보고서 정보
주관연구기관 |
강원대학교 Kangwon National University |
보고서유형 | 최종보고서 |
발행국가 | 대한민국 |
언어 |
한국어
|
발행년월 | 2011-09 |
과제시작연도 |
2010 |
주관부처 |
농림축산식품부 Ministry of Agriculture, Food and Rural Affairs(MAFRA) |
등록번호 |
TRKO201400026385 |
과제고유번호 |
1545001783 |
사업명 |
농림기술개발 |
DB 구축일자 |
2014-11-10
|
DOI |
https://doi.org/10.23000/TRKO201400026385 |
초록
▼
○ 연구결과
1. 소형 PTC 태양열집열 시스템 개발 : 실험용 PTC 태양열집기 설계 및 제작, 흡수관이 PTC 태양열 시스템 성능에 미치는 영향분석, 실험용 PTC 태양열 집열시스템 시뮬레이션 모델, PTC 태양열 집열 시스템 시큘레이션 모델 검증 및 성능분석
2. 실증 실험용 PTC형 태양열 집열 시스템 개발: PTC형 태양열집열기 설계 및 제작, 태양추적 제어장치 설계 및 제작, 축열조 및 열매체 보충탱크 설계.제작, 차온 제어장치 설비, PTC형 태양열 집열시스템 성능분석, PTC형 태양열 집열 시스템 열전
○ 연구결과
1. 소형 PTC 태양열집열 시스템 개발 : 실험용 PTC 태양열집기 설계 및 제작, 흡수관이 PTC 태양열 시스템 성능에 미치는 영향분석, 실험용 PTC 태양열 집열시스템 시뮬레이션 모델, PTC 태양열 집열 시스템 시큘레이션 모델 검증 및 성능분석
2. 실증 실험용 PTC형 태양열 집열 시스템 개발: PTC형 태양열집열기 설계 및 제작, 태양추적 제어장치 설계 및 제작, 축열조 및 열매체 보충탱크 설계.제작, 차온 제어장치 설비, PTC형 태양열 집열시스템 성능분석, PTC형 태양열 집열 시스템 열전달 모델 시뮬레이션
3. 태양열 건조시스템 개발 : 태양열 건조장치 설계 및 제작, 건조기 내 온습도 및 풍속 분석, PTC 태양열 건조장치에 의한 농산물 건조 특성 분석
4. 태양열 건조장치의 건조성능 및 경제성분석
Abstract
▼
Our country has very good advantages on using the solar energy because of receiving the sufficient sun energy due to the geographical position and seasonal weather conditions. The development of technology for the utilization of solar radiation as an alternative energy is very important for the use
Our country has very good advantages on using the solar energy because of receiving the sufficient sun energy due to the geographical position and seasonal weather conditions. The development of technology for the utilization of solar radiation as an alternative energy is very important for the use in agricultural industry as an agricultural energy source. Thus, the objective of this study was to develop the solar drying system with the parabolic trough collector (PTC) for energy saving in the drying of agricultural products. The results were obtained as follows:
1. Development for the solar collecting system of lab scale with the PTC
(1) Design and construction of experimental solar collector with the PTC
Parabolic trough solar collector constructed as lab scale was composed of parabolic trough refractor, absorber tube, and supporter. Rim angle of parabolic trough solar collector is 90˚, and the arc length of refractor is 596.8 mm. An absorber tube was installed at the focus of reflector.
(2) Analysis for performance of the PTC system according to absorber type
Stainless tube as an absorber had better effects on the performance of the PTC system in compared with copper tube. However, Stainless tube coated in black had better effects on the performance of the PTC system in compared with it without coating. Also, absorber tube with polycarbonate (PC) tube was better than it without PC tube on the performance of the PTC system. An absorber of stainless tube coated in black with PC tube was the best one onthe performance of the PTC system among various absorber types.
(3) Simulation model of the PTC system
This study was conducted to simulate and analyze the performance of a parabolic trough solar collector. Working fluid in the storage tank is pumped and heated by collected solar radiation passing through the absorber pipe and goes back to the storage tank. This heated working fluid can be reached up to 200 ℃ depending on the weather conditions and a system composition and can be used as a thermal energy source. The simulation of the PTC showed that the calculated working fluid temperature reached 160 ℃ at 4 PM. The predicted results against experimental data were compared to verify the performance of the PTC. The experimental data were used from the previous study by Eskin (1988). The simulated results were agreed well with the measured values. The dominant factors influencing working fluid temperature are the solar radiation, the size of a solar reflector, and flow rate. Considering unchangeable solar radiation, the size of the reflector and flow rate should be the main factors to achieve target fluid temperature.
(4) Simulation and performance analysis of a parabolic trough solar collector
This work presents the simulation and model validation of a lab scale parabolic trough collector (PTC) for water heating system. The PTC simulation was performed using energy balances and heat transfer relationships and the developed model was compared with the experimental results. The PTC was continuously operated for 72 hours. The temperature of the water in the storage tank was increased from 33.5°C to 63.6°C within the test period. The average beam radiation was 495.11 W/㎡ during the collection period (daylight hours) and the instantaneous efficiency of collector was 60%. Significant amount of heat loss was noticed from the storage tank. The predicted temperatures of the water in the storage tank were in good agreement with the measurements.
2. Development for the solar collecting system of real size with the PTC
(1) Design and construction of solar collector with the PTC
Parabolic trough solar collector constructed as real size was composed of parabolic trough refractor, absorber tube, and supporter. Rim angle of parabolic trough solar collector is 73˚, and the arc length of refractor is 2450.4 mm. Also it has parabola length of 1,868 mm and parabola height of 422.8 mm. An absorber tube with stainless tube inside vacuumed glass was installed at the focus of reflector.
(2) Design and construction of solar tracker
Solar tracker was constructed with the linear actuator for tracking an altitude angle and the slew drive for tracking an azimuth angle. Azimuth and altitude controllers of solar tracker are operated by the signal of solar tracking sensor with dual axis.
(3) Design and construction of water storage tank and supplemental tank of heating medium
Storage tank with the capacity of 1,500ℓ was constructed as stainless container insulated with polyurethane of 120 mm thickness on outside wall. Heat exchanger was installed inside the storage tank. The water in storage tank is heated by the working fluid as heating medium circulating inside the heat exchange and absorber tube of the PTC. Heating medium is stored in the supplemental tank, and it is supplied into the absorber tube when it is needed for making up.
(4) Construction of temperature difference controller
Temperature difference controller was constructed to control the fluid circulation pump by detecting the difference of outlet fluid temperatures of an absorber tube of the PTC and the heat exchanger in the storage tank. If the temperature difference is more than 8℃, the pump is operated. However, the pump is stopped in the case of the temperature difference below 4℃.
(5) Performance analysis of solar collecting system with the PTC
In an experiment for the performance analysis of solar collecting system with the PTC, water was used as working fluid for heating medium which is circulating inside an absorber tube and heat exchanger. Also water of 1,000ℓ as filled up in the storage tank. Various flow rates and absorber inlettemperatures of heating medium were investigated for the effects on the performance of solar collecting system with the PTC. The flow rate of heating medium circulating inside an absorber tube and heat exchanger was varied as 2 ℓ/min, 4 ℓ/min, and 6 ℓ/min. Absorber inlet temperatures of heating medium were also varied from 25℃ to 60℃ with constant flow rate of 5.5ℓ/min. Solar collecting efficiency was decreased according to an increase of absorber inlet temperatures of heating medium. However, the degree of efficiency decrease is very small in compared with that of evacuated solar collector. Also, the optimum flow rate of heating medium circulating inside an absorber tube and heat exchanger was presented as 4 ℓ/min.
(6) Simulation model of the PTC system
This work studies the simulation of a parabolic trough solar collector (PTC) for water heating system. The mathematical model was simulated, compared with the experiments and calibrated for the better results. The model was calibrated by reducing RMSE (Root mean square error) values. Calibration was performed on the convective heat transfer coefficient between the absorber pipe and the ambient air. The maximum, minimum and mean deviation between the measured and simulated results were only 0.9°C, 0.09°C and 0.31°C respectively in the calibrated model. The temperature of water was increased from 33.7°C to 48°C in 12 hours of experimental time span. The instantaneous efficiency of the collector was calculated as 70%. The simulation results showed good agreement with the experimental results. The calibrated model was better fitted with the experimental model.
3. Development of solar drying system using the PTC
(1) Design and construction of solar drying system
Drying chamber was equipped with controller, heat exchanger, auxiliary heater, fan, temperature sensor, tray, ventilating hole, and electric power wattmeter. Heated water inside storage tank is circulated into the heat exchanger with heating air inside the drying chamber. Heat transfer area of heat exchanger is 14.3 ㎡. Fan of 350 mm diameter which, is operated with the motor of 66 W is attached in front of the heat exchanger. An auxiliary heater of 5 kW is also fixed at the rear of heat exchanger. Solar drying system which was designed and constructed in this study is composed of the PTC, water storage tank, and drying chamber.
(2) Analysis of temperature, relative humidity and air velocity inside drying chamber
Temperatures were measured at three positions of each top, middle, bottom part of drying chamber. Humidity was also measured at a center inside drying chamber. Air velocity was measured at each two positions for top, middle, and bottom parts inside drying chamber. The variation of temperature was 5, 4, and 3℃ for each setting temperature of 40, 50, and 60℃. At the setting temperature of each 40, 50, and 60℃, relative humidity inside drying chamber was 11, 7, and 3,7% with each variation of 2, 1.2, and 1.0%. Air velocity was each 0.88 and 0.82 m/s, 0.51 and 0.49 m/s, and 0.49 and 0.45 m/s at left and right sides of each top, middle, and bottom position inside the drying chamber. Air velocity was greater values at left part and higher position rather than right part and lower position inside the drying chamber.
(3) Drying characteristics of agricultural products with the PTC solar drying system
Drying characteristics of apple and radish were investigated with using the PTC solar drying system. Apple and radish were sliced into the thickness of 1, 2, and 3 mm, and dried at the drying temperature of 50, 60, and 70℃. Weight of drying sample was measured at constant time interval during drying period to analyze the change of moisture content. Equilibrium moisture content was lowered, and half and total drying times were shortened with increasing the drying temperature for all of apple and radish slices. Color difference (△E) were increased with increasing the drying temperature for all of apple and radish slices. Moisture ratio (MR) with drying time was well presented as an exponential function. The thermal diffusivity was increased with increasing the drying temperature, and it was at the ranges of 3.96629×10-7~ 7.08264×10-7 ㎡/hr for apple and 3.10773×10-7~ 4.64735×10-7 ㎡/hr for radish.
4. Analyses for the performance and the economic values of the PTC solar drying system
Suitable amount and temperature of water inside the storage tank were determined according to drying temperature. Energy needed for drying by using heated water inside storage tank was compared with that consumed by general dryer using kerosene for analyzing economic values of the PTC solar drying system. Water of 960ℓ at the temperature of 60℃ inside storage tank can be heated daily into 80℃ by using the PTC. This heated water of 960ℓ at the temperature of 80℃ can be used for drying at the temperature of 60℃ for 24 hours. Also, heated water of 411ℓ at the temperature of 80℃ is enough for drying at the temperature of 50℃ for 24 hours. The results of analysis for an economic value showed that the PTC solar drying system has great benefit, if it can be used above three years in compared with the general dryer using kerosene.
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