Views: 15 Author: Site Editor Publish Time: 2019-09-27 Origin: Site
Application of quick freezing equipment
The development of China's quick-frozen food started late, and its development rate is increasing annually25% or more. Even now China's annual per capita consumption is only one-tenth of that of developed countries. So there is great room for development.
With the development of the food quick freezing industry and its industrialized production, the quick freezing machine has become an irreplaceable essential equipment. At present our country28 kinds of food market access systems stipulate that quick-frozen foods, especially cooked foods, must use single-unit quick-freezing devices to ensure quality, and exporter inspections also have requirements.
This article explores why quick freezers are irreplaceable in the food industry, what are the differences between quick freezers and traditional quick freezers, how to choose a suitable quick freezer, how to meet the needs of many different foods and different processing technologies, and the direction of further development of quick freezers , And what kind of energy-saving and intelligent quick-freezing opportunities bring benefits to quick-freezing production enterprises.
I. Factors affecting quick freezing of food
When food freezes at an hourIn the case of 5-50 mm thickness, it can ensure that the number of ice crystals generated during the food freezing process is basically unchanged, and the grains are relatively small.To achieve the reversibility of freshness。
Food contains two kinds of water, one is free water, and its ice crystal formation stage is in0 to -5 degrees, a colloid-bound water, which adheres to the surface of food molecules. When frozen products are at -18 degrees, the crystallization rate is above 95%. In addition, storage of food under low temperature after ice crystallization inhibits microbial activity and reproduction, and achieves the purpose of long-term storage and preservation (fruits and vegetables inhibit respiratory heat).
The influencing factors of food quick freezing can be divided into:
1.Cooling medium temperature: food freezing speed and temperature difference between freezing point and cooling mediumΔt is directly proportional. The lower the temperature of the cooling medium, the faster the freezing speed.
2.The impact of frozen products on the wind: the surface area, wind speed, and cold air circulation rate affect the freezing speed: tests show that green beansIt takes 120 minutes at 0 wind speed under -30 degree cooling medium, and only 10 minutes at 4.5 m / s wind speed.
3.Influence of Latent Heat and Enthalpy Difference:It takes 80kcal to reduce 1kg of water from 80 degrees to 0 degrees, and it also requires 80kcal to change from 0 degrees water to 0 degrees ice. It can be seen that the latent heat of crystallization requires more cooling capacity. Similarly, when the enthalpy difference is large, such as a higher stock temperature, not only a larger amount of cooling capacity but also a longer freezing time is required.
4.The effect of food ingredients: Foods with high thermal conductivity freeze faster than foods with low thermal conductivity. If the plastic film on the surface of the food not only conducts heat slowly, it also hinders the wind. If the thermal conductivity of water is0.604w / mk, thermal conductivity of fat is 0.15, thermal conductivity of plastic film is 0.028, and thermal conductivity of wind is 0.066.
5.Effect of food thickness: The square of food thickness is directly proportional to the freezing time. Thicker foodThe longer the quick freezing time.
Second, the transition from quick-freezing warehouse to quick-freezing machine
From the factors that affect food freezing:
Due to the large number of goods received at one time when the door is opened, the temperature of the cooling medium rises and fluctuates due to the relatively high temperature of food.Δt; while the freezer keeps the room temperature almost unchanged.
Due to the placement of static food in the freezer, the non-uniformity of the wind is generated, and even the wind speed is reduced. The static unidirectional blower hinders the crystallization speed of the frozen product center, which is the winded part. It is large and uniform, and freezes more quickly due to changes in wind direction.
Since the food entering the quick-freezing store reaches the latent heat at the same time, it is necessary to suddenly and greatly increase the cold capacity to face the crystallization process, which will cause the temperature to rise and extend the crystallization time. However, the continuous operation of the quick freezer allows only a relatively small part of the originally frozen storage capacity to reach latent heat in succession, and its cooling capacity is sufficient to complete the rapid crystallization process at a stable temperature and speed.
It can be seen that the quick freezing machine is indispensable for the pursuit of a rapid food crystallization process to achieve a reversible food preservation effect.
Classification and characteristics of quick freezers using air as a cooling medium
①Flat mesh belt quick-freezer: suitable for meat, prepared food, aquatic products, dishes, ice cream, etc. It is a basic universal quick-freezer. Its output is100kg / h—2000kg / h.
②Multifunctional vibrating mesh belt quick-freezer: Dynamic device is added on the basis of universal flat mesh belt single-type freezer. In addition to the characteristics of a universal flat mesh belt type single-type freezer, it is also suitable for freezing frozen granular food.
③Tunnel pre-cooling and quick-freezing machine: creatively combine pre-cooling and quick-freezing into one to save energy. It is especially suitable for high-temperature purchases and cooked foods with rapid cooling.
④Tunnel-type impact mesh belt quick-freezer: It is suitable for products with a small floor area and a long freezing time.
2) Spiral Quick Freezer:
①Single spiral quick-freezer: suitable for meat, prepared food, aquatic products, dishes, ice cream, etc. Small footprint and high efficiency. The inlet and outlet are low input high output or high input low output.500-1500kg / h.
②Double Spiral Quick Freezer: Suitable for meat, prepared foods, aquatic products, dishes, ice cream and other frozen foods with long freezing time or large output. The inlet and outlet can be provided in various directions by the user's workshop process requirements; the inlet and outlet are low in and low out. Yield in1000-3000kg / h.
3) Fluidized Quick Freezer:
①Fluidized single-unit quick-freezing machine: bottom blowing type. The frozen product freezes during the drifting process , Suitable for fruits and vegetables, granular food, etc. Yield in100-3000kg / h.
②Surface layer fluidized single-type quick-freezing machine expands frozen varieties and saves energy. Creativity combines fluidization and tunnel freezing. The freezing effect is excellent.
③Fluidized monomer pre-cooling and freezing machine. Pre-cooling function is added on the basis of fluidized single-unit freezer.
4) Stepping quick-freezer:
①No power supply for transmission, quick freezing on stepping track, easy operation by gravity using dynamic and static friction to avoid running cold.
②Suitable for quick-frozen food, ice cream, bulk food, bag-in-box food.
Fourth, the energy-saving, reliable, reasonable and intelligent quick freeze machine
Food freezing speed and temperature differenceΔt is directly proportional. The pursuit of low temperature in the freezer is for rapid crystallization of food, and the set temperature is -35 degrees. Therefore, the nearer the freezing temperature of the food is, the faster the food freezes. The higher temperature before crystallization is left for the pre-cooling section to complete, so as to achieve the purpose of high-quality quick freezing and energy conservation. In addition, the approaching freezing temperature is the key to reducing dry consumption of food.
Avoiding the cold consumption of the quick freezing machine is also to avoid the cold consumption of the splicing gap of the thermal insulation board of the envelope structure. The insulation board of the quick-freezing machine's envelope structure adopts the overall polyurethane foaming form. All the joints of the library boards are sealed with double-sided special sealant and the secondary filling foaming is used to avoid the cold running of the insulation joints.
The requirements for air volume and air speed in various quick freezers are different, and their energy saving methods are also different. Tunnel type mesh belt single-speed freezer, designed on the basis of ensuring the cooling air volumeGetsan bar-shaped adjustable diversion assembly, greatlyIncrease the wind speed on the surface of the frozen product. At the same time, it increases the surface area of the frozen product and improves the circulation rate of the wind.
In addition, the symmetrically adjustable wind direction deviceGeshan bar-shaped adjustment guideControl the cold running of cold air from the inlet and outlet. Reduce the running power of the fan motor, thereby reducing the cooling power of the fan motor (reducing wind pressure and increasing wind speed), thereby improving efficiency.
In order to reduce the mechanical transmission and conveyor belt cooling method, the mechanical transmission and conveyor belt system is kept running at low temperature, and the inlet and outlet openings are insulated to take advantage of the cold air circulated from the freezer to achieve the purpose of saving cooling.