Murat K. Aktas

Nonzero Mean Oscillatory Flow in Symmetrically-Heated Shallow Enclosures: An Analysis of Acoustic Streaming

The effects of symmetric heating on a nonzero mean oscillatory fluid motion, namely acoustic streaming, in air-filled shallow enclosures and associated thermal convection in transient regime are investigated numerically. The fluid motion is driven by periodic vibration of the enclosure left wall. The vertical walls of the enclosure are adiabatic while the horizontal walls are heated symmetrically. A control-volume method-based explicit time-marching flux-corrected transport algorithm is used to simulate the transport phenomena in the enclosure. A symmetric temperature gradient strongly affects the acoustic streaming structures and velocities. The variation of the steady flow field becomes more noticeable and drastic with increasing wall temperature.

Experimental Investigation of Oscillation Controlled Heat Transport Tubes

The oscillatory flows are widely used to enhance heat transfer or as an alternative cooling technique. The oscillatory flows in liquids have the potential of augmenting heat transfer as demonstrated in literature. The subject needs to be investigated in order to fully understand the thermal transport mechanism and affecting parameters. In this investigation, heat transfer in an oscillatory pipe flow of water was studied, experimentally for low frequency regime flow conditions. Major research tasks are; setting up of the experimental apparatus, parametric experimental investigation of the convective heat transfer in oscillatory pipe flow and data reduction and analysis. An experimental apparatus was designed and constructed for the experimental investigation. The equipment consist a capillary pipe bundle connecting a cold fluid and a hot fluid reservoir. The effects of the maximum displacement amplitude of the vibrations and vibration frequency on the heat transfer were analyzed with a parametric study. Significant effect of oscillatory flow on the thermal transport compare to pure diffusion was measured. The heat transfer is greatly enhanced as vibration displacement increase. The results of the present investigation will be useful in choosing optimum operation parameters for cooling applications utilizing oscillatory flows.Copyright

Thermal Convection in an Enclosure With Sinusoidal Bottom Wall Temperature: Effect of Vibrating Side Wall

The effects of a vibrating side wall on flow structure and heat transport in an air-filled two dimensional rectangular shallow enclosure with sinusoidal spatial bottom wall temperature distribution is studied numerically. The vibrating side wall induces an oscillating flow having nonzero mean component in the enclosure. The side walls of the enclosure are adiabatic. The top wall is isothermal and kept at initial temperature. The fully compressible form of the Navier–Stokes equations are considered to predict the oscillatory and time averaged mean flow fields. A control-volume method based, explicit computational scheme is used to simulate the convective transport in the enclosure. The simulation results of a test case for an unheated enclosure are compared with the existing literature for code validation. The sinusoidal temperature gradient of the bottom wall strongly affects the flow structures and velocities. The mean fluid motion significantly alters the overall heat transfer from the bottom wall.Copyright

Acoustic Streaming Induced Thermal Convection in an Enclosure Subject to Uniform Heat Flux

The effects of acoustic streaming motion on transient convective heat transfer in an air-filled shallow enclosure with a vibrating side wall are investigated. The acoustic streaming phenomenon has been extensively studied by using theoretical and experimental methods. However, the investigations on the effects of longitudinal or transverse temperature gradients on acoustic streaming formation, associated transport phenomena and influence of various parameters on streaming structures are relatively scarce. To our knowledge, the influence of a transverse temperature gradient created by a uniform wall heat flux on streaming patterns has not been studied. In the present study, the fluid motion is driven by the periodic vibration of the enclosure side wall. The vertical walls of the enclosure are adiabatic while the bottom wall is subject to uniform heat flux and the top wall is isothermal or both bottom and top walls are subject to uniform, symmetric heat flux. The fully compressible form of the Navier–Stokes equations are considered to compute the primary oscillatory and secondary mean flow fields. A control-volume method based, explicit time-marching Flux-Corrected Transport (FCT) Algorithm is used to simulate the transport phenomena in the enclosure. The results of an isothermal test case simulation are compared with the existing literature for code validation. Transverse temperature gradient induced by uniform wall heating (symmetrically or non-symmetrically) strongly affects the acoustic streaming structures and velocities. The streaming motion significantly changes the transient behavior of heat transfer in the enclosure compared to pure conduction.Copyright

Heat Transfer Enhancement by Irregular Acoustic Streaming in a Shallow Enclosure

The effects of classical and irregular acoustic streaming structures on convective heat transport in air-filled two dimensional rectangular enclosures are investigated numerically. The oscillatory fluid motion and the resulting streaming motion are driven by cyclic vibration of the enclosure left wall. The fully compressible form of the Navier – Stokes equations are employed to model the transport phenomenon in the enclosure. An explicit time-marching Flux-Corrected Transport (FCT) Algorithm is used to simulate the oscillatory flow field, streaming patterns and associated thermal convection in the enclosure. The vertical walls of enclosure are thermally insulated. The bottom wall is heated isothermally while the top wall is kept at the initial temperature. The transverse temperature gradients strongly affect the acoustic streaming velocities and structures. The irregular streaming significantly augments the heat transfer from the enclosure bottom wall.Copyright