Chang-Hyo Son

Efficiency enhancement of the ocean thermal energy conversion system with a vapor–vapor ejector

In this article, 20 kW ocean thermal energy conversion with a vapor–vapor ejector is newly proposed. As a vapor–vapor ejector is installed in the system, the pressure difference between the turbine inlet and outlet increases. Therefore, the amount of the working fluid required for the total turbine work of 20 kW is less than when no vapor–vapor ejector is installed. Therefore, installing a vapor–vapor ejector in the system decreases the evaporation capacity and the pump work. The performance analysis considered the outlet pressure of the high-stage turbine, the mass flow ratio of the working fluid at the outlet of a separator just after the high-stage turbine, and the nozzle diameters of the vapor–vapor ejector. As the outlet pressure of high-stage turbine becomes lower, the turbine gross power of high-stage turbine and system efficiency increase although lower outlet pressure of high-stage turbine results in lower ejector performance. Similarly, in terms of mass flow ratio, the highest system efficiency was shown at mass flow ratio of 0.4 at the outlet of a separator just after the high-stage turbine. On the other hand, the performance of the ejector at mass flow ratio of 0.5 at the outlet of a separator was largest. When the nozzle diameters of the vapor–vapor ejector are properly designed, the vapor–vapor ejector shows the highest performance. After the optimization of the operation parameters, system efficiency of the proposed ocean thermal energy conversion power cycle was 2.47%, relatively 15% higher than that of the basic ocean thermal energy conversion power cycle (2.2%).

A Numerical Analysis on Heat Transfer Between the Air and the Liquid in a Hybrid Solar Collector

A hybrid solar collector, in this study, means the flat plate solar collector that has a fin-and-tube heat exchanger combining with a heat pump system. This collector can get the thermal energy from the ambient air for heating the circulated water in the collector when solar radiation is not enough. Thus, this collector can supply thermal energy to evaporator of the heat pump using heated water. For a foundation design of this collector, the numerical analysis was conducted for confirming the heat gain of water by the ambient air according to the length and the installation angle of fins in the fin-and-tube heat exchanger of solar collector. As a result, much of heat gain of water was obtained on the higher fin length with 30o of installation angle, but the pressure drop of air side increased adversely with heat transfer rate. Thus an area goodness factor considering both heat transfer enhancement and pressure drop of air side was also investigated. As a result, 50 mm of the fin length with 0o of installation angle has a good heat transfer enhancement than that of the other installation conditions compare with increment of pressure drop. However, mostly, higher heat transfer rate was obtained when the area goodness factor was low. So, it is needed to be considered whether the condition, maximum value of area goodness factor satisfying the heat transfer rate, can be expected or not.

Performance Analysis of Brine Chiller Refrigeration Cycles

Comparison analysis of vapor-injection, two-stage compression and cascade refrigeration systems is carried out in this paper. R22 and R404A are employed for working fluid. Analysis conditions have been set based on brine chiller for semi-conductor manufacturing process. Results are summarized as follow: (1) Vapor-injection system has the highest coefficient of performance (COP) among systems. (2) Vapor-injection and cascade systems have the optimal intermediate pressure in terms of COP while that of two-stage compression system increases along with it (3) The optimal intermediate pressure is varied by change degree of compression works in both levels of compressor.

Performance Analysis of R404A Refrigeration System with Internal Heat Exchanger Using R744 as a Secondary Refrigerant

A thermodynamic analysis of the R404A refrigeration system with an internal heat exchanger using R744 as a secondary refrigerant is presented in this paper to optimize the design for operating parameters of the system. The main results are summarized as follows: The COP increases with increasing subcooling and superheating degree of R404A, internal heat exchanger and compression efficiency of the R404A cycle and evaporating temperature of the R744 cycle and decreasing temperature difference of the cascade heat exchanger and condensing temperature of the R404A cycle. The mass flow ratio decreases with increasing evaporating temperature of the R744 cycle and internal heat exchanger efficiency of the R404A cycle and decreasing subcooling and superheating degree of the R744 cycle, temperature difference of the cascade heat exchanger and condensing temperature of the R404A cycle.

Study on Demand Prediction of Cold Storage Facilities

This paper describes the investigation on current state of cold storage facilities, and analysis on the demand prediction in the near future. And based on the analysis results, we prospect the scale of cold storage facilities in the near future. The main analysis results are summarized by the followings ; The present circumstances of cold storage facility are determined by investigating actual loading capacity, average stock amounts, and return number of cold storage facility. From the results, the present situation for cold storage facility is about 3% over. It is found that the average stock amounts increase gradually, and accordingly that the demand of cold storage facility is predicted to be increased, resulting that the capacity of cold storage facilities in 2013 expects to reach up to 5,250,000 ton. It is considered that the results of demand prediction has significant implications on the management of cold storage facility in the near future.

Present Situation and Analysis of Cold Storage Facilities for Fisheries Products

ABSTRACT:This paper describes the analysis on freeze and refrigeration capacity of cold storage facilities for fisheries products during the last 15 years. And based on the analysis results, we prospect the number and scale of cold storage facilities in the near future. The main analysis results are summarized by the followings; Under the present conditions, the number and scale of our facilities is 879 and 3,586,824 ton, respectively. In comparison of the present and last 15 years ago, the business number increases about 22%, the accommodation capacity increases approxima-tely 80%. In the reported update reference with the related data during the last 15 years, the capacity of cold storage facilities in 2011 expects to reach up to 4,600,000 ton. The newly- established facility in 2011 has the function of a multi-purpose distribution center as well as the existing cold storage, but this facilities converges in the capital area. Therefore, in this paper, we provided the basic reference data for the present situation and prediction of our cold storage facilities. But it is necessary to investigate and analyse widely our cold storage facilities for fisheries products in the near future.Keywords:Cold storage facility(냉동냉장설비), Present situation(현황), Analysis(분석), Freeze and refrigeration capacity(동결과 냉동능력)

Performance Characteristics of Water-Chilling Heat Pump Using CO 2 on Control of Inverter Frequency

The performance characteristics of water-chilling heat pump using CO2 for the control of inverter frequency was investigated experimentally. An experimental apparatus is consisted of a compressor, a gas cooler, an expansion valve, an evaporator and a liquid receiver. All heat exchangers used in the test rig are counter flow type heat exchangers with concentric dual tubes, which are made of copper. The gas cooler and the evaporator consist of 6 and 4 straight sections respectively arranged in parallel, each has 2.4m length. The experimental results summarize as the following: for constant inlet temperature of evaporator and gas cooler, as mass flow rate, compression ratio and discharge pressure increases with the inverter frequency. And heating capacity and compressor work increases, but coefficient of performance(COP) decreases with the inverter frequency of compressor. As inlet temperature of secondary fluid in the evaporator increases from to , compression ratio and compressor work decreases, but mass flow rate, heating capacity and COP increases with the inverter frequency of compressor. The above tendency is similar with performance variation with respect to the variation of inverter frequency in the conventional vapor compression refrigeration cycle.

Heat Transfer Characteristics of Flood-type Evaporator Using R22 and R134a for Fishing Vessels

ABSTRACT Most of fishing vessels pour plain ice into fish storages to maintain freshness of catches, which causes varying storage temperatures and changes in the salinity, and damages in catches. In contrast, seawater cooling systems that directly chill the seawater in the storage provide seawater with a constant temperature and salinity. Furthermore, the application of a flood-type evaporator enables the size of the system to be reduced due to the enhanced heat transfer performance of the evaporator. This study conducts experimental research on the boiling heat transfer characteristics of flood-type evaporators under various operating conditions. The test section of the experiment consists of the flood-type evaporator including tubes made of three different materials and having two different shapes, and R134a and R22 are used. As a result, low-fin tubes were found to present a higher heat transfer coefficient than that of the plain tube. Aluminum-brass low-fin tubes exhibited relatively 4.5% higher heat transfer coefficient than that of copper-nickel low-fin tubes when R22 was used, and relatively 5.3% higher value when the R134a was used. When R22 was used with an aluminum-brass low-fin tube, the heat transfer coefficient was relatively 6.9% higher than that when using R134a.

Experimental Study for Estimation of Air Heating Performance and Improvement of Thermal Performance of Hybrid Solar Air-water Heater

Solar energy is one of the important renewable energy resources. It can be used for air heating, hot water supply, heat source of desiccant cooling system and so on. And many researches for enhancing efficiency have been conducted because of these various uses of solar thermal energy. This study was performed to investigate the air heating performance of hybrid solar air-water heater that can heat air and liquid respectively or simultaneously and finding method for improving thermal performance of this collector. This collector has both liquid pipe and air channel different with the traditional solar water and air heater. Fins were installed in the air channel for enhancing the air heating performance of collector. Also air inlet & outlet temperature, ambient temperature and solar collector’s inner part temperature were confirmed with different air velocity on similar solar irradiance. As a result, temperature of heated air was shown about 43°C to 60°C on the 30°C of ambient temperature and thermal efficiency of solar collector was shown 28% to 73% with respect to air velocity. Also, possibility of improvement of thermal performance of this collector could be ascertained from the heat transfer coefficient calculated from this experiment. Thus, it is considered that the research for finding optimal structure of hybrid solar air-water heater for enhancing thermal performance might be needed to conduct as further study based on the method for improving air heating performance confirmed in this study.

A Study on the Heat Exchange Performance of Hybrid Solar Collector with Air to Water Heat Exchanger Type

Solar assisted heat pump system is the heat pump system using solar thermal energy as a heat source of evaporator of the heat pump and most of these systems have been used ordinary solar collector that can get a thermal energy only from solar radiation. Thus, the hybrid solar collector that has air to water heat exchanger of fin-and-tube type have been developed for obtaining thermal energy from not only solar radiation but also ambient air. It is the flat plate solar collector installed fin-and-tube heat exchanger beneath absorbing plate. Thus the thermal energy obtained from ambient air can be supplied to evaporator of heat pump when the solar radiation is not enough. At this time, heat exchange performance between air and circulated water is one of most important factor. Hence, in this study, heat exchange performance of hybrid solar collector and effect of parameters that affect heat exchange performance were investigated experimentally. As a result, heat transfer rate between air and water was shown from 180 W to 820 W and it was increased linearly with increment of temperature difference between inlet air and water. In case of effectiveness, it was shown from 0.5 to 0.6 and it was increased by decrement of air mass flow rate independently on temperature difference between inlet air and water. From these results, heat exchange performance of the collector is considered as a sufficient capacity for applying for heat pump system and it also could be confirmed that optimal operation condition of solar assisted heat pump system integrated with hybrid solar collector need to be established base on the relationship obtained from this research as a further study.