Zainal Ambri Abdul Karim

Numerical Investigation of Turning Diffuser Performance by Varying Geometric and Operating Parameters

This paper presents a numerical investigation of pressure recovery and flow uniformity in turning diffusers with 90o angle of turn by varying geometric and operating parameters. The geometric and operating parameters considered in this study are area ratio (AR= 1.6, 2.0 and 3.0) and inflow Reynolds number (Rein=23, 2.653E+04, 7.959E+04, 1.592E+05 and 2.123E+05). Three turbulence models, i.e. the standard k-e turbulence model (std k-e), the shear stress transport model (SST-k-W) and the Reynolds stress model (RSM) were assessed in terms of their applicability to simulate the actual cases. The standard k-e turbulence model appeared as the best validated model, with the percentage of deviation to the experimental being the least recorded. Results show that the outlet pressure recovery of a turning diffuser at specified Rein improves approximately 32% by varying the AR from 1.6 to 3.0. Whereas, by varying the Rein from 2.653E+04 to 2.123E+05, the outlet pressure recovery at specified AR turning diffuser improves of approximately 24%. The flow uniformity is considerably distorted with the increase of AR and Rein. Therefore, there should be a compromise between achieving the maximum pressure recovery and the maximum possible flow uniformity. The present work proposes the turning diffuser with AR=1.6 operated at Rein=2.653E+04 as the optimum set of parameters, producing pressure recovery of Cp=0.320 and flow uniformity of su=1.62, with minimal flow separation occurring in the system.

Design and Development of Low Subsonic Wind Tunnel for Turning Diffuser Application

In practice, it is basically difficult even with controlled measurement environment to acquire a steady, uniform and fully developed flow. The flow entering diffuser was severely distorted despite a sufficient hydrodynamic entrance length already introduced. This was mainly due to the imperfect joining of duct and the abrupt change of the inlet cross-section applied. In this study, several basic features of a low subsonic wind tunnel, i.e. a centrifugal blower with 3-phase inverter, a settling chamber, screens and a contraction cone, are designed and developed for a turning diffuser application in order to improve the flow quality. The flow profiles are examined using Pitot static probe at five measurement points within the range of inflow Reynolds number, Rein= 5.786E+04-1.775E+05. The steady, uniform and fully developed turbulent flow profiles with an average deviation with theory of about 3.5% are obtained. This proves that a good flow quality could be produced by means of incorporating some basic features of a low subsonic wind tunnel to the system.

The Performance of Turning Diffusers at Various Inlet Conditions

A turning diffuser is often introduced in the flow line to recover the energy losses by converting the kinetic energy to pressure energy. There are two types of turning diffusers, i.e. a 2-D and 3-D diffuser that are commonly defined by their expansion direction. This study aims to investigate the performance of a 2-D and a 3-D turning diffuser with 90o angle of turn and an area ratio, AR=2.16 by means of varying operating conditions. The geometry configurations applied for a 2-D turning diffuser are outlet-inlet configurations, W2/W12-D=2.160, X2/X12-D =1.000 and an inner wall length to an inlet throat width ratio, Lin/W12-D=4.370, whereas for a 3-D turning diffuser, they are W2/W13-D=1.440, X2/X13-D =1.500 and Lin/W13-D=3.970. The operating conditions represented by inflow Reynolds numbers, Rein are varied from 5.786E+04 to 1.775E+05. Particle image velocimetry (PIV) is used to examine the flow quality, and a digital manometer provides the average static pressure at the inlet and outlet of the turning diffuser. A compromise between the maximum permissible pressure recovery and flow uniformity is determined based upon the need. Whenever the flow uniformity being the need it is promising to apply a 3-D turning diffuser for Rein=1.027E+05 - 1.775E+05 and a 2-D turning diffuser for Rein=5.786E+04-6.382E+04. On the other hand, it is viable to opt for a 3-D turning diffuser for Rein=5.786E+04-6.382E+04 and a 2-D turning diffuser for Rein=1.027E+05-1.775E+05 in the case of the outlet pressure recovery being the need. The secondary flow separation takes place prior at 1/2Lin/W1 for a 2-D turning diffuser, whereas approximately at 3/4Lin/W1 for a 3-D turning diffuser.

Verification of Fully Developed Flow Entering Diffuser and Particle Image Velocimetry Procedures

3-Dstereoscopic PIV is capable of measuring 3-dimensional velocity components. Itinvolves a very sophisticated routine during setup, calibration, measurementand data processing phases. This paper aims to verify the 3-D stereoscopic PIVmeasurement procedures and to prove that the flow entering thediffuser is a fully developed flow. A diffuser inlet of rectangularcross-section, 130 mm x 50 mm is presently considered. For verification, thevelocities from PIV are compared with the velocities from pitot static probeand theory. The mean velocity obtained using pitot static probe is 2.44 m/s,whereas using PIV is 2.46 m/s. It thus gives the discrepancy of 0.8%. There isalso a good agreement between the mean velocity measured by PIV and theoreticalvalue with the discrepancy of 1.2%. This minor discrepancy is mainly due touncertainties in the experiments such as imperfect matching of coordinatesbetween the probe and laser sheet, unsteadiness of flow, variation in density andless precision in calibration. Basically, the operating procedures of 3-Dstereoscopic PIV have successfully been verified. Nevertheless, the flowentering diffuser is not perfectly developed due to the imperfect joining ductand the abrupt change of inlet cross-section introduced. Therefore, improvementto the existing rig is proposed by means of installing settling chamber withmultiple screens arrangement and contraction cone.

A class of exact solutions to the three-dimensional incompressible Navier―Stokes equations

Abstract An exact solution of the three-dimensional incompressible Navier–Stokes equations with the continuity equation is produced in this work. The solution is proposed to be in the form V = ∇ Φ + ∇ × Φ where Φ is a potential function that is defined as Φ = P ( x , y , ξ ) R ( y ) S ( ξ ) , with the application of the coordinate transform ξ = k z − ς ( t ) . The potential function is firstly substituted into the continuity equation to produce the solution for R and S . The resultant expression is used sequentially in the Navier–Stokes equations to reduce the problem to a class of nonlinear ordinary differential equations in P terms, in which the pressure term is presented in a general functional form. General solutions are obtained based on the particular solutions of P where the equation is reduced to the form of a linear differential equation. A method for finding closed form solutions for general linear differential equations is also proposed. The uniqueness of the solution is ensured because the proposed method reduces the original problem to a linear differential equation. Moreover, the solution is regularised for blow up cases with a controllable error. Further analysis shows that the energy rate is not zero for any nontrivial solution with respect to initial and boundary conditions. The solution being nontrivial represents the qualitative nature of turbulent flows.

On a special class of analytical solutions to the three-dimensional incompressible Navier–Stokes equations

Abstract The three-dimensional incompressible Navier–Stokes equations with the continuity equation are solved analytically in this work. The spatial and temporal coordinates are transformed into a single coordinate ξ . The solution is proposed to be in the form V = ∇ Φ + ∇ × Φ where Φ is a potential function that is defined as Φ = P ( x , ξ ) R ( ξ ) . The potential function is firstly substituted into the continuity equation to produce the solution for R and the resultant expression is used sequentially in the Navier–Stokes equations to reduce the problem to the class of nonlinear ordinary differential equations in P terms. Here, more general solutions are also obtained based on the particular solutions of P . Explicit analytical solutions are found to be mathematically similar for the cases of zero and constant pressure gradient. Two examples are given to illustrate the applicability of the method. It is also concluded that the selection of variables for the potential function can be interchanged from the beginning, resulting in similar explicit solutions.

Analytical investigation of collector optimum tilt angle at low latitude

An analytical investigation on the optimum tilt angle for solar collectors at low latitude, a case study of Universiti Teknologi PETRONAS (UTP), 4.39°N and 100.98°E, Malaysia is presented in this work. The study employed Hay, Davies, Klucher, and Reindl (HDKR) anisotropic sky model to evaluate the available hourly solar radiation on inclined surface using the location metrological data. The tilt angles considered were 0° to 30° in step of 3° with the inclusion of the location latitude angle. The study employed the ratio of global solar radiation on tilted surface to the global solar radiation on horizontal surface in the decision of the optimum tilt. The system equations were converted to MATLAB codes to solve for the optimum tilt angles. The results show that the optimum tilt varies monthly but gave zero degree for south facing collector for the months of April to August; thus, the investigation also considered north facing orientation for the months of April to September. The optimum annual tilt angle f...

Cooling System for Electric Motor of an Electric Vehicle Propulsion

Electric motor performance directly affects the overall performance of an electric vehicle (EV). The electric motor windings heats up when operated under extreme load and hence, reducing the efficiency of the vehicle. As such, EV propulsion system requires cooling systems, not only to the electric motor but also to the battery banks in order to ensure efficient operation and maximizing the electric components and vehicle lifetime. The project focuses on the design and development of a liquid cooling system for an electric vehicle propulsion system to determine the optimum size and cooling capacity by thermodynamic analysis. This paper described the analysis of energy transfer (heat removal) by using thermal resistance network approach in determining the suitable design for the cooling system of an AC-50 induction electric motor. The CAD drawing was generated to suit the dimension constrain and the cooling system was completed using CATIA software. The results showed that the optimal design for the water jacket for the maximum heat removal of 5500 W from the electric motor, should have a wall thickness of 0.5 cm with an annular thickness of 2.4 cm. Both copper and aluminium exhibited similar cooling capabilities with the latter having lower cost and ease of manufacturing.

Numerical Simulation of High Frequency Electromagnetic Wave in Microwave Cavity for Soot Oxidation

Soot oxidation temperature by high frequency electromagnetic energy was proposed using numerical simulation by combining electromagnetic with transient thermal analyses. Equation of electric field distribution in a microwave cavity with perfect electric conductor surfaces and TE10 mode is formulated from Helmholtz equation. The dissipated heat distribution is calculated from the electric field distribution. Six study cases for electric field and dissipated heat distributions were implemented by using ANSYS software based on finite element method. The impact of dielectric sample properties, position, size and shape inside the microwave cavity were predicted. The results from the simulation of electric field and dissipated heat were compared with available data in literature and showed the validity of the analysis. It was found that the electric field forming hot spots at penetration depth and front corners of the soot sample and penetration depth is equal to 12mm but equal to 0 for samples with dimensions less than penetration depth. Dissipated heat pattern depend on electric field pattern and dielectric properties.

Experimental Investigation of In Situ Soot Oxidation Using Electromagnetic Waves

This paper presents the experimental results of smoke opacity and exhaust gas measurements due to the oxidation of soot at different microwave power levels to the exhaust gas. The experiment attempts to ascertain the soot oxidation capability of using microwave in reducing smoke from the diesel engine. The exhaust gas from a diesel engine was directed into the microwave generator system which then flows through the chamber assembly that contains the soot trap. Three different microwave power levels of 0.5, 1.0 and 1.5 kW were generated and exposed to the soot at different exposure time. The results showed that when the power level of the electromagnetic waves was increased, the amount of smoke opacity reduced between 32 to 65 % depending on the microwave power levels. Due to the oxidation of the carbon particles of the soot, CO2 gas increased in corresponding to the decreased in the smoke opacity. The experimental work also found that NOx gas was also reduced due to the breaking down of NOx at the localised high temperature of the soot trap. Hence, the microwave generator system has proven its capability as an in-situ soot oxidation device for deployment in diesel vehicles.