THEORETICAL EVALUATION OF LOUDSPEAKER FOR A 10 WATTS COOLING POWER THERMOACOUSTIC REFRIGERATOR

B. G. PRASHANTHA,M. S. GOVINDE GOWDA,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2013 International Journal Of Air-Conditioning and Refr Vol.21 No.4

This paper presents a design of moving coil loudspeaker for a 10W cooling power thermoacoustic refrigerator. An electrical model is presented which simulates the behavior of the loudspeaker. The gas spring system for matching the frequency of the commercially available loudspeaker with the frequency of the acoustic resonator tube for maximizing electro-acoustical e±ciency of the loudspeaker is discussed. The optimum back volume for the gas spring system is found to be 59.7 cc, which is about 1.9% of the total resonator volume when the loudspeaker frequency and the acoustic resonator frequency is made equal at 400 Hz with a moving mass of 20 g. The effect of force factor Bl on loudspeaker performance is discussed. Analysis results shows that for better performance of a refrigerator, the loudspeaker should be chosen to have a large force factor and small values for electrical and mechanical resistances. The refrigerator system is tested with DeltaEC software and its results are in good agreement with an electrical model results.

DESIGN AND OPTIMIZATION OF A LOUDSPEAKER DRIVEN 10-W COOLING POWER THERMOACOUSTIC REFRIGERATOR

B. G. PRASHANTHA,M. S. GOVINDE GOWDA,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2014 International Journal Of Air-Conditioning and Refr Vol.22 No.3

The design and optimization procedure for a loudspeaker driven 10-W cooling power thermoacoustic refrigerator components with a temperature difference of 120 K has been discussed using the linear thermoacoustic theory. The resonator losses are proportional to surface area and the optimum diameter ratio of small and large resonator tubes for minimum heat loss for a quarter-wavelength hemispherical ended resonator design is discussed. The hemispherical ended resonator design is further analytically optimized to increase COP, cooling effect at cold heat exchanger and power density by decreasing total resonator surface area and volume. An alternate convergent-divergent resonator design is proposed which is found to be more efficient compared to previous published designs. Resonator designs are tested with DeltaEC software, which predicts a lowest temperature of -48°C and -47°C for the improved hemispherical and convergent-divergent resonator designs, respectively. Theoretical results are in good agreement with DeltaEC results.

Resonator Optimization and Studying the Effect of Drive Ratio on the Theoretical Performance of a 10-W Cooling Power Thermoacoustic Refrigerator

B. G. PRASHANTHA,M. S. Govinde Gowda,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2015 International Journal of Air-Conditioning and Refr Vol.23 No.3

This paper deals with the basic insight of thermoacoustic refrigeration concepts, and the working principle, history and the role of linear thermoacoustic theory in designing a thermoacoustic refrigerator system are discussed. Resonator design optimization procedure for a 10W cooling power thermoacoustic refrigerators is discussed. The optimized resonator designs proposed in this paper are found to be efficient compared to published resonator designs. The effects of drive ratio on the theoretical performance by varying dynamic pressure amplitude from 0.2 bar to 0.4 bar in the steps of 0.05 bar on the optimized resonator designs are discussed. Performance simulation results for the optimized resonator designs using DeltaEC software are discussed. Simulation results are in agreement with theoretical results.

Design and Analysis of Thermoacoustic Refrigerators Using Air as Working Substance

B. G. PRASHANTHA,S. SEETHARAMU,G. S. V. L. NARASIMHAM,M. R. Praveen Kumar 대한설비공학회 2019 International Journal Of Air-Conditioning and Refr Vol.27 No.1

In this paper, the design of 50 W thermoacoustic refrigerators operating with air as working substance at 10 bar pressure and 3% drive ratio for a temperature difference of 28 K is described. The design strategies discussed in this paper help in design and development of low cost thermoacoustic coolers compared to helium as the working substance. The design and optimization of spiral stack and heat exchangers, and the promising 0.2λ and 0.15λ resonator design with taper and divergent section with hemispherical end are discussed. The surface area, volume, length and power density of the hemispherical end design with air as working substance is found better compared to the published 10 and 50 W coolers using helium as the working substance. The theoretical design results are validated using DeltaEC software simulation results. The DeltaEC predicts 51.4% improvement in COP (1.273) at the cold heat exchanger temperature of −2.7∘C with air as working substance for the 50W 0.15λTDH resonator design compared to the published 50W 0.25λTDH resonator design with helium as working substance.

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

B. G. PRASHANTHA,S. SEETHARAMU,G. S. V. L. NARASIMHAM,M. R. Praveen Kumar 대한설비공학회 2019 International Journal Of Air-Conditioning and Refr Vol.27 No.2

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 −30∘C with helium compared to air (COP 0.616 at8.8∘C) for the 50 W cooling power 100 mm diameter quarter-wavelength resonator designs.

Design Construction and Performance of 10W Thermoacoustic Refrigerators

B. G. PRASHANTHA,M. S. Govinde Gowda,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2017 International Journal Of Air-Conditioning and Refr Vol.25 No.3

In this paper, the construction and performance of the 10W cooling power thermoacoustic refrigerators designed for a temperature difference of 120 K at 3% drive ratio are discussed. The construction and assembly procedure of the optimized thermoacoustic refrigerator components viz. spiral stack, heat exchangers, 0.28λλ-taper, small diameter tube and divergent section with hemispherical end (TSDH) and 0.24λλ-taper and divergent section with hemispherical end (TDH) resonator designs and loudspeaker found in the published literature, and instrumentation are discussed. The performance of the 0.28λλ-TSDH, and 0.24λλ-TDH resonator designs, and the uncertainties involved in the experimental measurements are discussed. Both the resonator designs show good behavior. A decent low temperature of −−11.3∘∘C and −−8.7∘∘C at 10W cooling power is achieved at the cold heat exchanger for the 0.28λλ-TSDH and 0.24λλ-TDH resonator designs, respectively. The comparative analysis of the experimental results with the theoretical and DeltaEC results is discussed.

Design and Comparative Analysis of Thermoacoustic Refrigerators

B. G. PRASHANTHA,M. S. Govinde Gowda,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2017 International Journal Of Air-Conditioning and Refr Vol.25 No.1

In this paper, the design of a loudspeaker driven 10 W cooling power stack-based thermoacoustic refrigerator at 3% drive ratio for a temperature difference of 80 K using helium as working fluid is discussed. The refrigerator is designed using linear thermoacoustic concepts. Using linear thermoacoustic equations, a theoretical minimum cold heat exchanger temperature is estimated at 75% porosity of stack-heat exchanger system. This paper focuses on the comparative analysis of the present design with the similar 10 W thermoacoustic refrigerator designs found in the literature. The theoretical performance comparison of TSDH, TDH and CDH resonators designed at 2% and 3% drive ratio is discussed. The resonator designs are validated using DeltaEC software and the results are discussed. DeltaEC simulation results show that the diameter of the vibrating diaphragm of the loudspeaker equal to the diameter of the stack-heat exchangers system has higher electroacoustic efficiency (74.7%) and better performance compared to the smaller diaphragm (42.6%) used in the past research.

DESIGN AND ANALYSIS OF THERMOACOUSTIC REFRIGERATOR

B. G. PRASHANTHA,M. S. GOVINDE GOWDA,S. SEETHARAMU,G. S. V. L. NARASIMHAM 대한설비공학회 2013 International Journal Of Air-Conditioning and Refr Vol.21 No.1

This paper deals with the design and analysis of a quarter-wavelength, 10W capacity, thermoacoustic refrigerator using short stack boundary layer approximation assumptions. The e®ect of operating frequency on the performance of the refrigerator is studied using dimensional normalization technique. The variation of stack diameter with average gas pressure and cooling power is discussed. The resonator optimization is discussed and the calculation results show a 9% improvement in the coe±cient of performance and 201% improvement in power density for the optimized quarter-wavelength resonator compared to published optimization studies. The optimized resonator design is tested with DeltaEC software and the results show better performance compared to past established resonator designs.

Effect of Gas Blockage on the Theoretical Performance of Thermoacoustic Refrigerators

B. G. Prashantha,G. S. V. L. NARASIMHAM,S. SEETHARAMU,K. Manjunathachari 대한설비공학회 2021 International Journal Of Air-Conditioning and Refr Vol.29 No.3

Thermoacoustic refrigeration is an emerging green, novel and promising alternate technology compared to vapor compression refrigerator systems for domestic cooling. It uses environmentally benign gases like air or helium or the mixture of inert gases as working substances and has no moving parts, no lubrication and no vibration. The cooler is designed and optimized with helium and air as refrigerants operating at 10bar with 3% drive ratio for the temperature difference of 28K and stack diameter of 200mm using linear thermoacoustic theory. In this paper, the effect of gas blockage (porosity) of the spiral-stack heat exchanger system ranging from 45% to 85% on the theoretical performance of the cooler is discussed. The one-third and one-fourth wavelength convergent–divergent resonator designs are optimized with air and helium as working substances, respectively, to improve performance and power density. The optimized coolers show best performance with 85% porosity. The theoretical results are validated with DeltaEC software simulation results. The simulation results show the coefficient of performance and cooling capacity of 0.93 and 219W for helium and of 0.50 and 139W for air, respectively, at the cold heat exchanger temperature of 0∘C.

Theoretical evaluation of stack-based thermoacoustic refrigerators

Prashantha B. G.,Narasimham G. S. V. L.,Seetharamu S.,Hemadri Vinayak B. 대한설비공학회 2022 International Journal of Air-Conditioning and Refr Vol.30 No.1

Standing wave thermoacoustic refrigerator uses stack, is the heart of the thermoacoustic cooling system. The porous stack in the resonator tube develops temperature difference across the stack for heat pumping upon loudspeaker sound interaction of oscillating gas. In this paper, the optimization of stack-heat exchangers system and resonator is discussed using linear thermoacoustic theory for better COP and cooling power of refrigerator. The loudspeaker is assumed to provide the required acoustic power with the back volume gas spring system. Helium and air are chosen because of their better thermophysical properties and cost, compared to other competent gases. The 200 mm diameter stack is optimized for the temperature difference of 28 K. The theoretical results of the optimized refrigerator models are compared with the DeltaEC simulation results for deriving conclusions. DeltaEC predicts the cooling power and COP of 349 W at 0.998 for helium, and 139 W at 1.133 for air, respectively.