Deep fat fryer with improved heat transfer

An improved heat exchange mechanism for a deep fat fryer is described. The improvement includes a baffle plate wherein the walls are corrugated and horizontally aligned holes are provided along the length of the plate with the interior two rows of such holes having decreasing diameter in the direction of flow of the combustion gases through the heat tube. In addition, holes are formed at the edges of the corrugations. A burner shield is provided restricting the flow of secondary air to the burner tube.

FIELD OF THE INVENTION

This invention relates to deep fat fryers and in particular to deep fat fryers which use gas burners as a source of heat to be transferred to cooking oil.

DESCRIPTION OF THE PRIOR ART

Commercial deep fat fryers are used to cook a variety of foods including fast foods such as French fries and fish. In operation, it is necessary to have the cooking oil at a substantially elevated temperature and to maintain the oil during the cooking process at a high temperature to provide a crisp relatively fat free, cooked product.

Typically a deep fat fryer will include a vat or tank for the cooking oil with a plurality of heat tubes extending through the lower portion thereof. Gas burners are provided at one end of each tube and the products of combustion after passing through the tubes are exhausted through a flue or similar device.

In certain prior art fryers the heat tubes where U-shaped or S-shaped to assist in heat transfer by maintaining the products of combustion from the burner within the tube for an extended period of time. However, when the products of combustion travel around a bend in the tube, corrosion can occur ultimately causing tube failure.

If the heat tubes extend through the tank without a bend therein it is likely that the unit will be inefficient in its heat transfer as the hot gases will pass through the tube and be exhausted very rapidly. Accordingly, it is known to provide a baffle mechanism within the tube to assist in heat transfer, and to generate a swirling motion to the products of combustion as they pass through the tube to more efficiently transfer heat to the tube walls. In U.S. Pat. No. 6,196,118 assigned to the assignee of this invention there was described such a baffle system wherein each baffle plate was a rectangular plate extending longitudinally along the longitudinal axis of each heat tube with wings struck therefrom in vertical columns and longitudinal horizontal rows. The wings left openings in the plate so that the hot gases passing there along would be deflected through the plate resulting in a back and forth or swirling type motion to effectuate heat transfer.

At the entrance of each heat tube a burner is provided, and in many instances this will be a conventional in-shot burner. The burner axis can coincide with the longitudinal axis of the heat tube, or if space is available a 90° burner may be used wherein the burner jet makes a 90° turn to align with the longitudinal axis of the heat tube. The burner could be mounted at an angle to the longitudinal axis of the heat tube. The burner could be mounted at an angle to the longitudinal axis of the heat tube or at a 90° angle. It is necessary, however, to provide secondary air at the entrance to the heat tube to assist in combustion of the gas at the burner nozzle, and obviously, the presence of the secondary air at a temperature below the temperature of the burner flame will affect efficiency.

In prior art deep fat fryers it was generally believed that increased efficiency depended upon increasing the dwell time of the products of combustion within the heat tube. As noted above, the increased dwell time was provided by S-shaped or U-shaped burner heat tubes, or in the case of straight heat tubes with baffle plates although baffle plates were known for use with U-shaped or S-shaped tubes also.

SUMMARY OF THE INVENTION

It has been discovered, however, the efficiency in a deep fat fryer with a gas fired burner can be increased to 65-70% by providing a shield around the burner at the entrance to the heat tube to restrict the secondary air admitted to the burner tube, and in addition, in a unique baffle design of this invention, the products of combustion can be directed through longitudinal holes in horizontal rows through a corrugated baffle plate wherein the walls are angled to the direction of flow so that combustion products will both pass through holes in the plate, and circulate around the plate for more efficient heat transfer. In addition, in the preferred embodiment, four longitudinal rows of holes are provided, mutually spaced, vertically with the center two rows of holes in each plate being of decreasing diameter in the direction of flow of the combustion products.

Accordingly, it is an object of this invention to provide an efficient heat transfer mechanism for a deep fat fryer to increase the efficiency thereof to 65-70%.

It is a further object to provide a deep fat fryer using a plurality of straight heat tubes extending through the vat of cooking oil wherein each heat tube contains a baffle plate and the burner for each heat tube is shielded to restrict access of secondary air thereto and wherein each fryer operates without a blower to force secondary air through the tubes.

It is further object of this invention to provide a baffle plate for a each heat tube in a deep fat fryer wherein the baffle plate is corrugated with the walls thereof forming 60° angles extending vertically along the plate and each wall has a vertical row of holes therein for admission of combustion products therethrough.

It is a further object of this invention to provide a baffle plate for a heat tube in a deep fat fryer wherein the plate is corrugated with walls angled in the direction of the flow of combustion products through the tube so that each angled wall presents itself to the flow of combustion products and a plurality of holes are provided in each wall to permit the admission of such combustion products.

It is yet another object of this invention to provide a corrugated baffle plate for a heat tube in a deep fat fryer wherein each plate has walls angled at an acute angle to the direction of flow and each wall has a vertical row of holes wherein two of such holes are of decreasing diameter along the lengths of the plate.

These and other objects will be readily apparent with reference to the drawings and following description wherein:

DETAILED DESCRIPTION OF THE INVENTION

With attention to the drawings andFIGS. 1-4in particular, a deep fat fryer of this invention10includes a tank12, a rear flue14and may be mounted on wheels16. The front18has an access door20for access to the burner or burners and the like. A filter system (not shown) also would be provided with access through door20.

In the embodiment ofFIG. 2there is shown schematically a burner22and a heat tube24extending through tank12to a flue pipe26in flue14. The source of gas for the burner22is not shown. Burner22then sends a jet of products of combustion through the heat tube24and the oil (not shown) disposed in tank12will be heated by conductive heat transfer from the wall of the tube24. The products of combustion then exit tube24into flue pipe26for exhaustion. As shown inFIG. 4the rear28of the fryer10defines an opening30which is a source of air for the burner22. In the embodiment ofFIG. 3four heat tubes24are shown extending through a single tank or vat12. Each tube24has a separate burner22and a baffle plate23(shown schematically). In the embodiment ofFIG. 5twin deep fat fryers10are shown each with two burner tubes24as will be obvious to those skilled in the art, typically two, four, or even five burner tubes may be provided. The embodiment ofFIG. 5is also known as a split vat and each of the fryers10′ may be independently operated.

The kitchen space requirements will dictate, at least in part, the size of the tank and deep fat fryer used. In some situations a single unit with two burner tubes would be sufficient whereas if more space is available and a higher volume of food to be cooked needed, it may be necessary to provide a larger tank with four or five heat tubes. In each instance each tube would have its own burner.

This invention is not intended to be limited to the type of deep fat fryer10or10′ shown or to the number of burners and heat tubes which are provided as will be subsequently described. The embodiments ofFIGS. 1-5are merely shown as illustrations.

In the preferred embodiment of this invention a burner is disposed at an angle to the longitudinal axis of the heat tube. In some instances a conventional in-shot burner may be used wherein the burner axis coincides with the longitudinal axis of the heat tube or, if space is available a 90° burner may be used where the burner jet makes a 90° turn to align with the longitudinal axis of the heat tube, as shown inFIG. 18. The burner can then be mounted at an acute angle to the longitudinal axis of the heat tube, coaxially with the longitudinal axis or at a 90° angle thereto. As will be obvious to those skilled in the art, this invention is not limited to the type of burner or its mounting angle to the heat tube.

Each heat tube24has an internal baffle plate according to this invention. The baffle plate50is shown inFIGS. 7-9and consists of a corrugated plate with walls52disposed at 60° angles as shown inFIG. 7.FIG. 8is a side view of the baffle plate of this invention andFIG. 9is an end view of the baffle plate ofFIGS. 7 and 8looking along the longitudinal axis of a burner tube in the direction of flow of combustion products shown by the arrow inFIG. 8.

In the preferred embodiment of this invention there are four rows of horizontally aligned holes in the face of each wall52of baffle50. Upper and lower holes54and56are uniform in diameter along the lengths of the baffle plate50. Interior holes58and60are of decreasing diameter along the direction of flow of the combustion products through a heat tube. In addition, alternate single and double holes62, and64and66, respectively are provided at the juncture of each wall52in plate50.

FIG. 6is a flattened version of the plate52for the purpose of illustrating the hole patterns for holes54,56,58,60,62,64and66. The holes with the exception of the hole pattern for holes58and56are uniform in diameter.

In order to further increase the efficiency of a deep fat fryer it has been discovered that a burner shield restricting the secondary air into the burner tube will achieve a much greater efficiency in the order of 65-70%. InFIGS. 10-15there is shown a burner shield for a full vat fryer such as shown inFIG. 3. The assembled burner shield ofFIGS. 10-15is also shown inFIG. 17. The shield consists of a plate70having oval cut out portions72for receiving a pair of burners22. Plate70then mounts directly on the burner assembly which in turn is mounted on the heat tube entrance in the conventional fashion. Plate72is notched in a wall with a notch74for the admission of the pilot flame to the burner for main burner ignition. In addition, a central divider plate76is provided which is shown inFIGS. 10 and 11and inFIG. 17. Plate76has a plurality of holes78for the admission of a pilot flame for main burner ignition. Divider plate10includes a lip80which hooks over the upper portion82of plate70. With attention toFIG. 15, notches84are further provided in plate70to assist in mounting the burner assembly.

FIG. 16shows a burner assembly similar toFIG. 5wherein a separate shield90is provided for each burner assembly22and each plate90has a notch94similar to notch74in plate70for the admission of the pilot flame for ignition of the burner22. As shown inFIG. 16, the burner shield90is mounted at an entrance to the tube of the burner assembly and the burner shield90substantially surrounds and encloses a first end of the tube of the burner shield.

As is known to those skilled in the art, in the case of the embodiment ofFIG. 17a single plot will be used, and flame will blow from one burner to the adjacent burner to ignite it across the plate76. In the case of the embodiment ofFIG. 16, a separate burner will be provided for each heat tube.

In summary, it has been discovered that the efficiency of the heat exchange in a deep fat fryer can be very substantially increased by providing a burner shield, and the specifically designed internal baffle plate of this invention. The burner shield is essentially a frame which surrounds the burner assembly and is mounted on the wall of the vat or on the support for the vat so that the shield is coupled between the burner and the heat tube and controls the secondary air admitted to the burner. A blower used in conventional high efficiency fryers for entraining primary and/or secondary air into the burner system is not necessary.

In addition, the baffle plate of a specific design of this invention is a corrugated rectangular shaped plate which is disposed along the longitudinal axis of the heat tube. The plate consists of a wall wherein each adjacent wall defines an interior angle of 60°. The face of each wall mounts a vertical row of holes and the holes on the adjacent walls are aligned so that the circular holes have centers in a common horizontal plane. The preferred embodiment of this invention has four of such holes in each wall, and the center two of such holes are of decreasing diameter along the lengths of the plate in the direction of flow of the combustion gases.

In addition, each wall forms a junction with adjacent walls and the junction also forms a plurality of holes. In the preferred embodiment of this invention the holes in such junctures are alternating one or two such holes along the length of the plate.

It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth above. After reading the foregoing specifications, one of ordinary skill will be able to effect various changes, substitutions or equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.