Search results

This study aims to develop a new design for the fluid-safety valve to make it more environmentally friendly.

Computational fluid dynamics is carried out to analyse the behaviour of flow in both traditional and new safety valves.

The possibility of failure in the new design under the maximum allowable working pressure is analysed using finite element analysis.

Investigating a new low-fluid pressure safety valve design.

The purpose of this paper is to investigate the heat transfer of laminar and turbulent pulsating Al203/water nanofluid flow in a two-dimensional channel. In the laminar flow range, with increasing Reynolds number (Re), the velocity gradient is increased. Also, the Nusselt number (Nu) is increased, which causes increase in the overall heat transfer rate. Additionally, in the change of flow regime from laminar to turbulent, average thermal flux and pulsation range are increased. Also, the effect of different percentage of Al₂O₃/water nanofluid is investigated. The results show that the addition of nanofluids improve thermal performance in channel, but the using of nanofluid causes a pressure drop in the channel.

The pulsatile flow and heat transfer in a two-dimensional channel were investigated.

The numerical results show that the Al₂O₃/Water nanofluid has a significant effect on the thermal properties of the different flows (laminar and turbulent) and the average thermal flux and pulsation ranges are increased in the change of flow regime from laminar to turbulent. Also, the addition of nanofluid improves thermal performance in channels.

The originality of this work lies in proposing a numerical analysis of heat transfer of pulsating Al₂O₃/Water nanofluid flow -with different percentages- in the two-dimensional channel while the flow regime change from laminar to turbulent.

The purpose of this study is to investigate the pulsating flow in a three-dimensional channel. Channel flow is laminar and turbulent. After validation, the effect of different channel cross-sectional geometries (circular, hexagonal and triangular) with the pulsating flow are investigated. For this purpose, the alumina nanofluid was considered as a working fluid with different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent).

In this study, the pulsatile flow was investigated in a three-dimensional channel. Channel flow is laminar and turbulent.

The results show that the fluid temperature decreases by increasing the volume percentage of particles of Al₂O₃; this is because of the fact that the input energy through the wall boundary is a constant value and indicates that with increasing the volume percentage, the fluid can save more energy at a constant temperature. And by adding Al₂O₃ nanofluid, thermal performance improves in channels, but it should be considered that the use of nanofluid causes a pressure drop in the channel.

Alumina/water nanofluid with the pulsating flow was investigated and compared in three different cross-sectional channel geometries (circular, hexagonal and triangular). The effect of different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent) of Al₂O₃ nanofluid on temperature, velocity and pressure are studied.

Using the computational fluid dynamics (CFD) technique, this paper aims to investigate the influence of key parameters such as throat diameter; the suction ratio on the flow field behaviors such as Mach number; pressure; and temperature.

To investigate the effect of throat diameter, it is simulated for 4, 6, 8 and 10 mm as throat diameters. The governing equations have been solved by standard code of Fluent Software together with a compressible 2 D symmetric and turbulence model with the standard k–ε model. First, the influence of the throat diameter is investigated by keeping the inlet mass flow constant.

The results show that a place of shock wave creation is changed by changing the throat diameter. The obtained results illustrate that the maximum amount of Mach number is dependent on the throat diameter. It is obtained from the results that for smaller throats higher Mach numbers can be obtained. Therefore, for mixing purposes smaller throats and for exhausting bigger throats seems to be appropriate.

The obtained numerical results are compared to the existing experimental ones which show good agreement.

This study aim to use the finite volume method to solve differential equations related to three-dimensional simulation of a solar collector. Modeling is done using ANSYS-fluent software program. The investigation is done for a photovoltaic (PV) solar cell, with the dimension of 394 × 84 mm², which is the aluminum type and receives the constant heat flux of 800 W.m⁻². Water is also used as the working fluid, and the Reynolds number is 500.

In the present study, the effect of fluid flow path on the thermal, electrical and fluid flow characteristics of a PV thermal (PVT) collector is investigated. Three alternatives for flow paths, namely, direct, curved and spiral for coolant flow, are considered, and a numerical model to simulate the system performance is developed.

The results show that the highest efficiency is achieved by the solar cell with a curved fluid flow path. Additionally, it is found that the curved path’s efficiency is 0.8% and 0.5% higher than that of direct and spiral paths, respectively. Moreover, the highest pressure drop occurs in the curved microchannel route, with around 260 kPa, which is 2% and 5% more than the pressure drop of spiral and direct.

To the best of the authors’ knowledge, there has been no study that investigates numerically heat transfer, fluid flow and electrical performance of a PV solar thermal cell, simultaneously. Moreover, the effect of the microchannel routes which are considered for water flow has not been considered by researchers so far. Taking all the mentioned points into account, in this study, numerical analysis on the effect of different microchannel paths on the performance of a PVT solar collector is carried. The investigation is conducted for the Reynolds number of 500.

This study aims to simulate Hunter turbine in Computer Forensic Examiner (CFX) environment dynamically. For this purpose, the turbine is designed in desired dimensions and simulated in ANSYS software under a specific fluid flow rate. The obtained values were then compared with previous studies for different values of angles (θ and α). The amount of validation error were obtained.

In this research, at first, the study of fluid flow and then the examination of that in the tidal turbine and identifying the turbines used for tidal energy extraction are performed. For this purpose, the equations governing flow and turbine are thoroughly investigated, and the computational fluid dynamic simulation is done after numerical modeling of Hunter turbine in a CFX environment.

The failure results showed; 11.25% for the blades to fully open, 2.5% for blades to start, and 2.2% for blades to close completely. Also, results obtained from three flow coefficients, 0.36, 0.44 and 0.46, are validated by experimental data that were in high-grade agreement, and the failure value coefficients of (0.44 and 0.46) equal (0.013 and 0.014), respectively.

In this research, at first, the geometry of the Hunter turbine is discussed. Then, the model of the turbine is designed with SolidWorks software. An essential feature of SolidWorks software, which was sorely needed in this project, is the possibility of mechanical clamping of the blades. The validation is performed by comparing the results with previous studies to show the simulation accuracy. This research’s overall objective is the dynamical simulation of Hunter turbine with the CFX. The turbine was then designed to desired dimensions and simulated in the ANSYS software at a specified fluid flow rate and verified, which had not been done so far.

The main objective of this paper is to investigate the response of human skin to an intense temperature drop at the surface. In addition, this paper aims to evaluate the efficiency of finite difference and finite volume methods in solving the highly nonlinear form of Pennes’ bioheat equation.

One-dimensional linear and nonlinear forms of Pennes’ bioheat equation with uniform grids were used to study the behavior of human skin. The specific heat capacity, thermal conductivity and blood perfusion rate were assumed to be linear functions of temperature. The nonlinear form of the bioheat equation was solved using the Newton linearization method for the finite difference method and the Picard linearization method for the finite volume method. The algorithms were validated by comparing the results from both methods.

The study demonstrated the capacity of both finite difference and finite volume methods to solve the one-dimensional and highly nonlinear form of the bioheat equation. The investigation of human skin’s thermal behavior indicated that thermal conductivity and blood perfusion rate are the most effective properties in mitigating a surface temperature drop, while specific heat capacity has a lesser impact and can be considered constant.

This paper modeled the transient heat distribution within human skin in a one-dimensional manner, using temperate-dependent physical properties. The nonlinear equation was solved with two numerical methods to ensure the validity of the results, despite the complexity of the formulation. The findings of this study can help in understanding the behavior of human skin under extreme temperature conditions, which can be beneficial in various fields, including medical and engineering.

The purpose of this paper is to study the two-dimensional micropolar fluid flow with conjugate heat transfer and mass transpiration. The considered nanofluid has graphene nanoparticles.

Governing nonlinear partial differential equations are converted to nonlinear ordinary differential equations by similarity transformation. Then, to analyze the flow, the authors derive the dual solutions to the flow problem. Biot number and radiation effect are included in the energy equation. The momentum equation was solved by using boundary conditions, and the temperature equation solved by using hypergeometric series solutions. Nusselt numbers and skin friction coefficients are calculated as functions of the Reynolds number. Further, the problem is governed by other parameters, namely, the magnetic parameter, radiation parameter, Prandtl number and mass transpiration. Graphene nanofluids have shown promising thermal conductivity enhancements due to the high thermal conductivity of graphene and have a wide range of applications affecting the thermal boundary layer and serve as coolants and thermal management systems in electronics or as heat transfer fluids in various industrial processes.

Results show that increasing the magnetic field decreases the momentum and increases thermal radiation. The heat source/sink parameter increases the thermal boundary layer. Increasing the volume fraction decreases the velocity profile and increases the temperature. Increasing the Eringen parameter increases the momentum of the fluid flow. Applications are found in the extrusion of polymer sheets, films and sheets, the manufacturing of plastic wires, the fabrication of fibers and the growth of crystals, among others. Heat sources/sinks are commonly used in electronic devices to transfer the heat generated by high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes to a fluid medium, thermal radiation on the fluid flow used in spectroscopy to study the properties of materials and also used in thermal imaging to capture and display the infrared radiation emitted by objects.

Micropolar fluid flow across stretching/shrinking surfaces is examined. Biot number and radiation effects are included in the energy equation. An increase in the volume fraction decreases the momentum boundary layer thickness. Nusselt numbers and skin friction coefficients are presented versus Reynolds numbers. A dual solution is obtained for a shrinking surface.

This paper aims to investigate the effects of different volume fractions of Al₂O₃-water nanofluid on flow and heat transfer under chaotic convection conditions in an L-shaped channel, comparing the difference of numerical simulation results between single-phase and Eulerian–Lagrangian models.

The correctness and accuracy of the two calculation models were verified by comparing with the experimental values in literature. An experimental model of the L-shaped channel was processed, and the laser Doppler velocimeter was used to measure the velocities of special positions in the channel. The simulated values were compared with the experimental results, and the correctness and accuracy of the simulation method were verified.

The calculated results using the two models are basically consistent. Under the condition of Reynolds number is 500, when the volume fractions of nanofluid range from 1% to 4%, the heat transfer coefficients simulated by single-phase model are 1.49%–25.80% higher than that of pure water, and simulated by Eulerian–Lagrangian model are 3.19%–27.48% higher than that of pure water. Meanwhile, the friction coefficients are barely affected. Besides, there are obvious secondary flow caused by lateral oscillations on the cross sections, and the appearance of secondary flow makes the temperature distributions uniform on the cross section and takes more heat away, thus the heat transfer performance is enhanced.

The originality of this work is to reveal the differences between single-phase and two-phase numerical simulations under different flow states. The combination of chaotic convection and nanofluid indicates the direction for further improving the heat transfer threshold.

This paper aims to present the most influential factors on classroom indoor PM_2.5 (Particulate Matter < 2.5 µ), determining the level of PM_2.5 concentration in five pre-schools located in the most densely populated district of the Tehran metropolitan area (district 6) as a case study to consider the children's exposure to air pollutants and introducing a suitable model, for the first time, to predict PM_2.5 concentration changes, inside pre-schools.

Indoor and outdoor classes PM_2.5 concentrations were measured using two DUSTTRAK direct-reading instruments. Additional class status information was also recorded; concurrently, urban PM_2.5 concentrations and meteorological data were obtained from the fixed monitoring stations and Meteorological Organization. Then, the predicted concentrations of the indoor PM_2.5, from introduced multiple linear regression model via SPSS, compared with the nearest urban air pollution monitoring stations data.

The average outdoor PM_2.5 concentration (43 ± 0.32 µg m⁻³) was higher than the mean indoor (32 ± 0. 21 µg m⁻³), and both were significantly (p < 0.001) surpassing the 24-h EPA standard level. The indoor PM_2.5 concentrations had the highest level in the autumn (48.7 µg m⁻³) and significantly correlated with the outdoor PM_2.5 (r = 0.94, p < 0.001), the number of pupils, ambient temperature, wind speed, wind direction and open area of the doors and windows (p < 0.001). These parameters, as the main determinants, have led to present a 7-variable regression model, with R² = 0.705, which can predict PM_2.5 concentrations in the pre-school classes with more than 80% accuracy. It can be presumed that the penetration of outdoor PM_2.5 was the main source of indoor PM_2.5 concentrations.

This study faced several limitations, such as accessibility to classrooms, and limitations in technicians' numbers, leading to researchers monitoring indoor and outdoor PM concentrations in schools once a week. Additionally, regarding logistical limitations to using monitoring instruments in pre-schools simultaneously, correction factors by running the instruments were applied to obtain comparable measurements.

The author hereby declares that this submission is his own work and to the best of its knowledge it contains no materials previously published or written by another person.