Abstract:
A heat exchanger has a body with an inside surface and an outside surface forming a hole along a predetermined length of the body, wherein the inside surface is of a predetermined size. Additionally, the heat exchanger has an inlet at one end of the predetermined length and an outlet at another end of the predetermined length. The inlet and outlet disposed on the body facilitate flow of material in and out of the body. In one embodiment, included in the body is a rod, having a number of grooves, being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide a long travel path of the material through the body. The predetermined length is of a length sufficiently long to cause the material to exit with a stable temperature that is insensitive to a small variant of the length.

Description:
RELATED APPLICATION  
       [0001]    This patent application claims benefit of priority to provisional patent application No. 60/339,765, titled “AN IMPROVED HEAT EXCHANGER TO FACILITATE ACCURATE TEMPERATURE CONTROL”, filed Nov. 1, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to the field of heat exchangers. More specifically, the invention relates to an improved convective heat exchanger that facilitates precise temperature control.  
         BACKGROUND OF THE INVENTION  
         [0003]    Recently, inspection methods involving thermal signatures of materials are being utilized, in particular, infrared (IR) detection imaging. A turbine component inspection method utilizing IR imaging involves applying a thermal differential to the component. An example of a turbine component may be a thin or flat object that may be referred to as vanes or blades utilized to cause fluid flow or direct fluid.  
           [0004]    For example, often times, applying a thermal differential involves delivering a thermal stimulus, such as a gas, at a high temperature thermal stimulus to the component, and then, immediately following the high temperature inspection medium, delivering another thermal stimulus, such as the gas, at a cold temperature (i.e., cold, relative to the high temperature thermal stimulus) to the component.  
           [0005]    Often times, in inspecting a turbine component, hot and cold gases are used as thermal stimuli. An example of an IR inspection apparatus may be found in copending U.S. patent application Ser. No. ______, titled “TURBINE COMPONENT INSPECTION SYSTEM”, contemporaneously filed, and having at least partial common inventorship with present application. Furthermore, in order to increase quality of results from such an inspection apparatus, inspection conditions such as, but not limited to, temperature, pressure, humidity, etc. may be required to be identical for various blade types.  
           [0006]    Often times, in order to heat the gas, heat exchangers may be utilized. Heat exchangers are designed to transfer heat between fluids at different temperatures. Examples of common heat exchangers may be a vessel in which hot and cold streams are mixed, two streams at different temperatures separated by a wall or tubes, where conductive heat transfer occurs, and so forth. Furthermore, control of the different temperature streams may increase the cost and difficulty associated with manufacturing these types of heat exchangers.  
           [0007]    Other types of heat exchangers may involve convective heat transfer, where a gas is allowed to flow through an area of high temperatures to heat the gas, such as a common hair dryer. In a common hairdryer, air at ambient temperature is forced through heating elements. As the air flows past the heating elements, the heating elements are hot enough to heat the air to very hot temperatures within a relatively short distance. However, the precise temperature at the outlet of the hairdryer is difficult to predict because typical prior art heat exchangers are designed to maximize the amount of hear transfer, i.e. minimizing the amount of time required to bring a fluid to a desired temperature. Thus, slight variations in length air travels past heating elements and temperature and humidity at an inlet of a heat exchanger having an intrinsic steep gradient of heat exchange, substantially affects the temperature at the outlet.  
           [0008]    Another type of heat exchanger that involves convective heat transfer may be where the gas is allowed to travel through a heated metal pipe. However, here again, for the same reasons discussed earlier, a small variation of the length of the heated metal pipe substantially affects the temperatures of the gas at the outlet of the pipe.  
           [0009]    [0009]FIG. 1 illustrates an exemplary graph of convective heat transfer to a gas as it flows through a heated metal pipe, where the metal pipe is heated over its entire length. Shown in FIG. 1 is a graph  100  having heat transfer coefficient as it vertical axis and length down the pipe as it horizontal axis. As illustrated by the graph  100 , as gas enters the heated metal pipe at an inlet, a value for local coefficient of heat transfer is infinity at the inlet  101  (i.e., heat transfer is highest at the inlet). In FIG. 1, as the gas continues to flow through the heated metal pipe, the local coefficient of heat transfer diminishes to an asymptotic value (i.e., minimal or no heat transfer is approached)  105 . Examples of the principles correlating to the graph of FIG. 1 may be found in Momentum, Heat, and Mass Transfer, by C. O. Bennett and J. E. Myers (3 rd  ed., 1982).  
           [0010]    Thus, an improved heat exchanger providing a more precise control over the temperature of an exiting fluid, while inexpensive and simple to manufacture, is desired.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like references indicate similar elements and in which:  
         [0012]    [0012]FIG. 1 illustrates an exemplary graph of convective heat transfer to a gas as it flows through a heated metal pipe, where the metal pipe is heated over its entire length;  
         [0013]    [0013]FIG. 2 illustrates a convective heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention;  
         [0014]    [0014]FIG. 3 illustrates a grooved rod to provide a long travel path for a gas within a relatively short linear distance, in accordance with one embodiment of the present invention;  
         [0015]    [0015]FIG. 4 illustrates the heat exchanger body with an internal feature to receive a grooved metal rod, in accordance present invention;  
         [0016]    [0016]FIG. 5 illustrates an exploded view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention;  
         [0017]    [0017]FIG. 6 illustrates a cut-away view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention; and  
         [0018]    [0018]FIG. 7 illustrate an alternate embodiment of a heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    In the following description, various aspects of the invention will be described. However, it will be apparent to those skilled in the art that the invention may be practiced with only some or all described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. However, it will also be apparent to one skilled in the art that the invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the invention.  
         [0020]    Various operations will be described as multiple discrete steps in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.  
         [0021]    In various embodiments of the present invention, an improved convective heat exchanger that facilitates precise temperature control is disclosed. This and other advantages will be evident from the disclosure.  
         [0022]    In designing a heat exchanger, if a gas is allowed to flow through a very long heated metal pipe, the temperature of the gas will eventually reach the same temperature of the heated metal pipe. If the temperature of the long metal pipe is precisely known, the temperature is held constant over the entire length of the long metal pipe, and the behavior of the flow (i.e., turbulent, laminar, or transitional), the temperature of the gas at the outlet may also be precisely known. However, the length required to heat a gas convectively might be long enough to make its use difficult, costly, or difficult to manufacture.  
         [0023]    Further, in order to have the gas flow through a very long path (i.e., very long effective length of a metal pipe) while reducing the overall length of the metal pipe, the very long metal pipe may be coiled. A coiled metal pipe provides a long path for the gas flow within a relatively short overall length. But, heating a coiled metal pipe is difficult because all of the surface areas of the coiled metal pipe may dissipate heat into its surroundings, and proper connections between parts may also be difficult to achieve.  
         [0024]    [0024]FIG. 2 illustrates a convective heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 2, a convective heat exchanger  200  in the shape of a rectangle, and having, in particular, a predetermined length  201 . The heat exchanger  200  has a heat exchanger body  202 . The heat exchanger body  202  has an inlet  203  at one end and an outlet  205  at the end opposite of the heat exchanger body  202  and two end caps  207 , one at each end of the heat exchanger body  202 . The gas to be heated enters through the inlet  203 , flows through the entire length of the heat exchanger body  202 , and exits through the outlet  205  at a precise temperature.  
         [0025]    Heat may be provided to the heat exchanger  200  by an electric heater (not shown) that is coupled to the heat exchanger body  202 . The electric heater heats the heat exchanger body  202  to a predetermined temperature, such as, but not limited to, 400° C. (752° F.). The gas enters the inlet  203  at a temperature below that of the heat exchanger body  202 , such as, but not limited to, an ambient temperature of 20° C. (68° F.). The gas flows through the length of the heat exchanger body  202  and exits through the inlet  205  at the same temperature of the heat exchanger  202  i.e., 400° C. (752° F.). The material of the heat exchanger body  202  and the end caps  207  may be any type of thermally highly conductive material, such as, but not limited to, pure copper.  
         [0026]    Utilizing the convective heat transfer principles of gas flowing through a heated tube, the predetermined length  201  of the heat exchanger body  202  may be inadequate to heat the gas to the same temperature of the heat exchanger body  202 . However, as will be described in further detail below, the effective length of flow for the gas within the heat exchanger body  202  is made adequate to heat the gas to the same temperature of the heat exchanger  200 , in accordance with the present invention.  
         [0027]    [0027]FIG. 3 illustrates a grooved rod to provide a long travel or path for a gas within a relatively short linear distance, in accordance with one embodiment of the present invention. Shown in FIG. 3, a metal rod  300  of a predetermined length  305  has grooves  310  machined into its surface. The grooves  310  may be of a threaded type with a flat top, such as, but not limited to, an American Standard Acme threads, and a 10 degrees modified square threads. The size of the grooves  310  may be the size required to allow gas flow. Shown in FIG. 3, grooves  310  are machined to facilitate gas flow; however, it should be appreciated by those skilled in the art that any type of machined groove may be utilized to facilitate the gas flow.  
         [0028]    As will be described in further detail below, the space between the grooves  310  is utilized as a coiled metal pipe, thereby increasing the effective length of flow for the gas. Thus, utilizing the effective length of the path through the grooves  310  and correlating the effective length of the path through the grooves  310  with the principles of convective heating for a gas flowing through a tube determine the predetermined length  305 . Furthermore, the predetermined length is then of a length sufficiently long to cause the gas to be exhausted at the outlet  205  at a stable temperature that is insensitive to small variations in effective length of the path through the grooves  310  (in other words, operationally, the temperature is deemed invariant relatively to a small variant length). The predetermined length is based at least upon the thermal properties of various gases as they flow through the heat exchanger  200 , such as, but not limited to, the behavior of the gas flowing through the grooves  310  (i.e., turbulent flow, laminar flow, and so forth).  
         [0029]    The material of the metal rod may be any type of thermally highly efficient conductive material that also provides enough mass to reduce the thermal dissipation effects, such as significant temperature drops. An example of the thermally highly conductive material that can efficiently yield the desired mass may be a material, such as, but not limited to, pure copper. Additionally, the metal rod  300  may have a coating of another type of metal to inhibit corrosion from the gas, such as, but not limited to, gold. However, the thickness of the coating is preferably thin enough not to interfere with gas flow, such as, but not limited to, 1000 Angstroms. Furthermore, preferably, the coating is accounted for during design, when practicing the present invention, to ensure that the desired volume of flow is maintained after application of the coating and any subsequent coating (i.e., as the initial coating wears).  
         [0030]    [0030]FIG. 4 illustrates the heat exchanger body with an internal feature to receive a grooved metal rod, in accordance with the present invention. Shown in FIG. 4 is the heat exchanger body  202  (shown in FIG. 2) with it end caps  207  and the metal rod  300  removed. As shown in FIG. 4, the heat exchanger body  202  has a hole  405  machined along length of the heat exchanger body  202  to connect the inlet  203  and the outlet  205 . The length of the heat exchanger body  202  without the end caps matches the predetermined length  305  of the metal rod  300  (both shown in FIG. 3).  
         [0031]    [0031]FIG. 5 illustrates an exploded view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 5, the heat exchanger  200  has the metal rod  300  with the grooves  310  inserted into the hole  405  in the heat exchanger body  202 . At each end of the heat exchanger body  200 , one of the two caps  207  seals the metal rod  300  inserted into the heat exchanger body  202 .  
         [0032]    It should be appreciated by one skilled in the art that the heat exchanger  200  may only have one end cap  207  at one end of the heat exchanger body  202 . That is, the hole  405  may not run the entire length of the heat exchanger body  202 , but instead, a tapped hole deep enough to accommodate the metal rod  300 . Because of the requirement that the gas flow into the heat exchanger  200  at the inlet  203  and exhaust out the outlet  205 , the heat exchanger body should be properly sealed to prevent gas leakage.  
         [0033]    Additionally, to ensure proper flow of the gas through the grooves  310  to maximize the effective flow path through the heat exchanger body  202 , the diameter of the metal rod  300  and the through hole  405  are closely matched. The extent to which the metal rod  300  and the through hole  405  are matched is that the coefficient of thermal expansion for the metal rod  300  and the heat exchanger body  202  is utilized to insert the metal rod  300  into the heat exchanger body  202 . That is, one is heated while the other is cooled before insertion, and allowed to return to ambient temperatures, at which point, a very tight fit will occur. This ensures that the gas will flow through the grooves  310  to reach the outlet  205  and exhaust at the same temperature of the heat exchanger body  200 , in accordance with one embodiment of the present invention. Referring briefly back to FIG. 1, the one embodiment of the present invention heats the gas towards the asymptotic value (i.e., minimal or no heat transfer is approached)  105  facilitating heating the gas to highest temperatures, saturation temperatures.  
         [0034]    [0034]FIG. 6 illustrates a cut-away view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 6, the gas at ambient temperature enters the inlet  203 , flows through the grooves  310 , and exits the heat exchanger  200  at the outlet  205 .  
         [0035]    As a result, precise control of temperatures of the gas flowing through a heat exchanger while increasing a  
         [0036]    [0036]FIG. 7 illustrates a heat exchanger that facilitates precise temperature control, in accordance with an alternate embodiment of the present invention. Show in FIG. 7 is a portion of a heat exchanger body  710  of a heat exchanger  700 , in accordance with this alternate embodiment of the present invention. The portion of the heat exchanger body  710  is shown to detail a heating chamber method. In FIG. 7, the portion heat exchanger body  710  represents one end of the heat exchanger body  202  (shown in FIG. 2), and may represent either end of the heat exchanger body  202 .  
         [0037]    Shown in FIG. 7, a number of disks  720  are held together by a center rod  721 . The disks  720  are spaced apart at predetermined intervals along the center rod  712 . Each of the disks  720  has a notch  725  to facilitate flow of gas between the disks  720 . Additionally, the each of the disks  720  is oriented such that the notch  725  of an adjacent disk  720  does not align with the notch  725  of a previous disk  720 . The orientation is achieved by rotating each of the disks  720  a predetermined angle about the center rod  730 , such as each adjacent disk  720  having the notch  725  oriented such that they are 90 degrees out.  
         [0038]    In FIG. 7, the gas may enter the portion of the heat exchanger body  710  at the inlet  203  and enter a heating chamber  735  (i.e., the space between the disks  720 ). Because the notches  725  are not aligned, the gas fills the heating chamber  735  before the passing through the notch  725  in the adjacent disk  720 . The gas continues to travel down the length of the heat exchanger  700  through the notches, while being heated at each heating chamber  735  (i.e., the space between the disks). Each of the heating chamber helps to heat the gas, and the number of disks  720  is based at least upon a notch size, notch orientation, and temperature for the exhaust gas to achieve at the outlet  205 .  
         [0039]    The material of the disks  720  and the center rod  730  are also any type of highly thermally conductive material, such as copper.  
         [0040]    While the present invention has been described with regard to a rectangular heat exchanger, it should be appreciated by those skilled in the art that present invention may be practiced to with different shaped heat exchangers, such as, but not limited to, a heat exchanger in the shape of a cylinder. Additionally, the present invention has been described with gas flowing through the heat exchanger; however, it should be appreciated that the heat exchanger may be modified to accommodate any type of flowing matter, such as, but not limited to, liquids and be within the spirit and scope of the present invention. Different embodiments and adaptations besides those shown and described herein, as well as many variations, modifications and equivalent arrangements will now be apparent or will be reasonably suggested by the foregoing specification and drawings, without departing from the substance or spirit and scope of the invention. While the present invention has been described herein in detail in addition to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full an enabling disclosure of the invention.  
         [0041]    Thus, an improved convective heat exchanger that facilitates precise temperature control has been disclosed