Numerical investigation of thermal comfort in an isolated family house under natural cross-ventilation

Thermal comfort for naturally ventilated buildings mainly depends on parameters such as the outside weather, building configuration and neighborhood effects. Even though most research works include studies on indoor thermal comfort coupled with outdoor conditions, they are generally limited to singlesided ventilation. In addition, only a very few such investigations employ the human thermal comfort index (PMV) in the analysis of the indoor environment, which is generally held to be more realistic than other indices. Simulations using computational fluid dynamics (CFD) have been carried out for the wind-driven natural ventilation (for a cooling purpose) of a residential building with two inlet openings to understand the relationship between the wind speed and human thermal sensation index. The numerical model is validated against available experimental data. The CFD results show that human thermal comfort is significantly affected by the wind speed, and this factor can be more active in this type of building if the wind has a relatively high speed

Impact of an external boundary wall on indoor flow field and natural cross-ventilation in an isolated family house using numerical simulations

The external boundary wall is a main architectural feature of a typical residential building in Iraq, which is expected to decrease the rate of airflow entering the openings of the building. In this study, the impact of an external boundary wall on natural cross-ventilation and flow patterns inside an isolated family house was analyzed using computational fluid dynamics (CFD) simulations. The wall was located in front of the building and three different conditions were tested: basic case (without a wall) and two cases using walls of different heights. The study employed the techniques of large eddy simulation (LES) with the dynamic Smagorinsky subgrid-scale model because of the unsteady flow and high turbulence around the building. The CFD simulations were validated against the available wind tunnel experiments. It was observed that the external boundary wall created well distributed indoor air flow and improved the indoor environment regarding the mean velocity inside the building. Also, increasing the height of the wall by 20% did not offer noticeable improvement on the mean velocity distribution, whereas the ventilation airflow rate was reduced significantly to less than half when the wall was present. The results of this study are expected to inform building designers of the impact of an external boundary wall on the flow patterns in relation to the rate of ventilation and indoor mean velocity

Computational study of unsteady mixed convection heat transfer of nanofluids in a 3D closed lid-driven cavity

Mixed heat convection of three-dimensional unsteady flow of four different types of fluids in a double lid-driven enclosure is simulated by a two-phase mixture model in this project. The cubic cavity with moving isothermal sidewalls has uniform heat flux on the middle part of the bottom wall, and the other remaining walls forming the enclosure are adiabatic and stationary. The relevant parameters in the present research include Reynolds number Re (5000–30,000), nanoparticle diameter (25 nm–85 nm), and nanoparticle volume fraction (0.00–0.08). In general, remarkable effects on the heat transfer and fluid patterns are observed by using nanofluids in comparison to the conventional fluid. Different types of nanofluids or different diameters of nanoparticles can make pronounced changes in the heat convection ratio. In addition, increasing in either volume fraction of nanoparticles or Reynolds number leads to increasing in the Nusselt number, fluctuation kinetic energy and root mean square velocity of the fluid in the domain. It is also found that both URANS and LES methods have shown good performance in dealing with unsteady flow conducted in this project. However, the comparisons have elucidated clearly the advantages of the LES approach in predicting more detailed heat and flow structures

Impact of windward inlet-opening positions on fluctuation characteristics of wind-driven natural cross ventilation in an isolated house using LES

This paper presents a computational fluid dynamics (CFD) simulation of coupled outdoor wind flow and indoor airflow in the investigation on the horizontal positions of openings on the fluctuation of cross ventilation and flow-field inside an isolated family house. Two inlet-opening positions located at the same height are used to investigate the impact of the position of windward inlet openings on the ventilation rate and flow-field inside the building. Due to unsteady flow and high turbulence near the openings, the study employed the large eddy simulation with the dynamic Smagorinsky subgrid-scale model techniques, with the CFD simulations being validated against data from available wind tunnel experiments. The study showed that the rate of ventilation through openings located near the centre of the building is higher and more steady than the flow rate of openings located near the sides of the building

Numerical investigation of height impact of local exhaust combined with an office work station on energy saving and indoor environment

A healthy and comfortable working environment is very important for improving its occupants' productivity. In this study, the evaluation of the height impact for the proposed local exhaust ventilation system on the indoor thermal comfort, inhaled air quality and energy savings was explored numerically. In the proposed system, the exhaust opening was combined with the office workstation in a single unit. The intention was to help extract the warmed and contaminated air locally before it disperses across the room. The performance of the new system at three different heights of the combined system (1.4 m, 1.6 m and 2.0 m) above floor level was investigated numerically with a validated CFD model in a room with and without inclusion of the novel local exhaust ventilation system. The performance of using this system was evaluated using the main evaluation indices for any ventilation system such as energy saving, occupant thermal comfort, draught risk and the quality of the indoor air. The results showed that by selecting a suitable height for the combined system, a significant improvement on energy savings (up to 22.56%) and inhaled air quality can be realised with an acceptable level of the indoor thermal comfort. It was found that in comparison to cases 2 (1.4 m) and 4 (2.0 m), case 3 (1.6 m) was considered to be the best height at which optimal performance could be achieved from the LEVO system

Mixed convection heat transfer of turbulent flow in a three-dimensional lid-driven cavity with a rotating cylinder

A numerical study has been carried out to investigate the combined forced and natural convection heat transfer in a differentially heated 3D obstructed cavity with a thermally insulated rotating circular cylinder. The cavity has a hot stationary bottom wall and a cold top lid-driven wall, and all the other walls completing the domain are motionless and adiabatic. The simulations are performed for different Reynolds numbers, Re = 5000, 10,000, 15,000 and 30,000, and for dimensionless rotational speeds of the cylinder, 0 ≤ Ω ≤ 10. The performance of two turbulence methods, Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS), has been evaluated in this research. The flow and thermal fields are studied through flow vectors, isotherm contours and iso-surfaces temperature, as well as through the average Nusselt number (Nuav) and velocity components. The results demonstrate clearly that the flow patterns and the thermal fields are influenced strongly by increasing either the rotating cylinder speed or the Reynolds number. Furthermore, both LES and URANS solutions can capture the essential feature of the primary eddies in the cavity. But this study has shown convincing evidence that only the LES method can predict the structure details of the secondary eddies that have profound effects on the heat transfer behaviour within the enclosure

A comparison study of mixed convection heat transfer of turbulent nanofluid flow in a three-dimensional lid-driven enclosure with a clockwise versus an anticlockwise rotating cylinder

A turbulent 3D mixed convective flow of pure water, H 2 O, and nanofluid, SiO 2 -H 2 O, inside a differentially heated moving wall enclosure containing an insulated rotating cylinder over a range of rotational speeds, − 5 ≤ Ω ≤ 5, Reynolds numbers, 5000 and 10,000, and constant Grashof number, is numerically investigated. A cooled lid-driven top wall and a heated bottom wall are the only thermally uninsulated walls in this domain. A standard k-ε for the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach is applied to the turbulence calculation. Nusselt number, mean velocity profile, streamline, isothermal and isosurface temperatures are derived and presented in this paper to gain a better understanding of the effects of clockwise and anti-clockwise rotating cylinder directions on the heat transfer and flow patterns. Interesting changes in flow structure and heat transfer have been analysed for all rotational speeds and fluid types at both Reynolds number values. Nonlinear increases in Nusselt number have been observed by using nanofluid instead of pure water. The wall shear stress and turbulent kinetic energy profiles are found to be influenced by changing the Reynolds number and rotational speed and direction. Furthermore, incremental heat transfer rates at the walls can be achieved by increasing the cylinder rotation speeds, but these increases have weaker influences on the top wall than on the bottom wall

Unsteady simulations of mixed convection heat transfer in a 3D closed lid-driven cavity

Unsteady mixed convection heat transfer in a 3D closed cavity with constant heat flux on the centre part of the bottom wall and isothermal sidewalls moving in the same vertical direction is investigated numerically in this research. The other remaining walls forming the geometry are kept stationary and adiabatic. This research is accomplished with different Reynolds number, Re = 5000, 10,000, 15,000 and 30,000. Numerical methodology based on the finite volume method is utilised. The simulations and analysis have been carried out by evaluating the performance of two turbulence methods, Unsteady Reynolds-Averaged Navier–Stokes (URANS) and Large Eddy Simulation (LES), in terms of flow vectors, isotherm contours, turbulent kinetic energy, the average Nusselt number (Nuav) and the local Nusselt (Nulocal) number along the hot part of the bottom wall. The results show that by increasing the Reynolds number leads to enhanced Nusselt number and turbulent kinetic energy of the fluid in the domain. Moreover, both LES and URANS solutions captured the existence of the two primary vortexes (clockwise and anticlockwise). However, the comparisons have demonstrated clearly the ability and accuracy of the LES method in predicting the secondary vortexes in the corners of the cavity

Simulation of molten steel refining in a gas-stirred ladle using a coupled CFD and thermodynamic model

In secondary steelmaking, the gas-stirred ladle refining process is enhanced by applying a vacuum. A three phase (steel/gas/slag) mathematical model based on the fundamental transport equations has been reported in the literature. This model was used to study the steelmaking refining process. In this approach, the gas-stirred ladle system fluid flow prediction from Computational Fluid Dynamics (CFD) analysis was linked with thermodynamic analysis, with some thermal simplification. The model predicts the changes in the mass concentration of the elements of concern (Al, O, and S) during the refining process. In the present work we aim to enhance the modeling in the literature. Here we use Fluent as the CFD package to predict the flow pattern of the three phase (steel/gas/slag) system. The thermodynamic package is MTDATA from the National Physical Laboratory (NPL), which has the capability to make thermodynamic predictions for multi-component systems containing up to 30 elements. Therefore, it is possible to solve for the properties of the slag as a function of composition and temperature. The two packages are being linked in a Visual Basic environment. The mass concentration of the different elements at the steel/slag interface is being updated at a pre-defined Δt time step. Comparison of the model calculated results with data from the literature show the potential of this model. Real plant data will be used to validate this multi phase simulation model

The effect of inflow conditions on the transition to turbulence in large eddy simulations of spatially developing mixing layers

The effect of inflow conditions on the transition to turbulence in large eddy simulations of spatially developing mixing layer