The present embodiments relate to apparatus and methods for providing and controlling air flow and heat transfer effect across products in freezing systems.
Known freezers have a fan or a plurality of fans used to provide a convective airflow environment to accelerate the freezing rate of products, such as food products, being processed in the freezer. Fans require electrical energy to operate and contribute the thermal loads to the freezing processes which reduces the overall efficiency of the freezer.
The present inventive embodiments provide a freezer which eliminates the need for fans without reducing the effectiveness of the heat transfer effect upon the products.
For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which:
Referring to
As used herein, “oscillating flow” refers to the flow of gas moving or traveling back and forth between two points regardless of the manner, number of repetitions or frequency of repetitions by which the oscillating flow is implemented.
The apparatus 10 includes a housing 12 in which a space 14 is provided for providing a chilling or freezing convective gas flow 16 to correspondingly chill or freeze products 18, such as food products, transported through the space 14 in the housing. The housing 12 also includes and inlet 20 and an outlet 22. An inlet skirt 24 or flap is provided at the inlet 20, while an outlet skirt or flap is provided at the outlet 22 to retain the gas flow 16 within the space 14. A transport apparatus 28, such as a conveyor belt for example, is disposed for operation to transport the products 18 from the inlet 20 through the space 14 to the outlet 22.
The space 14 is provided with a baffle 30 disposed beneath the conveyor belt 28. The baffle 30 may be of solid construction. An inlet exhaust flue 32 is disposed proximate the inlet 20 of the housing 12. An outlet exhaust flue 34 is disposed proximate the outlet 22 of the housing 12.
A pair of piston assemblies 36,38 are disposed at different sides of the housing 12. As shown in
The sidewall 40 is constructed to provide a cylinder for the piston assembly 36 in which the piston 44 is disposed for reciprocating movement. The piston 44 is connected to a shaft 46 which can be of the screw jack or hydraulic type, which in turn is connected to a motor 48 for operating the piston. Seals 50 or gaskets mounted to the piston 44 prevent a majority if not all of the gas 16 from getting behind the pistons 44,52 into the respective cylinders. The sidewall 42 is constructed to provide a cylinder for the piston assembly 38 in which the piston 52 is disposed for reciprocating movement. The piston 52 is connected to a shaft 54 which can be of the screw jack or hydraulic type, which in turn is connected to a motor 56 for operating the piston. Seals 58 or gaskets mounted to the piston 52 prevent a majority if not all of the gas from getting behind the pistons into the respective cylinders.
As mentioned above, the sidewalls 40,42 are interconnected in the space 14 and therefore, for purposes of this disclosure, that portion of the sidewalls 40,42 in the space is referred to as the upper baffle 31.
The upper baffle 31 may be of solid construction and is provided with at least one hole 62 or port extending therethrough such that a pipe 64 or conduit can be inserted through the hole to introduce liquid cryogen into the freezer apparatus 10. The liquid cryogen provided, CO2 or N2, will usually phase change into a gaseous-solid phrase when injected into the chamber 15. The pipe 64 has a first end connected to a manifold 66 from which at least one or a plurality of nozzles 68 are in communication therewith. The manifold is disposed in the chamber 15. An opposite end of the pipe 64 is connected to a source of liquid cryogen (not shown). The pipe includes a control valve 70 for controlling an amount of the liquid cryogen to be introduced into the pipe and through to the manifold 66.
The baffles 30,31 coact to provide the freezing chamber 15 within the space 14. The cross section of the freezing chamber 15 is kept to as small a volume as possible in order to provide for increased velocity of a cryogen airflow 74 across the product 18, which in turn provides for increased heat transfer to the product.
A length of the housing 12 may be for example 3-20 meters and constructed as a tunnel freezer. The inlet and outlet skirts 24,26 can be constructed of rubber, plastic or stainless steel and are adjustable depending upon the dimensions of the product 18 entering and being discharged from the freezing chamber 15.
The sidewall 42 at the cylinder for the piston 52 is provided with a bleed gas pipe 76 or conduit which is in communication with an interior of the cylinder as shown in the Figures.
The apparatus functions as follows during operation. Referring to
The pistons 44,52 work in unison, that is, the pistons will be at least approximately 180 degrees out of phase with each other, such that when the inlet piston 44 is moving in a downstroke, the discharge piston 62 is moving in an upstroke. Referring still to
When the pistons 44,52 have finished their respective strokes as shown in
A temperature gradient may also be provided by the apparatus 10 and the method employed by the apparatus. For example, from the inlet 20 to discharge at the outlet 22, a stroke length of the discharge piston 52 is increased thereby pulling more of the gas 78 in the direction of the outlet 22. The gas 78 can then be bled from the piston cylinder at the bleed gas pipe 76. A swing check valve 83 disposed in the bleed gas pipe 76 permits the gas to be bled from the piston cylinder and discharged as exhaust. A larger portion of the overall gas mass is therefore directed to the outlet 22 and therefore, the gas warms during the freezing process and the temperature gradient is established. The pistons 44,52 may be electronically controlled, and therefore a temperature gradient can be entered as an input to a control apparatus 84 connected to the pistons for operating the apparatus 10 at its most efficient setting. A desired temperature can be entered into the controller 84 by an operator. The control valve 70 is actuated to permit a desired flow of cryogen to the nozzles 68 to satisfy the temperature requirement for the product 18 and the freezing chamber 72. Control of the temperature gradient is not dependant upon a temperature set point. As described above, a delta T (ΔT) is entered into the controller 84 and same controls the mass flow of cryogen vapor along a length of the freezing chamber 72 to achieve the temperature gradient selected.
Another embodiment of the apparatus 10 includes moving the pistons 44,52 at shorter, quicker strokes along a distance of from approximately 2-6 mm. The frequency of reversing the airflow 16 more quickly will create a vibratory action of the airflow to increase heat transfer to the products 18 without expending as much energy as moving the pistons 44,52 through their full strokes.
The apparatus 10 and method of the present inventive embodiments provides for increased efficiency for using cryogen to chill or freeze the products 18 because no energy from fans is necessary in the apparatus. The apparatus 10 being able to operate its specific temperature gradients will also contribute toward higher efficiencies. There are fewer moving parts and therefore less maintenance for the apparatus 10.
It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.