Design and Comparative Analysis of Thermoacoustic Refrigerators

2017 ◽  
Vol 25 (01) ◽  
pp. 1750002 ◽  
Author(s):  
B. G. Prashantha ◽  
M. S. Govinde Gowda ◽  
S. Seetharamu ◽  
G. S. V. L. Narasimham
Keyword(s):  
Comparative Analysis ◽  
Heat Exchanger ◽  
Past Research ◽  
Performance Comparison ◽  
Working Fluid ◽  
Cooling Power ◽  
The Past ◽  
Present Design ◽  
Theoretical Minimum ◽  
Thermoacoustic Refrigerator

In this paper, the design of a loudspeaker driven 10[Formula: see text]W cooling power stack-based thermoacoustic refrigerator at 3% drive ratio for a temperature difference of 80[Formula: see text]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[Formula: see text]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.

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

2019 ◽  
Vol 8 (4) ◽  
pp. 2704-2712
Keyword(s):  
Heat Exchanger ◽  
Temperature Difference ◽  
Parallel Plate ◽  
Sheet Material ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Operating Pressure ◽  
Parallel Plates ◽  
Refrigeration System ◽  
Thermoacoustic Refrigerator

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 (∆T). 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 ∆T 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.

Aerodynamic and Thermal Measurements in a Standing Wave Thermoacoustic Refrigerator

2010 ◽  
Author(s):  
Gaelle Poignand ◽  
Emmanuel Jondeau ◽  
Philippe Blanc-Benon
Keyword(s):  
Heat Transfer ◽  
Standing Wave ◽  
Heat Exchangers ◽  
System Performance ◽  
Heat Fluxes ◽  
Acoustic Energy ◽  
Working Fluid ◽  
Cooling Power ◽  
Thermal Measurements ◽  
Thermoacoustic Refrigerator

Thermoacoustic refrigerators produce a cooling power from an acoustic energy. Over the last decades, these devices have been extensively studied since they are environment-friendly, robust and miniaturizable. Despite all these advantages, their commercialization is limited by their low efficiency. One reason for this limitation comes from the complex thermo-fluid process between the stack and the two heat exchangers which is still not sufficiently understood to allow for optimization. In particular, at high acoustic pressure level, vortex shedding can occur behind the stack as highlight by [Berson & al., Heat Mass Trans, 44, 10151023 (2008)]. The created vortex can affect heat transfer between the stack and the heat exchangers and thus, they can reduce the system performance. In this work, aerodynamic and thermal measurements are both conducted in a standing wave thermoacoustic refrigerator allowing investigation of vortex influence on the system performance. The proposed device consists on a resonator operated at frequency of 200 Hz, with hot and cold heat exchangers placed at the stack extremities. The working fluid is air at ambient temperature and atmospheric pressure. The aerodynamic field behind the stack is described using high-speed Particle Image Velocimetry. This technique allows the acoustic velocity field measurement at a frequency up to 3000 Hz. Thermal measurements consist on the acquisition of both the temperature evolution along the stack and the heat fluxes extracted at the cold heat exchanger. These measurements are performed by specific micro-sensors developed by MEMS technology. The combination of these two measurements should be helpful for the further understanding of the heat transfer between the stack and the heat exchangers.

Control of a Standing-Wave Thermoacoustic Refrigerator

2010 ◽  
Author(s):  
Tim Ryan ◽  
Laura A. Schaefer ◽  
Jeffrey S. Vipperman
Keyword(s):  
Acoustic Pressure ◽  
Frequency Control ◽  
Acoustic Power ◽  
Phase Locked Loop ◽  
Performance Comparison ◽  
Cooling Power ◽  
Test Bed ◽  
Gradient Ascent ◽  
Control Scheme ◽  
Thermoacoustic Refrigerator

A demonstration thermoacoustic refrigerator was used to test the effectiveness of three operating frequency control schemes. The goal was to determine which control scheme would be most beneficial in terms of efficiency when a driver and resonator are mismatched as may be the case where manufacturing tolerances are involved. The first control scheme was a phase-locked loop, which is the type of control most often used in the literature; the second and third were a gradient ascent algorithm applied to root-mean-squared acoustic pressure and time-averaged acoustic power supplied to the resonator, respectively. The controllers, each operating on a different parameter associated with a strong thermoacoutic effect, were simulated using an identified model of the plant, and adjustments were made to the controller parameters. Finally, the controllers were applied to the test bed device. The performance comparison of the controllers was based on thermoacoustic efficiency, electroacoustic efficiency, and electrothermal efficiency. The phase-locked loop was found to perform better thermoacoustically, but the acoustic pressure gradient ascent control performed better in terms of electroacoustic and electrothermal performance. The acoustic power gradient ascent controller resulted in the thermoacoustic core producing the most steady-state cooling power.

scholarly journals Design Analysis of Thermoacoustic Refrigerator Using Air and Helium as Working Substances

2017 ◽  
Vol 13 (2) ◽  
Keyword(s):  
Heat Exchanger ◽  
Low Temperature ◽  
Sheet Thickness ◽  
Design Strategy ◽  
Cooling Power ◽  
Resonator Design ◽  
Helium Gas ◽  
Penetration Depths ◽  
Shape And Size ◽  
Thermoacoustic Refrigerator

In this paper, thermoacoustic refrigerator design strategy with parameters normalization and literature review covering the recent development in the modification of the resonator shape and size is discussed. The design of a 10 W cooling power thermoacoustic refrigerator using air as working substance and the effect of operating frequency on viscous and thermal penetration depths, and on stack sheet thickness and spacing are discussed. The promising 10 W cooling power TDH (Taper and Divergent section with Hemispherical end) resonator design operating with air and helium gases as working substances is analyzed using DeltaEC software. The analysis results show that the TDH resonator design using helium as working substance operates at lower drive ratio (14%) compared to air (25%). In comparison, DeltaEC predicts a decent low temperature of -35.4 o C at cold heat exchanger with a COP of 0.5294 when operated using helium gas, and for air is -9 oC and 0.8113 respectively, and the results are discussed.

Design Construction and Performance of 10W Thermoacoustic Refrigerators

2017 ◽  
Vol 25 (03) ◽  
pp. 1750023 ◽  
Author(s):  
B. G. Prashantha ◽  
M. S. Govinde Gowda ◽  
S. Seetharamu ◽  
G. S. V. L. Narasimham
Keyword(s):  
Comparative Analysis ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Small Diameter ◽  
Cooling Power ◽  
Experimental Measurements ◽  
And Performance ◽  
Assembly Procedure ◽  
Design Construction ◽  
Thermoacoustic Refrigerators

In this paper, the construction and performance of the 10[Formula: see text]W 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, 0.28[Formula: see text]-taper, small diameter tube and divergent section with hemispherical end (TSDH) and 0.24[Formula: see text]-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 0.28[Formula: see text]-TSDH, and 0.24[Formula: see text]-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 [Formula: see text]11.3[Formula: see text]C and [Formula: see text]8.7[Formula: see text]C at 10[Formula: see text]W cooling power is achieved at the cold heat exchanger for the 0.28[Formula: see text]-TSDH and 0.24[Formula: see text]-TDH resonator designs, respectively. The comparative analysis of the experimental results with the theoretical and DeltaEC results is discussed.

Exploring the Boundaries of the Number–Temporal Order Association

2015 ◽  
Vol 62 (3) ◽  
pp. 198-205 ◽  
Author(s):  
Dana Ganor-Stern
Keyword(s):  
Embodied Cognition ◽  
Mental Representation ◽  
Temporal Order ◽  
Past Research ◽  
Numerical Comparison ◽  
Negative Number ◽  
Comparison Task ◽  
Negative Numbers ◽  
The Past

Past research has shown that numbers are associated with order in time such that performance in a numerical comparison task is enhanced when number pairs appear in ascending order, when the larger number follows the smaller one. This was found in the past for the integers 1–9 ( Ben-Meir, Ganor-Stern, & Tzelgov, 2013 ; Müller & Schwarz, 2008 ). In the present study we explored whether the advantage for processing numbers in ascending order exists also for fractions and negative numbers. The results demonstrate this advantage for fraction pairs and for integer-fraction pairs. However, the opposite advantage for descending order was found for negative numbers and for positive-negative number pairs. These findings are interpreted in the context of embodied cognition approaches and current theories on the mental representation of fractions and negative numbers.

Impact of Globalisation on Pandemics: A comparative study on SARS and Covid-19 (Preprint)

2020 ◽  
Author(s):  
Johann Johann And Devika
Keyword(s):  
Comparative Analysis ◽  
Comparative Study ◽  
Descriptive Analysis ◽  
Qualitative Comparative Analysis ◽  
Global Scale ◽  
Global Level ◽  
Economic Stability ◽  
The Past ◽  
The World ◽  
Close Relationship

BACKGROUND Since November 2019, Covid - 19 has spread across the globe costing people their lives and countries their economic stability. The world has become more interconnected over the past few decades owing to globalisation and such pandemics as the Covid -19 are cons of that. This paper attempts to gain deeper understanding into the correlation between globalisation and pandemics. It is a descriptive analysis on how one of the factors that was responsible for the spread of this virus on a global scale is globalisation. OBJECTIVE - To understand the close relationship that globalisation and pandemics share. - To understand the scale of the spread of viruses on a global scale though a comparison between SARS and Covid -19. - To understand the sale of globalisation present during SARS and Covid - 19. METHODS A descriptive qualitative comparative analysis was used throughout this research. RESULTS Globalisation does play a significant role in the spread of pandemics on a global level. CONCLUSIONS - SARS and Covid - 19 were varied in terms of severity and spread. - The scale of globalisation was different during the time of SARS and Covid - 19. - Globalisation can be the reason for the faster spread in Pandemics.

scholarly journals Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): sensitivity analysis on the Newberry volcanic setting

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Hannah R. Doran ◽  
Theo Renaud ◽  
Gioia Falcone ◽  
Lehua Pan ◽  
Patrick G. Verdin
Keyword(s):  
Sensitivity Analysis ◽  
Heat Exchanger ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Energy Flow ◽  
Closed Loop ◽  
Working Fluid ◽  
Valuable Insight ◽  
Deep Borehole

AbstractAlternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths.

scholarly journals Ecodesign—A Review of Reviews

2020 ◽  
Vol 13 (1) ◽  
pp. 315
Author(s):  
Malte Schäfer ◽  
Manuel Löwer
Keyword(s):  
Success Factors ◽  
Research Question ◽  
Pollution Prevention ◽  
Past Research ◽  
The Past ◽  
Review Articles ◽  
Complete Life Cycle ◽  
Review Of Reviews ◽  
Research Questions ◽  
Over Time

With the intent of summing up the past research on ecodesign and making it more accessible, we gather findings from 106 existing review articles in this field. Five research questions on terminology, evolution, barriers and success factors, methods and tools, and synergies, guide the clustering of the resulting 608 statements extracted from the reference. The quantitative analysis reveals that the number of review articles has been increasing over time. Furthermore, most statements originate from Europe, are published in journals, and address barriers and success factors. For the qualitative analysis, the findings are grouped according to the research question they address. We find that several names for similar concepts exist, with ecodesign being the most popular one. It has evolved from “end-of-pipe” pollution prevention to a more systemic concept, and addresses the complete life cycle. Barriers and success factors extend beyond the product development team to management, customers, policymakers, and educators. The number of ecodesign methods and tools available to address them is large, and more reviewing, testing, validation, and categorization of the existing ones is necessary. Synergies between ecodesign and other research disciplines exist in theory, but require implementation and testing in practice.

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