Search

• A high-fidelity model of CO 2 booster refrigeration systems is proposed. • Critical but normally unavailable in practice variables are inferred. • Model has a minimum requirement on real measurements as inputs. • Onsite data from three UK supermarkets are used for demonstration. • Data integrity and thermodynamic laws are secured in the model. Supermarket refrigeration systems adopting traditional refrigerants with high global warming potential (GWP) have impacts on global warming for indirect and direct greenhouse gases (GHG) emissions. CO 2 is a popular low-GWP alternative. The transcritical operation of CO 2 systems worsens their energy performance, but provides recoverable heat as a heat source to reduce gas consumption. To evaluate operation performance, data-driven models, trained by historical data, are weak in implementation with datasets outside the scope of training data; in contrast, theoretical models have better extrapolation ability to calculate all operation conditions of CO 2 systems at supermarket. Existing theoretical modeling approaches often lack validation against the limited public-access data, which reduces model reliability for further applications, and adopt oversimplified inference methods for unmeasured variables, which increases the risks of breaking thermodynamic laws and lowering model accuracy. This study therefore develops a steady-state theoretical model for CO 2 booster refrigeration systems validated against field measurements from three UK supermarkets. The available measurements are utilized to the best level to ensure model accuracy and physical interpretability. Proposed methods to infer missing variables in CO 2 systems include condenser outlet temperature, evaporating temperature, compressor isentropic efficiency and compressor mass flow rate. Results show that proposed inference methods enhance the abilities of the proposed modeling approach to ensure data integrity, avoid breaking thermodynamic laws, and improve model accuracy by reflecting real-time actual values of unmeasured variables rather than rough assumptions. The proposed modeling approach provides satisfactory accuracy validated using high-resolution measurements across the whole year from three real supermarkets. [ABSTRACT FROM AUTHOR]

• A two-stage gas-coupled Stirling/pulse tube refrigerator with a second-stage active phase shifter is developed. • The effect of the active phase shifter on the acoustic power and phase distribution is investigated. • The regulation of the inter-stage refrigeration capacity shift by the active phase shifter phase and amplitude is analyzed. • Experiment results are carried out to verify the theoretical and simulated analyses. The Stirling/pulse tube cryocooler (SPC) is one of the most promising cryocoolers for space applications due to its advantages like high efficiency and long lifetime. The second pulse tube stage is coaxial pneumatically coupled in series with the first Stirling stage. The SPC possesses a distinctive capability to dynamically adjust the inter-stage refrigeration capacity by actively controlling the Stirling displacer in the first stage. This enables the SPC to effectively cater to varying heat loads over time. Nevertheless, the investigation into the regulation mechanism of the second-stage phase shifter on inter-stage refrigeration capacity shift is hindered by the presence of the second-stage passive phase shifter. This manuscript proposes an SPC with a second-stage active phase shifter (APS), which can actively control the phase difference between the pressure wave and mass flow at the second-stage hot end of the pulse tube in real time. The effect of the APS phase and amplitude on the inter-stage refrigeration capacity shift is analyzed using the theoretical and numerical model proven by the experiment. The first experimentally reported SPC with a second-stage APS demonstrates a refrigeration capacity of 0.22 W at 20 K plus 3.11 W at 70 K, requiring a compressor electrical power of 220 W. The SPC achieves a no-load minimum temperature of 13.5 K. [ABSTRACT FROM AUTHOR]

The variable-geometry ejector (VGE) is feasible for unstable heat-source utilization; the ejector can be adjusted to its design point to obtain high efficiency. Moreover, as the adjustable nozzle in the VGE significantly affects the performance of the ejector, a theoretical model is necessary to evaluate VGE performance. In this study, a two-dimensional theoretical model was proposed based on an adjustable-nozzle theory. Method of characteristics was employed to accurately predict the driving-flow development in the mixing section. In addition, the suction-flow velocity distribution on the effective area was considered. The proposed model was validated by employing the data from literature and additional experimental data obtained from a VGE test setup using R134a. The validation result shows that the proposed model predicts the ejector performance accurately; moreover, the model is more adaptive while the nozzle configuration changes. The theoretical model, proposed herein, is practical for the design and application of the VGE. [ABSTRACT FROM AUTHOR]

Cumulative effects assessment (CEA) is a sub-discipline of environmental impact assessment that is concerned with appraising the collective effects of human activities and natural processes on the environment. Aspirations for CEA have been expressed by many authors since 1969, when the foundation of environmental appraisal was laid by the US National Environmental Policy Act. This paper's purposes are ( i) to review aspirations for CEA, relative to current practice; and ( ii) to fully explain and critique the logic that connects CEA's operational steps and underlying philosophies. A literature review supports the following statements: Some conceptualizations emphasize the delivery of information to support decision making as the key purpose of CEA; others deem collaboration, debate, and learning as most important. Consensus on CEA's operational steps has been reached, but each step requires practitioners to make analytical decisions (e.g., about the scope of issues to include or the time horizon to consider) and objective rules for how to approach those decisions are lacking. Numerical methods for assessing cumulative effects are largely available, meaning that CEA's biggest problems are not scientific. CEA cannot succeed without substantive public engagement, monitoring, and adaptive management. CEA is best undertaken regionally, rather than project-by-project. CEA and planning are complementary, and should be merged. In its most enlightened form, CEA is a useful tool for ensuring that human undertakings ultimately conform to Earth's finite biosphere, but current practice falls short of the ideal, and CEA's logical derivation is not entirely sound. As regards CEA's big problems, sustainability has not been defined clearly enough to make criteria for judging the significance of cumulative effects indisputable; legal, regulatory, and institutional frameworks are poorly aligned for CEA; and objective criteria for judging the adequacy of CEA's scope, scale, and thresholds do not exist, which makes the question of how to provide general guidance to practitioners intractable. Recommendations call for sustainability goals to be clearly expressed as measurable targets. Furthermore, precaution in human enterprise should be exercised by avoiding, minimizing, restoring, and offsetting negative cumulative effects. CEA can assist by quantifying and optimizing trade-offs. [ABSTRACT FROM AUTHOR]

Asthma is a very common chronic disease that occurs in all age groups and is the focus of various clinical and public health nterventions. Both morbidity and mortality from asthma are significant. The number of disability-adjusted life years (DALYs) lost due to asthma worldwide is similar to that for diabetes, liver cirrhosis and schizophrenia. Asthma management plans have, however, reduced mortality and severity in countries where they have been applied. Several barriers reduce the availability, affordability, dissemination and efficacy of optimal asthma management plans in both developed and developing countries. The workplace environment contributes significantly to the general burden of asthma. Patients with occupational asthma have higher rates of hospitalization and mortality than healthy workers. The surveillance of asthma as part of a global WHO programme is essential. The economic cost of asthma is considerable both in terms of direct medical costs (such as hospital admissions and the cost of pharmaceuticals) and indirect medical costs (such as time lost from work and premature death). Direct cost are significant in most countries. In order to reduce costs and improve quality of care, employers and health plans are exploring more precisely targeted ways of controlling rapidly rising health costs. Poor control of asthma symptoms is a major issue that can result in adverse clinical and economic outcomes. A model of asthma costs is needed to aid attempts to reduce them while permitting optimal management of the disease. This paper presents a discussion of the burden of asthma and its socioeconomic implications and proposes a model to predict the costs incurred by the disease. [ABSTRACT FROM AUTHOR]

The emerging HIV epidemics in countries of Asia and Eastern Europe will contribute significantly to the future of the HIV pandemic. Forecasts of the scale of these epidemics are subject to massive uncertainty, however, mainly because of the sensitivity of predictions to small alterations in parameters that are difficult to estimate. In most of these countries, HIV is currently concentrated among vulnerable populations such as injecting drug users, sex workers and their clients, or men who have sex with men. This distribution suggests an alternative to disease forecasting based on the techniques of risk assessment routinely used by environmental epidemiologists. Exposure mapping, dose-response curves and the concept of acceptable risk are some of the tools that may be useful for HIV risk management. This approach is illustrated by a description of exposure in Indonesia and an assessment of currently accepted risk of death for different causes including HIV in the Russian Federation. Although inappropriate for forecasts of heterosexual HIV transmission, mathematical models are shown to be useful for making qualitative predictions about the relative importance of different behaviours for the spread of HIV over time and for interpreting observed trends in HIV prevalence from sentinel surveillance sites. [ABSTRACT FROM AUTHOR]

Objective To quantify the public health and economic burden of endemic canine rabies in Africa and Asia. Methods Data from these regions were applied to a set of linked epidemiological and economic models. The human population at risk from endemic canine rabies was predicted using data on dog density, and human rabies deaths were estimated using a series of probability steps to determine the likelihood of clinical rabies developing in a person after being bitten by a dog suspected of having rabies. Model outputs on mortality and morbidity associated with rabies were used to calculate an improved disability-adjusted life year (DALY) score for the disease. The total societal cost incurred by the disease is presented. Findings Human mortality from endemic canine rabies was estimated to be 55 000 deaths per year (90% confidence interval (CI) = 24 000-93 000). Deaths due to rabies are responsible for 1.74 million DALYs lost each year (90% CI = 0.75-2.93). An additional 0.04 million DALYs are lost through morbidity and mortality following side-effects of nerve-tissue vaccines. The estimated annual cost of rabies is US$ 583.5 million (90% CI = US$ 540.1-626.3 million). Patient-borne costs for post-exposure treatment form the bulk of expenditure, accounting for nearly half the total costs of rabies. Conclusions Rabies remains an important yet neglected disease in Africa and Asia. Disparities in the affordability and accessibility of post-exposure treatment and risks of exposure to rabid dogs result in a skewed distribution of the disease burden across society, with the major impact falling on those living in poor rural communities, in particular children. [ABSTRACT FROM AUTHOR]