Patent Publication Number: US-2021172675-A1

Title: Nozzle structure for a quick freezer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority from Chinese Patent Application No. 201911255793.0, filed on Dec. 10, 2019. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to quick-freezing food machinery, particularly to a nozzle structure for a quick freezer having a structure similar to a shower head for improving the performance of a quick freezer. 
     BACKGROUND 
     Since there are higher requirements for the quality of quick-frozen food, blast freezers, as an efficient food-freezing device, have been widely used in the food freezing industry. Circular orifice plate nozzles are commonly used as jet nozzles of the blast freezers. However, during the operation of the freezers, the cold air passing through the nozzles has a small sectional area along a cross-flow direction, leading to a relative large frictional drag and a cross-flow impact. As a result, non-uniform freezing temperature is created in freezing areas, which directly affects the quality of frozen food. 
     SUMMARY 
     In order to overcome the defects of existing orifice plate nozzles of quick freezers, the present invention provides a nozzle structure for a quick freezer. 
     The present invention aims to design a novel nozzle structure, which can effectively increase the flow area of the cross flow, reduce the cross-flow effect, improve the heat exchange rate on the surface of the steel belt, thereby reducing the freezing time of food. 
     Specifically, provided is a nozzle structure for a quick freezer, comprising a plurality of conical diversion channels, a plurality of jet channels, a plurality of hemispherical nozzles and a steel belt; the conical diversion channels are arranged in a linear arrangement, and a distance between two adjacent conical diversion channels is 60-100 mm; a bottom of each conical diversion channel is a circle having a diameter of 45-55 mm; a height of the conical diversion channel is 20-30 mm, and a wall thickness of the conical diversion channel is 1-3 mm; a diameter of a throat of the jet channel is 30-40 mm; a height of the jet channel is 20-30 mm, and a wall thickness of the jet channel is 1-3 mm; a diameter of each hemispherical nozzle is 10-20 mm, and a wall thickness of the hemispherical nozzle is 1-3 mm; each hemispherical nozzle comprises a plurality of peripheral nozzle holes and a central nozzle hole; an angle between a center line of each peripheral nozzle hole and a center line of the central nozzle hole is 40-50°; the steel belt is located under the hemispherical nozzle, and a vertical distance between an outlet of the hemispherical nozzle and the steel belt is 10-50 mm. 
     In some embodiments, the distance between two adjacent conical diversion channels is 70-90 mm; the bottom of the conical diversion channel is a circle having a diameter of 40 mm; and a height of the conical diversion channel is 25 mm, and a wall thickness of the conical diversion channel is 2 mm; the diameter of the throat of the jet channel is 35-45 mm; the height of the jet channel is 25 mm, and a wall thickness of the jet channel is 2 mm; the diameter of the hemispherical nozzle is 15 mm, and a wall thickness of the hemispherical nozzle is 2 mm; each hemispherical nozzle comprises comprising the peripheral nozzle holes and the central nozzle hole; the angle between the center line of each of the peripheral nozzle holes and the center line of the central nozzle hole is 45°; the steel belt is located under the hemispherical nozzle, and the vertical distance between the outlet of the hemispherical nozzle and the steel belt is 20-40 mm. 
     In some embodiments, the distance between two adjacent conical diversion channels is 80 mm; the circle of the conical diversion channel is a circle having a diameter of 50 mm; the height of the conical diversion channel is 25 mm, and a wall thickness of the conical diversion channel is 2 mm; the diameter of the throat of the jet channel is 40 mm; the height of the jet channel is 25 mm and a wall thickness of the jet channel is 2 mm; the diameter of the hemispherical nozzle is 15 mm, and the wall thickness of the hemispherical nozzle is 2 mm; each hemispherical nozzle comprises the peripheral nozzle holes and the central nozzle hole, and the angle between the center line of each of the peripheral nozzle holes and the central nozzle hole is 45°; the steel belt is located under the hemispherical nozzle, and the vertical distance between the outlet of the hemispherical nozzle and the steel belt is 30 mm. 
     The novel nozzle structure of the quick freezer of the present invention can effectively increase the cross-flow area, reduce the cross-flow effect, increase the heat exchange rate on the surface of the steel belt, and reduce the freezing time of food. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a nozzle structure according to the present invention; 
         FIG. 2  is a perspective view from bottom of the nozzle structure according to the present invention, in which the steel belt is not shown; 
         FIG. 3  is a front view of the nozzle structure; 
         FIG. 4  is a top view of a nozzle; 
         FIG. 5  is a front view of the nozzle; 
         FIG. 6  is a sectional view of a hemispherical nozzle; 
         FIG. 7  shows a distribution of a velocity range at the nozzle outlets when the diameter of the throat of the jet channel changes; 
         FIG. 8  shows a distribution of the average Nusselt number on the surface of the steel belt when the diameter of the throat of the jet channel changes; 
         FIG. 9  shows a distribution of the velocity range at the nozzle outlets when the diameter of the nozzle hole changes; and 
         FIG. 10  shows a distribution of the average Nusselt number on the surface of the steel belt when the diameter of the nozzle hole changes. 
     
    
    
     In the drawings:  1 , conical diversion channel;  2 , jet channel;  3 , hemispherical nozzle;  4 , steel belt;  11 , bottom;  21 , throat;  31 , nozzle hole;  311 , peripheral nozzle hole;  312 , central nozzle hole. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention is further illustrated as follows with reference to the accompanying drawings, from which the operation process and characteristics of the present invention will be easy to be understood. 
     This embodiment illustrates a nozzle structure for a quick freezer, comprising a plurality of conical diversion channels  1 , a plurality of jet channels  2 , a plurality of hemispherical nozzles  3 , and a steel belt  4 . The conical diversion channels  1  are arranged in a linear arrangement, and a distance S between two adjacent conical diversion channels  1  is 80 mm; δ is a thickness of the nozzle structure; a bottom  11  of the conical diversion channel  1  is a circle having a diameter D 1  of 50 mm, and a height H 1  of the conical diversion channel is 25 mm and a wall thickness of the conical diversion channel is 2 mm. A diameter D 2  of the throat  21  of the jet channel  2  is 40 mm, and a height H 2  of the jet channel is 25 mm, and a wall thickness of the jet channel is 2 mm. A diameter of each hemispherical nozzle  3  is 15 mm, and a wall thickness of the hemispherical nozzle is 2 mm, and each hemispherical nozzle comprises five nozzle holes  31  comprising peripheral nozzle holes  311  and a central nozzle hole  312 . D 3  is a diameter of each nozzle hole. An angle θ between a center line of each peripheral nozzle hole  311  and a center line of the central nozzle hole  312  is 45°. 
     The steel belt  4  is located under the hemispherical nozzles  3 , and a vertical distance between an outlet of the nozzle structure and the steel belt is 30 mm. One end of the jet channel  2  having the throat  21  is connected with one end of the conical diversion channel  1  far away from the bottom of the conical diversion channel, and the other end of the jet channel  2  is connected with an end of the hemispherical nozzle  3  having a cross section of the hemispherical nozzle of a larger diameter. 
     An impacting freezing test bench is used as a model in this embodiment. The size of the plenum chamber is 400*400*600 mm, and the size of the orifice plate is 400*400*2 mm.  FIG. 1  is a schematic diagram of a nozzle structure for a quick freezer. The nozzle structure includes the conical diversion channels, the jet channels and the hemispherical nozzles. Each hemispherical nozzle has five nozzle holes, and the central nozzle hole  312  is perpendicular to a surface of the steel belt, and an angle θ is formed between each peripheral nozzle hole  311  and the central nozzle hole  312 . In this embodiment, air is used as the fluid, and the following assumptions are made: (1) air is an incompressible fluid; (2) during normal operation of the model, the internal flow field is in a steady state; (3) the wall of the plenum chamber is thermal-insulating. A k−ε turbulence model is used in the model. Due to the temperature change during the impacting, the energy equation is used. The pressure inlet boundary condition is P in =250 Pa, and the pressure outlet boundary condition is P out =0 Pa. The inlet temperature of the frozen area is set to 230 K and the outlet temperature of the frozen area is set to 235 K. The conveyor belt is treated as the steel belt, and the thermal conductivity thereof is 16.3 W/(m*° C.). 
     1. The diameter D 2  of the throat  21  of the jet channel  2  is changed while other structural parameters of the nozzle structure for the quick freezer remain unchanged. 
     Research shows that the position under the nozzle hole  31  has the highest heat transfer coefficient. When the diameter D 2  of the throat  21  is smaller, the distribution of Nusselt number at the surface of the steel belt is more concentrated. As the diameter of the throat  21  increases, the distribution of Nusselt number at the surface of the steel belt  4  becomes more and more dispersed, and the heat transfer coefficients of positions under the inclined peripheral nozzle holes  311  become smaller and smaller. 
       FIG. 7  shows a distribution of velocity range at the nozzle outlets with different diameters D 2  of the throat of the jet channel. It can be seen that when the diameter D 2  of the throat  21  increases while the inclination angle of the peripheral nozzle holes  311  remains unchanged, a straight-line distance H 3  between a center of an outlet of the peripheral nozzle hole  311  and a center line of the central nozzle hole  312  increases, and the distribution of the velocity range of the five nozzle holes  31  becomes more and more dispersed. When the diameter D 2  of the throat  21  is appropriately increased, the acting area of the impacting jet on the internal flow field increases, so the velocity at the outlet of the hemispherical nozzle  3  increases, resulting in an increase in the average Nusselt number on the surface of the steel belt  4 , thereby enhancing a heat exchange effect on the surface of the steel belt  4 . 
     As the diameter D 2  of the throat  21  continues to increase, the distribution of the velocity range of the five nozzle holes  31  becomes more and more dispersed, and the force of the jet impacting on the internal flow field is dispersed, so that the advantages of the jet impacting is not shown, causing the velocity at the outlet of the hemispherical nozzle  3  to decrease. Therefore, the average Nusselt number on the surface of the steel belt  4  is reduced, and the heat exchange effect on the surface of the steel belt  4  is reduced. 
       FIG. 8  shows a distribution of the average Nusselt number on the surface of the steel belt with different diameters D 2  of the throat of the jet channel. It can be seen that the average Nusselt number on the surface of the steel belt  4  reaches the maximum value when D 2 =40 mm, while other structural parameters of the nozzle structure for the quick freezer remain unchanged. 
     2. The diameter D 3  of the nozzle hole  31  of the hemispherical nozzle  3  is changed while other structural parameters of the nozzle structure for the quick freezer remain unchanged. 
     Based on the numerical simulation, it is found that when the diameter D 3  of the nozzle hole  31  is small, the distribution of the Nusselt number on the surface of the steel belt  4  is concentrated. With the increase of the diameter of the nozzle hole  31 , the Nusselt number in the upstream area (that is, the left side area) of the surface of the steel belt  4  decays, and the heat transfer peak of the jet center gradually moves downstream. 
       FIG. 9  shows a distribution of velocity range at the outlet of the hemispherical nozzle  3  with different diameters D 3  of the nozzle holes  31 . It can be seen that proper increasing in the diameter D 3  of the nozzle hole will increase the mass flow rate of the impacting jet, so the Nusselt number on the surface of the steel belt  4  will increase, resulting in a better heat transfer effect. As the diameter D 3  of the nozzle holes  31  continues to increase, the upstream area away from the pressure outlet will have a greater frictional drag, and the outlets of the nozzle holes  31  have a lower velocity. As a result, the Nusselt number on the surface of the steel belt  4  will be smaller, resulting in a poor heat transfer effect. 
       FIG. 10  shows the distribution of the average Nusselt number on the surface of the steel belt with different diameters D 3  of the nozzle holes  31 . It can be concluded that the average Nusselt number on the surface of the steel belt has the maximum value when D 3 =15 mm under the condition that other structural parameters of the nozzle structure for the quick freezer remain unchanged. 
     Numerical simulation is carried out for the frozen area of the quick freezer, and the simulation results show that: with the same outlet area of the hemisphrical nozzle  3 , the average Nusselt number on the surface of the steel belt  4  of the hemisperical nozzle  3  of the quick freezer is 282.39. The average Nusselt number of positions under the conventional circular nozzle on flat profile plates is 255.64. It can be seen that the average Nusselt number of the nozzle structure of the quick freezer has increased by about 10.4% compared with the conventional circular nozzle. Such structure can greatly increase the flow area at the cross-flow direction and reduce the cross-flow effect. 
     The present invention provides the nozzle structure for the quick freezer, which can effectively increase the flow area at the cross-flow direction, reduce the cross-flow effect, increase the heat exchange rate on the surface of the steel belt, and reduce the freezing time of food. 
     The above-mentioned embodiment is only intended to illustrate the principle and uses of the present invention, and its description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present disclosure. It should be pointed out those of ordinary skill in the art may further make a plurality of variations and improvements without departing from the concept of the present invention, and these all pertain to the protection scope of the present invention. Therefore, all equivalent modifications or changes made by those ordinary skill without departing from the spirit and technical ideas of the present invention shall fall within the scope of the appended claims of the present invention.