Güneş enerjili absorbsiyonlu soğutucu sistemin bilgisayar programı yardımıyla simülasyonu
The Simulation of the solar absorbtion cooling system with the help of computer programming
- Tez No: 14294
- Danışmanlar: DOÇ.DR. AHMET KARAKAŞ
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Güneş enerjisi, Soğurmalı soğutma sistemleri, Termodinamik analiz, Solar energy, Absorption cooling systems, Thermodynamic analysis
- Yıl: 1990
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Güneş enerjili absorbsiyonlu sistemler, hem kaynak olarak güneş enerjisini kullanabildikleri hem de soğutucu olarak freon gazlarından farklı soğutucular kullanabildikleri için ilgi çekicidirler. Bu çalışmada soğutma ve ısıtmanın birlikte yapıldığı bir sistem ele alınmış ve kullanılabilirlik yardımıyla verim analizi yapılmıştır. Çalışmanın ilk bölümünde güneş enerjili absorbsiyonlu soğutucu sistemin niye ele alındığı açıklanmıştır. İkinci bölümde güneş enerjili absorbsiyonlu sistemler hakkında genel bilgi verilmiştir. Ayrıca bu sistemler üzerinde yapılan çalışmalar anlatılmıştır. Daha sonra absorbsiyonl. soğutucularda çoğunlukla kullanılan LiBr-FLO ve HLO-NHo solüsyonlarının kullanıldığı çevrimler tanıtılmıştır. Üçüncü bölümde kompleks termodinamik sistemlerin analizinde yararlanabilen kullanılabilirlik incelenmiştir. Açık sistem için kullanılabilir enerji denklemi yardımıyla kayıp kullanılabilirlik elde edilmiştir. Bu bölümde ayrıca kullanılabilirlik vasıtasıyla verime ulaşılmıştır. Dördüncü bölümde soğutma ve ısıtmanın birlikte yapıldığı bir sistem tanıtılmıştır. Sonra bu sistemin her noktası termodinamik olarak analiz edilmiş her noktada kullanılabilirlik bulunmuş her eleman için kullanılabilirlik farkı elde edilmiş ve verime ulaşılmıştır. Bu sayede sistemin analizi yapılmıştır. Beşinci bölümde ise dış yüklerin ve absorbsiyonlu soğutucu sistemin parametrelerinin değişiminin verimi ve kütle akışını nasıl değiştirdiğini gösteren grafikler çizilmiştir. Bu grafikler izah edilmiştir. Bu grafiklerin elde edilmesi için hazırlanan bilgisayar programı ekde verilmiştir. -vı-
Özet (Çeviri)
SUMMARY THE SIMULATION OF THE SOLAR ABSORBTION COOLING SYSTEM WITH THE HELP OF COMPUTER PROGRAMMING With the development of technology and industrialization, two promlems has been formed '.decrease of energyy sources and pollution. Especially in recent years, after the effect of freon gesses on atmosphere were found, the industrialized countries decided on decreasing the use of freon gasses problem on using vaporcompression cooling systems, So absorbtion cooling systems which use LiBr/H^O and H^O/NHo as working fluids, will gain great important. In this study the solar assisted absorbtion cooling cycle is investigated. The investigation includes the second law of thermodynamic. In the second section solar cooling systems are explained generally. Then some detail knowledges are given about absorbtion cooling systems. Absorbtion cycles can be adapted to operation from flat-plate collectors, So in this study, the main source of energy is taken from a solar collector. an absorbtion cooling cycle differs from a vapor-compression system in requiring a negligible amount of work. In such systems, a solution inluding an absorbent, and a refrigerant, is used as the working fluid. The compression and expansion parts in a conventional refrigeration system are replaced by a generator used for seperating the refrigerant from the solution and an absorber where the refrigerant is absorbed in an absorption cooling system. In absorption cooling cycles mostly LiBr/H^O and HpO/NHo are used as working fluids. The behaviours of working fluids and the processes in the system are described as follows: The refrigerant fluid, HNo for ammonia / water systems and H“0 for lithium bromide/water system, is seperated in generator by the means of heat given to this component. The mass flow rate of the refrigerant depends on the temperature to which the solution is heated. After it reaches to the desired temperature, the refrigerant goes through the condenser and evaparator. Meanwhile the weak solution which has -vii-less amount of the refrigerant fluid as a result of dissol ving in the generetor, expands in the throttling valv;e and goes through the absorber. Here it absorbs the refrigerant coming from the evaporator and a strong solution which has more amount of the refrigerant, as a results of this absorbtion, forms. Then the strong solution pomped to the generator through the solution pump. The heat released in condenser and absorber is rejected by the cooling water system. The cooling water cools down in the cooling tower to be sent to the absorber. The required heat for generator is supplied from the hot water cycle by means of the collector plates and the storage. When the solar energy is insufficient, the auxilary source is used. In the third section, for the investigation of solar absorption cooling cycle, availability is examined. Availability and irreversibility are particalarly applicable in the aid of a digital computer, Irreversibility and availability are very powerfool tools in design and optimization studies of such systems. This analysis is based on o-rî the availability concept and reducing the availability defination for a steadystate flow. Let's a system which has heat transfer with only its environment, undergoing a reversible process. Accoding to the first law; Q0- W = dV (1) Second law for the reversible process dS = QQ/To (2) dw =dw TT - ”+ **.__ (3) Usefull ENV K ' and for a steady - state system, Wflow=PoVo - P1V1 <4) -viii-where environment state is the outlet and the state 1 is the inlet of the flow, replaces the W“Nrr If equations (1), (2), (3), (4) are combined, the relation WUSEFULIT (H1 - W (H°”T°So) which defines the maximum work may be obtained for a system undergoing a reversible process from a given state to the environmental conditions. If there is a heat flux from a source at the temperature T“ to the system, the maximum work abtained from this transformation can be written by means of cornot efficiency: Wmak= ncarQ = ^ ~ VTH> <* This quantity may be named as the available energy of heat, because it is the maximum available work obtained by the transformation of this amount of heat. The definition of availability may be given as; Kl = <hl ”ToTl>“ <ho ”W the availability differences for a steady-state steady flow which is valid for every conponent in this study is. ^K = mlkl- mik;L-QH(l-To/TH) where i and 1 repsents the inlets and the outlest of the conponent respectively. The decrease of the availability means that the lost work or the entropy generation increases. The effectiveness assumed according to the second law may be defined in various ways. One of them p is the ratio of availability change of the aim to ^the sum of the availability differences belonging to all the other components. The second one is the ratio of the availability change of the aim, to the one which occurs -ix-in the colector. If we would like to use the energy source with maximum effectiveness in long term, the first approach is more realistic. The second definition on the other hand is more general because it change due to only the cooling load and climatic conditions. The formula for calculation of availability are applied to each component of both the lithium bromide/water and the ammonia/water system. For calculating availability and effectiveness for lithium bromide/water and ammonia/water system, the P,T,h,s diagrams and Redlich-kwong eqvation for binary mixtures are used. In the forth secton, the system of which the simulatione is made by the help of computer progmammmg is explained. As the combination of solar cooling and heating should improve the economics, compered to heating alone, space heating, space cooling and water heating can be done in this system. For finding the availabilities of each point in the system, thermodynamic analys is made. This is done for both LiBr/H^O and H20/NH3 working fluids. For these calculation 'diagrams, tables and equations are used. Then by using these dates, availabilities at each point are found. And the availability differences of components are calculated. By using these the effectiveness of the system for different conditions can be found. In fifth section the conclusion of the thermodynamic analysis are taken together. And the graphics of different variables are drawn. In arrangement of these graphics, the amount of heat transfer to the collecter, Qcol the generator leaving temperature To and eveporation temperature T“ are taken as parameters. Also the environment conditions are taken as parameters. Changing these parameters, the results are obtained for various conditions and figures illustrating these results are formed. From the figures we can reach that solutions: the irreversibility in the collector plates increases with the amount of heat collected. So the design of the collector plates has an influence on reducing the lost work. In LiBr/H”0 systems, increase in entropy generation, &K, in the generator, condenser and absorber are balanced with the decrease in irreversibility in heat exchanger due to Tg. This balance is not valid for -x-NH^/HpO because of the different thermodynamic properties ox solution. For NH^/H^Ocase the refrigerant concentration of the solutions between the points leaving the generator and the absorber differs too much as T~ increases. For LiBr/H20 araund the limit resulting from crystallization the mentioned difference and entropy changes get smaller. So the rate of availability decrease slows down. However this advantage of LiBr/H«0 causes an economic disadvantage, as the concentrations of weak and strong solutions approach each other, the needed amount of the working fluid increases. As the conclusion, for the effective operation of absorbtion cooling system, the following criteria must generally be satisfied: the hoice of the working fluid and the design prameters of the components. For the comparable region, where temperature is above 0°C lithium bromide /water system is more effective than ammonia/water system. However, lithium bromide/water system creates more design problems than ammonia/water system because the pressure values corresponding to the convenient temperatures are sub-atmospheric. This disadvantage can be partly reduced by takxng into consideration of the minimum entropy generation in choosing the design parameters of the components of the lithium bromide/water system. The solar energy is especially useful for abtaining high efficiency. -xi-
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