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Search Results: 1 - 10 of 411 matches for " HamidReza Goshayeshi "
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Improvment of Free Convection Heat Transfer Rateof Rectangular Heatsink on Vertical Base Plates  [PDF]
HamidReza Goshayeshi, Mahdi Fahiminia, Mohammad Mahdi Naserian
Energy and Power Engineering (EPE) , 2011, DOI: 10.4236/epe.2011.34064
Abstract: In this paper, the laminar heat transfer of natural convection on vertical surfaces is investigated. Most of the studies on natural convection have been considered constantly whereas velocity and temperature domain, do not change with time, transient one are used a lot. Governing equations are solved using a finite volume approach. The convective terms are discretized using the power-law scheme, whereas for diffusive terms the central difference is employed. Coupling between the velocity and pressure is made with SIMPLE algorithm. The resultant system of discretized linear algebraic equations is solved with an alternating direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and heat transfer of natural convection on these surfaces without sliding is studied and finally optimization is investigated.
Heat Transfer by Natural Convection from a Vertical and Horizontal Surfaces Using Vertical Fins  [PDF]
H. R GOSHAYESHI, F. AMPOFO
Energy and Power Engineering (EPE) , 2009, DOI: 10.4236/epe.2009.12013
Abstract: Natural convective heat transfer from a heated horizontal and vertical surfaces directly exposed into air which vertical fins, attached to a surface, project vertically downwards has been numerically studied. It has been assumed that the fins are everywhere at the temperature of the surface. The governing equations, written in dimensionless form, have been solved using the finite element procedure. The results show that vertical plate with vertical fins gives the best performance for natural cooling.
Investigation on Evaluation of a Solar Intermittent Refrigeration System for Ice Production with Ammonia/Calcium Chloride and Activated  [PDF]
Hamid R. Goshayeshi, Mehdi Gewad, Hojat Nazari
Energy and Power Engineering (EPE) , 2015, DOI: 10.4236/epe.2015.710042
Abstract: Experimental results of an intermittent solar absorption cooling system using parabolic collector are presented in this paper. The system used 6 kg of ammonia as refrigerant, 6 kg of calcium chloride as absorbent and 2 kg activated carbon as a solvent. The generator temperature was found to be 105°C. The system could produce ice at 16°C on the average. These are the most advanced results for a solar ice maker so far. All these successful achievements will speed up the commercial processing of a solar ice maker.
Modeling of Rotary Kiln in Cement Industry  [PDF]
Hamid Reza Goshayeshi, Fariba Kerdar Poor
Energy and Power Engineering (EPE) , 2016, DOI: 10.4236/epe.2016.81003
Abstract: Cement production is a highly energy-intensive process, and the rotary kiln is the most important part of the process. Having a comprehensive model of the kiln in order to reduce manufacturing costs, better performance can be created. In this paper, the influence processes in a simulated cement rotary kiln and operating parameters on the output of the study were to develop and validate the systems using the same batch. The followings were examined: solid phase, gas and coating temperature change in a rotary kiln.
Modified f(R) Gravity and Thermodynamics of Time-Dependent Wormholes at Event Horizon  [PDF]
Hamidreza Saiedi
Journal of High Energy Physics, Gravitation and Cosmology (JHEPGC) , 2017, DOI: 10.4236/jhepgc.2017.34053
Abstract: In the context of modified \"\" gravity theory, we study time-dependent wormhole spacetimes in the radiation background. In this framework, we attempt to generalize the thermodynamic properties of time-dependent wormholes in \"\" gravity. Finally, at event horizon, the rate of change of total entropy has been discussed.
Synthesis and Characterization of Copper Nanoparticles by Bis-(Acetylacetonato)-Copper (II) Using Nonionic Surfactants and the Effect of Their Structures on Nanoparticles Size and Yield  [PDF]
Hamidreza Kamrani
Open Journal of Inorganic Non-metallic Materials (OJINM) , 2018, DOI: 10.4236/ojinm.2018.82002
Abstract: Between all precursors of copper complex, bis-(acetylacetonato)-copper (II) and bis-oxalate copper (II) with very close structures are two of the best representatives for copper nanoparticles synthesis. In this research, only bis-(acetylacetonato)-copper (II) in presence of some effective non-ionic surfactants such as Triton X-100, Dodecylamine, Tween 80 and also triphenylphosphine as a reducing agent via thermal decomposition process was used for copper nanopaticles synthesis. Two shif-base E19 and E22 complexes were also used for the investigation of these kinds of shif-base complexes capabilities by this method as precursors and all results were compared with each other. Between all surfactants, Triton X-100 gave the best yield with the largest grains. The techniques used for characterization of copper nanoparticles were TEM, EDX, FT-IR and XRD. TG-DTA and CV were used for characterization of bis-(acetylacetonato)-copper (II) complex.
Investigation of Natural Convection Heat Transfer Coefficient on Extended Vertical Base Plates  [PDF]
M. Fahiminia, M. M. Naserian, H. R. Goshayeshi, D. Majidian
Energy and Power Engineering (EPE) , 2011, DOI: 10.4236/epe.2011.32022
Abstract: In this research, Computational analysis of the laminar natural convection on vertical surfaces has been in-vestigated. Natural convection is observed when density gradients are present in a fluid acted upon by a gravitational field. Our example of this phenomenon is the heated vertical plate exposed to air, which, far from the plate, is motionless. The CFD simulations are carried out using fluent software. Governing equa-tions are solved using a finite volume approach. Coupling between the velocity and pressure is made with SIMPLE algorithm. The resultant system of discretized linear algebraic equations is solved with an alternat-ing direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and natural convection heat transfer coefficient on these no slope surfaces is studied and finally optimization is done.
Fabrication and Studying the Mechanical Properties of A356 Alloy Reinforced with Al2O3-10% Vol. ZrO2 Nano-particles through Stir Casting  [PDF]
Mohsen Hajizamani, Hamidreza Baharvandi
Advances in Materials Physics and Chemistry (AMPC) , 2011, DOI: 10.4236/ampc.2011.12005
Abstract: Al2O3-ZrO2 with a high level of hardness and toughness is known as ceramic steel. Due to its unique properties it can be used as a reinforcement in fabrication of metal matrix composites. In this study, nanoparticles of Al2O3-10% ZrO2 with an average size of 80 nm were used to fabricate Al matrix composites containing 0.5, 1, 1.5 and 2 wt.% of the reinforcement. The fabrication route was stir casting at 850?C. There is no report about usage of this reinforcement in fabrication of composites in the literature. The microstructures of the as-cast composites were studied by scanning electron microscope (SEM). Density measurement, hardness and tensile properties were carried out to identify the mechanical properties of the composites. The results revealed that with increasing the reinforcement content, density decreased while yield, ultimate tensile strength and compressive strength increased. Also, hardness increased by increasing the reinforcement content up to 1 wt.% Al2O3-10% ZrO2 but it decreased in the samples containing higher amounts of reinforcement.
Training Based Channel Estimation in MIMO-OFDM Systems  [PDF]
Maryam Imani, Hamidreza Bakhshi
Communications and Network (CN) , 2012, DOI: 10.4236/cn.2012.41008
Abstract: OFDM combined with the MIMO technique has become a core and attractive technology in future wireless communication systems and can be used to both improve capacity and quality of mobile wireless systems. Accurate and efficient channel estimation plays a key role in MIMO-OFDM communication systems, which is typically realized by using pilot or training sequences by virtue of low complexity and considerable performance. In this paper, we discuss some methods for channel estimation based training symbols in MIMO-OFDM systems. The results confirm the superiority of the represented methods over the existing ones in terms of bandwidth efficiency and estimation error.
The Tight Bound for the Number of Pilots in Channel Estimation for OFDM Systems  [PDF]
Maryam Imani, Hamidreza Bakhshi
Communications and Network (CN) , 2012, DOI: 10.4236/cn.2012.42019
Abstract: Coherent detection in OFDM systems requires accurate channel state information (CSI) at the receiver. Channel estimation based on pilot-symbol-assisted transmissions provides a reliable way to obtain CSI. Use of pilot symbols for channel estimation, introduces overhead and it is desirable to keep the number of pilot symbols as minimum as possible. This paper introduces a new tight bound for the number of pilots in channel estimation using adaptive scheme in OFDM systems. We calculate the minimum number of necessary pilots using two approaches. The first approach for the number of pilots is obtained based on Doppler frequency shift estimation and the second approach is acquired based on channel length estimation using second order statistics of received signal. Finally we obtain the tight bound for the number of pilots using attained values.
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