Performance Analysis of a Reciprocating Compressor under Typical Transients of Refrigeration Systems

The performance of reciprocating compressors is usually evaluated under steady-state operating conditions defined in standards. However, the compressor is submitted to quite different conditions in actual refrigeration systems, such as transients associated with the on/off cycling operation. This paper presents a simulation model developed to evaluate the performance of reciprocating compressors during typical transients of refrigeration systems. The model is formed by the coupling of two sub models, one for the compression chamber and the other to calculate the temperatures and mass flow rates in components other than the compression chamber. As the model only simulates the compressor, experimental data was required to provide input from the remaining components of the system. The model was validated by comparing predictions and experimental data of discharged mass flow rate and power consumption of a compressor operating under two transient system conditions. Then, the simulation model was employed to predict the variation of the compressor efficiencies and temperatures during the typical transients analyzed

Comparative Analysis of Two Types of Positive Displacement Compressors for Air Conditioning Applications

Different types of positive displacement compressors are employed in low-capacity air conditioning applications. Understanding the advantages and drawbacks of each of these technologies is important in order to identify the ranges of cooling capacities at which a specific compression technology is more efficient. This paper presents a comparative analysis between two positive displacement compressors (rolling piston and scroll) designed for air conditioning applications. The compressors operate with R-22 and present a nominal cooling capacity of 18000 BTU/h at the AHRI-A checkpoint condition. First, the compressors were tested in a hot-cycle test bench to measure the mass flow rate and power consumption for MBP and HBP operating conditions. The results showed that the most efficient compressor depends on the operating condition. Â After this, simulation models for each compressor were validated against the experimental data, showing good agreement. Therefore, through the simulation models, it was possible to evaluate the effect of different aspects, such as leakage, heat transfer and discharge process, on the efficiency of each compressor

Experimental Determination of Correlations for Heat Transfer Coefficients in the Suction Muffler of a Hermetic Reciprocating Compressor

The efficiency and reliability of hermetic reciprocating compressors adopted for household refrigeration are affected by the temperature distribution of their components. Simulation models developed to assist the thermal design of compressors require heat transfer coefficients in different components, usually estimated from correlations available for simplified geometries. However, the geometries of some components are complex and require more representative heat transfer coefficients. This paper presents experimental results for heat transfer coefficients obtained from measurements of heat flux and temperature in different regions of the suction muffler of a small reciprocating compressor under different operating conditions. A least square method was employed to obtain correlations for local heat transfer coefficients, which were then compared with estimates given by correlations available in the literature for simplified geometries

Experimental Investigation of Heat Transfer in Components of a Hermetic Reciprocating Compressor under Thermal Transient

Heat transfer has an important role on the efficiency and reliability of hermetic reciprocating compressors adopted for household refrigeration. Most analyses of such compressors are carried out for fully-cyclic operating conditions based on established procedures and standards. However, since household refrigeration systems work by alternating periods in which the compressor is on (ON) and idle (OFF), the performance assessment of compressors should take into account the ON/OFF cyclic operation. This paper presents an experimental study of the heat transfer in components of a hermetic reciprocating compressor during thermal transients due to ON/OFF cyclic operation. The compressor was instrumented with thin-film heat flux sensors and thermocouples to evaluate time-varying heat transfer coefficients. We found that heat flux in some regions is significantly affected by the cyclic operating condition. Moreover, the investigation revealed the presence of different time scales due to distinct thermal inertia and heat transfer associated with each component

Experimental Investigation of Damping Coefficient for Compressor Reed Valves

Reed valve dynamics has a major role on the performance and reliability of compressors and has been the subject of many studies over the years. In terms of mathematical modeling, most of these studies describe valve dynamics through a mass-spring-damper system, in which a damping coefficient has to be empirically adjusted. This is a consequence of little knowledge about the effect of different parameters on valve damping. For instance, in spite of great effort to understand viscous effects on the pressure distribution acting on the valve surface, very few works have addressed such effects on valve damping, especially for valve geometries found in compressors. The present study aims to experimentally quantify valve damping under controlled conditions, considering the effects of clamping geometry, clamping force, gasket thickness and the presence of fluid around the valve. Finally, experimental data of damping coefficients are used to predict valve dynamics and compressor efficiency. We found that the damping coefficients of typical valves adopted in small reciprocating compressors have negligible effect on compressor efficiency and valve bending stress, but can change by up to17% the valve impact velocity against the seat

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks

Rising rural body-mass index is the main driver of the global obesity epidemic in adults

Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities(.)(1,2) This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity(3-6). Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017-and more than 80% in some low- and middle-income regions-was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing-and in some countries reversal-of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.Peer reviewe

Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era

The LHCb Upgrade II will fully exploit the flavour-physics opportunities of the HL-LHC, and study additional physics topics that take advantage of the forward acceptance of the LHCb spectrometer. The LHCb Upgrade I will begin operation in 2020. Consolidation will occur, and modest enhancements of the Upgrade I detector will be installed, in Long Shutdown 3 of the LHC (2025) and these are discussed here. The main Upgrade II detector will be installed in long shutdown 4 of the LHC (2030) and will build on the strengths of the current LHCb experiment and the Upgrade I. It will operate at a luminosity up to 2×1034 cm−2s−1, ten times that of the Upgrade I detector. New detector components will improve the intrinsic performance of the experiment in certain key areas. An Expression Of Interest proposing Upgrade II was submitted in February 2017. The physics case for the Upgrade II is presented here in more depth. CP-violating phases will be measured with precisions unattainable at any other envisaged facility. The experiment will probe b → sl+l−and b → dl+l− transitions in both muon and electron decays in modes not accessible at Upgrade I. Minimal flavour violation will be tested with a precision measurement of the ratio of B(B0 → μ+μ−)/B(Bs → μ+μ−). Probing charm CP violation at the 10−5 level may result in its long sought discovery. Major advances in hadron spectroscopy will be possible, which will be powerful probes of low energy QCD. Upgrade II potentially will have the highest sensitivity of all the LHC experiments on the Higgs to charm-quark couplings. Generically, the new physics mass scale probed, for fixed couplings, will almost double compared with the pre-HL-LHC era; this extended reach for flavour physics is similar to that which would be achieved by the HE-LHC proposal for the energy frontier

LHCb upgrade software and computing : technical design report

This document reports the Research and Development activities that are carried out in the software and computing domains in view of the upgrade of the LHCb experiment. The implementation of a full software trigger implies major changes in the core software framework, in the event data model, and in the reconstruction algorithms. The increase of the data volumes for both real and simulated datasets requires a corresponding scaling of the distributed computing infrastructure. An implementation plan in both domains is presented, together with a risk assessment analysis

Contributions of mean and shape of blood pressure distribution to worldwide trends and variations in raised blood pressure: A pooled analysis of 1018 population-based measurement studies with 88.6 million participants

© The Author(s) 2018. Background: Change in the prevalence of raised blood pressure could be due to both shifts in the entire distribution of blood pressure (representing the combined effects of public health interventions and secular trends) and changes in its high-blood-pressure tail (representing successful clinical interventions to control blood pressure in the hypertensive population). Our aim was to quantify the contributions of these two phenomena to the worldwide trends in the prevalence of raised blood pressure. Methods: We pooled 1018 population-based studies with blood pressure measurements on 88.6 million participants from 1985 to 2016. We first calculated mean systolic blood pressure (SBP), mean diastolic blood pressure (DBP) and prevalence of raised blood pressure by sex and 10-year age group from 20-29 years to 70-79 years in each study, taking into account complex survey design and survey sample weights, where relevant. We used a linear mixed effect model to quantify the association between (probittransformed) prevalence of raised blood pressure and age-group- and sex-specific mean blood pressure. We calculated the contributions of change in mean SBP and DBP, and of change in the prevalence-mean association, to the change in prevalence of raised blood pressure. Results: In 2005-16, at the same level of population mean SBP and DBP, men and women in South Asia and in Central Asia, the Middle East and North Africa would have the highest prevalence of raised blood pressure, and men and women in the highincome Asia Pacific and high-income Western regions would have the lowest. In most region-sex-age groups where the prevalence of raised blood pressure declined, one half or more of the decline was due to the decline in mean blood pressure. Where prevalence of raised blood pressure has increased, the change was entirely driven by increasing mean blood pressure, offset partly by the change in the prevalence-mean association. Conclusions: Change in mean blood pressure is the main driver of the worldwide change in the prevalence of raised blood pressure, but change in the high-blood-pressure tail of the distribution has also contributed to the change in prevalence, especially in older age groups