In this paper, fully developed flow of a couple-stress fluid between two long vertical walls in presence of viscous dissipation and radiative heat flux with heat and mass transfer is considered. Temperature and concentration fields at one of the walls are oscillating around a non-zero value. The coupled equations governing the problem are discretized using Differential Quadrature Method, and solved using Newton-Raphson Method and Evolutionary Algorithm hybrid scheme. The expressions for velocity, temperature, and concentration fields for fully developed unsteady flow are obtained.

The repeated failure of Agitator in the Phosphoric acid Reactor in MPC was a major incident causing high downtime and production loss. While doing the root cause analysis of this “Class A” incident many causes not considered in normal agitator design were considered and analyzed. This paper lists such special cases and the proposed solutions and calculations to be incorporated in design of critical systems with varying process fluid parameters for different applications. Agitators constitute almost 20% of rotating equipment in a fertilizer and similar plants but are given less priority compared to others until a severe failure happens. There are no standard analytical design criteria for agitator design due to large variations and uncertainties in the process conditions in the reactor or tank. Most designs are left to the EPC companies using preformatted design models based on experimental results, on the combination of few variables. (Like Power Number, Pumping Number, Geometrical ratios etc.) However, none these models considers the fluid flow conditions which changes inside the reactor which affects the agitator design in many ways like Localized flow, non-homogenous fluid, solid contents, Liquid additives or recycling etc. which can cause much higher alternating forces and bending stresses at the joints holding the blades causing fatigue and other failures. This paper gives more quantitative design calculations to determine the forces acting on the agitator and blades as listed above which can be used in similar application even with different fluids.

A numerical analysis of mixed convection in a vertical channel filled with metal foam partially heated at uniform heat flux is studied numerically. Local thermal non-equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 pore per inch (PPI) and ε=0.909, the fluid is air. Results, for different Reynolds numbers and geometrical aspect ratios, are given in terms of solid and fluid temperatures, at heated walls and inside the channel at several heights, velocity profile along the channel, local and average Nusselt numbers. Results show that diffusive effect resulted lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. For heated channel with smaller aspect ratios, an average Nusselt number increase is found for solid and fluid phases.

Transient laminar free convection in a water-filled rectangular enclosure has been studied experimentally and numerically. The study aimed at gaining an insight into the physical phenomena, illustrated by the flow patterns and the temperature stratification, from the initial stage of a homogeneous fluid through the transient evolving process. The experimental setup consisted of two rectangular water-filled enclosures: the smaller one contained a heat source and was centrally immersed in the larger one. Dye was injected for visualization of the rising boundary layer over the inner container walls, and the accumulation of the colored layers in the upper zone of the outer container. Simultaneously, the temperature measurements, by thermocouples and an infra-red camera, displayed the formation of a stratified structure. The numerical study was conducted three-dimensionally, using the Fluent 6.3 software. The stratified temperature field, observed experimentally, was well-predicted by the numerical model. The heat transfer rates and the transient averaged Nusselt numbers were compared with the data in the literature. The current, constant power input yielded Nu/Ra 0.25 ∼0.7 in the range of Fo/Ra 0.25 = 0–3.

This paper handles numerical analyses that give attention to the relation between the thermal performance of concentric tube heat exchangers and its operational parameters. For this purpose, an iterative computational code is developed to compute thermal performance. The computations are based on supplying the code with the exchanger length, inner/outer diameters, inner/outer fluids, inner/outer flow rates and inner/outer inlet temperatures. A parametric analysis that examines the relation between the thermal performance of heat exchanger and inner/outer flow rates is presented. It is originated that the thermal performance and the overall heat transfer coefficient of a concentric tube heat exchanger increase through a rational function with the inner and outer flow rates.

To enhance the cooling performance of a metal-foam heat sink, this work increases the surface area of the heat sink wall in contact with the electronic component by vertically placing a solid aluminum cylinder in the center (i.e., core) of an aluminum-foam heat sink. The contact ratio, defined as the ratio of the surface area of the extended heat sink wall in contact with the electronic component to the solid-fluid interface area inside the aluminum-foam heat sink, was systematically varied to experimentally investigate the heat transfer characteristics. The experimental results on the measured Nusselt number, solid-phase and gas-phase temperatures and temperature difference between the solid and gas of the aluminum foam under different contact ratios were reported and discussed in this work.

In this study, three-dimensional computational fluid dynamics (CFD) analyses are performed to assess the thermal-hydraulic characteristics of a commercial Gasketed Plate Heat Exchangers (GPHEx) with 30 degrees of chevron angle (Plate1). The results of CFD analyses are compared with a computer program (ETU HEX) previously developed based on experimental results. Heat transfer plate is scanned using photogrammetric scan method to model GPHEx. CFD model is created as two separate flow zones, one for each of hot and cold domains with a virtual plate. Mass flow inlet and pressure outlet boundary conditions are applied. The working fluid is water. Temperature and pressure distributions are obtained for a Reynolds number range of 700–3400 and total temperature difference and pressure drop values are compared with ETU HEX. A new plate (Plate2) with corrugation pattern using smaller amplitude is designed and analyzed. The thermal properties are in good agreement with experimental data for the commercial plate. For the new plate, the decrease of the amplitude leads to a smaller enlargement factor which causes a low heat transfer rate while the pressure drop remains almost constant.

Counter current flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. This paper describes experimental and numerical results obtained in a circular column of 240 mm inner diameter with two inner pipes. The counter current flow studied concerns an upward flow of air and a downward flow of water at ambient temperature and pressure. The following range of operating conditions is analyzed: superficial air velocities up to 0.25 m/s and superficial water velocities up to 0.04 m/s, corresponding to global void fractions up to 27.7%. The experimental investigations concerns (i) flow visualization, (ii) local data from a double optical probe and (iii) global void fraction data. Images obtained from an optical camera are used to observe the general flow pattern and to support the boundary conditions of the numerical simulations, in terms of average bubble diameter. Data obtained from the double optical probe are used to study local flow characteristics. The gas disengagement technique is used to obtain the global void fraction over a range of superficial air velocities for the validation of the numerical method. Numerical calculations are performed with an Eulerian two-fluid model using the commercial code ANSYS Fluent Release 14.5.7 and results are compared with experimental data. The effects of bubble diameter and various interfacial drag coefficients are studied. The formulation of the drag coefficient is found to have significant effects on the global void fraction predictions. However, using merely the drag law, numerical results are inaccurate.

In this paper a vibration isolated design of the Coriolis Mass-Flow Meter (CMFM) is proposed, by introducing a compliant connection between the casing and the tube displacement sensors with the intention to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of casing excitations. Analyses are focussed on changing the transfer function of support excitations to the relative displacement measurement. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimised. Based on simulation results, a prototype is built and validated. The validated design show a 20dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.

During the manufacture of energetic materials, the dehydration process of nitrocellulose doughs provides a residual liquid mixture consisting of water, alcohol and nitrocellulose (NC) fibers. The separation of such fibers is required for distillation of alcohol, in order to make possible its reutilization in subsequent processes. In this work, an experimental analysis of sedimentation mechanisms of NC fibers contained in the fluid mixtures from nitrocellulose plants, is presented. The goal of the work is to obtain the time periods needed for complete sedimentation of these solid fractions (NC fibers). Cylindrical tanks with vertical or horizontal orientation are considered in this study, and the results obtained for both tank configurations are compared. From the experimental observations about sedimentation mechanisms of solid fraction in these fluid mixtures, recommendations about optimum times for NC fibers removal are proposed. These optimum times should be assumed as basic guidelines for scheduling and execution of the distillation process, due to its high influence on minimization of the overall operational costs for this process. Great discrepancies were registered between sedimentation times of NC fibers in vertical or horizontal tanks, with reductions in sedimentation rate of until 40% for recipients located in vertical orientation.

The aim of this numerical study is to investigate the lubrication system of a household hermetic reciprocating compressor. The effects of the rotational speed, oil viscosity and crankshaft-to-oil sump bottom distance on the oil-air two phase flows are investigated in detail. Necessary oil to lubricate the components of the compressor is sucked from the oil sump through an asymmetrically opened suction hole of the crankshaft by its rotational movement and climbs as an oil film on the helical channel carved on the shaft wall. This oil film is directed to crankshaft outlet. The oil forms an immiscible mixture with air, thus a two phase flow model should be analyzed using Volume of Fluid (VoF) method in the flow solver. Main findings related to the oil mass flow rate released from the crankshaft outlet reveal that with increasing rotational speed, the mass flow rate from the crankshaft outlet also increases, but with increasing viscosity and decreasing crankshaft-to-oil sump bottom distance, the oil mass flow rate decreases.

This paper reports experimental measurements of film thickness for continuous fluid flow within a spinning cone. The results are compared to analytical theory for thin film flow and found to be in good agreement. Spinning cones are used in various industrial process machines, including spinning cone distillation columns, centrifugal film evaporators and continuous centrifugal filters. In each case a fluid is fed continuously into the centre of a conical vessel which spins about a vertical axis with the cone apex pointing downwards. The fluid acquires the angular velocity of the cone and migrates up the internal wall of the cone under centrifugal force. Knowledge of the film thickness and flow velocity is often important in order to understand other performance parameters of the process such as evaporation or filtration rates. This paper aims to aid the design of new process machines by providing a mathematical model for film thickness that is validated by experimental results. Experiments have been conducted in which the angle of cone, angular velocity and input flow rate were all varied. Film thickness measurements were obtained via a novel optical method based on photographing the displacement of a projected grid on the surface of the flow within the cone. The method has the advantages of not disturbing the flow in any way and can provide thickness measurements over the whole cone depth. Measurements are also made insensitive to any transients by use of relatively long photographic exposures. Measurements are compared to analytical theory for axisymmetric, steady state, free-surface laminar flow of a Newtonian fluid in a spinning cone. The theory assumes the flow is thin but takes account of gravity. The theoretical model is found to be in good agreement with the experimental results.

Interest to sailing in arctic zone is increasing, as due to the climatic change, the seasons when northeast and northwest passages are open enough for see transportation, are getting every year longer and longer. Some other activities like oil and gas exploration and drilling at Barents Sea require also regular sea traffic connections to be opened. Sea operations at arctic zone are challenging, because thick ice generates a high magnitude dynamic load against the hull and the propulsion units. Turning and backward sailing in thick ice field are the most critical operations, in which the steerable propulsion units are in totally different service as in the regular open sea cruising. In such operations the ice field, when guided downwards along the slope of the hull, is broken to large plates, which then are fed against the propulsion unit. The steering propulsion unit itself is a vertically mounted inverse mast column, at the top of which the horizontally spinning propeller(s) can be vertically turned to follow the steering commands. Such cantilever structure is now under random collision process when the column is breaking the underwater ice plates to smaller blocks. For hydrodynamic reasons the column has a limited cross-sectional area as compared to the propeller area making it sensitive to bending vibrations. Another dynamic interaction with ice is coming from the periodical blade-ice contact when the ice blocks pushed down to the propulsion depth are completely milled by the units. These two parallel dynamic processes have been the reason for several serious damages and losses of propulsion units leading to expensive service operations by means of support vessels. The purpose of this study has been to model the underwater propulsion system with all essential structures, parts and interactions with the surrounding fluid field and floating ice blocks. This brings a complex analysis, in which random collisions and periodical machining forces are loading the elastic hull-mounted inverse mast column with high end mass. The response behavior led to predictions for the reasons of the observed damages especially in case of collapsed bolt connections in the units.

In the last decade, there is a renewed interest in the integration of a sloshing tank into structural systems to decrease the vibrations of the structure. The purpose of this study is to try different numerical simulation programs for further use in studies in evaluation of the effectiveness of the sloshing tank absorbers for structural systems. The programs chosen for sloshing simulations are COMSOL Multiphysics®, ANSYS CFX and ANSYS-FLUENT. In the numerical simulations, the free surface shape during sloshing will be simulated under small and large amplitude sinusoidal displacements. The results obtained using different software will be compared with the results of the experiments reported in literature. Since the purpose is to use the sloshing forces on the container to decrease the structural response, the total force on the container walls is calculated and compared with the reported experimental results. The dynamics of a container coupled with the a structural model is simulated and forces applied on the container walls are analyzed in the frequency domain which is important in understanding the tuning of the vibration absorber. To the best of authors’ knowledge, in a fluid-structure coupled system the frequency domain analysis of the container wall forces at varying amplitudes of sinusoidal excitation is not presented in literature. The results showed even though higher harmonic forcing magnitudes increase with increasing base motion, the fundamental harmonic component does not change significantly.

Reducing carbon dioxide (CO 2 ) emissions from power plants utilizing fossil fuels is expected to become substantially more important in the near- to medium-term due to increasing costs associated to national and international greenhouse gas regulations, such as the Kyoto protocol and the European Union Emission Trading Scheme. However, since net efficiency penalties caused by capturing CO 2 emissions from power plants are significant, measures to reduce or recover efficiency losses are of substantial interest. For a state-of-the-art 400 MW natural gas-fueled combined cycle (NGCC) power plant, post-combustion CO 2 removal based on chemical solvents like amines is expected to reduce the net plant efficiency in the order of 9–12 percentage points at 90% overall CO 2 capture. A first step that has been proposed earlier to improve the capture efficiency and reduce capture equipment costs for NGCC is exhaust gas recirculation (EGR). An alternative or complementary approach to increase the overall plant efficiency could be the recovery of available low temperature heat from the solvent-based CO 2 removal systems and related process equipment. Low temperature heat is available in substantial quantities in flue gas coolers that are required upstream of the CO 2 capture unit, and that are used for exhaust gas recirculation, if applied. Typical temperature levels are in the order of 80°C or up to 100 °C on the hot end. Additional low-grade heat sources are the amine condenser which operates at around 100–130 °C and the amine reboiler water cooling that could reach temperatures of up to 130–140°C. The thermal energy of these various sources could be utilized in a variety of low-temperature heat recovery systems. This paper evaluates heat recovery by means of an Organic Rankine Cycle (ORC) that — in contrast to traditional steam Rankine cycles — is able to convert heat into electricity efficiently even at comparably low temperatures. By producing additional electrical power in the heat recovery system, the global performance of the power plant can be further improved. This study indicates a theoretical entitlement of up to additional 1–1.5 percentage points in efficiency that could be gained by integrating ORC technology with a post-combustion capture system for natural gas combined cycles. The analysis is based on fundamental thermodynamic analyses and does not include an engineering- or component-level design and feasibility analysis. Different ORC configurations have been considered for thermal energy recovery at varying temperature levels from the above-mentioned sources. The study focuses on simultaneous low-grade heat recovery in a single ORC loop. Heat recovery options that are discussed include in series, in parallel or cascaded arrangements of heat exchangers. Different organic operating fluids, including carbon dioxide, R245fa, and N-butane were considered for the analysis. The ORC performance was evaluated for the most promising organic working fluid by a parametric study. Optimum cycle operating temperatures and pressures were identified in order to evaluate the most efficient approach for low temperature heat recovery.

Digital Displacement (DD) fluid power machines utilizes electronically controlled seat valves connected to pressure chambers to obtain variable displacement with high operational efficiency and high bandwidth. To achieve high efficiency, fast valve switching is essential and all aspects related to the dynamic behaviour of the seat valves must be considered to optimize the machine efficiency. A significant effect influencing the valves switching performance is the presence of oil stiction when separating the contact surfaces in valve opening movement. This oil stiction force is limited by cavitation for low pressure levels, e.g. valves connected to the low pressure manifold, however for valves operated at higher pressure levels, the oil stiction force is dominating when the separating surfaces are close to contact. This paper presents an analytic solution to the oil stiction force for annular seat valves suitable for DD applications based on the Reynolds equation and considers contact surface curvature and attack angle. A dynamic cavitation zone is included in the stiction model, and cavitation is found to be present even for seat valves surrounded by high pressure levels.

The flow patterns in two phase and multi-phase flows is a significant factor which influences many other parameters such as drag force, drag coefficient and pressure drop in pipe lines. One of the major streams in the gas and oil industries is oil-water two phase flow. The main flow patterns in oil-water flows are bubbly, slug, dual continuous, stratified and annular. In the present work flow patterns in two phase oil-water flow were investigated in a 0.5in diameter pipe with length of 2m. 3D simulation was used for this pipe and six types of mesh grid were used to investigate mesh independency of the simulation. The proposed numerical analyses were performed by a CFD package which is based both on volume of fluid (VOF) and Eulerian-Eulerian methods. The results showed that some flow patterns can be simulated better with VOF method and some other maybe in Eulerian-Eulerian method, so these two methods were compared with together for all flow patterns. The flow patterns may be a function of many parameters in flow. One of the important parameter which may affect flow patterns in pipe line is pipe inclination angle; therefore flow patterns in the different pipe inclination angles were investigated in two phase oil-water flow. The range of inclinations has been varied between −45 to +45 degree about the horizon. In the presented simulation oil is mixed with water via a circular hole at center of the pipe, the ratio of oil surface to water surface at entrance is 2/3 so water phase was considered as the main phase. Flow patterns were investigated for every angle of pipe and numerical results were compared with available experimental data for verification. Also the flow patterns simulated by numerical approaches were compared with available flow regime maps in the previous literatures. Finally, effect of pipe inclination angle and flow patterns on the pressure loss were investigated comprehensively.

Development of IC engines with low emissions and low fuel consumption causes interest in direct injection engine, especially diesel engines that work with lean mixture. This goal may be achieved with separation of mixture formation and combustion processes, in diesel engines. A practicable way to reach this target is the use of porous medium (PM) inside the combustion chamber. The PM has benefits to enhance the evaporation of droplets in liquid-fuel burners, reduce emissions and minimize instabilities. This paper represents the numerical study of liquid-fuel injection and combustion inside constant-volume chemically inert PM to stabilize lean mixture. 3D numerical results have obtained based on a modified version of KIVA-3V code. Diesel was directly sprayed inside hot and high pressure PM chamber. Complete evaporation and self-ignited was achieved due to the initial temperature of PM. The results in an especial condition have compared with an experimental data in the literature. Effect of injection in cold condition has investigated. Contours of diesel vapor, fluid and solid temperature of PM in a cross section, have shown. Also, effects of pore density on a constant high-porosity PM and mass of spray fuel were studied. The results show considerable reduction in carbon monoxide, nitrogen monoxide and elimination of soot.

This study presents a numerical simulation of precursors and characteristics of rotating stall in a centrifugal compressor with vaned diffuser. The aim is to further understand the causes of stall inception, characteristics of stall process and to investigate reliable simulation of stall control methods and aid in their optimization. Initial numerical results show that the tip leakage flow and early separation in the impeller blades are causing weakness of radial velocity and deviation of fluid angle at impeller exit. Also, results show that the vaneless region between impeller and diffuser near shroud surface is the key factor of developing radial velocity deficiency into stall cells leading to pressure fluctuations on impeller blades. The present study confirms that injection of air at the shroud surface of the vaneless region has an effect on modifying fluid angle entering diffuser and on delaying of stall inception to occur at lower mass flow rates.

This paper concerns the role of air injection method in stabilization and stall control in centrifugal compressors. The main aim is to find the best arrangement of air injection parameters such as injection angle and injection mass flow rate in order to optimize the injection performance for stabilizing the compressor and increasing the surge margin. Numerical model was built to simulate high speed transonic centrifugal compressor working at an operating point close to surge. Air was injected at 12 locations at the vaneless region between the impeller and the diffuser at shroud surface with 5 different injection angles and 3 different injection mass flow rates. Results showed that the best injection method is when using an injection angle of 30° with injection mass flow rate of 1.5% of the design mass flow rate and the worst injection method is the injection at angle of 180° (reverse tangent injection). Results also indicated that by using air injection, the number of stalled diffuser passages is decreased compared to the case of no injection. The most significant result of this paper is that using an angle of injection around twice the value of the diffuser vane angle gives the best results and makes the ideal correction of the fluid kinetic energy and fluid angle at the diffuser inlet. It was found that injecting air at an angle less than the diffuser vane angle weakens the effect of injection and doesn’t increase kinetic energy of the fluid at diffuser inlet. It was also found that injecting air at an angle larger than the diffuser vane angle corrects the fluid direction but, at the same time, decreases the fluid kinetic energy at diffuser inlet.