A Discussion about the Methodology to Validate the Correlations of Heat Transfer Coefficients and Pressure Drop during the Condensation in a Finned-Tube Heat Exchanger

As already demonstrated by others authors, when the performance of a heat exchanger is analyzed, a semi-empirical model allows getting good prediction of the experimental results provided that it is accompanied by the application of the suitable correlations for calculating heat transfer coefficients (HTC) and pressure drop (PD) in both refrigerant and air side. Many correlations for calculating these coefficients are available in literature, therefore choose the more suitable of them turns out to be not an easy task. This paper presents a discussion about the methodology to perform a comparison aimed to define the criterion for choosing the most suitable correlation to be used in a simulation model for prediction of heat exchangers performance in refrigeration systems. Differently from others works, where the results of each correlation are compared with those obtained by means specific experiments focused on the local phenomenon visualization, in this work the correlations are compared against the measurements of a complete finned-tube condenser integrated in a traditional air-to-water heat pump. The comparison has been carried out using a model able to discretize the heat exchanger through a finite volume method (FVM). The discussion is supported with a case study which was experimentally tested and numerically modeled. The condenser is a finned tube coil that characterized by two asymmetric circuits. The tube diameter is 7 mm and the fin pitch is 2.6 mm. The experimental test bench includes a single-speed 34.3 cm3 reciprocating-hermetic compressor, a plate evaporator and an electronic valve as expansion device. An accumulator allow adjusting the condenser sub-cooling. A specific test campaign has been designed in order to cover a wide range operating points of the condenser: different air velocities (from 1.5 m/s to 4 m/s), inlet temperatures (20-46°C) and sub-cooling (0-5-10°C) have been taken into account. All the correlations considered were programmed and simulated with the software IMST-ART. In order to avoid the overlapping of the effects of the different correlations, during the analysis of the two-phase flow, the heat transferred in the one-phase section of the exchanger and the air-side heat transfer coefficient were maintained constant. The analysis of air-side heat transfer coefficient and pressure drop was carried out in the same way but keeping constant the coefficients of the refrigerant side. Different accuracy parameters were defined in order to assist the final decision about which correlation is able to provide the best agreement with experimental data. The paper aims to present a discussion about the validation methodology, the analysis of the correlations impact on the model results rather than define the parameters to choose the best correlation

Role of age and comorbidities in mortality of patients with infective endocarditis

[Purpose]: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. [Methods]: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015.Patients were stratified into three age groups:<65 years,65 to 80 years,and ≥ 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. [Results]: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 ≥ 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients ≥80 years who underwent surgery were significantly lower compared with other age groups (14.3%,65 years; 20.5%,65-79 years; 31.3%,≥80 years). In-hospital mortality was lower in the <65-year group (20.3%,<65 years;30.1%,65-79 years;34.7%,≥80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%,≥80 years; p = 0.003).Independent predictors of mortality were age ≥ 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI ≥ 3 (HR:1.62; 95% CI:1.39–1.88),and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared,the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. [Conclusion]: There were no differences in the clinical presentation of IE between the groups. Age ≥ 80 years, high comorbidity (measured by CCI),and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Magnetic structures and magnetocaloric effect in RVO4(R = Gd, Nd)

We report the magnetic properties and magnetic structure of the zircon-type compound GdVO4, together with the magnetic structure of the isostructural NdVO4. At T≃2.5 K, GdVO4 undergoes a phase transition to antiferromagnetic Gz, driven mainly by the exchange interactions, while the magnetic anisotropy and dipolar interactions are minor contributions. Near the liquid-helium boiling temperature, the magnetocaloric effect of GdVO4 is nearly as large as that of the structurally closely related GdPO4. It is noteworthy that GdVO4 has been recently proposed as a good passive regenerator in Gifford-McMahon cryocoolers, since adding a magnetization-demagnetization stage to the cryocooler refrigeration cycle would increase its efficiency for liquefying helium. NdVO4 is a canted Gz-type antiferromagnet and shows enhancement of the magnetic reflections in neutron diffraction below ca. 500 mK, due to the polarization of the Nd nuclei by the hyperfine field.M.E. thanks the Donostia International Physics Center (DIPC) for the support of his stay in San Sebastián. This work has been funded by the Spanish Ministerio de Economía, Industria y Competitividad through Projects No. MAT2017-86019-R and No. MAT2015-68204-R, DGA Consolidated Group E100, and Comunidad de Madrid Project S2009/PPQ1626.Peer reviewe

Contemporary use of cefazolin for MSSA infective endocarditis: analysis of a national prospective cohort

Objectives: This study aimed to assess the real use of cefazolin for methicillin-susceptible Staphylococcus aureus (MSSA) infective endocarditis (IE) in the Spanish National Endocarditis Database (GAMES) and to compare it with antistaphylococcal penicillin (ASP). Methods: Prospective cohort study with retrospective analysis of a cohort of MSSA IE treated with cloxacillin and/or cefazolin. Outcomes assessed were relapse; intra-hospital, overall, and endocarditis-related mortality; and adverse events. Risk of renal toxicity with each treatment was evaluated separately. Results: We included 631 IE episodes caused by MSSA treated with cloxacillin and/or cefazolin. Antibiotic treatment was cloxacillin, cefazolin, or both in 537 (85%), 57 (9%), and 37 (6%) episodes, respectively. Patients treated with cefazolin had significantly higher rates of comorbidities (median Charlson Index 7, P <0.01) and previous renal failure (57.9%, P <0.01). Patients treated with cloxacillin presented higher rates of septic shock (25%, P = 0.033) and new-onset or worsening renal failure (47.3%, P = 0.024) with significantly higher rates of in-hospital mortality (38.5%, P = 0.017). One-year IE-related mortality and rate of relapses were similar between treatment groups. None of the treatments were identified as risk or protective factors. Conclusion: Our results suggest that cefazolin is a valuable option for the treatment of MSSA IE, without differences in 1-year mortality or relapses compared with cloxacillin, and might be considered equally effective