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Investigation of oil retention and pressure drop in suction lines using R1234yf, R134a and R410A with POE ISO 100

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Title: Investigation of oil retention and pressure drop in suction lines using R1234yf, R134a and R410A with POE ISO 100
Author(s): Ramakrishnan, Aravind
Advisor(s): Hrnjak, Predrag
Department / Program: Mechanical Sci & Engineering
Discipline: Mechanical Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Oil Retention Pressure Drop PolyOl Ester oil (POE) R1234yf Horizontal and Vertical Suction Lines
Abstract: Compressors of typical vapor compression refrigeration systems require the presence of oil, primarily for the purpose of lubrication. A small portion of this oil is transported out of the compressor by the high velocity refrigerant vapor exiting the compressor or by the refrigerant forming an equilibrium mixture with the oil. This results in a refrigerant/oil liquid mixture being circulated in the system, thereby leading to a decrease in system performance in terms of heat transfer coefficient and pressure drop. Of particular interest is studying the retention of oil at suction lines to the compressor, where conditions lead to a mixture that is rich in oil, consequently leading to high oil retention due to high mixture viscosity. The current work presents experimental data for oil retention and pressure drop in suction lines using R1234yf, the low Global Warming Potential (GWP) refrigerant which was developed as a consequence of the European Union’s Mobile Air-Conditioning Directive. Tests were conducted in 10.2 mm internal diameter horizontal and vertical suction lines that were about 2 m long, using POE ISO 100 lubricant. A saturation temperature of 13 °C and a superheat of 15 °C were employed, while the superficial refrigerant vapor velocity was varied between 1-6 m/s. Experiments were also performed in R134a in order to study if R1234yf is a suitable drop-in replacement for R134a. Also, comparisons were made with data obtained using POE ISO 32 to study the effect of lubricant viscosity. Experimental tests in R410A using POE 32 and POE 100 served as data for further comparison. Results show that at similar operating conditions, the more viscous POE 100 yields upto 40 % more oil retention and upto 60 % more pressure drop in comparison to POE 32. It was also observed that at a similar system cooling capacity, R1234yf had upto 15 % more oil retention and upto 60 % more pressure drop in comparison to R134a. A semi-empirical model has also been proposed in order to predict oil retention and pressure drop in vertical suction lines. An improved critical mass flux is also predicted in order to properly design vertical suction line sizes. Flow visualization studies were also performed in order to identify various regimes and the transitions between different regimes.
Issue Date: 2012-09-18
URI: http://hdl.handle.net/2142/34322
Rights Information: Copyright 2012 Aravind Ramakrishnan
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08
 

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