Anjuman College Of Engineering & Technology, Sadar, Nagpur LABORATORY

DEPARTMENT OF MECHANICAL ENGINEERING MANUAL

Practical Experiment Instruction Sheet YEAR : 2017-18

Final Year SEM-VIII SUBJECT: REFRIGERATION AND AIR CONDITIONING

Experiment No: 03
Aim:- To study construction and working of hermetically sealed compressor.

Apparatus: Hermetically sealed compressor, cut section.

Theory:

Introduction: The hermetically sealed compressor is widely used for the refrigeration
and air conditioning applications. You can find it in all the household refrigerators, deep freezers
,window air conditioners, split air conditioners, most of the packaged air conditioners. In
hermetically sealed compressor, the compressor and the motor are enclosed in the welded steel
casing and the two are connected by a common shaft. This makes the whole compressor and the
motor a single compact and portable unit that can be handled easily. The hermetically sealed
compressor is very different from the traditional open type of compressors in which the compressor
and the motor are different entities and the compressor is connected to the motor by coupling or
belt.

Types of Hermetic compressors:

One of the most popular types of hermetically compressors are the reciprocating
compressors. They were the first to be used as the hermetically sealed compressors and still being
widely used. The days the vane type of rotary compressor has become more popular. It is considered
that the rotary type of hermetically compressor consumes less electricity, makes lesser noise,
requires lesser maintenance, and is cheaper than the reciprocating type of compressor. This is
because the rotary compressors have less frictional parts and have only a rotor. The centrifugal
types of hermetically sealed compressors are used for the larger units.

Construction of Hermetically sealed reciprocating compressor:

In hermetically sealed compressor, in one side of the enclosed casing the various parts of the
compressor like cylinder, piston, connecting rod, and the crank shaft are located. If it is multi-
cylinder compressor, there are more than two cylinders inside the casing. On the other side of the

Prepared By : Prof. M. N. Nasim Approved By : Dr. A. M. Langde

 Anjuman College Of Engineering & Technology, Sadar, Nagpur LABORATORY
DEPARTMENT OF MECHANICAL ENGINEERING MANUAL

Practical Experiment Instruction Sheet YEAR : 2017-18

Final Year SEM-VIII SUBJECT: REFRIGERATION AND AIR CONDITIONING

casing is the electric winding inside which the

shaft of the motor rotates. This motor can be
single speed or multi-speed motor. In
hermetically sealed compressor the crank shaft
of the reciprocating compressor and the
rotating shaft of the motor are common. The
rotating shaft of the motor extends beyond the
motor and forms the crankshaft of the
hermetically reciprocating compressor.

All these parts of the hermetically sealed Fig. 01: Vertival Hermatic Compressor

compressor are assembled and enclosed in a strong and rigid casing made up of welded steel shell.
The steel shell comprises of two half rounded steel bodies that are welded together to form the
casing for the hermetically sealed compressor. In some cases, the two halves of the shell can be
bolted together instead of welding, which permits easy opening of the casing in case of compressor
burnout. The hermetically sealed compressors have inbuilt lubrication system for the lubrication of
the piston and cylinder and crank shaft. The lubricant also acts as the coolant for the piston and
cylinder. Additionally, the cool suction refrigerant also offers cooling effect. Externally , the casing
has refrigerant suction and discharge connections that are connected to the evaporator and
condenser respectively. There is also socket for the electrical connection. The typical condenser
unit with the hermetically sealed compressor is shown in fig. Such condenser units are called s
hermetic condenser units.

Working of Hermetically sealed compressor:

In hermetically sealed compressor, the motor and the

compressor are enclosed in the same housing to prevent
leakage. The housing has welded connections for
refrigerant inlet and outlet and for power input socket. As
Fig. 02 : Hermatic Compressor
a result of this there is virtually no possibility of
refrigerant leakage from compressor. All motors reject a part of the power supplied to it due to

Prepared By : Prof. M. N. Nasim Approved By : Dr. A. M. Langde

 Anjuman College Of Engineering & Technology, Sadar, Nagpur LABORATORY
DEPARTMENT OF MECHANICAL ENGINEERING MANUAL

Practical Experiment Instruction Sheet YEAR : 2017-18

Final Year SEM-VIII SUBJECT: REFRIGERATION AND AIR CONDITIONING

eddy current and friction. Similarly, compressor also gets heated up due to friction and due to
temperature rise of the refrigerant during compression. In open type both the compressor and the
motor reject heat to the surrounding air for efficient operation. In hermetic compressor heat cannot
be rejected to the surrounding air since both are enclosed in a shell.

Hence, the cold suction gas is made to flow over the motor and compressor before entering
the compressor. This keeps the motor cool. The motor winding is in direct contact with the
refrigerant, hence only those refrigerants which have dielectric strength, can be used in
hermetically sealed compressor. The cooling rate depends upon the flow rate of the refrigerant, its
temperature and the thermal properties of the refrigerant. If flow rate is not sufficient of if the
temperature is not low enough the insulation on the winding of the motor can burn out and short
circuiting may occur. Hence, hermetically sealed compressor give satisfactory and safe
performance over a very narrow range of design temperature and should not be used for off-design
conditions.

The COP of the hermetically sealed compressor based systems is lower than that of the pen
compressor based systems since a part of the refrigeration effect is lost in cooling the motor and
the compressor. However hermetically sealed compressor are almost universally used in small
systems such as domestic refrigerators, water coolers, air conditioners, etc where efficiency is not
as important as customer convenience. In addition to this the use of hermetically sealed
compressors is ideal in the systems which uses capillary tube as expansion devices. Hermetically
sealed compressors are normally not serviceable.

Application:

The hermetically sealed compressor is widely used for the refrigeration and air conditioning
applications because of several advantages like:

1) The hermetically sealed compressor can be moved easily from one place to the other place, they
are highly portable. One does not have to dissemble the compressor form the motor and no
coupling, belt and pulley arrangement is involved.

Prepared By : Prof. M. N. Nasim Approved By : Dr. A. M. Langde

 Anjuman College Of Engineering & Technology, Sadar, Nagpur LABORATORY
DEPARTMENT OF MECHANICAL ENGINEERING MANUAL

Practical Experiment Instruction Sheet YEAR : 2017-18

Final Year SEM-VIII SUBJECT: REFRIGERATION AND AIR CONDITIONING

2) The whole condenser unit of the refrigeration and air conditioning unit comprising of the
condenser and the compressor can be moved easily from one place to the other.

3) Since no coupling, belt or pulley is involved, the maintenance is lesser.

4) The lubrication system of the hermetically sealed compressor is inherent and no external
lubrication is required, unless the fresh gas charge is done.

5) The installation of the hermetically sealed compressor is very easy. The suction and
discharge connections and the electrical connections are available externally.

6) Hermetically sealed compressor have very long life , the companies offer warranty period upto
seven years for these compressors.

Conclusion: Thus we have studied the construction and working of hermetically compressor.

Prepared By : Prof. M. N. Nasim Approved By : Dr. A. M. Langde