History[ edit ] The history of thermoacoustic engines is long but sparsely populated. A review of Putnam and Dennis describes experiments of Byron Higgins in in which acoustic oscillations in a large pipe were excited by suitable placement of a hydrogen flame inside. The Sondhaus tube is the earliest thermoacoustic engine that is a direct antecedent of the thermoacoustic prime movers. Over years ago, glass blowers noticed that when a hot glass bulb was attached to a cool glass tubular stem, the stem tip sometimes emitted sound, and Sondhauss quantitatively investigated the relation between the pitch of the sound and the dimensions of the apparatus. The English physicist, Lord Rayleigh explained the Sondhauss tube qualitatively in "In almost all cases where heat is communicated to a body, expansion ensues and this expansion may be made to do mechanical work.
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History[ edit ] The ability of heat to produce sound was noted by glassblowers centuries ago. Rijke demonstrated that adding a heated wire screen a quarter of the way up the tube greatly magnified the sound, supplying energy to the air in the tube at its point of greatest pressure. Further experiments showed that cooling the air at its points of minimal pressure produced a similar amplifying effect. In about , Lord Rayleigh discussed the possibility of pumping heat with sound. In , Rott reopened the topic.
Swift continued with these equations, deriving expressions for the acoustic power in thermoacoustic devices. Score Ltd. The system has slight theoretical advantages over other generator systems like existing thermocouple based systems, or a proposed Stirling engine used in ASRG prototype. The device uses argon gas. The device amplifies sound created by the waste heat, and converts the resulting pressure back into and uses a Stirling cycle to produce the cooling effect.
It basically consists of heat exchangers , a resonator and a stack on standing wave devices or regenerator on travelling wave devices. Depending on the type of engine a driver or loudspeaker might be used to generate sound waves.
In a tube closed at both ends, interference can occur between two waves traveling in opposite directions at certain frequencies. The interference causes resonance and creates a standing wave. The stack consists of small parallel channels. When the stack is placed at a certain location in the resonator having a standing wave, a temperature differential develops across the stack.
By placing heat exchangers at each side of the stack, heat can be moved. The opposite is possible as well: a temperature difference across the stack produces a sound wave. The first example is a heat pump, while the second is a prime mover. Heat pump[ edit ] Creating or moving heat from a cold to a warm reservoir requires work. Acoustic power provides this work. The stack creates a pressure drop. Interference between the incoming and reflected acoustic waves is now imperfect.
The difference in amplitude causes the standing wave to travel, giving the wave acoustic power. Heat pumping along a stack in a standing wave device follows the Brayton cycle. A counter-clockwise Brayton cycle for a refrigerator consists of four processes that affect a parcel of gas between two plates of a stack. Adiabatic compression of the gas.
When a parcel of gas is displaced from its rightmost position to its leftmost position, the parcel is adiabatically compressed, increasing its temperature.
At the leftmost position the parcel now has a higher temperature than the warm plate. Isobaric heat transfer. Adiabatic expansion of the gas. The gas is displaced back from the leftmost position to the rightmost position. Due to adiabatic expansion the gas cools to a temperature lower than that of the cold plate.
Travelling wave devices can be described using the Stirling cycle. Temperature gradient[ edit ] Engines and heat pumps both typically use stacks and heat exchangers. The boundary between a prime mover and heat pump is given by the temperature gradient operator, which is the mean temperature gradient divided by the critical temperature gradient.
History[ edit ] The ability of heat to produce sound was noted by glassblowers centuries ago. Rijke demonstrated that adding a heated wire screen a quarter of the way up the tube greatly magnified the sound, supplying energy to the air in the tube at its point of greatest pressure. Further experiments showed that cooling the air at its points of minimal pressure produced a similar amplifying effect. In about , Lord Rayleigh discussed the possibility of pumping heat with sound. In , Rott reopened the topic. Swift continued with these equations, deriving expressions for the acoustic power in thermoacoustic devices.
For typical sound frequencies the thermal penetration depth is ca. That means that the thermal interaction between the gas and a solid surface is limited to a very thin layer near the surface. The effect of thermoacoustic devices is increased by putting a large number of plates with a plate distance of a few times the thermal penetration depth in the sound field forming a stack. Stacks play a central role in so-called standing-wave thermoacoustic devices. Thermoacoustic systems[ edit ] Acoustic oscillations in a medium are a set of time depending properties, which may transfer energy along its path.
Thermoacoustic heat engine