1 Refrigerating System. Liquid coolers

seobrand@gmail.com (Administrator) — Fri, 21 Jan 2011 17:14:47 +0000

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Refrigerating Systems. Liquid coolers

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Shell-and-tube heat exchangers type (Fig. 3.20) are the most common form evaporating apparatus for cooling water and cooling applications. These forms are used for cooling of liquids that can be used as a secondary refrigerant or for cooling the finished product directly. In practice, these types of heat exchangers are known as liquid coolers or chillers.

Some examples of applications in the food and refrigeration industry are:

Cooling of drinking water,
The cooling water for air conditioning coils,
Cool the milk after pasteurization and
The cooling process.

Chilled water systems can be used with flooded evaporation or direct expansion evaporator, which is usually a shell-and-tube heat exchangers. In the flooded evaporator refrigerant filled shell side of the heat exchanger and controlled valve. The water cooled passes through the tubes. On the contrary, in direct expansion evaporator, water is carried in the shell and the refrigerant is cooked inside the tubes. The speed of the flow of refrigerant do not have resources to ensure that only REFRIGERANT gas outlet of the evaporator.{loadposition banner2} Copper tubes are mounted in a carbon steel shell is the most common structure used for chilled water vaporizers.

It is important to note that if the refrigerant evaporates on the outer surface of pipes of the flooded evaporator cooler; if it vaporizes inside the tubes evaporator dry cooler (note that in this more General type, a mixture of liquid and vapor completely evaporated, as a rule, with some degree of overheating (Hewitt et al., 1994). In a flooded water cooler or in brine is distributed through pipes, which, as a rule, finned, to ensure the growth of the heat transfer rate and a decrease in the evaporator size. In a dry cooler liquid refrigerant contained in the pipes, and water, or in brine distributed through the shell of the cooler, which serves as an evaporator. Flooded coolers are often specified for applications where the shell side of the evaporation of the coolant other liquids, preferably. Due to a rapid boil in a shell, in order to obtain high purity pair, separation vessel often welded to the main shell. Flooded refrigerators, especially those in several compressor units.

Thermal storage

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:51:23 +0000

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Thermal storage

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Phase change materials (PCMs) for thermal storage are available in several forms to suit different applications. In its simplest form, the variations in the cooling load can be provided by the latent heat of fusion of ice or frozen eutec-TIC. Ice can be formed, allowing her to build up on the surface of the evaporator coil in the tank. Brines more, as a rule, are held in closed tanks or plates again condenser coils inside, the outside of the tank formation of secondary heat exchange surface. Eutectics can be formulated depending on the required temperature.

An example of alternative PCM paraffin-based material. The specific heat and latent heat paraffins is about 2.1 kJ/(KGC). They melt enthalpy lies between 120 and 160kJ/kg, which is very high for organic materials. The combination of these two values leads to high energy storage density. Therefore, the latent heat of paraffins/waxes offer four to five times higher heat capacity, by volume or mass, than in water at low temperature that the differences. They have low thermal conductivity, but also for accumulation of heat this can be overcome by introducing enough surface.

Variations have pumped liquid, such as one of glycols, and contain PCM inside the capsule into the tank.{loadposition banner2} Capsules in the form of plastic balls and PCM can be formulated to meet any required thermal storage temperature.

Associated PCMs include PCM into an existing structure. When the PCM changes in fluid inside the supporting structure, the combined action of capillary forces auxiliary materials and special multifunctional additive ensures that the PCM, even when in the liquid phase, remains within the structure. This means that he always works with the " dry " material and liquid handling problems are eliminated. Free places within associated PCMs allow volume expansion PCM to take place in the...

Phase change materials as secondary coolants

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:50:59 +0000

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Phase change as secondary materials coolants

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The pump ice slurry can be used instead of chilled water or in brine. The composition of these fluids is quite simple, consisting of water with ice crystals mixed with other liquids, such as ethylene glycol, ethanol, ammonia, NaCl. Only part of the water turns into a small crystals of ice (about 1 mm). It provides a uniform solution, while enhancing the cold transfer. Ice slurry can take advantage of the high latent heat of freezing, while retaining the ability to pump liquids for heat exchangers. Optimization is aimed at the search of the less viscous secondary refrigerant from within the available range, which has high energy efficiency.

Ice crystals can be produced by scratches the surface of the generators, which can be quite costly. Alternative methods of generation, which are being investigated. Various methods, products, and applications are given to Paul (1997, 2002).

Properties of carbon dioxide makes it very suitable for applications in the form of volatile secondary coolant. Liquid carbon dioxide of about 10C and 25-26 bar pressure can be pumped up coolers, where part evaporates.{loadposition banner2} Two-phase mixture is returned to the reservoir, where it is separated. In conventional refrigeration circuit maintains the pressure at the corresponding temperature of saturation.

Liquid carbon dioxide has a very low viscosity; and because of its high latent heat, the amount to be distributed is very small compared with any water-based solutions. Carbon dioxide exhibits a high boiling heat transfer coefficient, which contributes to the design of the coolers. Such a system is applied in supermarkets for medium temperature refrigeration. She also has significant potential in air conditioning systems (Pearson, 2004).

Secondary coolants

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:50:34 +0000

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Secondary coolants

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Where a secondary refrigerant is circulated and working temperatures below 0C, some forms of non-stop mix should be used. Aqueous solutions of sodium chloride and calcium chloride were the first type of sub-zero secondary fluid, and therefore the collective term is sometimes used brine. Propylene glycol-water mixtures of the most widespread glycols used as secondary refrigerants in the refrigeration and allowed where contact with food is possible. Ethylene glycol is a different type and there are many other products on the market, some of which do not contain water. Thermophysical properties of Propylene glycol-water mixtures are shown in Fig. 12.1 .

Any decision will be one of concentration that remains liquid, until it reaches the freezing point, and then it will freeze. This eutectic mixture, and its freezing point-eutectic point of dissolved substances (see Fig. 12.2). On all other concentrations, as the solution is cooled, it will reach the temperature at which the excess of water or solution, will crystallize out to form a slushy suspension rigid body in a fluid, until the eutectic point is reached when all freeze.{loadposition banner2} For the economy of costs and reduce viscosity (and so improve heat transfer), decision weaker than eutectic are used, as a rule, in the absence of a risk of freezing in the evaporator.

The concentration of the dissolved substance renders significant influence on the viscosity of the fluid, and on the surface convective resistance to heat flow. There is little data published on these effects, so that applications should be checked from basic principles.

Brine can be injected for each of the cooling device, and control the flow through disable or bypass valves to maintain the required temperature (see Fig. 12.3). Brine pump, as a rule, in the return pipe for cooling, as shown in the figure, so the pumping rate is based on the return temperature, density.

Where the brine system services license temperature for example, a number of food shops, coolant can be too cold for some conditions, causing dehydration product. In such cases, to cool these rooms brine to be mixed. Private three-way mixing valve and the pump will be required for each room (see Fig. 12.4).

with the divided tank, as shown in Fig. 12.4. except that the tank will be, with separate feed and expansion tank. To reduce the effects of corrosion inhibitors are added, as a rule, chlorate sodium salts of sodium and phosphates in glycols. These alkaline salts and counteract the effects of oxidation, but periodic inspections shall be taken, and the Boers or similar alkali is added if the pH falls below 7.0 or 7.5.

Brines hygroscopic and will weaken the absorbing atmospheric moisture. Checks should be made on the strength of the solution and more salt or glycol is added as necessary to maintain the freezing temperature to the desired value.

Ice manufacture

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:50:13 +0000

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Ice production

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Ice storage goes back to the earliest days of low temperature preservation, storage winter ice was used. Mechanical cooling was subsequently introduced to the ice and it will be transported to the place where the cooling effect was necessary. Refrigeration energy contained in this path, mainly its latent heat of melting, 334 kJ/kg, as it changes back to the water.

Today ice is used in some industries, such as fishing vessels, and as a heat carrier data. Small icemakers generate ice for drinks and food displays. Ice can be made as thin plates on the surface of the evaporator drums, and removed mechanically with the correct thickness formed: either drum or a scraper can rotate. It is a continuous process and ice flakes fall directly on the product or in the bunker under the car.

Smaller units are in the form of packages, bin integral and is cooled by a few turns of the suction line or individual evaporator. Small pieces of ice can be formed or pipes or other prismatic forms, as evaporator pipe positioned vertically. Surface water is being pumped freeze, height or shape you want. The tube is then switched to 'defrost' and stucco section thaw enough to slide off, perhaps, chopped into small pieces, milling rotation. The machine is made in the form of a package, and the smaller sizes will include condensing unit...

Baudelot coolers and ice bank coils

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:49:38 +0000

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Baudelot coolers and ice Bank coil

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Water can be cooled safely near the freezing point, evaporators with the help of which the refrigerant inside, with a place for ice to form on the outside surface without causing damage. Two types:

Baudelot coolers . The evaporator is above the tank, and the water flows down on the outer surface of a thin layer. Evaporator construction can be coils or plates, stamping. The latter, as a rule, of stainless steel to prevent corrosion. Evaporators can be flooded with water or direct expansion. During operation Baudelot cooler can sometimes create a thin layer of ice, but it does not cause damage to the evaporator, and should melt off again when the load changes.
Coils in a water tank. As flooded and direct expansion evaporator used. Water is circulated by pumps and/or special agitators. This type of cooler water can be operated without the formation of ice, or ice can be allowed to accumulate intentionally (see below).

Water chillers of these two types, as a rule, is not listed as one packages with their condensing unit, with the bulk of the system and subsequent complexity of installation works..

Distributed Cooling, Thermal Storage

seobrand@gmail.com (Administrator) — Wed, 08 Sep 2010 12:48:11 +0000

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Distributed Units, Heat Storage

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Building or process, the presence of large numbers separated cooling, could cooling system for each of these workloads, but it is usually more convenient to concentrate cooling in one factory. The cooling effect of the Central refrigeration system can be distributed by thermal transfer fluid or secondary refrigerant. Where the operating temperature is always above 0C, such as air conditioning, water is commonly used. At temperatures below this, non-freezing liquids are used.

Internal use of thermal storage are very familiar. Ice cubes are used for chilling drinks. Plastic containers holding " phase transition frozen material, placing them in a domestic freezer Cabinet. Once frozen, they can be used for short-term storage for cold food and drinks.

I n commercial use, thermal storage is used to smooth cooling, or take advantage of the peak electricity rates. It can be used to make them available to a large cooling capacity is limited plant size and typical applications include:

To make ice for several hours and then use ice water for cooling of the party of warm milk at the dairy farm.{loadposition banner2} It is also used in the main vegetable oil, to reduce peak electricity load. Water is very close to freezing point, which is the ideal temperature for the cooling of milk.
Start of the refrigeration and heat pump systems in the night, or at another time when electricity is cheaper. It is also used in areas where the electricity supply is unreliable. Where cold water is to be used at high temperatures, for example, in air-conditioning, circuit requires three-way mixing valves.
How to hold the cooling plates of transport.