12 research outputs found
Lubricants Optimized for use with R-32 and Related Low GWP Refrigerant Blends
Lubricants are important components of almost all air conditioning and refrigeration systems. Their primary function is to lubricate the compressor, provide sealing of clearances between low and high pressure sides of the compressor and remove frictional heat. But the lubricant is in contact with refrigerant at all times and plays a thermo-fluidic role in the air conditioning system that can impact both system capacity and coefficient of performance (COP). Lubricants can influence capacity by altering the refrigerant-side heat transfer coefficients, and increasing pressure drop required to maintain set point temperatures. Lubricants can also affect the isentropic efficiency of the compressor. The transition to lower global warming potential (GWP) alternative refrigerants is critical to the realization of environmentally sustainable and more energy efficient refrigeration technologies. Leading candidates to replace R-22 and R-410A in air conditioning and heat pump applications include R-32 (difluoromethane) and a plethora of HFC/hydrofluoro-olefin blends with GWPs in the range of 400-650. Considerable data has been generated comparing R-410A with various low GWP alternative refrigerants in full system tests. Most notable is the work sponsored by AHRI under the Alternative Refrigerant Evaluation Program (AREP). But these studies have either been refrigerant âdrop inâ tests to commercial R-410A systems or âsoft optimizedâ tests, where minor component modifications were made to better adapt a system to the properties of the new refrigerants. In all cases, the lubricants used for these studies were the commercial polyol ester (POE) lubricants used with R-410A. But commercial POE lubricants used today are much less compatible with R-32 and HFC/HFO blends. There is concern that issues may arise with long term reliability of compressors due to inadequate lubrication, poor oil return to the compressor and undesirable lubricant hold up in the system; problems that would not be observed in the short term capacity and energy efficiency tests. But regardless, there is also interest in understanding if properly optimized lubricants can improve the overall performance of low GWP-based systems. This paper presents the results of a study of the solution phase behavior and lubricating performance of several commercial and new developmental POE lubricants with low GWP R-410A replacement refrigerants. The results suggest that POE lubricants used today with R-410A may not be acceptable for use with R-32 or related HFC/HFO blends. An undesirable miscibility gap is observed in mixtures of traditional POEs with R-32 in the concentration range of 10-40 wt% lubricant in refrigerant. In addition, the viscosity dilution of refrigerant/lubricant mixtures at high lubricant concentrations (typical of those observed in the compressor sump) is as much as 50% more pronounced with R-32 than R-410A. Studies conducted with a new class of advanced polyol esters show that it is possible to design synthetic lubricants optimized for R-32, combining good refrigerant miscibility with limited viscosity dilution
Solution Properties Of Polyol Ester Lubricants Designed For Use With R-32 And Related Low GWP Refrigerant Blends
Since the Montreal and Kyoto protocols mandated the phase-out of refrigerants which deplete the ozone layer and have high global warming potential, respectively, there has been an extensive global initiative to identify suitable environmentally sustainable alternatives. Replacement of CFCs and HCFCs with HFCs has successfully addressed the objectives of the Montreal protocol. However, most HFCs used today are not acceptable for the long term because they have GWPs greater than 1,000. Low GWP refrigerants that are, or will be, considered as replacements for HFCs include R32, hydrocarbons such as R290, carbon dioxide (R744), and hydroflouro olefins such as HFO1234yf and HFO1234ze(E).It has already been determined that in many cases new lubricants will be required for these refrigerants to ensure long term compressor reliability and the best possible system performance. The primary issue that must be addressed is the unacceptable high mutual solubility of the refrigerant and lubricant at high lubricant concentrations. The first consequence of this high solubility is the excessive reduction of viscosity that affects proper lubrication of the compressor and components, sealing of clearances between low and high pressure sides of the compressor. The second is a significant change in the steady state amount of oil in the circulation stream in the system, which can impact the heat transfer performance in both the evaporator and condenser.Another potential minor issue is refrigerant flash evaporation at discharge creating excessive foaming and noise. This paper describes details of a method used to measure the thermophysical properties of refrigerant lubricant mixtures. The general methods for data acquisition and processing, along with creation of Daniel charts were in accord with those developed by Chris Seeton. The results of measurements involving mixtures of traditional POEs with R-32 or R-410A shows that lubricant viscosities in the compressor at various conditions within the normal operating envelope decrease by as much as 25-54%. This illustrates the excessive lubricant viscosity dilution of R-32 relative to R-410A with traditional POs used today with HFCs refrigerants. The solution property measurement technique was also used to develop a class of advanced ester POE lubricants optimized for R-32 to eliminates the viscosity dilution problem. Significant energy savings can be achieved through proper optimization of lubricant/refrigerant solution properties to provide the best balance of lubrication in the compressor while maintaining excellent heat transfer in the refrigeration cycle
Solution Properties Of Polyol Ester Lubricants Designed For Use With R-32 And Related Low GWP Refrigerant Blends
Since the Montreal and Kyoto protocols mandated the phase-out of refrigerants which deplete the ozone layer and have high global warming potential, respectively, there has been an extensive global initiative to identify suitable environmentally sustainable alternatives. Replacement of CFCs and HCFCs with HFCs has successfully addressed the objectives of the Montreal protocol. However, most HFCs used today are not acceptable for the long term because they have GWPs greater than 1,000. Low GWP refrigerants that are, or will be, considered as replacements for HFCs include R32, hydrocarbons such as R290, carbon dioxide (R744), and hydroflouro olefins such as HFO1234yf and HFO1234ze(E).It has already been determined that in many cases new lubricants will be required for these refrigerants to ensure long term compressor reliability and the best possible system performance. The primary issue that must be addressed is the unacceptable high mutual solubility of the refrigerant and lubricant at high lubricant concentrations. The first consequence of this high solubility is the excessive reduction of viscosity that affects proper lubrication of the compressor and components, sealing of clearances between low and high pressure sides of the compressor. The second is a significant change in the steady state amount of oil in the circulation stream in the system, which can impact the heat transfer performance in both the evaporator and condenser.Another potential minor issue is refrigerant flash evaporation at discharge creating excessive foaming and noise. This paper describes details of a method used to measure the thermophysical properties of refrigerant lubricant mixtures. The general methods for data acquisition and processing, along with creation of Daniel charts were in accord with those developed by Chris Seeton. The results of measurements involving mixtures of traditional POEs with R-32 or R-410A shows that lubricant viscosities in the compressor at various conditions within the normal operating envelope decrease by as much as 25-54%. This illustrates the excessive lubricant viscosity dilution of R-32 relative to R-410A with traditional POs used today with HFCs refrigerants. The solution property measurement technique was also used to develop a class of advanced ester POE lubricants optimized for R-32 to eliminates the viscosity dilution problem. Significant energy savings can be achieved through proper optimization of lubricant/refrigerant solution properties to provide the best balance of lubrication in the compressor while maintaining excellent heat transfer in the refrigeration cycle
Effect of Lubricant-Refrigerant Mixture Properties on Compressor Efficiencies
Lubricants are utilized on compressors to lower friction thus increasing efficiency while decreasing wear and increase longevity. While pure lubricant properties are commonly cited in literature due to more readily available property data, far more meaningful results are obtained when lubricant-refrigerant mixture properties are utilized. The most critical of these properties are the vapor-liquid equilibrium data, which relates temperatures, pressures, and concentrations, to other intensive properties such as density and viscosity. To determine the impact of fundamental refrigerant-lubricant mixture properties on compressor performance, a series of lubricants having known mixture properties where utilized in a semi-hermetic transcritical carbon dioxide compressor. This compressor was installed in a calorimeter which allowed compressor electrical power consumption to be accurately measured. Likewise, refrigerant temperatures, pressures, and mass flows were measured. As this calorimeter utilized the full refrigeration cycle with both a gas-cooler and evaporator, it was possible to accurately determine the oil circulation ratio (OCR) via the sample based method given by ASHRAE Standard 41.4. The compressor was operated at a series of suction and discharge pressures and temperatures which were near the edge of the operating envelop. Combining the property information with experimental data from the calorimeter experiments allow for analysis of the impact of refrigerant-lubricant mixture properties on compressor efficiencies. Due to the relatively small changes in performance, it was necessary to properly account for the presence of lubricant in the definitions of isentropic and volumetric efficiencies. After accounting for these properties, multivariate least square curve fitting was utilized to understand the relative impact of mixture properties and OCR on compressor efficiency. The analysis is furthered to show the impact of compressor efficiency on system performance for the purpose of pointing towards selecting lubricants to minimize energy consumption
Effects of Refrigerant-Lubricant Combinations on the Energy Efficiency of a Convertible Split-System Residential Air-Conditioner
Polyol ester (POE) lubricants of different viscosity ISO grades (32-80) and possessing distinctly different compatibilities (miscible vs. immiscible) were tested with R-410A, R-32, and L-41b. For each refrigerant-lubricant pair tested, the cooling coefficient of performance (COP), heating performance factor (HPF), and oil circulation ratio (OCR) were determined while operating at AHRI Standard 210/240 conditions A, B, C, H1 & H2. The results were correlated to the properties of the working fluids. Due to its higher density, yet comparable specific heat, R-32 showed increased cooling capacity compared to R-410A. However, the COPs of these refrigerants were similar because the capacity increase was offset by increased compressor power consumption. L-41b required the least compressor power, but also had the lowest cooling capacity and COP of the three refrigerants. Lubricant choice had minimal impact on cooling capacity. However, immiscible lubricants lowered cooling capacity by about 4% for R-32, condition B. A larger effect was observed in the compressor, where lubricants specifically designed for R-32 lowered discharge temperatures by 6 °C and reduced power consumption by up to 10%. For R-32-lubricant pairs tested under AHRI cooling condition B, the highest and lowest COPs measured were 4.19 (optimized ISO 68 POE) and 3.72 (commercial ISO 32 POE) ? a 12% improvement by replacing the standard R-410A lubricant
Refrigerant and Lubricant Mass Distribution in a Convertible Split System Residential Air-Conditioner
Lubricants are utilized in air-conditioning systems for the purpose of decreasing friction and wear within the compressor. While ideally the lubricant remains in the compressor, some lubricant is entrained and transported by the refrigerant to the other system components. During operational transients, the lubricant is redistributed throughout the various system components. The equilibrium distribution of lubricant depends among other things on fluid properties, phase change processes, flow rates, geometries, and operating conditions. Experiments were conducted in a commercially available, split-system, residential, air-conditioning system with a nominal 3-ton capacity that could be operated both as an air-conditioner and a heat-pump. While the system was designed to operate with R410A, most of the testing was conducted with pure R32, which is a leading candidate for R410A replacement pending regulatory discontinuation of its other constituent: R125. The lubricants used in this study were traditional and advanced polyol ester lubricants. Advanced polyol ester lubricants promise to improve lubricity and wear protection compared to current lubricants. The lubricants had nominal viscosities ranging from 32 to 80 cSt. To inventory the distribution of refrigerant and lubricant, the system was modified by the installation of ball valves which could be utilized to separate the system into its constituents: compressor, condenser, liquid line, evaporator, suction line, and accumulator. The system was brought to equilibrium at conditions A, B, C, H1, and H2 which are defined in AHRI Standard 210/240. After maintaining equilibrium, simultaneously the compressor being shut off and the ball valves were closed which isolated refrigerant and lubricant within each component. The components were subsequently removed and weighed in a manner which allowed the mass of refrigerant and lubricant in each component to be determined. Analysis of the results focuses on the change in mass distribution due to refrigerant-lubricant mixture properties and due to changes in operating conditions. The implications of the net migration of lubricant from the compressor to the remainder of the system will also be discussed
The IDENTIFY study: the investigation and detection of urological neoplasia in patients referred with suspected urinary tract cancer - a multicentre observational study
Objective
To evaluate the contemporary prevalence of urinary tract cancer (bladder cancer, upper tract urothelial cancer [UTUC] and renal cancer) in patients referred to secondary care with haematuria, adjusted for established patient risk markers and geographical variation.
Patients and Methods
This was an international multicentre prospective observational study. We included patients aged â„16 years, referred to secondary care with suspected urinary tract cancer. Patients with a known or previous urological malignancy were excluded. We estimated the prevalence of bladder cancer, UTUC, renal cancer and prostate cancer; stratified by age, type of haematuria, sex, and smoking. We used a multivariable mixed-effects logistic regression to adjust cancer prevalence for age, type of haematuria, sex, smoking, hospitals, and countries.
Results
Of the 11 059 patients assessed for eligibility, 10 896 were included from 110 hospitals across 26 countries. The overall adjusted cancer prevalence (n = 2257) was 28.2% (95% confidence interval [CI] 22.3â34.1), bladder cancer (n = 1951) 24.7% (95% CI 19.1â30.2), UTUC (n = 128) 1.14% (95% CI 0.77â1.52), renal cancer (n = 107) 1.05% (95% CI 0.80â1.29), and prostate cancer (n = 124) 1.75% (95% CI 1.32â2.18). The odds ratios for patient risk markers in the model for all cancers were: age 1.04 (95% CI 1.03â1.05; P < 0.001), visible haematuria 3.47 (95% CI 2.90â4.15; P < 0.001), male sex 1.30 (95% CI 1.14â1.50; P < 0.001), and smoking 2.70 (95% CI 2.30â3.18; P < 0.001).
Conclusions
A better understanding of cancer prevalence across an international population is required to inform clinical guidelines. We are the first to report urinary tract cancer prevalence across an international population in patients referred to secondary care, adjusted for patient risk markers and geographical variation. Bladder cancer was the most prevalent disease. Visible haematuria was the strongest predictor for urinary tract cancer
A Comparative Study of Traditional and Non-Traditional Polyol Ester Lubricants for Carbon Dioxide (R-744) Applications
STERICALLY HINDERED 4-AMINO-3,5-DIALKYLBENZENETHIOL DERIVATIVES: SYNTHESIS AND CHARACTERIZATION
Antibody 10-1074 suppresses viremia in HIV-1-infected individuals
Monoclonal antibody 10-1074 targets the V3 glycan supersite on the HIV-1 envelope (Env) protein. It is among the most potent anti-HIV-1 neutralizing antibodies isolated so far. Here we report on its safety and activity in 33 individuals who received a single intravenous infusion of the antibody. 10-1074 was well tolerated and had a half-life of 24.0 d in participants without HIV-1 infection and 12.8 d in individuals with HIV-1 infection. Thirteen individuals with viremia received the highest dose of 30 mg/kg 10-1074. Eleven of these participants were 10-1074-sensitive and showed a rapid decline in viremia by a mean of 1.52 logic copies/ml. Virologic analysis revealed the emergence of multiple independent 10-1074-resistant viruses in the first weeks after infusion. Emerging escape variants were generally resistant to the related V3-specific antibody PGT121, but remained sensitive to antibodies targeting nonoverlapping epitopes, such as the anti-CD4-binding-site antibodies 3BNC117 and VRC01. The results demonstrate the safety and activity of 10-1074 in humans and support the idea that antibodies targeting the V3 glycan supersite might be useful for the treatment and prevention of HIV-1 infection