Papers by Author: Wen Lih Chen

Abstract: The current thesis proposed the integration of air conditioners that exhaust heat with solar energy to enhance the overall efficiency of thermal energy conversion. The analysis of thermal storage tanks of different volumes revealed that a two-ton air conditioner operating for an hour produced double energy than normal sunshine for a day. With thermal storage tanks of fixed volume, the integration of air conditioners of different tons with solar energy indicated that air conditioners of less tons produced faster and more efficient energy conversion. Therefore, the current thesis proposed that the modification of condenser in domestic air conditioner into water-cooled condenser not only enhanced the energy efficiency of air conditioners but also increased hot water supplies since hot water from air conditioners could be integrated into solar water heaters. By doing so, energy conservation and carbon reduction could be achieved.

Abstract: In this study, the maximum and smallest vertical principle stresses σ₁ and σ₃ as well as maximum shear stress τ_max distributions, obtained from Mohr circle in each quadrant, are used to investigate the applicability of various ductile material failure theories. Based on the yield tensile stress σ_yt equals to yield compressive stress σ_yc (σ_yt=σ_yc=σ_y) and the known practical yield shear stress and yield stress ratio τ_y/σ_y=0.42~0.75 of ductile materials, we prove that the maximum vertical stress failure theory cannot be applied to the first quadrant (σ₁>σ₃≧0) as well as the third quadrant (σ₃<σ₁≦0) while τ_y/σ_y< 0.5, and it does also not applicable to the second or fourth quadrant (σ₁>0 and σ₃<0). In this study, the modified maximum shear stress failure line can be fit all ductile material depending on τ_y/σ_y=0.42~0.75 in all quadrants, thus the more reasonable results can be obtained.

Abstract: In this study, fixed mole number proportion of CuCl, ZnCl2, SnCl2‧2H2O and sulfide compounds and the reacted solution are added to the autoclave, then the CZTS powders are prepared by changing the heating temperature and time. It is found from the experimental results that better result with less secondary phase can be obtained at the heating temperature 250°C and heated time of 36 hours.

Abstract: Log mean temperature difference (LMTD) method neglecting the influence of heat radiation is conventionally used to calculate the total heat transfer rate of heat exchangers. From recent investigation of a single-pipe heat exchanger in some practical situations, it is found that the total heat transfer rate error of single-pipe heat exchanger obtained by LMTD method is up to 40% in the situation of oxidized metal heat exchanger with higher surface emissivity located in ambient air with low heat convection coefficient. A log mean heat transfer rate (LMHTR) method considering heat radiation has been developed to calculate the total heat transfer rate of a single-pipe heat exchanger and more accurate results can be achieved. It is also found in the present investigation that LMTD method is also not suitable to apply to non-insulated double-pipe heat exchangers and a more accurate LMHTR method considering heat radiation is developed to obtain the more reasonable results.

Abstract: A heat radiation equation contains 4th exponential order of temperature which makes mathematics analysis complicated and time-consumption. Most heat transfer experts and scholars believe, based on their own experiences, that the heat radiation effect can be ignored in situations of small temperature difference between duct surfaces and surroundings. This paper studies in detail for complete heat transfer characteristics of a circular duct with heat radiation effect taken into account. It is found that, in some practical conditions, the heat radiation effect can not be ignored especially in cases of lower ambient convection heat coefficients and larger surface emissivities, as well as the smaller the duct size and/or the greater the duct conductivity and/or internal fluid convection coefficients, even though the temperature-difference between inner and outer fluid-temperatures of duct is low to 1 °C. It is found that the conventional LMTD method (ignoring heat radiation) cannot be applied to calculate the total heat transfer rate of a single-duct heat exchanger located in ambient air, such as condenser and evaporator.

Abstract: The main function of junction box on a solar photovoltaic module is to transmit the electricity from solar photovoltaic panel to the load. The invented smart junction box is designed for the following purposes: (1) to optimize efficiency through auto control, (2) to reduce the vicious effect of the cloud and dust on electricity output, and (3) to prevent the battery from overcharging. When actuated, the temperature of inner transistor is raised up to 158 °C because it consumes more solar electric power than a conventional junction box. Thus, a more effective thermal diffusion system is invented to cool down inner transistor to avoid failure. It is found that the presented heat plate diffusion system modified from heat pipe is capable of satisfying all required thermal diffusion conditions of the smart junction box.

Abstract: In this work, cadmium sulphide (CdS) buffer layer of CuInSe2 (CIS) thin film solar cell is fabricated by separate-melting Chemical Bath Deposition (CBD) methods. The reason of adopting the CdS thin film as the buffer layer of CIS thin film solar cell is that the CdS can act as energy gap buffer and reduce the band-offset between CIS absorbing layer and the Transparent Conductive Oxide layer. The CdS thin films are generated by the separate-melting CBD methods in situation of atmosphere. In order to analyze the characteristics of the CdS thin films conveniently, the CdS thin films are firstly fabricated on Soda-lime, and the final found optimal CdS thin film is fabricated on the CIS/Mo/Soda-lime glasses. Then the p-n diode characteristic of the CdS/CIS/Mo/Soda-lime glasses is measured by four-point probe. And the CdS thin films are fabricated by the separate-melting CBD methods through various combinations of time interval from 40 and 60 minutes and temperature range from 70,75,80 and 85°C. It is found that the combination of 85°C and 60 minutes is optimal to obtain smoother surface and more uniform thickness of CdS thin film. Additionally from optical characteristic analysis, in situation of emitted light wave length 500 nm, the transmittance of the cadmium sulphide thin film is 61%. Meanwhile, the band gap is close to theoretical value of 2.4 eV.