Varying Input Power Research Articles

Dynamic simulation of a single nitrogen expansion cycle for natural gas liquefaction under refrigerant inventory operation

Nitrogen (N2) expansion natural gas liquefaction technology is wildly used for liquefied natural gas production due to its unique advantages. However, few works have been reported about the detailed unit operating performance of N2 expansion system under refrigeration inventory operation that is one of the most effective operations for adjusting system refrigeration capacity. In this study, we have comprehensively investigated the dynamic characteristics of a single N2 expander liquefier under inventory operation. Firstly, system model of the liquefier is developed based on rigorous first principles, valid empirical correlations and accurate physical property. Meanwhile, plate-fin heat exchanger model, as a key component, is reasonably and greatly simplified according to symmetric layer arrangements. Using the system model, the transient system behaviors are identified and evaluated. The primary performance parameters of centrifugal compressor train, e.g. efficiency, surge margin and input power, experience the most dramatic changes during the first several seconds after the operation starts. ±6% variations in total nitrogen refrigerant mass result in −4.5 and +5.6°C variations in LNG temperature, +8.7% and −8.4% variations in liquefier input power and maximum −7.8% variation in compressor surge margin, eventually. In general, the liquefier exhibits strong nonlinear behaviors.

Nonlinearities of High-Speed p-i-n Photodiodes and MUTC Photodiodes

The linearity, the RF output power, and the bandwidth for p-i-n photodiodes (PDs) and modified uni-traveling carrier (MUTC) PDs are analyzed for a variation of bias voltage and optical input power. Based on an equivalent circuit, equations for analytic calculation of these PD parameters are derived. Good agreement between the measurements and the calculated results of a p-i-n PD and a MUTC PD could be observed for frequencies up to 135 GHz. As a result, the linearity is improved and its photocurrent dependence can be reduced when the bandwidth of the PD is limited by the RC time constant.

THERMOACOUSTIC REFRIGERATOR SYSTEM PERFORMANCE USING THE PVC (POLYVINYL CHLORIDE) STACK BY POWER INPUT VARIATION

<p>The thermoacoustic refrigerator is an innovative alternative and did not use substances that had a negative impact on the environment such as freon, but using air as the working substance. The materials used the refrigerator were easily obtained and the construction components were simple so that made this refrigerator was cheap, easy to make and easy to maintain. Stack was used in the thermoacoustic refrigerator system used PVC (Polyvinyl chloride) which is parallel cylindrical shape and diameter (1.50 ± 0.05) mm and length of 8 cm. Variations of loudspeaker input power that used were 20 watt, 30 watt, 40 watt, 50 watt and 60 watt. Variations of the input power that used to determine the effect of loudspeaker input power to decreasing temperature in the operating of the thermoacoustic refrigerator system using PVC stack. From the result, loudspeaker input power influenced on the decreasing temperature that was 6.0 °C for 20 watts, 6.7 °C for 30 watts, 7.2 °C for 40 watts, 8.0 °C for 50 watts and 9.0 °C for 60 watts. From these results indicated optimum decreasing temperature depended on the amount of loudspeaker power that was directly proportional to the decreasing temperature obtained.</p>

Glow discharge plasma polymerized nanostructured polyaniline thin film optical waveguide

In this work, glow discharge continuous wave plasma polymerization technique was used to deposit nanostructured polyaniline (PANI) thin film by varying input power. The radio frequency (RF) used for plasma polymerization was 13.56 MHz and working pressure was 0.15 mbar. It was found that, changes in the input power can be used to control the properties of the plasma polymerized PANI thin films. Highly cross-linked structure with an increase in chain length was observed from FTIR spectra with input RF power, whereas the film surface morphology was found to be highly uniform, densely packed and smooth from FE-SEM images. The surface roughness of the film was found to increase with RF power. The refractive index and adhesion of the film was found to be increased while the optical band gap and surface energy decreased with input RF power. The plasma polymerized PANI film showed outstanding optical transmission loss properties and proved itself as excellent optical waveguide.

Large-scale silicon nitride nanophotonic phased arrays at infrared and visible wavelengths.

We demonstrate passive large-scale nanophotonic phased arrays in a CMOS-compatible silicon photonic platform. Silicon nitride waveguides are used to allow for higher input power and lower phase variation compared to a silicon-based distribution network. A phased array at an infrared wavelength of 1550 nm is demonstrated with an ultra-large aperture size of 4 mm×4 mm, achieving a record small and near diffraction-limited spot size of 0.021°×0.021° with a side lobe suppression of 10 dB. A main beam power of 400 mW is observed. Using the same silicon nitride platform and phased array architecture, we also demonstrate, to the best of our knowledge, the first large-aperture visible nanophotonic phased array at 635 nm with an aperture size of 0.5 mm×0.5 mm and a spot size of 0.064°×0.074°.

Link Optimization and Performance Analysis of a 40 Gbps DQPSK Modulated Ultra DWDM System with 32 Orthogonally Polarized channels

Abstract The demand for higher speed at a lesser transmission cost per bit resulted in growth of optical networks with improved spectral efficiency even at narrower channel spacing. Incorporation of multilevel modulation formats in DWDM system led to the exploration of the 25 GHz channel grid, popularly known as Ultra Dense Wavelength Division Multiplexed (UDWDM) systems, opening new research frontiers. At such channel spacing's, non-linear optical effects impose severe system impairments and hence robust modulation schemes are currently being investigated. This paper presents a simulative model to implement and analyze alternative polarized DQPSK modulated UDWDM system to evaluate its resilience to XPM and fiber nonlinearity. An UDWDM system supporting 32 channels, each operating at 40 Gbps and spaced at 25 GHz is studied numerically for long-haul optical communication system using OptiSystem simulator to estimate OSNR penalties to mitigate XPM effects. The major detrimental factors encountered in link design have been estimated to evaluate the system performance in terms of Q value for different number of channels and with varied input power. The analysis reports acceptable performance for DQPSK format up to a link distance of 1500 Km and also claims a better tolerance to dispersion and nonlinearities at higher input power levels.

Gain variation induced by power transient in thulium-doped fiber amplifier at 2 µm and its reduction by optical gain clamping technique

This paper investigates the dynamic behavior of a thulium doped fiber amplifier (TDFA) operating in the 2µm region for reconfigurable wavelength division multiplexing (WDM) systems. We show deleterious channel power fluctuations may be generated by input power variation at the amplifier and we propose the use of an optical gain-clamping technique. The investigated system consists of 20 channels with −4dBm total input power. Our findings revealed that the effects of power transients due to channel reconfigurations are significantly reduced by a lasing feedback signal. Simulation results show that a power excursion of 4.3dB is produced after dropping 19 channels when the amplifier gain is unclamped and only 0.0062dB when the amplifier gain is clamped. The dynamics of GC-TDFA are mainly influenced by the value of the pump power factor and thus the laser signal achieves a stronger stabilization condition with increasing pump power factor. Hence, optical gain clamping is a simple and robust technique to control the power transient in the thulium-doped fiber amplifier of WDM systems at 2µm.

Numerical and experimental investigation of pulsating heat pipes with corrugated configuration

A single loop pulsating heat pipe with corrugated configuration in evaporation, adiabatic, and condensation section is numerically and experimentally investigated in present work. The investigation is carried out under the condition of varying input power ranged from 5W to 40W and filling ratio ranged from 30% to 60%. In the numerical investigation, VOF model is used to probe the feature of two-phase flow inside the single loop pulsating heat pipe. The present numerical results such as vapor–liquid flow pattern and variation trend of the thermal resistance show a good consistency with those of the experiments. It’s found that the pulsating heat pipe with corrugated configuration in evaporation section has the best performance of start-up and heat transfer of present considered cases. The results show 28.96% decrease in start-up time and 37.57% in thermal resistance due to the application of corrugated configuration, which presents a remarkable improvement in the overall performance of pulsating heat pipe.

Stochastic Analysis of an Adaptive Line Enhancer/Canceler With a Cyclostationary Input

This paper studies the second moment behavior of the adaptive line enhancer (ALE)/adaptive line canceler (ALC) for a cyclostationary input consisting of a fixed amplitude random phase sine wave plus a white Gaussian process with periodic power variations. Both transient and steady-state results are shown to be in good-to-excellent agreement with Monte Carlo simulations. The main conclusion is that periodic input power variations cause periodic processing gain variations of the ALE/ALC with the same period as the input power. However, these variations do not cause a large degradation in the ALE/ALC performance.

Savonius rotor based grid connected hydrokinetic power generation scheme

Abstract In this paper, a grid connected hydrokinetic power generation scheme with asynchronous generator coupled to Savonius rotor is presented. The Savonius rotor acts as prime mover to the asynchronous generator and thus, the proposed scheme presents a system with variable input power similar to that of a wind energy conversion system. In order to mitigate the effect of changes in input power to the generator and resulting variations in utility voltage and frequency which affects the system performance, an AC–DC–AC converter with a dc link capacitor is designed and modeled. The operation of the power converter is realized by decoupled d–q control method. A Matlab/Simulink model of Savonius rotor, asynchronous generator, power converter, LCL filters and control schemes is presented. The proposed scheme is tested under various load conditions under varying input power and the performances are observed to be satisfactory.

Feedforward control techniques for Erbium–doped fiber amplifiers — challenges and solutions

Feedforward control of optical amplifiers is mandatory in wavelength routed networks to avoid traffic interruption resulting from fast input power variations. Effects limiting the efficiency of this control technique are discussed and an overview over techniques compensating for the most important ones is presented. Detailed insight into the wavelength dependence of the optimum pump power setting is provided by a mathematical model. Taking this dependence into account requires to filter the input signal. Three different techniques are explained that make use either of an additional filter placed in front of the input monitor, an embedded gain–flattening filter, or even the erbium–doped fiber itself. Timing is another important issue. Besides introducing a delay in front of the first doped fiber, sophisticated control schemes working without additional optical components by modifying the waveform of the pump signal are analyzed. Different setups such as cascaded amplifier stages with intermediate dispersion compensating fiber are considered. The stages are either controlled individually or are coupled via a pump splitter. Finally, solutions complementing the pump power control by fast adaptation of the attenuation of a variable attenuator are contemplated.

Analytical and Experimental Investigation to Determine the Variation of Hottel–Whillier–Bliss Constants for a Scaled Forced Circulation Flat-Plate Solar Water Heater

Fixed tilt flat-plate solar thermal collectors, popularly known as solar water heaters, still remain as one of the most interesting technologies for utilization of solar energy. The system performance deteriorates due to scaling because of the continuous use of hard water as feed water. The present study deals with the experimental and analytical approach to determine the variation of Hottel–Whillier–Bliss (H–W–B) constants (which compactly represent the efficiency characteristics of a solar water heater) due to variation in solar power input and degree of scaling in case of forced circulation system (FCS) without considering the variation of input power to the circulating pump. Indoor tests are performed with a copper tube to investigate the flow characteristics. This forms a part of conventional FCS, in place of the usual nine-fin tube array in a full-fledged collector. In indoor tests, electrical heating is favored to simulate solar radiation level. Various energy parameters are determined and compared by incorporating the developed numerical code FLATSCALE. Variation between experimental and analytical mass flow rate, overall heat loss coefficient, and H–W–B constants with simulated solar radiation level is plotted. In scaled condition, the drop in instantaneous efficiency is due to both scale thickness and reduced water flow rate. Scale thickness acts as an additional thermal conductive resistance between absorber plate and flowing water. Overall heat loss coefficient increases as absorber plate temperature is high during reduced flow rate. The maximum deviation observed is 21.68% in mass flow rate, 14.64% in absorber plate mean temperature, 7.86% in overall heat loss coefficient, and 12.04% in instantaneous efficiency. Compared to a clean tube, a highly scaled tube of 3.7 mm scale thickness indicates a drop of 4.76% in instantaneous efficiency and 40.28% in mass flow rate. It is concluded that the growth of scale in FCS does not affect the instantaneous efficiency significantly because of the margin in heat carrying capacity of water in spite of high drop in the flow rate.

A Directional Interstitial Antenna for Microwave Tissue Ablation: Theoretical and Experimental Investigation.

Microwave ablation (MWA) is a minimally invasive thermal therapy modality increasingly employed for the treatment of tumors and benign disease. For successful treatment, complete thermal coverage of the tumor and margin of surrounding healthy tissue must be achieved. Currently available interstitial antennas for MWA have cylindrically symmetric radiation patterns. Thus, when treating targets in proximity to critical structures, caution must be taken to prevent unintended thermal damage. A novel coaxial antenna design for MWA with an asymmetrical cylindrical heating pattern is presented in this paper. This radiation pattern is achieved by employing a hemicylindrical reflector positioned at a critical distance from a conventional coaxial monopole antenna. Finite-element method simulations were employed to optimize the geometric dimensions of the antenna with the objective of minimizing the antenna reflection coefficient at the 2.45-GHz operating frequency, and maximizing volume of the ablation zone. Prototype antennas were fabricated and experimentally evaluated. Simulations indicated an optimal S11 of -32 dB at 2.45 GHz in close agreement with experimental measurements of -29 dB. Ex vivo experiments were performed to validate simulations and observe effects to the antennas' heating pattern with the varying input power and geometry of the reflector. Ablation zones up to 20 mm radially were observed in the forward direction, with minimal heating (less than 4 mm) behind the reflector.

Extended linear regime of cavity-QED enhanced optical circular birefringence induced by a charged quantum dot

Giant optical Faraday rotation (GFR) and giant optical circular birefringence (GCB) induced by a single quantum-dot spin in an optical microcavity can be regarded as linear effects in the weak-excitation approximation if the input field lies in the low-power limit [Hu et al., Phys. Rev. B 78, 085307 (2008); Hu et al., Phys. Rev. B 80, 205326 (2009)]. In this work, we investigate the transition from the weak-excitation approximation moving into the saturation regime comparing a semiclassical approximation with the numerical results from a quantum optics toolbox [Tan, J. Opt. B 1, 424 (1999)]. We find that the GFR and GCB around the cavity resonance in the strong-coupling regime are input field independent at intermediate powers and can be well described by the semiclassical approximation. Those associated with the dressed state resonances in the strong-coupling regime or merging with the cavity resonance in the Purcell regime are sensitive to input field at intermediate powers, and cannot be well described by the semiclassical approximation due to the quantum-dot saturation. As the GFR and GCB around the cavity resonance are relatively immune to the saturation effects, the rapid readout of single-electron spins can be carried out with coherent state and other statistically fluctuating light fields. This also shows that high-speed quantum entangling gates, robust against input power variations, can be built exploiting these linear effects.

Rectenna Design and Signal Optimization for Electromagnetic Energy Harvesting and Wireless Power Transfer

This work addresses two key topics in the field of energy harvesting and wireless power transfer. The first is the optimum signal design for improved RF-DC conversion efficiency in rectifier circuits by using time varying envelope signals. The second is the design of rectifiers that present reduced sensitivity to input power and output load variations by introducing resistance compression network (RCN) structures. key words: rectenna, energy harvesting, wireless power transfer, resistance compression network, rectifier

Dual-Band Resistance Compression Networks for Improved Rectifier Performance

In this work, the concept of dual-band resistance compression networks is introduced and applied to the design of rectifier circuits with improved performance. The use of resistance compression networks (RCNs) minimizes the sensitivity of rectifier circuits to variations in the surrounding environment, such as input power level and changes in the rectifier load. The proposed dual-band RCN can be used as the matching network located between the antenna and the rectifying element of a dual-band rectifier for energy harvesting applications. A dual-band ( 915 MHz /2.45 GHz) rectifier based on RCN is designed and characterized showing improved performance in comparison with a conventional dual-band envelope detector by exhibiting improved RF-dc conversion efficiency and reduced sensitivity versus output load and input power variations.

Performance Analysis of Four Wave Mixing: A Non-Linear Effect in Optical fibers

Linear effects in Optical fibers are caused due to the refractive index of the optical medium's dependence on the intensity of light. One of the prominent non-linear effects in Optical fibers is the Four-wave mixing (FWM) phenomenon. FWM effect is resonant when the phase matching condition is satisfied. It only occurs for particular combinations of fiber dispersion and signal frequencies. The FWM is a very unpleasant transmission phenomenon occurring in a transparent optical network based on Dense Wave Division Multiplexing, but it could be used advantageously for implementing optical devices such as wavelength converters, parametric amplifiers, optical de-multiplexers, chromatic dispersion compensators, as well as signal to noise regenerators. This paper discusses the effect of channel spacing, laser power, and dispersion, length of the optical fiber and the variation of input power to compensate the effect of FWM when implemented in a short haul environment. General Terms

Phase-Preserving Amplitude Noise Compression of 40 Gb/s DPSK Signals in a Single SOA

Wavelength-preserving and wavelength-converting amplitude regeneration of 40 Gb/s DPSK data in a saturated semiconductor optical amplifier (SOA) with limited excess phase noise feature is reported and investigated. By injecting simultaneously in the amplifier the noisy data and a CW beam with proper power levels, both the pass-through (PT) signal and the wavelength-converted data by four-wave-mixing (FWM) can be regenerated. The strongest regenerative effect is observed for the converted FWM data. The effect of input power variations on the regenerative performance of the device is thoroughly investigated in terms of Bit-Error Rate (BER) versus threshold margin improvement. We observe that regenerative behavior is attained for different levels of the data and CW power levels at SOA input. Experimental investigation of small-signal amplitude and phase SOA response reveals indeed the role of data/CW power balance for reducing the impact of excess phase noise from the amplifier. The analysis also confirms the stronger regenerative capability of the FWM process due to the strong amplitude-limiting SOA response at lower input data power in respect to the PT signal. The scheme offers the advantages of simplicity, compactness, and low operating power levels, making it a practical candidate for all-optical regeneration of high-speed DPSK signals.

Operational characteristics of pulsating heat pipes with a dual-diameter tube

A series of experiments was performed to investigate the effect of a dual-diameter tube on the flow and heat transfer characteristics of single-turn pulsating heat pipes (PHPs). Various types of PHPs were made of glass capillary tubes with various inner diameters. Using thermometry and high-speed photography, experiments to quantitatively observe operational characteristics of the PHPs were performed with varying input power and inclination angle. The results show that circulating flow promoted by a dual-diameter tube reduces thermal resistance of the PHP by as much as 45%. Based on experimental observations, a simplified model was developed to predict thermal performance of PHPs with circulating flow, and the results based on the model matched well with experimental data to within the error of 15%. The data calculated by the proposed model show that there is an optimum range of diameter difference where the thermal performance enhancement is maximized. The optimal range of the dimensionless diameter difference is found to be 0.25<ΔD/Davg<0.4.

Optimization of Operational and Constitutional Geometric Parameters for Thermoaoustic Energy Output

The effects of geometric parameters (stack position, stack length, resonator tube length) and varying input power over acoustic energy output were investigated. The acoustic laser kit (Garret 2000) was used for the construction of TA lasers. A series of sound pressure level measurements in different orientations did not differ significantly confirming that the sound wave generated could be assumed as a spherical wave. An increase in acoustic pressure was recorded with respective increase in input power, stack and resonator tube lengths owing to their relative influence over heat transfer rate and critical temperature gradient across the stack.