RU2577462C2 - Method of producing icy slush - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to methods for producing icy slush using refrigeration and can be implemented in fishing, poultry and dairy industries.

Method includes pre-cooling a stream of water to a temperature close to freezing temperature, then cooling stream of water to a temperature below 0°C in channels of a heat exchanger of a nonmagnetic material while exposing stream cooling water to a magnetic field along length of channel. Water flow rate in cooled channels from non-magnetic material is selected from ratio:

where:

w - water velocity in cooling passage, m/s,

l - size of channel, m,

µ - coefficient of dynamic viscosity of water, Pa·s,

ρ - density of water, kg/m³,

Re - Reynolds number equal to 2300.

EFFECT: compared to counterparts, method enables to obtain a continuous flow of ice slush with uniform ice granules, and is characterised by minimum noise level and high energy efficiency.

2 cl, 1 dwg

Description

The invention relates to refrigeration, in particular to methods for producing ice-containing pulps or suspensions, and can be used for cooling and preserving fish raw materials directly on ships in the fishing area, on dairy farms for cooling milk, as well as in the processing industry, for example, cooling carcasses chickens after slaughter, as well as in the production of sausages.

Ordinary ice water meets these requirements to the fullest extent - to obtain rapid cooling of the cooled product, its temperature should be as low as possible, i.e. have a temperature close to freezing point. However, from a technical point of view, obtaining ice water with a temperature of 0.5 ° C - 1 ° C is a rather difficult task.

Widely used flow-tight sealed shell-and-tube and plate heat exchangers in the production of ice water have limited use. This is due to the danger of destruction when negative boiling points are reached and ice water freezes inside the heat exchanger circuit. Therefore, open heat exchangers are widely used in the production of ice water.

The simplest type of open heat exchanger is an evaporator made in the form of a pipe immersed in a tank. The refrigerant boiling inside the pipe cools the liquid in the tank. To intensify heat transfer, the liquid in the tank is forcibly mixed either with a mechanical stirrer or with air, which is supplied to the bottom of the tank. This method of producing ice water also allows you to accumulate a certain amount of "cold" in the form of ice, which freezes on the surface of the evaporator.

Film evaporators - are panel evaporators in which cooling of ice water to temperatures close to zero is achieved by draining a thin layer of ice water on the surface of the evaporator. Water is supplied to a distribution tank located above the battery of film evaporators. From the distribution tank, water is uniformly supplied to vertically arranged panels having a negative temperature.

A thin layer of water flowing down the surface of the panel forms a water film, and is intensively cooled. Chilled water flows into the storage tank for subsequent supply to consumers. The temperature of ice water at the outlet of the film evaporator ranges from 0.5 ° C - 2.0 ° C. Most often, film evaporators are used in systems with a constant load during the entire cycle of equipment operation.

The disadvantage of most of these methods of producing ice water is their high metal consumption and the cyclical nature of the production of ice water.

In recent years, unconventional methods for producing ice water have been actively developed, which make it possible to obtain an ice suspension or pulp. However, it is more correct to call a mixture of water and solid ice particles a sludge, since these are two different aggregate states of the same substance - water.

du comportement thermique et

, International Journal of Refrigeration, vol. 22, pp. 175-187].A known method of producing an ice-containing suspension, according to which the saline solution is cooled until water ice is formed on the inner surface of the evaporator generator, is made in the form of a horizontal cylindrical pipe, on the outside of which a pump is pumped with a coolant having a temperature below the solution crystallization point. The formed water ice is removed by means of a screw from the heat exchange surface to the storage tank. In the storage tank, crushed ice is mixed with the liquid phase of the initial solution to the state of an ice-containing pulp, which is then pumped to the storage tank [Bel O., Lallemand A., 1999, Etude d′un fluide frigoporteur diphasique - 2: Analyse

du comportement thermique et

, International Journal of Refrigeration, vol. 22, pp. 175-187].

The main disadvantage of this method is that the ice layer released on the heat exchange surface of the evaporator generator is a thermal resistance that impedes the passage of heat from the crystallizing solution to the refrigerant. A device that removes ice from the heat exchange surface has a limited service life, because ice has high strength and roughness. In addition, the rotation of the device requires energy reaching 10% of the energy required to drive the compressor of the refrigeration unit, which removes heat from the crystallizing solution.

There is also known a method of producing an ice-containing pulp by cooling sea water to form water ice. Water ice is frozen on the vertical surface of the generator-evaporator, made in the form of a plate and having a temperature below the cryoscopic point of the solution. After the formation of a thin layer of water ice on the surface of the evaporator plate, the boiling of the refrigerant in the evaporator ceases and hot steam is supplied to the evaporator cavity, which leads to the fall of the ice layer into the storage tank. In the storage tank, ice is destroyed by a mechanical type device and mixed with the liquid phase of the initial solution to the state of an ice-containing pulp, after which the pulp is pumped to the storage tank (“A METHOD AND APPARATUS FOR PRODUCING HOMOGENOUS FLUID ICE.” WO / 2004/081469. Priority date 03/10/2003 Authors: ARNASON, Ingolfar; SIMONSSEN, Johannes; KRISTJANSSON, Theodor).

The disadvantage of this method is the high specific energy consumption for obtaining an ice-containing pulp. A mechanical type device for breaking ice and mixing it with the liquid phase of the initial solution to a pulp state is difficult to operate and has a high cost, and also requires high energy costs for its drive, which reach 10% of the compressor's cooling capacity.

There is a method of producing ice-containing suspensions, which consists in isolating the solid phase from vacuum water or aqueous solutions of various salts (NaCb, CaCl ₂ ), and layer-by-layer freezing of individual portions of the liquid phase (Marinyuk B.T. Vacuum-freeze-drying apparatus for producing water ice. - Refrigeration, 2008, No. 3, p. 36).

The author of the method emphasizes its main advantage over the traditional ones: "ice formation occurs practically on the water-vapor interface and the thermal resistance of a layer of water ice does not adversely affect the intensity of its formation." However, the increased thermal resistance to heat flow leads to the need to increase the temperature head between the media involved in heat transfer, which entails an increase in energy consumption.

Known RF patent No. 2475684 "Method for producing ice-containing pulp", author Lapshin V.D. In it, an ice-containing pulp is obtained by cooling sea water to form a pulp, when liquid CO ₂ is introduced into sea water in a ratio of 1: 1.6 at a temperature of minus 2 ° C under a pressure of 3.3 MPa, with its subsequent removal when the pressure drops to 0 , 1 MPa to the storage tank. The method is very promising, however, it can be implemented only for a given volume of ice water, i.e. The disadvantage of this method is its cyclical nature.

One of the ways to obtain ice water is to freeze sprayed water droplets in a stream of air or low temperature evaporating refrigerant. Such a method for producing a stream of ice granules is described in the invention patent No. 2077683 by V. Bulimov, authors. et al., publication date 04/20/1997, it provides for mixing a gas stream and jets of refrigerant with its partial evaporation and spraying a liquid in the form of a torch of fine droplets. A mixture of the first two components is blown over the torch of the third component with the formation of a stream of ice granules. The disadvantage of this method is its aerodynamic noise.

As a prototype of the solution proposed by the authors, the patent SU No. 1483211 A1, publ. 05/30/1989, authors S.K. Dymenko et al. “Method for producing ice sludge”, MKI F25C 1/16. This method of producing ice sludge involves cooling water by evaporating its vapor from an open surface under vacuum, desublimating liquid vapor on the surface of the desublimator to be cooled, removing ice from the surface of the desublimator due to vibration and mixing the resulting sludge with a mixer to increase the uniformity of the phase composition in the sludge. Due to a number of disadvantages, this method has a limited scope, mainly in periodically operating experimental plants, where the issues of energy efficiency and noise characteristics do not play a decisive role. The main disadvantage of the prototype method is the low energy efficiency of producing sludge, since the method of its production uses vacuum pumps for surface cooling of water, which requires the use of powerful vacuum pumps, and as you know, vacuum pumps are always characterized by high energy consumption. Another disadvantage of this method is the increased noise from the operation of vibrators. In addition, the use of a mechanical mixer does not allow to obtain high homogeneity of the sludge.

The aim of the invention is to eliminate these drawbacks, namely, obtaining ice slurry with small uniform ice crystals, as well as improving energy efficiency and reducing noise when implementing the proposed method.

This goal is achieved by the fact that in the method of producing ice sludge, including cooling water, pre-cooling the water stream to a temperature close to its freezing temperature, subsequent cooling of the water stream to a temperature below 0 ° C is carried out in the channels of the heat exchanger from a non-magnetic material with exposure to this is the flow of cooled water by a magnetic field along the entire length of the channel, while the speed of the water flow in each channel of non-magnetic material is selected from the ratio

Where:

W is the water velocity, m / s,

l is the size of the cooled channel, m,

µ is the coefficient of dynamic viscosity of water, Pa · s,

ρ is the density of water, kg / m ³ ,

Re - Reynolds criterion equal to 2300.

The basis of the proposed method uses the results of a study of Japanese scientists and inventors Norio Osada and Kurita Satoru obtained in the study of stationary liquids. In 2006, these Japanese inventors working in the field of food freezing received the Russian patent No. 2 279 407 “Method for quick freezing and installation of quick freezing”, MKP F25D 13/00, A23L 3/36, patent holder by ABI Limited (Japan). This technology is described, in addition to the patent itself, in the article “CAS-freezing - science fiction or reality?”, Refrigeration Business Magazine, No. 2, 2009, p. 12-16, in the article "From the Preservation of Products to the Preservation of Human Organs ... The Revolutionary Freezing System - Cells Alive System is Improving" in the magazine Refrigeration Business, No. 8, 2011, p. 10-12, in the article “CAS-freezing saves people teeth. Other authorities are next in turn ”in the magazine“ Refrigeration Business ”, No. 8, 2013, p. 22-24., As well as in foreign journals Journal of Criobiology, Forbes Magazine and Journal of Biomedical Research.

ABI has developed a way to freeze food products that changes the physics of the process itself. Japanese authors have proposed using the traditional effect of a cold environment on the product while simultaneously exposing the product to an electromagnetic field containing water. The use of electromagnetic oscillations causes water molecules to rotate around their own axis (in contrast to vibrations, as in a microwave oven), which prevents their clustering (splicing) and the formation of ice crystals that damage cell walls. This rotation of the molecules also lowers the freezing point of water to about -7 ° C. When the product, including water, reaches this temperature, the electromagnetic field is turned off and freezes through almost instantly. At international exhibitions, in articles and videos, the authors demonstrated how their proposed method of freezing prevents the formation of ice crystals when freezing a glass bottle filled with water. The water level has remained unchanged, the glass is intact, and the water is clean. At the same time, CAS technology uses 30% less energy than conventional freezers, and acts several times faster, depending on the type of product. However, the authors only cool a fixed, fixed volume of liquid in the product being cooled, limited by the walls of the refrigerator. In this case, the product is placed in the refrigerator compartment with a temperature significantly higher than the freezing temperature of water.

The conducted patent studies have shown that the set of distinctive features characterizing the proposed technical solution is unknown to the authors, which allows us to conclude that the method for producing ice slurry meets the criterion of "significant differences".

The technical result when using the proposed method for cooling a liquid medium is achieved due to the fact that, unlike the currently existing similar methods, it has the following positive properties:

- pre-cooling the water to a temperature close to the freezing point, allows you to reduce the size of the heat exchanger with cooled channels and reduce energy costs for creating a magnetic field. The amount of cold required to cool the water below its freezing point will exactly correspond to cooling the water flow from + 1 ° C to minus 7 ° C (in fact, this is the limit temperature to which water can be cooled in a magnetic field without visible ice crystals). If you cool water in this heat exchanger with an initial temperature of + 18 ÷ + 20 ° C, then the dimensions of the heat exchanger, the energy consumption for creating a magnetic field along the cooled channels, as well as the cost of cold for cooling water to a temperature of minus 7 ° C will increase several times;

- the use of electromagnetic oscillations causes water molecules to rotate around their own axis, which prevents their clustering (adhesion to each other) and the formation of ice crystals. This rotation of the molecules artificially lowers the freezing point of water to about -7 ° C. Moreover, when the magnetic field ceases to interact with water, the water freezes almost instantly. Therefore, at the exit from the cooling tubes, the magnetic field ceases to affect water and it turns into small ice crystals. Varying the magnitude of the magnetic induction, the flow rate of the cooled liquid, and also the final temperature to which the water is cooled in the cooled channels (from -2 ° C to -7 ° C), an ice slurry with a different percentage of the proportion of water can be obtained at the outlet of the channels and its frozen particles, the so-called "liquid ice".

- the choice of the flow rate of the liquid medium from the specified ratio creates a guaranteed turbulent liquid flow in the cooled channels, which sharply increases the heat transfer coefficient from the material of the cooling channels to the cooled water compared to the laminar flow, which in turn reduces the energy cost of cooling the liquid, for example, lower system cooling capacity.

The practical implementation of the proposed method will be considered on the example of obtaining ice sludge for cooling milk at the points of reception on dairy farms.

In FIG. 1 schematically depicts the implementation of the proposed method for producing ice sludge, where the numbers denote:

1 - heat exchanger from non-magnetic material

2 - cooled channels

3 - water inlet pipe

4 - refrigerant inlet pipe

5 - pipe outlet refrigerant

6 - magnetic field generator

7 - sludge-shaped ice water

8 - milk cooler

9 - capacity for chilled milk.

The proposed method is implemented as follows. Cooled water with a temperature of + 2 ÷ + 1 ° C enters the heat exchanger 1 from non-magnetic material, such as copper, with cooled channels 2 through the water inlet 3. The channels 2 are cooled by a vapor-liquid mixture of refrigerant, for example, freon R 507, which enters the heat exchanger for 1 s temperature -10 ÷ 12 ° C through the inlet pipe of the refrigerant 4 and leaving with a temperature of minus 5 ° C ÷ -7 ° C through the pipe in the outlet of the refrigerant 5. Around the side surface of the heat exchanger 1 of non-magnetic material there is a magnetic field generator 6, which produces 1 m inside the heat exchanger gnitnoe field induction value of 1500-2000 gauss. The flow of water with a temperature of + 2 ÷ + 1 ° C, entering the channels 2 cooled by freon, is cooled below the freezing point, while under the influence of a magnetic field the water flowing through the channels 2 passes into a supercooled state, the so-called “bound water”. The temperature of crystal formation in such water in a magnetic field of a certain intensity can drop to minus 7 ° C. Water, after passing through channels 2 in an electromagnetic field, is cooled to temperatures around minus 5 ÷ 6 ° C and after leaving the heat exchanger 1 and stopping the influence of a magnetic field on it, it begins to lose the properties of a supercooled state and turns into a slush-like ice water 7, consisting of shallow ice crystals and water. This sludge-like mass 7 enters the milk cooler 8, where it cools the container for cooled milk 9 to the temperature + 2 ÷ + 4 ° C necessary for storing and transporting milk.

, задав внутренний диаметр d охлаждающего канала равным 0,02 м, определим значение минимальной скорости движения жидкости, которое гарантирует турбулентный режим течения жидкости. Учитывая соотношение динамической µ и кинематической вязкости ν, определяемое формулой $$\nu =\frac{\mu }{\rho }$$

, минимальная скорость течения воды в охлаждаемом канале определяется из соотношения $$W>\frac{\mathrm{Re}\cdot \nu }{d}$$

. Кинематическая вязкость ν воды вблизи температуры замерзания будет равна ν=1,78×10^-6 м²/c, тогда значение скорости течения воды в канале должно быть не менее w=0,4 м/c. Исходя из этой скорости определяем расход воды в одном канале по формуле Q=F·W и получаем расход через один канал 125 см³/с. По паспорту на молокоохладитель требуется гарантировать расход не менее 4 м³/ч. Тогда получаем, что для обеспечения данного расхода при указанной скорости потребуется не менее 10 каналов.Considering that the total heat transfer coefficient from freon to cooled water in the channels during laminar flow will be lower than during turbulent (this is known from the theory of heat transfer), the water flow rate for heat exchanger 1 is chosen on the basis of the condition that the turbulent flow of water is observed in each cooled channel . Then from the relation $$W>\frac{\mathrm{Re}\cdot \mu }{d\cdot \rho }$$

by setting the inner diameter d of the cooling channel equal to 0.02 m, we determine the value of the minimum fluid velocity, which guarantees a turbulent mode of fluid flow. Given the ratio of dynamic µ and kinematic viscosity ν defined by the formula $$\nu =\frac{\mu }{\rho }$$

, the minimum water flow rate in the cooled channel is determined from the relation $$W>\frac{\mathrm{Re}\cdot \nu }{d}$$

. The kinematic viscosity ν of water near the freezing temperature will be equal to ν = 1.78 × 10 ^-6 m ² / s, then the value of the water flow velocity in the channel should be at least w = 0.4 m / s. Based on this speed, we determine the flow rate of water in one channel using the formula Q = F · W and obtain a flow rate of 125 cm ³ / s through one channel. According to the passport for the milk cooler, a flow rate of at least 4 m ³ / h is required. Then we get that to ensure this flow rate at the indicated speed, at least 10 channels will be required.

Thus, the main advantage of the proposed method for producing ice sludge is the maximum possible uniformity of the obtained ice granules, which are small in size, which is ensured by the action of a magnetic field on water molecules, preventing them from being grouped into large clusters. The method is practically silent in operation, which is an important advantage when used in technological workshops with working personnel present, which cannot be said about the methods for producing ice sludge using various types of vortex tubes and mechanical scraper mechanisms. Important advantages of the proposed method is its energy efficiency due to the forced creation of a turbulent flow of water in the cooled channel.

In addition, the implementation of this method allows you to create compact, simple and reliable devices for producing ice sludge in various sectors of the food and industrial industries.

Claims (2)

1. A method of producing an ice slurry, including cooling water, characterized in that the water stream is pre-cooled to a temperature close to freezing, and the water stream is subsequently cooled to a temperature below 0 ° C in non-magnetic material heat exchanger channels with the impact on the stream cooled water by a magnetic field along the entire length of the channel. 2. A method of producing an ice sludge according to claim 1, characterized in that the water flow rate in each channel from a non-magnetic material is selected from the ratio

Where:
w is the velocity of water in the cooled channel, m / s,
l - channel size, m,
µ is the coefficient of dynamic viscosity of water, Pa · s,
ρ is the density of water, kg / m ³ ,
Re - Reynolds criterion equal to 2300.

Images