the internals of the tube  12 , and every contact with the inner surface of the tube  12  has a higher frictional force thereon. The higher frictional force improves the abrading of the inner surface of the tube  12  and thus provides for more efficient cleaning of the tube  12 . 
         [0028]    In a foregoing manner, a method of cleaning a heat exchanger  10  is described according to an exemplary embodiment of the invention. Although only one embodiment of the invention is disclosed in this document, it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modifications can be made to the disclosed embodiment without departing from the scope and spirit of the invention.