M. Z. Yusoff

The transient response for different types of erodable surface thermocouples using finite element analysis

The transient response of erodable surface thermocouples has been numerically assessed by using a two dimensional finite element analysis. Four types of base metal erodable surface thermocouples have been examined in this study, included type-K (alumel-chromel), type-E (chromel-constantan), type-T (copper-constantan), and type-J (iron-constantan) with 50 mm thick- ness for each. The practical importance of these types of thermocouples is to be used in internal combustion engine studies and aerodynamics experiments. The step heat flux was applied at the surface of the thermocouple model. The heat flux from the measurements of the surface temperature can be commonly identified by assuming that the heat transfer within these devices is one-dimensional. The surface temperature histories at different positions along the thermocouple are presented. The normalized surface temperature histories at the center of the thermocouple for different types at different response time are also depicted. The thermocouple response to different heat flux variations were considered by using a square heat flux with 2 ms width, a sinusoidal surface heat flux variation width 10 ms period and repeated heat flux variation with 2 ms width. The present results demonstrate that the two dimensional transient heat conduction effects have a significant influence on the surface temperature history measurements made with these devices. It was observed that the surface temperature history and the transient response for thermocouple type-E are higher than that for other types due to the thermal properties of this thermocouple. It was concluded that the thermal properties of the surrounding material do have an impact, but the properties of the thermocouple and the insulation materials also make an important contribution to the net response.

Buoyancy-assisted mixed convective flow over backward-facing step in a vertical duct using nanofluids

Laminar mixed convective buoyancy assisting flow through a two-dimensional vertical duct with a backward-facing step using nanofluids as a medium is numerically simulated using finite volume technique. Different types of nanoparticles such as Au, Ag, Al2O3, Cu, CuO, diamond, SiO2 and TiO2 with 5 % volume fraction are used. The wall downstream of the step was maintained at a uniform wall temperature, while the straight wall that forms the other side of the duct was maintained at constant temperature equivalent to the inlet fluid temperature. The walls upstream of the step and the backward-facing step were considered as adiabatic surfaces. The duct has a step height of 4.9 mm and an expansion ratio of 1.942, while the total length in the downstream of the step is 0.5 m. The downstream wall was fixed at uniform wall temperature 0 ≤ ΔT≤ 30 °C, which was higher than the inlet flow temperature. The Reynolds number in the range of 75 ≤ Re ≤ 225 was considered. It is found that a recirculation region was developed straight behind the backward-facing step which appeared between the edge of the step and few millimeters before the corner which connect the step and the downstream wall. In the few millimeters gap between the recirculation region and the downstream wall, a U-turn flow was developed opposite to the recirculation flow which mixed with the unrecirculated flow and traveled along the channel. Two maximum and one minimum peaks in Nusselt number were developed along the heated downstream wall. It is inferred that Au nanofluid has the highest maximum peaks while diamond nanofluid has the highest minimum peak. Nanofluids with a higher Prandtl number have a higher peak of Nusselt numbers after the separation and the recirculation flow disappeared.

Multigrid solution of Euler equations using high-resolution NVD differencing scheme for unstructured meshes

High-speed compressible flows in a nozzle and over an airfoil have been computed by solving the Euler equations using the GAMMA differencing scheme for spatial discretisation on unstructured grid. This high-resolution technique originally developed in a segregated algorithm has now been modified for the present coupled solver by introducing a non-linear blending factor to enhance its convergence property while preserving the Total Variation Diminishing (TVD) criterion. The efficiencies of the GAMMA scheme and its variant have been augmented with a novel agglomeration multigrid scheme to accelerate the convergence to steady state using the multi-stage Runge-Kutta time-marching technique.

Numerical and experimental comparative study on nanofluids flow and heat transfer in a ribbed triangular duct

Numerical and experimental investigation is carried out to study the effect of combined vortex generator and nanofluids on turbulent heat transfer and fluid flow characteristics in an equilateral triangular duct. A triangular duct provides a lower heat transfer rate and lower pressure drop compared to other duct configurations. The improvement of heat transfer of these ducts increases their importance for providing higher heat transfer and lower pressure drop. Two different types of nanoparticles, namely Al2O3 and SiO2, suspended in distilled water with two particle concentrations are successfully prepared and experimentally tested. The numerical and experimental results show dramatic heat transfer enhancement by using a vortex generator and nanofluids, simultaneously accomplished with a moderate increase in the friction factor. A low deviation has been seen between the present numerical and experimental results.

The effect of scratch technique on the thermal-product value of temperature sensors

The effect of different scratch techniques, mainly abrasive papers and scalpel blades used to form the junctions of temperature sensors, on the thermal-product value of these sensors, was examined. A dynamic calibration procedure of scratched sensors in a shock tube facility which allows easy evaluation of their thermal-product value is outlined. The thermal product of a particular sensor was found to be dependent on the flow Mach number, junction scratch technique, junction location, and also on the enthalpy conditions. It was shown that using different scratch techniques normally results in different thermal-product values of sensors. The experimental procedure used in the present study has yielded practical data on characteristics of scratched temperature sensors; these data can be used in accurate measurement of transient heat transfer under hypersonic flow conditions.

Fast response surface temperature sensor for hypersonic vehicles1

This paper describes the design, fabrication, and evaluation technique of fast response Surface Temperature Sensor (STS). This STS was made of chromel-constantan elements with 2.2 and 0.8 mm in diameter. The calibration technique using shock tube facility for measuring the transient surface temperature and heat transfer rate is also presented. It has been proved that the STS response time is very short (less than 50 µs), and a rise time in studies of a transient surface temperature is less than 0.5 µs.

Intelligent Water Dispersal Controller: Comparison between Mamdani and Sugeno Approaches

This paper presents a comparison of fuzzy inference methods in intelligent water dispersal controller primarily focuses on grass watering. In irrigation system, measuring and monitoring soil moisture from the soil information and climatologic factors would determine the amount of water for sufficient soil moisture. Mamdani-style and Sugeno-style inference methods have been tested and evaluated using this information. These methods were tested on normal subsets. Fuzzy rules were determined based on three inputs namely; Bermuda Turf grass coefficient, evapotranspiration (FT) rate, and tensiometer data. The result illustrated that the most convincing fuzzy inference method applied was the Mamdani-style compared to Sugeno-style. It was shown that the controller used less water in turf grass irrigation. Overall, both of the tested methods give significant result to the recognition of soil moisture level.

Parametric study of an improved gamma differencing scheme based on normalized-variable formulation for low-speed flow with artificial compressibility technique

Based on the normalized-variable formulation (NVF), the modified GAMMA (MGAMMA) scheme previously devised for compressible flow calculations is now incorporated into an incompressible multigrid solver using the artificial compressibility (AC) technique on an unstructured grid. The MGAMMA scheme used in the present work is parameterized in order to further assess its accuracy and convergence compared to other well-known second-order high-resolution (HR) schemes, such as GAMMA and MINMOD. Testing is performed on three sets of problems: (1) advection of four scalar profiles; (2) flow in the Binnie-Green nozzle; and (3) flow past the NACA 0012 and NACA 4412 airfoils. It is shown that when lowering the diffusion-controlled parameter (β m ), which serves as an attempt to reduce the numerical diffusion of the HR schemes tested, only the MGAMMA scheme is able to provide a converged solution while attaining solution accuracy.

Optimal Design of Opening Ventilation Shaft by Kriging Metamodel Assisted Multi-objective Genetic Algorithm

Ventilation shaft designs are the most effective devices used for ventilating underground shelter. A Kriging Metamodel assisted Multi-Objective Genetic Algorithm (MOGA) was utilised for the evaluation of an optimal design for the opening ventilation shaft, which improved the ventilation rate of a naturally-ventilated underground shelter. Computational Fluid Dynamics (CFD) was employed as a simulation tool, and the result was validated with experimental data from the previous literature. For the optimisation, three parameters were considered for the effectiveness of the ventilation rate. The generated results found an excellent performance of the strength correlation between parameters and the recommended optimised design. This revealed that an equal opening area has a better ventilation rate for naturally-ventilated underground shelters. Overall, these results can provide support selecting ventilation shaft opening areas in relation to the design of ventilation systems.

Numerical Modeling of Wet Steam Flow in Steam Turbine Channel

In power station practice, work is extracted from expanding steam in three stages namely High Pressure(HP), Intermediate Pressure(IP) and Low Pressure(LP) turbines. During the expansion process in the LP turbine, the steam cools down and at some stages, it nucleates to become a two-phase mixture. It is well-acknowledged in the literature that the nucleating and wet stages in steam turbines are less efficient compared to those running with superheated steam. With the advent of water-cooled nuclear reactor, the problem becomes more prominent due to the fact that in water-cooled nuclear reactor, the steam generated is in saturated condition. This steam is then supplied to the HP steam turbine which therefore has also to operate on wet steam. One of the tangible problems associated with wetness is erosion of blading. The newly nucleated droplets are generally too small to cause erosion damage but some of the droplets are collected by the stator and rotor blades to form films and rivulets on the blade and casing walls. On reaching the trailing edges or the tips of the blades, the liquid streams are re-entrained into the flow in the form of coarse droplets. It is these larger droplets that cause the erosion damage and braking loss in steam turbine. However, the formation and behaviour of the droplets have other important thermodynamic and aerodynamic consequences that lower the performance of the wet stages of steam turbines.