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Schmid G.,National Taiwan University | Huang Z.-L.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Chen S.-L.,National Taiwan University
Applied Energy | Year: 2017

The present study examines the use of a vertical double-pipe single-flow heat exchanger as part of an active air cooling system for a 150 W LED street light. The air is circulated inside the lamppost by an internal fan to form a closed-loop system. The heat is dissipated to the surrounding air by natural convection, reaching Rayleigh numbers up to Ra = 6.5 × 1010. Experiments with a 5 m high prototype were conducted, and the data were used to validate the numerical model. The experimental results show that the LED excess temperature can be lowered to about 42 °C. A two-dimensional axisymmetric numerical simulation was performed to study the influence of various parameters, including pipe length, material conductivity, flow direction, pipe diameter ratio, and mass flow rate, on the heat transfer rate. The findings show that the additional heat loss created by extending the lamppost largely depends on the flow rate. When extending the lamppost from 3 to 5 m at a high mass flow rate of 0.014 kg/s, the heat loss increases by 34.1% to 120.2 W. The numerical study was also used to visualize the hydrodynamic boundary layers on the surface of the lamppost and the temperature contours in and outside of the heat exchanger. © 2017 Elsevier Ltd

Chen I.-M.,National Taiwan University | Huang Y.-Y.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Liu T.,National Taiwan University
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2017

This study investigates the limited-slip and steering characteristics of a dual continuously variable transmission system. The dual continuously variable transmission is a unique final drive system composed of two continuously variable transmissions, with one continuously variable transmission connected to each rear wheel. In this study, a dynamic model of the dual continuously variable transmission system is derived, and models of the conventional final drive systems, i.e. the solid axle and the open differential, are used as benchmarks. In the simulations, the dual continuously variable transmission model, the solid axle model and the open differential model are applied to a vehicle dynamic model for split-μ road tests and a series of steering tests. According to the results of the split-μ road tests, the limited-slip function of a dual continuously variable transmission system is verified. The results of the steering tests show that different torque distributions for the inside wheels and the outside wheels while cornering can be controlled with different gain values of the continuously variable transmissions; for this reason, the application of the dual continuously variable transmission system as a torque-vectoring device is proposed, and a basic setting principle is presented. The results of this study establish a fundamental knowledge for developing the dual continuously variable transmission as an advanced final system for improving the vehicle dynamics. © IMechE 2016.

Schmid G.,National Taiwan University | Yang L.-H.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Chen S.-L.,National Taiwan University
Applied Thermal Engineering | Year: 2016

In the present study we analyzed the effect of varying the inter-fin base length of free hanging rectangular heat sinks with a central heat source cooled by natural convection. Typical applications for this type of heat sink are modern high-power LED street and flood lights. We compared heat sinks with two different fin orientations, one with the fins along the longer base side (Type A) and one along the shorter base side (Type B). The parameters in this study are the fin spacing, the power input, the base length, and the inter-fin base length. A numerical parametric study using ANSYS Icepak with a total of 189 different geometries was carried out. For a closed base with outer dimensions of 18 cm × 40 cm Type B can achieve an about 15% better thermal performance than Type A. For shorter inter-fin base lengths the thermal resistance of Type A is significantly lowered by up to 36.7%, while for Type B the maximum reduction is just 9.7%. It was further shown that the inter-fin base length greatly influences the optimal fin spacing. For the complete data Nu-correlations including a parameter for the inter-fin base length were developed. © 2016 Elsevier Ltd

Schmid G.,National Taiwan University | Hsu C.-Y.,National Taiwan University | Chen Y.-T.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Chen S.-L.,National Taiwan University
Journal of Thermal Science and Engineering Applications | Year: 2016

This paper investigates the cooling performance of a shallow geothermal energy method in relation to the cooling system of a 75 kVA oil-immersed transformer. A thermal analysis of the complete system is presented and then validated with experimental data. The cooling performance of the shallow geothermal cooling method is indicated by its cooling capacity and average oil temperature. The results of this study show that the average oil temperature can be reduced by nearly 30 °C with the aid of an 8m deep U-pipe borehole heat exchanger, thereby making it possible to increase the capacity of the transformer. By increasing the water flow rate from 6 L/m to 15 L/m, the average oil temperature could be lowered by 3 °C. In addition, the effects of changing the circulating water flow direction and the activation time of the shallow geothermal cooling system were investigated. The results of the thermal analysis are consistent with the experimental data, with relative errors below 8%. The results of the study confirm that a larger temperature differencebetween the cooling water and the transformer oil at the inlet of the heat exchanger can increase the overall heat transfer rate and enhance the cooling performance of the shallow geothermal cooling system. © 2016 by ASME.

Schmid G.,National Taiwan University | Chen C.-H.,National Taiwan University | Ma W.-C.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Chen S.-L.,National Taiwan University
Journal of the Chinese Institute of Engineers, Transactions of the Chinese Institute of Engineers,Series A/Chung-kuo Kung Ch'eng Hsuch K'an | Year: 2016

Rooftop turbine ventilators are widely used to improve indoor air quality in residential buildings and industrial complexes. This study presents an approach to enhance the operational performance of commercially available turbine ventilators using wind deflectors. Wind deflectors guide the wind flow to minimize the forces acting on the turbine blades in a negative direction, thereby increasing the rotational speed and exhaust ability of turbine ventilators. Two different prototypes were built and experimentally analyzed, one with adjustable size that covered up to half of the turbine, and one made of flat metal sheets, which were placed in front of the turbine. Compared with traditional turbine ventilators, the results of the two different prototypes showed an average increase in air extraction rate at different wind speeds of 34 and 11%, as well as an average rise in the rotational speed of 36 and 33%, respectively. The present study clearly demonstrates the high potential of wind deflectors to enhance the efficiency of turbine ventilators, and shows that a cover-style wind deflector is the more efficient design. © 2016 The Chinese Institute of Engineers

Chen C.-H.,National Taiwan University | Huang P.-C.,National Taiwan University | Yang T.-H.,Giant Lion Know How Co. | Chiang Y.-C.,Chinese Culture University | Chen S.-L.,National Taiwan University
International Journal of Refrigeration | Year: 2016

The periodic total heat exchanger system consists of four centrifugal fans and two desiccant beds. During the half-period, one fan drives air through one desiccant bed for adsorption and the other fan operating in the opposite direction induces air through the other desiccant bed for desorption. In the next half-period, both air-flow directions are reversed by the other two fans. In this work, periodic operations are tested under different regeneration temperatures (40°C and 25°C), along with six different desiccant beds: silica gel, polyacrylic acid, activated alumina, a molecular sieve, diatomite and a polymer/alumina composite. A silica gel-packed bed provides an alternative to high-cost honeycomb silica gel in 40°C regeneration temperature systems. Alumina shows comparable performance to honeycomb silica gel and has further cost advantages in low regeneration systems. The power consumption of low pressure drop composite desiccant systems shows an improvement of 33% over packed bed systems. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.

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