Pilot operated cartridge valve - Dynamic characteristics measurements for energy efficient operation and application

The two-stage on/off valve scheme is studied in this thesis which is able to rapidly actuate within the fraction of a second for directional flow control applications. And also, it was able to replicate characteristics of direct operated solenoid on/off valves in the same category, with the addition of higher flow rate capacity up to 200 l/min and above with pressure drop under 5 bar. The valves utilized for piloting of the hydraulic operated cartridge valve are the normally closed and normally open direct solenoid operated on/off valve. In the experiments, the internal piloting structure is adopted to avoid external pressure source and keeping valve operation dependencies minimum to the electric power. The switching time was found to be lowest at 100 bar, that is approximately 12 ms for opening and 30 ms for closing from the point of activation signal. It is also observed that the flow rate has negligible effect on the switching duration and changing the poppet area ratio to 50% of Ax from 96% can reduce down the closing time. Further, it was observed that the internal piloting has its drawbacks which creates a closed loop between main valve metering edge and pilot chamber. This resulted in oscillations in form of poppet movement near the dead end on either side of the stroke, and also if the system is not stiff or due to pressure waves traversing in the long hoses. Another positive outcome from the measurements showed that different switching methods such as, intermittent, continuous and pulse switching can be performed in a controlled manner, but the study was limited to the capability of the valve scheme. Moreover, the simulation model is also built in the Matlab/Simscape environment to refine the valve model based on the experiment results for further measurements that were limited by the physical system. Additional simulations are conducted to reduce the marginal difference between the opening and closing duration by restricting the stroke length to 5 mm, contrary to the original 8.5 mm, at 200 l/min and the switching duration was considerably reduced by half of the original duration. The experiments were conducted for flow in one direction only, whereas in simulation also the bi-direction flow capability is also carried out to displace an actuator with constant velocity, while lifting and lowering and holding of the load to certain position

MODELLING AND FAULT DIAGNOSIS APPROACH FOR PROTON EXCHANGE MEMBRANE FUEL CELL SYSTEMS INCORPORATING AMBIENT CONDITIONS

Proton exchange membrane fuel cell (PEMFC), as a source of electrical power, provides numerous benefits such as zero carbon emission and high reliability as compared to wind and solar energy. PEMFC operates at very low temperature, high power density, and has very high durability as compared to other fuel cells. Being a non-linear power source with high sensitivity to ambient conditions variation, the prediction of PEMFC voltage and temperature is a complicated issue. The most common PEMFC models are classified as mechanistic models, semi-empirical models, and purely empirical methods. The mechanistic models are complex and require differential equations to predict the voltage and temperature of PEMFC. However, the semi-empirical models are less complicated and can be used easily for the online prediction of PEMFC outputs. Therefore, the first part of this thesis attempt to model the voltage of PEMFC using simple and effective semi-empirical equations. The initial feature of the proposed technique is to incorporate the features of a mechanistic model with less complex equations. The model considers the internal currents and the internal voltage drop associated with the PEMFC. Besides, activation and concentration voltage drops are addressed based on theoretical functions. Thus, the proposed model provides an additional benefit that not only does the output voltage model satisfy the voltage for both loaded and unloaded conditions but also the component voltage drops waveforms match with the theoretical waveforms given in the mechanistic models. The second part of the thesis focuses on modelling the PEMFC temperature. Previously most temperature models use complex equations incorporating PEMFC output voltage which is not a good option as the temperature must be predicted using only load current and ambient temperature. The model proposed in this thesis is developed through an algorithm that tracks the online changes in the load current and ambient temperature. It provides the accurate temperature of PEMFC by using a simple first-order equation with the help of a tracking algorithm. Quantum lig tening search algorithm (QLSA) is used for the optimization of constant parameters for both voltage and temperature models. The PEMFC performance is affected by factors such as variations in ambient temperature, pressure, and air relative humidity and thus they are vital for predicting PEMFC performance. The thesis also attempts to directly predict the variations in PEMFC voltage under varying ambient conditions at different load resistance. For this purpose, statistical analysis is used to propose empirical equations that can predict the variations in PEMFC voltage for varying ambient conditions. In this context of the model development, the parameters which are significantly varying with ambient changes are identified with the help of statistical regression analysis and represented as ambient temperature and air relative humidity dependent parameters. The enhanced semi-empirical voltage model is verified by performing experiments on both the Horizon and NEXA PEMFC systems under different conditions of ambient temperature and relative humidity with root mean square error (RMSE) less than 0.5. Results obtained using the enhanced model are found to closely approximate those obtained using PEMFCs under various operating conditions, and in both cases, the PEMFC voltage is observed to vary with changes in the ambient and load conditions. Inherent advantages of the proposed PEMFC model include its ability to determine membrane-water content and water pressure inside PEMFCs. The membrane-water content provides clear indications regarding the occurrence of drying and flooding faults. For normal conditions, this membrane water content ranges between 12.5 to 6.5 for the Horizon PEMFC system. Based on simulation results, a threshold membrane water- content level is suggested as a possible indicator of fault occurrence under extreme ambient conditions. Limits of the said threshold are observed to be useful for fault diagnosis within the PEMFC systems

Analysing the Resolution of Security Bugs in Software Maintenance

Security bugs in software systems are often reported after incidents of malicious attacks. Developers often need to resolve these bugs quickly in order to maintain the security of such systems. Bug resolution includes two kinds of activities: triaging confirms that the bugs are indeed security problems, after which fixing involves making changes to the code. It is reported in the literature that, statistically, security bugs are reopened more often compared to others, which poses two new research questions: (a) Are developers “rushing” to triage security bugs too soon under the pressure of deadlines? (b) Do developers need to spend more time fixing security bugs to avoid frequent reopening? This thesis explores these questions in order to determine whether security bug fixing should take a higher priority than other bugs to avoid malicious attackers exploiting vulnerabilities before the problems are fixed, and whether security bug fixing should take a higher priority than other bugs. In this thesis a quantitative approach has been adopted by conducting statistical empirical studies to observe the behaviour of software developers engaged in dealing with security bugs. Firstly, the concept of "rush'' has been borrowed from the time management literature to refer to the behaviour of people delivering work under the pressure of deadlines. By observing how developers deliver bug resolution before the deadline of releases, the degree of rush has been measured as the ratio between the actual time spent by developers during triaging and the theoretical time the developers have by delaying the fixes until the next regular release. In this thesis, a suggest that delaying bug assignment helps find the right developer and gives the developer more time to prepare for the same workload with more relaxed planning constraints. Secondly, to analyse the complexity of security bug fixes, the fan-in complexity of functions relevant to security bugs has been measured, rather than simply measuring the time spent by the software developers on the fixing of such bugs. The first null hypothesis is tested using a Man-Whitney method on five software case studies, Samba, MozillaFirefox, RedHat, FreeBSD and Mozilla. The second null hypothesis is tested by comparing the results of fixing security and non-security bugs from the Samba and MozillaFirefox case studies. Statistically significant results suggest that security bugs are triaged in a rush compared to non-security bugs for RedHat, FreeBSD and Mozilla. In terms of fan-in, the results of the Samba and MozillaFirefox case studies suggest that security bugs are more complex to fix compared to non-security bugs

Harmonizing the Tenth Malaysia Plan priorities with the new economic model and the green world order

The New Economic Model (NEM) integrates innovative ideas in socio‐economic development of Malaysia. Specifically, it aims at achieving high income, sustainability and inclusiveness in the economic transformation through this new policy initiative. NEM will build resilience into the economic system for sustainable benefits to the society. The sustainability dimension of NEM will require focus on natural resources. This is achievable by aligning our activities with the new concept of ‘Green World Order’. Under this concept, there is a need for making changes in our activities. Development planning will require resetting in the light of environmental limitations to achieve the goals of NEM. With the valuation of ecosystem services becoming increasingly important, we should pursue this matter with a sense of urgency for positioning Malaysia as a major player in the global environmental governance and claimant to a substantial stake in the fund to mitigate the effects of climate change. Out of US$33 trillion per year as the economic value of world ecosystems, our resources such as forests, mangroves and seagrasses, wetlands and groundwater recharge systems, coral refs and ability to implement green technology projects should enable the country to have a significant stake and role in global environmental mitigation programs. With an effective action plan, Malaysia can take advantage of the growing carbon market and green economy. Investment in carbon sinks should be a sort of foreign direct investment free of strings and riders while supporting our national goals of food security, environmental conservation, education, health care and socio‐economic development. However, we need to develop expertise to deal with international institutions in carbon economy. We propose setting up an autonomous center to address all such matters related to human resource needs and global environmental governance to position Malaysia for a fair share of benefits that will accrue

The Thermodynamic Behavior Of Low-GWP Zeotropic Mixtures On Water-Source Heat Pump Equipment

Regulatory changes, aimed at mitigating climate change, are forcing air-conditioning and heat pump manufacturers to change refrigerants in their products, including all Water-Source Heat Pumps (WSHPs). These changes require substantive changes to WSHP equipment design in order to continue to deliver heat pumps that meet product specifications and energy efficiency regulations. Some of the proposed low-GWP refrigerants to replace R410A, such as R452B and R454A, are zeotropic mixtures of refrigerants. Zeotropes with a significant glide may be taken advantage of in the refrigerant-to-water heat exchanger in a WSHP to improve overall system efficiency. However, there is a potential to also reduce system efficiency if not designed appropriately. This work presents a four-component heat pump model which includes a moving boundary condenser model, lumped element evaporator model, and fixed efficiency compressor model. This model was validated against the data of a R410A water-to-water heat pump operated in heating mode with an average 9.7% MAE in prediction of COP. This model was exercised using R452B and R454A and discovered that the latter provided an opportunity to increase the system COP as a result of the increased enthalpy of vaporization of the fluid. Additionally, the moderate glide that these two refrigerants produce is not significant enough to warrant significant consideration for a water-to-water heat pump

Predicting and testing the performance of next generation heat exchangers with low-GWP refrigerants

Energy efficiency regulations are forcing air conditioning (AC) and heat pump (HP) manufacturers to replace existing high global warming potential (GWP) refrigerants in their systems with more climate friendly alternatives. Air-to-refrigerant fin-and-tube heat exchangers (FTHXs), and water-to-refrigerant coaxial heat exchangers are commonly found in residential and commercial AC and HPs. To adapt to these new refrigerants, heat exchanger manufacturers need to make design changes in their equipment, in order to ensure that the next generations of their products is energy efficient, climate friendly, and cost effective. This thesis aims to develop a set of guidelines for pseudo-optimal design of FTHXs in order to accommodate the next generation of low-GWP refrigerants, with the goal to obtain near optimal performance under current manufacturing constraints.A novel pumped refrigerant loop was developed, and coupled with an airside setup and a psychrometric chamber facility, to test FTHXs. The experimental facility was used for validating a segment-by-segment heat exchanger model called cross-fin (Xfin), by comparing model predictions against data collected from three custom designed FTHXs with distinct refrigerant circuitries. The mean absolute percentage error (MAPE) between the experimental, and model predicted capacities was found to be 1.0%, 2.4%, and 0.9%, for the interleaved, vertical, and block circuited FTHXs, respectively. A preliminary simulation study was performed using a four-component HP model to investigate the change in system performance metrics of an R410A based water-to-water HP, using R454B and R452B as low-GWP 'drop-in' alternatives. A four-component heat pump model, validated against the performance datasheet, was used for simulations and showed that some design changes may be necessary to existing equipment, in order to adapt them for near optimum performance with low-GWP fluids. Then, Xfin model predictions were compared against experiments performed on the block circuited FTHX with R1234ze(E). The MAPE between the experimental and model predicted capacities was found to be 1.4%. A parametric simulation study was done by modifying the refrigerant circuitry and fin pitch, showing that FTHX performance metrics such as capacity (Qevap) and refrigerant pressure drop ([Delta]Pref), are influenced by changes in geometry. Finally, simulations were executed to compare the performance of R1234yf and R1234ze(E) on the R410A based block circuited indoor evaporator FTHX. It was found that the performance, in terms of the ratio Qevap/[Delta]Pref, was most sensitive to the number of circuits, followed by the tube diameter, number of tubes in the FTHX, and the fin density. Based on the simulation results, two customized FTHX designs were suggested, with different changes to the FTHX slab size. One design prioritized increased FTHX capacity, and the other prioritized reduction in refrigerant pressure drop to acceptable limits

Giant adrenal endothelial cyst associated with acute and chronic morbidity in a young female: a case report

Adrenal cysts are rare clinical entities that can present as acute abdomen through rupture and internal hemorrhage as well as chronic symptoms such as gastrointestinal disturbances. A 20-year-old girl presented to our hospital with a 4-years history of abdominal pain and diarrhea. Ultrasound of the abdomen revealed a cystic area measuring 10 × 10 cm between the spleen and left kidney. Computed tomography scan showed a large cystic, homogeneous mass measuring 12.8 × 9.5 × 9.4 cm in the left hypochondrium with most likely origin from the left adrenal gland. Limited work up for hormone hypersecretion was negative. The patient was then encountered in the emergency room with an acute abdomen secondary to intracystic hemorrhage. A laparotomy with left adrenalectomy was performed. Final pathology showed a benign adrenal endothelial cyst. Post-operatively, the patient's long standing complaints of diarrhea and abdominal pain completely resolved. Surgical resection appears a safe and reasonable management strategy in a patient with intracystic hemorrhage of adrenal cyst