Pumping Power Requirements Research Articles

Pressure and partial wetting effects on superhydrophobic friction reduction in microchannel flow

Friction reduction in microchannel flows can help alleviate the inherently taxing pumping power requirements associated with the dimensions involved. One possible way of achieving friction reduction is through the introduction of surface microtexturing that can lead to a superhydrophobic Cassie-Baxter state. The Cassie-Baxter state is characterized by the presence of air pockets within the surface microtexturing believed to act as an effective “shear free” (or at least shear reduced) layer, decreasing the overall friction characteristics of the surface. Most work in this area has concentrated on optimizing the surface microtexturing geometry to maximize the friction reduction effects and overall stability of the Cassie-Baxter state. However, less attention has been paid to the effects of partially wetted conditions induced by pressure and the correlation between the liquid-gas interface location within the surface microtexturing and the microchannel flow characteristics. This is mainly attributed to the difficulty in tracking the interface shape and location within the microtexturing in the typical top-down view arrangements used in most studies. In this paper, a rectangular microchannel with regular microtexturing on the sidewalls is used to visualize and track the location of the air-water interface within the roughness elements. While visually tracking the wetting conditions in the microtextures, pressure drops versus flow rates for each microchannel are measured and analyzed in terms of the non-dimensional friction coefficient. The frictional behavior of the Poiseuille flow suggests that (1) the air-water interface more closely resembles a no-slip boundary rather than a shear-free one, (2) the friction is rather insensitive to the degree of microtexturing wetting, and (3) the fully wetted (Wenzel state) microtexturing provides lower friction than the non-wetted one (Cassie state), in corroboration with observations (1) and (2).

One-to-Nine Multicasting of RZ-DPSK Based on Cascaded Four-Wave Mixing in a Highly Nonlinear Fiber Without Stimulated Brillouin Scattering Suppression

One-to-nine multicasting of a 10.7-Gb/s RZ-DPSK signal is demonstrated on the basis of cascaded four-wave mixing (FWM) in a and fluorine-doped highly nonlinear fiber. This structure could significantly improve the FWM efficiencies of most channels with the required pump power of only . Therefore, no stimulated Brillouin scattering suppression scheme is required. All the nine channels exhibit high signal-to-noise ratio values with power penalty measured at bit error rate.

Investigation of bipolar plate geometry on direct methanol fuel cell performance

Abstract The effect of bipolar plate (BPP) channel width on the performance of a single-cell direct methanol fuel cell (DMFC) stack was investigated. Three BPPs with a single-channel serpentine configuration were fabricated with three different channel widths having the same effective flow areas. Experimental tests showed that the fuel cell with the narrowest channel width had the best overall performance while the one with the widest channel width had the worst overall performance. A computational fluid dynamics (CFD) model was developed and simulated to investigate and understand the reasons for this change in performance. The CFD simulation showed that in the narrower channel the diffusion of the fuel within the diffusion layer was higher and the fuel distribution was more uniform. However, the pressure drop across the inlet and outlet was higher in the narrower channel, which increased the pumping power requirements.

Design considerations for hydraulic backfilling with coal combustion products (CCPs) at high solids concentrations

Abstract The rheological characteristics for the complex hydro-mixture of coal combustion products (CCPs) such as fly ash and fly ash-bottom ash mixture slurry at high solids concentration in the range of 60–70% by weight were investigated. Based on the rheological data, a non-Newtonian pseudo-plastic power law head loss model was used to evaluate the head loss of ash slurry pipelines having nominal bores in the range of 100–300 mm. The results indicated that the addition of bottom ash fractions to fly ash slurry at a given solids concentration has a beneficial effect in reducing the pumping power requirement. A monogram (design chart) for the ash mixture slurry has been formulated indicating the variation of backfilling rate WS with H/L ratio for a range of pipe sizes and transport velocities which may provide relevant pipe flow and operational conditions for hydraulic disposal of these coal combustion products for mine backfilling purpose.

Performance improvement of a double-pass solar air heater with fins and baffles under recycling operation

The performance of a solar air heater featured with double-pass as well as fins and baffles design was investigated for the effect of recycling operation via both experimental and theoretical approaches. The experimental results deviate by 1.5–23% from the theoretical predictions. The performance of solar air heaters with different designs are compared, including the single-pass, double-pass with recycle, fined double-pass with recycle, and fined plus baffled double-pass with recycle. The double-pass device introduced in this study was proposed for aiming to strengthen the convective heat transfer coefficient and enlarge the heat transfer area. Based on both theoretical and experimental results, the collector efficiency of the fined plus baffled double-pass with recycle design is much higher than the other designs under different reflux ratios and mass flow rates. The optimal reflux ratio for the fined plus baffled double-pass design is about 0.5 while considering both the collector efficiency and the pumping power requirement. An economic consideration in terms of the heat transfer efficiency and power consumption increment for double-pass operation is delineated.

Mixed convection with surface radiation between two asymmetrically heated vertical parallel plates

The effect of surface radiation on the developing laminar mixed-convection flow of a transparent gas between two asymmetrically heated vertical parallel plates is investigated. The effect of surface radiation on wall temperatures, fluid temperature profiles, location of the channel height at which the buoyancy forces balance the viscous forces, the location of the onset of pressure build up, the location of the onset of flow reversal, average friction factor, and Nusselt number are illustrated. The values of the emissivity at which surface radiation engenders minimum pumping power requirements are obtained. Finally, threshold values of the surface emissivity at which radiation effects can be neglected are presented.

Design and Demonstration of REAM-Based WDM-PONs With Remote Amplification and Channel Fault Monitoring

The use of reflective electro-absorption modulators (REAMs) as colorless upstream transmitters for wavelength-division-multiplexing passive optical networks is attractive for providing 10 Gb/s and above data rates. We address the feasibility of applying the remotely pumped optical amplifier to boost all upstream channels when REAMs are used at the optical network units. This scheme can avoid the use of more complicated devices, such as integrated REAMs with semiconductor optical amplifiers. The remote pumping scheme can simultaneously boost the upstream and downstream signals as well as the monitoring signals by the gain from the erbium-doped fiber and Raman amplification. The required pump power and the limitation on the seeding power are analyzed in order to optimize the bidirectional transmission performance for different access network spans.

Laser cooling with PbSe colloidal quantum dots

We present a theoretical scheme for laser cooling with colloidal lead-salt PbSe quantum dots (QDs) doped in a glass host. The laser cooling process is based on the anti-Stokes fluorescence in QDs. The relatively short (microsecond range) lifetime of the excited level of the PbSe QD allows the cooling process to be accelerated and new materials with higher phonon energy to be used as hosts, which are normally considered unsuitable for cooling with rare-earth ions. The considerable increase (by ∼104) in the absorption cross section of the PbSe QD in comparison with the absorption cross section of rare-earth ions doped in glasses or crystals increases the efficiency of the cooling process considerably, lowering the pump power requirements.

Tunable, low-repetition-rate, cost-efficient femtosecond Ti:sapphire laser for nonlinear microscopy

We report on a broadly tunable, long-cavity Ti:sapphire laser oscillator being mode-locked in the net negative intracavity dispersion regime by Kerr-lens mode-locking, delivering τ FWHM<300 fs pulses at 22 MHz repetition rate. The wavelength of the laser can be tuned over a 170 nm wide range between 712 nm and 882 nm. Having a typical pump power of 2.6 W, the maximum pulse peak power is 60 kW. Comparison of the reported laser with a standard, 76 MHz Ti:sapphire oscillator regarding two-photon excitation efficiency in a laser scanning microscope shows that the 22 MHz laser generates the same fluorescence signal at considerably, 1.82 times lower average power, which is expected to result in a reduced photothermal damage probability of biological samples. This fact along with the broad tunability and a low pump power requirement makes this cost-effective laser an ideal light source for nonlinear microscopy.

Continuous-wave ultraviolet emission through fourth-harmonic generation in a whispering-gallery resonator

We experimentally demonstrate continuous-wave ultraviolet emission through forth-harmonic generation in a millimeter-scale lithium niobate whispering-gallery resonator pumped with a telecommunication-compatible infrared source. The whispering-gallery resonator provides four spectral lines at ultraviolet, visible, near-infrared and infrared, which are equally spaced in frequency via the cascaded-harmonic process and span a 2-octave frequency band. Our technique relies on a variable crystal poling and high transverse order of the modes for phase-matching and a resonator quality factor of over 10(7) to allow cascaded-harmonic generation up to the fourth-harmonic at input pump powers as low as 200 mW. The compact size of the whispering gallery resonator pumped at telecommunication-compatible infrared wavelengths and the low pump power requirement make our device a promising ultraviolet light source for information storage, microscopy, and chemical analysis.

Gain Characteristics of LaF3:Er, Yb Nanoparticle-Doped Waveguide Amplifier

Fundamental rate equations and power propagation equations were used to simulate the gain factors of LaF3:Er, Yb nanoparticle-doped waveguide amplifiers excited at 980 nm. The gain first increased and then remained nearly constant with pump power increasing. The gain and the threshold pump power increased with increasing concentration of Er3+. The calculated gain of the concentration 0.75 x 10(26) ions/m3 on a 4 cm long waveguide was 3.6 dB. An optimum waveguide length was found for the highest gain and it was getting larger with the increase of the pump power. When the lifetime decreases from the Judd-Ofelt calculated value of 13.34 ms to the measured value of 60 micros, the required pump power of a 0.5 dB gain increased one level. We obtained a longer 4I(13/2) lifetime (100 micros) through decreasing the proportions of Er3+ and Yb3+ in nanoparticles and found that the threshold pump power decreased more at the expenses of saturated gain.

Fiber optical based parametric amplifier in a highly nonlinear fiber (HNLF) by using a ring configuration

A four-wave mixing (FWM) effect in a fiber-based optical parametric amplifier (FOPA) is reported. The novelty in the setup used is a ring cavity as opposed to the commonly used method of linear cavity. This reduces the required pump power, P p, for the amplification of the signals and also the generation of the idlers. The achieved gain for signal amplification is about 30 dB with a P p of 25 dBm. It has a flat gain response within range of 22 nm from 1570 nm to 1592 nm, with an average value of 28 dB within the 3 dB region. The average conversion efficiency is approximately −5 dB, with a peak value of −4 dB within the 2 dB region, with a range of 24 nm from 1576 nm to 1600 nm.

Effects of Corrugated Roughness on Gaseous Slip Flow Forced Convection in Microtubes

Because of technological restrictions, it is actually impossible to fabricate smooth microchannels. Therefore, exploring the roughness effects on the flow characteristics at microscale is of great importance for scientific communities. The present investigation deals with the effects of corrugated roughness on the fully developed slip flow forced convection in micropipes. The governing equations subject to first-order slip boundary conditions are solved by means of the straightforward perturbation method. Closed-form expressions are obtained for the dimensionless velocity and temperature distributions, for the friction coefficient and pressure drop, and finally for the Nusselt number. The results demonstrate that the corrugated roughness increases both the pressure drop and the heat transfer rate, with the amount of the increase in the pressure drop being a little more. Despite increasing the heat transfer rate, the effect of roughness is found to be unfavorable as it leads to smaller values of the channel performance, defined as the ratio of the heat transfer rate to the pressure drop. In other words, for a given heat transfer rate some increase in pumping power requirements is incurred.

The study of latent heat transport characteristics by solid particles and saccharide solution mixtures

The purpose of this study is the development of latent heat transport system by using the mixture of the minute latent heat storage materials and the saccharine solution as medium. The experimental studies are carried out by the evaluation of viscosity and pressure loss in a pipe. Polyethylene (P.E.) is selected as the dispersed minute material that has closeness density (920kg/m3) of ice (917kg/m3). D-sorbitol and D-xylose solutions are picked as continuum phase of the test mixture. The concentration of D-sorbitol solution is set 48mass% from measured results of saturation solubility and the melting point. 40mass% solution of D-xylose is selected as the other test continuum phase. The non-ion surfactant, EA157 Dai-ichiseiyaku CO. Ltd, is used in order to prevent of dispersed P.E. powder cohere. The pressure loss of test mixture is measured by the straight circular pipe that has smooth inner surface. The measuring length for pressure loss is 1000 mm, and the inner diameter of pipe is 15mm. The accuracy of experiment apparatus for measuring pressure loss is within ±5%. The pressure loss data is estimated by the relationship between the heat transport ratio and the required pump power. It is clarified that the optimum range of mixing ratio exists over 10mass% of latent heat storage material.

Evaluate the Performance of Optical Time Division Demultiplexing with the Gain Saturation effect of Semiconductor Optical Amplifier

Optical Time Division Multiplexing (OTDM) system technique is the extend time division multiplexing by optically combining a number of lower speed electronic baseband digital channels. In addition, the Semiconductor Optical Amplifiers (SOA's) are important components for optical networks. In this paper, we propose a novel model for an OTDM demultiplexer based on Cross Gain Modulation in a SOA. Analysis are extended to find the output of an optical IM/DD receiver to receive the demultiplexed optical signal and to find the output signal to noise ratio (SNR) taking into account the amplified spontaneous emission (ASE) noise. The results are evaluated in terms of BER, SNR and pump power for various input signal power level. It is found that, at a given signal input power the BER can be reduced by increasing the pump power and the required pump power is higher at higher level of input power.

Optimization of forced convection heat sinks with pumping power requirements

In this paper we address the optimization of a heat sink formed by parallel circular or non-circular ducts in a finite volume. The flow is considered to be laminar and steady and the fluid properties are assumed to be constant. Results for optimum dimensionless thermal length, optimum hydraulic diameter and maximum heat transfer rate density are presented for five different duct shapes subjected to a fixed pumping power constraint. Simple equations for the calculation of these optimum values are presented, and the influence of the local pressure drops at the inlet and outlet plenums, and of Prandtl number is discussed. The optimization results are then extended for the case of pumping power minimization at fixed heat transfer density.

Flow boiling in constructal tree-shaped minichannel network

Flow boiling in constructal tree-shaped minichannel network with an inlet diameter of 4 mm is numerically investigated using a one-dimensional model, taking into consideration the minor losses at junctions. The pumping power requirement, pressure drop, temperature uniformity and coefficient of performance of the constructal tree-shaped minichannel network are all evaluated and compared with those of the corresponding traditional serpentine channel, and the fluid stream undergoes a phase change from saturated liquid to saturated vapor. The effects of the length dimension and top view area (i.e. the path length) on saturated gas–liquid two-phase flow boiling heat transfer in tree-shaped minichannel networks are all analyzed and discussed. The results indicated that, the tree-shaped network configured with length dimension of two is able to maximum flow access; the path length plays a significant role in the determination of flow boiling in tree-shaped minichannel networks. In particular, compared to the traditional serpentine channel, flow boiling in constructal tree-shaped minichannnel network possesses less pressure drop, lower pumping power requirement, better temperature uniformity and higher coefficient of performance ( COP).

Constructal design of distributed cooling on the landscape

Here we constructal design to determine the area size (or number of users N) to be allocated to a central refrigeration plant, and to configure the distribution network for the distributed cooling system. The main objective is to maximize the net cooling capacity delivered to every user, and to minimize the pumping power required for transporting the chilled water. Two types of distribution networks are investigated: radial and tree-shaped networks. First, when ducts with a single diameter are used, the net cooling capacity delivered to every user is almost the same, while the pumping power requirement for the tree network is greater than that for the radial network. Multi-diameter tree networks are investigated next. The pumping power requirement for multi-diameter tree-shaped network is less than for radial network when N is greater than 19 if the flow is laminar, and when N is greater than 80 if the flow is turbulent. The global performance of the area-based cooling system can be improved by increasing the freedom to morph the configuration. Copyright © 2010 John Wiley & Sons, Ltd.

An Air-Based Cavity-Receiver for Solar Trough Concentrators

Abstract A cylindrical cavity-receiver containing a tubular absorber that uses air as the heat transfer fluid is proposed for a novel solar trough concentrator design. A numerical heat transfer model is developed to determine the receiver’s absorption efficiency and pumping power requirement. The 2D steady-state energy conservation equation coupling radiation, convection, and conduction heat transfer is formulated and solved numerically by finite volume techniques. The Monte Carlo ray-tracing and radiosity methods are applied to establish the solar radiation distribution and radiative exchange within the receiver. Simulations were conducted for a 50 m-long and 9.5 m-wide collector section with 120°C air inlet temperature, and air mass flows in the range 0.1–1.2 kg/s. Outlet air temperatures ranged from 260°C to 601°C, and corresponding absorption efficiencies varied between 60% and 18%. Main heat losses integrated over the receiver length were due to reflection and spillage at the receiver’s windowed aperture, amounting to 13% and 9% of the solar power input, respectively. The pressure drop along the 50 m module was in the range 0.23–11.84 mbars, resulting in isentropic pumping power requirements of 6.45×10−4−0.395% of the solar power input.

Influence of temperature and properties variation on nanofluids in building heating

Theoretical investigations on the application of nanofluids in the hydronic heating system of buildings have been presented in this paper. Realistic fluid velocities and temperatures employed in heat exchange equipment were used to compare the convective heat transfer coefficient and the pumping power requirement of nanofluids of various particle volume concentrations. The base fluid used in the analyses as a basis for comparison was a solution comprised of 60% ethylene glycol and 40% water (by weight). The thermophysical and heat transfer performance of the base fluid have been compared with copper oxide nanoparticles dispersed in the same base fluid with volumetric particle concentration ranging up to 4%. First, the variations of thermophysical properties such as viscosity, thermal conductivity, specific heat and density have been evaluated for different concentrations. Using these properties, several plots have been developed for quantitatively determining the enhancement of convective heat transfer coefficient as a function of flow velocity, Reynolds number and the nanoparticle volumetric concentration. For constant Reynolds number for flow in tubes, the Nusselt number and convective heat transfer coefficient increases as nanoparticle volume concentration increases. As the properties of nanofluids and the base fluid are temperature dependent, we have performed calculations for two fluid temperatures (323 K and 360 K). The results show that a higher convective heat transfer coefficient is achieved at higher temperatures for a nanofluid of equal concentration circulating at equal velocity. Frictional pressure loss and pumping power increases relative to the base fluid with particle volume concentration, but decreases with mean fluid temperature.