Evaluation of the liquid channel influence on heat transfer performance in a plate-fin heat exchanger by means of three-dimensional CFD simulations

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Compact Heat Exchangers (CHEs) play an important role in a wide range of applications, e.g. in windmill gear units, machine tools, mobile hydraulic systems and so on. For each field, specific requirements are needed (i.e. heat transfer rate, mass, size and pressure drop), which are achieved also through different types of configuration for the fin geometry in both the oil and the air channel. By means of CFD simulations of a small part of the CHE core, it is possible to know how a certain coupling of air and oil channels performs. However, when the number of configurations to be analysed is consistent, it is preferable to choose the smallest meaningful computational domain, in order to reduce computational resources while keeping all important physical phenomena. The purpose of this paper is to demonstrate that, despite oil flow can lead to convective heat transfer coefficient several times higher with respect to air flow, a change in the fin geometry affects significantly the “conjugate heat transfer” and the CHE performance. Besides, it is presented a simplified model for the heat exchanger element where the oil channel conductive and convective heat exchange are modelled by using a fixed temperature boundary condition and an effective thermal resistance. 3-D simulations were carried out considering a fixed fin geometry for the air channel and five different fin geometries for the oil channel. Two cases of operative conditions were taken into account. Furthermore, for each coupling of channels, the simplified model was applied. Results demonstrate that a change in the fin geometry for the oil channel affects the overall heat transfer, and this influence is greater or smaller depending on the operative conditions. Secondly, the reduced model is shown to yield results with a reduction in accuracy that can not be neglected.dc201

Performance Analysis of a Novel Air-based Cavity Receiver

AbstractIn this paper a new design of a novel CSP cavity receiver for parabolic trough collector is analyzed by means of an analytical Matlab model. The receiver, designed by the Swiss company Airlight Energy Manufacturing SA, is 212 m long consisting essentially of a feed pipe, a run-back pipe and 4608 helically coiled heat exchangers designed to capture the incident solar energy concentrated by a parabolic trough. The heat transfer fluid is air heated to temperatures above 600°C.The analytical Matlab model based on a pneumatic - electric circuit analogy was developed to assess the receiver performance in terms of mass flow rate distribution, pressure drop, air outlet temperature and thermal efficiency. A solution was proposed to approximately ensure the same mass flow rate for each cavity.Different skew angles for the incoming solar radiation were considered and the receiver geometry was optimized minimizing the pressure drop and the thermal losses through the runback pipe. The main requirement was to achieve, at the outlet section of the receiver, an air temperature of 650°C; therefore, the total inlet mass flow rate was tuned accordingly.The helically coiled heat exchanger and the receiver insulation sub-models were validated against accurate computational fluid dynamics simulations

Vitamin D and ω-3 Supplementations in Mediterranean Diet During the 1st Year of Overt Type 1 Diabetes: A Cohort Study

Vitamin D and omega 3 fatty acid (\u3c9-3) co-supplementation potentially improves type 1 diabetes (T1D) by attenuating autoimmunity and counteracting inflammation. This cohort study, preliminary to a randomized control trial (RCT), is aimed at evaluating, in a series of T1D children assuming Mediterranean diet and an intake of cholecalciferol of 1000U/day from T1D onset, if \u3c9-3 co-supplementation preserves the residual endogen insulin secretion (REIS). Therefore, the cohort of 22 \u201cnew onsets\u201d of 2017 received \u3c9-3 (eicosapentenoic acid (EPA) plus docosahexaenoic acid (DHA), 60 mg/kg/day), and were compared retrospectively vs. the 37 \u201cprevious onsets\u201d without \u3c9-3 supplementation. Glicosilated hemoglobin (HbA1c%), the daily insulin demand (IU/Kg/day) and IDAA1c, a composite index (calculated as IU/Kg/day 7 4 + HbA1c%), as surrogates of REIS, were evaluated at recruitment (T0) and 12 months later (T12). In the \u3c9-3 supplemented group, dietary intakes were evaluated at T0 and T12. As an outcome, a decreased insulin demand (p < 0.01), particularly as pre-meal boluses (p < 0.01), and IDAA1c (p < 0.05), were found in the \u3c9-3 supplemented group, while HbA1c% was not significantly different. Diet analysis in the \u3c9-3 supplemented group, at T12 vs. T0, highlighted that the intake of arachidonic acid (AA) decreased (p < 0.01). At T0, the AA intake was inversely correlated with HbA1c% (p < 0.05; r;. 0.411). In conclusion, the results suggest that vitamin D plus \u3c9-3 co-supplementation as well as AA reduction in the Mediterranean diet display benefits for T1D children at onset and deserve further investigation

Periprocedural and Short-Term Outcomes of Transfemoral Transcatheter Aortic Valve Implantation With the Sapien XT as Compared With the Edwards Sapien Valve

ObjectivesThe aim of this study was to analyze the short-term outcomes after transcatheter aortic valve implantation with the Edwards Sapien THV (ESV), compared with the Sapien XT THV (SXT) (Edwards Lifesciences, Irvine, California).BackgroundThe SXT has been recently commercialized in Europe, but there are no studies analyzing the efficacy and safety of SXT, compared with ESV.MethodsAll consecutive patients (n = 120) who underwent transcatheter aortic valve implantation in our center via the transfemoral approach with either ESV (n = 66) or SXT (n = 54). Valve Academic Research Consortium endpoints were used.ResultsMean age was 80 ± 8 years, and mean Logistic-European System for Cardiac Operative Risk Evaluation was 24.9 ± 17.0. The ilio-femoral artery minimal lumen diameter was smaller in patients treated with the SXT (7.27 ± 1.09 mm vs. 7.94 ± 1.08 mm, p = 0.002). Device success was high in both groups (96.3% vs. 92.4%, p = 0.45). Major vascular events were 3-fold lower in the SXT group (11.1% vs. 33.3%, relative risk: 0.40, 95% confidence interval: 0.28 to 0.57; p = 0.004). Life-threatening and major bleeding events were not significantly different between groups (18.5% vs. 27.3% and 35.2% vs. 40.9%, respectively). The SXT group had a lower 30-day Valve Academic Research Consortium combined safety endpoint (20.4% vs. 45.5%; relative risk: 0.44, 95% confidence interval: 0.24 to 0.80; p = 0.004). The 30-day mortality was 1.7% (n = 2). At 30 days, mean transaortic gradient was approximately 10 mm Hg in both groups and the aortic regurgitation was mild-to-moderate in 70.2% of SXT and 76.3% of ESV.ConclusionsThe new SXT valve has the same short-term performance as the ESV but seems to be associated with a lower risk of major vascular complications and thus has a broader clinical application

Role of cellular senescence and NOX4-mediated oxidative stress in systemic sclerosis pathogenesis.

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by progressive fibrosis of skin and numerous internal organs and a severe fibroproliferative vasculopathy resulting frequently in severe disability and high mortality. Although the etiology of SSc is unknown and the detailed mechanisms responsible for the fibrotic process have not been fully elucidated, one important observation from a large US population study was the demonstration of a late onset of SSc with a peak incidence between 45 and 54 years of age in African-American females and between 65 and 74 years of age in white females. Although it is not appropriate to consider SSc as a disease of aging, the possibility that senescence changes in the cellular elements involved in its pathogenesis may play a role has not been thoroughly examined. The process of cellular senescence is extremely complex, and the mechanisms, molecular events, and signaling pathways involved have not been fully elucidated; however, there is strong evidence to support the concept that oxidative stress caused by the excessive generation of reactive oxygen species may be one important mechanism involved. On the other hand, numerous studies have implicated oxidative stress in SSc pathogenesis, thus, suggesting a plausible mechanism in which excessive oxidative stress induces cellular senescence and that the molecular events associated with this complex process play an important role in the fibrotic and fibroproliferative vasculopathy characteristic of SSc. Here, recent studies examining the role of cellular senescence and of oxidative stress in SSc pathogenesis will be reviewed

DHA modifies lipid raft structure and function in MDA-MB-231 breast cancer cells

In vivo and in vitro studies suggest that omega-3 poliunsaturated fatty acids (n-3 PUFA) can be cancer chemopreventive, chemosuppressive and auxiliary agents for cancer therapy (1). N-3 PUFA, like docosaexaenoic acid (DHA), could alter tumor growth by influencing cell replication, interfering with cell cycle components or increasing cell death, either by inducing necrosis or apoptosis. We have observed that DHA induces in MDA-MB-231 cells apoptosis and reduction of cell viability. Moreover, DHA significantly reduces the EGFR level and completely inhibits EGFR activation. However, the mechanism by which n-3 PUFA inhibit breast cancer growth, is not yet well understood. It was suggested that these fatty acids might change cell membrane fluidity and structure, especially of lipid rafts. Our data obtained by HPLC-GC analysis demonstrate that DHA is incorporated and metabolized in MDA-MB-231 membrane. In particular, DHA is incorporated in breast cancer lipid rafts with different specifity for the phospholipid moiety and induces a reduction of cholesterol and sphingomyelin content, indicating a possible change in raft organization. Changes in the lipid raft structure were also analyzed with atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). The AFM analysis of breast cancer lipid rafts indicates after DHA incorporation a reduction of microdomains number. Moreover PUFA treated rafts are dimensionally different from control rafts (2). Then, when DHA is incorporated into the cell membrane, it may induce the formation of \u201cdeclustered rafts\u201d with reorganization of lipids and proteins that may greatly influence signal transduction. 1 Calviello G et al., Nutr Cancer. 2009. 2 Corsetto PA et al., Cell Biochem Biophys. 2012