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Many oil fires have resulted from the crude oil train derailments in recent years. Given the importance of crude oil shipping by rail to the energy security of the US, it is important to consider various methods that will decrease the likelihood of crude oil catching fire in case of a crude oil derailment. Present study examines the effect of polybutadiene polymer on the combustion properties and soot deposits of Bakken and Pennsylvania crudes. Treating these crudes as multicomponent liquid fuels and polybutadiene as an additive, droplet combustion experiments were conducted with sub-millimeter sized spherical droplets suspended on very fine support fibers. Polybutadiene polymer additive of two different chain lengths has been investigated. Results show that both polymer chain length and origin of crude oil have a significant effect on various combustion properties like combustion rate, ignition delay, total combustion time, and flame stand-off ratio. Polymeric additives also change the soot deposit structure and particle size compared to the base fuel. Present research is envisioned to aid in theoretical combustion modeling of complex multicomponent liquid fuels, as well as generate interest in investigating more polymeric additives for liquid fuels., 37 pages, 25 figures, article under review in Elsevier Appl Energy

The performance and flow field of hydropower turbine in shallow water can be affected by the presence of free surface. Therefore, the influence of free surface on the turbine performance was studied through transient computational fluid dynamics (CFD) analysis. The turbine included three blades made of NACA0018 hydrofoil. Submerged depths and different tip speed ratio (TSR) were two main variables in this numerical simulation. A comprehensive simulation of quantities was performed for submerged depths ranging from h / R = 1.2 to 2.0, and tip speed ratio from λ = 1.0 to 30. The results revealed that the presence of the free surface decreased the power coefficient by 19.05% for the closest submerged depth of h / R = 1.2 at optimal tip speed ratio of λ = 2.5. The wave breaking also occurred when the submerged depth was smaller than h / R = 2.0. In the case of variable pitch, the top speeds for free-to-spin cases were investigated by 6DOF method. The top speed had a 4.24% drop by comparing the largest and the smallest submerged depths. Variable pitch also improved the power coefficient by 28.09% when the free surface was far from the hydropower turbine. However, the power coefficient improvement became significantly small when the hydropower turbine was placed close to the free surface.

Temperature profiles are a fundamental input into mechanistic-empirical pavement analysis and design, and the enhanced integrated climatic model (EICM) is the state-of-the-practice for calculating those profiles. The EICM has also been used in other applications, such as analysis to evaluate the effects of climate change on pavements and to estimate the effects of pavements on urban heat islands. The calculations in the EICM for pavement temperatures can be viewed as having two primary components that together act as a system: the thermal model describing conductance of temperatures throughout the pavement, and the boundary conditions that include the convective terms at the pavement surface, an energy balance model to predict the solar radiation at the surface of the pavement and a specified lower boundary condition (generally constant temperature at defined depth). As is shown in this paper, the current EICM models overpredict temperatures during hot times and in no-wind conditions, while also underpredicting (albeit to a lesser magnitude) during cold conditions. This result implies that the increases in pavement temperatures predicted to occur with climate change are likewise overestimated. Conversely, because the convection coefficient is incorrect, the predicted amount of energy contributing to urban heat islands will also not be correctly predicted using the current EICM models. Although improvements to the solar model are noted, this paper focuses on improvements to the thermal model and convective boundary condition using modern heat transfer principles and data from the Long-Term Pavement Performance database.

This study uses Computational Fluid Dynamics (CFD) to investigate the effect of guide vanes on power output of turbine installed in a solar chimney. A full scale three-dimensional CFD simulation of solar chimney power plant based on Manzanares prototype is performed to simulate the air flow inside the solar chimney. First, the flow field is simulated in presence of guide vanes with no turbine inside the chimney. Three guide vanes with different tip angles of 30°, 60° and 90° are considered. It is observed that the presence of guide vanes significantly affects the flow direction and the heat stored inside the blade chamber. Moreover, the change in output power of solar chimney under different turbine rotational velocities and different guide vanes is studied. A twelve-blade turbine is placed right above the exit of the guide vanes at the start of chimney. Various cases including three angles, 30°, 60°, and 90° guide vanes, and three rotational velocities, 40, 80, and 120 rpm are run to find output power. The Multiple Reference Frame (MRF) method is used to treat the rotation of the turbine. The analysis of power output of the turbine shows that the maximum power of 82.2 kW is reached by the case of 30° guide vane at 80 rpm. Comparing to the power of the 90° guide vane at the same rotational velocity, which is 66.3 kW, the increase is about 23.9%.

The design of a piezoelectric based device that uses interference bluff body to harvest wind energy is presented. Different prototypes including cantilever beam, cylinder as oscillating body, and cylinder as interference body were used and tested to investigate the effects of interference bluff body’s properties such as the size and distance from fix oscillating body on the performance of energy harvesting system. To compare the frequency of oscillating beam and its natural frequency, a numerical simulation based on Finite Element Method was performed to obtain the natural frequency of cantilever beam. It was found that the energy harvester can be greatly improved by placing a fixed bluff body as interference bluff body in upstream of the oscillating bluff body. Through experimental tests, this study reveals that both diameter of interference cylinder and the distance between oscillating and interference cylinder play a key role in the energy harvester’s performance. Moreover, two different modes of oscillation were observed, depending on diameter of interference cylinder and its distance from bluff body. For all cases, the Fast Fourier Transform (FFT) analysis was used to monitor the frequency of oscillating cylinder and these values were compared with the natural frequencies obtained by Finite Element Method’s analysis. The results showed that the shorter beams oscillate with a frequency of about 5 Hz, close to the natural frequency of 6Hz, while the longer beams oscillate with a frequency of about 2.2 Hz, close to the natural frequency of 2.17Hz.

The addition of nanomaterials to base liquid fuels for the enhancement of combustion properties has long generated interest, since it is linked to improvement in combustion properties in petroleum-derived fuels. This work investigates the effect of acetylene black nanoparticles on soy-based biodiesel and petrodiesel. These nanoparticles were added in various proportions to base fuels to make suspensions. Sub-millimeter-sized spherical droplets of such suspensions were ignited using hot wire loops, and the combustion process was recorded using a high-speed camera. An infrared imaging camera was also used to record the droplet combustion process. Properties such as ignition delay, combustion rate, total combustion time, flame stand-off ratio, and droplet temperature were measured with post-processing of the resulting images. The results showed an increase in ignition delay of up to 10% in biodiesel and up to 8% in petrodiesel. An up to 13% decrease in biodiesel combustion rate and 1.5% decrease in diesel combustion rate was also observed. Moreover, a maximum of 14% decrease in the total combustion time of biodiesel was observed, compared to a 13% decrease in that of petrodiesel. The results are expected to spark further interest in the exploration of acetylene black as an additive for other liquid fuels.

The optimum design of the microchannel heat sinks needs to consider both the heat transfer and pressure drop limitations of the microchannel. In this paper, a novel configuration of the microchannel heat sink is proposed to obtain improved thermo-hydraulic performance. The proposed microchannel includes porous fins that form adjacent converging–diverging channels. Three-dimensional steady laminar simulations were conducted to access the performance of this novel microchannel and compare it with the conventional parallel ones with porous and solid fins. The results showed that by using this novel design, a 9.75% decrease in pressure drop is observed when compared to conventional solid fin parallel microchannel. Also, the mean Nusselt number of the microchannel heat sink with converging–diverging porous fins showed a maximum improvement of 16.5% compared to the parallel microchannel with solid fins. The overall thermo-hydraulic performance evaluation factor of the converging–diverging microchannel showed also a significant 20% improvement compared to conventional designs. The analysis of the flow fields showed that the converging–diverging design with porous fins leads to a local pressure difference between two adjacent neighboring channels inducing a cross-wise velocity component within the porous fins leading to enhanced thermal performance. Moreover, it was shown that only for converging–diverging angles above 0.5 [Formula: see text], performance enhancement was observed compared with a microchannel with solid fins showing the existence of an optimum range for converging–diverging angles. The response surface method was used to find the optimum range of fin porosity and converging–diverging angle where the performance of the microchannel heat sink is maximum.

In this study, the prediction of different turbulence models for simulation of transition heat transfer in forced convection over flat plate and natural/mixed convection between two flat plates was investigated. These turbulence models included Spalart-Allmaras (S-A), Low-Re k - e , Re-Normalisation Group (RNG) k - e , Low-Re k - ω Shear Stress Transport ( k - ω SST), k - k L - ω , γ - Re θ and V-SA transition models. In forced convection flow over horizontal flat plate, variation of skin friction coefficient and Stanton number with local Reynolds number, Re x , were studied. The simulations showed that in forced convection V-SA, γ - Re θ and k - k L - ω transition models can closely predict the critical distance of flow transition from laminar to turbulence regime comparing to other turbulence models, while in natural convection k - k L - ω and k - e models provided better prediction. In the case of mixed convection, the effects of different parameters such as heated wall temperature, inlet velocity, inclination angle and Richardson number on fluid flow and heat transfer were investigated in details. It was found that the changes in the transition point depends on the relative strength of the natural to forced convective flow and heat transfer. The transition point was delayed when the inclination angle of the channel was increased while increase in Richardson number promoted the transition to turbulence. In addition, Low-Re k - ω SST and RNG k - e predicted a shorter transition region, while γ - Re θ model also predicted a delayed transition point.

An example of vascular anastomosis is coronary artery bypass grafting (or CABG), which is the most common open-heart surgery in the United States today. It is used to treat people with coronary heart disease. Although it generally produces good outcomes, it is not without risk of failure. Due to rotation-related fluid stress on the graft at the point of attachment, possibility of clots forming at extraction and perfusion sites is high. The possibility of endothelialization at the suture joints carries a further risk of flow obstruction. Present research proposes a new blood contacting medical device that is attached to both ends of a vascular graft, and aids in flow rotation at the points of blood extraction and perfusion, thereby alleviating the possibility of clotting at those sites. It also shifts the suture lines such that the endothelialization causes minimal flow obstruction compared to current techniques. Simplified 3D models of both the current grafting technique and the proposed device are evaluated with periodic rectified sine pulse acting as a surrogate for human blood pulse. For both perfusion and extraction, better outcomes were observed for vascular anastomosis with the proposed blood contacting medical device.

The use of in-situ burning (ISB) as a clean-up response in the event of an oil spill has generated controversy because of unburned hydrocarbons and products of incomplete combustion left behind on an ISB site. These substances threaten marine life, both in the ocean and on the ocean floor. Treating crude oil as a multicomponent liquid fuel, this manuscript investigates the effect of carbon-based nanomaterials, acetylene black (AB) and multi-walled carbon nanotube (MWNT), on the combustion and flame characteristics of crude sourced from the Bakken formation (ND, USA). Sub-millimeter droplets of colloidal suspensions of Bakken crude and nanomaterials at various particle loadings were burned, and the process was captured with CMOS and CCD cameras. The resulting images were post-processed to generate burning rate, ignition delay, total combustion time, and flame stand-off (FSR) ratio data for the various crude suspensions. A maximum combustion rate enhancement of 39.5% and 31.1% was observed at a particle loading of 0.5% w/w acetylene black nanoparticles and 0.5% w/w multi-walled carbon nanotubes, respectively. Generally, FSR for pure Bakken was noted as larger than for Bakken with nanoparticle additives. These results are expected to spur further investigations into the use of nanomaterials for ISB crude oil clean-ups., 30 pages, 13 figures, publication submitted to Elsevier Energy

A methodology is presented to predict density stratified flows in the near-field of naval vessels. The approach uses a single-phase level set method for the free surface, a dynamic overset technique to handle motions and controllers for self-propulsion and maneuvering. The density is solved with a higher-order transport equation coupled with momentum and mass conservation. Turbulence is implemented with a k − e / k − ω based Delayed Detached Eddy Simulation (DDES) approach modified to add density gradients. Evaluation tests were performed for a two-dimensional square cavity, including grid and time step studies, and the stratified flow past a sphere, showing good agreement with available data. The stratified flow was studied for a self-propelled ship and a submarine. Density, velocity, pressure and turbulent quantities at the exit plane of the near-field contain a description of the relevant scales of the flow and can be used to compute the far-field stratified flow. It is shown that, as is the case of surface waves, the generation of internal waves requires energy that results in an increase in resistance. Moreover, the presence of a density interface against the hull results in a thickening of the boundary layer, just as in a solid/free surface juncture flow.

A numerical study is performed on the effects of surface waviness and nanoparticle dispersion on solidification of Cu–water nanofluid inside a vertical enclosure for different Grashof numbers. A geometry with sinusoidally curved wavy surface can be used to enhance heat transfer performance if it is carried out in an appropriate way. Therefore, the enclosure has wavy surfaces on right side with higher temperature and left side with lower temperature, while the top and bottom walls are both flats with insulated condition. Computations are conducted for the surface waviness ranging from 0 to 0.4, Grashof number from 104 to 106 and nanoparticle dispersion from 0 to 0.1. An enthalpy porosity technique is used to trace the solid and liquid interface inside the enclosure. To validate the results, the numerical solutions for special cases in a rectangular cavity were compared with previously published works which are in good overall agreement with those results. The numerical results show that for surface waviness of 0.25 and 0.4, a maximum of 60% decrease in solidification time for Gr = 106 is observed in comparison with Gr = 105 which indicates the increasing effects of natural convection on solidification due to distortion on surface. Therefore, surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.

The dead water problem, in which under certain conditions a vessel advancing in a stratified fluid experiences a considerable increase in resistance respect to the equivalent case without stratification, was studied using computational fluid dynamics (CFD). The advance of a vessel in presence of a density interface (pycnocline) results in the generation of an internal wave that in the most adverse conditions can increase the total resistance coefficient by almost an order of magnitude. This paper analyses the effects of stratification on total and friction resistance, the near field wake, internal and free surface waves, and resistance dynamics. Some of these effects are reported for the first time, as limitations of previous efforts using potential flow are overcome by the use of a viscous, free surface CFD solver. A range of densimetric Froude numbers from subcritical to supercritical are evaluated changing both the ship speed and pycnocline depth, using as platform the research vessel athena. It was found that the presence of the internal wave causes a favorable pressure gradient, acceleration of the flow in the downstream of the hull, resulting in thinning of the boundary layer and increases of the friction resistance coefficient of up to 30%. The total resistance presents an unstable region that results in a hysteretic behavior, though the characteristic time to establish the speed–resistance curve, dominated by the formation of the internal waves, is very long and unlikely to cause problems in modern ship speed controllers.

The effects of geometrical arrangement on the heat transfer and pressure drop characteristics in compact louvered fin-and-tube heat exchangers were studied experimentally and numerically along with ε−NTU method. Different geometrical parameters including louver angle, louver pitch, louver number, the nonlouvered inlet and exit fin length, and redirection of fluid flow are considered to determine their effects on the flow field. The study is performed for different louver angles varying from θL=12 to 60 deg, and optimal heat transfer rate is obtained at louver angle of θL=28deg. Also, it is found that increasing the louver number, NL, on the fin surface enhances the heat transfer performance. It is shown that the average Nusselt number is increased as the louver pitch is decreased and its optimum value is obtained at Lp=0.9 mm. However, comparing to the effect of louver number, the louver pitch has a small effect on the performance of the heat exchanger. Additionally, the optimum values of nonlouvered inlet and exit fin length and redirection length of fin are obtained with different flow conditions.

Effects of Grashof number and volume fraction of Cu–water nanofluid on natural convection heat transfer and fluid flow inside a two-dimensional wavy enclosure has been investigated numerically. Also, in the presence of nanofluid, the second law of thermodynamics is applied to predict the nature of irreversibility in terms of entropy generation. Finite-Volume numerical procedure with non orthogonal body fitted collocated grid arrangement is used to solve the governing differential equations. Calculation were performed for the Grashof numbers from 104 to 106, nanoparticles volume fraction from 0% to 10% and surface waviness ranging from 0.0 to 0.4 for different patterns of wavy enclosure. Streamlines, isothermal lines, counters of local entropy generation and the variation of local and average Nusselt number are presented and compared with considering the effects of different parameters. The results show that the average heat transfer rate decreases as nanoparticles volume fraction and Grashof number increase. Also, besides decreasing heat transfer rate, the nanoparticles can be used for decreasing the entropy generation.

In this study, air-side heat transfer and pressure drop characteristics of flow over louvered fins in compact heat exchangers have been investigated experimentally. The test samples consist of two types of fin configurations. A series of tests were conducted to examine the geometrical parameters of louver pitch, louver arrangement and number of louver regions. The calculated results indicate that a symmetrical arrangement of louvered fins provides a 9.3% increase in heat transfer performance and a 18.2% decrease in pressure drop than the asymmetrical arrangement of louvered fin. Also, for a constant rate of heat transfer and pressure drop, a 17.6% decrease of fin weight is observed for the symmetrical arrangement of fins and this is following by considerable decrease in total weight and cost of the heat exchanger. The results from this investigation indicate that the configuration of the louvered fins has the dominant influence on the heat transfer and pressure drop from that louver.

In this article, a transient behavior simulation of fin-and-tube heat exchangers has been studied. Energy equation for fluid flow and tube wall is derived and solved numerically. The variation of the temperatures of both fluids with time and position are obtained for a step-change in the inlet temperatures of the water and air fluids. The results show that in step-change of inlet water-side temperature, outlet water-side temperature will get steady faster than air-side, while in step-change of inlet air-side temperature, outlet air-side temperature will become steady state faster than water-side. Also, the time constant (the time interval that the flow will reach steady state) of the system is not influenced by the step-change amplitude of inlet air and water temperatures. The inlet water temperature expands along the tube and after a time interval, it reaches the outlet section of the tube. But, the inlet air temperature reaches the outlet section without time delay.

Laminar stagnation flow, axisymmetrically yet obliquely impinging on a moving circular cylinder, is formulated as an exact solution of the Navier–Stokes equations. Axial velocity is time-dependent, whereas the surface transpiration is uniform and steady. The impinging free stream is steady with a strain rate k. The governing parameters are the stagnation-flow Reynolds number Re=ka2/2ν, and the dimensionless transpiration S=U0/ka. An exact solution is obtained by reducing the Navier–Stokes equations to a system of differential equations governed by Reynolds number and the dimensionless wall transpiration rate, S. The system of Boundary Value Problems is then solved by the shooting method and by deploying a finite difference scheme as a semi-similar solution. The results are presented for velocity similarity functions, axial shear stress and stream functions for a variety of cases. Shear stresses in all cases increase with the increase in Reynolds number and suction rate. The effect of different parameters on the deflection of viscous stagnation circle is also determined. Copyright © 2010 John Wiley & Sons, Ltd.

In this article, a powerful analytical method, called the Homotopy Analysis Method (HAM) is introduced to obtain the exact solutions of heat transfer equation of a non-Newtonian fluid flow in an axisymmetric channel with a porous wall for turbine cooling applications. The HAM is employed to obtain the expressions for velocity and temperature fields. Tables are presented for various parameters on the velocity and temperature fields. These results are compared with the solutions which are obtained by Numerical Methods (NM). Also the convergence of the obtained HAM solution is discussed explicitly. These comparisons show that this analytical method is strongly powerful to solve nonlinear problems arising in heat transfer.

In this study, He’s Energy Balance Method (EBM) was applied to solve strong nonlinear Duffing oscillators with cubic-quintic nonlinear restoring force. The complete EBM solution procedure of the cubic-quintic Duffing oscillator equation is presented. For illustration of effectiveness and convenience of the EBM, different cases of cubic-quintic Duffing oscillator with different parameters of α, β and γ were compared with the exact solution. We found that the solutions were valid for small as well as large amplitudes of oscillation. The results show that the EBM is very convenient and precise, so it can be widely applicable in engineering and other sciences.

In this Letter, the problem of forced convection over a horizontal flat plate is presented and the homotopy perturbation method (HPM) is employed to compute an approximation to the solution of the system of nonlinear differential equations governing on the problem. It has been attempted to show the capabilities and wide-range applications of the homotopy perturbation method in comparison with the previous ones in solving heat transfer problems. The obtained solutions, in comparison with the exact solutions admit a remarkable accuracy. A clear conclusion can be drawn from the numerical results that the HPM provides highly accurate numerical solutions for nonlinear differential equations.

Knowledge of the temperature dependence of the physical properties such surface emissivity, which controls the radiative problem, is fundamental for determining the thermal balance of many scientific and industrial processes. The current work studies the ability of a strong analytical method called parameterized perturbation method (PPM), which unlike classic perturbation method do not need small parameter, for nonlinear heat transfer equations. The results are compared with the numerical Runge-Kutta method showed good Agreement.

Results of an experimental study of a two-phase jet are presented, with the jet issued near and below a free surface, parallel to it. The jet under study is isothermal and in fresh water, with air injectors that allow variation of the inlet air volume fraction between 0 and 13 %. Measurements of water velocity have been performed using LDV, and the jet exit conditions measured with PIV. Air volume fraction, bubble velocity and chord length distributions were measured with sapphire optical local phase detection probes. The mean free surface elevation and RMS fluctuations were obtained using local phase detection probes as well. Visualization was performed with laser-induced fluorescence. Measurements reveal that the mean free surface elevation and turbulent fluctuations significantly increase with the injection of air. The water normal Reynolds stresses are damped by the presence of bubbles in the bulk of the liquid, but very close to the free surface the effect is reversed and the normal Reynolds stresses increase slightly for the bubbly flow. The Reynolds shear stresses $$\left\langle {u^{\prime } w^{\prime } } \right\rangle$$ decrease when bubbles are injected, indicating turbulence attenuation, and are negative at deeper locations, as turbulent eddies shed downward carry high axial momentum deeper into the flow. Flow visualization reveals that the two-phase jet is lifted with the presence of bubbles and reaches the free surface sooner. Significant bubble coalescence is observed, leading to an increase in mean bubble size as the jet develops. The coalescence near the free surface is particularly strong, due to the time it takes the bubbles to pierce the free surface, resulting in a considerable increase in the local air volume fraction. In addition to first explore a bubbly surface jet, the comprehensive dataset reported herein can be used to validate two-phase flow models and computational tools.

In this paper the problem of fully developed laminar steady forced convection inside a porous-saturated pipe with uniform wall temperature is presented and the homotopy perturbation method (HPM) and the variational iteration method (VIM) are employed to solve the differential equations governing the problem. The obtained results are valid for the whole solution domain with high accuracy. These methods can be easily extended to other linear and nonlinear equations and so can be found widely applicable in engineering and science. Copyright © 2009 John Wiley & Sons, Ltd.