•A heat sink geometry with perforated staggered fins was proposed for LED light bulbs.•Numerical and experimental analyses were made to compare its thermal performance.•Perforated fins significantly ...reduced thermal resistance as well as mass of heat sink.•Effect of orientation angle on thermal resistance of proposed heat sink was small.
A radial heat sink with circular base and perforated short fins arranged in staggered manner, proposed for LED light bulbs was investigated under natural convection and radiation heat transfer. Numerical model was established by considering the effect of finning factor, porosity factor, and orientation angle for improving the thermal performance and reducing the mass of the heat sink. The results obtained were validated through experiments. It was found that the perforated staggered configuration of heat sink reduced the thermal resistance by approximately 7% to 12% at different orientation angles and mass by about 9%, when compared with non-perforated staggered heat sink.
•A new solver based on OpenFOAM is developed to solve porous media heat transfer.•For porous media attached near to the walls, heat transfer can be enhanced up to 65%.%•Increase in heat transfer rate ...for core side configuration is about 938%.%•There is a critical thickness of porous media for each of the porosity value.•Increasing porosity at the wall side increases Nu but for the core side, it deceases.
In the present work, forced convective heat transfer and pressure drop in the entrance and fully developed regions of a square duct, which is partly filled by porous medium, is numerically investigated. The porous medium is placed (i) adjacent to the wall or (ii) at the core of the square duct. This 3D analysis was essential because in the earlier studies the thermal hydraulic characteristics were predicted by considering the flow to be between two parallel plates or as axisymmetric, which is not applicable for square ducts. Apart from the thickness of the porous medium, changes in porosity is also considered in the analysis. The porous medium is taken to be wire mesh screens, as it is the most common case. The flow through porous medium is modelled using Darcy–Forchheimer model and the heat transfer is modelled using local thermal equilibrium model. For solving this problem, a new solver is developed using the open source CFD package OpenFOAM. From the results it is observed that, adding porous inserts at the core of the duct provides better heat transfer rate with lesser pressure drop. The effect of porosity on heat transfer and pressure drop is accentuated only if the porous medium thickness ratio is greater than 0.625. The maximum heat transfer that can be achieved for wall side case when thickness ratios in the range 0.8-1.0 is approximately 1.65 times than that of a duct without porous medium. If the porous medium is at the core side case, maximum heat transfer is 10.4 times when the thickness ratio is between 0.85-0.95. It is also found that, when the porous medium is at the wall side, the Nusselt number increases with increases in porosity. However, if the porous medium is in the core side, the Nusselt number increases with decreasing porosity.
Enhancement in heat transfer due to helical coils has been reported by many researchers. While the heat transfer characteristics of double pipe helical heat exchangers are available in the ...literature, there exists no published experimental or theoretical analysis of a helically coiled heat exchanger considering fluid-to-fluid heat transfer, which is the subject of this work. After validating the methodology of CFD analysis of a heat exchanger, the effect of considering the actual fluid properties instead of a constant value is established. Heat transfer characteristics inside a helical coil for various boundary conditions are compared. It is found that the specification of a constant temperature or constant heat flux boundary condition for an actual heat exchanger does not yield proper modelling. Hence, the heat exchanger is analysed considering conjugate heat transfer and temperature dependent properties of heat transport media. An experimental setup is fabricated for the estimation of the heat transfer characteristics. The experimental results are compared with the CFD calculation results using the CFD package FLUENT 6.2. Based on the experimental results a correlation is developed to calculate the inner heat transfer coefficient of the helical coil.
Background
The neutrophil to lymphocyte ratio (NLR) is a measure of systemic inflammation, whereas Heart type fatty acid protein (HFABP) is a cytosolic protein released early after acute coronary ...syndrome (ACS). The aim of this research study is to determine whether NLR and H-FAB are useful in predicting the prognosis in patients with ST segment elevation myocardial infarction (STEMI) 48 h after admission. This is a prospective observational study conducted on 97 patients who had been admitted to emergency room with ST-elevation myocardial infarction in their ECG in a tertiary care centre of south India. The neutrophil–lymphocyte ratio was measured at the time of admission, 24th hour and 48th hour, and then compared with the outcome. To determine their significance in the MI episode, troponin-I and H-FABP were also measured.
Results
A significant correlation was found in the final outcomes of patients and the NLR at the time of admission and at 48 h (
p
= 0.01). Additionally, a substantial correlation between NLR and various degrees of LV dysfunction was also observed (
p
= 0.01). H-FABP was found to be positive in all 97 of the patients examined, whereas Troponin-I was only found to be positive in 56.7%.
Conclusion
The study's findings, indicated strong correlations between NLR and LVEF, indicated that NLR might serve as an early predictor of cardiac events which could be either poor prognosis or higher mortality. This research found that H-FABP may serve as an early MI diagnostic marker.
This paper focuses on thermal destratification and pressurisation inside thermally stratified storage tanks by continuous gas bubbling. The primary purpose of doing these studies is to better ...understand the effect of bubble dynamics on thermal destratification and quantify the extent of destratification. The volume of fluid and interface compression method of OpenFOAM CFD code is utilised for the present analysis. Different values of inlet gas velocities (Vg), orifice diameters (do), and arrangement of the orifices in triangular and square fashion with different pitches (p/do) are considered. In addition, the effect of gravitational forces (g/ge) on thermal destratification is also reported. For all these cases, the effectiveness of thermal destratification is quantified in terms of a newly defined parameter, the destratification index (Id). For Vg = 1 m/s, the Id value is maximum compared to lower Vg values. It is seen that when the gas velocity increased from 0.3 m/s to 1.0 m/s, the average effectiveness in thermal destratification (Idavg) and pressure at the ullage increased by 44.38% and by 64.81%, respectively. The Idavg and pressure at ullage increased by 96.29% and 14.91%, respectively, when the g/ge ratio changed from 0.3 to 3. Compared to the triangular arrangement with p/do = 10, the calculated Idavg increased by 30.67% when gas inlets were arranged with a square pitch of 10. For p/do = 4, 6 and 8, the increments in Idavg are of the order of 12.86%, 19.43% and 21.92%, respectively, for gas inlets arranged in a square fashion as compared to the triangular arrangement. It is found that continuous bubbling with gas inlets arranged in square pitch p/do = 10 gives higher effectiveness in thermal destratification. Thus, by these studies, one can develop a thermal destratification mechanism with continuous bubbling for optimum performance. Also, these studies give an overall idea of sparger design for getting the correct gas flow rate for thermal destratification within the cryogenic liquid storage tanks.
•A modified version of multiphase solver compressibleInterFoam of OpenFOAM is used to analyse the thermal destratification.•A new parameter called the destratification index is introduced to quantify the extent of destratification.•The influence of various geometric and operating parameters on destratification is reported.•Gas inlets in square arrangement with p/do = 10 give higher effectiveness in thermal destratification.•Results can be used for sparger design to get optimum thermal destratification by continuous bubbling.
Nanocomposite made of La0.7Sr0.3MnO3 (LSMO) and reduced graphene oxide (rGO) is a promising candidate for non-volatile memory application in oxide electronics. Here, we report bipolar resistive ...switching (RS) behaviour in (1-x)LSMO.(x)rGO nanocomposite system, for 0.001 ≤x≤ 0.010. The structural characterization revealed the presence of individual constituent phases. The switching behaviour is observed to be very stable over 1000 switching cycles and robust against different voltage sweeping rates with a minimum switching speed of 1.1 μs. An oxygen vacancy induced conduction filament based model is proposed to understand the origin of the switching phenomenon and similar observation is made through high-resolution transmission electron microscopy (HRTEM) measurements.
Resistive switching (RS) is a physical process in which the resistance of a system can be switched between the high and low resistance states through the application of an external electric field that can be used for non-volatile memory application. In this work, we have studied the switching behaviour of a novel Nanocomposite system made of La0.7Sr0.3MnO3 (LSMO) and reduced graphene oxide (rGO). For a small percentage of rGO, the switching behaviour is observed to be very stable over 1000 switching cycles, robust against different voltage sweeping rates, resulting in a large ON/OFF ratio ∼ 10.2. We have proposed an oxygen vacancy induced conduction filament based model to understand the origin of the switching phenomenon and compared it with similar observation made through high-resolution transmission electron microscopy (HRTEM) measurements. Display omitted
The present investigation is to find the enhancement of heat transfer in the recirculation region when additional centrifugal forces due to streamline curvature are imposed on to the shear-layer. ...Backward Faced Step (BFS) have got great importance to study the separated and recirculating flows and their heat and mass transfer effects due to its geometrical simplicity. The effects of the radial pressure gradient existing in case of the curved stream line and how it affects the turbulence are investigated in this present study. The stabilizing and destabilizing effects with heat transfer have been studied in this paper for three different curvatures (flat, concave, and convex). Numerical results obtained by the use of the open source code OpenFOAM-3.0.1 is compared with the experimental results. The three-dimensional analysis has been done using an aspect ratio of 18 (AR=18:1) at Reynolds number based on step height as 80000. The distribution of Nusselt number (Nu), skin friction coefficient (Cf), and coefficient of pressure (Cp) were found on the bottom wall with close heed. The results show that the convex surface stabilizes the flow whereas the concave surface introduce more disturbances and destabilizes the flow.
Humidification Dehumidification (HDH) desalination is a convenient process to produce drinking water from low temperature saline water in waterfront areas. High energy consumption of the system ...remains as a limiting factor, besides many enhancements done in improving the system performance. Though HDH system cycles are classified on the basis of air and water cycles, detailed performance analysis of different HDH cycles is absent till date. The present study aims at carrying out parametric analysis of possible HDH layouts and finally proposing a layout with high Gain Output Ratio (GOR) and Recovery Ratio (RR) at the low equipment volumes. Simulations are carried out using the Scilab® software. Simulation results are validated using the experimental data obtained from a pilot plant of open-air open-water single stage system. Variation of system parameters like humidifier volume, dehumidifier volume, GOR and RR were analysed in detail for each individual layouts. Out of the eight different layouts investigated, Layout 8 is found to be the best based on GOR, RR, equipment volume and specific energy consumption. Hence it is recommended to use Layout 8 with an inlet temperature of 74 °C and MFR of 2.4 for productivity of 90 LPH.
Display omitted
•Detailed study on the performance analysis of 8 different layouts are carried out for a fixed productivity.•Optimal feedwater temperature in humidifier of layouts are directly related with the GOR and RR of the system.•Least equipment volume and highest RR is obtained at the highest feedwater temperature, independent of type of layout.•Highest GOR is obtained at the least feed water temperature if air or water or both streams operate in closed cycle.•Layout 8 is found to have the highest GOR and RR at the lowest value of specific energy consumption.
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