Amonyaklı soğutma sistemi tasarımı
Amonyaklı soğutma sistemi tasarımı
Dosyalar
Tarih
2020
Yazarlar
Altunacar, Tugay
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Özet
Soğutma endüstrisinde 20.yy ile birlikte sentetik soğutkanların ortaya çıkmasıyla eğilim CFC ailesinin soğutkanlarına doğru idi. Lakin bu yüzyılın sonlarına doğru gelen şikayetler değerlendirilerek Montreal'de soğutkanların geleceğiyle ilgili önemli kararlar alındı. CFC grubunun ozon tüketme potansiyeli ve sera etkisine sebep olması sebebiyle kullanımı yasaklandı. Geçiş döneminde ise en yaygın grup olarak HCFC ailesi kullanıldı. Moleküle H atomunun ilavesiyle nispeten ODP değerinde düşüş sağlanmıştı. Lakin Cl'un bulunması sebebiyle hala ozonla reaksiyon oluşturması ve sera gazı etkisinin hala yüksek seviyelerde seyretmesi HCFC ailesinin de kademeli olarak azaltılmasını ve 2030 yılında kaldırılmasını şart koşuyordu. Klor içermeyen HFC grubu ise ODP 0 değeri ile ozona zarar vermezken, sera etkisi değeri hala yüksek mertebelerdedir. Yönetmelikler gereği HFC grubunun da önümüzdeki yıllarda kullanımını azaltmaya yönelik programlar oluşturulmaktadır. Çevreye yönelik alınan bu önlemler ve programlar tekrardan doğal soğutkanları endüstriyel alanda kullanıma itmiştir. Bu akışkanlardan biri de amonyaktır. R717 olarak adlandırılan amonyak ozon tüketme potansiyeli ve sera etkisi olmaması sebebiyle çevresel etkiler bazında oldukça dikkat çekmektedir. Keza amonyağın kullanıldığı sistemlerde enerji verimliliğinin de yüksek olması soğutkanlar içerisinde amonyağı tercih edilebilir nitelikte kılıyor. Ancak güvenlik problemleri sebebiyle, kullanımı belli alanlarla kısıtlanmış durumdadır. Çevre dostu olması ve verimli sistemler vermesi ile projenin geliştirilmesine yönelik motivasyon oluşturan R717 ile buhar sıkıştırmalı soğutma sistemi tasarımı gerçekleştirilmiştir. Tipik olarak bir buhar sıkıştırmalı soğutma sistemi, kompresör, yoğuşturucu, kısılma vanası ve buharlaştırıcı içerir. Bu bağlamda kompresör olarak açık tip pistonlu bir kompresör, ısı değiştiricisi olarak plakalı ısı değiştiriciler ve kısılma vanası olarak termostatik kısılma vanası tercih edilmiştir. Bir soğutma sisteminin işlevini yerine getirebilmesi için sistem yardımcı elemanlara da ihtiyaç duyar. Bu yardımcı elemanların tayininde de çevrimde kullanılacak olan soğutucu akışkanla uyumu önemli bir faktördür. R717'nin yağ ile karışmama ya da çok az karışma durumundan kaynaklı bir yağ ayırıcı düşünülmüştür. Kompresör ile yoğuşturucu arasında, akışkanın az bir miktarı by-pass hattına ayrılır. Sıcaklık kontrollü su vanası, basınç düşürücü vana ve basınç dengeleme hattı ile basıncın düzenlenmesi sağlanır. Sıvı deposu ile herhangi bir arıza da akışkanın depolanabileceği bir yer mevcut olur. Devrede bulunan filtre-kurutucular ile nem, çapak, tortu vs. gibi maddelerin tutulması sağlanır. Gözetleme camları ile akışkanın faz durumu gözlemlenir. Kompresöre sıvı girişini önlemek için de buharlaştırıcıdan sonra sıvı ayırıcı konulur. Soğutma devresi tasarımında ana ve yardımcı elemanların seçim işlemine kompresör seçimi ile başlanmıştır. Adı üstünde buhar sıkıştırmalı soğutma çevrimi olduğu için, sıkıştırma işlemini gerçekleştiren kompresör soğutma sisteminin en önemli elemanıdır. Bu çalışmada, seçilen kompresöre girdi değerler vererek teorik olarak performans tabloları oluşturulmuştur. Bitzer'in yazılım programıyla çalıştırılan sistemden COP, soğutma kapasitesi gibi parametrelerin çıktıları alınmıştır. Aynı zamanda buharlaşma ve yoğuşma sıcaklıklarına bağlı olarak Bitzer'in verdiği kübik fonksiyon soğutma kapasitesi, kütle debisi, kompresör tarafından çekilen güç için farklı sabitlerle ifade edilerek oldukça faydalı bir bağıntı oluşturur. Bu parametrelerin buharlaşma ve yoğuşma sıcaklığıyla değişimi gözlenmiştir. Girdi değerleri CoolPack programında da girilerek aralarında bu iki paket program hakkında bir kıyaslama yapılmıştır. Kıyaslama gerçekleştirilirken CoolPack'de girdi değerlere Bitzer programının verdiği soğutma kapasitesi sonucu olan 22.1 kW da girilir. Sonuçların paralel olduğu görüldükten sonra aşırı soğutma ve aşırı ısıtma işlemlerinin etkisini görmek için CoolPack'te sıcaklık değerleri değiştirilerek COP, kütle debisi, kompresör tarafından çekilen güç kıyaslaması yapılmıştır. İkinci yasa verimi de dört farklı durum için kıyaslanmıştır. Deneysel süreçte 16 farklı ölçüm alınarak soğutma kapasitesi, kompresör tarafından çekilen güç, COP gibi parametrelerin ölçümü gerçekleşmiştir. Kompresör tarafından çekilen gücün tayininde analizör, soğutma kapasitesinin belirlenmesinde sistem suyunun hacimsel debisini ölçen akış ölçer ve sistem suyu sıcaklıklarını belirleyen sıcaklık sensörü kullanılmıştır. Emme ve basma tarafından alınan gösterge basınç değerleriyle belirli kabuller alınarak her noktada iki yeğin özelik tespit edilmiştir. Yeğin özelikler tespit edilerek, ana elemanlar olan kompresör, yoğuşturucu, kısılma vanası ve buharlaştırıcıdan geçen soğutucu akışkanın kütle debisi hesaplanmıştır. Ölçüm cihazlarının hassasiyetleri sebebiyle deneysel bulguların hatalarını analiz etmek için belirsizlik analizi kullanılmıştır. Deneylerde 16 farklı ölçüm ile tespit edilen gösterge basınçlarından buharlaşma ve yoğuşma sıcaklığına geçilerek teorik ve deneysel akışkan miktarı kıyası gerçekleştirilmiştir. Bitzer'in sağladığı kübik fonksiyonda ölçümlerde tespit edilen buharlaşma ve yoğuşma sıcaklıkları girilerek, kütle debisi, COP, kompresörden çekilen güç ve soğutma kapasitesi teorik olarak belirlenmiştir. Birinci yasa verimini simgeleyen COP değeri teorik durumda deneylere göre daha fazladır. Soğutma kapasitesi değerleri ise teorik ve deneysel durumda yaklaşık olarak benzer profil göstermiştir. En fazla akışkan debisinin kompresörden, en düşük miktarın buharlaştırıcıdan geçtiği görülmüştür. İkinci yasa verimi için ise deneylerde alınan 16 ölçüm arasında kıyaslama yapılmıştır ve en verimli durum son ölçümde gerçekleşmiştir. Ölçüm sonuçları değerlendirildiğinde, sistemin bir rejim noktasının olduğu ve bu rejime erişinceye kadar enerji verimliliğinin arttığı, rejim noktasını aşınca verimlilik değerinin azaldığı görülmektedir.
With the discovery of synthetic refrigerants in refrigeration industry in the 20th century, the use of CFCs increased. However, increasing complaints were evaluated at the end of this century and important decisions were made regarding the future of refrigerants in Montreal. The use of CFCs was prohibited owing to ozone depletion potential and global warming potential. In the transition period, HCFCs were used as the most common. ODP values of HCFCs were lower compared to CFCs because of the addition of hydrogen. However, the ODP values of HCFCs were still not 0 and global warming potentials of HCFCs were high, which made it possible to use HCFCs until 2030. While the chlorine-free HFC does not harm ozone, GWP is still at high levels. Based on the regulations, programs are created to reduce the use of HFCs in the coming years. In the refrigeration industry, with these measures and programs taken for the use of refrigerant, the importance of natural refrigerants has increased. Ammonia, which is referred to with R717, draws considerable attentian on the basis of environmental effects. The ozone depletion potential value of R717, one of these refrigerants, is 0 and the global warming potential value of R717 is less than 1. Likewise, high energy efficiency in systems where ammonia is used makes ammonia preferred in refrigerants. For these reasons, the use of ammonia in cooling systems and conducting studies in this field are increasing. Also, R717 is a economically preferable refrigerant. However, due to security problems, its use is restricted to certain areas. With the R717, which is a motivation for the development of the project with its environmental friendliness and efficient systems, the vapor compression refrigeration system was designed. Typically a vapor compression refrigeration system includes compressor, condenser, throttling valve and evaporator. R717 enters the compressor as a vapor and is compressed to the condenser pressure. It leaves the compressor at a high temperature-high pressure and cools down and condenses as it flows through the condenser by rejecting heat. While the throttle valve is an element that allows the high pressure fluid to be reduced to low pressure, the low temperature refrigerant then enters the evaporator where it evaporates by absorbing heat. In this context, a reciprocating compressor as a compressor, plate heat exchangers as a heat exchanger and a thermostatic throttle valve as a throttle valve are preferred. In order for a cooling system to function, the system also needs auxiliary elements. In the determination of these auxiliary elements, compatibility with the refrigerant to be used in the cycle is an important factor. An oil separator is used becaue of R717 not mixing or very little mixing with oil. Between the compressor and the condenser, a small amount of fluid turns to the by-pass line. Regulating the pressure is provided by thermostatically controlled water valve, pressure reducing valve and pressure equalizing pipe. Liquid receiver provides resting of fluid with in the system and is used for storing refrigerant from the system when maintenance is needed. With filter-dryers, substances such as moisture and sediment are prevented from circulating in the cycle. With the sight glasses, we observe the phase state of the fluid. A liquid separator is put to prevent liquid phase in the compressor. The selection process of the main and auxiliary elements began with the selection of the compressor. Since it has a steam compression cooling cycle, it is the most crucial element of the compressor cooling system that performs the compression process. By giving input values to the selected compressor, theoretically performance tables were created. We got the output of parameters such as COP and cooling capacity from the system run by Bitzer's software program. At the same time, depending on the evaporation and condensation temperatures, Bitzer's cubic function cooling capacity, mass flow rate, shaft power are expressed in different constants, creating a very useful relation. The variation of these parameters with evaporation and condensation temperature was observed. An increase in cooling capacity, COP and mass flow of the refrigerant was observed with the increase of evaporation temperature and decrease of condensation temperature. Shaft power was increased with the increase of the condensation temperature. In was determined that the shaft power reaching the maximum value at a certain value of the evaporation temperature. Input values were also entered in the CoolPack program and a comparison was made between these two programs. While comparing, 22.1 kW, which is the result of Bitzer program, is entered in CoolPack. After seeing the results are parallel, temperature values are changed in CoolPack so as to see the impact of subcooling and superheating processes; COP, mass flow rate and shaft power were compared. In these examinations carried out with the same cooling capacity, it was determined that the COP value was highest only in the process in which subcooling was performed. On the other hand, COP value was observed to be the smallest only when superheating was applied. In the mass flow of the refrigerant, the smallest amount was determined when both superheating and subcooling were applied. The second law efficiency was compared for four different scenarios. The most efficient situation in terms of the second law is the process without superheating and subcooling, which can be described as the ideal situation. In the experimental process, 16 different measurements were taken and the parameters such as cooling capacity, shaft power and COP were measured. The analyzer was used to determine the shaft power. Flow meter measuring the volumetric flow rate of the system water and temperature sensor determining the system water temperatures were used to determine the cooling capacity. Two intensive properties were determined at each point by taking certain assumptions with the gauge pressure values taken by suction and compression. The error findings that may be owing to measurement precisions were determined by uncertainty analysis. The error rate of the first law efficiency is about %1, and the error rate of the first law efficiency is approximately %3. By determining the intensive properties, the amount of fluid per unit second passing through the main components, compressor, condenser, throttle valve and evaporator were calculated. In the cubic function provided by Bitzer, the evaporation and condensation temperatures determined in the measurements were entered, and the mass flow, COP, shaft power and cooling capacity were determined theoretically. The COP value, which symbolizes the first law efficiency, is more in theory than the experiments. Cooling capacity values show approximately similar profiles in theoretical and experimental situations. In mass amounts, the highest amount of fluid passes through the compressor and the lowest amount through the evaporator. For exergy efficiency, a comparison was made between the 16 measurements taken in the experiments, and the most efficient situation occurred in the last measurement. When the measurement results are evaluated in general, it is seen that the system has a regime point and energy efficiency increases until it reaches this regime, and the efficiency value decreases when it exceeds the regime point.
With the discovery of synthetic refrigerants in refrigeration industry in the 20th century, the use of CFCs increased. However, increasing complaints were evaluated at the end of this century and important decisions were made regarding the future of refrigerants in Montreal. The use of CFCs was prohibited owing to ozone depletion potential and global warming potential. In the transition period, HCFCs were used as the most common. ODP values of HCFCs were lower compared to CFCs because of the addition of hydrogen. However, the ODP values of HCFCs were still not 0 and global warming potentials of HCFCs were high, which made it possible to use HCFCs until 2030. While the chlorine-free HFC does not harm ozone, GWP is still at high levels. Based on the regulations, programs are created to reduce the use of HFCs in the coming years. In the refrigeration industry, with these measures and programs taken for the use of refrigerant, the importance of natural refrigerants has increased. Ammonia, which is referred to with R717, draws considerable attentian on the basis of environmental effects. The ozone depletion potential value of R717, one of these refrigerants, is 0 and the global warming potential value of R717 is less than 1. Likewise, high energy efficiency in systems where ammonia is used makes ammonia preferred in refrigerants. For these reasons, the use of ammonia in cooling systems and conducting studies in this field are increasing. Also, R717 is a economically preferable refrigerant. However, due to security problems, its use is restricted to certain areas. With the R717, which is a motivation for the development of the project with its environmental friendliness and efficient systems, the vapor compression refrigeration system was designed. Typically a vapor compression refrigeration system includes compressor, condenser, throttling valve and evaporator. R717 enters the compressor as a vapor and is compressed to the condenser pressure. It leaves the compressor at a high temperature-high pressure and cools down and condenses as it flows through the condenser by rejecting heat. While the throttle valve is an element that allows the high pressure fluid to be reduced to low pressure, the low temperature refrigerant then enters the evaporator where it evaporates by absorbing heat. In this context, a reciprocating compressor as a compressor, plate heat exchangers as a heat exchanger and a thermostatic throttle valve as a throttle valve are preferred. In order for a cooling system to function, the system also needs auxiliary elements. In the determination of these auxiliary elements, compatibility with the refrigerant to be used in the cycle is an important factor. An oil separator is used becaue of R717 not mixing or very little mixing with oil. Between the compressor and the condenser, a small amount of fluid turns to the by-pass line. Regulating the pressure is provided by thermostatically controlled water valve, pressure reducing valve and pressure equalizing pipe. Liquid receiver provides resting of fluid with in the system and is used for storing refrigerant from the system when maintenance is needed. With filter-dryers, substances such as moisture and sediment are prevented from circulating in the cycle. With the sight glasses, we observe the phase state of the fluid. A liquid separator is put to prevent liquid phase in the compressor. The selection process of the main and auxiliary elements began with the selection of the compressor. Since it has a steam compression cooling cycle, it is the most crucial element of the compressor cooling system that performs the compression process. By giving input values to the selected compressor, theoretically performance tables were created. We got the output of parameters such as COP and cooling capacity from the system run by Bitzer's software program. At the same time, depending on the evaporation and condensation temperatures, Bitzer's cubic function cooling capacity, mass flow rate, shaft power are expressed in different constants, creating a very useful relation. The variation of these parameters with evaporation and condensation temperature was observed. An increase in cooling capacity, COP and mass flow of the refrigerant was observed with the increase of evaporation temperature and decrease of condensation temperature. Shaft power was increased with the increase of the condensation temperature. In was determined that the shaft power reaching the maximum value at a certain value of the evaporation temperature. Input values were also entered in the CoolPack program and a comparison was made between these two programs. While comparing, 22.1 kW, which is the result of Bitzer program, is entered in CoolPack. After seeing the results are parallel, temperature values are changed in CoolPack so as to see the impact of subcooling and superheating processes; COP, mass flow rate and shaft power were compared. In these examinations carried out with the same cooling capacity, it was determined that the COP value was highest only in the process in which subcooling was performed. On the other hand, COP value was observed to be the smallest only when superheating was applied. In the mass flow of the refrigerant, the smallest amount was determined when both superheating and subcooling were applied. The second law efficiency was compared for four different scenarios. The most efficient situation in terms of the second law is the process without superheating and subcooling, which can be described as the ideal situation. In the experimental process, 16 different measurements were taken and the parameters such as cooling capacity, shaft power and COP were measured. The analyzer was used to determine the shaft power. Flow meter measuring the volumetric flow rate of the system water and temperature sensor determining the system water temperatures were used to determine the cooling capacity. Two intensive properties were determined at each point by taking certain assumptions with the gauge pressure values taken by suction and compression. The error findings that may be owing to measurement precisions were determined by uncertainty analysis. The error rate of the first law efficiency is about %1, and the error rate of the first law efficiency is approximately %3. By determining the intensive properties, the amount of fluid per unit second passing through the main components, compressor, condenser, throttle valve and evaporator were calculated. In the cubic function provided by Bitzer, the evaporation and condensation temperatures determined in the measurements were entered, and the mass flow, COP, shaft power and cooling capacity were determined theoretically. The COP value, which symbolizes the first law efficiency, is more in theory than the experiments. Cooling capacity values show approximately similar profiles in theoretical and experimental situations. In mass amounts, the highest amount of fluid passes through the compressor and the lowest amount through the evaporator. For exergy efficiency, a comparison was made between the 16 measurements taken in the experiments, and the most efficient situation occurred in the last measurement. When the measurement results are evaluated in general, it is seen that the system has a regime point and energy efficiency increases until it reaches this regime, and the efficiency value decreases when it exceeds the regime point.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2020
Anahtar kelimeler
soğutma makineleri,
refrigerating machinery,
soğutma,
cooling