Farm Milk Coolers

Milk chilling means cooling the milk below 4 o C at production and collection centers so that to preserve the quality as produced until it is transported and distributed.The equipment used for initial chilling/ cooling of milk depends on variety of variable factors such as quantity of milk, availability of chilling facilities etc. In general the milk chilling at production farm or collection centre can be done in two ways i.e.

1. Can cooling

2. Bulk milk cooling

These methods are described in detail as follows:

i. Can Cooling

In this method, the milk is stored in cans after milking at production centre. The milk remains in cans until it is used or processed. These cans are cooled by any of the cooling methods as described below:

a) Use of ice-chambered non-insulated cans

The cans are of special type in which the milk is filled in the inside chamber and ice cubes are filled in the outside chamber. The temperature of ice is 0 o C, less than that of milk. So, it absorbs heat of milk through the wall of inside chamber and cools it. While cooling the milk the ice melts and changes into water. As the cans are non-insulated to the atmosphere, the cooling loss to the atmosphere is high. The method requires supply of ice and large space for storage of cans. This method is not so commonly used because wastage of ice is more.

b) Immersion of milk cans in chilled water insulated tank

In this method, there is an insulated metallic tank . Insulated means, any type of insulating material is applied on the outside surface of tank. The insulated material reduces to a large extent the transfer of heat from surrounding to the cold tank and thus reduces considerable cooling loss to the atmosphere.

The tank is filled with chilled water and the cans are placed in water such that the water level remains at the neck of cans. The chilled water will chill the milk by absorbing heat of milk in cans through the wall of can. The chilled water can be available naturally in cold regions or the chilled water may be formed by putting ice blocks in water. Ice blocks can be purchased from market. Here the rate of cooling is slow. But the method avoids the use of separate refrigeration machine/equipment.

c)Immersion of milk cans in a chilled water insulated tank with separate refrigeration unit

This method is generally used in large dairy farms where quantity of milk produced is large. In this method, there is an insulated tank, which is filled with water . At the top of tank a small refrigeration unit is placed consisting of a hermetic compressor and an air-cooled condenser. The evaporator coil connected to the condenser via a capillary tube is dipped in water in the tank. The milk cans are placed in the water within tank.When refrigeration unit runs, the evaporating coil cools the water. An agitator fitted in the tank circulates the chilled water around the cans. The agitator increases the heat transfer and decreases the chilling time. In this way, the milk placed in the cans is chilled. This is a very efficient method. But it is also costly due to power consumption by the refrigeration unit.

d) Immersion cooler with a refrigerating unit

It is the most compact, fast and effective method of milk can cooling. In this method, there is a small capacity hermetic compressor and air-cooled condensing unit. The condenser is connected to a specially designed evaporator through a capillary tube. The evaporator is a double wall hollow cylinder, which can be directly dipped in the milk can. Inside the cylindrical jacket between the two walls, the refrigerant expands and evaporates and absorbs heat from the milk through walls of evaporator. An agitator fixed in the hollow space of cylindrical evaporator increases the speed of cooling. A thermostatic control switch automatically switches off the compressor when milk is chilled up to required temperature. In this way, immersion cooler is easy to operate and works automatically. It is generally preferred where the power is easily available. This type of cooler is very convenient for use in small farms having power supply facility as it does not need water for cooling, easy to operate and maintain and is automatic in operation.

e) Surface Coolers

These are generally used when production of milk is high in individual farms or when collection center is established to collect the milk produced by small farmers.In this system, as shown in fig.6.4 a tubular type of cooler is mounted on a stand at a sufficient height such that below it a milk-can can be placed. Above the tubular cooler there is a milk distribution trough and below is the collection trough. The tubular cooler is cooled up by flowing chilled water through the tubes or by directly using it as evaporator coil of a refrigeration unit. When milk falls from distribution trough over the surface of tubes it gets chilled and collected in the collection trough.From the collection trough, it is directly taken in a milk can placed below. In this way, it is a continuous process and as the unit runs, milk is continuously chilled.

i. Bulk Milk Cooling

When the production of milk at one time of milking in a dairy farm is in thousands of litres, the bulk milk coolers can be used. These are easy to clean and wash and remain hygienic in use. The construction of bulk milk chiller.There is a huge size bulk milk tank fabricated of alloy steel. This tank is permanentlyCooling Systems for Milk and Milk Products fixed in an outer metallic tank insulated from outside. In the bottom space left between inner milk tank and outer metallic tank, the evaporator coils made of copper are placed. A thermostatic expansion valve is generally used with the evaporating coils. The compressor and condensing unit is placed nearby at a suitable place. Water is filled in all the space left between milk tank and outer tank. When the compressor runs, the refrigerant flowing through evaporating coil evaporates and absorbs heat from the surrounding water. Thus the water gets chilled and even some ice formation takes place around the coil. This chilled water is spread over the outer surface of milk tank top by chilled water pump for better heat transfer.

In this way, the chilled water circulates around the inner milk tank and cools the milk filled in. At the top of milk tank, an agitator motor is fixed which rotates the agitator in milk through an elongated steel shaft. The agitator is also made of steel.When agitator rotates, it circulates the milk along the inner surface of tank and increase heat transfer. The refrigeration unit works automatically and stops when there is sufficient quantity of ice and chilled water outside the milk tank. Due to ice, cooling of milk continues even when refrigeration unit i.e. compressor is not running.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.


Most Reading