K. David Huang

Flow Structure in an Inner Rotating Annular Channel with Ribbed Wall Cylinder

In this investigation, we explore the flow field of an annular channel between two horizontal concentric rotating cylinders, i.e., between a rotating inner cylinder and a stationary outer cylinder. Resulting from interactions between centrifugal force, viscous force and different boundary conditions, flow fields in an annular channel probably develop groups of opposite Taylor vortices when the Taylor number is higher than a critical value. Geometrical parameters of rotating cylinder channels, such as the channel widths and circumferential ribs are also affected by the flow field. Four types of rotating inner cylinder are available in this experiment: smooth walled (Model A), and circumferential ribs of three different sizes (Models B–D). The aspect ratios for circumferential ribs are 5/3, 5/2, and 10/3, which generate periodically embedded cavities of 10, 15, and 20 mm. The radius ratios between the inner and outer cylinders were ηs=0.89, and ηrib=0.94, respectively. Taylor numbers ranged between (8.565–1312.943)×103, and centrifugal force arising from the rotation of Model A was Fs=0.22–3.3 N. The centrifugal forces arising from the inner cylinders with embedded circumferential ribs were Frib=0.23–3.49 Nt. Because the wavelength of the Taylor vortices was subjected to the influence of different geometrical conditions, the flow field structure of Model A was different at both ends of the cylinder. Conversely, various forms of Taylor vortices occurred between annular channels with circumferential ribs in the case of Models B–D, and the vortex evolved from the edge of the circumferential ribs in a more stable manner than in Model A. The wavelengths of the Taylor vortices were λA=30 mm, λB and λD=20 mm, and λC=15 mm. Experimental results of flow visualization demonstrated it to be well suited for benchmarking engineering designs for heat transfer, cooling, and tribology of rotating machinery.

Study of Electrical Control Systems of a New Parallel Hybrid Electric Heavy Motorcycle

In a world where environment protection and energy conservation are growing concerns, the development of hybrid electric vehicles (HEV) has taken on an accelerated pace. We put our attention on the development and research of parallel hybrid electric heavy motorcycle. In this paper, electrical control system is mainly focused on a new parallel hybrid system; among them include cars using the instant battery charger, Li-ion battery management system and electrical control system. In the sliding mode motor control of the system, we design a modified output feedback controller. The controller using only output variable is proposed to stabilize the motor control system robustly. The variable structure system is asymptotically stable with better performance.

Study of a Micro Thermal Environment of a Personal Air-Conditioning

In a highly developed living, people are always looking for a comfortable indoor environment with minimum energy use. Regional air conditioning mechanism (RACM) can create a personal thermal comfort control in a workroom which can contribute to save air-conditioning energy. In this study, we analyze the airflow circulation cell of the RACM with varied inlet port opening and inlet port position dimensions using the computational fluid dynamics (CFD) technique. We created a RACM, two workstations, lightings, and a cabinet in a 3-dimensional room. The fluid was assumed to be Newtonian, unsteady, and incompressible. A Bossinesq approximation was determined in order to consider the buoyancy effect. We examined the effects of the inlet port opening and inlet port position on airflow circulation establishing process. Air temperatures along the various midline of the occupied zone were predicted and compared for a range of inlet port opening and inlet port position by using nondimensional form. We also showed the occupied zone temperature at various planes in the workroom. Results will indicate the suitable inlet port opening and inlet port position for maintaining individual satisfied occupants’ requirements and improving energy saving potential.

Energy Merger Pipe Optimization of Hybrid Pneumatic Power System by Using CFD

Outstanding characteristics of the hybrid pneumatic power system (HPPS) are the maintenance of the internal combustion engine (ICE) operation at its sweet spot of maximum efficiency, the recycling of the exhaust energy of the ICE, and the replacement of the batterys electric–chemical energy with flow work. Thus, the HPPS can be considered as a promising solution to increase energy efficiency and improve exhaust emissions. This paper presents study results concerning the flow energy merger capability of an innovative energy merger pipe which has been used in the HPPS. This energy merger pipe plays a major role in the merging process of both the high-temperature exhaust gas flow of an ICE and the high-pressure compressed airflow. This merging process can be significantly improved based on the analysis and evaluation of influences of the dimensions and contraction of the cross-sectional area (CSA) at the merging region of the energy merger pipe on the flow energy merger by using a computational fluid dynamic simulation. The results show that the flow energy merging process not only strongly depends on optimum dimensions of the energy merger pipe but is also significantly influenced by CSA adjustment for the change in the compressed airflow pressure. Under the optimum dimensions and the CSA adjustment for a better merging process, the exhaust gas energy recycling can reach about 80%; therefore, a vehicle equipped with HPPS can achieve efficiency that is approximately 40% higher than that of conventional vehicles.

NUMERICAL STUDY OF TRANSPORT PHENOMENA IN SESSILE DROPLETS DURING INTERNAL SOLIDIFICATION

A unified equation is derived, which describes transport phenomena induced by thermocapillary effects in a sessile drop with internal solidification, by means of a point cooling at the center of the drop base. The effect of the buoyancy force is taken into account. Based on experimental observation, the entire solidification process is divided into the early solidification stage, where the solid phase grows in a hemispherical form until its front reaches the top of the drop, and the late solidification stage, with the solidification front propagating in a cylindrical form until the completion of solidification. Two mathematical models are developed: one for the early-stage solidification, with a vorticity-stream function scheme in a spherical coordinate system, and the other for the late-stage solidification, with a pressure-velocity component scheme in a cylindrical coordinate system. A finite volume technique is employed to solve the early-stage model using an alternating-direction implicit method and late-stage model using a modified SIMPLER procedure. Numerical results are obtained for the distribution of surface temperature and velocity, isotherms, streamlines, and velocity vectors

Effects of forced convection and roughness of surface on viscous coupling unit of crossover utility vehicles

An experiment was conducted to analyse the local heat transfer and flow characteristics in the viscous coupling unit (VCU) of a crossover utility vehicle (CUV). Heat is transferred by free convection and forced convection, and affected by the lubrication effect of the smooth wall and the embedded circumferential ribs, at various rotational speeds. In the simulation of the practical operational range of VCU of CUV under experimental conditions, both rotational speed and geometric parameters must correspond closely to the real situation. In addition, the test section is designed such that the cooling characteristics of the power transmission system of the CUV of actual size could be investigated. The overall temperature distribution is measured and the local heat transfer coefficient is analysed. The impact of the centrifugal force upon the Taylor vortex is clarified with reference to the flow-field distribution. Finally, some empirical formulae by CUV designers are obtained from the experimental results.

GRAVITATIONAL EFFECTS ON THERMOCAPILLARY CONVECTION WITH SOLIDIFICATION

This study is concerned with the solidification of a sessile drop (i.e., a drop on a flat plate) induced by a point cooling at its base center (by means of a thin metal connected to a heat sink). A finite-volume numerical method is applied to determine the effects of high and reduced gravity on thermocapillary convection during the solidification process. The drop profile is assumed to be a spherical segment based on experimental observation. Liquid, drop height and gravitational acceleration are varied to determine their effects on the transport phenomena. The system simulates a solidification process inside a containerless liquid volume in space flight, which is surface-tension controlled.