Vakum borulu kollektörlerin İstanbul şartlarında teorik analizi
Analysis of different of types vacuum tubular collectors for the condition of İstanbul
- Tez No: 39355
- Danışmanlar: PROF.DR. KEMAL ONAT
- Tez Türü: Yüksek Lisans
- Konular: Enerji, Makine Mühendisliği, Energy, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 66
Özet
ÖZET Düz toplayıcıların vehmi düşük olduğundan sadece sıcak su sistemleri için uygundur. Yutucu ile saydam örtü arası boşaltılarak taşınım kayıplarının azaltılması, yutucu üzerinin seçici yüzeyle kaplanması, yansıtıcı yüzeylerin kullanımı, saydam örtülerin iyileştirilmesiyle verimi artırmak ve yüksek sıcaklıklar elde etmek mümkündür. Bu çalışmada vakum borulu kollektörler tanıtılarak Corning Glass vakum borulu kollektör İstanbul şartlarında analiz edilmiştir. Corning Glass ve ısı borulu vakum toplayıcılar verim açısından karşılaştırılmıştır. Işınımı yıl boyunca ortalama 1.6 oranında yoğunlaştırarak gerekli yutucu alanım azaltan V-yansıtıcıların kullanımı İstanbul şartlarında incelenmiştir. V-yansıtıcılı vakum borulu kollektör eğimi enleme eşit eğik yüzey üzerinde vakum borulu alıcı ile biri kuzeyde diğeri güneyde olmak üzere iki yansıtıcıdan oluşmaktadır. Yansıtıcılar için yılda bir kez eğim değişikliği gerektirecek bir uygulama tanıtılmaktadır. Yansıtıcılar olduğu halde yutucu plakaya gelen ışınım bulunarak yansıtma oram gün-gün, saat-saat bilgisayar programı ile hesaplanmıştır. Ne maksimum faydalı ısı sağlayan kollektörün ne de ucuz kollektörün ekonomik kollektöre cevap olmadığı anlaşılmış, kıyaslama yapabilmek amacıyla yeni bir parametre enerji maliyeti tanımlanmıştır. Ayrıca güneş enerjisi sistemlerinin geri ödeme sürelerinin maliyet ve yıllık faydalı enerji değerlerine bağlı olarak değişimi incelenmiştir. vuı
Özet (Çeviri)
ANALYSIS OF DIFFERENT OF TYPES VACUUM TUBULAR COLLECTORS FOR THE CONDITION OF ISTANBUL SUMMARY Flat-plate solar collectors are characterized by low efficiency and therefore are suitable only for solar hot-water systems. Solar energy collectors with a selective absorbing coating and glass tubular collectors with vacuum insulation are promising. The efficiency of an solar energy systems can be raised by increasing its optical efficiency and decreasing the coefficient of heat losses, which is achived by the use in the collector's construction of: -vacuum insulation of the radiation-absorbing surface, heat losses by conduction and convection reducing to a minimum, -a selective coating on the radiation-absorbing surface with high absorptivity in the range of shortwave solar radiation and low emissivity in the infrared region, -a solar radiation concentrater which reduces heat losses by radiation, as a consequence of the decrease in surface area absorbing solar radiation, - transparent structure which suppress convection of air in the space between the absorber and the glazing. The conventional flat plate collektor has been studied and built in various forms for almost a hundred years. Present cost projections for these types of collektors will probably not reduce significantly since material requirements are substantially the same regardless of variation in structural design. In the early I9601 the use of vacuum tube collector and vee-trough reflector made to improve collector performance and to reduce its cost. Several systems have been employed to remove thermal energy from evacuated tubes. Some manifacturers use a U-shaped copper tube along the inside wall of the collector tube, as in the General Electric collector, or a straight tube running all the way through as in the Sanyo collector. In another design collector is filled with water through a thin glass tube running down the center line such as the Owens-Illionis. Some manifacturers have also explored the use of metal heat pipes in evacuated-tube solar collectors. Heat pipes altough seemingly complex have advantages over other heat removel systems. Heat pipes have a well known advantage of high effective thermal conductance due to their exploitation of phase change phenomena. An all- glass heat-pipe is corrosion resistant and easily sealed. Owens-Illionis's“Sunpak”design is composed of three glass pipes or tubes insert one inside another. The name“evacuated tube”, often given to such collectors, describes only one characteristic -its vacuum between the absorber and cover tubes. IXBoth the thermal performance and economic aspects of collectors employing reversible vee-trough concentrators are discussed. Criteria for the optimum design are 1) maximum efficiency for a given design and expenditure 2) minimum cost of the energy collected for each particular application. The latter of these two criteria must be applied for cost effective solutions although the first criteria may lead to a design which enables collection of more heat per unit area. Energy cost, C ; can be expressed simply as C=Total Yearly Expenditure / Total Yearly Energy Collected Most of the efforts to minimize energy costs are directed toward increasing the total yearly energy collection by means of efficiency improvements. Another way to reduce the energy cost is to reduce the total yearly expenditure, which implies a reduction of collector installation and operating costs and/or an increase in life expectancy. The suggested vee-trough concentrators could improve collection effciency due to increased insolation on the absorber plate and also could reduce collector cost through reduction of material requirements. Improvements in collection efficiency by use of a vee-trough concentrator can be illustrated by using the flat plate collector efficiency expression based on the absorber area ^Qu/Qin^RKtaX-UL-CTrTj/y Most of the efforts to improve the evacuated tubular collector efficiency have been aimed at reducing the value of UL. This has been achieved primarily by the use of multiple glazings and selective absorbers or honeycomb convection suppressors. Reduction of convection losses has tended to reduce the total transmissivity while trying to improve the heat loss coefficent. The approach taken herein doubles the value of \ instead of halving the value of UL. When using the vee-trough concentrator, about 1/3 of the incident area is covered with the receiver, which is about an order of magnitude more expensive than the reflector itself. The designs suggested use material only where required; thus, the cost of a combination collector will be lower than conventional designs. Flap angles Qt and 82 may be varied to obtain the combination which yields the maximum year-round averaged concentration ratio for the case in which there is a demand for both heating and cooling. In the case of only heating or only cooling, the optimum combination of Gjand 92 would be different. Either good summer and good winter performance or good year-round performance can be obtained by choosing 0l3 82 properly.The yearly total heat collected and overall collector efficiencies tabulated in Table 5-9 are predictions. There is little uncertainty in these performance predictions, whereas cost estimates are much more uncertain. It is possible to predict concentrated flux intensity and net useful heat at any time. Results of the thermal performance analysis given with and without reflector. The merit of the collector concept is in combining the relatively expensive vacuum tube with an inexpensive concentrator, which enhances the tube performance by increasing the incident flux and reducing its cost due to the low cost feature of the vee-concentrator. The vee-truogh /vacuum tube collector competes with conventional flat plate collectors costing 80 $/m2and operating at 121 °C.The predicted vee-trough collector cost with 150 $/m2 tubes and 5 $/m2 reflectors yields thermal energy costs 2/3 that of a flat plate collectors costing 80 $/m2.At 121 °C and higher, the advantages of the vee-trough collector are obvious. This report outlines the mathematical analysis of the vee-trough/ vacuum tube collector proposed for use in solar heating and cooling applications. Owing to its high-temperature capabilities (150-200 C), the proposed scheme could also be used for power generation purposes in combination with an organic Rankine conversion system. X1UBoth the thermal performance and economic aspects of collectors employing reversible vee-trough concentrators are discussed. Criteria for the optimum design are 1) maximum efficiency for a given design and expenditure 2) minimum cost of the energy collected for each particular application. The latter of these two criteria must be applied for cost effective solutions although the first criteria may lead to a design which enables collection of more heat per unit area. Energy cost, C ; can be expressed simply as C=Total Yearly Expenditure / Total Yearly Energy Collected Most of the efforts to minimize energy costs are directed toward increasing the total yearly energy collection by means of efficiency improvements. Another way to reduce the energy cost is to reduce the total yearly expenditure, which implies a reduction of collector installation and operating costs and/or an increase in life expectancy. The suggested vee-trough concentrators could improve collection effciency due to increased insolation on the absorber plate and also could reduce collector cost through reduction of material requirements. Improvements in collection efficiency by use of a vee-trough concentrator can be illustrated by using the flat plate collector efficiency expression based on the absorber area ^Qu/Qin^RKtaX-UL-CTrTj/y Most of the efforts to improve the evacuated tubular collector efficiency have been aimed at reducing the value of UL. This has been achieved primarily by the use of multiple glazings and selective absorbers or honeycomb convection suppressors. Reduction of convection losses has tended to reduce the total transmissivity while trying to improve the heat loss coefficent. The approach taken herein doubles the value of \ instead of halving the value of UL. When using the vee-trough concentrator, about 1/3 of the incident area is covered with the receiver, which is about an order of magnitude more expensive than the reflector itself. The designs suggested use material only where required; thus, the cost of a combination collector will be lower than conventional designs. Flap angles Qt and 82 may be varied to obtain the combination which yields the maximum year-round averaged concentration ratio for the case in which there is a demand for both heating and cooling. In the case of only heating or only cooling, the optimum combination of Gjand 92 would be different. Either good summer and good winter performance or good year-round performance can be obtained by choosing 0l3 82 properly.The yearly total heat collected and overall collector efficiencies tabulated in Table 5-9 are predictions. There is little uncertainty in these performance predictions, whereas cost estimates are much more uncertain. It is possible to predict concentrated flux intensity and net useful heat at any time. Results of the thermal performance analysis given with and without reflector. The merit of the collector concept is in combining the relatively expensive vacuum tube with an inexpensive concentrator, which enhances the tube performance by increasing the incident flux and reducing its cost due to the low cost feature of the vee-concentrator. The vee-truogh /vacuum tube collector competes with conventional flat plate collectors costing 80 $/m2and operating at 121 °C.The predicted vee-trough collector cost with 150 $/m2 tubes and 5 $/m2 reflectors yields thermal energy costs 2/3 that of a flat plate collectors costing 80 $/m2.At 121 °C and higher, the advantages of the vee-trough collector are obvious. This report outlines the mathematical analysis of the vee-trough/ vacuum tube collector proposed for use in solar heating and cooling applications. Owing to its high-temperature capabilities (150-200 C), the proposed scheme could also be used for power generation purposes in combination with an organic Rankine conversion system. X1U
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