Current Issue : April - June Volume : 2011 Issue Number : 2 Articles : 7 Articles
This article experimentally and numerically investigates the thermal performance of a 2350-kW completely enclosed motor, which is cooled through an air-to-air heat exchanger. The air in the heat exchanger includes external and internal flow paths. The external air driven by the rotation of the centrifugal fan goes through the heat exchanger mounted on the top of the frame. The internal air absorbs heat released from the stator and the rotor and then transfers the heat to the heat exchanger through the motion of two axial fans and the rotor. Several test rigs have been set up to measure the performance of the fan and the motor. The Fluent software package is adopted to analyze the complicated thermal-fluid interactions among the centrifugal fan, two axial fans, heat exchanger, stator, and rotor. The measured data, including the fan performance curves and the temperature profiles of the heat exchanger and the stator, show good agreement with the simulated results. The numerical calculations also show that the non-uniform external flow distribution through the heat exchanger and the air leakage between the axial fan and the rotor reduce the cooling ability of the motor. A detailed discussion is also included to improve the motor cooling performance....
This paper proposes an adaptive neurofuzzy interface system (ANFIS) approach to identify the real power transfer between generators. Based on solved load flow results, it first uses modified nodal equation method (MNE) to determine real power contribution from each generator to loads. Then the results of MNE method and load flow information are utilized to train the designed ANFIS. It also incorporated an enhanced feature extraction method called principle component analysis (PCA) to reduce the input features to the ANFIS. The 25-bus equivalent system of south Malaysia is utilized as a test system to illustrate the effectiveness of the ANFIS output compared to that of the MNE method. The ANFIS output provides promising results in terms of accuracy and computation time. Furthermore, it can be concluded that the ANFIS with enhanced feature extraction method reduces the time taken to train the ANFIS without affecting the accuracy of the results....
The human body communication (HBC) is a technology that enables short range data communication using the human body as a medium, like an electrical wire. Thus it removes the need for a traditional antenna. HBC may be used as a type of data communication in body area network (BAN), while the devices are being in contact with body. One of important issues in BAN is an emergency alarm because it may be closely related to human life. For emergency data communication, the most critical factor is the time constraint. IEEE 802.15.6 specifies that the emergency alarm for the BAN must be notified in less than 1?sec and must provide prioritization mechanisms for emergency traffic and notification. As one type of BAN, the HBC must follow this recommendation, too. Existing emergency handling methods in BAN are based on the carrier sensing capability on radio frequencies to detect the status of channels. However, PHY protocol in HBC does not provide the carrier sensing. So the previous methods are not well suitable for HBC directly. Additionally, in the environment that the emergency rate is very low, the allocation of dedicated slot(s) for emergency in each superframe is very wasteful. In this work, we proposed specific emergency handling operation for human body communication's medium access control (HBC-MAC) protocol to meet the emergency requirements for BAN. We also showed the optimal number of emergency slots for the various combinations of beacon intervals and emergency rates....
On-site power and mass flow rate measurements were conducted in a hydroelectric power plant (Mexico). Mass flow rate was obtained using Gibson's water hammer-based method. A numerical counterpart was carried out by using the commercial CFD software, and flow simulations were performed to principal components of a hydraulic turbine: runner and draft tube. Inlet boundary conditions for the runner were obtained from a previous simulation conducted in the spiral case. The computed results at the runner's outlet were used to conduct the subsequent draft tube simulation. The numerical results from the runner's flow simulation provided data to compute the torque and the turbine's power. Power-versus-efficiency curves were built, and very good agreement was found between experimental and numerical data....
Different surface and bulk defects in solar cell wafer have undesirable influence upon device properties, as its efficiency and lifetime. When reverse bias voltage is applied to the wafer, a magnitude of electric signals from defects can be measured electronically, but the localization of defects is difficult using classical optical far-field methods. Therefore, the paper introduces a novel combination of electric and optical methods showing promise of being useful in detection and localization of defects with resolution of 250 nm using near-field non-destructive characterization techniques. The results of mapped topography, local surface reflection and local light to electric energy conversion measurement in areas with small defects strongly support the development and further evaluation of the technique....
Wireless Sensor Networks (WSNs) consist of spatially distributed autonomous sensors to cooperatively monitor physical conditions. Thus, the node battery autonomy is critical. To outperform it, most WSNs rely on the harvesting capability. As nodes can recharge whenever energy is available, the problem is to determine at design time the node autonomy. For our project, we solve it by creating a power/energy estimator that simulates business scenarios to predict node autonomy; the estimation concerns both power and energy features. Based on node architecture configuration, its Dynamic Power Management (DPM) policy, and environmental conditions, we present a simulator that helps identify power consumption hot spots and make critical choices during the system design. It also helps to scale the energy storage system as well as the energy harvesters correctly. The hardware part is modelled using the FLPA methodology to develop different node component models with a variable accuracy. For the logical part, we developped a specific DPM by integrating meteorology and weather forecast behaviours. The novelty comes from the ability to simulate the WSN harvesting capability and to estimate at runtime the remaining duration of each service....
Every optical system for sunlight concentration requires following the sun in its movement. The sun tracking method is essentially chosen on the base of collection geometry and optical system configuration. A simple, useful and original technique to realise sun tracking is proposed. It is based on a double guiding system using two complementary procedures. A passive tracking device performs a preliminary collector orientation. Then an active tracking system realises its fine positioning and adjustments exploiting an optical pointing sensor. The core of this active tracking device is the sun finder. Pointing sensors for fibre-coupled, CPV (Concentrating PhotoVoltaic) and linear collectors are presented, illustrating in detail working principle and practical use. All sensors were optically characterised in laboratory, under controlled and reproducible conditions. Some field tests completed the experimentation evaluating the sensors performance in outdoor working conditions....
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