Yong-Shik Han

Experimental Investigation of Variations in Inclination Angle of Natural Convective Heat Sink with Plate Fins

In this paper, an experimental investigation is performed to estimate the thermal performance of a natural convective heat sink with plate fins subject to the uniform wall temperature condition. Extensive experiments are performed with various input powers, fin spacings, and heights of the natural convective heat sinks with plate fins. In particular, the effect of the inclination angle on the thermal performance of the heat sink is studied. In order to validate the experimental data, the experimental results are compared with results from previous studies. Based on the experimental results, the appropriate ranges of the previous correlations between the input power, the fin spacing, the fin height, and the inclination angle for the natural convective heat sink with plate fins are evaluated.

Application of a Fixed Water Mist System in a Power Transformer Room

This study deals with the fire suppression capability and cooling characteristics required to prevent spontaneous re-ignition in a power transformer room. A water mist system was considered as a possible alternative to a gaseous suppression system. High- and lowpressure water mist systems were examined. The power transformer examined in this study occupied about 7% of a 10 m × 10 m × 10 m test room. Full-scale suppression tests were performed for six different fire scenarios: two spray fires, three pool fires, and one cascade fire. Three reduced-scale models were used to estimate the cooling characteristics required for the power transformer and to calculate the necessary discharge time for the water mist to prevent spontaneous re-ignition. The fire suppression test results demonstrated that the high-pressure system was superior to the low-pressure system, especially considering oxygen depletion and the ambient temperature distribution. In the cooling tests, the discharge time required to prevent spontaneous reignition was estimated to be about 12 h for both the high- and low-pressure systems.

The Study on the Lifetime Estimation using Fault Tree Analysis in Design Process of LNG Compressor

Fault Tree Analysis to predict the lifetime in the design process of LNG compressor is considered. Fault Trees for P & ID of the compressor are created. Individual components that comprise the compressor are configured with the basic event. The failure rates in the PDS and OREDA are applied. As results, the system failure rate and the reliability over time are obtained. Further, the power transmission and the shaft seal system is confirmed to confidentially importantly contribute to the overall lifetime of the system. These techniques will help to improve the reliability of design of large scale machinery such as a plant.

First-Order Perturbation Solutions for Liquid Pool Spreading with Vaporization

We solve the simple physical model for liquid pool spreading with vaporization semi-analytically for the first time, using perturbation techniques. The results are compared with those obtained using numerical methods. We use the evaporation rate per unit area as a perturbation parameter, and first-order solutions are obtained for continuous and instantaneous release. The two solutions are nearly identical with respect to the pool radius. The pool volumes are nearly the same at the early stage of the spread and then start to diverge.

Optimization for the Internal Structure of a Recuperator with Offset Strip Fins

In the present study, a recuperator is suggested to improve the thermal efficiency of a micro gas turbine. Primary design parameters of the recuperator are determined from the ideal cycle analysis. The counter flow plate-fin heat exchanger with offset strip fins is chosen as the type of the recuperator. In order to satisfy the design constraints which are the minimum effectiveness and the maximum pressure drop, the optimization for the internal structure of the recuperator is performed with varying the fin spacing and the fin height of offset strip fins. Also the effects of the thermal conductivity of fins and separation plates and the longitudinal heat conduction on the thermal performance of the recuperator are investigated.

Experimental Investigation of Water Hammer Phenomena in a HelicalCoil Tube for Examination of Water Hammer Models

Extended Abstract Since all flows will eventually be changed, either suddenly or gradually, all pipeline systems inevitably experience transient effects [1]. These effects can normally produce sudden increase in pressure in the pipeline systems. These phenomena are called water hammer. Water hammer phenomena in the pipeline systems can result in not only damage to equipment, but also possible injury to plant personnel. Due to these safe problems, it is important to predict water hammer in the pipeline systems. In this study, water hammer phenomena in a helical coil tube are experimentally investigated. First of all, a friction factor is very important to estimate pressure propagation behaviour in water hammer prediction. Several models for the friction factors in a helical coil tube have been developed. However, there exists discrepancies between the models and there is no model for a friction factor of a helical coil tube in transition regime. Therefore, friction factors in a helical coil tube are experimentally obtained for laminar, transition, and turbulent regimes and compared with the previous models. Based on the comparison, the appropriate models are used for estimation of water hammer phenomena. Then, experiments are performed for water hammer phenomena. Because pressure propagation in water hammer phenomena is very fast, a helical coil tube should be long in order to have time enough to measure the pressure propagation. So, the length of a helical coil tube is determined as 100 m. For the implementation of sudden change of flows, a shutdown valve is located at the end of a helical coil tube. After the valve is suddenly closed, water hammer phenomena are occurred and the increased pressure wave travels along the tube. In order to measure the pressure propagation along the tube, pressure transducers with high frequency are installed every 10 meters along the tube. Experiments are performed as varying flow rate. As a result, the amplitude of pressure wave increases as increasing flow rate but the period of pressure wave is constant regardless to flow rate. Sometimes, the pressure in a pipeline drops to the vapour pressure at high flow rate. Then, cavitation is occurred in the tube. In this state, the amplitude of pressure wave is very large, it is not cyclic, and its period is not constant. Finally, experimental results for water hammer in a helical coil tube are compared with the models developed by previous researchers. In this study, the water hammer models are considered because they have high accuracy compared to the other models [1]. The water hammer models and the method how to solve them are well explained in [2, 3]. By comparison between experimental results and the models, it is shown that the unsteady friction coefficient model developed by Reddy et al. [4] corresponds well experimental results in this study. The results based on the other models have some deviations from the experimental results. In addition, when the cavitation is occurred during the water hammer phenomena, the pressure wave propagations are totally different from the water hammer models considered in this study. For this case, it is necessary to develop new models to predict pressure wave propagations under the cavitation.

Study on the Thermal Performance of a Solar Assisted Heat Pump System with a Hybrid Collector

>> In the present work, a solar assisted heat pump (SAHP) system with a hybrid collector was analyzed. For this, a simplified thermodynamic model was developed. Based on the proposed model, the heat transfer rate, COP, and the annual operating hour of the SAHP system were estimated. The effect of the variation of system design parameters on the performance of the system was also examined. From the results, the performance was improved with increasing the effectiveness of heat exchangers and decreasing the difference between the evaporation temperature and the outlet brine temperature of the hybrid collector loop. Finally, the performance of SAHP system with a hybrid collector was compared with that of conventional serial and parallel SAHP systems. The SAHP system with a hybrid collector was substantially better than a series system and slightly worse than a parallel system for both the yearly averaged heat transfer rate and COP. However, the annual operating hour of the SAHP system with a hybrid collector was much better than that of a parallel system.

Experimentally Evaluation of a Liquid Pool Spreading Model with Continuous Release

>> In this study, an experimental investigation is performed for evaluation of a liquid pool spreading model with continuous release. The model considered in this study was developed based on a concept which means that the liquid pool spreading is governed by a balance between an inertia force from gravity and a frictional force from friction with the ground under the whole base of the liquid pool. For evaluation of the model, experimental study is performed. Experimental apparatus is setup for measuring release rate, spreading velocity, and evaporation rate from a liquid pool. The experimental results are compared with results from the model. By applying release and evaporation rates obtained from experiments to solving the model, liquid pool radius variation according to time can be obtained. For evaluation of an effect of friction force in the spreading model, results obtained from the models with and without the friction force are compared with those obtained from the experiments. As a result, it is shown that there exists a large deviation between the results obtained from the model without the friction force and the experimental results. On the other hand, the tendency of liquid pool radius variation according to time is similar between the results obtained from the model without the friction force and the experimental results.

Experimental Study of a Recuperator with Offset Strip Fins

Abstract - In the present study, a recuperator to improve the t hermal efficiency of a micro gas turbine is considered. The counter flow plate-fin heat exchanger with o ffset strip fins is chosen as the type of the recuperator. From the optimization study as varying design parameters of the recuperator determined from the ideal cycle analysis, the internal structure of the re cuperator is determined. The recuperator is made from stainless steel 304. In order to evaluate performance of the recuperator, experimental investigation is performed. The effects of inlet temperature of hot-side of the recuperator on the thermal performance of the recuperator are investigated. As a result, e ffectiveness of the recuperator obtained from the experiments is well consistent with that obtained from the correlations. Key words : Recuperator, Offset strip fin, Correlations, Pressure drop, Effectiveness에너지공학, 제24권 제2호(2015) Journal of Energy Engineering , Vol. 24, No. 2, pp.72~78(2015)http://dx.doi.org/10.5855/ENERGY.2015.24.2.072

Study on a Quantitative Risk Assessment of a Large-scale Hydrogen Liquefaction Plant

Abstract >> In the present study, the frequency of the undesired accident was estimated for a quantitative riskassessment of a large-scale hydrogen liquefaction plant. As a representative example, the hydrogen liquefaction plant located in Ingolstadt, Germany was chosen. From the analysis of the liquefaction process and operating conditions, it was found that a LH 2 storage tank was one of the most dangerous facilities. Based on the accidentscenarios, frequencies of possible accidents were quantitatively evaluated by using both fault tree analysis and eventtree analysis. The overall expected frequency of the loss containment of hydrogen from the LH 2 storage tank was6.83×10 -1 times/yr (once per 1.5 years). It showed that only 0.1% of the hydrogen release from the LH 2 storagetank occurred instantaneously. Also, the incident outcome frequencies were calculated by multiplying the expectedfrequencies with the conditional probabilities resulting from the event tree diagram for hydrogen release. The resultsshowed that most of the incident outcomes were dominated by fire, which was 71.8% of the entire accident outcome.The rest of the accident (about 27.7%) might have no effect to the population.