불활성 가스를 주입한 이중투과체 구조 평판형 태양열집열기의 열성능 비교 분석

이기원(Ki-Won Lee),김정석(Jung-Seok Kim),조성구(Sung-Goo Cho),강병국(Byung-Guk Kang),최준영(Jun-Young Choi) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6

A comparative investigation of solar-assisted heat pumps with solar thermal collectors for a hot water supply system

Kim, Taehoon,Choi, Byung-Il,Han, Yong-Shik,Do, Kyu Hyung Elsevier 2018 Energy conversion and management Vol.172 No.-

<P><B>Abstract</B></P> <P>The concept of a hybrid solar collector was newly proposed, which has a solar thermal receiver part and air-source receiver part that can operate as a fin-tube exchanger with fans when there is no solar radiation. This is the distinguishing feature of the hybrid solar collector. The solar-assisted heat pump system applying the hybrid solar collectors was also introduced. To analyze the proposed solar-assisted heat pump system, a simple thermodynamic model considering the electric power consumption for fans and circulation pumps was developed. The model results for the air-source heat gain were validated from the corresponding experimental data with the maximum error of 8.8%. Based on the parametric study, the increase of the collector area and the absorption coefficient led to the enhancement of the system performance of the solar-assisted heat pump with hybrid solar collectors. In addition, a comparative investigation was carried out for three different indirect solar-assisted heat pumps. Regarding of annual operation hour, the serial-type solar-assisted heat pump was worst at 3509 h over a year. On the other hand, the solar-assisted heat pump with hybrid solar collectors had the superior performance of 7036 h. If the efficiency of the hybrid solar collector was as superior as the conventional flat plate solar collector, the system COP of the suggested solar-assisted heat pump system in the winter season could be improved by 5.1% compared with that of the parallel-type solar-assisted heat pump system. Consequently, it clearly showed the feasibility of the suggested solar-assisted heat pump system as a standalone system for hot water supply due to the merits of significantly extending the annual operation hour, the simple system configuration, and the economic aspect with lower capital cost.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The concept of a hybrid solar collector was newly proposed. </LI> <LI> A thermodynamic model for the SAHP with hybrid solar collectors was developed. </LI> <LI> The model considered electric power consumption models for auxiliary components. </LI> <LI> A comparative study was done to predict the efficiency of the proposed SAHP. </LI> <LI> Numerical results show feasibility of the SAHP as a standalone for a DHW system. </LI> </UL> </P>

태양열급탕시스템의 집열기 배열에 따른 에너지성능 분석 및 평가

고명진(Ko Myeong-Jin),임보민(Lim Bo-Min),김용식(Kim Yong-Shik) 한국태양에너지학회 2016 한국태양에너지학회 논문집 Vol.36 No.4

The objective of this work is to analyze the variation in energy performance for each flat plate collector connected in series. In this study, it was assumed that solar water heating system with annual solar fraction of 60% was installed in an office building in Seoul, South Korea. The transient energy performance corresponding to four cases, which are selected using different solar radiation and outdoor air temperature, is studied by analyzing the variation in outlet temperature, solar useful heat gain, and thermal efficiency of each collector. It is observed that the useful heat gain and the collector efficiency decrease continuously, and outlet temperature increases when increasing the number of collector connected in series. The long-term performance is assessed by evaluating the thermal efficiency of each collector for two solar radiation conditions ranging from 780 to 820 W/㎡ and from 380 to 420 W/㎡. It is found that the differences between the intercept and slope of the efficiency curves for first and eighth collectors are 3.68% and 6.74% for solar radiation of 800 ± 20 W/㎡ and 8.57% and 12.90% for solar radiation of 400 ± 20 W/㎡, respectively. In addition, it is interesting to note that annual useful heat gain and collector efficiency are reduced with similar rate of about 6.13% when increasing the collector area by connecting the collectors in series.

Agricultural Process and Food Engineering ; A Study for the Use of Solar Energy for Agricultural Industry -Solar Drying System Using Evacuated Tubular Solar Collector and Auxiliary Heater-

( Gwi Hyun Lee ) 한국농업기계학회 2013 바이오시스템공학 Vol.38 No.1

Purpose: The objectives of this study were to construct the solar drying system with evacuated tubular solar collector and to investigate its performance in comparison with indoor and outdoor dryings. Methods: Solar drying system was constructed with using Cl`C (compound parabolic concentrator) evacuated tubular solar collector. Solar drying system is mainly composed of evacuated tubular solar collector with Cl`C reflector, storage tank, water-to-air heat exchanger, auxiliary heater, and drying chamber. Performance test of solar drying system was conducted with drying of agricultural products such as sliced radish, potato, carrot, and oyster mushroom. Drying characteristics of agricultural products in solar drying system were compared with those of indoor and outdoor ones. Results: Solar drying system showed considerable effect on reducing the half drying time for all drying samples. However, outdoor drying was more effective than indoor drying on shortening the half drying time for all of drying samples. Solar drying system and outdoor drying for oyster mushroom showed the same half drying time. Conclusions: Oyster mushroom could be dried easily under outdoor drying until MR (Moisture Ratio) was reached to about 0.2. However, solar drying system showed great effect on drying for most samples compared with indoor and outdoor dryings, when MR was less than 0.5.

A Study for the Use of Solar Energy for Agricultural Industry - Solar Drying System Using Evacuated Tubular Solar Collector and Auxiliary Heater -

이귀현 한국농업기계학회 2013 바이오시스템공학 Vol.38 No.1

Purpose: The objectives of this study were to construct the solar drying system with evacuated tubular solar collector and to investigate its performance in comparison with indoor and outdoor dryings. Methods: Solar drying system was constructed with using CPC (compound parabolic concentrator) evacuated tubular solar collector. Solar drying system is mainly composed of evacuated tubular solar collector with CPC reflector, storage tank, water-to-air heat exchanger, auxiliary heater, and drying chamber. Performance test of solar drying system was conducted with drying of agricultural products such as sliced radish, potato, carrot, and oyster mushroom. Drying characteristics of agricultural products in solar drying system were compared with those of indoor and outdoor ones. Results: Solar drying system showed considerable effect on reducing the half drying time for all drying samples. However, outdoor drying was more effective than indoor drying on shortening the half drying time for all of drying samples. Solar drying system and outdoor drying for oyster mushroom showed the same half drying time. Conclusions: Oyster mushroom could be dried easily under outdoor drying until MR (Moisture Ratio) was reached to about 0.2. However, solar drying system showed great effect on drying for most samples compared with indoor and outdoor dryings, when MR was less than 0.5.

A Study for the Use of Solar Energy for Agricultural Industry - Solar Drying System Using Evacuated Tubular Solar Collector and Auxiliary Heater -

Lee, Gwi Hyun Korean Society for Agricultural Machinery 2013 바이오시스템공학 Vol.38 No.1

Purpose: The objectives of this study were to construct the solar drying system with evacuated tubular solar collector and to investigate its performance in comparison with indoor and outdoor dryings. Methods: Solar drying system was constructed with using CPC (compound parabolic concentrator) evacuated tubular solar collector. Solar drying system is mainly composed of evacuated tubular solar collector with CPC reflector, storage tank, water-to-air heat exchanger, auxiliary heater, and drying chamber. Performance test of solar drying system was conducted with drying of agricultural products such as sliced radish, potato, carrot, and oyster mushroom. Drying characteristics of agricultural products in solar drying system were compared with those of indoor and outdoor ones. Results: Solar drying system showed considerable effect on reducing the half drying time for all drying samples. However, outdoor drying was more effective than indoor drying on shortening the half drying time for all of drying samples. Solar drying system and outdoor drying for oyster mushroom showed the same half drying time. Conclusions: Oyster mushroom could be dried easily under outdoor drying until MR (Moisture Ratio) was reached to about 0.2. However, solar drying system showed great effect on drying for most samples compared with indoor and outdoor dryings, when MR was less than 0.5.

An analytical study on the thermal characteristics of flat-plate and evacuated solar collectors

Jeongbae Kim,Hee Youl Kwak,Dong Won Lee 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.12

In this study, we highlighted differences in the standards used in performance tests of solar collectors. We analyzed testing results for different types of solar collectors to determine the effects of the collector area and mass flow rate, which were not necessarily consistent across all tests. Our analysis showed that the factor, F′ (τα), including collector efficiency factor (F′), could be correlated with the flow rate or area regardless of the collector type. Moreover, the collector loss coefficient (F′UL) per flow rate or area for an evacuated collector was less that of a flat-plate collector; this was also correlated with the flow rate or area, regardless of the type of evacuated collector. As a result of this analysis, we propose a modified heat loss coefficient that includes the effects of all parameters that can be considered in a performance test and show that this coefficient could better describe the thermal characteristics of various types of solar collectors.

태양열 집열효율 향상을 위한 최적 설계 및 운전조건 분석

김용기(Yong-Ki Kim),이덕희(Duk-Hee Lee),서재상(Jae-Sang Seo),이태원(Tae-Won Lee) 대한설비공학회 2012 대한설비공학회 학술발표대회논문집 Vol.2012 No.11

Optimization of the spectral absorption coefficient of a plasmonic nanofluid for a direct absorption solar collector

Qin, Caiyan,Kang, Kyeonghwan,Lee, Ikjin,Lee, Bong Jae Elsevier 2018 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.169 No.-

<P><B>Abstract</B></P> <P>Direct absorption solar collector (DASC) has been a prevalent research topic in utilizing the solar energy. Usually, a nanofluid is employed in a DASC so that the solar radiation can be absorbed directly and the heat loss is reduced substantially compared to a traditional surface-based solar collector. Theoretical and experimental studies have been conducted to enhance the absorption performance of nanofluids from the perspective of the nanoparticle’s shape and material. Optimization of the DASC has also been performed, mostly from the perspective of the collector’s geometry. However, one of the most important parameters, i.e., spectral distribution of the absorption coefficient of a nanofluid, has not been received much attention so far. In this research, the spectral absorption coefficient of a plasmonic nanofluid is optimized for a DASC, so that the thermal efficiency can be maximized while maintaining the magnitude of the average absorption coefficient at a certain value. This will lower the cost of DASC because the absorption coefficient is proportional to the particle concentration and the noble metal, such as gold, silver and copper, is usually used for plasmonic nanofluids. Sufficiently low concentration of nanoparticles can also avoid particle agglomeration which is critical for maintaining stable solar collector performance. We show that when the constraint on the average absorption coefficient is above the saturation level, a uniform spectral absorption coefficient just at the saturation level maximizes the DASC efficiency. On the other hand, if this constraint is below the saturation level, the spectral absorption coefficient following the solar spectrum maximizes the DASC efficiency. In addition, the effect of collector channel height on the optimal distribution of the spectral absorption coefficient is also investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spectral absorption coefficient ( <SUB> α λ </SUB> ) is optimized for a volumetric solar collector. </LI> <LI> A saturation value for the constraint on average absorption coefficient ( <SUB> α ¯ c </SUB> ) exists. </LI> <LI> If <SUB> α ¯ c </SUB> is greater than the saturation value, then <SUB> α λ </SUB> should be uniform. </LI> <LI> Otherwise, <SUB> α λ </SUB> should follow the solar spectrum. </LI> </UL> </P>

Concentrating solar collectors for the greenhouse heating

( M. Imtiaz Hussain ),( Gwi Hyun Lee ) 한국농업기계학회 2023 한국농업기계학회 학술발표논문집 Vol.28 No.1

This paper compares the thermal performance characteristics of line and point focused solar collectors for heating identical greenhouses in South Korea. Both solar collectors with similar storage capacities and Fresnel lens surface areas were tested under the same weather and operating conditions. Both systems were equipped with a dual-axis solar tracker for tracking the sun position and a circulating pump for forced convective heat transfer. Economic analyses of the solar collectors were performed by considering the current interest rate, inflation rate, and electricity prices in South Korea. The available energy per unit area and thermal efficiency were higher for the point focused solar collector than for the line focused collector. The discounted payback period decreased and electricity savings increased when the storage capacity was increased with either collector. All results indicate that point focused solar collector performance was better than that of line focused s collector. It is also noticed that changing the inlet flow rate of the greenhouse heat exchanger may be a good solution for obtaining the seed germination temperatures needed for different crops.