Performance Of Thermoacoustic Refrigerator Research Articles

Performance evaluation of 10 W cooling power thermoacoustic refrigerator with spiral stacks using air and helium as working fluids

The current research work involves the effect of different operating parameters on the performance of the thermoacoustic refrigerator. The thermoacoustic refrigerator is fabricated by using Poly Vinyl Chloride (PVC), which reduces the conduction heat loss. Two spiral stacks have been used to study the performance of the thermoacoustic refrigerator by varying the gap between two spirals (0.33 mm and 0.38 mm). The variants of spiral stacks are made up of PVC sleeves and mylar sheets of thickness 0.12 mm. In this work, Air and Helium are used as working fluids. The experiments have been carried out for different drive ratios ranging from 0.6% to 1.6%, with operating frequencies of 200–600 Hz with a step of 100 Hz. Also, the mean operating pressure of 2 to 10 bar with a step of 2 bar and a cooling load of 2 to 10 W with a step of 2 W has been considered. The temperature difference between the hot end and cold end of the stack is recorded using RTDs and Bruel & Kjaer data acquisition system. The effect of different parameters on the performance of thermoacoustic refrigerator, such as operating frequency, cooling load, mean operating pressure and drive ratios have been studied. The TAR is modeled in DeltaEC environment, simulation of significant operating conditions are analyzed and found that the results are in good agreement with experimental results. The experimental result shows that the lowest temperature measured at the cold heat exchanger is 1.12 °C by maintaining the hot heat exchanger temperature at about 32 °C when helium is used as the working fluid. Also, 30.56 °C and 28.03 °C are the highest values of temperature differences (∆T) achieved for 0.33 mm and 0.38 mm spaced spiral stacks respectively, whereas 28.56 °C and 26.04 °C are the corresponding results with air as the working fluid.

Effect of parallel plate stack spacing on the performance of thermoacoustic refrigerator in terms of temperature difference using air as a working fluid

The existing conventional refrigerators are operated by using hazardous refrigerants, which produces CFCs and HCFCs resulting in the depletion of the ozone layer. However, these disadvantages can be overcome using inert gases in the thermoacoustic refrigeration system. The present research involves the effect of the spacing of a parallel plate stack on the performance of the thermoacoustic refrigerator (TAR). TAR is fabricated by using Poly-Vinyl-Chloride (PVC), which is designed for 10W cooling power. Three parallel plate stacks have been used to study the performance of TAR considering different porosity ratios by varying the gap between the parallel plates (0.28 mm, 0.33 mm and 0.38 mm). The parallel plate stacks are fabricated by using aluminium and mylar sheet material, and the working fluid used for the experimental study is zero air. The experiments have been carried out with different drive ratios ranging from 0.6% to 1.6%, with operating frequencies of 200 – 600 Hz. Also, the mean operating pressure used for the experiment is 2 to 10 bar, and the cooling load of 2 to 10W is considered. The temperature difference (ΔT) between the hot heat exchanger and cold heat exchanger is recorded using RTDs and Bruel and Kjaer data acquisition system. Experimental results show that the lowest temperature measured at cold heat exchanger is 1.23 °C by maintaining the hot heat exchanger temperature at about 32 °C. The maximum ΔT of 30.77 °C is achieved.

Experimental Performance Evaluation of Thermoacoustic Refrigerator made up of Poly-Vinyl-Chloride for different Parallel Plate Stacks using Air as a working medium

Abstract Most of the experimental work carried out by fabricating Aluminium and other metallic resonator system in order to evaluate the performance of thermoacoustic refrigerator. In this experimental work, poly-vinyl-chloride has been used to fabricate all the structural parts including the resonator system to study the performance of thermoacoustic refrigerator for different operating conditions. Three parallel plate stacks are fabricated by using Aluminum and the Mylar sheet material of 0.12 mm thickness by considering three different porosity ratios. In this research work, only pure air is used as a working fluid. The experiments are conducted for the drive ratios ranging from 0.6% to 1.6% with an operating frequency varies from 200Hz to 600Hz with a step of 100 Hz. Also, the mean operating pressure and cooling load varies from 2 to 10 bar and 2 to 10 W respectively. In this work, Bruel and Kjaer data acquisition system and RTDs are used to measure and record the temperature difference between two heat exchangers. The effect of different parameters such as operating pressure, operating frequency, cooling load and drive ratios on the performance of thermoacoustic refrigerator in terms of temperature difference and coefficient of performance (COP) are studied.It is observed from experimental results that 1.23 oC is the lowest measured temperature at the cold heat exchanger by maintaining 32 oC at the hot heat exchanger. It is important to note that 30.77 oC is the highest value of temperature difference measured between two sides of stack, which is about 41% improvement in the temperature difference as compared to previous findings

Influence of Parallel Plate Stack Spacing on the Temperature Difference of Thermoacoustic Refrigerator by using Helium as a Working Medium

The refrigerants are usually provided in the conventional refrigeration system despite the fact that, they produce CFCs and HCFCs, which are hazardous to the environment. However, these disadvantages can be overcome using air or inert gas in the thermoacoustic refrigeration system. The present research involves the effect of spacing of parallel plate stack on the performance of thermoacoustic refrigerator (TAR) in terms of temperature difference (ΔT). The entire resonator system as well as other structural parts of the refrigerator are fabricated by using PVC to reduce conduction heat loss. Three parallel plate stacks have been used to study the performance of TAR considering different porosity ratios by varying the gap between the parallel plates (0.28 mm, 0.33 mm and 0.38 mm). The parallel plate stacks are fabricated by using aluminium and mylar sheet material and the working fluid used for the experimental study is helium. The experiments have been carried out with different drive ratios ranging from 0.6% to 1.6% with operating frequencies of 200 – 600 Hz. Also the mean operating pressure used for the experiment is 2 to 10 bar and cooling load of 2 to 10W are considered. The ΔT between the hot heat exchanger and cold heat exchanger is recorded using RTDs and Bruel and Kjaer data acquisition system. Experimental results shows that the lowest temperature measured at cold heat exchanger is -2.1 oC by maintaining the hot heat exchanger temperature at about 32 oC. The maximum temperature difference of 32.90 oC is achieved.

Effect of Stack Spacing on the Performance of Thermoacoustic Refrigerators Using Helium and Air as Working Substances

This paper deals with the design of thermoacoustic refrigerators using linear thermoacoustic theory. The refrigerator components are designed at 3% drive ratio by considering the practical limitations of providing sufficient spacing for attaching the loudspeaker to the resonator tube and accommodating instrumentation. The effects of spiral stack spacing in terms of thermal penetration depth on the theoretical performance of refrigerator using helium and air as working substances are discussed. The quarter-wavelength resonator designs with taper and divergent section terminated with hemispherical end are optimized with helium and air for better performance. Theoretical results are validated with DeltaEC software results and are in agreement with each other. Helium shows better performance compared to air but lacks power density. The DeltaEC predicts COP 0.514 at the cold heat exchanger temperature of [Formula: see text]C with helium compared to air (COP 0.616 at [Formula: see text]C) for the 50[Formula: see text]W cooling power 100[Formula: see text]mm diameter quarter-wavelength resonator designs.

Experimental study of the stack geometric parameters effect on the resonance frequency of a standing wave thermoacoustic refrigerator

ABSTRACTThermoacoustic refrigeration is an emerging technology that makes use of acoustic power to pump heat. The resonance frequency is important for the performance of thermoacoustic refrigerators, as it affects the temperature difference across the stack. This paper aims to optimize the performance of thermoacoustic refrigerators by experimentally investigating the effect of the stack geometric parameters (i.e. stack position, stack length, and the stack size) on the resonance frequency of a standing wave loudspeaker driven thermoacoustic refrigerator. Celcor Ceramic stacks of normalized positions of 0.764, 1.05, 1.43, and 1.72, normalized lengths of 0.076, 0.114, 0.153, and 0.191, and two porosities of 0.8 and 0.85 are used. The clarification of the relationship between the stack geometric parameters and the resonance frequency of the thermoacoustic refrigerator is presented. Moreover, the coefficient of performance of the thermoacoustic refrigerator is observed to increase at the resonance frequency of each stack configuration.

Influence of heat exchangers blockage ratio on the performance of thermoacoustic refrigerator

In this paper, a numerical study is carried out to assess the effect of heat exchangers plates inter-spacing on the performance of a thermoacoustic refrigerator (TAR). Considering that typically most of the heat loss occurs near the heat exchangers, a great emphasis will be placed on the space between the latter and the stack. Several geometric arrangements of heat exchangers plates inter-spacing were tested. The numerical method used is based on two-dimensional low Mach number model. This model assumes that the length of the assembled heat exchangers and stack is less than the wavelength. The results are in agreement with those provided by the DeltaEC software. It can also be observed that the larger the heat exchangers plates inter-spacing, the greater the cooling impact through the thermoacoustic effect.

Effect of Dynamic Pressure on the Performance of Thermoacoustic Refrigerator with Aluminium (Al) Resonator

In practice the refrigerants are being used in the conventional refrigeration system to get the required cooling effect. These refrigerants produce Chlorofluorocarbons (CFCs) and Hydro chlorofluorocarbons (HCFCs) which are highly harmful to the environment, particularly depleting of ozone layers resulting in green house emissions. In order to overcome these effects, the research needs to be focused on the development of an ecofriendly refrigeration system. The thermoacoustic refrigeration system is one among such system where the sound waves are used to compress and expand the gas particles. This study focuses on the effect of dynamic pressure on the thermoacoustic refrigerator made of aluminium with overall length of 748.82 mm, and the entire inner surface of the resonator tube was coated with 2mm thickness of polyurethane to minimize the heat losses to the atmosphere. Experiments were conducted with different stack geometries i.e. parallel plates having 0.119 mm thick with spacing between the plates maintained at 0.358 mm, 1mm diameter pipes, 2mm diameter pipes and 4 mm diameter pipes. Experiments were also conducted with different drive ratios of 0.6%, 1% and 1.6% for a constant dynamic pressure of 2 bar and 10 bar for helium and air as working medium. The results were plotted with the help of graphs, the variation of coefficient of performance (COP) and the relative coefficient of performance (COPR) for the above said conditions were calculated.

The Influence of Stack Position and Acoustic Frequency on the Performance of Thermoacoustic Refrigerator with the Standing Wave

Abstract Thermoacoustic refrigerator uses acoustic power to transport heat from a low-temperature source to a high-temperature source. The increasing interest in thermoacoustic technology is caused due to its simplicity, reliability as well as application of environmentally friendly working fluids. A typical thermoacoustic refrigerator consists of a resonator, a stack of parallel plates, two heat exchangers and a source of acoustic wave. The article presents the influence of the stack position in the resonance tube and the acoustic frequency on the performance of thermoacoustic refrigerator with a standing wave driven by a loudspeaker, which is measured in terms of the temperature difference between the stack edges. The results from experiments, conducted for the stack with the plate spacing 0.3 mm and the length 50 mm, acoustic frequencies varying between 100 and 400 Hz and air as a working fluid are consistent with the theory presented in this paper. The experiments confirmed that the temperature difference for the stack with determined plate spacing depends on the acoustic frequency and the stack position. The maximum values were achieved for resonance frequencies and the stack position between the pressure and velocity node.

Influence of stack geometry on the performance of thermoacoustic refrigerator

The work reported in this paper is focused on the performance of a thermoacoustic refrigerator under various operating conditions. The experiments were conducted with various stack geometries fabricated with epoxy glass and Mylar material. Four stacks with different pore sizes are used to evaluate the performance of the refrigerator. Stack 1 has parallel plates of Mylar material 0.12 mm thick spaced 0.36 mm apart. Stacks 2, 3 and 4 are made of epoxy glass with pores of circular cross-section having 1, 2 and 3 mm diameter, respectively. The entire resonator system was constructed from aluminium material coated with polyurethane material from inside to reduce conduction heat losses. Helium gas was used as a working fluid. The experiments were conducted with different drive ratios ranging from 1.6% to 2% with varying cooling load from 2 to 10 W. For the experiments, operating frequencies from 200 to 600 Hz with mean pressure varying from 2 to 10 bar in steps of 2 bar each were considered. The temperatures of the hot end and cold end of the heat exchangers were recorded using RTDs and a data acquisition system under various operating conditions. The coefficient of performance (COP) and relative COP (COPR) are evaluated. Results show that COP of the refrigerator rises with increase of cooling load and decreases at higher drive ratio. It was also observed that the temperature difference between the hot end and cold end of the stack is higher at 2 W cooling load for 400 Hz operating frequency. The temperature difference between the hot end and cold end of the stack was observed to be 19.4, 17.2, 14 and 12.4°C for stacks 1, 2, 3 and 4, respectively, for 10 bar mean pressure and 2 W cooling load. The temperature difference and COP of the parallel plate stack are better compared with other stack geometries.

Maximum cooling and maximum efficiency of thermoacoustic refrigerators

This work provides valid experimental evidence on the difference between design for maximum cooling and maximum efficiency for thermoacoustic refrigerators. In addition, the influence of the geometry of the honeycomb ceramic stack on the performance of thermoacoustic refrigerators is presented as it affects the cooling power. Sixteen cordierite honeycomb ceramic stacks with square cross sections having four different lengths of 26, 48, 70 and 100 mm are considered. Measurements are taken at six different locations of the stack hot ends from the pressure antinode, namely 100, 200, 300, 400, 500 and 600 mm respectively. Measurement of temperature difference across the stack ends at steady state for different stack geometries are used to compute the cooling load and the coefficient of performance. The results obtained with atmospheric air showed that there is a distinct optimum depending on the design goal.

Numerical simulation and parameter optimization of thermo-acoustic refrigerator driven at large amplitude

Two-dimensional numerical simulation of thermo-acoustic refrigerator driven at large amplitude is carried out in this paper. Computation of the parameters is based on a pressure-correction algorithm for compressible flows, removing the limitations of traditional simplified linear model of the thermo-acoustic systems. Firstly, the numerical algorithm is applied to an acoustic resonance chamber. The numerical results are found to be in good agreement with those reported in the literature. We explore the growth of pressure amplitude for harmonic waves of various orders according to the growth of driving amplitude, and show the non-linear phenomena in the refrigerator. Then the parameters affecting the refrigerating performance (including fixing position of the thermo-acoustic stacks, length of the stacks and the heat exchanger, thickness of parallel plates, and the spacing), are investigated in detail, which shows that the performance of thermo-acoustic refrigerators is best when the normalized plate thickness ranges from 0.28 to 0.33, the normalized spacing between plates ranges from 1.37 to 1.51, and the length of heat exchanger is about the peak-to-peak displacement amplitude of the gas in it. Finally these optimized parameters are verified under different charging pressures, driving amplitudes, and working gases, providing references for optimal design of thermo-acoustic refrigerator driven at large amplitude.

Scalability of Thermoacoustic Refrigerator

The uses of thermoacoustic effect are the conversion of heat onto acoustic wave by thermoacoustic prime mover and pumping heat by acoustic wave using a thermoacoustic refrigerator. Thermoacoustic refrigerator is a good alternative to conventional vapor compression device. It can be very compact, using a minimum of uncomplicated, economical components. It can also provide variable cooling capacity and scalability to different sizes in ways that conventional vapor compression technology is not capable of. We are investigating the minimum size of a thermoacoustic refrigerator that can meet the cooling requirement for different applications. The coefficient of performance (COP) of small thermoacoustic refrigerators is in the range of 20% of the ideal (Carnot cycle) COP, which is actually better than similarly scaled vapor compression coolers which is at about 10%. The efficiency of thermoacoustic refrigerator can be improved by better designing of its components. In this paper the effect of components design on the performance of thermoacoustic refrigerator is discussed. The scalability of such devices is also investigated.

Cooling load and coefficient of performance of thermoacoustic refrigerators: the role of the working fluid

Thermoacoustic refrigeration is a technology that uses mechanical energy in the form of sound waves to drive a heat pumping process that offers an environmentally safe, relatively low maintenance alternative to vapor compression refrigeration. Improving the design of the thermoacoustic core, composed of the stack plates and heat exchangers, may have the potential to bring thermoacoustic technology closer to commercial use. The stack plates have been analyzed to increase efficiency (expressed in terms of the coefficient of performance, COP) but in some applications a very high efficiency can lead to a smaller cooling load. The thermoacoustic stack was analytically optimized for maximum heat transfer (cooling load) and coefficient of performance (COP) for a range of working fluids of interest. Different noble gas mixtures were analyzed as the working fluid and helium was found to produce the highest cooling load because of its low molecular weight. The thermoacoustic stack plate center location, length, thickness and spacing were analyzed and optimum values to maximize cooling load and COP were found to exist for the specific input parameters considered. These optimization techniques may be used to design devices where maximum cooling load is more desirable than high efficiency.