Unsteady Energy Research Articles

Fuel system control design based on mass conservation

Fuel entering and ejecting high-pressure fuel pipe is the basis of fuel engine operation. The intermittent operation of high-pressure oil pump and injector will lead to the change of pressure in high-pressure oil pipe. This paper studies the influence of the opening and closing of one-way value and the speed of cam angle on the pressure in high-pressure oil pipe. Because the fuel flow is unstable in the high-pressure fuel pipe, it is necessary to determine the influence of pressure change on fuel density, and then calculate the mass of fuel supply and fuel injection in unit time. Considering the principle of mass conservation, the problem can be transformed into the length of single opening time of one-way valve when the mass of fuel entering and leaving the high-pressure oil pipe is equal in unit time interval. At the same time, by deducing the influence of the single opening time of the one-way value on the pressure in the high-pressure oil pipe, the single opening time of the one-way valve when the pressure of the high-pressure oil pipe reaches equilibrium after 2s, 5s and 10s is 0.610895ms, 0.425998ms and 0.373376ms respectively. Consider the working principle of the fuel system on the basis of the above considerations. Fit the function relationship between the needle lift and working time, deduce the change rule of flow volume of injector with time, and calculate the volume and mass of fuel injected by the injector in the working cycle. The results show that the high-pressure oil pump supplies oil 94 times in a working cycle of the injector, and the time required for the cam to rotate for one circle is 1.064ms, and the angular velocity of the cam is 5.906rad/ms. In this paper, based on the theory of unsteady liquid motion, mass conservation and energy conservation of fluid mechanics, many elements involved in the problem stem are analysed and related, and the control model of one-way valve switch and cam angular velocity is given.

Energetics of Seamount Wakes. Part I: Energy Exchange

AbstractSeamounts have been theorized to act as “stirring rods,” converting barotropic flow into an unsteady wake, turbulence, and diapycnal mixing. The energetics of these processes are not well understood, but they may have implications for basin-scale mixing calculations. This study presents the results of a series of simulations for idealized seamounts in steady barotropic flow, with varying degrees of stratification and rotation. The kinetic energy within each simulation domain is decomposed into the mean kinetic energy, unsteady eddy energy, and turbulent kinetic energy; evolution equations are derived for each. Within the evolution equations, energy exchange terms arise, which relate the various forms of kinetic energy and potential energy. Key exchange terms, such as the rate at which the mean flow is converted into eddy energy, are compared across the Froude–Rossby parameter space. It is shown that the conversion terms associated with mesoscale motions are a function of the Burger number, which is consistent with a quasigeostrophic flow regime. Conversely, conversion terms associated with turbulent processes scale with the product of the Froude and Rossby number. The amount of energy extracted from the mean flows suggests that wake effects may be significant for the parameter range and model assumptions studied. These results suggest that some seamounts may indeed act as oceanic stirring rods.

Numerical study on characteristics of flow and thermal fields around rotating cylinder

In this paper, a numerical simulation has been performed to study the fluid flow and heat transfer around a rotating circular cylinder over low Reynolds numbers. Here, the Reynolds number is 200, and the values of rotation rates (α) are varied within the range of 0 < α < 6. Two-dimensional and unsteady mass continuity, momentum, and energy equations have been discretized using the finite volume method. SIMPLE algorithm has been applied for solving the pressure linked equations. The effect of rotation rates (α) on fluid flow and heat transfer were investigated numerically. Also, time-averaged (lift and drag coefficients and Nusselt number) results were obtained and compared with the literature data. A good agreement was obtained for both the local and averaged values.

Stability of the numerical solution of unsteady heat conduction: A mechanical approach

This work proposes a mechanical analog of the unsteady energy conservation equation for analysis of the stability of its numerical solution. The space discretized energy conservation equation is the analog of the linear momentum equation, from which no relevant information can be extracted concerning the stability of its numerical solution. The corresponding angular momentum equation can be obtained from the space discretized energy conservation equation, from which relevant information can be extracted concerning stability of the numerical solution. In that equation, the angular perturbation is the analog of the temperature perturbation. This approach/analogy and results help for a better understanding of the stability/instability of the numerical solution of unsteady diffusion problems.

Numerical investigations of the energy performance and pressure fluctuations for a waterjet pump in a non-uniform inflow

As a way of exploitation and utilization of ocean energy, the waterjet pump is used in a wide range of high-speed marine vessels over 30 knot. This paper aims to investigate the mechanism of the energy loss and pressure fluctuations caused by the non-uniform inflow for a waterjet pump. Unsteady internal flows inside the waterjet pump are simulated using the Reynolds-averaged Navier-Stokes equations with the SST k-ω turbulence model. The predicted pump head and efficiency are in reasonable accordance with the experimental data. The inflow non-uniformity would decrease the hydraulic head, efficiency and increase the axial force fluctuations in the impeller, causing large pulsations in the unsteady energy performance. Based on analyses of the energy loss, the turbulent kinetic energy production and the diffusion of the Reynolds stress are major sources of the energy loss in the waterjet pump. The non-uniform inflow induces a dramatic energy loss in the intake duct and diffuser with an apparent flow separation observed near the trailing edge of the diffuser blade. Due to the inflow non-uniformity, the pressure fluctuates violently at the impeller rotating frequency (fn) in the intake duct, impeller and near the diffuser inlet, but a dominant frequency of 2fn is generated by the unsteady flow separation near the diffuser outlet.

Dynamic simulation and control of solar biomass gasification for hydrogen-rich syngas production during allothermal and hybrid solar/autothermal operation

Solar biomass steam gasification using concentrated sunlight offers an efficient means of storing intermittent solar energy into renewable solar fuels while upgrading the carbonaceous feedstock. Such solar-driven (allothermal) processes have demonstrated the ability and the effectiveness for the production of high quality hydrogen-rich syngas, but they suffer from inherent barriers related to the variability of solar energy caused by cloud passages and shut off at night. The concept of hybrid solar/autothermal gasification appears promising to meet the requirement for stable and continuous operation under fluctuating or intermittent solar irradiation. To date, dynamic modelling to simulate coupled solar/combustion heating and steam gasification using real solar irradiation data has never been proposed and could be used to predict the annual performance of large-scale solar gasification plants. In this study, a dynamic mathematical model of a scaled-up solar gasification reactor was developed. The model was composed of a system of differential equations that were derived from unsteady mass and energy conservation equations. After an experimental validation step with the results from a lab-scale solar reactor, the dynamic model was applied at large scale to determine the reactor temperature and syngas production evolution during continuous day and night operation in both solar-only (allothermal) and hybrid solar/autothermal modes. Different reactants feeding management strategies were proposed and compared with the aim of achieving enhanced syngas productivity and optimized use of solar energy during solar-aided steam gasification. It was shown that the hybrid mode with partial oxy-combustion of the feedstock and dynamic feeding control results in the most stable process operation upon fluctuating solar power input, while ensuring continuous production of H2 and CO at night and during cloudy periods.

Hybrid lattice Boltzmann––Finite difference formulation for combined heat transfer problems by 3D natural convection and surface thermal radiation

In this study, a hybrid model for 3D natural convection combined with surface thermal radiation in a closed differentially heated cube was developed. Within this model, numerical procedure for fluid flow was considered in terms of the lattice Boltzmann method under Bhatnagar-Gross-Krook approximation with D3Q19 scheme. On the other hand, unsteady three-dimensional energy equation was solved by means of the finite difference technique. Developed hybrid approach was validated against experimental and up to date numerical data. Mathematical modelling was conducted for two-dimensional and three-dimensional problem formulations under variation of Rayleigh number, conduction-radiation number and surface emissivity. It was found that discrepancy between 2D and 3D results was increased with an enhancement in the radiation heat transfer rate. Computational performance of hybrid lattice Boltzmann method was several times higher than conventional CFD approach.

Numerical Calculations for a Boundary Layer Flow past a Moving Vertical Porous Plate with Suction/Injection and Thermal Radiation

The work presented herein investigates the velocity, heat transfer, Nusselt number and skin friction profiles involved in boundary layer flow past a moving vertical porous plate. Similarity transformations are employed to convert the governing nonlinear unsteady momentum and energy equations from their partial differential equation forms to boundary value ordinary differential equations. The resulting equations are then solved numerically by the Runge-Kutta fourth order method with the help of a shooting technique. Several features of the flow and heat transfer characteristics for different values of problem parameters are analyzed and discussed. These include the effects of the radiation parameter (R), suction and injection parameter (c), Grashof (Gr) and Prandtl (Pr) numbers on the flow and heat profiles. Numerical results show the impact of blowing and sucking as well as radation on boundary layer flows of this type. Both the skin frictions as well as the heat transfer rate are also significantly related to the radiation parameter. For all these cases; the numerical results are found to be in agreement with the physics of the problem.

Three-dimensional unsteady energy simulation of building envelopes composed of hollow concrete blocks

Building Energy Simulation (BES) tools commonly use 1-D formulation for computing conductions loads through building envelopes. As this assumption may cause significant errors on the prediction of building energy and thermal performance, this work proposes a methodology for taking into account the 3-D heat transfer phenomenon nature and compare the results for three case studies. The different approach is also used to investigate the effects of considering brick’s cavity detailing with convection and radiation phenomena on the results of transient simulations at the building scale. The present method has the potential to increase precision in the energy analysis of buildings and analyse more precisely the performance of elements of complex geometry. The results demonstrate that traditional simulation methods may not ensure good precision. The magnitude of relative errors varies significantly in each case study.

Modification of building energy simulation tool TRNSYS for modelling nonlinear heat and moisture transfer phenomena by TRNSYS/MATLAB integration

Software for numerical simulation of various types of energy used in buildings, i.e. building energy simulation (BES), have become an essential tool for recent research pertaining to building physics. TRNSYS is a well-known BES used in both academia and the construction industry for a wide range of simulations, such as the design and performance evaluation of buildings and related facilities for heating, cooling, and ventilation. TRNSYS has a modular structure comprising various components, and each component is interconnected and compiled through a common interface using a FORTRAN compiler. Its modular structure enables interactions with various external numerical simulation tools, such as MATLAB, Python, and ESP-r. For ordinary simulations of building energy load using TRNSYS, the generic module Type 56 is usually recommended, which provides detailed physics modelling of building thermal behaviours based on unsteady energy conservation equations and Fourier’s law for each building material. However, Type 56 explicitly depends on the transfer function method to discretise the original differential equations; therefore, it cannot model nonlinear phenomena, such as latent heat and moisture transfer between a building surface and ambient air. In other words, the current TRNSYS cannot be used to estimate the effectiveness of evaporation during cooling, which is a typical passive design method. Hence, the authors developed a MATLAB/TRNSYS integration scheme, in which TRNSYS was modified to model simultaneous heat and moisture transfer from the wet roof surface of a building. This scheme enabled TRNSYS to calculate the rate of evaporative heat and moisture transfer dynamically from the roof surface, assuming a control volume approximation of the roof surface. Finally, the effect of evaporative cooling on the thermal performance of an Indian building was estimated using the modified model.

Flows of real gas in nozzles with unsteady local energy supply

When gas flows at a high speed in a channel with a variable cross sectional area and high-intensity energy supply, it experiences complicated physical and chemical processes producing high-temperature gas effects. High-temperature gas effects are a key issue related to design and optimization of nozzles of plasmatron of alternating current. The finite volume method is applied to solve unsteady compressible Euler equations with high-temperature gas effects. Solutions of some benchmark test cases are reported, and comparison between computational results of chemically equilibrium and perfect air flowfields is performed. The results of numerical simulation of one-dimensional and two-dimensional under- and over-expanded nozzle flows with a moving region of energy supply are presented. Output nozzle parameters are calculated as functions of a number and time of burning of plasmatron arcs. The results obtained show a qualitative pattern of gas dynamics and thermal processes in the nozzle with unsteady energy supply demonstrating the displacement of the nozzle shock wave towards the nozzle outlet in the over-expanded nozzle flow in comparison to perfect gas flow.

Fabrication of potassium sodium niobate nano-particle/polymer composites with piezoelectric stability and their application to unsteady wind energy harvesters

We investigated the effects of poling conditions on the piezoelectric performance of potassium sodium niobate [(K,Na)NbO3, KNN]/polymer composites, to obtain their unsteady energy harvesting potential. KNN nanoparticle/polymer composites were designed and fabricated and the poling condition test was performed. The composites were polarized using the corona poling method for various poling conditions and then the piezoelectric coefficient d33 was measured. It was found that piezoelectricity does not decrease over days. Scanning electron microscopic observations were conducted to study the distribution of the nanoparticles in the matrix. Meanwhile, the microstructure of the composites was studied by X-ray diffraction. Unsteady wind energy harvesting tests were accomplished to investigate the output voltage characteristics in the KNN nanoparticle/polymer composites in unsteady winds. The study represents an important step in developing flexible energy harvesters with stable performance.

Analysis of entropy generation in biomimetic electroosmotic nanofluid pumping through a curved channel with joule dissipation

Biomimetic designs are increasingly filtering into new areas of technology in recent years. Such systems exploit characteristics intrinsic to nature to achieve enhanced adaptivity and efficiency in engineering applications. Peristaltic propulsion is an example of such characteristics and in the current article it is explored as a feasible mechanism for deployment in electrokinetic pumping of nanofluids through a curved distensible conduit as a model for a bioinspired smart device. The unsteady mass, momentum, energy and nanoparticle concentration conservation equations for a Newtonian aqueous ionic fluid under an axial electrical field are formulated and simplified using lubrication approximations and low zeta potential (Debye Hückel linearization). A dilute nanofluid is assumed with Brownian motion and thermophoretic body forces present. The reduced non-dimensional conservation equations are solved with the symbolic software, Mathematica 9 via the NDSolve algorithm for velocity, temperature, nano-particle concentration distributions for low zeta potential. An entropy generation analysis is also conducted. The influence of curvature parameter, maximum electroosmotic velocity (Helmholtz-Smoluchowski velocity), inverse EDL thickness parameter, zeta potential ratio and Joule heating parameter on transport characteristics is evaluated with the aid of graphs and contour plots. Temperature profiles are elevated with positive Joule heating and reduced with negative Joule heating whereas the opposite behaviour is observed for the nano-particle concentrations.

Numerical investigation of forced convective heat transfer around a solid circular cylinder utilizing nanofluid in unsteady regime

This paper presents a numerical solution for low Reynolds number, unsteady flow around, and heat transfer from a stationary circular cylinder placed in a uniform flow. The fluid is assumed to be incompressible and of constant property. Twodimensional and unsteady mass continuity, momentum, and energy equations have been discretized using finite volume method. A SIMPLE algorithm has been applied for solving the pressure linked equations. The range of Reynolds numbers was investigated which varied from 50 to 300 with volume fraction on Cu nanoparticles varying from 1 to 5 % at the constant wall temperature. The results of the heat transfer characteristics of nanofluid flow over a circular cylinder showed marked improvement comparing with the base fluid. It is found that the vorticity, pressure coefficient, and recirculation length are increased by the addition of nanoparticles into base fluid. Moreover, the local and mean Nusselt numbers are enhanced due to adding nanoparticles into base fluid.

Natural convection in inclined channel for air cooling of photovoltaic panels

Reducing the operating temperature of a photovoltaic (PV) module is an effective way to improve efficiency and prevent damage from overheating. The present paper focuses on the study of the effect of inclination on air natural convection in an asymmetrically heated channel (at uniform heat flux), in laminar regime. This configureuration models the passive and natural air-cooling of PV panels by inclined chimneys. The computational procedure solves the unsteady two-dimensional Navier-Stokes and energy equations by a finite volume approach while the projection method decouples the pressure from the velocity. The heat transfer and fluid flow are analyzed for a wide range of modified Rayleigh numbers varying from 102 to 105 and for inclination angles between 15o and 90o with respect to horizontal position. The results show that the mass flow rate and the average Nusselt number increase with the angle of inclination as well as with the modified Rayleigh number. However, a significant reduction in heat transfer rate and induced flow rate is observed for the low angles of inclination. To enhance the cooling of the PV panel, extensions are added at the inlet and outlet of the channel. The simulations show that only the downstream extensions of the channel are effective in improving the induced mass flow rate and therefore the convective heat transfer.

Corona Poling Conditions for Barium Titanate/Epoxy Composites and their Unsteady Wind Energy Harvesting Potential

The objective of this paper is to design and fabricate barium titanate (BTO)/epoxy composites, investigate the effect of poling conditions on their piezoelectric properties, and obtain their unsteady energy harvesting potential. The poling condition test deals with the effect of the poling conditions on the piezoelectricity of BTO/epoxy composites. The specimens are polarized by corona poling under different conditions, and their piezoelectric coefficient d33 is measured. The distribution of the piezoelectric particles in the matrix is studied using scanning electron microscopy (SEM), and the microstructure of the particle is investigated using X‐ray diffraction (XRD). A wind harvesting test is then performed, and the output voltage is measured for the composite sheets under unsteady air flow. This study opens the way for the development of flexible energy harvesting devices.

Thermal radiation effects on MHD flow with heat and mass transfer of micropolar fluid between two vertical walls

In the present study, the boundary layer free convective unsteady flow of an incompressible micropolar fluid under a uniform magnetic field is considered with thermal radiation in symmetric and asymmetric boundary conditions. The governing unsteady boundary layer momentum, angular momentum, energy and concentration equations with initial and boundary conditions are nondimensionalised and solved numerically. For validation of numerical solutions, analytical expression for velocity, micro-rotation, temperature and concentration profiles of steady state case have been obtained and compared through the tabular form. It is found that magnetic field , vortex viscosity and its steady state time has retarding effect on velocity and micro-rotation of micropolar fluid. For both cases (asymmetric and symmetric), thermal radiation parameter tends to improve velocity and micro-rotation profiles. Physically, due to increasing Nr, heat is generated in fluid flow, which leads to improvement in heat transfer as well as velocity throughout the fluid flow region.

Numerical Research on the Energy Loss of a Single-Stage Centrifugal Pump with Different Vaned Diffuser Outlet Diameters

Unsteady pressure pulsation and energy loss both in diffuser and volute of a single-stage centrifugal pump with three different vaned diffuser outlet diameters were investigated. Reynolds-Averaged Navier-Stokes (RANS) equations combined with shear stress transport (SST) turbulence model were used to predict flow field in the centrifugal pump. Results showed that pressure pulsation amplitudes of blade-passing frequency and high-frequencies both in diffuser and volute gradually decrease with the vaned diffuser outlet diameter increases. Moreover, energy loss in diffuser showed better periodicity than that in volute due to the interaction between diffuser and impeller.

Thermodynamic analysis of energy dissipation and unsteady flow characteristic in a centrifugal dredge pump under over-load conditions

The present paper aims to investigate the energy dissipation related to unsteady flow phenomena inside a three-bladed impeller of a centrifugal dredge pump under over-load operating conditions. Three-dimensional unsteady numerical simulations of the centrifugal pump are performed by adopting the SAS SST-curvature correction turbulence model with the total energy equation. The simulating results are verified by comparing the performance results and pressure fluctuation with available experimental data. The unsteady flow patterns and energy dissipation in the rotating impeller are analysed by entropy distribution and pressure fluctuation spectra. A high-entropy area appears in the impeller flow passage when the discharge increases. It is indicated in the unsteady simulation results that a vortex flow with high entropy generates and detaches periodically, which causes the hydraulic energy loss under over-load operating conditions. In numerical simulations, a frequency as 3.3 times of rotating frequency is found in the pressure spectral analysis at 1.45 Q0 operating condition, which is related to the unsteady flow structure. The secondary flow near the volute tongue is found at 1.45 Q0 operating condition due to the large angle of attack when discharge increases.

Corona Poling Conditions for Barium Titanate/Epoxy Composites and their Unsteady Wind Energy Harvesting Potential

Corona Poling Conditions for Barium Titanate/Epoxy Composites and their Unsteady Wind Energy Harvesting Potential