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Heat Transfer Processes in Oscillatory Flow Conditions

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (31 May 2017) | Viewed by 56276

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Special Issue Editor

Prof. Artur J. Jaworski

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Guest Editor

Chair in Energy Technology & Environment, Faculty of Engineering, University of Leeds, Leeds LS2 9JT, UK
Interests: energy; heat transfer; thermodynamics; thermoacoustics; fluids; aerodynamics; multiphase flow; process tomography; sensors and instrumentation; heterogeneous mixtures; microfluidics; nanofluids

Special Issue Information

Dear Colleagues,

I would like to extend a warm invitation to all colleagues who would like to submit their research papers to the Special Issue of Applied Sciences (ISSN 2076-3417; CODEN: ASPCC7) on "Heat Transfer Processes in Oscillatory Flow Conditions". Heat exchange processes in steady flows have been studied extensively over the last two hundred years, and are now part of undergraduate syllabi of most engineering courses. However, heat transfer processes in oscillatory flow conditions are still not very well understood. Their importance is well recognized in applications, including Stirling machines, thermoacoustic devices or pulsed-tube coolers in cryogenics. Additionally, enhancement of heat transfer by using oscillatory, and, in some cases, pulsating flows is important in many areas of mechanical and chemical engineering for intensification of heat transfer processes and possible miniaturization of heat exchangers of the future. This Special Issue will give an opportunity of consolidating the recent advances in this important research field. All types of research approaches are equally acceptable: Experimental, theoretical, CFD, and their mixtures; the papers can be both of a fundamental and/or applied nature; the heat transfer phenomena can be looked at from either global/macroscopic perspective (e.g., whole heat exchanger units working in oscillatory flow regime) or local/microscopic perspective (e.g., fundamentals of heat transfer in individual channels where such processes occur in oscillatory flow regime). Contributions are also invited from all disciplines, including, but not limited to, engineering, physics and chemistry, and biological and medical sciences – the underlying theme being heat transfer processes in oscillatory flow conditions.

Prof. Artur J. Jaworski
Guest Editor

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Keywords

Oscillatory flow
oscillatory heat transfer
heat exchanger design
complex transport coefficients,
experimental, theoretical, numerical, fundamentals & applications

Published Papers (11 papers)

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Editorial

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149 KiB

Open AccessEditorial

Editorial for Special Issue: “Heat Transfer Processes in Oscillatory Flow Conditions”

by Artur J. Jaworski

Appl. Sci. 2017, 7(10), 994; https://doi.org/10.3390/app7100994 - 26 Sep 2017

Cited by 2 | Viewed by 2744

Abstract

Heat exchange processes in steady flows have been studied extensively over the last two hundred years, and are now part of undergraduate syllabi of most engineering courses [...]
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(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

Research

Jump to: Editorial

3389 KiB

Open AccessArticle

Comparative Performance of Thermoacoustic Heat Exchangers with Different Pore Geometries in Oscillatory Flow. Implementation of Experimental Techniques

by Antonio Piccolo, Roberto Siclari, Fabrizio Rando and Mauro Cannistraro

Appl. Sci. 2017, 7(8), 784; https://doi.org/10.3390/app7080784 - 02 Aug 2017

Cited by 26 | Viewed by 4795

Abstract

Heat exchangers (HXs) constitute key components of thermoacoustic devices and play an important role in determining the overall engine performance. In oscillatory flow conditions, however, standard heat transfer correlations for steady flows cannot be directly applied to thermoacoustic HXs, for which reliable and univocal design criteria are still lacking. This work is concerned with the initial stage of a research aimed at studying the thermal performance of thermoacoustic HXs. The paper reports a detailed discussion of the design and fabrication of the experimental set-up, measurement methodology and test-HXs characterized by two different pore geometries, namely a circular pore geometry and a rectangular (i.e., straight fins) pore geometry. The test rig is constituted by a standing wave engine where the test HXs play the role of ambient HXs. The experiment is conceived to allow the variation of a range of testing conditions such as drive ratio, operation frequency, acoustic particle velocity, etc. The procedure for estimating the gas side heat transfer coefficient for the two involved geometries is described. Some preliminary experimental results concerning the HX with straight fins are also shown. The present research could help in achieving a deeper understanding of the heat transfer processes affecting HXs under oscillating flow regime and in developing design optimization procedures. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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13880 KiB

Open AccessArticle

Numerical Predictions of Early Stage Turbulence in Oscillatory Flow across Parallel-Plate Heat Exchangers of a Thermoacoustic System

by Fatimah A. Z. Mohd Saat and Artur J. Jaworski

Appl. Sci. 2017, 7(7), 673; https://doi.org/10.3390/app7070673 - 30 Jun 2017

Cited by 24 | Viewed by 4768

Abstract

This work focuses on the predictions of turbulent transition in oscillatory flow subjected to temperature gradients, which often occurs within heat exchangers of thermoacoustic devices. A two-dimensional computational fluid dynamics (CFD) model was developed in ANSYS FLUENT and validated using the earlier experimental data. Four drive ratios (defined as maximum pressure amplitude to mean pressure) were investigated: 0.30%, 0.45%, 0.65% and 0.83%. It has been found that the introduction of the turbulence model at a drive ratio as low as 0.45% improves the predictions of flow structure compared to experiments, which indicates that turbulent transition may occur at much smaller flow amplitudes than previously thought. In the current investigation, the critical Reynolds number based on the thickness of Stokes’ layer falls in the range between 70 and 100. The models tested included four variants of the RANS (Reynolds-Averaged Navier–Stokes) equations: k-ε, k-ω, shear-stress-transport (SST)-k-ω and transition-SST, the laminar model being used as a reference. Discussions are based on velocity profiles, vorticity plots, viscous dissipation and the resulting heat transfer and their comparison with experimental results. The SST-k-ω turbulence model and, in some cases, transition-SST provide the best fit of the velocity profile between numerical and experimental data (the value of the introduced metric measuring the deviation of the CFD velocity profiles from experiment is up to 43% lower than for the laminar model) and also give the best match in terms of calculated heat flux. The viscous dissipation also increases with an increase of the drive ratio. The results suggest that turbulence should be considered when designing thermoacoustic devices even in low-amplitude regimes in order to improve the performance predictions of thermoacoustic systems. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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5421 KiB

Open AccessArticle

Modeling of Heat Transfer and Oscillating Flow in the Regenerator of a Pulse Tube Cryocooler Operating at 50 Hz

by Xiufang Liu, Chen Chen, Qian Huang, Shubei Wang, Yu Hou and Liang Chen

Appl. Sci. 2017, 7(6), 553; https://doi.org/10.3390/app7060553 - 05 Jun 2017

Cited by 7 | Viewed by 5603

Abstract

The regenerator of the pulse tube refrigerator (PTR) operates with oscillating pressure and mass flow, so a proper description of the heat transfer characteristics of the oscillating flow in the regenerator is crucial. In this paper, a one-dimensional model based on Lagrangian representation is developed to simulate the oscillating flow in the regenerator of the PTR. The continuity equation, momentum equation and energy equation are solved iteratively using the SIMPLER algorithm. The Darcy-Brinkman-Forchheimer model is used in the momentum equation, and a thermal non-equilibrium model is implemented in the energy equation. Lagrangian representation is employed to describe the thermodynamics of fluid parcels while the Eulerian representation (control volume method) is adopted for the energy equation of the solid matrix. The boundary conditions are set as the periodic flow of the sine function. The thermodynamic parameters of the gas parcels are obtained, which reveal the critical processes of the heat transfer in the regenerator under oscillating flow. The performance of the regenerator with different geometries is evaluated based on the numerical results. The present study provides insight for better understanding the physical process in the regenerator of the PTR, and the proposed model serves as a useful tool for the design and optimization of the cryogenic regenerator. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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14481 KiB

Open AccessArticle

The Effect of Temperature Field on Low Amplitude Oscillatory Flow within a Parallel-Plate Heat Exchanger in a Standing Wave Thermoacoustic System

by Fatimah A.Z. Mohd Saat and Artur J. Jaworski

Appl. Sci. 2017, 7(4), 417; https://doi.org/10.3390/app7040417 - 20 Apr 2017

Cited by 20 | Viewed by 7953

Abstract

Thermoacoustic technologies rely on a direct power conversion between acoustic and thermal energies using well known thermoacoustic effects. The presence of the acoustic field leads to oscillatory heat transfer and fluid flow processes within the components of thermoacoustic devices, notably heat exchangers. This paper outlines a two-dimensional ANSYS FLUENT CFD (computational fluid dynamics) model of flow across a pair of hot and cold heat exchangers that aims to explain the physics of phenomena observed in earlier experimental work. Firstly, the governing equations, boundary conditions and preliminary model validation are explained in detail. The numerical results show that the velocity profiles within heat exchanger plates become distorted in the presence of temperature gradients, which indicates interesting changes in the flow structure. The fluid temperature profiles from the computational model have a similar trend with the experimental results, but with differences in magnitude particularly noticeable in the hot region. Possible reasons for the differences are discussed. Accordingly, the space averaged wall heat flux is discussed for different phases and locations across both the cold and hot heat exchangers. In addition, the effects of gravity and device orientation on the flow and heat transfer are also presented. Viscous dissipation was found to be the highest when the device was set at a horizontal position; its magnitude increases with the increase of temperature differentials. These indicate that possible losses of energy may depend on the device orientation and applied temperature field. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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828 KiB

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Excitation of Surface Waves Due to Thermocapillary Effects on a Stably Stratified Fluid Layer

by William B. Zimmerman and Julia M. Rees

Appl. Sci. 2017, 7(4), 392; https://doi.org/10.3390/app7040392 - 13 Apr 2017

Cited by 1 | Viewed by 2990

Abstract

In chemical engineering applications, the operation of condensers and evaporators can be made more efficient by exploiting the transport properties of interfacial waves excited on the interface between a hot vapor overlying a colder liquid. Linear theory for the onset of instabilities due to heating a thin layer from above is computed for the Marangoni–Bénard problem. Symbolic computation in the long wave asymptotic limit shows three stationary, non-growing modes. Intersection of two decaying branches occurs at a crossover long wavelength; two other modes co-exist at the crossover point—propagating modes on nascent, shorter wavelength branches. The dispersion relation is then mapped numerically by Newton continuation methods. A neutral stability method is used to map the space of critical stability for a physically meaningful range of capillary, Prandtl, and Galileo numbers. The existence of a cut-off wavenumber for the long wave instability was verified. It was found that the effect of applying a no-slip lower boundary condition was to render all long waves stationary. This has the implication that any propagating modes, if they exist, must occur at finite wavelengths. The computation of 8000 different parameter sets shows that the group velocity always lies within

\frac{1}{2}

\frac{2}{3}

of the longwave phase velocity. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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5610 KiB

Open AccessArticle

Heat Transfer Investigation of the Unsteady Thin Film Flow of Williamson Fluid Past an Inclined and Oscillating Moving Plate

by Taza Gul, Abdul Samad Khan, Saeed Islam, Aisha M. Alqahtani, Ilyas Khan, Ali Saleh Alshomrani, Abdullah K. Alzahrani and Muradullah

Appl. Sci. 2017, 7(4), 369; https://doi.org/10.3390/app7040369 - 07 Apr 2017

Cited by 11 | Viewed by 5091

Abstract

This investigation aims at analyzing the thin film flow passed over an inclined moving plate. The differential type non-Newtonian fluid of Williamson has been used as a base fluid in its unsteady state. The physical configuration of the oscillatory flow pattern has been demonstrated and especial attention has been paid to the oscillatory phenomena. The shear stresses have been combined with the energy equation. The uniform magnetic field has been applied perpendicularly to the flow field. The principal equations for fluid motion and temperature profiles have been modeled and simplified in the form of non-linear partial differential equations. The non-linear differential equations have been solved with the help of a powerful analytical technique known as Optimal Homotopy Asymptotic Method (OHAM). This method contains unknown convergence controlling parameters

C_{1}, C_{2}, C_{3}, ...

which results in more efficient and fast convergence as compared to other analytical techniques. The OHAM results have been verified by using a second method known as Adomian Decomposition Method (ADM). The closed agreement of these two methods and the fast convergence of OHAM has been shown graphically and numerically. The comparison of the present work and published work has also been equated graphically and tabulated with absolute error. Moreover, the effect of important physical parameters like magnetic parameter

M

, gravitational parameter

m

, Oscillating parameter

ω

, Eckert number

E c

and Williamson number

W e

have also been derived and discussed in this article. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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826 KiB

Open AccessArticle

Measurement of Heat Flow Transmitted through a Stacked-Screen Regenerator of Thermoacoustic Engine

by Shu Han Hsu and Tetsushi Biwa

Appl. Sci. 2017, 7(3), 303; https://doi.org/10.3390/app7030303 - 20 Mar 2017

Cited by 5 | Viewed by 6287

Abstract

A stacked-screen regenerator is a key component in a thermoacoustic Stirling engine. Therefore, the choice of suitable mesh screens is important in the engine design. To verify the applicability of four empirical equations used in the field of thermoacoustic engines and Stirling engines, this report describes the measurements of heat flow rates transmitted through the stacked screen regenerator inserted in an experimental setup filled with pressurized Argon gas having mean pressure of 0.45 MPa. Results show that the empirical equations reproduce the measured heat flow rates to a mutually similar degree, although their derivation processes differ. Additionally, results suggest that two effective pore radii would be necessary to account for the viscous and thermal behaviors of the gas oscillating in the stacked-screen regenerators. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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3119 KiB

Open AccessArticle

Friction Factor Correlation for Regenerator Working in a Travelling-Wave Thermoacoustic System

by Fatimah A. Z. Mohd Saat and Artur J. Jaworski

Appl. Sci. 2017, 7(3), 253; https://doi.org/10.3390/app7030253 - 05 Mar 2017

Cited by 10 | Viewed by 5975

Abstract

Regenerator is a porous solid structure which is important in the travelling-wave thermoacoustic system. It provides the necessary contact surface and thermal capacity for the working gas to undergo a thermodynamic cycle under acoustic oscillatory flow conditions. However, it also creates a pressure drop that could degrade the overall system performance. Ideally, in a travelling-wave system, the phase angle between oscillating pressure and velocity in the regenerator should be zero, or as close to zero as possible. In this study, the hydrodynamic condition of a regenerator has been investigated both experimentally (in a purpose-built rig providing a travelling-wave phasing) and numerically. A two-dimensional ANSYS FLUENT CFD model, capturing the important features of the experimental conditions, has been developed. The findings suggest that a steady-state correlation, commonly used in designing thermoacoustic systems, is applicable provided that the travelling-wave phase angle is maintained. However, for coarse mesh regenerators, the results show interesting “phase shifting” phenomena, which may limit the correlation validity. Current experimental and CFD studies are important for predicting the viscous losses in future models of thermoacoustic systems. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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3041 KiB

Open AccessArticle

Influence of the Water-Cooled Heat Exchanger on the Performance of a Pulse Tube Refrigerator

by Wei Wang, Jianying Hu, Jingyuan Xu, Limin Zhang and Ercang Luo

Appl. Sci. 2017, 7(3), 229; https://doi.org/10.3390/app7030229 - 28 Feb 2017

Cited by 5 | Viewed by 5403

Abstract

The water-cooled heat exchanger is one of the key components in a pulse tube refrigerator. Its heat exchange effectiveness directly influences the cooling performance of the refrigerator. However, effective heat exchange does not always result in a good performance, because excessively reinforced heat exchange can lead to additional flow loss. In this paper, seven different water-cooled heat exchangers were designed to explore the best configuration for a large-capacity pulse tube refrigerator. Results indicated that the heat exchanger invented by Hu always offered a better performance than that of finned and traditional shell-tube types. For a refrigerator with a working frequency of 50 Hz, the best hydraulic diameter is less than 1 mm. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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4660 KiB

Open AccessArticle

A Comprehensive Empirical Correlation for Finned Heat Exchangers with Parallel Plates Working in Oscillating Flow

by Jiale Huang, Mianli Liu and Tao Jin

Appl. Sci. 2017, 7(2), 117; https://doi.org/10.3390/app7020117 - 08 Feb 2017

Cited by 10 | Viewed by 3669

Abstract

The oscillating-flow heat transfer performance in finned heat exchangers is one of the main factors affecting the working efficiency of regenerative heat engines and refrigerators. In addition to the working parameters, the geometrical parameters of finned heat exchangers are also major influencing factors. In the present study, the ratio of the heat exchanger length and hydraulic diameter is applied as an independent similarity criterion. An experimental study has been carried out with six different geometrical dimensions of finned heat exchangers with parallel plates, in order to analyze the impacts of fin length, plate spacing, and corresponding relative fluid displacement amplitude, under various working conditions. Based on 298 tested points, a comprehensive empirical correlation for the finned heat exchangers with parallel plates working in oscillating flow has been proposed, providing a relatively accurate prediction, with 98.6% of data in the ±20% deviation and 83.9% of data in the ±10% deviation, within the range discussed. Full article

(This article belongs to the Special Issue Heat Transfer Processes in Oscillatory Flow Conditions)

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