Papers by Author: Ho Dong Yang

Abstract: In the present study, aluminum alloy casting mold which consist of eight pieces is introduced as a new technique of tire manufacturing. For the numerical analysis, finite element method (FEM) was used to investigate the thermal strain of casting mold using aluminum alloy during the cooling process. In the concrete, the temperature distributions on the inside of each casting mold, the displacement and stress occurred by temperature variations are investigated to predict the accurate measurement variations of casting mold during the cooling process. In the end, numerical simulation results such as temperature distributions, displacement and stress are presented to help to make the effective and the best mold products. Moreover, the introduced technique of numerical simulation applying a FEM is very useful and important things in the mechanical behavior of materials, especially needs the accuracy improvement such as aluminum alloy casting mold products.

Abstract: This study focused on observing the melting phenomena and investigated a principle factor of enhanced heat transfer in phase change material when the ultrasonic vibrations were applied during the melting process. For visualization, particle image velocimetry and thermal-vision camera for observing the flow phenomenon was used. Also, experiments were performed to obtain the experimental results such as melting time and temperature distribution. Besides, structural vibration simulator which is applying a coupled finite element-boundary element method (Coupled FE-BEM) was used for calculation of acoustic pressure occurred by ultrasonic vibrations in liquid region. The results of experimental and numerical observations show that acoustic streaming induced by ultrasonic vibrations is one of the prime effects acoustically enhanced phase change heat transfer and help to accelerate the melting of phase change material. Also, the application technique of visualization and computational simulation introduced in this study is very useful and important to analyze the mechanical behavior of material in a fast fluid dynamic or acoustic field.

Abstract: The present study was experimentally investigated the effect of ultrasonic vibrations on boiling heat transfer augmentation during the heating process. The experiments were carried out under the constant wall temperature condition and were divided into two cases applying with and without ultrasonic vibrations, respectively. Also, the temperature distributions in a vessel filled with water were measured using thermocouples during the heating process, heat transfer coefficient and augmentation ratio of heat transfer on states of convection, subcooled boiling and saturated boiling were calculated from obtained temperature profiles. In addition, the profiles of pressure variations measured using a hydrophone were compared with the augmentation ratio of heat transfer in acoustic fields. The results of experimental study were revealed that general profiles of heat transfer coefficient and augmentation ratio of heat transfer is more increased the convection state than the others states. Moreover, the profiles of acoustic pressure is relatively higher near ultrasonic transducer than other points where is no installed it and affects the augmentation ratio of heat transfer. In the end, as well as known “acoustic streaming” induced by ultrasonic vibrations is one of the prime effects acoustically augmented boiling heat transfer or phase change heat transfer.

Abstract: The present study is investigated the causes of enhanced heat transfer during the melting process of solid-liquid PCM (Phase Change Material) using an ultrasonic vibration. Paraffin (noctadecane) was selected as a PCM and experimental studies were performed as following. Heat transfer coefficient and enhancement ratio of heat transfer was measured, acoustic streaming induced by ultrasonic waves observed using a PIV (Particle Image Velocimetry) and thermally oscillating flow phenomenon observed using an infrared thermal camera during the melting process. For the numerical study, a coupled FE-BEM (Finite Element-Boundary Element Method) was applied to investigate acoustic pressure occurred by acoustic streaming in a medium. And then, the profiles of pressure variation compared with the enhancement ratio of heat transfer. The results of this study revealed that ultrasonic vibrations accompanied the effects like acoustic streaming and thermally oscillating flow. Such effects are a prime mechanism in the overall melting process when ultrasonic vibrations are applied. Also, as the acoustic pressure occurred by acoustic streaming increases, the higher enhancement ratio of heat transfer is obtained.

Abstract: In the present study, numerical work applying a finite element method (FEM) is used to analyze the characteristics of aluminum (Al) alloy mold for thermal strain control. In the concrete, the temperature distribution on the inside of Al alloy mold, the contraction rate and stress occurred by temperature variations are investigated to predict the accurate measurement variation of Al alloy mold during the cooling process. In addition, the numerical result of the Al alloy mold were compared with those of mild steel mold in order to obtain the improvement and good quality of mold. In the end, the numerical results such as temperature distributions, contraction rate and stress are presented to help to make the effective and the best mold products. Besides, the introduced technique of numerical analysis applying a FEM is very useful and important things in the fracture and damage mechanics, especially needs the accuracy improvement such as Al alloy mold products.

Abstract: The present study was investigated on the melting phenomena and the accelerative factors of phase change material (PCM) by acoustic streaming induced ultrasonic vibrations. To investigate the melting phenomena and accelerative factors, the experimental study was measured the liquid temperature and melting time of PCM and was observed the velocity vectors and thermal fluid flow induced acoustic streaming to investigate the heat transfer using particle image velocimetry (PIV) and infrared thermo vision camera, respectively. Also, the numerical study based on a coupled finite element-boundary element method (Coupled FE-BEM) was performed to investigate the analysis of pressure field in the PCM. The results of experimental works revealed that acoustic streaming observed by PIV and infrared thermo vision camera is one of the prime effects accelerating phase change heat transfer. And, the final temperature of PCM is lower and melting speed is 2.6 times faster than that without ultrasonic vibrations when ultrasonic vibrations are applied. The results of numerical work presented that acoustic pressure is higher near the ultrasonic transducer than other points where no ultrasonic transducer was installed and develops more intensive flow such as acoustic streaming, destroying the flow instability. Moreover, the profile of acoustic pressure variation is consistent with that of enhancement of heat transfer.