Experimental study of heat transfer in oscillating flow
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.
- SourceAvailable from: Changzhao Pan[Show abstract] [Hide abstract]
ABSTRACT: The heat transfer and pressure drop for oscillating flow in helically coiled tube heat-exchanger were numerically investigated based on the Navier-Stokes 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 heat-exchanger. The result showed that the smaller the volume average field synergy angle in the helically coiled tube, the better the rate of heat transfer.Computers & Chemical Engineering 10/2014; 69. DOI:10.1016/j.compchemeng.2014.07.001 · 2.45 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: A simplified physical model for calculating the onset temperature ratio and the frequency of a standing wave thermoacoustic engine (SWTE) in the time domain is built based on thermodynamic analysis. Coefficients of transient pressure drop and heat transfer are first deduced from linear thermoacoustic theory. By numerical computation, the evolutions of the pressure amplitude and the spectrum characteristics during the onset process are presented. Furthermore, the effects of stack spacing, charge pressure, and resonator length on the onset temperature ratio and the frequency are calculated. Relatively good agreement between the computational and the experimental results has been achieved, which validates the model for calculating the onset characteristics.Applied Acoustics 07/2014; 81:50–57. DOI:10.1016/j.apacoust.2014.02.002 · 1.07 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: 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 , 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 , 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 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 time-averaged heat transfer. For the backwards-facing step flow a low magnitude of augmentation ratio was observed, however, the thin film flows exhibited augmentation ratios of as high as 10%.International Journal of Heat and Mass Transfer 01/2013; 56(s 1–2):819–833. DOI:10.1016/j.ijheatmasstransfer.2012.09.017 · 2.52 Impact Factor