Sih-Li Chen

An experimental investigation of cold storage in an encapsulated thermal storage tank

This paper experimentally investigates the thermal performance and the pressure drop of an encapsulated thermal storage tank during the charging process. A polyvinyl chloride (PVC) hollow cylinder is used as the thermal storage tank. The cylindrical capsules inside the thermal storage tank utilize water added with nucleation agents as the phase change material (PCM), and the coolant is the aqueous solution of ethylene glycol. A series of experiments were carried out to investigate the effects of the inlet coolant temperature and coolant flow rate on nucleation of capsules, heat transfer and pressure drop of the tank. The results indicate that cool energy can be fully stored in the form of latent heat when the inlet coolant temperature is set below the temperature with 100% nucleation probability. The lower the inlet coolant temperature and the larger the coolant flow rate, the more efficient the storage tank. A correlation for the pressure drop of coolant during a charging process is also developed.

An experimental investigation of nucleation probability of supercooled water inside cylindrical capsules

This article experimentally investigates the nucleation probability of supercooled water inside cylindrical capsules with or without nucleators during a cold storage process. The nucleation probability curves of initial appearance of dendritic ice as a function of coolant temperature, size of capsule, and mass of different heterogeneous nucleators are characterized, respectively, by performing a number of experiments. The results show that the lower the coolant temperature, the greater the nucleation probability. The larger the volume of water contained, the higher the nucleation temperature. The addition of nucleating agents, such as iron ore, iron chips and silver iodide, into the water container can effectively improve the nucleation probability, and thus increase the coefficient of performance (COP) of a thermal storage air-conditioning system. Since the crystal structure of silver iodide is very similar to that of ice, the comparison among three types of agents indicates that it has the best effect in facilitating nucleation.

A study of supercooling phenomenon and freezing probability of water inside horizontal cylinders

This paper investigates the supercooling phenomenon and the freezing probability of water inside horizontal cylinders during a cooling process of thermal storage. The effect of such factors as cooling rate, inside diameter of cylinders and mass of different nucleation agents is experimentally examined. By measuring the time variations of temperature profiles at various locations inside the test cylinder and the photography observation at the time of nucleation, the supercooling period of water and the extent of dendritic ice growth is presented. The probability curves of initial appearance of dendritic ice as a function of various factors are characterized. Besides, a simple model to predict the critical cooling rate for dendritic ice blockage and supercooling period for container water is proposed. By incorporating the experimental results and the theoretical predictions, a correlation of supercooling period for water inside horizontal cylinders has also been developed. 0 1997 Elsevier Science Ltd.

Development of an intelligent energy management network for building automation

This paper describes the development of an intelligent energy management network (IEMN) using the concept of a surrogate object-communication model and three-layered network architecture. The proposed IEMN is characterized by its network architecture and application services. From the network architecture point of view, the IEMN is characterized by the area control and management center, the building control and management station, and the BACnet facility. From the application service point of view, the IEMN provides the intelligent energy service architecture to integrate the building management system functions and the facility management system. The IEMN offers several advantages such as the distributed intelligent management and the ability of data processing and analysis online. The hierarchical architecture makes it easy to integrate and to expand.Note to Practitioners-The paper describes an extension to the existing intelligent build network technology. The conventional intelligent building network facilitates the monitoring of sensor information and the issuing of controller commands by assuming that the network elements all have limited intelligence. The control decision is therefore centralized to some control servers. The proposed surrogate system, on the other hand, allows for intelligent control subunits on the network and transmits more complex information and directions for control decision making. The control subunit will have the freedom to make their own decision on how to achieve the instructions from the upper level. Thus, the network traffic may be reduced and the network no longer has to deal with time critical issues. This configuration allows more room for network flexibilities. We have constructed the basic network with SQL and active server page and run a primitive demonstration in our laboratory. Because the setup is configured over a standard BACnet facility over TCP/IP, the network implementation does not require too much effort. The layered servers are still necessary.

Latent Heat Storage in a Two-Phase Thermosyphon Solar Water Heater

This article experimentally studies the thermal performance of latent heat storage in a two-phase thermosyphon solar water heater, which utilizes the superior heat transfer characteristics of boiling and condensation, and eliminates drawbacks found in the conventional solar water heater. Experimental investigations are first conducted to study the thermal behavior of tricosane (paraffin wax 116), water, and sodium acetate NaCH3 COO·3H 2O used as energy storage materials. The results indicate that tricosane provides many advantages to be the energy storage material in the latent heat storage system. This study also examines the functions of charge and discharge thermal behaviors in a two-phase thermosyphon solar water heater. The results show that the system gives optimum charge and discharge performance under 40% alcohol fill ratio and with tricosane used as the energy storage material, and displays an optimum charge efficiency of 73% and optimum discharge efficiency of 81%. DOI: 10.1115/1.2147588

Experimental Investigation of Vapor Chamber Module Applied to High-Power Light-Emitting Diodes

This article experimentally investigates the thermal performance of the vapor chamber module applied to the high-power light-emitting diodes in natural convection. The flat-plate-type vapor chamber and the lamp-type vapor chamber are provided to solve the heat dissipation problem of the high-power light-emitting diodes. The results show that the spreading resistance and the corresponding temperature difference of the flat-plate-type vapor chamber at 30 W are lower than those of the copper plate by 34% and 4°C, respectively, and are lower than those of the aluminum plate by 56% and 6°C, respectively. Compared with the copper and aluminum plates, the lamp-type vapor chamber at 15 W is reduced about 8% and 12% for the total thermal resistance, respectively. In addition, it is also about 3°C and 5°C lower for the central wall temperature of the lighting side, respectively. This study provides a new thermal management method to solve the heat dissipation of the high-power light-emitting diodes. Furthermore, the vapor chamber can effectively lower the spreading resistance and diminish the hotspot effect.

Simulation Of Refrigerants Flowing Through Adiabatic Capillary Tubes

This paper presents a model for the flow of refrigerants through adiabatic capillary tubes. The flow of refrigerant is characterized by a subcooled liquid region, a metastable liquid region, a metastable two-phase region, and an equilibrium two-phase region. The mass and momentum conservation equations for each of these four regions are converted into finite difference forms and solved using a 4th order Runge-Kutta method. The calculated results compare well with experimental data on R-22. The predictions from the model are employed to develop correlations for the design of refrigerant 134a through adiabatic capillary tubes with the tube exit in the choked flow condition.

Two-Phase Closed-Loop Thermosyphon for Electronic Cooling

This study experimentally investigated the thermal performance of a two-phase closed-loop thermosyphon with a thermal resistance model for electronic cooling. The evaporator, rising tube, condenser, and falling tube, which are the four main devices, formed a closed-loop system with water as the working fluid. The experimental parameters were the evaporator surface type, fill ratio of working fluid, and input heating power. The results indicated that the evaporator and condenser thermal resistance decrease with increasing input heating power. The condenser thermal resistance clearly increased with increasing fill ratio. A groove-type evaporator surface with 0.2 mm height and 1 mm width had the best performance, decreasing the evaporator thermal resistance about 15.5% compared to a smooth surface. Correlations for evaporator and condenser thermal resistance were also developed, and their precisions, when compared with the experimental data, were about 9.6 and 11.6%, respectively. Because of the intermittent boiling mechanism at 47% fill ratio with input heating power from 60 to 80 W, the temperature showed obvious oscillations with the smooth evaporator surface.

Forced convective film condensation inside vertical tubes

Abstract A theoretical study of forced convective film condensation inside vertical tubes is presented. We propose a unified procedure for predicting the pressure gradient and condensation heat transfer coefficient of a vapor flowing turbulently in the core and associated with laminar or turbulent film on the tube wall. The analysis for the vapor flows is performed under the condition that the velocity profiles are locally self-similar. The laminar and turbulent film models equate the gravity, pressure and viscous forces, and consider the effect of interfacial shear. The transition from laminar to turbulent film depends not only on the liquid Reynolds number but also on the interfacial shear stress. In this work we also proposed a new eddy viscosity model which is divided into three regions: the inner region in liquid condensate near the wall; the interface region including both liquid and vapor; and the outer region for the vapor core. Comparisons of the theory with some published experimental data showed good agreement.

Effect of Water Chemical Corrosion on Strength and Cracking Characteristics of Rocks - A Review

Study of effect of water chemistry corrosion on strength and cracking characters of rocks is an important aspect to improve long-term stability of rock engineering and increase efficiency of geothermal and petroleum developing. This paper reviews new progress of study on this topic. It includes effect of water chemical corrosion on triaxial compressive strength, uniaxial compressive strength, shear strength, tensile strength, and cracking characteristics of rocks. The mechanism of water chemical corrosion is analyzed. The further study on this topic is also discussed.