• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.12
• /
• pp.927-934
• /
• 2015

In this study, we numerically investigated the concentration characteristics of a linear Fresnel reflector system that can drive a solar thermal absorption refrigeration system to be installed in Saudi Arabia. Using an optical modeling program based on the Monte Carlo ray-tracing method, we simulated the concentrated solar flux, concentration efficiency, and concentrated solar energy on four representative days of the year - the vernal equinox, summer solstice, autumnal equinox, and winter solstice. Except the winter solstice, the concentrations were approximately steady from 9 AM to 15 PM, and the concentration efficiencies exceed 70%. Moreover, the maximum solar flux around the solar receiver center changes only within the range of $13.0{\sim}14.6kW/m^2$. When we investigated the effects of the receiver installation height, reflector width, and reflector gap, the optimal receiver installation height was found to be 5 m. A smaller reflector width had a greater concentration efficiency. However, the design of the reflector width should be based on the capacity of the refrigeration system because it dominantly affects the concentrated solar energy. The present study was an essential prerequisite for thermal analyses of the solar receiver. Thus, an optical-thermal integration study in the future will assist with the performance prediction and design of the entire system.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.8 no.4
• /
• pp.242-249
• /
• 2006

Potential impacts of the future climate change on crop production can be inferred by crop simulations at a landscape scale, if the climate data may be provided at appropriate spatial scales. Northern Gyunggi Province is one of the few prospective regions in South Korea for growing quality soybeans. Any geographical shift of production areas under the changing climate may influence the current land planning policy in this region. A soybean growth simulation was performed at 342 land units in northern Gyunggi province to test the potential geographical shift of the current production areas for quality soybeans in the near future (form 2011 to 2100). The land units for soybean cultivation were selected by the land use, the soil characteristics, and the minimum arable land area. Daily maximum and minimum temperature, precipitation, the number of rain days and solar radiation were extracted for each land unit from the future digital climate models (DCM, 2011-2040, 2041-2070, 2071-2100). Daily weather data for 30 years were randomly generated for each land unit for each normal year by using a well-known statistical method. They were used to run CROPGRO-Soybean model to simulate the growth, phonology, and yields of 3 cultivars representing different maturity groups grown at 342 land units. According to the model calculations, the warming trend in this region will accelerate the flowering and physiological maturity of all cultivars, resulting in a 7 to 9 days reduction in overall growing season and a 1 to 15% reduction in grain yield of early to medium maturity cultivars. There was a slight increase in grain yield of the late maturing cultivar under the projected climate by 2070, but a decreasing tend was dominant by the year 2100.

• Korean Journal of Food Science and Technology
• /
• v.18 no.6
• /
• pp.479-484
• /
• 1986

Two different types of solar collector for farm dryer- the flatplate type and the modified tubular type-were constructed and analyzed on their performances. The transparent plastic film, black painted galvanized iron sheet and black vinyl film were used for the cover and absorber of the flat-plate types. The simplified tubular type was constructed with transparent films for the cover and black vinyl films for the absorber Two elliptical iron rings were used to form a tubular shape through which air could pass. No remarkable differences were found in thermal efficiences between the absorbers made with galvanized iron sheet and black vinyl film. The average thermal efficiencies of the solar collectors were 42.8%(max.48.2%, min.38.2%) for flat plate type and 22.971 (max. 25.4%, min. 14.8%)) for tubular one. The empirical equations were proved to be applicable to the prediction of temperature elevation. The tubular solar heat collector was successfully applied to red peppers drying as a practical farm dryer. The drying rate was almost doubled compared to a conventional sun drying.

• KIEAE Journal
• /
• v.17 no.1
• /
• pp.69-75
• /
• 2017

Purpose: Heat transfer analysis of recently developed 'slim type double-skin system window' were presented. This window system is designed for curtain wall type façade that main energy loss factor of recent elegant buildings. And the double skin system is the dual window system integrated with inner shading component, enclosed gap space made by two windows when both windows were closed and shading component effectively reflect and terminate solar radiation from outdoor. Usually double-skin system requires much more space than normal window systems but this development has limited by 270mm, facilitated for curtain wall façade buildings. In this study, we estimated thermophysical phenomena of our double-skin curtain wall system window with solar load conditions at the summer season. Method: A fully 3-Dimentional analysis adopted for flow and convective and radiative heat transfer. The commercial CFD package were used to model the surface to surface radiation for opaque solid region of windows' frame, transparent glass, fluid region at inside of double-skin and indoor/outdoor environments. Result: Steep angle of solar incident occur at solar summer conditions. And this steep solar ray cause direct heat absorption from outside of frame surface rather than transmitted through the glass. Moreover, reflection effect of shading unit inside at the double-skin window system was nearly disappeared because of solar incident angle. With this circumstances, double-skin window system effectively cuts the heat transfer from outdoor to indoor due to separation of air space between outdoor and indoor with inner space of double-skin window system.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.31 no.1
• /
• pp.43-48
• /
• 1986

The experiment was conducted to know the varietal difference in changing aspect of daily filling sink during of rice using three cultivars; ‘Suweon 295’ (japonica), ‘Suwoen 264’ and ‘IR 1317-70-1’ (semi-dwarf indica) cultivated in the field and green house of the Crop Experiment Station in 1983. There was not significant varietal difference in flowering habit and duration of flowering period each panicle. Semi-dwarf indica cultivars showed shorter days to physiological maturity of rice kernel than the japonica one. The former also displayed earlier decrease in water content of rice grain during ripening than the latter. Japonica variety revealed larger difference in ripening advancement between vigorous florets and inferior one than semi-dwarf indica varieties. The semi-dwarf indica rice cultivars expressed significantly shrewder parabola of daily filling of sink per panicle during ripening than the japonica one. The time showing maximum capacity of daily filling of sink per panicle during ripening was 10-12 days after anthesis. The filling capacity of daily sink filling per panicle for 'IR 1317-70-1', 'Suweon 264' and 'Suweon 265' at this time were about 240 mg, 165 mg and 145 mg, respectively. Pattern of sink filling per panicle during ripening was slightly changed by the cultural environment. ‘Suweon 295’ showed slightly sharper parabola and 2-3 days earlier time showing maximum capcity of daily sink demand per panicle during ripening in the field than those in the green house.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.35 no.6
• /
• pp.518-524
• /
• 1990

Actual evapotranspiration was measured over rice paddy field by Bowen ratio heat balance method and based on this, investigated was the reliability of actual evapotranpiration estimation from Class-A Pan and small pan evaporation and reference evapotranspiration calculated by modified Penman-Monteith model. Crop coefficients based on Class-A Pan and small pan evaporation and reference evapotranspiration by modified Penman-Monteith model were averaged to be 1.57. 1.10 and 1.49 over the whole rice growing season, respectively. Their respective coefficients of variation were 28.7. 22.7 and 12.8 percent, respectively. Crop coefficient based on modified Penman-Monteith model varied in good agreement with the trend of leaf area development, being greatest around heading stage.

• Weed & Turfgrass Science
• /
• v.2 no.4
• /
• pp.413-420
• /
• 2013

The climate change affects the growth and development of weeds as well as the outbreak of weeds. Especially, the occurrences of problematic paddy weeds due to climate change might cause the difficulties in weed control. This study therefore, investigated the current dominance and distribution of paddy weeds. As a result of the study on paddy weeds in northern Gyeonggi-do, there were total of 65 taxonomy groups including 23 family, 41 genus, 57 species, 7 subspecies and 1 variety. Among all the plants, 46 species were annual plants and 16 were perennial plants. Echinochloa crus-galli was the highest in importance analysis and the followings were in order of Ludwigia prostrate and Lemna paucicostata. The similarity of different paddy weeds in different regions observed through TWINSPAN analysis was distinguished by Fimbristylis miliacea, Rotala indica and Cyperus flaccidus. Regional differences shown in CCA analysis using weed species and soil environment revealed that Gimpo-si and Namyangju-si has difference soil and weeds, which are features that distinguished them from other regions. In northern Gyeonggi-do the result of paddy weed research showed the interregional difference not in dominant weeds but in distribution species.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.22 no.3
• /
• pp.164-170
• /
• 2020

The weather conditions, such as temperature, precipitation, and sunshine duration, play one of the key roles in Agriculture. In particular, extreme weather events have crucial impacts on growth and yields of crops. This study estimates statistics of extreme weather events in 167 Si-gun over South Korea derived from high-resolution(30 and 270m) topo-climatology model for key three meteorological variables(temperature, precipitation and sunshine duration). It is shown that the characteristic of each extreme weather frequency in the topo-climatology model is in good agreement with observation from Korean Meteorological Administration's Automatic Surface Observing System. Moreover, it is possible to analyze the statistics of extreme weather more realistically because this data can cover the weather at not-observed regions. Hence, this data is expected to be used as baseline data for assessing vulnerability to extreme weather and politic decisions for damage reduction in agricultural sector.

• Korean Journal of Agricultural Science
• /
• v.28 no.2
• /
• pp.99-107
• /
• 2001

It is difficult to install a ventilation window on the roof of single span greenhouses of arch shape. Investigation on the roof ventilation structures for those greenhouses was conducted. In small greenhouses with spans of 5 to 8 m, circular or chimney type ridge vents made of plastic were employed. In large greenhouses with spans of 12 to 18 m, even span roll-up ridge vents made of steel pipe were employed. The effect of roof ventilation was evaluated by comparative experiments between greenhouse installing ridge vents and having controlled side vents only. Roof ventilation contributed greatly to restraint of temperature rise and maintenance of uniform temperature distribution in greenhouses. And ventilation efficiency was analyzed by experiments on the opening and closing operation of the ridge and side vent. There were no temperature differences according to opening and closing sequence of ventilation window. But for greenhouse temperature control by ventilation, it is desirable to open side vents after ridge vents and to close ridge vents after side vents.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.19 no.1
• /
• pp.10-18
• /
• 2017

Korean Red Pine (Pinus densiflora) has been protected and used as the most ecologically and socio-culturally important tree species in Korea. However, as dieback of Korean red pines has occurred in the protected area of the forest genetic resources. The aims of this study is to identify causes for dieback of pine tree by investigating topographical characteristics of pine tree dieback and its correlation to meteorological factors. We extracted the dead trees from the time series aerial images and analyzed geomorphological characteristics of dead tree concentration area. As a result, 1,956 dead pine trees were extracted in the study region of 2,600 ha. Dieback of pine trees was found mostly in the areas with high altitude, high solar radiation, low topographic wetness index, south and south-west slopes, ridgelines, and high wind exposure compared to other living pine forest area. These areas are classified as high temperature and high drought stress regions due to micro-climatic characteristics affected by topographic factors. As high temperature and drought stress are generally increasing with climate change, we can evaluated that a risk of pine tree dieback is also increasing. Based on these geomorphological characteristics, we developed a pine tree dieback risk map using Maximum Entropy Model (MaxEnt), and it can be useful for establishing Korean red pine protection and management strategies.