Climate, Environment and Biodiversity
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- ItemEffect of solution treatment on high tempreature oxidation of Fe-33Ni-19Cr alloys Fe-40Ni-24Cr alloys.(Universiti Teknologi Malaysia, 2015) Parimin, NorazianaNickel-based superalloys have the ability to form protective surface oxide scales at high temperature that provides them with resistance against further high temperature oxidation. In this research two types of nickel-based alloys namely, Fe-33Ni-19Cr and Fe-40Ni-24Cr were solution treated to vary the austenite grain size in order to observe its effect on the oxidation properties. The alloys were heat treated at temperatures of 950ºC, 1000ºC, 1050ºC, 1100ºC, 1150ºC and 1200ºC for 3 hours followed by water quench. The untreated and heat treated alloys were then subjected to high temperature oxidation under isothermal and cyclic condition for 500 hours and 150 cycles respectively in a specially designed oxidation rig. Thermogravimetric analysis in high purity oxygen was also performed on the alloys. The alloys were then analysed using optical microscope, scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer. The results show that the oxide scales formed consist of various metal-based oxides with thickness of 1 µm to 10 µm. Both alloys show parabolic growth indicating the oxide was formed based on diffusion-controlled mechanism. It was found that the heat treatment processes at 950ºC, 1000ºC and 1050ºC produced fine austenite grains of 55 – 61 µm for Fe-33Ni-19Cr and 27 – 33 µm for Fe-40Ni-24Cr alloys. Alloys treated at 1100ºC, 1150ºC and 1200ºC produced coarse austenite grains of 65 – 100 µm for Fe-33Ni-19Cr and 36 – 41 µm for Fe-40Ni-24Cr alloys. Both alloys with fine austenite grains exhibited lower oxidation rate in isothermal and cyclic oxidation tests. This is due to the availability of ion diffusion path within the grain boundaries of fine grain alloys and hence allows the rapid formation of the protective oxide layer. Therefore, these alloys can be used for high temperature applications.
- ItemCombustion performance of various syngas compositions in swirl combustor.(Universiti Teknologi Malaysia, 2017) Samiran, Nor AfzanizamThe challenge of using syngas in combustion system is the composition variability and low calorific value. Syngas mainly consists of H2 and CO and other sub component such as N2, CO2 and H2O. High H2-enriched syngas would result in high NOx production for some combustion cases. Whereas high CO concentration is posed with stability issues. The presence of sub-component as a diluent improves the emission characteristic but slows down the chemical reaction rate and calorific values. The variability in syngas strongly depends on the type of gasification technique, feedstock and oxidation agent. The present study therefore aims to investigate the combustion performance of different configuration in composition of syngas using premixed swirl mode technique. Various simulated syngases of CO and H2-dominant syngas or CO-rich and H2-rich syngas were used as fuels to evaluate the performance of emissions, diluent effects, lean blowout limit and flame structure. Further investigation on combustion of syngas was fundamentally conducted using numerical approach in which a comparative study on flame structure and reaction zone species were evaluated between those syngas fuels. Measurement by gas analyser was used to evaluate the performance of combustion emission and direct photography was used to analyse the flame appearance. Lean blowout test was performed by gradually reducing the fuel flowrate until flame blowout occur. For numerical method, two different combustion models namely flamelet generated manifold (FGM) and chemical equilibrium (CE) models were implemented to predict the combustion characteristic of syngas and the result obtained was then validated with experimental results. The results indicate that high CO-rich syngas shows evidently less NOx and CO emissions as compared to the other dominant CO fuel. Higher fraction of CO2 dilution results in reduction of NOx emissions, with pronounced impact on fuel-rich cases. There was minimal effect on CO emissions with increased dilution of CO2. The lean blowout limit test shows that higher CO content results in blowout at higher equivalence ratio. Addition of hydrocarbon fuel such as CH4 or hydrogen extends the blowout limit as the flammability limit is stretched to ultra-lean region. Dilution of unreactive CO2 in syngases results in higher lean blowout limit. Higher fraction of H2 in syngas produces both lower NOx emission and lean blowout limits. The optimum characteristic of high H2-rich syngas is also validated by numerical approach using FGM method. The numerical computation found that the increasing content of H2 in syngas results in lower flame temperature, subsequently leading to reduced flame height and lower NO emissions.
- ItemActive vibration control of flexible beam incorporating recursive least square and neural network algorithms.(Universiti Teknologi Malaysia, 2017) Abd. Jalil, NurhanafifiIn recent years, active vibration control (AVC) has emerged as an important area of scient ific study especially for vibrat ion suppression of flexible structures. Flexible structures offer great advantages in contrast to the conventional structures, but necessary action must be taken for cancelling the unwanted vibration. In this research, a simulation algorithm represent ing flexible beam with specific condit ions was derived from Euler Bernoulli beam theory. The proposed finite difference (FD) algorithm was developed in such way that it allows the disturbance excitat ion at various points. The predicted resonance frequencies were recorded and validated with theoretical and experimental values. Subsequent ly, flexible beam test rig was developed for collecting data to be used in system ident ificat ion (SI) and controller development. The experimental rig was also utilised for implementation and validat ion of controllers. In this research, parametric and nonparametric SI approaches were used for characterising the dynamic behaviour of a lightweight flexible beam using input - output data collected experimentally. Tradit ional recursive least square (RLS) method and several artificial neural network (ANN) architectures were utilised in emulat ing this highly nonlinear dynamic system here. Once the model of the system was obtained, it was validated through a number of validation tests and compared in terms of their performance in represent ing a real beam. Next, the development of several convent ional and intelligent control schemes with collocated and non-collocated actuator sensor configurat ion for flexible beam vibrat ion attenuation was carried out. The invest igat ion involves design of convent ional proportional-integral-derivat ive (PID) based, Inverse recursive least square active vibrat ion control (RLS-AVC), Inverse neuro active vibration control (Neuro-AVC), Inverse RLS-AVC with gain and Inverse Neuro-AVC with gain controllers. All the developed controllers were tested, verified and validated experimentally. A comprehensive comparat ive performance to highlight the advantages and drawbacks of each technique was invest igated analyt ically and experimentally. Experimental results obtained revealed the superiorit y of Inverse RLS-AVC with gain controller over convent ional method in reducing the crucial modes of vibration of flexible beam structure. Vibration attenuation achieved using proportional (P), proportional-integral (PI), Inverse RLS-AVC, Inverse Neuro- AVC, Inverse RLS-AVC with gain and Inverse Neuro-AVC with gain control strategies are 9.840 dB, 6.840 dB, 9.380 dB, 8.590 dB, 17.240 dB and 5.770 dB, respectively.
- ItemSoft computing based controllers for automotive air conditioning system with variable speed compressor.(Universiti Teknologi Malaysia, 2015) Ng, Boon Chiang.The inefficient On/Off control for the compressor operation has long been regarded as the major factor contributing to energy loss and poor cabin temperature control of an automotive air conditioning (AAC) system. In this study, two soft computing based controllers, namely the proportional-integral-derivative (PID) based controllers tuned using differential evolution (DE) algorithm and an adaptive neural network based model predictive controller (A-NNMPC), are proposed to be used in the regulation of cabin temperature through proper compressor speed modulation. The implementation of the control schemes in conjunction with DE and neural network aims to improve the AAC performance in terms of reference tracking and power efficiency in comparison to the conventional On/Off operation. An AAC experimental rig equipped with variable speed compressor has been developed for the implementation of the proposed controllers. The dynamics of the AAC system is modelled using a nonlinear autoregressive with exogenous inputs (NARX) neural network. Based on the plant model, the PID gains are offline optimized using the DE algorithm. Experimental results show that the DE tuned PID based controller gives better tracking performance than the Ziegler-Nichols tuning method. For A-NNMPC, the identified NARX model is incorporated as a predictive model in the control system. It is trained in real time throughout the control process and therefore able to adaptively capture the time varying dynamics of the AAC system. Consequently, optimal performance can be achieved even when the operating point is drifted away from the nominal condition. Finally, the comparative assessment indicates clearly that A-NNMPC outperforms its counterparts, followed by DE tuned PID based controller and the On/Off controller. Both proposed control schemes achieve up to 47% power saving over the On/Off operation, indicating that the proposed control schemes can be potential alternatives to replace the On/Off operation in an AAC system.
- ItemThe effects of heating and tree configurations on pollutant dispersion and air temperature in Street Canyon(Universiti Teknologi Malaysia, 2015) Muhammad Yazid, Muhammad Noor Afiq WitriDeterioration of outdoor air quality and harsh outdoor microclimate in a street canyon posed a serious threat to the urban dweller’s physical and mental health. The main purpose of this study was to investigate the combined effects of presence of trees, different diurnal heating situations and different street ratios on wind speed, pollutant dispersion and air temperature in a street canyon by means of Computational Fluid Dynamics (CFD). Initially, investigation on the suitability of the existing wind tunnel were carried out. Wind tunnel results shows that the formation of a thick turbulent boundary layer had a good vertical mean velocity profile except for the turbulent intensity profile; hence an alternative wind tunnel study was adopted as benchmark data for CFD. Validation study of numerical simulation of wind flow in a street canyon under the influence of thermal effects shows that the prediction by the large eddy simulation (LES) against wind tunnel data was better than the Reynolds-averaged Navier-Stokes (RANS) at steady state and the unstable RANS (URANS). Qualitative comparison between the parameters that were adopted for parametric study against previous studies were adequately representing a street canyon at full scale. Parametric study shows that the street aspect ratio was identified as the dominant factor compared to the presence of trees in reducing wind speed and air quality in a street canyon because of low momentum transfer from ambient wind into lower region of street canyon. Furthermore, the presence of trees in a street canyon under different diurnal heating situations is an ideal condition to achieve simultaneous low air temperature and better air quality where tree shade can reduce the surface area being heated up by the sun whilst the buoyancy force produced in street canyon by diurnal heating situations can compensate for the wind reduction caused by the trees.