A comparative experimental and numerical study to investigate the relative merits of convectors and “C” inserts in cooling cold-rolled coils

The coil cooling and storage unit (CCSU) is used to cool cold-rolled coils to the temper rolling temperature after the annealing cycle is over at the batch annealing furnace (BAF) in a cold rolling mill (CRM). In the CCSU, the coils are kept on the cooling bases for any fixed time irrespective of the grade and tonnage. Therefore, the need for a mathematical model to accurately predict the cooling time of the coils was felt. The current study involves experimental and numerical analysis of a stack of coils with respect to heat transfer and fluid flow. A comparative study was carried out to ascertain the relative merits of convectors and “C” inserts (CIs) in the cooling the coils. The air flow distribution for the case of different convectors and CIs was measured by means of a full scale physical model. Two different mathematical models were applied to model the fluid flow and flow distribution through the stack of coils. The first flow model uses the hydraulic resistance concept for estimating the air flow rate distribution, whereas the second flow model uses commercial computational fluid dynamics (CFD) software and predicts the velocity distribution in the flow path between two coils in a stack. The predictions from these two models compare well with the experimental data. The flow models were used to calculate the average heat-transfer coefficient in different flow passages in a stack. The heat-transfer coefficients thus obtained were used to tune and validate a two-dimensional transient heat-transfer model of coils. The heat-transfer model predicts the cooling time of coils accurately and also suggests a possible reduction of cooling time if CIs are used in place of convectors.     

Isotherms and thermodynamics for the adsorption of n-butane on pitch based activated carbon

The adsorption isotherms of n-butane on pitch based activated carbon (type Maxsorb III) at temperatures ranging from 298 to 328 K and at different equilibrium pressures between 20 and 300 kPa have been experimentally measured by a volumetric technique. The porous properties such as, the density, Brunauer–Emmett–Teller (BET) surface area, pore size, pore volume along with pore size distribution (PSD) of Maxsorb III have been determined. The Dubinin–Astakhov (DA) adsorption isotherm model describes all of the isotherm experimental data within the acceptable error ranges. The present isotherm data are compared with other published data of activated carbon (AC)/n-butane and showed the superiority of the present findings in terms of uptake capacity. The isosteric heat of adsorption (ΔH_ads) of n-butane on Maxsorb III is calculated for different loading. Using the adsorption isotherms and ΔH_ads, the thermodynamic property maps as a function of pressure, temperature and adsorbate amount are also presented.     

Optimization of SIP Session Setup Delay for VoIP in 3G Wireless Networks

Wireless networks beyond 2G aim at supporting real-time applications such as VoIP. Before a user can start a VoIP session, the end-user terminal has to establish the session using signaling protocols such as H.323 and session initiation protocol (SIP) in order to negotiate media parameters. The time interval to perform the session setup is called the session setup time. It can be affected by the quality of the wireless link, measured in terms of frame error rate (FER), which can result in retransmissions of packets lost and can lengthen the session setup time. Therefore, such protocols should have a session setup time optimized against loss. One way to do so is by choosing the appropriate retransmission timer and the underlying protocols. In this paper, we focus on SIP session setup delay and propose optimizing it using an adaptive retransmission timer. We also evaluate SIP session setup performances with various underlying protocols (transport control protocol (TCP), user datagram protocol (UDP), radio link protocols (RLPs)) as a function of the FER. For 19.2 Kbps channel, the SIP session setup time can be up to 6.12s with UDP and 7s with TCP when the FER is up to 10 percent. The use of RLP (1, 2, 3) and RLP (1, 1, 1, 1, 1, 1) puts the session setup time down to 3.4s under UDP and 4s under TCP for the same FER and the same channel bandwidth. We also compare SIP and H.323 performances using an adaptive retransmission timer: SIP outperforms H.323, especially for a FER higher than 2 percent.     

Multiple conducting polymer microwire sensors

In this work, conducting polymer microwires of three commonly used conducting polymers were fabricated simultaneously on a common substrate using an intermediate-layer lithography (ILL) method. The three conducting polymers under consideration were polypyrrole (PPy), sulphonated polyaniline (SPANI) and poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT-PSS). The fabricated microwires were implemented as sensing elements in detecting humidity and two organic vapors (i.e., methanol and acetone). The sensitivity of a single PPy microwire was compared with a rectangular PPy film after both were exposed to 45–85% humidity. The microwire sensor, due to its higher surface-to-volume ratio, was found to be more sensitive than the film sensor at low levels of humidity (between 45 and 58%). Beyond 58% humidity, the responses of the film and microwire sensors were similar. Three different sets of conducting polymer microwires (of PPy, SPANI and PEDOT) were then fabricated and employed as sensors to detect methanol, acetone and their mixtures. These microwires exhibited wave-like responses when they were exposed to these targets. The PPy and PEDOT microwires showed higher sensitivities in detecting methanol and acetone, respectively. The SPANI microwires exhibited similar responses in detecting methanol and acetone. The results demonstrate that microwire sensors were more effective than film sensors in detecting little quantities of target molecules. A sensor platform which integrates multiple microwire detectors is promising to detect multiple targets, and it also provides more information in detecting and distinguishing targets.     

Rapid macromolecular synthesis in a microfluidic channel with an oscillating flap

This study explores a method of enhancing the rates of macromolecular transport through a microchannel by introducing an oscillating mechanical flap in the fluidic system. A theoretical model is developed to determine the enhancement of macromolecular transport to a reaction site located along the channel surface. A numerical analysis is performed by considering a hinged flap located on the top or bottom walls of the channel. An order of magnitude analysis is conducted to estimate the reaction time which is bounded by the diffusion and the flow residence time. The period of oscillation is chosen to match the surface reaction time. The values of the characteristic flow variables adopted in this study, are representative of typical biomolecular transport processes confined to microscale geometries. With background flow, the results of the numerical analysis show that the mechanical actuator behaves like a miniature pump that drives a favorable gradient of macromolecules towards the surface reaction sites within an initial lapse of time. In a stagnant fluid, the results show that the moving flap behaves like a stirring agent bringing fluid with a higher concentration in contact with the reaction site and enhancing the surface concentration. In the latter case, the effect of the moving flap increases as the reaction progresses. The moving flap has the largest beneficial effect on surface concentration in the presence of a background flow when the position of the moving flap is along the top wall above the reaction site.     

Performance Evaluation of Controlled-Capacitor-Charging-Type Inverters

This paper presents the performance of capacitor-charging-type inverters. Both single- and three-phase inverters are considered. A simple technique to design the L -C elements of such an inverter is introduced. The switching devices are operated in the discontinuous conduction mode to reduce the size of the inductor and also for better dynamic performance. The inverter is simulated in PSPICE. An experimental prototype is produced to verify the results from simulation. Experimentations have been conducted for single-phase and three-phase systems. The inverter is found to operate satisfactorily for various types of load including unbalanced load.     

A Combined Circuit-Electromagnetic-Fluidic Computational Methodology for Force Prediction in Lab-on-Chip Environments

This paper focuses on a computational method for the simulation of the motion and manipulation of bio-particles using dielectrophoretic and micro-fluidic forces. The presented method uses surface integral equations for modeling both electromagnetic (EM) and fluidic domains. A coupled circuit-EM methodology is used to model electrical excitations. A steady Stokes flow is assumed for computing the fluidic traction forces. The resulting simulator accurately predicts the fields and forces on arbitrarily-shaped three dimensional particles representing bio-species. The presented methodology is amenable to acceleration with state of the art oct-tree-based fast matrix-vector schemes for rapid linear time iterative solution. This integrated computational approach leads to a pathway for rapid simulation of coupled circuit-EM-fluidic systems for Lab-on-chip (LoC) manipulation of biological species, which provides medical device designers the capability to augment control of bio-species, and explore new system designs     

High-performance E-mode AlGaN/GaN HEMTs

Enhancement-mode AlGaN/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm. The small signal performance of these enhancement-mode devices shows a record current cutoff frequency (f/sub T/) of 85 GHz and a power gain cutoff frequency (f/sub max/) of 150 GHz.     

Study of Impact of Access Resistance on High-Frequency Performance of AlGaN/GaN HEMTs by Measurements at Low Temperatures

This letter studies the effect of access resistance on the high-frequency performance of AlGaN/GaN high-electron-mobility transistors. To systematically reduce the sheet access resistance, the transistors were measured at different temperatures. The increase of mobility at lower temperatures allowed more than four-fold reduction in the sheet access resistances. Both the current- and power-gain cutoff frequencies are observed to increase at low temperatures. Also, the intrinsic effective velocity has been estimated in these devices, as well as the parasitic delays involved in the final performance. Channel charging delay, which was expected to be most sensitive to parasitics, is observed to decrease at low temperatures. However, the drain delay, intrinsic delay, and effective electron velocity remain unaffected by temperature     

Static and dynamic modeling of solid oxide fuel cell using genetic programming

Modeling of solid oxide fuel cell (SOFC) systems is a powerful approach that can provide useful insights into the nonlinear dynamics of the system without the need for formulating complicated systems of equations describing the electrochemical and thermal properties. Several algorithmic approaches have in the past been reported for the modeling of solid oxide fuel cell stacks. However, all of these models have their limitations. This paper presents an efficient genetic programming approach to SOFC modeling and simulation. This method, belonging to the computational intelligence paradigm, is shown to outperform the state-of-the-art radial basis function neural network approach for SOFC modeling. Both static (fixed load) and dynamic (load transient) analyses are provided. Statistical tests of significance are used to validate the improvement in solution quality.