Design of Accelerated Fatigue Tests for Flame Free Refrigeration Fittings

Refrigerant leakage from failed braze joints is a multi-billion dollar problem for the global HVAC&R industry. Leaks are typically caused due to mechanical fatigue from extreme pressure cycling, temperature cycling including exposure to freeze/thaw cycles, or vibrational wear induced from rotating electrical machinery. Three tests to accelerate mechanical fatigue were devised to simulate real world extreme conditions to determine possible failure modes of refrigerant components. The first test is a freeze/thaw test which simulates ice buildup and defrost observed during heat pump operation. Field failures of brazed joints have been detected due to water being trapped in tight spaces and expanding during freezing, causing high stress on brazed joints and joining methods. The second test is a combined thermal/pressure shock test designed to simulate abrupt temperature and pressure changes due to start/stop cycles and frost/defrost mode changes. The third test is a vibration test, designed to simulate vibrational loads induced from rotating components in the system. The test article is a flame-free tube fitting designed to work with refrigerants. Six different fitting sizes designed to connect tubes between 6.35 mm and 28.5 mm were subjected to the three tests described above

Improvements in Refrigerant Flow Distribution Using an Expansion Valve with Integrated Distributor

Many factors, such as loading, flow circuiting, phase separation, and distributor effectiveness determine how uniformly refrigerant is distributed within a multicircuited heat exchanger. This work describes the development of a test procedure for evaluation of refrigerant flow distribution in a multicircuited round tube evaporator as well as a comparison between a typical valve/distributor combination and a novel expansion device that integrates the distributor into the valve body. The results of this study show that refrigerant flow distribution can be made more uniform through implementation of this device

Accelerated Thermal Cycling test for Heat Exchangers Used in Reversible Heat Pump

With increasing efficiency standards and higher energy costs, the demand for reversible air-conditioning/heat pump systems is increasing throughout the stationary market. The heat exchangers in such reversible systems must perform reliably as both evaporator and condenser. The outdoor coil, specifically, is subject to very large changes in both operational pressures and temperatures. With this increase in demand and the gradual shift of the industry to aluminum microchannel coil design, comes a need to better understand and quantify the reliability of the heat exchangers. This paper presents the development of an accelerated thermal cycling test method using refrigerant at typical pressures and temperatures to demonstrate the reliability of said heat exchangers. This method employs a technique of switching the heat exchanger between condensing and evaporation modes rapidly while monitoring strain at various locations of concern to quantify any shift in strain caused by fatigue

Successful Design, Implementation, And Validation Of Transcritical R744 Technology For Beverage Display Coolers

Glass door merchandisers are used in grocery and convenience stores to display chilled beverages or refrigerated foods. Among other possible choices for this application, carbon dioxide (R744, CO2) is seen as a promising low-GWP refrigerant alternative that is non-flammable and non-toxic. While R744 itself is less costly than synthetic alternatives, successful implementation of high-performance, low-cost transcritical R744 technology is challenging. This paper summarizes important R744-specific design issues and differences in comparison to conventional R134a bottle coolers. Due to cost reasons, it is highly desired to use relatively conventional components, including round-tube-plate-fin heat exchanger designs, fixed geometry capillary tubes (instead of variable geometry expansion valves), and single-speed compressors. While a conventional round-tube-plate fin evaporator designs deliver acceptable results, transcritical R744 systems require substantially different heat exchanger designs in order to deliver suitable performance when used as gas cooler. Internal heat exchange, which in conventional R134a systems is often achieved by wrapping the capillary tube around the compressor suction line, plays a much more important role in transcritical R744 systems, and shows large optimization potential. Experiments also show that proper capillary tube sizing and refrigerant charge optimization have much bigger impact on transcritical R744 systems in terms of cooling performance and energy efficiency in comparison to R134a systems. Presented is an example of a successful R744 bottle cooler design that is on par with a comparable R134a system in terms of performance and cost. This low-cost, high performance design has been implemented and experimentally validated

Low Risk Monitoring in Neurocritical Care

Background/Rationale: Patients are admitted to Intensive care units (ICUs) either because they need close monitoring despite a low risk of hospital mortality (LRM group) or to receive ICU specific active treatments (AT group). The characteristics and differential outcomes of LRM patients vs. AT patients in Neurocritical Care Units are poorly understood. Methods: We classified 1,702 patients admitted to our tertiary and quaternary care center Neuroscience-ICU in 2016 and 2017 into LRM vs. AT groups. We compared demographics, admission diagnosis, goal of care status, readmission rates and managing attending specialty extracted from the medical record between groups. Acute Physiology, Age and Chronic Health Evaluation (APACHE) IVa risk predictive modeling was used to assess comparative risks for ICU and hospital mortality and length of stay between groups. Results: 56.9% of patients admitted to our Neuroscience-ICU in 2016 and 2017 were classified as LRM, whereas 43.1% of patients were classified as AT. While demographically similar, the groups differed significantly in all risk predictive outcome measures [APACHE IVa scores, actual and predicted ICU and hospital mortality (p \u3c 0.0001 for all metrics)]. The most common admitting diagnosis overall, cerebrovascular accident/stroke, was represented in the LRM and AT groups with similar frequency [24.3 vs. 21.3%, respectively (p = 0.15)], illustrating that further differentiating factors like symptom duration, neurologic status and its dynamic changes and neuro-imaging characteristics determine the indication for active treatment vs. observation. Patients with intracranial hemorrhage/hematoma were significantly more likely to receive active treatments as opposed to having a primary focus on monitoring [13.6 vs. 9.8%, respectively (p = 0.017)]. Conclusion: The majority of patients admitted to our Neuroscience ICU (56.9%) had \u3c10% hospital mortality risk and a focus on monitoring, whereas the remaining 43.1% of patients received active treatments in their first ICU day. LRM Patients exhibited significantly lower APACHE IVa scores, ICU and hospital mortality rates compared to AT patients. Observed-over-expected ICU and hospital mortality ratios were better than predicted by APACHE IVa for low risk monitored patients and close to prediction for actively treated patients, suggesting that at least a subset of LRM patients may safely and more cost effectively be cared for in intermediate level care settings

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

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

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

In vivo monitoring of fetoplacental Vegfr2 gene activity in a murine pregnancy model using a Vegfr2-luc reporter gene and bioluminescent imaging

<p>Abstract</p> <p>Background</p> <p>Vascular endothelial growth factor receptor-2 (VEGFR2) plays a pivotal role in angiogenesis by eliciting vascular endothelial cell growth when bound to VEGF, a powerful pro-angiogenic ligand. While Vegf and Vegfr2 are expressed throughout gestation, the latter third of gestation in mice is characterized by a marked increase in fetoplacental angiogenesis. Thus, the objective of this study was to determine the feasibility of monitoring fetoplacental Vegfr2 gene activity non-invasively using a Vegfr2-luc reporter transgenic mouse and bioluminescent imaging.</p> <p>Methods</p> <p>Imaging parameters were optimized using two wild-type (WT) females, bearing Vegfr2-luc fetuses. Then, seven WT females, bred to Vegfr2-luc males, were imaged from gestational day (GD) 12 to 18 to determine the usefulness of the Vegfr2-luc mouse as a model for studying fetoplacental Vegfr2 activity during pregnancy. Semi-quantitative RT-PCR of Vegfr2 was also performed on whole fetoplacental units during this time. Additionally, resultant neonates were imaged at postnatal day (PND) 7, 14 and 21 to monitor Vegfr2 activity during post-natal development.</p> <p>Results</p> <p>Fetoplacental Vegfr2 gene activity was detected as light emissions beginning on GD 12 of gestation and increased throughout the imaging period (P < 0.05), and this paralleled the Vegfr2 mRNA data obtained from RT-PCR analysis. A decline in fetoplacental light emissions was associated with a poor pregnancy outcome in one pregnancy, indicating that this approach has potential use for studies monitoring pregnancy well being. Additionally, neonatal Vegfr2 activity was detected at PND 7, 14 and 21 but declined with time (P < 0.0001).</p> <p>Conclusions</p> <p><it>In utero </it>fetoplacental Vegfr2 gene activity was monitored longitudinally in a quantitative manner using a luciferase reporter gene and bioluminescent imaging during the latter third of gestation. This study demonstrates the feasibility of using the Vegfr2-luc mouse to monitor late gestation fetoplacental angiogenic activity under normal and experimental conditions. Additionally, neonatal Vegfr2 gene activity was monitored for three weeks postpartum, allowing continuous monitoring of Vegfr2 activity during the latter third of gestation and postnatal development within the same animals.</p

Low Risk Monitoring in Neurocritical Care

Background/Rationale: Patients are admitted to Intensive care units (ICUs) either because they need close monitoring despite a low risk of hospital mortality (LRM group) or to receive ICU specific active treatments (AT group). The characteristics and differential outcomes of LRM patients vs. AT patients in Neurocritical Care Units are poorly understood.Methods: We classified 1,702 patients admitted to our tertiary and quaternary care center Neuroscience-ICU in 2016 and 2017 into LRM vs. AT groups. We compared demographics, admission diagnosis, goal of care status, readmission rates and managing attending specialty extracted from the medical record between groups. Acute Physiology, Age and Chronic Health Evaluation (APACHE) IVa risk predictive modeling was used to assess comparative risks for ICU and hospital mortality and length of stay between groups.Results: 56.9% of patients admitted to our Neuroscience-ICU in 2016 and 2017 were classified as LRM, whereas 43.1% of patients were classified as AT. While demographically similar, the groups differed significantly in all risk predictive outcome measures [APACHE IVa scores, actual and predicted ICU and hospital mortality (p &lt; 0.0001 for all metrics)]. The most common admitting diagnosis overall, cerebrovascular accident/stroke, was represented in the LRM and AT groups with similar frequency [24.3 vs. 21.3%, respectively (p = 0.15)], illustrating that further differentiating factors like symptom duration, neurologic status and its dynamic changes and neuro-imaging characteristics determine the indication for active treatment vs. observation. Patients with intracranial hemorrhage/hematoma were significantly more likely to receive active treatments as opposed to having a primary focus on monitoring [13.6 vs. 9.8%, respectively (p = 0.017)].Conclusion: The majority of patients admitted to our Neuroscience ICU (56.9%) had &lt;10% hospital mortality risk and a focus on monitoring, whereas the remaining 43.1% of patients received active treatments in their first ICU day. LRM Patients exhibited significantly lower APACHE IVa scores, ICU and hospital mortality rates compared to AT patients. Observed-over-expected ICU and hospital mortality ratios were better than predicted by APACHE IVa for low risk monitored patients and close to prediction for actively treated patients, suggesting that at least a subset of LRM patients may safely and more cost effectively be cared for in intermediate level care settings