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Refrigeration Systems
Published in İbrahim Dinçer, Heat Transfer in Food Cooling Applications, 1997
Garrett and Holler [29] pointed out that two recent events are responsible for the new era in refrigeration before the beginning of the twenty-first century. The most significant of these is the international agreement (signing of the Montreal Protocol) on the production and consumption of CFCs, which were found to be causing the depletion of the stratospheric ozone layer. The second event was the discovery of “high-temperature” superconductors and the development of high-speed and high-density electronic circuits which require active cooling and hence a new approach to refrigeration, or thermoacoustic refrigeration, which was first discovered by Wheatley et al. [30] in August 1983. Thermoacoustic refrigeration utilizes high-density sound waves to pump heat, with inert gases as the working fluid. The interaction between acoustics and thermodynamics has been known ever since the dispute between Newton and Laplace over whether the speed of sound was determined by the adiabatic or isothermal compressibility of air. The thermoacoustic heat pump, which was a reverse process, is far less well known and was the first intentional demonstration of a new class of intrinsically irreversible heat engines. For Carnot-type heat engine cycles it is assumed that the individual steps in the cycle are reversible. The first and second laws of thermodynamics provide the limiting values for the system efficiencies (or system COPs), due to unavoidable irreversibilities (e.g., thermal diffusion and viscous dissipation) and variations in the thermophysical properties of working fluids with temperature and pressure. These nuisance effects always reduce performance below the ideal Carnot values [31].
Noise and Vibration
Published in Charles E. Baukal, Industrial Combustion Pollution and Control, 2003
The thermoacoustic efficiency of a process is a measure of the fraction of the thermal input energy that is converted into sound power. For turbulent flames, a general rule of thumb is that the thermoacoustic efficiency is approximately 1 x 10-7 times the energy input.
Investigation of an Atmospheric Gas Turbine Model Combustor with Large-Eddy Simulation Using Finite-Rate Chemistry
Published in Combustion Science and Technology, 2023
Jonas Eigemann, Kevin Roderigo, Pascal Gruhlke, Christian Beck, Andreas M. Kempf
Especially the prediction of self-excited high-frequency thermoacoustic oscillations, which can occur in gas turbines, remains a topic in the research community (Berger et al. 2017; Buschhagen et al. 2018; Sharifi et al. 2021). For the prediction of thermoacoustic properties of combustion chambers, different numerical methodologies have been developed and adopted, e.g. methods based on flame transfer functions or large-eddy simulations (LES). Methods using flame transfer function analysis employ a reduced order model to describe the thermoacoustic coupling mechanism. This methodology leads to accurate predictions for low-frequency thermoacoustic oscillations, however, high-frequency instabilities need further modeling due to locally changing influence of the acoustic wave on the flame’s heat release. In contrast, the largest eddies are resolved and the smallest turbulent scales are modeled in the LES approach. This enables the prediction of thermoacoustics in reacting flow simulations (Boudier et al. 2009; Sharifi et al. 2021; Sharifi, Beck, and Kempf 2018). However, the use of LES in the prediction of thermoacoustic behavior during the design stage of gas turbine combustors is currently limited due to the high associated computing cost.
Experimental study of the stack geometric parameters effect on the resonance frequency of a standing wave thermoacoustic refrigerator
Published in International Journal of Green Energy, 2019
Thermoacoustic refrigeration makes use of vibrational sound waves. It uses the input acoustic wave to pump heat from a low-temperature source to a high-temperature sink. The device, shown in Figure 1, is for a standing wave thermoacoustic refrigerator. The wave is transmitted into the resonator by the acoustic driver with the desired frequency and power from the function generator and the amplifier, respectively. After that, the wave propagates through the resonator producing hot and cold temperature areas because of the high- and low-pressure areas distributed through the resonator. The resonator contains the stack which separates the hot and cold areas and the stack, which is surrounded by two heat exchangers.
A compromise between the temperature difference and performance in a standing wave thermoacoustic refrigerator
Published in International Journal of Ambient Energy, 2020
Mahmoud A. Alamir, Ahmed A. Elamer
Thermoacoustic refrigeration uses the vibrational sound pressure waves. The heat is pumped from low-temperature source to high-temperature sink by the sound waves. Figure 1 shows a typical standing wave thermoacoustic refrigerator. The function generator and the amplifier feed the signal to the acoustic driver and transmit the required frequency and power into the resonator. Following this, the wave through the resonator produces hot and cold temperature regions due to the high- and low-pressure area distribution across the resonator. The stack, which has low thermal conductivity, separates the hot and cold areas inside the resonator, and it is surrounded by two heat exchangers to transfer heat.