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Papers by jafar ghorbanian

This paper concentrates on the unconventional temperature profiles and heat fluxes observed in no... more This paper concentrates on the unconventional temperature profiles and heat fluxes observed in non-equilibrium molecular dynamics (MD) simulations of force-driven liquid flows in nano-channels. Using MD simulations of liquid argon flows in gold nano-channels, we investigate the manifestation of the first law of thermodynamics for the MD system, and compare it with that of the continuum fluid mechanics. While the energy equation for the continuum system results in heat conduction determined by viscous heating, the first law of thermodynamics in the MD system includes an additional slip-heating term. Interaction strength between argon and gold molecules is varied in order to investigate the effects of slip-velocity on the slip-heating term and the resulting temperature profiles. Heat fluxes and temperature profiles from ''continuum'', ''continuum augmented with slip-heating'', and ''heat conduction due to the power input by the driving force'' are modeled and compared with the MD results. The continuum model can neither predict the heat fluxes nor the temperature profiles from MD simulations. While the continuum model augmented with slip-heating matches the MD heat fluxes, the resulting temperature profiles do not agree with the MD predictions. Overall the analytical model based on ''heat conduction due to power input by the driving force'' matches the heat fluxes from MD simulations, while the temperature profiles match MD predictions using an effective thermal conductivity that is about 70% of the thermodynamic value. Using different liquid–wall pairs affects the slip velocity, temperature jump, and the resulting thermal conductivity of the fluid, but results in similar physical observations. The inability of the MD method in mimicking continuum fluid mechanics in energy transport for force-driven liquid flows is scale independent, and it is more likely a numerical artifact.

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulati... more A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state, and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution, volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs.

Force-driven liquid Argon flows both in nano-scale periodic domains and in Gold nano-channels are... more Force-driven liquid Argon flows both in nano-scale periodic domains and in Gold nano-channels are simulated using non-equilibrium molecular dynamics to investigate the scale and wall-force ﬁeld effects. We examined variations in liquid density, viscosity, velocity profile, slip-length, shear stress and mass flow rate in different sized periodic-domains and nano-channels at a fixed thermodynamic state. In absence of walls, liquid Argon obeys Newton’s law of viscosity with the desired absolute viscosity in domains as small as 4 molecular diameters in height. Results prove that deviations from continuum solution is solely due to wall effects. Simulations in nano-channels with heights varying from 3.26 nm to 36 nm exhibit parabolic velocity profiles with constant slip length modeled by Navier-type slip boundary condition. Both channel averaged density and “apparent viscosity” decrease with reduced channel height, which has competing effects in determination of the mass flow rate. Density layering and wall force field induce deviations from Newton’s law of viscosity in the near wall region, while constant “apparent viscosity” with the deformation rate from a parabolic velocity profile successfully predicts shear stress in the bulk flow region.

Scientia Iranica, Jan 1, 2011

In this paper, rapid and globally convergent predictive tool for dynamically loaded journal beari... more In this paper, rapid and globally convergent predictive tool for dynamically loaded journal bearing design is developed. For accomplishment of such an aim, a neural network model of crankshaft and connecting rod bearings in an internal combustion engine is developed as an alternative for the complicated and time-consuming models. Six most important parameters are selected as inputs of neural network. These parameters are: oil viscosity, engine speed, bearing radial clearance, bearing diameter, slenderness ratio and maximum force applied on bearings. Also, some significant parameters
are calculated as neural network outputs. These parameters include: all components of friction loss, all components of oil consumption, minimum oil film thickness, eccentricity, oil temperature rise and displacement relative to shell. In addition, an optimum analysis is performed. To achieve such a target, multi-objective optimization methodology is a good approach inasmuch as several types of objective are minimized or maximized simultaneously. The optimization goal is to minimize friction loss and lubricant flow as the two objectives and develop a Pareto optimal front.

In order to develop more efficient engines, it is essential to optimize the lubrication circuit o... more In order to develop more efficient engines, it is essential to optimize the lubrication circuit of the power train systems. In this paper, during an engine design and development process, a network analysis of the engine lubrication system is described in detail. Two elements have been added to the lubrication circuit in the modified engine. These elements are hydraulic lifters and an Anti-drain valve. The effect of adding
and changing the mentioned elements and increasing the bearing clearance has been investigated on oil
pump capacity. Also, chain tensioner and anti-drain valve as two new important components in the lubrication
system have been investigated as well as other components from tribological point of view. Improving chain tensioner material from Nitride Butyl Rubber to Poly-Amid and changing the oil jet hole position and diameter, reduce the intensity of wear to the standard level without significant decreasing of main galley pressure. Adding an anti-drain valve near hydraulic lifter gallery decreases the time which oil needs to reach lifters with sufficient pressure at engine startup. The analyses are done by Flowmaster7.6 and AVL-EXCITE7.02 software and an accessory code. Finally, theoretical results are validated by a completely controlled lubrication functional test.

The beauty and application of thermal analysis concept leads researchers to one of the main steps... more The beauty and application of thermal analysis concept leads researchers to one of the main steps for thermomechanical design during engine development. The durability and output potential of such engines is strongly linked to the operating temperature of certain key components. Thus, accurate temperature predictions are an essential pre-requisite to the
continuing engine evolution. From material science
point of view, temperature field in engine main components
like cylinder head and block is required to evaluate component functionality under specific load and conditions. Moreover, need for more power and less weight is one of the most important targets in engine design, especially in the case of alternative fuel engines. In order to look at this issue, authors zero in on wide-ranging experimental and analytical study
to investigate temperature fields in cylinder head and
block of a recently developed turbocharged bi-fuel engine.
A bi-fuel turbocharged engine (CNG and gasoline)
were equipped with more than 40 sets of thermocouples
and a comprehensive thermal survey was carried out on the fired engine in the various conditions.
Thermocouples were installed on different positions of the cylinder block and head to measure material temperatures. Experiments were done both in natural gas and gasoline mode to compare the results. An analytical comparison was made between natural gas and gasoline modes to understand root and effect of heat transfer differences. The presented thermal analysis could be helpful to know material requirements
to design and develop turbocharged natural gas engine
which is a good candidate as an alternative fuel engine.

Among the alternative diesel engine fuels, dimethyl ether (DME) attracted so much attention as an... more Among the alternative diesel engine fuels, dimethyl ether (DME) attracted so much attention as an alternative fuel for the diesel engine since the properties of the DME are fitted to the diesel engine combustion. There are high expectations for DME as a new alternative fuel in heavy-duty diesel engines. This research investigates a natural aspirated diesel engine combustion and performances characteristics while using DME. In the experimental part of the work, OM314 direct-injection diesel engine was used as a base engine. A comprehensive full cycle was coupled with a multi zone combustion model to simulate performance characteristics of the engine. Results of the volumetric efficiency show that the highest brake torque is achievable in the middle speed range. The power speed diagram shows that brake torque in diesel mode operation is much higher than DME operation, where the engine speed is less than 1900rpm. However in engine speeds over than 1900rpm, brake torque in DME mode operation would be higher. Emissions results show that, almost zero soot is produced in DME operation and PM emissions is also reduced up to 75 percent in comparison with diesel mode operation.

Scientia Iranica, Jan 1, 2011