Analysis of the Inner Fluid-Dynamics of Scroll Compressors and Comparison between CFD Numerical and Modelling Approaches

Scroll compressors are widely adopted machines in both refrigeration systems and heat pumps. However, their efficiency is basically poor and constitutes the main bottleneck for improving the overall system performance. In fact, due to the complex machine fluid dynamics, scroll design is mainly based on theoretical and/or semi-empirical approaches. Designs strategies that do not guarantee an in-depth analysis of the machine behavior can be supplemented with a Computation Fluid Dynamics (CFD) approach. To this purpose, in the present work, the scroll compressor inner fluid dynamics is numerically analyzed in detail using two CFD software and two different modelling strategies for the axial gap. The analysis of the fluid evolution within the scroll wraps reveals unsteady phenomena developing during the suction and discharge phases, amplified by the axial clearance with negative impact on the main fluid flow (e.g., 1213% of average mass flow rate for an axial gap of 30 \ub5) and on the scroll performance (e.g., +26% of average absorbed power for an axial gap of 30 \ub5). In terms of accuracy, the k-" offers good performance on the estimation of average quantities but proves to be inadequate for capturing the complexity of the unsteady phenomena caused by the axial gap (e.g., 1219% of the absorbed power in case of perfect tip seal). The need for considering specific geometric details in design procedures is highlighted, and guidelines on the choice of the most suitable numerical model are provided depending on the analysis need

Uncertainty quantification and missing data for turbomachinery with probabilistic equivalence and arbitrary polynomial chaos, applied to scroll compressors

This work presents a framework for predicting unknown input distributions for turbomachinery applications starting from scarce experimental measurements. The problem is relevant to turbomachinery where important parameters are obtained using indirect measurements. In this paper a scroll compressor is used as example but the suggested framework is completely general and can be used to infer missing data on material composition (carbon fiber properties, laser melted specimens for additive manufacturing etc) or input data (such as the turbine inlet temperature). Scroll compressors are small devices with a very complex geometry that is difficult to measure. Moreover these compressors are highly sensitive to manufacturing errors and clearances. For these reasons we have chosen this example as an ideal candidate to prove the effectiveness of the framework. An input probability distribution for the scroll height is recovered based on a scarce, synthetic data set. The scroll height is used as an example of a missing distribution for a geometric parameter as it has the highest variance and is challenging to measure experimentally. The framework consists of two main building blocks: an equivalence in a probabilistic sense and a Non-Intrusive Polynomial Chaos formulation able to deal with scarce data. The probabilistic equivalence is defined by a Probability Density Function (PDF) matching approach in which the statistical distance between probability distributions is quantified by either the Kolmogorov-Smirnov (KS) distance or the Kullback-Leibler (KL) divergence. By representing the missing inputs with a generalised Polynomial Chaos Expansion (gPCE) the back-calculation problem can be recast as an optimisation problem in which an arbitrary Polynomial Chaos (aPC) formulation was used to propagate the uncertain input distributions through a computational model of the system and generate a probability distribution for the Quantity of Interest (QoI). The framework has been tested with multiple non-Askey scheme distributions to prove the generality of the proposed approach

Imaging transcriptomics: Convergent cellular, transcriptomic, and molecular neuroimaging signatures in the healthy adult human brain

The integration of transcriptomic and neuroimaging data, “imaging transcriptomics,” has recently emerged to generate hypotheses about potential biological pathways underlying regional variability in neuroimaging features. However, the validity of this approach is yet to be examined in depth. Here, we sought to bridge this gap by performing transcriptomic decoding of the regional distribution of well-known molecular markers spanning different elements of the biology of the healthy human brain. Imaging transcriptomics identifies biological and cell pathways that are consistent with the known biology of a wide range of molecular neuroimaging markers. The extent to which it can capture patterns of gene expression that align well with elements of the biology of the neuroinflammatory axis, at least in healthy controls without a proinflammatory challenge, is inconclusive. Imaging transcriptomics might constitute an interesting approach to improve our understanding of the biological pathways underlying regional variability in a wide range of neuroimaging phenotypes

Short and long-term results of air-filled intragastric balloon in obese patients

Introduction: The aim of this study was to analyze the effect of the Heliosphere\uae BAG in terms of early weight reduction and trend of weight at a distance of 18 months after removal. Methods: Between November 2006 and November 2010, 45 patients underwent the placement of endoscopic intragastric air-filled balloon. All patients were selected by a multidisciplinary team according to international guidelines. At 18 months after removal, weight control was performed by telephone questionnaire. Results: 32 patients completed the 6-month stay of the balloon and showed a mean weight reduction of 12 Kg with a reduction in BMI of about 5 points. 15 were contacted by telephone 18 months after device removal: the mean basal BMI was 40.62 kg/ m2 and mean weight was 113.37 Kg. The mean BMI at the end of 6 months was 35.75 kg/m2 and the mean weight was 99.75 kg; the BMI at 18 months after removal was 37.28 kg/m2 and the mean weight was 103.56 kg. No technical problems were recorded at balloon insertion and removal. Conclusion: Heliosphere\uae BAG showed good weight loss in the short term. In patients with 18 months follow-up, we observed a minimal weight increase (a mean of 4 kg). This device, within a few months after removal, may reduce surgical and anesthesiological risks for bariatric or other elective surgery. Moreover Heliosphere\uae BAG with dietary support can offer a potential benefit in the long-term treatment of obesity