• Energy Research

In this study, fluid flow and heat transfer in a vertical lid-driven CuO–water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian–Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young’s modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young’s modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young’s modulus of 250 compared to configuration for the cavity having the Young’s modulus of 5000.

For prediction of limit cycle oscillations of linearly unstable thermo-acoustic systems, a frequency-domain, low-order system with explicit modal coupling is developed. To this purpose, a model for the nonlinear heat source dynamics is obtained from unsteady computational fluid dynamics in combination with feed-forward neural network identification. From the neural network, an equivalent representation for the input-output relation in Volterra series form is derived, where Volterra kernels are computed in terms of the weights of the neural network. Then the kernels are transformed into the frequency domain to obtain the higher order transfer functions, through which the modes are coupled. In this way nonlinear energy exchange among the modes can be described explicitly. Comparison with a Galerkin time domain simulation shows that deviations from purely sinusoidal behaviour in the limit cycle are captured correctly, while the computational cost is drastically reduced.

Purpose The purpose of this paper is to examine the coupled heat and mass transport of different shaped porous moist objects in a rectangular channel under the effects of convective drying. Numerical simulations were performed under turbulent conditions for cylindrical, triangular and rectangular shaped different food products in a two-dimensional channel. Design/methodology/approach Finite element method was used for the unsteady problem and, effects of drying air velocity (AV) and temperature on transport mechanism were evaluated. Three different food materials were used for the circular shaped object and drying performance of the products under different conditions was compared. Findings Results showed that, changing the air temperature has an important effect on drying for all shaped objects and all materials. The same effect was seen for the AV as, increasing the velocity had positive effects on drying. Two identical objects were placed in the channel one behind the other, and this configuration showed that location of the object in the channel is also important for drying. The moisture content in the object at the front is lower than in the object behind at the end of drying. Originality/value This paper can provide technical support to optimize drying performance in the industry with comprehensive data for the process.

In current text, we developed CVFEM code for nanomaterial hydrothermal management through a permeable compound cavity including two temperature model. Radiation and Lorentz source terms were added in formulations. Impacts of radiation parameter, Rayleigh, Hartmann number, interface heat transfer parameter and nanoparticles’ shape on nanofluid behavior were demonstrated. Contours indicate that convective mode becomes stronger with augment of buoyancy term. By increasing Nhs, conduction becomes more effective and Nusselt number reduces. As radiation term enhances, Nusselt number augments.

AbstractNumerical study of double jet impingement cooling of an isothermal surface with Al2O3-water nanofluid under the influence of magnetic field was performed. Galerkin-weighted residual finite ...

In this study, thermoelectric generation with impinging hot and cold nanofluid jets is considered with computational fluid dynamics by using the finite element method. Highly conductive CNT particles are used in the water jets. Impacts of the Reynolds number of nanojet stream combinations (between (Re1, Re2) = (250, 250) to (1000, 1000)), horizontal distance of the jet inlet from the thermoelectric device (between (r1, r2) = (−0.25, −0.25) to (1.5, 1.5)), impinging jet inlet to target surfaces (between w2 and 4w2) and solid nanoparticle volume fraction (between 0 and 2%) on the interface temperature variations, thermoelectric output power generation and conversion efficiencies are numerically assessed. Higher powers and efficiencies are achieved when the jet stream Reynolds numbers and nanoparticle volume fractions are increased. Generated power and efficiency enhancements 81.5% and 23.8% when lowest and highest Reynolds number combinations are compared. However, the power enhancement with nanojets using highly conductive CNT particles is 14% at the highest solid volume fractions as compared to pure water jet. Impacts of horizontal location of jet inlets affect the power generation and conversion efficiency and 43% variation in the generated power is achieved. Lower values of distances between the jet inlets to the target surface resulted in higher power generation while an optimum value for the highest efficiency is obtained at location zh = 2.5ws. There is 18% enhancement in the conversion efficiency when distances at zh = ws and zh = 2.5ws are compared. Finally, polynomial type regression models are obtained for estimation of generated power and conversion efficiencies for water-jets and nanojets considering various values of jet Reynolds numbers. Accurate predictions are obtained with this modeling approach and it is helpful in assisting the high fidelity computational fluid dynamics simulations results.

Abstract In this study, mixed convection in a lid driven trapezoidal cavity filled with Al2O3–water nanofluid under the effect of an inclined magnetic field was numerically investigated for various electrical conductivity models. The top and bottom wall of the trapezoidal cavity were maintained at constant cold and hot temperatures and the top wall is moving at a constant speed in positive x direction. The governing equations are solved with finite element method. Numerical simulations were performed for different values of Richardson numbers (between 0.01 and 25), strength and orientation of the uniform magnetic field (Hartmann number (between 0 and 40), magnetic inclination angle (between 0 o and 90 o )) and solid volume fraction of the nanofluid (between 0 and 0.03) for different electrical conductivity models. It was observed that as the value of the Richardson number, strength of the magnetic field and solid particle volume fractions enhance, discrepancy between the average Nusselt number increases for systems with different electrical conductivity models. Magnetic inclination angle for which the difference between average heat transfer rate is minimized for different electrical conductivity models depends on the side wall inclination angle of the trapezoidal cavity. After performing an optimization study, it was found that the optimum value of magnetic inclination angle is dependent on the electrical conductivity model.

Abstract In the present study, an efficient methodology is proposed for optimizing the convective drying performance of multiple porous moist objects in a channel. As the first step of the method, a PDE constraint optimization routine is utilized to obtain the optimum values of distance between the objects for maximizing the transfer rates while in the second part, unsteady coupled field equations for the channel and porous moist object domains are invoked for convective drying of multiple objects for the optimum spacing values. Finite element method is used for the numerical simulations. It was observed that the recirculation zones established behind the rectangular objects are profoundly affected with the distance between the objects. There is 12.5 % variation in the average Nu for the first block with varying the horizontal distance between the objects. The effects of vertical spacing on the average Nu is profound for the second object. while up to 80 % enhancement in the average Nu is obtained when the value is changed from sy = 0 to sy = 1.5hp. However, the optimum values of the distance that maximize the heat transfer are obtained as sx = 1.1hp and sy = 1.931hp for the horizontal distance and vertical distance. At this optimum values of parameters, reduction in the moisture content becomes 33.4 % and 98.015 % for drying times at 1000 s and 5000 s. These values are also checked with the parametric unsteady coupled field equations for the porous moist objects which shows the improved time dependent drying features for the two blocks at the optimum points.

Abstract In the present study, free convection in a cavity with a corrugated partition which have different fluids on different parts of the partition was numerically examined. In one of the domains carbon nanotube (CNT)-water nanofluid with an inclined uniform magnetic field is considered. A triangular wave form of conductive corrugated partition is used. The numerical simulation was performed with Galerkin weighted residual finite element method. Various values of pertinent parameters of current thermal configuration such as Rayleigh number (between 104 and 106), Hartmann number (between 0 and 50), magnetic inclination angle (between 0° and 90°), solid particle volume fraction (between 0 and 0.03), number of triangular waves (between 1 and 40), height of triangular waves (between 0.01H and 0.2H) and thermal conductivity ratio (between 0.1 and 100) and their influence on the hydro-thermal behavior were examined. It was observed that significant enhancements in the Nusselt number is obtained with CNTs. The average heat transfer decreases for higher values of Hartmann number but slightly varies as the value of magnetic inclination angle changes. As the number and height of the triangular waves increase, the average heat transfer reduce which are 32 % and 27 % for the highest values of number and height of triangular waves both for water and nanofluid. For forecasting the average heat transfer coefficient of the current thermal system, a novel method based on Proper Orthogonal Decomposition (POD) and Adaptive-Network-Based Fuzzy Inference System (ANFIS) is used which yields highly accurate results that are computationally inexpensive.