Chien-Nan Lin

Heat Transfer and Fluid Flow Analysis for Plate-Fin and Oval Tube Heat Exchangers With Vortex Generators

This article investigates the effectiveness of embedded vortex generators in enhancing the heat transfer performance of a plate-fin heat exchanger with a four-row staggered oval tube bundle. Two different types of vortex generator are considered, namely annular and inclined block. Numerical simulations are performed to analyze the effects of the three-dimensional turbulence induced by the vortex generators on the heat transfer and fluid flow characteristics of the heat exchanger. The results indicate that compared to a plate-fin heat exchanger with circular tubes, the use of oval tube fins and vortex generators increases the heat transfer rate by 3 to 16% and reduces the pressure drop by 17 to 35% for inlet velocities in the range of 1 to 8 m/s. Furthermore, the vortex generators make possible an average area reduction ratio of 14 to 18%. Overall, the results show that the inclined block shape vortex generators yield the greatest improvement in the heat transfer performance at medium to high inlet velocities.

Temperature Prediction for Tumor Hyperthermia with the Behavior of Thermal Wave

In magnetic nanoparticle hyperthermia for cancer treatment, controlling the heat distribution and temperature elevations is an immense challenge in clinical applications. It is expected for treatment quality to understand the heat transport occurring in biological tissue. The non-Fourier thermal behavior in biological tissue has been experimentally observed. This work uses the thermal wave model to predict the temperature excess occurring in a two-layer concentric spherical tissue with the heat source of Gaussian distribution. The solutions to the hyperbolic bio-heat equation with the space-dependent source term in the spherical coordinate system are presented. The influences of relaxation time, blood perfusion rate, and heating strength on the thermal response in tumor and normal tissue are discussed.

Analysis of Heat Transfer and Flow Characteristics for the Arrangement of Piezoelectric Fan on Heated Cylinder

Piezoelectric fans are an effective device for heat transfer enhancement in low convective regions due to their low power consumption, low noise, and operational simplicity. This study performs a numerical and experimental investigation into the effects of a piezoelectric fan on the velocity and temperature fields near a cylindrical heat source with a constant heat flux on the sidewalls and upper flat surface. In performing the investigation, the blade is placed at various locations along the cylindrical axis and is arranged such that it vibrates in either the vertical direction or the horizontal direction. The results show that the airstream induced by the vibrating fan covers a broader area of the heated surface when the blade vibrates in the vertical direction, and therefore yields a better heat transfer performance than that achieved when the fan vibrates in the horizontal direction. In addition, it is found that the maximum heat transfer augmentation ratio is obtained at dimensionless fan positions ranging from 0.6 to 0.75, and has values of 1.94, 1.53, and 1.44 given dimensionless fan tip clearances of 0.5, 1.0, and 1.5, respectively. Finally, it is shown that while the numerical results underestimate the effect of the vibrating piezoelectric fan in enhancing the heat transfer performance by around 1–14%, a good qualitative agreement is observed between the numerical and experimental results.

Nonlinear Surface Waves of the Thin Gravity-Driven Liquid Film Flows Under Magnetohydrodynamic Field And Rotating Centrifugal Force

The effects of magnetohydrodynamic field and rotating centrifugal force on nonlinear hydrodynamic stability in a layer of viscous gravity-driven fluid flow are considered. The multiple-scales method is used to examine the nonlinear dynamics of the liquid film. When the fluid film flows down the outside surface of a stationary vertical cylinder, the stability of the flow field is dominated by the radius of the cylinder and the magnitude of the magnetic force. As the cylinder starts to rotate, however, a centrifugal force is produced and thus the stability of the thin-film system is governed by the interaction between the cylinder radius and the speed of rotation. The size of the explosive supercritical instability region increases significantly as the cylinder rotates. At higher values of the Reynolds number, the tendency of the rotation effect to prompt thin-film instability increases with an increasing cylinder radius. Moreover, it is observed that by increasing the intensity of the magnetic field tends to increase the stability as traveling down along the rotating vertical cylinder.

Magnetohydrodynamic field on nonlinear waves of a thin electrically conducting micropolar liquid film flow down a vertical column

The effect of the microrotation and couple stress will be taken into account in the Non-Newtonian fluid with the suspension micro-particle. The rheological behaviors of the interaction between a hydrodynamic film flow and a magnetic field is extremely different from the flow of no applied magnetic field. The multiple-scales method is used to examine the weak nonlinear dynamics of the micropolar liquid film. The results display the flow becomes relatively more stable as the micropolar parameter K is increased at larger values of the Hartmann number. Furthermore, the working conditions can be found through the use of a system to alter stability of the film flow by controlling the applied magnetic field.