UTAR Engineering Student

Free Turbulent Jet Wall turbulence is turbulence motions which are constrained by one or more boundaries. In wall turbulence, the turbulence is generated in velocity gradient caused by the no-slip condition. Free turbulence is turbulence motions which are unaffected by walls and develop and spread in an open ambient fluid. Three examples of free turbulence are free-shear layer (mixing layer), free jet, and wake behind a body immersed in a stream.               Free jets can be defined as a pressure driven unrestricted flow of a fluid into a quiescent ambiance, the wall ceiling or obstruction does not influence the jet. Free turbulent jet occurs when the fluid is discharged between nozzle orifices into a stationary or moving liquid. Just downstream of the disturbance that caused the velocity gradients, the flow will be developing and non-similar. Further downstream, the flow will be similar and the velocity profiles w...

Cooling Tower Demonstration System Figure 1 : Cooling Tower Demonstration System No Component 1 Orifice 2 Water Distributor 3 Temperature Indicator 4 Make-up tank 5 Heater 6 Inclined Manometer 7 Valves 8 Receiver Tank 9 Blower 10 Temperature Sensor INTRODUCTION AND THEORY: Cooling tower function is used to cool down hot water by removing the heat. The heat of the water is mainly removed by evaporation process. Besides that, water also cooled down by radiation, conduction, convection. However, the effect of cooling is not significant compared to evaporation. Figure  2 : Schematic Diagram of Mass flow for cooling Tower Cooling tower is widely used in industry and it main function is removing excessive unwanted heat from high temperature water. Hea...

Ideal Gas Law Ideal gas law: pV=mRT Where p = pressure             V = volume             m = mass             R = gas constant and       T = temperature When we allow an ideal gas in a container to expand into a larger volume, we get the following relationship:                           Where subscripts 1 denote the initial state  and subscripts 2 denote the final state after the expansion. The Graph of Mass After Mixing, m2 Against Mass Before Mixing, m1 First and foremost, the ideal gas is a type of hypothetical gas which all collisions between atoms or molecules are perfectly elastic and in which there are no intermolecular attractive forces. One can think of it as a set of perfectly hard balls that collide but otherwise do not interact with each oth...

Transient Response of a Position Controller When a step input is given to a position controller, the loop takes time to react to the applied input. Also, depending upon the given system parameters, oscillation can occur at the output during the transient time period. The major cause of the time delay comes from the added inertia of the moving parts. Therefore, the higher the inertia, there will be more delay.  Usually, the system gain is preferred to be high to improve system response time. However, when the gain becomes excessive, it will cause undesired overshoot at the output. Transient response of a system can be easily observed on an oscilloscope when the system is stimulated with a square wave input. Such an arrangement is shown in Figure 4. Figure 4 : System diagram for Transient Respond Experiment The function generator in Figure 4 provides synchronized square-wave and ramp signals. As it is shown in the figure, the ramp signal is used to drive the X-...

Closed Loop Position Controller In a closed loop position controller system, the positional information from an output potentiometer (Po) which is mechanically coupled to a motor is fed back to a control amplifier. Then, the reference position input from the input potentiometer (Pi) is combined with the feedback signal at the input of the amplifier which drives the motor in proportion to the difference between two signals. When the two positions are identical, the output of the amplifier becomes zero. A simplified system diagram of a closed loop position controller which will be used in this experiment is shown in Figure 2. Figure 2 : Close loop position controller There are three amplifiers in Figure 2. The A 1 is an error signal generator, A 2 is an error signal amplifier and A 3 is the driver for the motor M. As Pi is turned away from Po, the difference between two potentiometers voltages become an error signal which appears at the input of A 1 . The error signa...

Closed Loop Control System  Closed loop control system is defined as feedback control system. Closed loop control system is almost identical to open loop control system except it has at least one feedback loop from output to input. Figure 1 : Schematic diagrams of closed loop and open loop             Feedback loop is used to monitor the output and feedback to input. Thus, inaccuracy at output can be corrected and desired output can obtained. Therefore, the output of closed loop control system is more accurate than open loop control system but more expensive and difficult to design. The main advantages of closed loop system are wider bandwidth, output error can be detect, reliable and accurate output. Examples of closed loop system are air conditioner, automatic electric iron, water level controller and servo voltage stabilizer. For air conditioner, fans speed and heats exchange rate of condenser and evapor...

Stabilizing an Unstable Position Controller For a properly designed system, the transient response effect should gradually decay within a few seconds, and the system should reach a steady state operation. However, for an improperly designed system, the transient response can lead into an oscillation which can be sustained over a long period of time. Such a system is unstable and should be corrected for a stable operation. The instability of a system is mainly caused by either a long time constant in the system or an excessive gain in the system. A closed loop speed controller can mitigate oscillation up to certain extent. However, in case a highly stable system is desired with a maximum gain, the system needs more advanced technique than a simple speed control loop. The experiment in this section is limited to a speed controlled stabilization method. The same experiment system as in the previous section is used for this experiment.

Position Control with Speed Feedback When the gain is raised in a position control system to minimize the deadband effect, the closed loop system responded with an overshoot which resulted in undesired system oscillation. One way to mitigate oscillation is to add a brake which is proportional to the speed to the output shaft. The brake method may produce a satisfactory result. However, it consumes a significant power and makes acceleration of the load difficult. Better way of preventing oscillation is to add a speed control loop to the position control loop. The speed control loop provides a negative feedback signal from the output of the Tachogenerator which is proportional to the speed of the motor. The effect of adding a speed loop is illustrated in Figure 1 (a), (b), and (c). An optimum control of the speed feedback loop produces a system response as shown in (b). Figure 1 : Effect of a speed feedback loop...

Metal Fatigue Metallic fatigue occurred at both low and high temperature. It is considered mainly from the perspective of the interaction between the microstructure, the deformation mode, and the mechanical state (Pineau, et al., 2016). The fatigue strength of metals is depending on the crack growth resistance provided by the grain boundaries, the phase boundaries, and various dislocations present in the material (Vallellano, et al., 2009). Therefore, fatigue crack initiation position and the minimum load cycle number before initiation of fatigue are essential to determine in the fatigue analysis. (Topaç, et al., 2009). Fatigue is a type of failure that takes place in the structures when exposed to dynamic forces. Those dynamic forces will produce dynamic stresses and give rise to fatigue failure of structures. The real-life example is fatigue failure of vehicle’s axle housing arisen due to dynamic stresses that induce by rough and uneven road surface (Topaç, et al., 2009). Ne...

Material Selection for Heat Insulation The selection of insulating material is depend on the properties of material such as thermal resistance, heat capacity, density and thermal conductivity. The purpose of insulation is to ensure is to avoid the heat from radiating away and also to improve the working environment condition. Generally, insulation idea is approach by the heat capacity of material and the existing of pocket air , air has lower thermal conductivity than solid and the stagnant air has low convection air coefficient in the absence of bulk movement flow of fluid.  (1) Mineral Rock Form by spun molten glass, stone, ceramic fiber into fiber structure. (2) Calcium Silicate Form by react polyol (alcohol with two or more hydroxyl group) with polymeric isocyanate. (3) Fiber Glass Form by finely woven silicon, glass powder and tiny shards of glass spun into microfibers. (4) Polyurethane Foam Form by react methylene diphenyldiisocyanate (MDI) and...