Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system

Shi, Lei; Yu, Zhibin; Jaworski, Artur J.

doi:10.1016/j.ijthermalsci.2010.03.015

Cited by 42 publications

(31 citation statements)

References 44 publications

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“…Such a method is employed herein, by using the temperature-sensitive dye Rhodamine B. Fluorescence methods have proven popular in evaluating the heat exchange of microchannel devices [26,29], in plate heat exchangers with oscillating flow [27,28] and has also been used to measure fluid film temperatures elsewhere [30,31].…”

Section: Case Study I: Heated Falling Filmsmentioning

confidence: 99%

Heat transfer augmentation in unsteady conjugate thermal systems – Part II: Applications

Mathie

Nakamura

Markides

2013

International Journal of Heat and Mass Transfer

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Many energy conversion and other thermal-fluid systems exhibit unsteady convective heat exchange. In such systems, generic spatiotemporal variations in the flow give rise to variations in the heat flux for a given fluid-solid temperature difference, which can be interpreted as spatiotemporal fluctuations of the instantaneous heat transfer coefficient. These variations can lead to unsteady conjugate heat transfer, in which the exchanged heat flux arises from an interaction between the bulk fluid temperature and the temperature in the solid. Further, the nonlinear coupling between the fluctuating temperature differences and the heat transfer coefficient can lead to an effect we refer to as augmentation, which quantitatively describes the ability of a particular arrangement to have a different time-mean heat flux from the product between the mean heat transfer coefficient and the mean temperature difference across the fluid. It is important to be able to understand and to model in a simple framework the effects of the material properties, the geometry and the character of the heat transfer coefficient on the thermal response of the fluid-solid system, and consequently to predict the overall heat transfer performance of these systems. This paper, which follows on from its predecessor (Mathie and Markides, 2012a), is concerned with the phenomenon of augmentation in simple, one-dimensional, unsteady and conjugate fluid-solid systems. A simple semi-analytical one-dimensional model of heat transfer with a time-varying heat transfer coefficient, which was presented in Mathie and Markides (2012a), is applied herein to two different paradigm problems. Such a model can be an important tool in the design of improved heat exchangers and thermal insulation, through for example, the novel selection of materials to exploit these augmentation effects. The first flow considered is a thin, wavy fluid film flowing over a heated plate. This film flow exhibits a periodic fluctuation in the heat transfer coefficient, that is linked to the wavy interfacial deformations of free surface of the liquid film. The second flow considered concerns the heat transfer behind a backwards-facing step, which exhibits broadband fluctuations in the heat transfer coefficient due to the flow separation and turbulence behind * Corresponding author.

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Section: Case Study I: Heated Falling Filmsmentioning

confidence: 99%

Heat transfer augmentation in unsteady conjugate thermal systems – Part II: Applications

Mathie

Nakamura

Markides

2013

International Journal of Heat and Mass Transfer

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“…[7,9,18]) the natural convection effect was neglected. This effect however was observed in many experimental works [1,11,17].…”

Section: Introduction and Literature Reviewmentioning

confidence: 87%

“…This result, however, is not very conclusive because the temperature difference investigated was not widely varied. Furthermore, it is speculated that the presence of additional structures such as the stack and heat exchanger may alter the influence of the natural convection effect on the flow even when the velocity is relatively small [11].…”

Section: Introduction and Literature Reviewmentioning

confidence: 99%

“…However, the presence of a temperature gradient on solid boundaries is necessary for the thermoacoustic effect to take place. Temperature effects must be considered to account for additional phenomena such as temperature-driven buoyancy [11,[15][16][17][18] and non-linear effects [4] that could affect the flow symmetry. Experimental studies often reveal signs of nonlinearities that are insufficiently addressed by the linear model [1,11].…”

Section: Introduction and Literature Reviewmentioning

confidence: 99%

“…The novelty of this study stems from the fact that the model used attempts to take into account a far wider range of physical effects which are commonly neglected in numerical works related to thermoacoustics (i.e., natural convection or the use of a full array of plates to handle asymmetrical flow features). This is undertaken to explain the phenomena reported in [11,17]. In addition, the study of device orientation provides a new perspective of the importance of considering such seemingly minor details in modelling heat transfer phenomena in thermoacoustics.…”

Section: Introduction and Literature Reviewmentioning

confidence: 99%

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

Saat

Jaworski

2017

Applied Sciences

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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.

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Generalization of the thermoacoustic form functions for evaluating the transverse temperature gradient effect

2015

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Section average of the viscous form function F 0 for perfect fluid g i (0) Section average of the ith thermal form function G i for perfect fluid G i Thermal form functions g i Section average of the viscous form function G i h n Helmholtz number express the ratio l * / * r between the length of channel and the scale of the acoustic wave length * r = 2π ω * r C * r using the scales C * r and ω * r for speed of sound and for angular frequency respectively MaMach number expressing the ratio formed by scales of fluid speed u * r and speed of sound C * r q i Dimensionless heat flux density respectively following the axial and transversal direction i = 1 or 2 q y0 0th order heat flux density following the transverse directionDimensionless coordinate of y * = d * y using length scale d * Y| 0 , Y| 1 Scaled variable of fluid at the interface Γ 1 and Γ 2where or 1 is the order of the variable Y according to Mach number Greek letters δ κScaled thermal penetration depth defined as in literature [7,21], according the length scale d * AbstractThe main purpose of this paper is to study analytically the effect of transverse gradient of time averaged temperature on the oscillating flow between parallel plates that occurs in thermoacoustic device such as resonator, stack and heat exchanger. In fact, this transverse gradient of temperature is not taken into account in standard linear theory and can have considerable consequences on the thermoacoustic machines operating as the onset parameters. For this purpose, an asymptotic model generalizing the standard linear theory is proposed. This approach is done without making supplementary assumptions compared to the known model in literature. Consequently, generalized viscous and thermal form functions are deduced by analytical development. Hence, the results of the thermal nonuniformity according to transverse direction are analyzed using these form functions. Furthermore, the critical temperature gradient is calculated analytically for this case.

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Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system

Abstract: AJ (2010) Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system.

Cited by 42 publications

References 44 publications

Heat transfer augmentation in unsteady conjugate thermal systems – Part II: Applications

Heat transfer augmentation in unsteady conjugate thermal systems – Part II: Applications

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

Generalization of the thermoacoustic form functions for evaluating the transverse temperature gradient effect

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