The document discusses the principle and operation of pulse tube refrigeration. It begins with an introduction to pulse tube refrigerators and their history. It then describes the basic components of a pulse tube refrigerator, including the pulse tube, regenerator, pressure wave generator, and heat exchangers. The document explains how compression and expansion of the working gas, typically helium, leads to cooling at one end of the pulse tube. It also briefly discusses modifications like the orifice pulse tube refrigerator. Applications include military, environmental, transportation and energy uses.

1. Principle And Operation
of Pulse Tube
Refrigeration
University of the South Pacific
School of Engineering and Physics
MM321- Refrigeration and Air conditioning
°
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2. Objective
• To demonstrate the principle and operation of the pulse tube
refrigeration system.
• To describe the processes involved and the governing
equations in the basic pulse tube refrigerator
• To briefly describe the modifications made to the basic pulse
tube refrigerator.
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3. Introduction
• A pulse tube refrigerator is a Cryocooler capable of
reaching temperatures of a few tens of Kelvin in a single
stage and a few kelvin in two stage.
• Unlike ordinary VCR cycle, a pulse tube refrigeration
system implements the oscillatory compression and
expansion of gas within a closed volume to achieve the
desired refrigeration.
• In other words, generation of low temperature is
achieved due to compression and expansion of a gas.
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4. Brief History
• Pulse tube refrigeration is a recent innovation.
• They were first reported by Prof. W. Gifford and his
graduate student, R Longworth, of Syracuse University at
around 1960 [1].
• They noticed that a closed end of a pipe became very hot
when there was a pressure oscillation inside, whereas
the open end towards the compressor was cool.
• Connecting such a line to a compressor through a
regenerator produced cooling at one end and heating at
the other.
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5. Literature Review
• It is not generally realized that delivery of a constant
temperature gas into a closed volume, thus increasing
the pressure, will result in large temperature gradients.
• By suitable arrangement of a thermal regenerator, heat
exchangers it is possible to preserve this temperature
gradient in an essentially static state even though there is
a rapid flow of gas in and out of the volume, pressure
variation is great, and pressure oscillation from a
maximum to a minimum occurs many times per minute
[2].
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6. Literature Review
• These temperature gradients are maintained by pulsating gas.
• Therefore, if the hot end of the gradient is cooled to room
temperature, the cold end will descend to a lower
temperature.
• Pulse tube refrigeration is a method which uses this principle
to achieve low temperature refrigeration in small compact
tubes [3].
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7. Literature Review
• Pulse tube refrigerator units operate as closed systems where
no mass is exchanged between the Cryocooler and the
environment.
• The only moving component is the piston ( and the rotary
valve) which oscillates back and forth to generate periodic
pressure oscillation of the working fluid.
• Mostly helium is chosen as the working fluid because it offers
the lowest critical temperature compared to other available
gases.
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8. Literature Review
Working Fluid
• The most common working fluid for the pulse tube
refrigerator is Helium.
• Helium non toxic and environment friendly.
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9. Literature Review
Working Fluid
• Helium was a choice of coolant as its properties allow
components to be kept cool over long distances. At
atmospheric pressure gaseous helium becomes liquid at
around 4.2 K (-269.0°C). However, if cooled below 2.17 K (-
271.0°C), it passes from the fluid to the superfluid state.
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10. Literature Review
Basic Pulse Tube Refrigerator:
• Its basic components include a pulse tube, regenerator, a
pressure wave generator and two heat exchangers and an
after cooler as shown in the figure below.
Fig 1
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11. Literature Review
• The piston, compressor or similar pressure wave generator is
attached to the warm end of the regenerator and provides the
pressure oscillations that drives the refrigeration.
• The regenerator is a periodic flow heat exchanger.
• It absorbs heat from the gas pumped into the pulse tube precooling
it, and stores the heat for half a cycle then transfers it back to
outgoing cold gas in the second half of the cycle cooling the
regenerator.
• The interior of the regenerator tube is filled with either stacked fine
mesh screens or packed spheres to increase its heat capacity.
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12. Literature Review
• The pulse tube is a simple tube, with one open end and
closed end.
• The closed end is the hot end and is capped with a heat
exchanger that cools it to the ambient temperature.
Fig 2
Closed end
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13. Literature Review
• The open end is the cold end.
• It is connected to the regenerator and a cold stage by a
second heat exchanger
Fig 3
Open end
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14. Literature Review
Components
Fig 4
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15. Literature Review
• The pulse tube works by transporting heat against a
temperature gradient in a process called surface heat
pumping [4].
• It occurs in many systems subjected to pressure oscillations.
• The piston compresses the working gas and this high pressure
gas in turn compresses the gas already in the tube acting as a
gas piston.
• At the same time, the temperature of the gas rises as they
undergo adiabatic compression.
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16. Literature Review
• All the gas that was initially in the tube will be compressed to
the hot end.
• The extra gas that flows in from the regenerator has a
pressure gradient.
• The pressure is highest closest to the hot end and lowest at
the bottom of the pulse tube.
Fig 5
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17. Literature Review
• The pressure gradient directly results in a temperature
gradient.
• At the hot end of the pulse tube, the gas conducts its heat to
the heat exchanger and the temperature falls.
• The piston then retracts and the gas undergoes adiabatic
expansion cooling it even more.
• As the expanding gases passes from the pulse tube into the
regenerator, it absorbs heat from the regenerator and pulse
tube walls cooling them.
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18. Literature Review
• The next cycle starts by compressing the gas back through the
precooled regenerator.
• The gas begins at a lower temperature and it therefore
reaches an even lower temperature after finishing its
compression and expansion cycle.
• Record temperatures of 74K have been achieved with the
basic pulse tube refrigerator.
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19. Literature Review
Analysis of Pulse Tube Refrigerator
• If a mass of gas 𝑀𝑐 with specific heat 𝐶 𝑝 is compressed to a
temperature 𝑇 𝑚 just before it enters the hot end heat
exchanger at a temperature 𝑇ℎ, then when it enters this heat
exchanger it will give up an amount of heat equal to the
refrigeration effect 𝑄 𝑟 .
• During the exhaust phase of the cycle, gas leaves the hot end
heat exchanger at temperature 𝑇ℎ and expands to an exhaust
temperature 𝑇𝑎 which is less than 𝑇𝑐 creating a refrigeration
effect 𝑄 𝑟.
𝑄 𝑟 = 𝑀𝑐 𝐶 𝑝(𝑇𝑐 − 𝑇𝑎)
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20. Literature Review
• The relation for the temperature at any point x in the
tube, Tx in terms of the volume of the hot end heat
exchanger, 𝑉ℎ, and the total volume from the top of the
tube point to point x , 𝑉𝑥, for a gas whose ratio of specific
heat is 𝛾, is given by:
𝑇ℎ
𝑇𝑥
= [
𝑉 𝑥
𝑉ℎ
+𝛾−1
𝛾
]
𝛾−1
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21. Literature Review
Orifice Pulse Tube Refrigeration
• The basic pulse tube and more generally the surface heat
pumping technique is of limited use when very low
temperatures are required.
• Modifications made to the basic design involved adding an
orifice outside the heat exchanger and a reservoir closing the
orifice [5].
• With the improvements, a low temperature of 60K was
achieved.
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22. Literature Review
Fig 6 (Orifice Pulse Tube Refrigerator)
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23. Literature Review
• The hot end heat exchanger is equivalent to the condenser
and the cold end heat exchanger is equivalent to the
evaporator in the vapor compression cycle.
• During the PTR operation, most of the heat generated due to
the compression is rejected through the after cooler.
• The rest of the energy that is not rejected is carried to the
regenerator by enthalpy flow 𝐻𝑟𝑔.
• The regenerator enthalpy flow and the additional
refrigeration load are absorbed at the cold heat exchanger.
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24. Literature Review
• The enthalpy flow enters the pulse tube, and travels down the
tube, reaches the HHX and part of this enthalpy is rejected to
the environment.
• The portion of the enthalpy that has not been rejected
through the heat exchanger flows to the reservoir through the
orifice.
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25. Literature Review
Applications
• Military
• Environmental
• Transportation
• Energy
Problems
• Reliability
• Efficiency
• Cost
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26. Conclusion
• Pulse tube refrigeration is still a developing technology in the
field of refrigeration
• We have briefly studied the basic pulse tube and the
modifications made to it by the addition of the orifice tube
and the reservoir.
• Although they are very much similar, the method of analysis is
somewhat different.
• Pulse tube refrigeration is very important in cryogenics
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27. Referencing
• 1. Gifford, W.E. and Longsworth, R.C. Pulse tube refrigeration,
Trans ASME B J Eng Industry 86(1964), pp.264-267.
• 2. Gifford, W.E. and Longsworth, R.C. Pulse tube refrigeration
progress, Advances in cryogenic engineering 3B (1964), pp.69-
79.
• 3. Gifford, W.E. and Longs worth, R.C. Surface heat pumping,
Advances in cryogenic engineering 11(1966), pp.171-179.
• 4. Gifford, W.E. and Kyanka, G.H. Reversible pulse tube
refrigerator, Advances in cryogenic engineering 12(1967),
pp.619-630.
• 5. de Boer, P. C. T., Thermodynamic analysis of the basic pulse-
tube refrigerator, Cryogenics34(1994) ,pp. 699-711 .
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