Annular impinging jet controlled by radial synthetic jets

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This experimental study focuses on generation and control of annular impinging jets. An annular nozzle was designed with an active flow control system using twelve radial synthetic jets issuing from the central body of the nozzle. Measurements of the wall pressure and wall mass transfer were performed with air as the working fluid. The control action causes modification of the flowfield resulting in changes of the corresponding heat/mass transfer distributions. The convective transfer rate on the stagnation circle can be demonstrably enhanced by 20% at a moderate nozzle-to-wall distance, equal to 0.6 of the nozzle outer diameter.dc201

ADAPTIVE PREDICTIVE FUNCTIONAL CONTROLLER

A controller device and a method for controlling a system that utilizes an adaptive mechanism to self-learn the system char acteristics and incorporates this adaptive self-learning ability to predict a control parameter correctly to provide precise control of a system component

Novel Water Hydraulic On/Off Valves and Tracking Control Method for Equal Coded Valve System

Water hydraulics is an interesting alternative to oil hydraulics since it uses a clean, environment friendly, and non-inflammable pressure medium. However, the availability of good control valves, which are essential components in many hydraulic systems, is limited in water hydraulics owing to the challenging characteristics of water. This, in turn, considerably limits the application of water hydraulics. In this thesis, a new digital hydraulic valve technology is investigated in order to promote the applicability of this clean technology; the method using equal-size on/off valves is preferred.This equal coding method suffers from a lack of suitable valves. Thus, a fast-acting and low-power-consuming miniature valve is developed. The valve development is based on previous experience with oil hydraulic miniature valves and is carried out mainly with heuristic methods, by using simplified electromagnetic equations and scaling. However, the prototypes show good properties for the intended purpose. As another challenge, a high number of these valves are needed in order to achieve sufficient resolution for demanding control. To decrease this requirement, the circulating switching control method is proposed, which can increase the effective flow resolution of the valve system using the existing valves. The method divides the switching duty equally among the valves and can diminish the drawbacks that exist in typical non-circulating switching control.As the main goal, a water hydraulic servo axis was implemented using the developed miniature valves and the control method. The control system comprises a simple model based valve controller as the lower level part and a filtered P-controller as the upper level motion controller. Excellent tracking and positioning accuracy was achieved with a valve system having 16 miniature valves in total and using this relatively simple controller structure. This verifies that high-performance water hydraulic motion control can be realized with a reasonable effort using on/off seat valves. This gives hope for increasing the applicability of water hydraulics

Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System

The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves

5 European & African Conference on Wind Engineering

The 5th European-African Conference of Wind Engineering is hosted in Florence, Tuscany, the city and the region where, in the early 15th century, pioneers moved the first steps, laying down the foundation stones of Mechanics and Applied Sciences (including fluid mechanics). These origins are well reflected by the astonishing visionary and revolutionary studies of Leonardo Da Vinci, whose kaleidoscopic genius intended the human being to become able to fly even 500 years ago… This is why the Organising Committee has decided to pay tribute to such a Genius by choosing Leonardo's "flying sphere" as the brand of 5th EACWE

Heat removal in axial flow high pressure gas turbine

The demand for high power in aircraft gas turbine engines as well as industrial gas turbine prime mover promotes increasing the turbine entry temperature, the mass flow rate and the overall pressure ratio. High turbine entry temperature is however the most convenient way to increase the thrust without requiring a large change in the engine size. This research is focused on improving the internal cooling of high pressure turbine blade by investigating a range of solutions that can contribute to the more effective removal of heat when compared with existing configuration. The role played by the shape of the internal blade passages is investigated with numerical methods. In addition, the application of mist air as a means of enhanced heat removal is studied. The research covers three main area of investigation. The first one is concerned with the supply of mist on to the coolant flow as a mean to enhancing heat transfer. The second area of investigation is the manipulation of the secondary flow through cross-section variation as a means to augment heat transfer. Lastly a combination of a number of geometrical features in the passage is investigated. A promising technique to significantly improve heat transfer is to inject liquid droplets into the coolant flow. The droplets which will evaporate after travelling a certain distance, act as a cooling sink which consequently promote added heat removal. Due to the promising results of mist cooling in the literature, this research investigated its effect on a roughened cooling passage with five levels of mist mass percentages. In order to validate the numerical model, two stages were carried out. First, one single-phase flow case was validated against experimental results available in the open literature. Analysing the effect of the rotational force, on both flow physics and heat transfer, on the ribbed channel was the main concern of this investigation. Furthermore, the computational results using mist injection were also validated against the experimental results available in the literature. Injection of mist in the coolant flow helped achieve up to a 300% increase in the average flow temperature of the stream, therefore in extracting significantly more heat from the wall. The Nusselt number increased by 97% for the rotating leading edge at 5% mist injection. In the case of air only, the heat transfers decrease in the second passage, while in the mist case, the heat transfer tends to increase in the second passage. Heat transfer increases quasi linearly with the increase of the mist percentage when there is no rotation. However, in the presence of rotation, the heat transfers increase with an increase in mist content up to 4%, thereafter the heat transfer whilst still rising does so more gradually. The second part of this research studies the effect of non-uniform cross- section on the secondary flow and heat transfer in order to identify a preferential design for the blade cooling internal passage. Four different cross-sections were investigated. All cases start with square cross-section which then change all the way until it reaches the 180 degree turn before it changes back to square cross-section at the outlet. All cases were simulated at four different speeds. At low speeds the rectangle and trapezoidal cross-section achieved high heat transfer. At high speed the pentagonal and rectangular cross-sections achieved high heat transfer. Pressure loss is accounted for while making use of the thermal performance factor parameter which accounts for both heat transfer and pressure loss. The pentagonal cross-section showed high potential in terms of the thermal performance factor with a value over 0.8 and higher by 33% when compared to the rectangular case. In the final section multiple enhancement techniques are combined in the sudden expansion case, such as, ribs, slots and ribbed slot. The maximum heat enhancement is achieved once all previous techniques are used together. Under these circumstances the Nusselt number increased by 60% in the proposed new design