STUDY OF MIXED-CONVECTION HEAT TRANSFER FROM AN IMPINGING JET TO A SOLID WALL USING A FINITE-ELEMENT METHOD—APPLICATION TO COOKTOP MODELING

The mixed-convection flow from a hot vertical impinging jet on a colder horizontal disc has been studied. The geometry is analogous to a conventional burning gas cooktop. A numerical simulation of the system has been carried out using the finite-element method to study the dependence of fluid flow and heat transfer on the geometric, thermal, and fluid flow parameters. Results show that heat transfer efficiency versus several parameters such as inlet velocity magnitude and flue gas temperature has an optimum value, in which heat transfer efficiency is maximum. With thermal conductivity of the solid wall, velocity angle, and solid wall diameter heat transfer efficiency has increasing behavior. Finally, with solid wall height and solid wall thickness, heat transfer efficiency has diminishing behavior.     

Immersed boundary method for the simulation of heat transfer and fluid flow based on vorticity–velocity formulation

ABSTRACT

The present paper, based on the vorticity–velocity formulation of the Navier–Stokes equations, proposes an immersed boundary method for the simulation of heat transfer problems within a geometrically complex domain. The desired boundary conditions are imposed by the direct modification of the initial conditions of vorticity transport and energy equations using smooth interpolations. The time advancement of both transport equations is performed by the explicit fourth-order Runge–Kutta method. One of the main objectives of this paper is to present global smooth interpolations to evaluate the local Nusselt number. The forced convection of moving and fixed circular cylinders, natural convection problem in complex geometries, and the mixed convection between two concentric cylinders—at various Reynolds numbers—are studied.     

A Review of Heat Transfer and Pressure Drop Correlations for Laminar Flow in Curved Circular Ducts

Heat transfer and pressure drop correlations for fully developed laminar Newtonian fluid flow in curved and coiled circular tubes are reviewed. Curved geometry is one of the passive heat transfer enhancement methods that fits several heat transfer applications, such as power production, chemical and food industries, electronics, environment engineering, and so on. Centrifugal force generates a pair or two pairs of cross-sectional secondary flow (based on the Dean number), which are known as the Dean vortices, and improves the overall heat transfer performance with an amplified peripheral Nusselt number variation. The main purpose of this review paper is to provide researchers with a comprehensive list of correlations and concepts that they may need during their research. The paper begins with an introduction to the governing equations and important dimensionless numbers for the flow in curved tubes. The correlations for developing flow in curved and coiled circular tubes are also presented. The main contribution of this study is reviewing the numerical and experimental correlations to calculate friction factor and Nusselt number in curved circular tubes. Nusselt number correlations are categorized based on the thermal boundary condition, as well as on the method. A Dean number range of 1 to 20,000 for the pressure drop correlations and 1 to 7000 for the heat transfer correlations and a Prandtl number range of 0.1 to 7,000 are covered with the reviewed correlations.     

A Numerical Study on Natural Convention Heat Transfer From a Horizontal Isothermal Cylinder Located Underneath an Adiabatic Ceiling

A numerical analysis is performed for steady-state and two-dimensional natural convection heat transfer from a horizontal isothermal cylinder located underneath a horizontal adiabatic ceiling. The finite-volume method based on the SIMPLE algorithm and a nonorthogonal grid discretization scheme are used to solve the continuity, momentum, and energy equations for the Rayleigh numbers in the range from 10^?1 to 10⁴. The Poisson equations are solved to find the grid points, which are distributed in a nonuniform manner with higher concentration close to the solid regions. In addition, the HYBRID differencing scheme is used for the approximation of the convective terms in the curvilinear coordinate. The effects of the Rayleigh numbers and cylinder spacing from the adiabatic ceiling on both the local and average Nusselt numbers around the cylinder are investigated. Numerical results are performed for the plate-to-cylinder spacing ranging from 0.1 to 1.4.     

A macro-level decision analysis of wind power as a solution for sustainable energy in the USA

This study aims to quantify the socio-economic and environmental impacts of producing electricity by wind power plants for the US electricity mix. To accomplish this goal, all direct and supply chain-related impacts of different onshore and offshore wind turbines are quantified using a hybrid economic input-output-based triple bottom line (TBL) life cycle assessment model. Furthermore, considering TBL sustainability implications of each onshore and offshore wind energy technology, a multi-criteria decision-making tool which is coupled with Monte Carlo simulation is utilised to find the optimal choice of onshore and offshore wind energy. The analysis results indicate that V90-3.0 MW wind turbines have lower impacts than V80-3.0 MW for both socio-economic and environmental indicators. The Monte Carlo simulation results reveal that when environmental issues are more important than socio-economic impacts, V90-3.0 MW offshore is selected among the alternatives.     

A branch-and-bound algorithm for minimizing the sum of maximum earliness and tardiness with unequal release times

This article addresses the problem of minimizing the sum of maximum earliness and tardiness on a single machine with unequal release times. It is proven that this problem is NP-hard in the strong sense and a branch-and-bound algorithm is developed as an exact method. In the proposed algorithm, modified dispatching rules based on different release times are proposed as the upper bound, while a procedure considering preemption assumption is used to obtain a good lower bound. Also, dominance rules based on no unforced idle time, adjacent pairwise interchanges in the base problem, and job blocks are used to fathom the nodes. In order to evaluate the efficiency of the proposed algorithm, 4,860 instances were randomly generated, varying from 7 to 1,000 jobs. It is shown that the branch-and-bound algorithm was capable of optimally solving 94.1% of the instances, showing its efficiency in solving all problem sizes.     

Effect of dopant concentration and particle size on fluorescence properties of Y2O3:Eu3+ derived in presence of NIPAM/AAc copolymer

Y₂O₃:Eu³⁺ nano phosphors (about 65 nm in size) were prepared via co-precipitation method by using co-polymer NIPAM/AAc as a template with narrow size distribution. The aim of the paper is to indicate the co-polymer influence on size and luminescence characteristics of nano phosphors. In this respect, phase content and morphology were characterized by X-ray diffraction and transmission electron microscopy. All the powders were well crystallized and the particles were clearly spherical with good dispersibility. Luminescence measurements were used to investigate the role of precursor in powders and the utmost luminescence intensity was observed at 4 mol% of Eu³⁺ while the quenching concentration of Eu³⁺ ions has occurred at 5 mol%.     

Biological evaluation of polyvinyl alcohol hydrogel crosslinked by polyurethane chain for cartilage tissue engineering in rabbit model

Polyvinyl alcohol (PVA) hydrogel chains were crosslinked by urethane pre-polymer (PPU) in order to fabricate a new substitute for cartilage lesions. The microscopy images showed that the cultured chondrocytes had spherical morphology on PVA–PPU sample after 4 weeks of isolation in vitro. The alcian blue and safranin O staining proved the presence of proteoglycan on the surface of PVA–PPU sample secreted by cultured chondrocytes. This was confirmed by the detection of sulfate ions in the wavelength dispersive X-ray (WDX) analysis. In addition, the expression of collagen type II and aggrecan were observed in chondrocytes cultured on PVA–PPU by RT-PCR. Moreover, the implantation of the PVA–PPU sample with autologous cultured chondrocytes revealed the formation of neocartilage tissue in a rabbit model during 12 weeks follow up. In conclusion, the results verified that isolated chondrocytes cultured on PVA–PPU retain their original phenotype and this composition can be considered as promising substrate for cartilage tissue engineering.     

Off-Line Detection of Multiple Change Points by the Filtered Derivative with p-Value Method

Abstract

This article deals with off-line detection of change points, for time series of independent observations, when the number of change points is unknown. We propose a sequential analysis method with linear time and memory complexity. Our method is based, on a filtered derivative method that detects the right change points as well as false ones. We improve the filtered derivative method by adding a second step in which we compute the p-values associated to every single potential change point. Then, we eliminate false alarms; that is, the change points that have p-values smaller than a given critical level. Next, we apply our method and penalized least squares criterion procedure to detect change points on simulated data sets and then we compare them. Eventually, we apply the filtered derivative with p-value method to the segmentation of heartbeat time series, and the detection of change points in the average daily volume of financial time series.     

A Fast Adaptive Salt and Pepper Noise Reduction Method in Images

In this paper, an effective filtering method is proposed to remove impulse noise from images. In this two-stage method, detected noise-free pixels remain unchanged. Afterwards, a Gaussian filter with adaptive variances according to the image noise level is applied on the noisy pixels. Experimental results show that the proposed method outperforms recent impulse denoising methods in terms of PSNR, MAE, IEF, and SSIM. Moreover, the speed of the method is comparable with them, and it can be used effectively in real-time applications.