Jin-Kyung Kwon

Solar Energy Storage Effectiveness on Double Layered Single Span Plastic Greenhouse

This study was carried out in order to reduce the amount of underground water which is used in the double layered single span plastic greenhouse for retaining heat. For this research, two plastic green houses of the double layered single span plastic greenhouse were installed. There was equipped of internal small tunnel for keeping warm air in the interior of the house. Then the internal small tunnel for keeping warm air was fitted with PVC duct of 50 cm in diameter filled with subsurface water. The surplus solar energy in the greenhouse was stored in the water in the PVC duct. Four FCUs (Fan Coil Unit), which has the capacity of 8,000 kcal per hour, were installed in the middle of the house, and a circulation motor in heat storage water tank was operated from 10:30 a.m. to 16:00 p.m. in order to circulate water between the water tank and the FCUs. Consequently about 5 degrees celsius could be maintained in the interior of the internal small tunnel for keeping warm air with the external temperature of lower than minus 5 degrees celsius. It appeared that the alteration of an internal temperature of the house was flexible depending on the sunlight during daytime. To prevent the water freezing, mixing antifreezing liquid in the water or operating FCU continuously was needed. Also, in order to use the surplus solar thermal energy on plastic green house of water curtain system efficiently, storing the surplus heat during daytime simultaneously finding a method of using water curtain systematic underground water happened to be important. As a result of this research, when the houses interior temperature is below zero the operation of FCU appeared to be impossible. Considering the amount of water used in the house with water-curtain-heating system is 150～ 200 ton per day, using the system mentioned in this research showed that reducing the underground water more than 80% in order to maintain the internal temperature as the level of 5 degree celsius at the extreme temperature of minus 5 degrees celsius.

CFD Simulation of Airflow and Heat Transfer in the Cold Container

To prevent deterioration of agricultural products during cold transportation, optimized temperature control is essential. Because the control of temperature and thermal uniformity of transported products are mainly governed by cooling air flow pattern in the transportation equipment, the accurate understanding and removal of appearance of stagnant air zone by poor ventilation is key to design of optimized cooling environment. The objectives of this study were to develop simulation model to predict the airflow and heat transfer phenomena in the cold container and to evaluate the effect of fan blowing velocity on the temperature level and uniformity of products using the CFD approach. Comparison of CFD prediction with PIV measurement showed that RSM turbulent model reveals the more reasonable results than standard model. The increment of fan blowing velocity improved the temperature uniformity of product and reduced almost linearly the averaged temperature of product.

ECR Ar/CH4/H2 plasma damage in HgCdTe

The capacitance-voltage (C-V) and the Hall effect measurements were used, in order to study electron cyclotron resonance (ECR) plasma damage in HgCdTe (MCT). In this study using ECR treatments of MCT and C-V measurements, we observed that the type conversion of MCT surface largely depended on the ECR etching conditions, when MCT was etched by ECR plasma as a function of the ECR power and dc bias. The n-type conversion was not observed when the p-type MCT was etched under the condition of ECR power 150 W and dc bias -20 V. As dc bias of ECR increased over -40 V at the constant ECR power 150 W, the p-type MCT was converted to n-type. The p-type MCT was also converted to n-type when ECR power increased to 500 W at the constant dc bias -20 V. These results probably were due to the inter-diffusion of a large amount of excess mercury, liberated during the ECR treatment, into MCT, which were similar to the results of ion milling process. Another interesting result, observed in C-V measurements, was the p- type conversion from n-type MCT when the n-type MCT was etched under the condition of ECR power 150 W and dc bias -20 V. As dc bias of ECR increased over -40 V, the C-V curve was the results of n-type MCT characteristics. We considered that a low dc bias of -20 V, the hydrogen passivation and the deficiency of mercury in the etched surface were dominant and resulted in conversion to p-type. As dc bias increased over -40 V, the inter-diffusion of excess mercury into MCT was dominant and associated with keeping the n-type characteristics.

Greenhouse Heating Technology Development by using Riverbank Filtration Water

In order to heat greenhouse nearby river channel, riverbank filtration water source heat pump was developed for getting plenty of heat flux from geothermal energy. Recharging well, thermal storage tank with separating insulation plate and filtering tank for eliminating iron, manganese were mainly developed for making the coefficient of performance (COP) of heat pump higher. Heating system using riverbank filtration water source heat pump was installed at a paprika greenhouse in the Jinju region where a single fold of vinyl cover and 2 layers of horizontal thermal curtain were installed as a part of temperature keeping and heat insulation with a greenhouse area of 3,185 . 320,000 kcal/h was supplied for performing a site application tests. A greenhouse heating test was performed from Feb. 1, 2011 to Apr. 30, 2011. As the result of that, COPh of the heat pump was measured in the range of 4.0~4.5, while COPS of the system was represented as 2.9~3.3. COP measured of the heat pump was very good and well responded to indoor heating temperature of the environment control system of a greenhouse.

Development of Ground Filtration Water Source Heat Pump for Greenhouse heating system

We have developed ground filtration water source heat pump for getting plenty of heat flux from geothermal energy. Surface water in river channel was used for getting a lots of geothermal heat by penetrating water through underground soil layer of the riverbank that make heat transmission to passing water. The range of water temperature after the process of Ground filtration was 13~18 degrees Celsius which made the number of geothermal heat exchanging holes fewer and the construction expense for geothermal heat exchanger reduced. Recharging well was also used for returning filtration water to the aquifer that keeps the water good recirculation from losing geothermal heat and water resource. For the COP improvement of Heat pump, we have developed thermal storage tank with separating insulation plate according to the temperature difference which make the COP of Heat pump higher than existing thermal storage tank. Filtering tank for eliminating iron, manganese in ground filtration water was used for improving water quality that makes heat exchanger efficiency better. The heating system using the developed ground filtration water source heat pump was installed at a paprika greenhouse in the Jinju region in south Korea where a single fold of vinyl cover and 2 layers of horizontal thermal curtain were installed as part of temperature keeping and heat insulation with a greenhouse area of 3,300m2, to perform a site application test so that 320,000kcal/h can be supplied considering heating setup temperature and outdoor temperature. A greenhouse heating test was performed from Feb. 1, 2011 to Apr. 30, 2011. As the result, COPh of the heat pump was measured in the scope of 3.7~4.7, while COPS of the system was represented as 3.0 ~ 3.5. The coefficient of performance (COP) measured of the heat pump was very good and well responded to heating setup temperature of the environment control system of a greenhouse. Installation costs can be reduced since The ground filtration water source heat pump can considerably reduce installation water of a recharging well due to sufficient water volume to collect and can overcome the limited volume of water collection of a general ground filtration water source heat pump.

Analysis of Flow Characteristics of Forced Ventilated Pre-drying Facility for Mandarin

Uniform and rapid pre-drying of mandarin is important to improve the storage quality. The aim of this study was to suggest the basic design of forced ventilated pre-drying facility for mandarin by thermal flow analysis using computational fluid dynamics software (FLUENT 6.2). Developed CFD simulation model was verified by comparison with experimental data. Airflows and temperature distributions in the five conceptional designs including existing ordinary temperature storage rooms were analyzed and appropriate basic design was determined. Analysis of the effect of arrangement of windows and exhaust fans on thermal flow in facility was carried out for more detailed design. The results of this investigation showed that the predicted airflow velocity by CFD simulation showed a good agreement with the measured value and optimum design condition for simulated forced ventilated pre-drying facility of mandarin has two exhaust fans and two windows on both sidewalls and cover on loaded mandarin.

Design of Heat and Fluid Flow in Cold Container Using CFD Simulation

Because thermal non-uniformity of transported agricultural products is mainly affected by cooling air flow pattern in the cold transport equipment, the analysis and control of flowfield is key to optimization of cold transport equipment. The objectives of this study were to estimate the effects of geometric and operating parameters of cold container on the air flow and heat transfer, and find the optimum design parameters for the low temperature level and its uniformity in given cold container with CFD simulations. Existences of ducts, gaps between pallets and geometries of exit as geometric parameters and fan blowing velocity as operating parameter were investigated. CFD simulations were carried out with the FLUENT 6.2 code. The result showed that optimum design condition was bulk loading with no duct, wall exit and 8.0 m/s of fan blowing velocity.

Single-element photoconductive Hg0.79Cd0.21Te IR detector fabrications and their characteristics

Long wavelength infrared (LWIR) photoconductive (PC) detectors of single element Hg0.79Cd0.21Te (MCT) on sapphire substrate were fabricated, using three kinds of MCT etching processes, such as wet only, wet & dry mixed, and dry only process. The ohmic contact metals, which were used to the first contact layer in the IR detector fabrication, were Au, Ni, and Ti. The performance test of the fabricated IR detectors showed the good results in the wet etched MCT IR detectors with the detectivities (D*) of (1-3) X 1010 cmHz1/2W-1 and the responsivities of (2-3) X 104 VW-1 at field of view (FOV) of 180 degrees.

Cold Thermal Energy Storage Characteristics of Spherical PCM Capsule

The freezing characteristics of two kinds of phase change materials (PCM) encapsulated in a spherical container were investigated with various cooling air temperatures and velocities. The super cooling and solidification time of PCM were highly affected by cooling air temperature and velocity. The experimental equations are derived to express total solidification time of the PCM in terms of Nusselt number and dimensionless temperature.