Sharif Digital Repository

This study focuses on the numerical investigation and optimization of the heat-fluid transfer process within a novel cavity containing a ternary nanofluid (Cu–MgO–ZnO/water) influenced by a magnetic field. The research is conducted within a circular cavity featuring a cold wall and a complex internal heat source. The governing equations, converted into dimensionless form, are solved using a computational code based on the finite volume approach. The analysis encompasses the effects of a wide range of physical parameters, including the Rayleigh number (Ra), Hartmann number (Ha), magnetic field angle (α), radiation (Ra), nanoparticle shape factor (Sf), and porosity (ԑ). The results revealed... 

This article explores the significance of Shell and Tube Heat Exchangers (STHX), with a focus on various baffle types such as Segmental, Double segmental, Helical, Disc-and-Doughnut, Clamping anti-vibration, and Flower-B. In this study, the commercial software ANSYS FLUENT is used to simulate the problem. The study evaluates their impact on heat exchanger performance using parameters like overall heat transfer coefficient (OHT), pressure drop (PD), and Performance Evaluation Criteria (PEC). Clamping anti-vibration, Flower-B, Helical, and Double segmental baffles exhibit reductions in shell side PD by 14%-28%. Despite OHT reductions in these designs, Disc-and-Doughnut baffles demonstrate a... 

The current research aims to implement a reliable analytical model in order to scrutinize the transient behavior of a counter-flow non-premixed combustion system fueled by wet porous biomass particles under non-adiabatic conditions, including several processes such as phase change and dehumidification. A special term is added to the heat equation based on the law of conservation of energy as a means to assess the convective heat loss impacts. In order to analyze the structure of the diffusion flame and predict the time-dependent temperature and mass fractions of reactants distributions, transient forms of energy and mass equations are solved through the asymptotic method. Eventually, the... 

In this study, a thermal-diffusive model using a sinusoidal function for the oscillation term is presented. The model is employed to evaluate the pulsating behavior in a premixed counterflow flame fed with biomass particle cloud considering Lewis number and thermal radiation effects. In order to scrutinize the pulsating characteristics of a flame, time-related governing equations are written for the assumed multi-zone system and analytically solved utilizing Matlab and Mathematica software. To enforce continuity, suitable matching conditions for the temperature and heat flux at the interfaces are derived. Time-dependent characteristics of burning velocity, flame temperature, flame front... 

In the last decade, many potent analytical methods have been utilized to find the approximate solution of nonlinear differential equations. Some of these methods are energy balance method (EBM), homotopy perturbation method (HPM), variational iteration method (VIM), amplitude frequency formulation (AFF), and max-min approach (MMA). Besides the methods mentioned above, the Akbari-Ganji method (AGM) is a highly efficient analytical method to solve a wide range of nonlinear equations, including heat transfer, mass transfer, and vibration problems. In this study, it was constructed the approximate analytic solution for movement of two mechanical oscillators by employing the AGM. In the derived... 

The present article aims to investigate the Graetz-Nusselt problem for blood as a non-Newtonian fluid obeying the power-law constitutive equation and flowing inside the axisymmetric tube subjected to non-uniform surface heat flux. After the flow field is determined by solving the continuity and the momentum equations, the energy equation is handled by employing the separation of variables method. The resulting Eigen functions and Eigen values are numerically calculated using MATLAB built-in solver BVP4C. The analysis is first conducted for the situation of constant heat flux and subsequently generalized to apply to the case of sinusoidal variation of wall heat flux along the tube length,... 

In this paper we have reviewed Nevisa Persian speech recognition engine. Nevisa is an HMM-based, large vocabulary speaker-independent continuous speech recognition system. Like most successful recognition systems, MFCC with some modification has been used as speech signal features. It also utilizes a VAD based on signal energy and zero-crossing rate. Maximum likelihood estimation criterion the core of which are the classical segmental k-means and Baum-Welsh algorithms is used for training the acoustic models. The system is based on phoneme modeling and utilizes synchronous beam search based on lexicon tree for decoding the acoustic utterances. Language modeling for Persian has been... 

Adomian decomposition method was employed to obtain an approximate solution to two-dimensional and axisymmetric jet impinging flows in this work. Assumptions have been made to reduce the related full Navier-Stokes equations to a non-linear ordinary differential equation. A trial and error strategy has been used to obtain the constant coefficient in the approximated solution. Velocity Profiles, Shear stresses and displacement thickness were chosen to be compared with accurate numerical data. Sensitivity of the results to the number of terms have been discussed. The results showed for open boundary problems having at least one boundary condition at infinity, the applicable range of the... 

In the current research, a comprehensive analytical technique is presented to evaluate the non-Fourier thermal behavior of a 3-D hollow sphere subjected to arbitrarily-chosen space and time dependent boundary conditions. The transient hyperbolic thermal diffusion equation is driven based upon the Cattaneo-Vernotte (C-V) model and nondimensionalized using proper dimensionless parameters. The conventional procedure of separation of variables is applied for solving the 3-D hyperbolic heat conduction equation with general boundary conditions. In order to handle the time dependency of the boundary conditions, Duhamel's theorem is employed. Furthermore, for the purpose of demonstrating the... 

The polysaccharide, kappa-carrageenan (κC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N′-methylene bisacrylamide (MBA) were used as a free-radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either κC-g-PMAM or hydrolyzed κC-g-PMAM (PMAM: polymethacrylamide) was characterized by FT-IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and... 

To synthesize a novel biopolymer-based superabsorbent hydrogel, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was grafted onto kappa-carrageenan (KC) backbones. The graft copolymerization reaction was carried out in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator, N,N,N',N'-tetramethyl ethylenediamine (TMEDA) as an accelerator, and N,N'-methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for KC-g-AMPS formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The affecting variables on swelling capacity, i.e., the initiator, the crosslinker, and the monomer concentration, as well as reaction temperature,... 

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacrylamide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator andN,N′-methylenebisacrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g-PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-polymethacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the... 

The energy of a graph G, denoted by E(G), is defined as the sum of absolute values of all eigenvalues of G. In (MATCH Commun. Math. Comput. Chem. 83 (2020) 631{633) it was conjectured that for every graph G with maximum degree Δ(G) and minimum degree Δ (G) whose adjacency matrix is non-singular, E(G) +δ (G) + Δ (G) and the equality holds if and only if G is a complete graph. Here, we prove the validity of this conjecture for planar graphs, triangle-free graphs and quadrangle-free graphs. © 2021 University of Kragujevac, Faculty of Science. All rights reserved  

The energy of a graph G, denoted by E(G), is defined as the sum of absolute values of all eigenvalues of G. In (MATCH Commun. Math. Comput. Chem. 83 (2020) 631{633) it was conjectured that for every graph G with maximum degree Δ(G) and minimum degree Δ (G) whose adjacency matrix is non-singular, E(G) +δ (G) + Δ (G) and the equality holds if and only if G is a complete graph. Here, we prove the validity of this conjecture for planar graphs, triangle-free graphs and quadrangle-free graphs. © 2021 University of Kragujevac, Faculty of Science. All rights reserved  

An efficient and one-pot process has been developed for the synthesis of novel benzo[4,5]imidazo[2,1-b]pyrimido[4,5-d][1,3]thiazine-2,4(3H)-diones and benzo[4,5]imidazo[2,1-b][1,3]thiazin-4-ones from CH acids, aldehydes and 2-mercaptobenzimidazole using hexyltriphenylphosphonium bromide ionic liquid (HTPB) as a green promoter and solvent at ambient temperature. The reaction afforded products in high yields and short reaction times, bypassing the conventional harsh reaction conditions and without the need for using volatile solvents. In addition, we evaluated the anti-cancer activity of these compounds on different cancer cells, including A431, PC3, and Panc1 and HDF (human dermal fibroblast)... 

This contribution performs an energy, exergy, and exergoeconomic (3E) analysis of a dual-pressure evaporation organic Rankine cycle system employing twenty different binary zeotropic mixtures as working fluids for power production from a geothermal field. To this end, the designed system is modeled, invoking the mass and energy conservation laws and the exergy and cost balance analyses. Specific Exergy Costing (SPECO) procedure is utilized to provide practical insights into the exergoeconomic aspect of the system. Comparative optimization based on the multi-objective genetic algorithm is accomplished for each mixture in order to simultaneously maximize the exergy efficiency and minimize the... 

The use of nanoparticles in heat transmission is an interesting research subject and many scholars have shown an interest in this topic. In accordance with the motivating relevance of nanomaterials, the current research advocates for an evaluation of Casson nanofluid using porous medium thermal analysis in conjunction with vibrant implementations of mixed convection through a chemical reaction. Additionally, a nonlinear suction/injection phenomenon is taken into consideration. A consistent flow pattern is created by the stretched porous structure. The extended Casson nanofluid model is used to identify the heat production of non-Newtonian fluids. The essential incentives for choosing the... 

This letter presents a Ka-Band 0.1-μm GaAs pHEMT Power Amplifier with broad bandwidth. The isolating backvia wall (IBVW) has been proposed to improve the stability and performance. Over the frequency band of 31-40 GHz, implemented PA delivers 5 W saturated output power, 28% maximum power added efficiency (PAE) and 20 dB maximum small-signal gain. The chip size of the PA is 11.9 mm2. To the best of authors knowledge, the presented PA demonstrates widest bandwidth in Ka-band GaAs PAs while maintaining compact size  

It is believed that it is going to be a sizeable mismatch between supply and demand when it comes to renewable resources. Lately, researchers are on course to compensate for the unpredictabilityof such resources by the employment of phase change materials (PCMs). Having multiple advantages, PCMs generally suffer from inadequate thermal conductivity which causes prolonged transition procedures. To tackle this issue, this study is fixated on two parameterswhich are linked to fins addition and porous media incorporation in a melting process within a triple concentric tube heat exchanger (TCTHX). The results provided by multiple cases underlined the significance of natural convection in the bare... 

Let G be a graph. The first and second Zagreb index of G is defined as M1(G)= Σ degG(V)2 and M2(G)= Σ degG(u)degG(V) respectively. In this paper we compute Zagreb indices of chain graphs