Acoustic refrigeration pdf

Get help. Engineers Gallery. Share on Facebook. Thermo acoustic have been known for over years but the use of this phenomenon to develop engines and pumps is fairly recent. Thermo acoustic refrigeration is one such phenomenon that uses high intensity sound waves in a pressurized gas tube to pump heat from one place to other to produce refrigeration effect. In this type of refrigeration all sorts of conventional refrigerants are eliminated and sound waves take their place.

All we need is a loud speaker and an acoustically insulated tube. Thermo acoustic heat engines have the advantage of operating with inert gases and with little or no moving parts, making them highly efficient ideal candidate for environmentally-safe refrigeration with almost zero maintenance cost.

Now we will look into a thermo acoustic refrigerator, its principle and functions. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices. These two types of thermoacoustics devices can again be divided into two thermodynamic classes, a prime mover or simply heat engine , and a heat pump. The prime mover creates work using heat, whereas a heat pump creates or moves heat using work.

Thermo acoustic have been known for over years but the use of this phenomenon to develop engines and pumps is fairly recent. Thermo acoustic refrigeration is one such phenomenon that uses high intensity sound waves in a pressurized gas tube to pump heat from one place to other to produce refrigeration effect. In this type of refrigeration all sorts of conventional refrigerants are eliminated and sound waves take their place.

All we need is a loud speaker and an acoustically insulated tube. Thermo acoustic heat engines have the advantage of operating with inert gases and with little or no moving parts, making them highly efficient ideal candidate for environmentally-safe refrigeration with almost zero maintenance cost.

Now we will look into a thermo acoustic refrigerator, its principle and functions. Project Model Of thermoacoustic Refrigeration. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices.

These two types of thermoacoustics devices can again be divided into two thermodynamic classes, a prime mover or simply heat engine , and a heat pump. The prime mover creates work using heat, whereas a heat pump creates or moves heat using work. Compared to vapor refrigerators, thermoacoustic refrigerators have no ozone-depleting or toxic coolant and few or no moving parts therefore require no dynamic sealing or lubrication.

Thermoacoustic Refrigeration-Working principle. Leave a Reply Cancel reply Your email address will not be published.

As the acoustic wave propagates compressions and rarefractions occurs alternatively atively in a compression, particles move in the direction in which the wave advances where in rarefraction, the particles moves in the opposite direction in which the wave advances. When a compressed ed wave is sent through an organ pipe, the wave gets reflected refle at the ends of the pipe these incident and reflected waves waves which are in a same frequency, frequency travelling in opposite directions are super imposed along the length of the pipe and form longitudinal stationary waves.

Figure 6 Super -imposition imposition of wave As diaphragm vibrates the alternate Compressions and expansions occurs throughout the Gas medium in the resonant column. Stack It is also called as regenerator. The most important piece of a thermo acoustic 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. In a usual resonator tube, heat transfer occurs However, since the vast majority of the molecules are far from the walls of the chamber, the gas particles cannocannot exchange heat with the wall and just oscillate in place, causing no net temperature difference.

The purpose of the stack is to provide a medium where the walls are close enough so that each time a packet of gas moves, the temperature differential is tran transferred sferred to the wall of the stack. Most stacks consist of honeycombed plastic spacers that do not conduct heat throughout the stack but rather absorb heat locally. With this property, the stack can temporarily absorb the heat transferred by the sound waves between the walls of cylinder and the gas gas.

The length of the stack depends up on mean displacement of vibrating Gas molecules. If the holes are too narrow, the stack will be difficult to fabricate, and the viscous properties of the air will make it difficu difficult lt to transmit sound through the stack.

If the walls are too far apart, then less air will be able to transfer heat to the walls of the stack, resulting in lower efficiency. Heat Exchangers Heat exchangers are employed to trap and transfer the heat and cold generated at the ends of the stack. They are two heat exchangers, Hot heat exchanger and Cold heat exchanger exchanger.

Heat exchanger is a copper plate fitted in a copper sleeve. The plate is punched with a number of holes. The diameter of the holes matches with with the gap between stack plates. Hot heat exchanger is placed at hot end side and cold heat exchang exchanger er is placed at the colder end of the stack.

Figure ure 8 Heat eat exchanger assembly with stack 2. Helium Gas He-Gas Gas is a light weight inert gas with small atomic size. With usage of helium gas, gap between the stack plates will be minimized to a large extent.

Therefore kinematic viscosity is very low. So, the molecules are free to vibrate even in a small gaps resulting high utilization of gas molecules for to participate in heat transfer.

While acoustics is primarily concerned with the macroscopic effects of sound transfer like coupled pressure aandnd motion oscillations, thermo acoustics focuses on the microscopic temperature oscillations that accompany these pressure changes. Thermo acoustics takes advantage of these pressure oscillations to move heat on a macroscopic level. This results in a large temperature difference between the hot and cold sides of the device and causes refrigeration. The purpose of the stack is to provide a medium for heat transfer as the sound wave oscillates through the resonator tube.

A functional cross section of the stack we used is shown in figure 6. In typical standing wave devices, the temperature differences occur over too small of an area to be noticeable. Figure 10 Cyclic Cyclic process of system In a usual resonator tube heat transfer occurs between the walls of cylinder and the gas.

However, since the vast majority of the molecules are far from the walls of the chamber, the gas particles cannot exchange heat with the wall an adjust oscillate in place, causing no net temperature difference.

The purpose of the stack is to provide a medium where the walls are close enough so that each time a packet of gas moves, the temperature differential is transferred to the wall of the stack.

Most stacks consist of honeycombed plas plastic tic spacers that do not conduct heat throughout the stack but rather absorb heat locally. With this property, the stack can temporarily absorb the heat transferred by the sound waves. The spacing of these designs is crucial: if the holes are too narrow, th thee stack will be difficult to fabricate, and the viscous properties of the air will make it difficult to transmit sound through the stack.

If the walls are too far apart, then less air will be able to transfer heat to the walls of the stack, resulting in lower lower efficiency. Figure ure 11 Working of stack The actual thermodynamic cycle occurs in the stack.

The hot region forms at one end and cold region forms at the other end of the stack. In practical the volume of the gas which is present between gaps of the stack plates, only participate in the cycle. Babu Tanneru and Khannaji Pattapu placed at correct position from the driver such that one end of the stack will be at Compression area and other end at successive expansion area. Fig Figure 12 Copper tubes of cold side of stack as cold heat exchanger.

As the Acoustic wave propagates from driver end to other end the disturbance is transfer by the simple harmonic vibrations of the Gas molecules.

The Gas packets which are about a middle position of the stack displaces towards an en endd of stack, say Compression side.