Taebeom Seo

An Experimental Study of the Conduction Cooling System for the 600 kJ HTS SMES

The characteristic of the superconducting magnetic energy storage (SMES) system is more fast response, long life time, more economical, and environment-friendly than other uninterruptible power supply (UPS) using the battery. So, the SMES system can be used to develop methods for improving power quality where a short interruption of power could lead to a long and costly shutdown. Recently, cryogen free SMES is developed briskly based on BSCCO wire. We fabricated and tested the conduction cooling system for the 600 kJ class HTS SMES. The experiment was accomplished for simulation coils. The simulation coils were made of aluminum, and have inner and outer coil diameters of 460 mm and 728 mm and coil height of 237 mm. The mass of coil is 171.6 kg, it is equivalent to thermal mass of 600 kJ HTS SMES coil. The coil is cooled with two GM coolers through the copper conduction bar. In this paper, we report the test results of cool-down and heat loads characteristics of the simulation coils.

Heat Losses from the Receivers of a Multifaceted Parabolic Solar Energy Collecting System

Heat losses from the receivers of a dish-type solar energy collecting system at the Korea Institute of Energy Research (K.IER) are numerically investigated. It is assumed that a number of flat square mirrors are arranged on the parabolic dish structure to serve as a reflector. Two different types of receivers, which have conical and dome shapes, are considered for the system, and several modes of heat losses from the receivers are thoroughly studied. Using the Stine and McDonald model convective heat loss from a receiver is estimated. The Net Radiation Method is used to calculate the radiation heat transfer rate by emission from the inside surface of the cavity receiver to the environment. The Monte-Carlo Method is used to predict the radiation heat transfer rate from the reflector to the receiver. Tracing the photons generated, the reflection loss from the receivers can be estimated. The radiative heat flux distribution produced by a multifaceted parabolic concentrator on the focal plane is estimated using the cone optics method. Also, the solar radiation spillage around the aperture is calculated. Based on the results of the analysis, the performances of two different receivers with multifaceted parabolic solar energy collectors are evaluated.

Combined convection and radiation in a tube with circumferential fins and circular disks

Combined convection and radiation heat transfer in a circular tube with circumferential fins and circular disks is investigated for various operating conditions. Using a finite volume technique for steady laminar flow, the governing equations are solved in order to study the flow and temperature fields. TheP- 1 approximation and the weighted sum of gray gases model (WSGGM) are used for solving the radiation transport equation. The results show that the total Nusselt number of combined convection and radiation is higher than that of pure convection. If the temperatures of the combustion gas and the wall in a tube are high, radiation becomes dominant. Therefore, it is necessary to evaluate the effect of radiation on the total heat transfer. Key Words: Convection, Radiation, Nongray Radiation,P- 1 Approximation, Weighted Sum of Gray Gases Model

Design of Cryogenic Systems for 154 kV HTS Power Cable

Cryogenic cooling is necessary for HTS power cables to perform their intended function. In the cooling process, sub-cooled liquid nitrogen is circulated by a pump to absorb and dissipate the heat generated in the cable and introduced from outside. To ensure successful cooling, the hydraulic characteristics of the cooling passages of the HTS cable as well as the thermal load have to be understood. The thermal load of the cable determines the capacity of the cooling system, and the pressure drop in the cooling passage is an important design parameter that determines the length and diameter of the cable and the capacity of the circulation pump. In this study, a cryogenic cooling system equipped with two cooling passages was designed. In the system, sub-cooled liquid nitrogen flows through the core (former) and the circumferential side of the cable in the same direction to cool the cable, and then returns to the cryogenic cooling system through the return line. In this study, the thermal load of the cable system was analysed to determine the type and capacity of the cryogenic cooler, and the pressure drop in the cooling passage was analysed to determine the pressure of the liquid nitrogen and the size and shape of the cooling passages of the cable.

Experimental Investigation of Heat Transfer Enhancement in a Circular Duct with Circumferential Fins and Circular Disks

The characteristics of heat transfer and pressure drop for fully developed turbulent flow in a tube with circumferential fins and circular disks were experimentally studied. The various spacing and sizes of circumferential fins and circular disks were selected as design parameters, while the effects of these parameters on heat transfer enhancement and pressure drop were investigated. In order to quantify the effect of heat transfer enhancement and the increase of pressure drop due to the fins and disks in a tube, the Nusselt numbers and the friction factors for various configurations and operating conditions were compared to those for a corresponding smooth tube. The results showed that the heat transfer rate was significantly enhanced by increasing the height of circumferential fins and decreasing the pitch of circumferential fins. On the other hand, the influence of the disk size and the fin-disk spacing were not significant. Based on the experimental results, a correlation for estimating the Nusselt number was suggested.

Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project: Reforming Performance of Reactor Tubes During Intermittent Heating

Reforming performances for the double-walled reactor tubes with Na2 CO3 /MgO composite thermal storage was examined by an intermittent heating. The intermittent heating of the reactor tubes is composed of the heat-discharge (or cooling) mode and the subsequent heating mode. The heat-discharging mode simulates a fluctuating insolation for cloud passages. The heating mode simulates a heating of reactor due to concentrated solar radiation by using an electric furnace. The internal tube of the reactor was packed with the 2wt%Ru/Al2 O3 catalyst balls while the thermal storage materials were filled in the annular region of the reactor tubes. The reactor was heated up to 920°C in the cylindrical electric furnace and the CH4 /CO2 mixture was fed into the internal catalyst tube at gas hourly space velocity (GHSV) of 12500 h−1 . Through the cooling mode and the subsequent heating mode, temperature variations of reactor tubes, catalyst and composite material, H2 /CO ratio variations of effluent gas from the reactor, higher heating value (HHV) power of reformed gas were respectively examined for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage.Copyright

Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project: Metal-Plate-Bridged Double Tube Reactor

The Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project, which is jointly conducted by Niigata University, Japan, and Inha University, Korea, aims to develop a novel-type of “double-walled” tubular absorbers/reformers with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate their performances on sun with a 5-kWt dish-type solar concentrator. The new concept of “double-walled” reactor tubes was proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten salt in the annular region between the internal catalyst tube and the exterior solar absorber tube of the double reactor tube. In this work, “metal-plate-bridged” double reactor tubes are newly proposed for use in a solar reformer. Two different sized reactor tubes are constructed, and tested on chemical reaction performance for dry reforming of methane during cooling or heat-discharge mode of the reactor tube using an electric furnace. The experimental results obtained under feed gas mixture of CH4 /CO2 = 1:3 at a residence time of 0.36 s and at 1 atm showed that the double reactor tube with the heat storage medium Na2 CO3 in the annular region successfully sustained a high methane conversion above 90% with about 0.7-kW output power of the reformed gas based on HHV for 40 min of the heat-discharge mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.Copyright

Performance comparison of dish solar collector system with mirror arrays and receiver shapes

The thermal performance comparisons of the dish solar collector system are numerically investigated with mirror arrays and receiver shapes. In order to compare the performances of the dish solar collector systems, six different mirror arrays and four different receiver shapes are considered and the radiative heat flux distribution on the inside of the receiver is analysed. The solar irradiation reflected by mirrors is traced using the Monte-Carlo method. The results show that the dome type has the best performance in receiver shapes and the 2AND4INLINE has the best performance in mirror arrays except the perfect mirror.

The Outgassing Test of a HTS Power Cable Cryostat

An analysis and reduction of outgassing in a high temperature superconductor (HTS) cable cryostat are very important to achieve operation over a long period of time. Because the outgassing surface area is much larger than the vacuum space of the cable cryostat, the vacuum condition of cable cryostat degrades quickly. A cold trap effect, where the activity of the molecules decrease in very low temperature, is observed when the cable cryostat is filled with liquid nitrogen (LN2). In this paper, the outgassing rate of HTS cable cryostat sample was measured for different vacuum insulation configuration with or without multilayer insulation (MLI), filled or not filled in cable cryostat LN2. And the test, which maintained the vacuum below 1.0×10−4 Torr was performed for 20 days.

Coupled heat and mass transfer in absorption of water vapor into Libr-H2o solution flowing on finned inclined surfaces

The absorption characteristics of water vapor into a LiBr-H2O solution flowing down on finned inclined surfaces are numerically investigated in order to study the absorbing performances of different surface shapes of finned tubes as an absorber element. A three-dimensional numerical model is developed. The momentum, energy, and diffusion equations are solved simultaneously using a finite difference method. In order to obtain the temperature and concentration distributions, the Runge-Kutta and the Successive over relaxation methods are used. The flat, circular, elliptic, and parabolic shapes of the tube surfaces are considered in order to find the optimal surface shapes for absorption. In addition, the effects of the fin intervals and Reynolds numbers are studied. The results show that the absorption mainly happens near the fin tip due to the temperature and concentration gradient, and the absorbing performance of the parabolic surface is better than those of the other surfaces.