PPT based on the crayocooler

1. Prepared by:
DHRUVIT KHARADI[12bee023]
NIRMIT PANDAV[12BEE029]

2. OUTLINE OF PPT
 Topic : Cryocoolers
 What is a Cryocooler?
 Classification and basics of Cryocoolers
 J- t crayocooler
 Application

3. What is a Cryocooler???
 A Cryocooler is a mechanical device which generates
low temperature due to compression and expansion of
gas.
 It operates on a closed cycle manner, which means the
mass of the working gas is constant.
 A cryocooler consists of a compressor, a heat exchanger
and an expander as shown in the schematic.

4. CONTD………..
The cold generated in the
expander is exchanged between the
cold end and the object to be cooled
using an evaporator.
Cryocoolers capable of producing
temperatures as low as 77 K or 4.2 K
are used to replace the cryogens
(LN2, LHe respectively).

5. Classification:

6. Heat Exchanger :
Recuperative HX
In a recuperative heat exchanger, the flow
direction of two fluids is constant and is
simultaneous.
The two fluids are separated by a solid
boundary across which the warm and cold
fluids exchange heat.
The direction of the fluid flow may either
be counter flow, cross flow or parallel flow .

7. CONTD……..
Regenerative HX:
In a regenerative heat exchanger, a matrix
is used as an intermediate heat exchange
medium between the warm and cold fluids.
The flow is periodic in nature alternating
between the warm and cold fluids across
the matrix.
It is important to note that, it is an
example of indirect heat transfer.

8. J –T Cryocooler
A schematic diagram of a
JT liquefier is given in Fig.
 It consists of a compressor,
a counterflow heat
exchanger, a JT valve, and a
reservoir.

9. Working……
 At the inlet of the compressor the gas is at room
temperature (300 K) and a pressure of 1 bar (point a).
 The compression heat is removed by cooling water. After
compression the gas temperature is ambient temperature
(300 K) and the pressure is 200 bar (point b).
 Next it enters the warm (high-pressure) side of the
counterflow heat exchanger where it is precooled. It leaves
the exchanger at point c.
 After the JT expansion, point d, it has a temperature of
77.36 K and a pressure of 1 bar.

10. Contd…….
 The liquid fraction is x. The liquid leaves the system at
the bottom of the reservoir (point e) and the gas
(fraction 1-x) flows into the cold (low-pressure) side of
the counterflow heat exchanger (point f).
 It leaves the heat exchanger at room temperature
(point a). In order to keep the system in the steady
state gas is supplied to compensate for the liquid
fraction x that has been removed.

11. CONTD…..
Advantages
 No cold moving parts.
 Steady flow operation, no vibration.
 Cold end can be miniaturized.
Disadvantages
 Relies on real gas behavior.
 Requires high pressures, in the order of 200 bar.
 Small orifice, susceptible to clogging.
 Low efficiency.

12. J –T Cryocooler
Uses
Cooling IR sensors on missiles,
surveillance cameras.
Cooling semi conductor electronics.
Cryosurgery.
Liquefaction of natural gas.
Recent Developments
Mixed refrigerants.
Sorption compressor