08-05-2012, 11:58 AM
THERMOACOUSTIC REFRIGRATION
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INTRODUCTION
Thermoacoustic refrigeration is an innovative alternative for cooling that is both clean and inexpensive. From creating comfortable home environments to manufacturing fast and efficient electronic devices, air conditioning and refrigeration remain expensive, yet essential, services for both homes and industries. However, in an age of impending energy and environmental crises, current cooling technologies continue to generate greenhouse gases with high-energy costs.
BASIC CONCEPT
As we know that the Working of refrigerators relies on two basic thermodynamic principles:
Every fluid temperature will rise when compressed and falls when expands.
When two substances are placed in direct contact the heat will flow from higher temperature substance to low temperature substance.
Thermoacoustic refrigerator uses the above basic principle to transfer heat. It relies on sound to generate waves of pressure that alternatively compressed and expands gas particles within the tube. While the conventional refrigerators use heat pumps to transfer heat on a macroscopic scale.
SOUND AS PRESSURE WAVE
Thermoacoustics is based on the principle that sound waves are pressure waves. These sound waves propagate through the air via molecular collisions. The molecular collisions cause a disturbance in the air, which in turn creates constructive and destructive interference. The constructive interference makes the molecules compress, and the destructive interference makes the molecules expand. This principle is the basis behind the thermoacoustic refrigerator.
THERMODYNAMICS HEAT CYCLES
Ideal gas law states that pressure on a gas is directly proportional to the absolute temperature. In any heat cycle gases will expands and contract, circulating heat throughout the system. These movements of kinetic energy can be raised to do work.
Depending on how the heat oscillations are controlled, different heat cycles are become more important. But assuming ideal situations following TWO are important:
Carnot cycle
Stirling cycle
Heat pump or refrigerator operates on the same basic cycle as a heat engine, only in reverse. A heat pump requires an input of work to transfer heat from a cooler body to hotter body. This heat pump cycle is the basic mechanism by which thermoacoustic refrigerator is working.
THE EXPERIMENT
A simple experiment is also conducted to prove the reality of thermoacoustic refrigerator. Following are details and purpose of each component of thermoacoustic device:
Aluminum plug: Use as a heat sink and it also reflect the sound wave within the tube to generate standing wave.
Resonating tube: standing wave is produced within this tube.
Bowed loudspeaker: to produce sound waves.
Thermocouples: to measure temperature gradient.
Stack: The most important piece of a thermoacoustic device is the stack. The stack consists of a large number of closely spaced surfaces that are aligned parallel to the to the resonator tube. The purpose of the stack is to provide a medium for heat transfer as the sound wave oscillates through the resonator tube.
[attachment=21534]
INTRODUCTION
Thermoacoustic refrigeration is an innovative alternative for cooling that is both clean and inexpensive. From creating comfortable home environments to manufacturing fast and efficient electronic devices, air conditioning and refrigeration remain expensive, yet essential, services for both homes and industries. However, in an age of impending energy and environmental crises, current cooling technologies continue to generate greenhouse gases with high-energy costs.
BASIC CONCEPT
As we know that the Working of refrigerators relies on two basic thermodynamic principles:
Every fluid temperature will rise when compressed and falls when expands.
When two substances are placed in direct contact the heat will flow from higher temperature substance to low temperature substance.
Thermoacoustic refrigerator uses the above basic principle to transfer heat. It relies on sound to generate waves of pressure that alternatively compressed and expands gas particles within the tube. While the conventional refrigerators use heat pumps to transfer heat on a macroscopic scale.
SOUND AS PRESSURE WAVE
Thermoacoustics is based on the principle that sound waves are pressure waves. These sound waves propagate through the air via molecular collisions. The molecular collisions cause a disturbance in the air, which in turn creates constructive and destructive interference. The constructive interference makes the molecules compress, and the destructive interference makes the molecules expand. This principle is the basis behind the thermoacoustic refrigerator.
THERMODYNAMICS HEAT CYCLES
Ideal gas law states that pressure on a gas is directly proportional to the absolute temperature. In any heat cycle gases will expands and contract, circulating heat throughout the system. These movements of kinetic energy can be raised to do work.
Depending on how the heat oscillations are controlled, different heat cycles are become more important. But assuming ideal situations following TWO are important:
Carnot cycle
Stirling cycle
Heat pump or refrigerator operates on the same basic cycle as a heat engine, only in reverse. A heat pump requires an input of work to transfer heat from a cooler body to hotter body. This heat pump cycle is the basic mechanism by which thermoacoustic refrigerator is working.
THE EXPERIMENT
A simple experiment is also conducted to prove the reality of thermoacoustic refrigerator. Following are details and purpose of each component of thermoacoustic device:
Aluminum plug: Use as a heat sink and it also reflect the sound wave within the tube to generate standing wave.
Resonating tube: standing wave is produced within this tube.
Bowed loudspeaker: to produce sound waves.
Thermocouples: to measure temperature gradient.
Stack: The most important piece of a thermoacoustic device is the stack. The stack consists of a large number of closely spaced surfaces that are aligned parallel to the to the resonator tube. The purpose of the stack is to provide a medium for heat transfer as the sound wave oscillates through the resonator tube.