R1234yf FLOW BOILING HEAT TRANSFER INSIDE A 3.4 mm ID MICROFIN TUBE

The use of synthetic refrigerants with a non-negligible Global Warming Potential or, on the contrary, of natural but flammable or toxic natural fluids calls for the charge minimization of the refrigerating and air conditioning equipment. The refrigerant charge minimization as well as the use of eco-friendly fluids can therefore be considered two of the most important targets for these applications to cope with the new environmental challenges. Traditional microfin tubes are also widely used in air and water heat exchangers for heat pump and refrigerating applications during condensation or evaporation. The possible downsizing of microfin tubes can lead to more efficient and compact heat exchangers and thus to a reduction of the refrigerant charge of the systems. Furthermore, over the last several years, much research and development effort has been focused on potential refrigerants possessing low GWPs. Among the fluorinated propene isomers which have normal boiling point temperature data published in the public domain, several have low GWP and normal boiling temperatures relatively close to R134a; among them, R1234yf has as a normal boiling temperature approximately 3.4°C lower than that of R134a, with a GWP=4. This paper presents the R1234yf flow boiling heat transfer and pressure drop measurements inside a small microfin tube with internal diameter at the fin tip of 3.4 mm. This study is carried out in an experimental facility built at the Dipartimento di Ingegneria Industriale of the University of Padova especially designed to study both single and two phase heat transfer processes. The microfin tube is brazed inside a copper plate and electrically heated from the bottom. Several T-type thermocouples are inserted in the wall to measure the temperature distribution during the phase change process. In particular, the experimental measurements were carried out at constant saturation temperature of 30 °C, by varying the refrigerant mass velocity between 190 kg m-2 s-1 and 940 kg m-2 s-1, the vapour quality from 0.2 to 0.99, at three different heat fluxes: 10, 25, and 50 kW m-2. The experimental results are presented in terms of two-phase heat transfer coefficient, onset dryout vapour quality, and frictional pressure drop as a function of the operative test conditions

KEYNOTE PAPER UPDATE ON CONDENSATION HEAT TRANSFER AND PRESSURE DROP INSIDE MINICHANNELS

ABSTRACT The present paper reviews published experimental work focusing on condensation flow regimes, heat transfer and pressure drop in minichannels. New experimental data are available with high pressure (R410A), medium (R134a) and low pressure (R236ea) refrigerants in minichannels of different cross section geometry and with hydraulic diameters ranging from 0.4 to 3 mm. Because of the influence of flow regimes on heat transfer and pressure drop, a literature review is presented to discuss flow regimes transitions. The available experimental frictional pressure gradients and heat transfer coefficients are compared with semi empirical and theoretical models developed for conventional channels and with models specifically created for minichannels. Starting from the results of the comparison between experimental data and models, the paper will discuss and evaluate the opportunity for a new heat transfer model for condensation in minichannels; the new model attempts to take into account the effect of the entrainment rate of droplets from the liquid film

Análise do número de procedimentos de angioplastia transluminal percutânea em um serviço de alta complexidade no município de Cascavel – Paraná

Objetivo: Analisar o número de procedimentos de angioplastia transluminal realizados na cidade de Cascavel-PR, no período de junho de 2020 a julho de 2021 no hospital São Lucas comparando-se com a literatura atual no mesmo período. Métodos: Trata-se de um estudo transversal, observacional, quantitativo e descritivo. Os dados foram coletados através de prontuários do SAME (Sistema de Arquivamento Médico Hospitalar). Foram considerados pacientes de ambos os sexos, acima de 40 anos de idade e com indicação para realizar a angioplastia transluminal percutânea. Resultados: Do total de procedimentos avaliados (n=101), houve um aumento na realização de angioplastias de 2020 para 2021, sendo 71,3% dos pacientes, homens, com aumento na média de idade de um ano para o outro e no período de junho-dezembro de 2020 mais da metade dos casos (57,5%) foram na artéria descendente anterior, sendo que 37% dos casos eram de IAM com supra ST. Essa prevalência se manteve em 2021. Foram identificados cinco óbitos, com taxa de mortalidade de 4,9%. Conclusão: Mesmo em um contexto de pandemia, o número de angioplastias aumentou 52,5% no período analisado no hospital São Lucas em Cascavel -PR

Structural determinants of the specificity for synaptic vesicle-associated membrane protein/synaptobrevin of tetanus and botulinum type B and G neurotoxins

Tetanus and botulinum neurotoxins type B and G are zinc-endopeptidases of remarkable specificity. They recognize and cleave a synaptic vesicle- associated membrane protein (VAMP)/synaptobrevin, an essential protein component of the vesicle docking and fusion apparatus. VAMP contains two copies of a nine-residue motif, also present in SNAP-25 (synaptosomal- associated protein of 25 kDa) and syntaxin, the two other substrates of clostridial neurotoxins. This motif was suggested to be a determinant of the target specificity of neurotoxins. Antibodies raised against this motif cross-react among VAMP, SNAP-25, and syntaxin and inhibit the proteolytic activity of the neurotoxins. Moreover, the various neurotoxins cross-inhibit each other's proteolytic action. The role of the three negatively charged residues of the motif in neurotoxin recognition was probed by site-directed mutagenesis. Substitution of acidic residues in both copies of the VAMP motif indicate that the first one is involved in tetanus neurotoxin recognition, whereas the second one is implicated in binding botulinum B and G neurotoxins. These results suggest that the two copies of the motif have a tandem association in the VAMP molecule

From Monoamine Oxidase Inhibition to Antiproliferative Activity: New Biological Perspectives for Polyamine Analogs

: Monoamine oxidases (MAOs) are well-known pharmacological targets in neurological and neurodegenerative diseases. However, recent studies have revealed a new role for MAOs in certain types of cancer such as glioblastoma and prostate cancer, in which they have been found overexpressed. This finding is opening new frontiers for MAO inhibitors as potential antiproliferative agents. In light of our previous studies demonstrating how a polyamine scaffold can act as MAO inhibitor, our aim was to search for novel analogs with greater inhibitory potency for human MAOs and possibly with antiproliferative activity. A small in-house library of polyamine analogs (2-7) was selected to investigate the effect of constrained linkers between the inner amine functions of a polyamine backbone on the inhibitory potency. Compounds 4 and 5, characterized by a dianiline (4) or dianilide (5) moiety, emerged as the most potent, reversible, and mainly competitive MAO inhibitors (Ki < 1 μM). Additionally, they exhibited a high antiproliferative activity in the LN-229 human glioblastoma cell line (GI50 < 1 μM). The scaffold of compound 5 could represent a potential starting point for future development of anticancer agents endowed with MAO inhibitory activity

Insight into the mechanism of ferroptosis inhibition by ferrostatin-1

Ferroptosis is a form of cell death primed by iron and lipid hydroperoxides and prevented by GPx4. Ferrostatin-1 (fer-1) inhibits ferroptosis much more efficiently than phenolic antioxidants. Previous studies on the antioxidant efficiency of fer-1 adopted kinetic tests where a diazo compound generates the hydroperoxyl radical scavenged by the antioxidant. However, this reaction, accounting for a chain breaking effect, is only minimally useful for the description of the inhibition of ferrous iron and lipid hydroperoxide dependent peroxidation. Scavenging lipid hydroperoxyl radicals, indeed, generates lipid hydroperoxides from which ferrous iron initiates a new peroxidative chain reaction. We show that when fer-1 inhibits peroxidation, initiated by iron and traces of lipid hydroperoxides in liposomes, the pattern of oxidized species produced from traces of pre-existing hydroperoxides is practically identical to that observed following exhaustive peroxidation in the absence of the antioxidant. This supported the notion that the anti-ferroptotic activity of fer-1 is actually due to the scavenging of initiating alkoxyl radicals produced, together with other rearrangement products, by ferrous iron from lipid hydroperoxides. Notably, fer-1 is not consumed while inhibiting iron dependent lipid peroxidation. The emerging concept is that it is ferrous iron itself that reduces fer-1 radical. This was supported by electroanalytical evidence that fer-1 forms a complex with iron and further confirmed in cells by fluorescence of calcein, indicating a decrease of labile iron in the presence of fer-1. The notion of such as pseudo-catalytic cycle of the ferrostatin-iron complex was also investigated by means of quantum mechanics calculations, which confirmed the reduction of an alkoxyl radical model by fer-1 and the reduction of fer-1 radical by ferrous iron. In summary, GPx4 and fer-1 in the presence of ferrous iron, produces, by distinct mechanism, the most relevant anti-ferroptotic effect, i.e the disappearance of initiating lipid hydroperoxides

Historical Perspectives and Guidelines for Botulinum Neurotoxin Subtype Nomenclature

Botulinum neurotoxins are diverse proteins. They are currently represented by at least seven serotypes and more than 40 subtypes. New clostridial strains that produce novel neurotoxin variants are being identified with increasing frequency, which presents challenges when organizing the nomenclature surrounding these neurotoxins. Worldwide, researchers are faced with the possibility that toxins having identical sequences may be given different designations or novel toxins having unique sequences may be given the same designations on publication. In order to minimize these problems, an ad hoc committee consisting of over 20 researchers in the field of botulinum neurotoxin research was convened to discuss the clarification of the issues involved in botulinum neurotoxin nomenclature. This publication presents a historical overview of the issues and provides guidelines for botulinum neurotoxin subtype nomenclature in the future.Peer reviewe

Mini Vapour Cycle System For High Density Electronic Cooling Applications

This paper reports the preliminary experimental results of a mini Vapour Cycle System (VCS) for electronic thermal management applications. The water cooled miniature scale refrigeration system uses R134a as working fluid and implements a new concept oil-free linear compressor prototype. In the range of operating test conditions investigated, the cooling capacity of the system varied from 46 to 310 W while the coefficient of performance (COP) ranged between 1.05 and 5.54. Particular attention was dedicated to the cold plate design, which had to meet the requirements established by the aeronautical standards. The cold plate was equipped with 15 thermocouples in order to analyze the wall temperatures distribution. The suitability and feasibility of the proposed cold plate for electronic thermal management in aeronautical environment is critically discussed, basing on the experimental results

R32 Partial Condensation Inside A Brazed Plate Heat Exchanger

It is well known that when a superheated gas reaches a cold surface, the condensation starts immediately only if the wall temperature is lower than the dew temperature of the refrigerant; in this case, the heat transfer phenomenon can be also affected by the superheating temperature. This paper presents the experimental measurements of the heat transfer coefficient carried out during partial condensation of superheated R32 refrigerant in a commercial brazed plate heat exchanger prototype. The present work aims at highlighting the effects of the superheating during the partial condensation of R32 by imposing 5, 10, 15, and 25 K of vapour superheating at the inlet of the brazed plate heat exchanger prototype. The experimental measurements were carried out by varying the specific mass velocity between 15 and 40 kg m-2 s-1 and the outlet vapour quality between 0.0 and 0.65. The experimental data were collected at around 36.5 °C saturation temperature (saturation pressure of 2.27 MPa). The present data is used to validate a new step-by-step model for the calculation of the heat transfer coefficient, which accounts for the different superheating inlet temperatures