Düşük GWP'li soğutucu akışkanların ısı pompalı kurutucularda deneysel analizi
Experimental analysis of low-GWP refrigerant for heat pump tumble dryer application
Yazar: BARLAS BAŞARAN
Danışman: PROF. DR. NURDİL ESKİN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Mühendislik Bilimleri = Engineering Sciences

Özet:
Florlu gazlar küresel ısınmaya olan olumsuz etkileri nedeniyle bir çok yönetmelik ve protokol ile uluslararası boyutta kısıtlandırılması hedeflenmiştir. Bu sayede yüksek küresel ısınma potansiyeline sahip soğutucu akışkanlar piyasadan kaldırılarak yerine çevreci soğutucu akışkanların çalışılmasını sağlamıştır. Isı pompalı çamaşır kurutma makineleri içerisinde soğutucu akışkan bulunması nedeniyle yönetmeliklerin kapsam dahilindedir. Isı pompalı kurutma makinelerinde yaygın olarak yüksek küresel ısınma potansiyeline sahip R134a soğutucu akışkanı kullanılmaktadır. R134a soğutucu akışkanı ucuz, verimli ve kolay erişilebilir olması sayesinde yaygın olarak bir çok sektörde kullanılmaktadır.
Bu çalışmada ısı pompalı çamaşır kurutma makinelerinde düşük küresel ısınma potansiyeline sahip soğutucu akışkanların kullanılabilirliği değerlendirilmiştir. Bu amaçla alternatif soğutucu akışkanlara ilişkin literatür araştırması yapılarak uygun soğutucu akışkanlar belirlenmiştir. R450a ve R290 soğutucu akışkanları soğutucu akışkan seçim kriterlerine bağlı olarak kurutma makinesi için en uygun değerlendirilmiştir.
Alternatif soğutucu akışkanların değerlendirilmesi amacıyla bir deney düzeneği oluşturulmuştur. Referans ürün olarak yüksek miktarda R134a soğutucu akışkanı içermesi nedeniyle A+++ enerji sınıfı ürün seçilmiştir. Test boyunca ürün üzerinden sıcaklık, sistem basıncı, bağıl nem, fark basınç gibi verilerin elde edilmesi amacıyla ölçüm ekipmanları yerleştirilmiştir.
Birinci aşama olarak, R450a ve R290 soğutucu akışkanları sistem elemanlarında herhangi bir değişiklik yapılmadan deneysel olarak analiz edilmiştir. Güvenlik standardı gereği sistemde en fazla 150 gr R290 soğutucu akışkanın bulunabileceği ve bu miktarın mevcut sistem tasarımı için yetersiz olduğu görülmüştür.
İkinci aşama olarak, sistem iç hacminin küçültülerek daha az miktarda soğutucu akışkan kullanılması hedeflenmiştir. Bu amaçla boru çapları küçük olan yeni buharlaştırıcı ve yoğuşturucu tasarımları oluşturulmuştur.
Üçüncü aşama olarak, kompresör strok hacminde değişikliğe gidilerek kompresör giriş gücünün istenilen seviyeye ulaşması sağlanmıştır.
Dördüncü aşama olarak, belirlenen kompresör strok hacmi ve ısı değiştirici tasarımı için farklı kılcal boru uzunluğunun sistem performansına etkisi incelenmiştir.
Sonuç olarak, 150 gr R290 soğutucu akışkanlı, 6,75 cm3 kompresör strok hacmi, 5 mm boru çaplı yoğuşturucu, 7 mm boru çaplı buharlaştırıcı ve 1500 mm kılcal boru uzunluğu ile referans ürüne benzer sonuçlar elde edilmiştir.

Abstract:
Due to global warming impacts of flourinated refrigerants, various regulations and protocols were signed by internationally. Main purpose of these agreements is limit usage of the high gwp refrigerant and encourage manufacturers to produce environment friendly products. Flourinated refrigerants are mostly used for refrigeration systems, air conditioners, heat pump units, fire extinguishers and aerosols. One of the affected heat pump applications of these agreements is heat pump tumble dryers. This kind of dryers includes vapour compression refrigeration cycles and it consists of compressor, expansion valve, evaporator, condenser and refrigerant. Heat pump tumble dryers becoming more popular day by day in the market since tumble dryers provide quick laundry drying beside higher efficiency. Moreover, It enables users to dry laundries without any space limitation. 
In heat pump tumble dryers application, mainly R134a refrigerant has been used for a long time. This refrigerant is flourinated refrigerant and widely used in different sectors since it is efficient, cheap and easily accessible. However, It will be phased out in coming years since it has high global warming potential. In refrigerant industry, there is a lots of studies for alternative refrigerants which have low global warming potential. 
In this thesis, it is aimed to reduce the negative impact of heat pump tumble dryers on the environment by replacing with low gwp refrigerants. At this point, alternative refrigerants has been investigated based on refrigerant selection criterias. Among the lots of refrigerants, R450a and R290 were considered as optimum solution for heat pump tumble dryers based on basic properties. R450a refrigerant consists of %42 R134a and %58 R1234ze refrigerants. Thefore, thermopyhsical properties of R450a is mostly same with R134a refrigerant although global warming potential of R450a is lower than half of R134a. 
In this thesis, test rig was established to analyse different refrigerants by experimentally. As a reference product, A+++ energy class is selected since it includes more R134a refrigerant per system compared with other energy classes products. Reference product consists of 9,52 mm copper tube and aluminium fin type evaporator, 7 mm copper tube and aluminium fin type condenser, 8,20 cm3 compressor, 1200 mm capillary length, 520 gr R134a and BLDC type motor.
For experimental analysis, reference product is equipped with 36 pcs thermocouples, 4 pcs pressure transducers, 5 pcs relative humidity sensors and differential pressure sensor in order to obtain data during drying cycle. Based on system data, development steps of system were determined. Thermocouples and pressure transducers enabled us to draw lnP-h diagram of system and analyse system efficiency. By means of a scale, drying rate data is obtained experimentally during drying cycle.
Additionally, total power consumption of the product, compressor input power and humidity ratio of cottons were measured with sensitive equipments to verify declaration level of product. After each performance tests, energy level of systems were compared with reference test result.
In experimentals, 8 kg cotton loads were used for performance test and all performance tests were implemented based on tumble dryer performance test standard. In standard, All information for ambient condition, water temperature, water hardness, voltage level is clarified in order to provide same test condition for each tests.
As a first step, R450a and R290 refrigerants directly charged into the system without any change for system components. Main purpose of these tests compare the refrigerants behaviours in the same system. However, due to safety standard for tumble dryers, R290 refrigerant amount is limited to 150 gr in experimental test. In these tests, it was observed that 150 gr R290 refrigerant amount is not sufficient for existing system internal volume. With R290 test, System operating points far away from ideal operating points. To run R290 system effectively with 150 gr refrigerant, heat exchanger compactness should be improved. 
As a result of R450a drop-in test, humidity ratio of cotton loads is out of tolerance after 160 minute drying cycle. Reason of lower drying rate is mainly related to refrigerant capacity of R450a. In order to obtain similar humidity ratio with reference product, compressor displacement should be enlarged.
In second step, system internal volume decreased by recuding inner diameters of heat exchangers. By using coil designer program, several heat exchanger designs were examined and optimum designs were provided from manufacturers for experimental tests. With the aid of reduced diameter, system internal volume is decreased. Condenser tube outer diameter was reduced from 7 mm to 5 mm. To obtain similar heating capacity, number of tubes is increased from 24 to 32. Similarly, Evaporator outer diameter were reduced from 9,52 mm to 7 mm. Cooling capacity of evaporator were obtained almost same compared with previous design by means of increased internal heat transfer rate. In concecutive tests, 7 mm evaporator and 5 mm condenser heat exchanger design provide better performance for R290 test. As a result of small internal volume, requirement for refrigerant amount was reduced. In R450a tests, humidity ratio of cottons were not provided as good as reference products. In contrast to R450a, humidity ratio of cottons after drying cycle were improved with R290 while system internal volume was reducing. Because smaller system could run more effectively with 150 gr R290 refrigerant. At this point, R290 compressor displacement should be reduced to decrease compressor input power. On the contarary, R450a compressor displacement should be enlarged in order to obtain higher refrigeration capacity. In the next steps, performance tests were conducted with R290 refrigerant for displacement optimization. 
In third step, different compressor displacements were examined in order to obtain optimum performance results. Main reason of changing displacement is reduce refrigerant mass flow and adjust compressor power consumption. Among the several displacements, optimum test result was obtained with 6,75 cm3 compressor displacement. R290 6,75 cm3 compressor input power was matched with R134a 8,20 cm3 compressor input power. With 6,25 cm3 compressor displacement tests, operating points of system pretty lower than 6,75 cm3 and 8,20 cm3 compressor. Therefore, 160 minutes of drying duration should be extended to provide same drying performance for 6,25 cm3 system. 
In fourth step, system design is finalized by changing capillary length. In these test, 900 mm , 1200 mm and 1500 mm capillaries were investigated for R290 system with 6,75 cm3 compressor. With 1500 mm capillary length, optimum system operating point was obtained.
In conclusion, optimum test results was obtained with R290 refrigerant, 6,75 cm3 compressor, 5 mm condenser, 7 mm evaporator and 1500 mm capillary. As a result, A+++ existing products could be replaced with new system design with R290 refrigerant.