Element of Mechanical Engineering

Introduction

The mechanism used for lowering or

producing low temp. in a body or a space,

whose temp. is already below the temp. of

its surrounding, is called the refrigeration

system.

Here the heat is being generally pumped

from low level to the higher one & is

rejected at high temp.

Refrigeration

The term refrigeration may be defined as

the process of removing heat from a

substance under controlled conditions.

It also includes the process of reducing

heat & maintaining the temp. of a body

below the general temp. of its

surroundings.

Contd….

In other words the refrigeration means a

continued extraction of heat from a body

whose temp is already below the temp. of

its surroundings.

Refrigerator & Refrigerant

A refrigerator is a reversed heat engine or

a heat pump which takes out heat from a

cold body & delivers it to a hot body.

The refrigerant is a heat carrying medium

which during their cycle in a refrigeration

system absorbs heat from a low temp.

system & delivers it to a higher temp.

system.

Refrigeration Cycle

In refrigeration system the heat is being

generally pumped from low level to higher

one & rejected at that temp.

This rejection of heat from low level to

higher level of temp. can only be

performed with the help of external work

according to second law of

thermodynamics.

Contd….

The total amount of heat being rejected to

the outside body consist of two parts:- the heat extracted from the body to be

cooled .

- the heat equivalent to the mechanical

work required for extracting it.

Contd…..

Contd….

A refrigerator is a reverse heat engine run

in the reverse direction by means of

external aid.

Every type of refrigeration system used for

producing cold must have the following

four basic units:-

Contd….

• Low temp. thermal sink to which the heat

is rejected for cooling the space.

• Means of extracting the heat energy from

the sink, raising its level of temp. before

delivering...