Porous materials in building energy technologies—a review of the applications, modelling and experiments

Improving energy efficiency in buildings is central to achieving the goals set by Paris agreement in 2015, as it reduces the energy consumption and consequently the emission of greenhouse gases without jeopardising human comfort. The literature includes a large number of articles on energy performance of the residential and commercial buildings. Many researchers have examined porous materials as affordable and promising means of improving the energy efficiency of buildings. Further, some of the natural media involved in building energy technologies are porous. However, currently, there is no review article exclusively focused on the porous media pertinent to the building energy technologies. Accordingly, this article performs a review of literature on the applications, modelling and experimental studies about the materials containing macro, micro, and nano-porous media and their advantages and limitations in different building energy technologies. These include roof cooling, ground-source heat pumps and heat exchangers, insulations, and thermal energy storage systems. The progress made and the remaining challenges in each technology are discussed and some conclusions and suggestions are made for the future research

Optimization of flapping-wing micro aircrafts based on the kinematic parameters using genetic algorithm method

In this paper the optimization of kinematics, which has great influence in performance of flapping foil propulsion, is investigated. The purpose of optimization is to design a flapping-wing micro aircraft with appropriate kinematics and aerodynamics features, making the micro aircraft suitable for transportation over large distance with minimum energy consumption. On the point of optimal design, the pitch amplitude, wing reduced frequency and phase difference between plunging and pitching are considered as given parameters and consumed energy, generated thrust by wings and lost power are computed using the 2D quasi-steady aerodynamic model and multi-objective genetic algorithm. Based on the thrust optimization, the increase in pitch amplitude reduces the power consumption. In this case the lost power increases and the maximum thrust coefficient is computed of 2.43. Based on the power optimization, the results show that the increase in pitch amplitude leads to power consumption increase. Additionally, the minimum lost power obtained in this case is 23% at pitch amplitude of 25°, wing reduced frequency of 0.42 and phase angle difference between plunging and pitching of 77°. Furthermore, the wing reduced frequency can be estimated using regression with respect to pitch amplitude, because reduced frequency variations with pitch amplitude is approximately a linear function

Simulation of conjugate radiation-forced convection heat transfer in a porous medium using the lattice Boltzmann method

In this paper, a lattice Boltzmann method is employed to simulate the conjugate radiation–forced convection heat transfer in a porous medium. The absorbing, emitting, and scattering phenomena are fully included in the model. The effects of different parameters of a silicon carbide porous medium including porosity, pore size, conduction–radiation ratio, extinction coefficient and kinematic viscosity ratio on the temperature and velocity distributions are investigated. The convergence times of modified and regular LBMs for this problem are 15 s and 94 s, respectively, indicating a considerable reduction in the solution time through using the modified LBM. Further, the thermal plume formed behind the porous cylinder elongates as the porosity and pore size increase. This result reveals that the thermal penetration of the porous cylinder increases with increasing the porosity and pore size. Finally, the mean temperature at the channel output increases by about 22% as the extinction coefficient of fluid increases in the range of 0–0.03

Large eddy simulation of the flameless oxidation in the IFRF furnace with varying inlet conditions

In the present study, large eddy simulation methodology is applied to investigate the 3D non-premixed flameless oxidation in the IFRF furnace. In order to serve this purpose, to model the combustion and radiation, the partially stirred reactor and finite volume discrete ordinate model are used, respectively.Moreover, the detailed mechanism of GRI-2.11 is undertaken to represent chemistry reactions. The present simulations agree qualitatively well with published experimental data. Finally, the present study focusses on the assessment of the effects of variations in the fuel vertical injection by adding an inert gas as well as the fuel temperature on combustion behavior. The results revealed that important changes occur in the characteristics of the flameless oxidation process

Numerical analysis of wind turbines blade in deep dynamic stall

This study numerically investigates kinematics of dynamic stall, which is a crucial matter in wind turbines. Distinct movements of the blade with the same angle of attack (AOA) profile may provoke the flow field due to their kinematic characteristics. This induction can significantly change aerodynamic loads and dynamic stall process in wind turbines. The simulation involves a 3D NACA 0012 airfoil with two distinct pure-heaving and pure-pitching motions. The flow field over this 3D airfoil was simulated using Delayed Detached Eddy Simulations (DDES). The airfoil begins to oscillate at a Reynolds number of Re = 1.35 × 105. The given attack angle profile remains unchanged for all cases. It is shown that the flow structures differ notably between pure-heaving and pure-pitching motions, such that the pure-pitching motions induce higher drag force on the airfoil than the pure-heaving motion. Remarkably, heaving motion causes excessive turbulence in the boundary layer, and then the coherent structures seem to be more stable. Hence, pure-heaving motion contains more energetic core vortices, yielding higher lift at post-stall. In contrast to conventional studies on the dynamic stall of wind turbines, current results show that airfoils’ kinematics significantly affect the load predictions during the dynamic stall phenomenon