Refrigeration

Refrigeration

Refrigeration may be defined as the process of achieving and maintaining a

temperature below that of the surroundings, the aim being to cool some product or space to the required temperature.

Multiple Choice

Which of the following can be called as a refrigeration process?

• Cooling of hot ingot from 1000oC to room temperature

• Cooling of a pot of water by mixing it with a large block of ice

• Cooling of human beings using a ceiling fan

• Cooling of a hot cup of coffee by leaving it on a table

Multiple Select

The disadvantages of natural refrigeration methods are:

• They are expensive

• They are uncertain

• They are not environment friendly

• They are dependent on local conditions

Multiple Choice

Evaporative cooling systems are ideal for:

• Hot and dry conditions

• Hot and humid conditions

• Cold and humid conditions

• Moderately hot but humid conditions

Natural Refrigeration

In olden days refrigeration was achieved by natural means such as the use of ice or evaporative cooling. In earlier times, ice was either:

1. Transported from colder regions,

2. Harvested in winter and stored in ice houses for summer use or,

3. Made during night by cooling of water by radiation to stratosphere.

In Europe, America and Iran a number of icehouses were built to store ice. Materials like sawdust or wood shavings were used as insulating materials in these icehouses.

In 1806, Frederic Tudor, (who was later called as the “ice king”) began the trade in ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to various countries including India. In India Tudor’s ice was cheaper than the locally manufactured ice by nocturnal cooling.

Evaporative Cooling

As the name indicates, evaporative cooling is the process of reducing the temperature of a system by evaporation of water. Human beings perspire and dissipate their metabolic heat by evaporative cooling if the ambient temperature is more than skin temperature.

Evaporative cooling has been used in India for centuries to obtain cold water in summer by storing the water in earthen pots. The water permeates through the pores of earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent heat in part from the vessel, which cools the water.

Suitably located chimneys in the rooms augmented the upward flow of warm air, which was replaced by cool air.