Patent Publication Number: US-2021186265-A1

Title: Multi-pass Fryer Heat Exchanger

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
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     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to improvements in a heat exchanger for use in a deep fryer. More particularly, the present multi-pass fryer heat exchanger creates a heat exchanger with an increased thermal mass that more evenly provides constant even heat over an extended period of time. 
     Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     Deep fryers are used to fry a variety of foods in a vat of cooking oil or shortening. The food is placed into a basket where the heated cooking oil can pass through the basket and around the food that is immersed in the oil. The cooking oil is heated with a heating system or heat exchanger that is often a gas burner. The gas burner is cycled to maintain the temperature of the oil. It is also important to maintain an even temperature across the entire vat so all of the food in the basket is evenly fried. 
     A number of patents and or publications have been made to address these issues. Exemplary examples of patents and or publication that try to address this/these problem(s) are identified and discussed below. 
     U.S. Pat. No. 5,417,202 issued on May 23, 1995 to Joseph A. C. Cote and is titled Gas Fryer Heat Exchanger. This patent discloses a heat exchanger for a fryer having a vat or tank filled to a selected level with a cooking medium such as shortening or oil. The heat exchanger includes a plurality of heat transfer tubes each having an inlet end and an outlet end, and at least one of the plurality of heat transfer tubes extending at a first angle, at least one of the plurality of heat transfer tubes extending at a second angle generally opposite to the first angle, and at least one of the plurality of heat transfer tubes extending horizontally. While this patent discloses a heat exchanger, the heating tubes are a constant diameter and the heating is not consistent. 
     U.S. Pat. No. 6,016,799 issued on Jan. 25, 2000 to Albert Charles McNamara and is titled Vortex Chamber for Deep Fryer Heat Exchanger. This patent discloses a heat exchanger has a plurality of heat transfer conduits and a heating means for heating fluid flowing through the heat transfer conduits. At least one vortex chamber has at least one inlet opening, at least one outlet opening, and, preferably, at least one baffle positioned therein. A first portion of at least one heat transfer conduit is sealingly connected to a respective inlet opening of a vortex chamber. A second portion of the at least one heat transfer conduit is sealingly connected to a respective outlet opening of the vortex chamber. This patent uses baffles to disrupt the flow of hot gas, but does not include a thermal mass. 
     U.S. Pat. No. 8,905,015 issued on Dec. 9, 2014 to Hideo Chikazawa et al. and is titled Pulse Burner and Liquid Heating Cooker. This patent discloses a pulse burner includes: a combustion chamber provided in a liquid vat capable of storing liquid; a tail pipe that is connected to the combustion chamber and has a heat exchanging portion located in the liquid vat and bent in a predetermined shape; and a mixing chamber which communicates with the combustion chamber and to which fuel gas and combustion air is allowed to be supplied. When mixed gas including the fuel gas and the combustion gas is exploded and combusted, the combustion exhaust gas is exhausted through the tail pipe to allow heat exchange with the liquid, and the mixed gas is inhaled from the mixing chamber into the combustion chamber. This patent uses pulsed heating but does not provide a thermal mass and the temperature from the beginning to the end of the heat exchanger is not consistent. 
     U.S. Pat. No. 9,380,912 issued on Jul. 5, 2016 to Richard B. Manson and is titled Fryer and Associated Heat Exchange System. This patent discloses a fryer unit includes a vat and heat exchange system with multiple passes within the fryer vat. Additional heat exchange passes may be provided in ductwork along the exterior surface of the lateral vat sidewall. In this patent there is no mechanism to extend the heating after the gas is turned off. 
     What is needed is a heat exchanger that provides even heating and provides heat over an extended period of time. The multi-pass fryer heat exchanger disclosed in this document provides the solution. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the multi-pass fryer heat exchanger to include three passes through heating tubes. The use of multiple tubes increases the surface area where the heat is transferred into the cooking oil and therefore increases the efficiency of the fryer to extract the optimal amount of heat transfer from the gas burner. In each pass the directional flow the flue product is changed or rotated 180 degrees as the flue product enters into each collection boxes and then makes another turn and passes into a subsequent tube pass. 
     It is an object of the multi-pass fryer heat exchanger to include diffusers in each tube in the first pass. The diffusers ensure maximum heat transfer though the first pass tubes. The diffusers disrupt the laminar flow of the ignited gas and spreads the heat outward to the inside diameter of the tube in the first pass. The turbulent flow of hot flue product is further disrupted as the flue product enters each collection box. 
     It is another object of the multi-pass fryer heat exchanger to use a progressively reduction in the tube diameter with each pass of tube. The reduction in the interior cross-sectional area increases the velocity of the hot air and gas in each pass. The hot air and gas of the flue product is “squeezed” through increasingly less area cross-sectional area and increases the speed of the flow through each pass and creates some back pressure in the heat exchanger. 
     It is another object of the multi-pass fryer heat exchanger to include a bi-metal (heat sink) in each of the collection boxes, between the 1st and 2 nd  pass and the 2 nd  and 3 rd  pass. The bi-metal heat sink creates a thermal mass that retains heat and dissipates through the collection box wall to the medium (oil). Because the gas burner is cycled on when the oil is below a temperature threshold and is cycled off when the oil is above a temperature threshold the bi-metal heat sink increases the off-time cycle by storing and transferring heat within the bi-metal heat sink, conducting the heat into the tubes and into the oil. Without the thermal bi-metal mass, only the heated oil retains heat. 
     It is still another object of the multi-pass fryer heat exchanger to distributed load to reduces thermal stress in each of the tubes and collection box. Because the heating is cycled based upon the temperature of the cooling oil and not the flame temperature of the wall temperature of the heat exchanger, using a larger thermal mass in the heat exchanger allows the heat exchanger to dissipate heat into the oil after the flame has been turned off. 
     Various objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  shows a perspective view of the multi-pass fryer heat exchanger. 
         FIG. 2  shows a perspective view of a deep fryer with the multi-pass fryer heat exchanger. 
         FIG. 3  shows a cross-sectional view of the multi-pass fryer heat exchanger. 
         FIG. 4  shows flow of the flue product through the multi-pass fryer heat exchanger. 
         FIG. 5  shows a graph of the flue product velocity through the multi-pass fryer heat exchanger. 
         FIG. 6  shows a graph of a comparison of the heating cycle with and without a heat sink. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the drawings herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the drawings, is not intended to limit the scope of the invention, but is merely representative of various embodiments of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
     
       
         
           
               
             
               
                   
               
               
                 Item Numbers and Description 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 20 multi-pass fryer heat exchanger 
                 21 fryer enclosure 
               
               
                   
                 22 basket(s) 
                 23 oil vat 
               
               
                   
                 24 exhaust hood 
                 25 rolling caster 
               
               
                   
                 26 locking caster 
                 27 user interface 
               
               
                   
                 30 first pass tube(s) 
                 31 baffle 
               
               
                   
                 32 flame path 
                 33 first pass flow 
               
               
                   
                 40 second pass tube(s) 
                 41 second pass flow 
               
               
                   
                 50 third pass tube(s) 
                 51 third flow path 
               
               
                   
                 60 first collection box 
                 61 first thermal mass 
               
               
                   
                 62 enters first collection box 
                 63 direction change 
               
               
                   
                 70 second collection box 
                 71 second thermal mass 
               
               
                   
                 72 enters second collection box 
                 73 direction change 
               
               
                   
                 80 flame tube 
                 81 gas tube 
               
               
                   
                 82 exhaust 
                 83 air intake 
               
               
                   
                 90 into 
                 101 start 
               
               
                   
                 102 without heatsink 
                 103 with heatsink 
               
               
                   
                 104 upper set point 
                 105 lower set point. 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 1  shows a perspective view of a multi-pass fryer heat exchanger  20  in a preferred embodiment. As a general understanding of the multi-pass fryer heat exchanger  20 , one or a plurality of gas burners ignite natural gas that flames near and/or into the first pass tubes  30 . While the embodiment shows four first pass tubes, more or less than four tubes are contemplated. The diameter and quantity of the first pass tubes is selected based upon the desired amount of heating that is desired/required. Flue product from the burners pass through the first pass tubes  30  and is collected and co-mingled in a first collection box  60 . Within the end of the first collection box  60  is a first thermal mass  61  or bi-metal member. A more detailed description of the thermal mass(es) is shown and described in other figures herein. The collection boxes not only transfer heat from the flue product to other pass tubes, but also more evenly distribute heat from the first pass tubes  30  to the second pass tubes  40 . 
     In the preferred embodiment there are four first pass tubes  30  and three second pass tubes  40 . While there are less tubes in the second pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product. After the second pass tubes  40  is a second collection box  70  with its own second thermal mass  71 . The thermal mass is a dissimilar material from the tubes and collection boxes. Flue product from the second pass tubes  40  and is collected and co-mingled in a second collection box  70 . After the second collection box  70  is a third pass tube(s)  50 . In the preferred embodiment there can be two or three second pass tubes  40  and two third pass tubes  50 . While there can be less tubes in the third pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product, as well as less or smaller diameter tubes in the third pass. The multi-pass fryer heat exchanger  20  is oriented in the fryer with the first pass tube at the top of the exchanger and the flue product travels downward in the collection boxes  60  and  70 . This also ensures that any debris or soot is pushed downward and out of the tubes or collection boxes. 
       FIG. 2  shows a perspective view of a deep fryer with the multi-pass fryer heat exchanger  20 . This figure shows a typical embodiment with the multi-pass fryer heat exchanger  20  within a fryer enclosure  21 . There is an oil vat  23  where the multi-pass fryer heat exchanger  20  heats the oil within the oil vat  23  to the desired temperature. A user interface  27  provides a display of the temperature of the cooking oil and allows a user to select a desired cooking temperature or select a preset cooking temperature. Fries, onion rings or other food that will be fried are placed into a basket(s)  22  and immersed into the oil vat  23 . A timer may be used or included to provide an indicator that the proper frying time has been achieved. The rear of the deep fryer has an exhaust hood  24  or ducting that directs flue product that has passed through the multi-pass fryer heat exchanger  20 . The deep fryer may be supported on a plurality of rolling caster(s)  25  and or locking caster(s)  26 . 
       FIG. 3  shows a cross-sectional view of the multi-pass fryer heat exchanger  20 . In this figure, one of the flame tubes  80  is shown with a second flame tube shown in broken lines. It should be understood that there will be flame tubes associated with each first pass tube  30 . Gas enters a gas tube  81  and is ignited. The flame from natural gas burns at about 1,960° F. Air is drawn into the air intake and a flame enters into the first tube  30 . In this partial cross-sectional view one of the first tubes  30  is shown with diffusers or baffles  31 . The diffusers ensure maximum heat transfer though the first pass tubes  30 . The diffusers or baffles  31  disrupt the laminar flow of the ignited gas and spreads the heat outward to the inside diameter of the first pass tubes  30 . The turbulent flow of hot flue product is further disrupted as the flue product enters each collection box  60  or  70 . The tubes and collection box are typically fabricated from a stainless steel. The stainless-steel material can be fairly thin and has a thermal conductivity of about 14.3 W/m K and a heat capacity of about 0.120 Btu/(lb-° F.). As a reference, the heating capacity of the oil 0.4 Btu/(lb-° F.) depending upon temperature. 
     While the embodiment shows four first pass tubes  30 , more or less than four tubes are contemplated. The diameter and quantity of the first pass tubes is selected based upon the desired amount of heating that is desired/required. Flue product from the burners pass through the first pass tubes  30  and is collected and co-mingled in a first collection box  60 . At the end of the first collection box  60  is a first thermal mass  61  or bi-metal member. The bi-metal member is preferably made from a carbon steel. Carbon steel has a heat capacity of about 0.120 Btu/(lb-°F.). In the embodiment shown the first thermal mass  61  is a plate having a thickness of about 0.25 inches thick and a volume of about 13 cubic inches or about 3.8 pounds. The thickness of the one or both thermal mass  61  and  71  can be changed to increase or decrease the amount of heat that can be stored in the thermal mass. It is contemplated that the thermal mass can range from 10 to 100 cubic inches. While minimal heat is stored in the walls of the tubes and collection boxes, the thermal mass  61  and  71  are heated and can dissipate heat into the tubes and collection boxes after the heating flame is off. The thermal mass can also absorb heat more quickly than the oil and can obtain a higher temperature than the oil. 
     The collection boxes not only transfer flue product to other pass tubes, but also more evenly distribute heat from the first pass tubes  30  to the second pass tubes  40 . In the preferred embodiment there are four first pass tubes  30  and three second pass tubes  40 . While there are less tubes in the second pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product. After the second pass tubes  40  is a second collection box  70  with its own second thermal mass  71 . Flue product from the second pass tubes  40  and is collected and co-mingled in a second collection box  70 . After the second collection box  70  is a third pass tube(s)  50 . In the preferred embodiment there are three second pass tubes  40  and two third pass tubes  50 . While there are less tubes in the third pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product. The multi-pass fryer heat exchanger  20  is oriented in the fryer with the first pass tube at the top of the exchanger and the flue product travels downward in the collection boxes  60  and  70 . The second pass tubes  40  and the third pass tubes  50  may or may not include diffusers or baffles  31 . 
       FIG. 4  shows flow of the flue product through the multi-pass fryer heat exchanger  20 . This figure shows a pictorial diagram of the flame path  32  of the flue product entering from the four burners pass as it passes through the first pass tubes  30  and enters the first collection box  62  where it is collected and co-mingled in a first collection box  60 . At the end of the first collection box  60  is a first thermal mass  61  or bi-metal member. The collection boxes not only transfer flue product to other pass tubes, but also more evenly distribute heat from the first pass tubes  30 , changes direction in the  63  in the first collection box  80  and enters into the second pass tubes  40 . 
     In the preferred embodiment there are four first pass tubes  30  and three second pass tubes  40 . While there are less tubes in the second pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product. The flew product moves through the second flow path  41  and enters the second collection box  72 . After the second pass tubes  40  is a second collection box  70  with its own second thermal mass  71 . Flue product from the second pass tubes  40  and is collected and co-mingled in a second collection box  70 . The collection boxes not only transfer flue product to other pass tubes, and again more evenly distribute heat from the second pass tubes  40 , changes direction in the  73  in the second collection box  70  and enters into the third pass tubes  50 . 
     After the second collection box  70  is a third pass tube(s)  50  as a third flow path  51 . In the preferred embodiment there are three second pass tubes  40  and two third pass tubes  50 . While there can be less tubes in the third pass, the diameter of the second pass tubes can be smaller diameter to increase the velocity of the flue product, as well as less or smaller diameter tubes in the third pass. The multi-pass fryer heat exchanger  20  is oriented in the fryer with the first pass tube at the top of the exchanger and the flue product travels downward in the collection boxes  60  and  70 . All of the tubes and collection boxes are in the oil vat and transfer heat to the oil vat. 
     In the preferred embodiment the four first pass tubes  30  have a cross-sectional area of about 18 square inches, but it is contemplated that the cross-sectional area can range from 4 square inches to 40 square inches. The three second pass tubes  40  have a combined cross-sectional area of about 8 square inches, but it is contemplated that the cross-sectional area can range from 4 square inches to 20 square inches. The two third pass tubes  50  have a combined cross-sectional area of about 6 square inches, but it is contemplated that the cross-sectional area can range from 3 square inches to 20 square inches. While the tubes are shown as being round, it is also contemplated that the tubes can be ellipse as opposed to round. 
       FIG. 5  shows a graph of the flue product velocity through the multi-pass fryer heat exchanger. The flue product travel flows from left to right across the X-axis in this figure. The vertical or Y-axis of the graph shows a relative velocity of the flue product. The velocity is essentially and inverse of the cross-sectional area of the tubes and collection boxes. Starting from the first pass tubes  30 . Due to the increased cross-sectional volume of the first collection box  60  the velocity of the flue product slows as the flue product from all of the first pass tubes comingle. The flue product then enters the second pass tubes  40  that are smaller in diameter and significantly increases in velocity. The decreased cross-sectional area also creates some back-pressure to control the burn of the flue product in the first pass tubes  30 . 
     As the flue product enters into the second collection box  70  the larger volume of the second collection box slows the velocity of the flue product. The cross-sectional area of the third pass tubes  50  is smaller than the first and second pass tubes so the velocity will again increase in velocity. The change in the direction of flow in the collection boxes also creates some back-pressure. 
       FIG. 6  shows a graph of a comparison of the heating cycle with and without a heatsink or thermal mass. Time is shown in the horizontal X axis of this graph and temperature is vertical or Y axis. When heating the oil there is an upper set point  104  and a lower set point  105  where the temperature of the oil is maintained. In the graph, the deep fryer is started  101  where the cooking oil is at room temperature. Without a heatsink  102  the cooking oil will heat more quickly and will also require more frequent thermal cycling. With a heatsink  103  the heatsink(s) will retain heat from the burners and the heat that is stored in the heatsink(s) will transfer the stored heat into the cooking oil. This will reduce the frequency that the burners are activated. While the graph shows the burners completely on or off, in the case of multiple heating tubes, one, multiple or all of the burners can be operated to maintain the temperature of the cooking oil. 
     Thus, specific embodiments of a multi-pass fryer heat exchanger have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.