Article
Experimental study of heat transfer in oscillating flow
University of Nantes, Naoned, Pays de la Loire, France
International Journal of Heat and Mass Transfer (Impact Factor: 2.38). 06/2005; 48(12):24732482. DOI: 10.1016/j.ijheatmasstransfer.2005.01.037 ABSTRACT
This paper describes an experimental study of heat transfer in oscillating flow inside a cylindrical tube. Profiles of temperature are taken inside the wall and in the fluid from an instrumented test rig, in different conditions of oscillating flow. Profiles obtained allow the observation of the wall effect on heat transfer. A method using the inverse heat conduction principle allows the characterization of local heat transfers at the fluid–solid interface. Finally, a comparison between global and local approaches of heat transfer shows the difficulty of defining a dimensionless heat flux density to model local heat transfer in oscillating flow.

 "Yu et al. [22] and Chattopadhyay et al. [23] observed no change in timeaveraged Nusselt number due to flow pulsations. Bouvier et al. [24], performed an experimental study to understand heat transfer in oscillating flow in a circular pipe. Parameters used in this study were maximum Reynolds number, nondimensional frequency (Wo) and amplitude of oscillation. "
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ABSTRACT: Disturbing a singlephase laminar internal convective flow with a particular pulsating flow frequency alters the thermal and hydrodynamic boundary layer, thus affecting the interparticle momentum and energy exchange. Due to this externally imposed flow disturbance, augmentation in the heat transfer may be expected. Obviously, parameters like pulsating flow frequency visàvis viscous time scales and the imposed pulsating amplitude will play an important role. Conclusions from reported literature on this and related problems are rather incoherent. Lack of experimental data, especially in micro/mini internal convective flow situations, with imposed flow pulsations, motivates this study. Nonintrusive infrared thermography has been utilized to scrutinize heat transfer augmentation during singlephase laminar pulsating flow in a square minichannel of crosssection 3 mm × 3 mm, electrically heated from one side by a thin SS strip heater (70 μm, negligible thermal inertia); all the other three sides of the channel are insulated. The study is done at different pulsating flow frequencies of 0.05 Hz, 1.00 Hz and 3.00 Hz (Wo = 0.8, 3.4 and 5.9, respectively). These values are chosen because pulsatile velocity profiles exhibit different characteristics for Wo > 1 (annular effect, i.e., peak velocity near the channel walls) and Wo < 1 (conventional parabolic profile). Local streamwise heat transfer coefficient has been determined using the time averaged spatial IR thermograms of the heater surface and the local fluid temperature, linearly interpolated from measured value of inlet and outlet bulk mean mixing temperature. It is observed that for measured frequency range, the overall enhancement in the heat transfer is not attractive for laminar pulsating flow in comparison to steady flow with same timeaveraged flow Reynolds number. The change is either marginal or highly limited, primarily occurring in the developing length of the channel. Thus, the results suggest that heat transfer enhancement due to periodic pulsating flow is questionable, and at best, rather limited. 
 "Several literatures have studied the nature of oscillatory flows and presented the pressure drop and heat transfer coefficient in Stirling engine heat exchangers (Simon and Seume, 1988; Tew and Geng, 1992). Bouvier et al. (2005) described an experiment to study the oscillating flow inside a cylindrical tube and shown the difficulty of defining a dimensionless heat flux density to model local heat transfer in oscillating flow. Kuosa et al. (2012) studied the tubular heaters and coolers in Stirling engines. "
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ABSTRACT: The heat transfer and pressure drop for oscillating flow in helically coiled tube heatexchanger were numerically investigated based on the NavierStokes equations. The correlation of the average Nussel number and average friction factor were proposed considering the frequency and the inlet velocity. The oscillating flow heat transfer problems are influenced by many factors. Hence we need an easy way to reduce the numbers of simulation or experiment. Therefore, the method of uniform design was adopted and the feasibility of this method was verified. The field synergy principle was used to explain the heat transfer enhancement of oscillating flow in helically coiled tube heatexchanger. The result showed that the smaller the volume average field synergy angle in the helically coiled tube, the better the rate of heat transfer. 
 "Nevertheless, energyconversion devices involve for the most part unsteady heat transfer in the presence of compressible gaseous flows. In the treatment of most gaseous flows the assumption of a constant wall temperature is adequate [3] and the heat transfer process is not conjugate. These problems are simplified to obtaining information on the heat transfer coefficient (HTC) and using this to quantify the convective heat transfer in the fluid. "
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ABSTRACT: Many energy conversion and other thermalfluid 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 timemean 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 [1], is concerned with the phenomenon of augmentation in simple, onedimensional, unsteady and conjugate fluid–solid systems. A simple semianalytical onedimensional model of heat transfer with a timevarying heat transfer coefficient, which was presented in Mathie and Markides [1], 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 backwardsfacing step, which exhibits broadband fluctuations in the heat transfer coefficient due to the flow separation and turbulence behind the step. The model predictions of the augmentation ratio for these problems are also compared to direct measurements from each case. Good agreement is observed with the experimental results for the global heat transfer trends. In both cases the augmentation ratio was negative, reflecting a reduction in timeaveraged heat transfer. For the backwardsfacing step flow a low magnitude of augmentation ratio was observed, however, the thin film flows exhibited augmentation ratios of as high as 10%.
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