THERMOACOUSTIC REFRIGERATION

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ANAND KRISHNAN P

S8MA

ROLL NO. 6

GUIDE : Dr. B SHAJI MOHAN

WHAT IS REFRIGERATION?

THE PROCESS IN WHICH WORK IS DONE TO MOVE HEAT FROM A COLD REGION TO A HOT REGION.

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WHAT IS THERMOACOUSTIC REFRIGERATION?

1.Thermoacoustic refrigeration is a branch of thermoacoustics which uses principles of both thermodynamics and acoustics to produce refrigeration.

2. Thermoacoustic refrigerators use acoustic power to pump heat from a low temperature region to high temperature region. The temperature change comes from adiabatic compression and expansion of the gas by the sound pressure.

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PRINCIPLES OF THERMODYNAMICS USED IN THERMOACOUSTIC

REFRIGERATION

TEMPERATURE OF FLUID RISES WHEN COMPRESSED AND DECREASES WHEN EXPANDED -:When a gas is compressed, work is done on the gas molecules. That means that additional energy is transferred to the gas molecules from the source of compression so as to increase temperature of gas and vice-a-versa.

HEAT FLOWS FROM HIGHER TEMPERATURE REGION TO LOWER TEMPERATURE REGION-: When two substances are placed in direct contact, heat naturally flows from the hotter substance to the cooler one unless both the bodies attain equal temperatures.

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PRINCIPLES OF ACOUSTICS USED IN THERMOACOUSTIC

REFRIGERATION

Sound waves are pressure waves.These waves travel through the medium via molecular collisions.The incident and the reflected waves interfere constructively to produce a single waveform called standing wave.to obtain maximum heat transfer rate we have to use resonant frequency f=v/4L where v is the velocity of the wave, and L is the length of the closed tube.

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SCHEMATIC OF A THERMOACOUSTIC REFIGERATOR

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MAIN COMPONENTS OF THERMOACOUSTIC REFRIGERATOR

Acoustic driver - to produce sound wavesStack - to absorb heatHeat exchangers - to create temperature differenceResonator tube - to provide housing for the whole setup

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WORKING OF THERMOACOUSTIC REFRIGERATOR

Starting from left, the packet of gas is compressed and moves towards hot heat exchanger and thus gets heated.

When the gas packet is at maximum compression, the gas ejects the heat back into the hot heat exchanger.

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WORKING(contd)

Gas expands while moving to left and cools.

Cold gas takes heat from stack. Stack becomes colder.

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WORKING(contd)

Temperature gradient across the stack is established.

Circulating fluid picks up/loses heat at the heat exchangers.

Very coldVery hot

Cold fluid

Hot fluid

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ANIMATED WORKING

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THE P Vs V PLOT

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EXPERIMENTAL STUDY ON PERFORMANCE OF THERMOACOUSTIC REFRIGERATION BY EMMANUEL C. NSOFOR AND AZRAI ALI

• Hot heat exchanger was maintained at ambient temperature.

• Cold heat exchanger temperature was varied to achieve a number of temperature differences along the stack.

• Helium gas was selected as the working fluid.

• The resonator was constructed from aluminium tubing but with plastic tubing at the inner portion to reduce heat loss by conduction.

• Parallel plate stack made from a thermoplastic material was used.

• An audio generator with frequency range from 10Hz to 1MHZ was used to produce sound wave.

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DIAGRAM OF THE EXPERIMENTAL

SETUP

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LOCATION OF THERMOCOUPLE

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EXPERIMENTAL SETUP

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EXPERIMENTAL SETUP(contd)

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EXPERIMENTAL SETUP(contd)

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WORKING PARAMETERS

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Temperature-time history(at the hot end of the stack) for constant cooling load and mean pressure for various frequencies

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Temperature-time history(at the hot end of the stack) for constant mean pressure and frequency for various cooling load.

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Temperature-frequency history(at the hot end of the stack) for constant mean pressure and variable load

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Temperature difference at the ends of the stack verses mean pressure at constant frequency and cooling load.

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Cooling load verses temperature difference at the ends of the stack at constant frequency and mean pressure

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Temperature difference at the ends of the stack verses frequency for constant cooling load and mean pressure

EXPERIMENTAL RESULTS

•The temperature difference between the hot end and cold end of the stack ranged from 0ᵒC to 15ᵒC.

•Cooling load increases with the increase in the temperature difference between the two ends of the stack.

•For a thermoacoustic refrigerating system, there exist for a given frequency, an optimum pressure that results in a higher cooling temperature difference and thus a higher cooling load. This frequency is the resonance frequency.

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CONCLUSION

The thermoacoustic refrigeration is environment friendly method of refrigeration technique. The technique was effectively used in the US space shuttle DISCOVERY. So we can expect extensive application of this technology in various areas of refrigeration.

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REFERENCES

• B Ramesh Nayak, Bheemsha, Pundarika. G, Design of parallel plate stack for a thermoacoustic refrigerator, International Journal of Advanced Scientific and Technical Research, 2011.

• Emmanuel C. Nsofor, Azrai Ali, Experimental study on the performance of the thermoacoustic refrigerating system, Applied thermal engineering, 2009.

• Jonathan Newman, Bob Cariste, Thermoacoustic Refrigeration, GSET Research Journal, 2006.

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THANK YOUTHANK YOU

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