Abstract:
An oven includes a food chamber with an access door which houses a water evaporator chamber in fluid communication with the food chamber. By sensing the temperature of the water in the evaporator and the dry bulb temperature within the food chamber and by controlling a dry heat source that heats the air and a wet heat source that heats the water, the cook can control both the final food temperature and the degree of browning of the food.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for thermalizing or cooking food in an oven, using an evaporator to maintain the desired difference between the wet bulb and dry bulb temperatures in the food chamber. 
     Traditional ovens characteristically utilize a dry heat system. The limitations of this equipment have led users to develop alternate cooking techniques, such as papillote cooking (bag cooking) in an effort to have some control over the parameters which actually affect the quality of the end product. Winston Industries has manufactured ovens or thermalizers having evaporators, in which the temperature of water in the evaporator was controlled, and these ovens have provided a much improved ability to control the quality of the food. 
     SUMMARY OF THE INVENTION 
     The present invention provides an oven in which the evaporator is conveniently located on the access door to the oven. This facilitates the task of adding water to the evaporator, checking the water level in the evaporator, and draining the water from the evaporator. 
     An embodiment of the present invention also adds a control feature which allows the water in the evaporator to be brought up to boiling temperature to prevent bacteria build-up. 
     An embodiment of the present invention also adds a sparger, which injects air into the evaporator in order to enhance the transfer of moisture from the evaporator to the food chamber. 
     In a preferred embodiment, the cook has three settings he can control. First, he sets the wet bulb temperature inside the food chamber, which establishes the ultimate food temperature. The controller controls this temperature by controlling a heater inside an evaporator. Second, the cook sets the degree of browning of the food, which really is setting a differential between the wet bulb temperature and the dry bulb temperature in the food chamber. The control system controls the difference between the dry-bulb-temperature and the wet-bulb-temperature in the food chamber (thereby controlling the degree of browning) by controlling a heater that heats the air in the food chamber. Temperature sensors in both the evaporator and in the food chamber provide feedback to the controller. Third, the cook may set a timer. 
     The food itself, inside the food chamber, acts like a wet bulb sensor, since is it has a moist outer surface and is sensing the conditions inside the oven. The temperature in the evaporator establishes the wet bulb temperature in the food chamber, which, in turn, establishes the final food temperature. This means that the temperature sensor in the evaporator senses a temperature that is very close to the final temperature of the food. By being able to control the difference between the wet bulb temperature and the dry bulb temperature inside the food chamber (thereby controlling the driving force that causes evaporation of moisture from the food), the cook can control the browning of the food. 
     Thus, this oven gives the cook a superior ability to control the quality of food and to reproduce that quality on a regular basis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic front view of an oven made in accordance with the present invention; 
     FIG. 2 is a broken away side view of the oven of FIG. 1; 
     FIG. 3 is similar to the view shown in FIG. 2, except that the door is open and partially broken away to show the fill and drain ports to the door&#39;s evaporator; 
     FIG. 4 is a detailed, enlarged view of the fill and drain ports of FIG. 3; and, 
     FIG. 5 is schematic diagram of the controller for the oven of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 through 5 show an example of an oven  10  made in accordance with the present invention. The oven  10  includes a substantially closed food chamber  12 , having an access door  14 . Note that, in this embodiment 10, the door  14  has a horizontal axis hinge  15 , so that it swings down to open and up to close. However, the door  14  could also be hinged vertically or mounted in other known ways without departing from the scope of the invention as claimed. However, in that case, the fill and drain ports probably would be moved to a different location. There is a vent  17  from outside the oven  10  into the food chamber  12 , which permits ambient air to enter the food chamber  12 , be heated, and leave the food chamber  12 . 
     Referring now to FIGS. 2 and 3, inside the food chamber  12  there are racks  16  to hold the food. There are also a dry heat source  18  and a dry bulb temperature sensor  20 . A controller  22  adjusts the heat input to the food chamber  12  by controlling the heat source  18 , and the temperature sensor  20  provides feedback to the controller  22 , as will be described in more detail later. 
     The door  14  includes an arm  24  with a limit stop  26 , which limits how far the door  14  opens. In this embodiment 10, the door  14  opens until it is substantially parallel to the horizontal floor or countertop on which the oven  10  sits, at which point the limit stop  26  precludes any further opening of the door  14 . 
     As best seen in FIGS. 2 and 3, the door  14  includes an inside wall  28  and an outside wall  30  which are connected together to define a hollow cavity  32 , which serves as a water evaporator. As best illustrated in FIG. 4, there is an opening  34  on the inside wall  28 , which serves as a fill port. There is also an opening  38  in the outside wall  30 , which serves as a drain port. When the door  14  is open (as shown in FIG.  3 ), the inside wall  28  of the door  14  is facing up, and water can be poured into the evaporator  32  through the port  34 . This fill port opening  34  also serves as the outlet for vapor generated in the evaporator  32 , as is explained later. In this embodiment 10, the fill port  34  also provides access to remove or install a drain plug  36 , which covers the drain port  38  in the outside wall  30  of the door  14 . When the drain plug  36  is removed (and the door is in the open position as shown in FIG.  3 ), the liquid in the evaporator  32  is able to drain out of the evaporator  32  through the drain port  38 . Note that parts or all of the inside and outside walls  28 ,  30  may be made from a transparent material, such as tempered glass, to allow the user to readily determine the water level in the evaporator  32 , as well as to visually inspect the food in the food chamber  12 , without having to open the door  14 . 
     Inside the evaporator  32  are located another heat source  40  (which is referred to as a wet heat source, since it is in the water evaporator), a temperature sensor  42 , and a sparger  44  to inject air into the evaporator  32 . It should be noted that the heat source  40  in the evaporator  32  as well as the heat source  18  in the food chamber  12  are preferably electric (resistance) heat sources, but other known heat sources could also be used. Also, the wet heat source  40 , the temperature sensor  42 , and the sparger  44  are all located such that, when the access door  14  is closed (as shown in FIG.  1 ), they are all submerged below the water level  46 , and they all remain submerged until most of the water in the evaporator  32  has evaporated. 
     The sparger  44  includes a compressor or fan  48  which draws air, preferably from outside of the food chamber  12 , and conveys it via tubing  50  to the injection point in the evaporator  32 . The injection point may be a single injection point as illustrated in FIG. 1, or it may be an injection manifold with a plurality of openings to distribute the injected air bubbles in a more uniform manner. It should be noted that the sparger  44  may draw the air from inside the food chamber  12 , if desired, instead of or in addition to drawing outside air. The sparger  44  serves to enhance the mass and heat transfer from the water evaporator  32  in the access door  14 , to the food chamber  12 . This allows for a faster and more efficient transfer of the moisture laden environment in the water evaporator  32  to the food chamber  12 . It should also be noted that the food chamber  12  is vented to atmosphere by means of the vent  17 . 
     The controller  22  includes three inputs  56 ,  58 ,  60 , which the cook can set. The first input  58  is used to set the desired water temperature in the evaporator, which sets the wet bulb temperature in the food chamber, thus setting the end temperature of the food. The second input  60  is used to control the degree of browning by setting the differential between the wet bulb and dry bulb temperature. The third input  56  is used to set the cook time. 
     The controller  22  receives temperature readings from the temperature sensor  42  in the evaporator  32  and from the temperature sensor  20  in the food chamber  12 . The controller compares the evaporator temperature with the set point that was input by the cook and adjusts the evaporator heat source  40  accordingly to maintain the set point temperature. As is discussed in more detail later, the evaporator set point temperature corresponds to the long term equilibrium temperature of the food item in the food chamber  12 . The degree-of-browning input  60  allows the cook to select a value (such as within a range of 0-10) representing degrees of browning (0 meaning no browning; 10, high browning). This input  60  corresponds to increasing differences between the water evaporator temperature (the wet bulb temperature as sensed by the sensor  42 ) and the dry bulb temperature in the food chamber (as sensed by the sensor  20 ). The following table provides an example of how the browning scale may 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Difference in ° F. between sensor 42 
               
               
                   
                 Set Browning Value 
                 and sensor 20 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 0 
               
               
                   
                 1 
                 5 
               
               
                   
                 2 
                 10 
               
               
                   
                 3 
                 20 
               
               
                   
                 4 
                 30 
               
               
                   
                 5 
                 40 
               
               
                   
                 6 
                 50 
               
               
                   
                 7 
                 75 
               
               
                   
                 8 
                 100 
               
               
                   
                 9 
                 125 
               
               
                   
                 10 
                 150 
               
               
                   
                   
               
             
          
         
       
     
     Operation of the Oven 
     The cook fills the evaporator to the desired level by pouring water through the fill port  34 . The cook then inserts the food into the food chamber  12  of the oven  10 , sets the water evaporator temperature by means of the input  58 , thus setting the food temperature, and sets the degree of browning by inputting the desired value on the browning input  60 . As shown in the table above, when the cook selects a value to set the degree of browning, he is actually setting the differential between the wet bulb and dry bulb temperatures, which controls the degree of browning. These inputs may be by buttons, dials, or other known input means. The cook may then set the cook time using the input  56  or may simply use that input to turn the oven on. The controller  22  then controls the power to the wet heat source  40  and to the dry heat source  18 , to control the evaporator temperature measured by the sensor  42  and to control the dry bulb temperature relative to the evaporator temperature as measured by the sensor  20  based on the inputs. 
     The food generally will be colder than the evaporator set point temperature (as set by input dial  58 ) when the food is put into the food chamber. The vapor in the food chamber  12  will condense on the food surface, transferring its latent heat of vaporization to the food to warm up the food, and it will continue to do so until the food reaches the water evaporator set point temperature sensed by the sensor  42 . Since the food generally has a large mass and does not heat as quickly as the water in the evaporator, it will approach the evaporator set point temperature of the sensor  42  as the cooking time progresses. 
     The oven  10  includes the evaporator  32  with a heat source  40  to regulate the water temperature. The central controller  22  applies power to the wet heat source  40  as needed to maintain the pre-set evaporator set point temperature at the temperature sensor  42 . The central controller  22  also applies power to the dry heat source  18  as needed to maintain the pre-set temperature differential between the evaporator set point temperature at the sensor  42  and the dry bulb temperature at the dry bulb sensor  20  to reach the set degree of browning. 
     Once the water temperature has been set, for example at 135 degrees F., the water in the evaporator is heated to that temperature. The wet heat source  40  continues to evaporate water from the evaporator  32  until a partial pressure equilibrium is reached in the food chamber  12  corresponding to the partial pressure of water at that temperature (135 degrees F.). If the food temperature is below 135 degrees F., the food acts as a condenser, condensing some of the vapor in the food chamber  12 , which warms up the food (as the vapor gives up its latent heat of vaporization to the food) and which lowers the partial pressure of the vapor in the food chamber  12 . The lower partial pressure of vapor in the food chamber  12  causes more water to evaporate from the evaporator  32 , cooling down the remaining water in the evaporator  32  (via evaporative cooling) and thus causing the controller  22  to turn on the wet heat source  40 , causing more water to evaporate from the evaporator  32  in order to maintain the equilibrium pressure corresponding to the evaporator set point temperature of 135 degrees F. This process continues until the food has reached equilibrium at the set point temperature, which, in this example, is 135 degrees F. 
     At the same time, the central controller  22  will cause the dry heat source  18  to cycle on and off to maintain the pre-set difference in temperature between the dry bulb temperature and the evaporator set point temperature. This process continues until the food has reached equilibrium at the set point temperature of 135 degrees F. 
     The greater the difference between the dry bulb temperature and evaporator set point temperature, the greater the driving force causing evaporation from the surface of the food located in the food chamber  12 . This results in a higher degree of browning of the food item. As the moisture leaves the surface of the food item in the food chamber, chemical components are concentrated on the surface, and this, together with the high temperatures, causes the browning of the food item. 
     To improve the response characteristics of the food chamber  12 , a small amount of air is drawn by the compressor  48 , conveyed via the tubing  50  and injected into the evaporator  32  via the sparger  44 . This air bubbles through the water in the evaporator  32 , where it is warmed and becomes moisture laden to the degree corresponding to the partial pressure of water at the existing temperature. This moisture laden air is displaced by the continual supply of fresh air injected via the sparger  44 , which pushes the moisture laden air out through the opening  34  of the fill port and into the food chamber  12 . With the food chamber  12  vented properly by means of the vent  17 , the wet heat source  40  is cycled on and off as needed to control the temperature sensed by the evaporator sensor  42 , thus controlling the equilibrium food temperature. The dry heat source  18  is cycled on and off as needed to control the temperature difference between the dry bulb temperature sensed by the sensor  20  (which is simply the air temperature in the food chamber  12 ) and the evaporator set point temperature sensed by the sensor  42 . 
     Thus, a cook sets a desired food temperature by setting the desired evaporator set point temperature on the input  58 . The cook also sets the desired degree of browning on the browning control input  60 . The central controller  22  takes the browning setting and controls the dry heat source  18  to maintain a difference between the dry-bulb temperature at the dry bulb sensor  20  and the evaporator set point temperature at the sensor  42  corresponding to the degree of browning selected by the cook, in accordance with the aforementioned table. The result is a properly thermalized food item to the desired level of doneness (food temperature) and to the desired texture (degree of browning) on a consistent basis and without frequent inspections by the cook. 
     The controller  22  also includes a provision for heating the water in the evaporator  32  to a boiling temperature (as measured by the sensor  42 ) to prevent bacteria build-up. This provision may be manually activated by the user, or it may be programmed to activate itself periodically without further user interface. Safety features well known in the industry, such as a low water level cut off switch, may be incorporated in the event that operation with little or no water level is deemed undesirable. 
     It will be obvious to those skilled in the art that modifications may be made to the embodiment described above without departing from the scope of the invention as claimed.