scholarly journals Performance analysis of the thermoacoustic refrigerator with the standing wave and air as a working fluid

2018 ◽  
Vol 44 ◽  
pp. 00063 ◽  
Author(s):  
Jakub Kajurek ◽  
Artur Rusowicz
Keyword(s):  
Temperature Difference ◽  
High Reliability ◽  
Power Input ◽  
Acoustic Power ◽  
Operating Frequency ◽  
Working Fluid ◽  
Resonator Length ◽  
Environmental Friendliness ◽  
The Impact ◽  
Thermoacoustic Refrigerator

Thermoacoustic refrigerator is a new and emerging technology capable of transporting heat from a low-temperature source to a high-temperature source by utilizing the acoustic power input. These devices, operating without hazardous refrigerants and owning no moving components, show advantages of high reliability and environmental friendliness. However, simple to fabricate, the designing of thermoacoustic refrigerators is very challenging. This paper illustrates the impact of significant factors on the performance of the thermoacoustic refrigerator which was measured in terms of the temperature difference generated across the stack ends. The experimental device driven by a commercial loudspeaker and air at atmospheric pressure as a working fluid was examined under various resonator length and operating frequencies. The results indicate that appropriate resonator’s length and operating frequency lead to an increase in the temperature difference created across the stack. The maximum values were achieved for operating frequency equalled to 200 and 300 Hz whereas resonator length corresponded to the half-length of the acoustic wave for these frequencies. The results of experiment also confirm that relationship between these parameters is strongly affected by the stack spacing, which in this research was equalled to 0.4 mm.

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

2017 ◽  
Vol 38 (4) ◽  
pp. 89-107 ◽  
Author(s):  
Jakub Kajurek ◽  
Artur Rusowicz ◽  
Andrzej Grzebielec
Keyword(s):  
Standing Wave ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Acoustic Power ◽  
Working Fluid ◽  
Parallel Plates ◽  
Acoustic Frequency ◽  
Plate Spacing ◽  
Resonance Frequencies ◽  
Thermoacoustic Refrigerator

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.

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.

Effects of the Optimized Resonator Dimensions on the Performance of the Standing-Wave Thermoacoustic Refrigerator

2016 ◽  
Vol 819 ◽  
pp. 63-68
Author(s):  
Mawahib Hassan El-Fawal ◽  
Normah Mohd-Ghazali ◽  
Mohd Shafiek Yaccob
Keyword(s):  
Standing Wave ◽  
Cooling System ◽  
Small Diameter ◽  
Acoustic Power ◽  
Diameter Ratio ◽  
Coefficient Of Performance ◽  
Resonator Length ◽  
Environmentally Safe ◽  
And Performance ◽  
Thermoacoustic Refrigerator

Thermoacoustic refrigerator is an alternative cooling system, which is environmentally safe due to the absence of any refrigerants. The resonator tube of the system is of great importance; its design and dimensions influence the design and performance of the entire refrigerator. This work describes the design of the stack and the resonator along with the influence of its dimensions on the performance of the standing-wave thermoacoustic refrigerator. The resonator consists of two tubes, one larger than the other, characterized by the diameter ratio of the smaller over the larger diameter. A Lagrange multiplier method is used as a technique to optimize the coefficient of performance (COP) of the system. Results show that the resonator small diameter tube dissipates a minimum acoustic power at a diameter ratio of 0.46, which is 17 percent less than the published values. Moreover, the results show that the resonator length increases gradually with the increase of the mean design temperature which leads to the increase of the total acoustic power dissipated by the resonator, reducing the COP of the standing-wave thermoacoustic refrigerator.

Experimental study of thermohydraulic characteristics and irreversibility analysis of novel axial corrugated tube with spring tape inserts

2020 ◽  
Vol 92 (3) ◽  
pp. 30901
Author(s):  
Suvanjan Bhattacharyya ◽  
Debraj Sarkar ◽  
Ulavathi Shettar Mahabaleshwar ◽  
Manoj K. Soni ◽  
M. Mohanraj
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Thermal Performance ◽  
Working Fluid ◽  
The Novel ◽  
Heat Exchanger Tube ◽  
Heat Transfer Augmentation ◽  
Corrugated Tube ◽  
The Impact ◽  
Exchanger Tube

The current study experimentally investigates the heat transfer augmentation on the novel axial corrugated heat exchanger tube in which the spring tape is introduced. Air (Pr = 0.707) is used as a working fluid. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The experimental study is further extended by varying the important parameters like spring ratio (y = 1.5, 2.0, 2.5) and Reynolds number (Re = 10 000–52 000). The angular pitch between the two neighboring corrugations and the angle of the corrugation is kept constant through the experiments at β = 1200 and α = 600 respectively, while two different corrugations heights (h) are analyzed. While increasing the corrugation height and decreasing the spring ratio, the impact of the swirling effect improves the thermal performance of the system. The maximum thermal performance is obtained when the corrugation height is h = 0.2 and spring ratio y = 1.5. Eventually, correlations for predicting friction factor (f) and Nusselt number (Nu) are developed.

scholarly journals Crisis Management in Higher Education in the Time of Covid-19: The Case of Actor Training

2021 ◽  
Vol 11 (3) ◽  
pp. 132
Author(s):  
Anna McNamara
Keyword(s):  
Higher Education ◽  
Crisis Management ◽  
High Frequency ◽  
High Reliability ◽  
Actor Training ◽  
Management Actions ◽  
The Usa ◽  
The Uk ◽  
The Impact ◽  
High Frequency Words

The impact of Covid-19 placed Higher Education leadership in a state of crisis management, where decision making had to be swift and impactful. This research draws on ethea of mindfulness, actor training techniques, referencing high-reliability organisations (HRO). Interviews conducted by the author with three leaders of actor training conservatoires in Higher Education institutions in Australia, the UK and the USA reflect on crisis management actions taken in response to the impact of Covid-19 on their sector, from which high-frequency words are identified and grouped thematically. Reflecting on these high-frequency words and the thematic grouping, a model of mindful leadership is proposed as a positive tool that may enable those in leadership to recognise and respond efficiently to wider structural frailties within Higher Education, with reference to the capacity of leaders to operate with increased mindfulness, enabling a more resilient organisation that unlocks the locus of control.

Analysis of Multiplicity Phenomena in Longitudinal Fins Under Multi-Boiling Conditions

2004 ◽  
Vol 126 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Rizos N. Krikkis ◽  
Stratis V. Sotirchos ◽  
Panagiotis Razelos
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Solution Structure ◽  
Heat Dissipation ◽  
Heat Transfer Process ◽  
Working Fluid ◽  
Constant Thickness ◽  
Base Temperature ◽  
Operating Variables ◽  
Convection Parameter

A numerical bifurcation analysis is carried out in order to determine the solution structure of longitudinal fins subject to multi-boiling heat transfer mode. The thermal analysis can no longer be performed independently of the working fluid since the heat transfer coefficient is temperature dependent and includes the nucleate, the transition and the film boiling regimes where the boiling curve is obtained experimentally for a specific fluid. The heat transfer process is modeled using one-dimensional heat conduction with or without heat transfer from the fin tip. Furthermore, five fin profiles are considered: the constant thickness, the trapezoidal, the triangular, the convex parabolic and the parabolic. The multiplicity structure is obtained in order to determine the different types of bifurcation diagrams, which describe the dependence of a state variable of the system (for instance the fin temperature or the heat dissipation) on a design (Conduction-Convection Parameter) or operation parameter (base Temperature Difference). Specifically the effects of the base Temperature Difference, of the Conduction-Convection Parameter and of the Biot number are analyzed and presented in several diagrams since it is important to know the behavioral features of the heat rejection mechanism such as the number of the possible steady states and the influence of a change in one or more operating variables to these states.

Development and validation of men's sexualizing behaviors of women scale

2017 ◽  
Author(s):  
◽  
Dominique A. Malebranche
Keyword(s):  
Factor Analysis ◽  
Task Force ◽  
High Reliability ◽  
Future Research ◽  
Sexual Objectification ◽  
Adult Males ◽  
Gender Based Violence ◽  
Task Force Report ◽  
Traditional Masculinity ◽  
The Impact

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Sexualization has been posited to be a part of a larger process of socialization with negative implications (APA, 2010; Ward, 2016). Recent reviews of gender-based violence and exploitation have focused on important elements that highlight the impact of the pervasive experiences of sexual objectification and sexual commodification on women and girls, but relatively limited literature has explored domains of men's sexualizing behaviors. Using the theoretical domains outlined in the APA Task Force Report on the Sexualization of Girls (APA, 2010), the present study developed and validated a measure of men's sexualizing behaviors toward women (MSBWS) on a sample of 308 adult males (ages 18-34). Using exploratory factor analysis, results indicated three-factors that defined the MSBWS: Covert, Commodified, and Overt Sexualization. Analyses also revealed the MSBWS to have high reliability for the overall scale as well as the three subscales. Evidence for construct validity was revealed in significant correlations with all criterion variables (e.g., attitudes of sexual objectification, traditional masculinity and sexual aggression) and suggest broad implications that men's sexualizing behaviors is a measurable construct. Future research may further validate the MSBWS using confirmatory factor analysis on independent samples and examine relevant variables of the possible harm of sexualizing behaviors.

Development of Model for Acoustic Noise Generated from Bedload in Rivers 

2021 ◽  
Author(s):  
Mohamad Nasr ◽  
Thomas Geay ◽  
Sébastien Zanker ◽  
Recking Alain
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Impact Velocity ◽  
Acoustic Noise ◽  
Acoustic Power ◽  
Bedload Transport ◽  
Empirical Formulas ◽  
Impact Rate ◽  
Flux Measurements ◽  
The Impact

<p>Quantifying bedload transport is important for many applications such as river management and hydraulic structures protection. Bedload flux measurements can be achieved using physical sampler methods. However, these methods are expensive, time-consuming, and difficult to operate during high discharge events. Besides, these methods do not permit to capture the spatial and temporal variability of bedload transport flux. Recently, alternative measuring technologies have been developed to continuously monitor bedload flux and grain size distribution using passive or active sensors. Among them, the hydrophone was used to monitor bedload transport by recording the sounds generated by bedload particles colliding on the river bed (referred as self-generated noise SGN). The acoustic power of SGN was correlated with bedload flux in field experiments. To better understand these experimental results and to estimate measurement uncertainties, we developed a theoretical model to simulate the SGN. The model computes an estimation of the power spectral density (PSD)by considering the contribution of all signals generated by impacts between bedload particles and the riverbed, and accounting for the attenuation of the acoustic signal between the source and the hydrophone position due to river propagation effects,. In this model, we</p><p>The energy of acoustic noise generated from the collision between two particles is mainly dependent on the transported particles' diameter and the impact velocity. We tested different empirical formulas for the estimation of the number of impact (impact rate) and the impact velocity depending on particle size and hydraulic conditions. To characterize the acoustic power losses as a function of distance and frequency, we used an attenuation function which was experimentally calibrated for different French rivers.</p><p>We tested the model on a field dataset comprising acoustic and bedload flux measurements. The results indicate that the PSD model allows estimating acoustic power (in between a range of one order of magnitude) for most of the rivers considered.  The model sensitivity was evaluated. In particular, we observed that it is very sensitive to the empirical formulas used to determine the impact rate and impact speed. In addition, special attention should be kept in mind on the assumption of the grain size distribution of riverbed which can generate large variability in some rivers particularly in rivers with a significant sand fraction.</p>

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