Pumping Power Requirements Research Articles

Enhanced flow uniformity in parallel mini-channels with pin-finned inlet header

A key challenge concerning the design of mini-channel heat sinks pertains to minimization of flow maldistribution in parallel channels. Although this challenge has spurred several research efforts towards exercising control over flow resistance within parallel channels to enhance flow uniformity, some practical issues associated with fabrication and implementation, as well as the possibility of a high pressure drop render the efforts less useful. The present study concerns development of a strategy that utilizes staggered pin-fin arrays in the inlet header of mini-channel heat sinks with the aim of achieving uniform flow distribution within parallel channels without increasing total pressure drop. Two different header shapes, trapezoidal and rectangular, have been considered, and ten different pin-fin arrangements for each type of header have been designed to numerically investigate flow uniformity within channels. The three-dimensional computational domain included the entire heat sink consisting of inlet/outlet connection tubes, inlet/outlet headers, and twenty parallel rectangular mini-channels—each measuring 3 mm in hydraulic diameter and equidistantly spaced with a 2-mm solid-wall spacing. It has been demonstrated that compared to baseline inlet headers, best pin-fin arrangements obtained for both trapezoidal and rectangular inlet headers yield significant improvement in flow uniformity within channels along with uniform temperature distribution over the heat sink base with minimal influence on the pumping power requirement.

Experimental investigation of TiO2–water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel heat sinks having three different channel configurations. The performance of TiO2 nanofluids having concentrations of 0.006, 0.008, 0.01 and 0.012 vol% is compared with that of distilled water under laminar regime at heating powers of 25 W, 35 W and 45 W. Results indicated that for all heat sinks, nanofluids showed better heat transfer characteristics than distilled water. With an increase in heating power, TiO2 nanofluid thermal performance was decreased. Using 0.012% TiO2 nanofluids, minimum wall base temperature and maximum enhancement in Nusselt number are noted as 33.85 °C and 40.57%, respectively, for heat sink with wavelength of 5 mm and amplitude of 0.5 mm corresponding to Reynolds number of 894 at heating power of 25 W. Pumping power requirement is function of flow rate and pressure drop, and its maximum value of 0.0284 W is associated with heat sink with minimum wavelength. Moreover, variation in wavelength of channel is found to have dominating effect on heat transfer performance of heat sink as compared to the width of channel.

Study on Thermal and Hydrodynamic Performance of a Triple Fluid Heat Exchanger with Different Passes and Rows

Hybrid cooling system has become a promising thermal management system for data center considering its capability of removing heat from various electronic components systematically. Water cooling and air cooling can be used for cooling the active component and passive component respectively. A novel triple fluid heat exchanger (TFHEX) is designed to dissipate the heat from these fluids into the coolant. This paper discusses thermal and hydrodynamic performance of TFHEX that specially designed for hybrid cooling of data. In present work, the THFEX is designed to dissipate heat from 32kW rack in which the server that dissipates 90% of heat from the active component and 10% of from passive component. Since the water side has much higher load, heat transfer from tube to tube in TFHEX has to be carefully maintained without significant increase in pressure drop. It was found that TFHEX can dissipate heat from different heat source at various load without significant increase in the pressure drop if designed carefully and therefore this heat exchanger can be a feasible solution for hybrid cooling data center. The results critically evaluated the trade-off between the heat transfer capacity of TFHEX and its pressure drop i.e. the pumping power requirement. This can be a reference for data center engineers to select the appropriate configuration for TFHEX for hybrid cooling.

Viscosity of hybrid nanofluids: A critical review

The remarkable enhancement in heat transfer capabilities of conventional fluids with the addition of nanosized metallic and non-metallic particles appealed the attention of investigators towards the suspension of hybrid nanocomposites as a substitute of mono particles. Although these fluids manifest captivating thermal characteristics, the drawbacks associated with their application include high frictional effects and pumping power requirements. The major cause of aforementioned problems is the elevated viscosity. The current study summarizes the work of different investigators and discusses the critical factors affecting the viscosity of hybrid nanofluids such as temperature, particle concentration, pH value, particle size and morphology with a concise discussion on the reasons reported in the literature for the viscosity augmentation. Furthermore, the models developed by different investigators have also been discoursed with specified limitations. Comparison between the viscosity of mono and hybrid nanofluid is also presented comprehensively. It is observed that most of the studies considered the effect of particle concentration and temperature that the effect of these factors is more significant. Water-based nanofluids delivered better results in comparison of ethylene glycol-based nanofluids while the oil-based nanofluids preferred in the applications where the pumping power is not more significant. It has been noticed that the fluids containing tube shaped nanoparticles comparatively showed enhanced viscosity than that of spherically shaped nanoparticles. It has also been observed that the studies preferred to develop their own models for the prediction of viscosity rather than to use the existing models and failed to provide a universal correlation.

High-efficiency squeezed light generation for gravitational wave detectors

The engineering of strongly squeezed vacuum states of light is a key technology for the reduction of quantum noise in gravitational wave detectors. We report on the observation of up to 12.0 dB squeezed vacuum states of light at the wavelength of 1064 nm in the frequency band from 10 Hz to 100 kHz. This is the strongest squeezing reported to date within this detection band. The squeezed states were generated in a half-monolithic, standing-wave cavity optical parametric amplifier, which was resonant for the fundamental and harmonic light fields. We chose appropriate reflectivities to obtain a significant reduction of the required pump power, which was 8.6 mW only. Our analysis revealed that the residual measurement phase noise was smaller than 3.5 mrad rms and that the squeezed light source provided up to 14 dB of squeezing for a downstream application. The experiment was electronically stabilized in all relevant degrees of freedom, demonstrating the applicability of the linear, doubly resonant cavity topology for current and future gravitational wave detectors.

Cascaded downconversion interface to convert single-photon-level signals at 650 nm to the telecom band.

We present a device designed for two-step downconversion of single-photon-level signals at 650nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange periodically poled lithium niobate waveguide and a 2.19-μm pump laser. By testing the device in the linear regime with a classical input, we achieved 99% depletion efficiency for each stage, corresponding to an internal quantum efficiency of 63% at the optimum pump power for the complete cascaded process.

OPTIMISATION OF HYDRAULIC FRACTURING DESIGN IN LOWER OLIGOCENE RESERVOIR, KINH NGU TRANG OILFIELD

Kinh Ngu Trang oilfield is of the block 09-2/09 offshore Vietnam, which is located in the Cuu Long basin, the distance from that field to Port of Vung Tau is around 140 km and it is about 14 km from the north of Rang Dong oilfield of the block 15.2, and around 50 km from the east of White Tiger in the block 09.1. That block accounts for total area of 992 km2 with the average water depth of around 50 m to 70 m. The characteristic of Oligocene E reservoir is tight oil in sandstone, very complicated with complex structure. Therefore, the big challenges in this reservoir are the low permeability and the low porosity of around 0.2 md to less than 1 md and 1% to less than 13%, respectively, leading to very low fracture conductivity among the fractures. Through the Minifrac test for reservoir with reservoir depth from 3,501 mMD to 3,525 mMD, the total leak-off coefficient and fracture closure pressure were determined as 0.005 ft/min0.5 and 9,100 psi, respectively. To create new fracture dimensions, hydraulic fracturing stimulation has been used to stimulate this reservoir, including proppant selection and fluid selection, pump power requirement. In this article, the authors present optimisation of hydraulic fracturing design using unified fracture design, the results show that optimum fracture dimensions include fracture half-length, fracture width and fracture height of 216 m, 0.34 inches and 31 m, respectively when using proppant mass of 150,000 lbs of 20/40 ISP Carbolite Ceramic proppant.

Bio-inspired self-agitator for convective heat transfer enhancement

Convective heat transfer plays an important role in both the fundamental research and the development of high-performance heat exchangers. Inspired by blades of grass vibrating in the wind, we developed a self-agitator for convective heat transfer enhancement. Because of fluid-structure interactions, the agitator, with self-sustained vibration, can generate strong vortices to significantly break the thermal boundary layer and improve fluid mixing for enhanced convective heat transfer. In particular, we establish a methodology to link the vorticity field at a preferred frequency to the optimal improvement in the convective heat transfer. To identify the self-agitator preferred frequency, mode analysis is performed with simulation results using dynamic mode decomposition. Experimental results are also obtained to further validate the proposed approach. These results show that the proposed self-agitator design can improve the convective heat transfer by 120% in a conventional heat exchanger without additional pumping power requirements and can achieve a Nusselt number of up to 30 within the laminar flow region, which is improved by 200% with the same Reynolds number compared to the clean channel.

Substrate and operational conditions as regulators of fluid properties in full-scale continuous stirred-tank biogas reactors - implications for rheology-driven power requirements.

Understanding fluid rheology is important for optimal design and operation of continuous stirred-tank biogas reactors (CSTBRs) and is the basis for power requirement estimates. Conflicting results have been reported regarding the applicability of total solid (TS) and/or total volatile solid (TVS) contents of CSTBR fluids as proxies for rheological properties. Thus, the present study investigates relationships between rheological properties of 12 full-scale CSTBR fluids, their substrate profiles, and major operational conditions, including pH, TS and TVS contents, organic loading rate, hydraulic retention time, and temperature. Rheology-driven power requirements based on various fluid characteristics were evaluated for a general biogas reactor setup. The results revealed a significant correlation only between the rheological fluid properties and TS or TVS contents for sewage sludge digesters and thermophilic co-digesters (CD), but not for mesophilic CD. Furthermore, the calculated power requirements for pumping and mixing, based on the various fluid characteristics of the studied CSTBRs, varied broadly irrespective of TS and TVS contents. Thus, this study shows that the TS and/or TVS contents of digester fluid are not reliable estimators of the rheological properties in CSTBRs digesting substrates other than sewage sludge.

Predictive model for the scale-out of small channel two-phase flow contactors

In this paper, double manifolds are theoretically investigated for the scale-out of two-phase incompressible flows in small channels. Statistical descriptors are proposed to characterise the maldistribution of the total flow rate and the ratio of the flow rates in the two-phase channels, based on the variances and covariance of the flow rates of the two fluids. A novel resistance network model is developed that relates the flowrates of the fluids in the two-phase channels to the hydraulic resistances of the manifold. The statistical descriptors and the resistance network model are then used to develop relationships between the maldistribution coefficients and the hydraulic resistances of the double manifold, the overall pressure drop and the pumping power requirements for different parallel channel numbers. Based on these, scaling laws are proposed that maintain a constant degree of maldistribution for a scale-up factor up to 102. Double manifolds designed using these scaling laws have a constant pressure drop as the number of channels increases, whilst the power requirements increase linearly. The power requirements are inversely proportional to the phase ratio maldistribution descriptor. Recommendations for the design of double manifolds for the scale-out of two-phase systems are proposed.

Flow and heat transfer behaviour of nanofluids in microchannels

Flow and heat transfer of aqueous based silica and alumina nanofluids in microchannels were experimentally investigated. The measured friction factors were higher than conventional model predictions at low Reynolds numbers particularly with high nanoparticle concentrations. A decrease in the friction factor was observed with increasing Reynolds number, possibly due to the augmentation of nanoparticle aggregate shape arising from fluid shear and alteration of local nanoparticle concentration and nanofluid viscosity. Augmentation of the silica nanoparticle morphology by fluid shear may also have affected the friction factor due to possible formation of a core/shell structure of the particles. Measured thermal conductivities of the silica nanofluids were in approximate agreement with the Maxwell-Crosser model, whereas the alumina nanofluids only showed slight enhancements. Enhanced convective heat transfer was observed for both nanofluids, relative to their base fluids (water), at low particle concentrations. Heat transfer enhancement increased with increasing Reynolds number and microchannel hydraulic diameter. However, the majority of experiments showed a larger increase in pumping power requirements relative to heat transfer enhancements, which may hinder the industrial uptake of the nanofluids, particularly in confined environments, such as Micro Electro-Mechanical Systems (MEMS).

Heat transfer enhancement using corona wind generator

Heat transfer enhancement using corona wind generators in a square channel has been numerically examined in this study. Three configurations of the corona wind generator (separately with 4, 12, and 28 pins of emitting electrodes) are investigated for their effectiveness in the enhancement of heat transfer as well as the pumping power requirement. To achieve the maximum enhancement in heat transfer, the emitting electrodes of the corona wind generator are flush mounted on the channel walls so that the corona wind produced directly perturbs the momentum and thermal boundary layers. The Reynolds number considered varies in a range between 200 and 2000. The influence of electric field on the flow and temperature fields is examined for a wild range of operating conditions. It has been found that the thermal hydraulic parameter, a measure of the effectiveness in heat transfer enhancement, is not only greater than unity but also higher than those of other techniques, which indicates that EHD technique has a great potential for many engineering applications.

Design and Development of a Miniaturized Percutaneously Deployable Wireless Left Ventricular Assist Device: Early Prototypes and Feasibility Testing.

The current left ventricular assist devices (LVADs) are limited by a highly invasive implantation procedure in a severely unstable group of advanced heart failure patients. Additionally, the current transcutaneous power drive line acts as a nidus for infection resulting in significant morbidity and mortality. In an effort to decrease this invasiveness and eliminate drive line complications, we have conceived a wireless miniaturized percutaneous LVAD, capable of being delivered endovascularly with a tether-free operation. The system obviates the need for a transcutaneous fluid purge line required in existing temporary devices by utilizing an incorporated magnetically coupled impeller for a complete seal. The objective of this article was to demonstrate early development and proof-of-concept feasibility testing to serve as the groundwork for future formalized device development. Five early prototypes were designed and constructed to iteratively minimize the pump size and improve fluid dynamic performance. Various magnetic coupling configurations were tested. Using SolidWorks and ANSYS software for modeling and simulation, several geometric parameters were varied. HQ curves were constructed from preliminary in vitro testing to characterize the pump performance. Bench top tests showed no-slip magnetic coupling of the impeller to the driveshaft up to the current limit of the motor. The pump power requirements were tested in vitro and were within the appropriate range for powering via a wireless energy transfer system. Our results demonstrate the proof-of-concept feasibility of a novel endovascular cardiac assist device with the potential to eventually offer patients an untethered, minimally invasive support.

Wind-Turbine Trailing-Edge Noise Reduction by Means of Boundary-Layer Suction

Distributed boundary-layer suction has numerically and experimentally shown great potential to reduce flow-induced trailing-edge noise. The paper aims at the transfer of this potential to an industrial full-size wind turbine by means of a dedicated suction system design and, hence, is meant to point out whether the predicted, airfoil-related improvements carry over to wind turbines represented by the N117, not hitherto in liaison with active flow control. Guidance is given through the different design steps involving the suction-followed blowing of the fluid and being continually dictated by industrial constraints and requirements. Because the processes of trailing-edge noise reduction and effective power alteration are intimately bound together, great emphasis is put on an accurate prediction of pump power requirement, with the latter being based on a detailed suction hardware system implying pressure losses across each component. Exploiting the limited installation space, a total trailing-edge noise reduction of 3.6 dB is coupled with a net enhancement of total rotor power of 4.75%. As of a cross-over noise reduction level of 5 dB, the enhancement of aerodynamic power no longer compensates for the pump power requirement and, hence, aeroacoustic demands are implemented to the detriment of aerodynamic performance.

Design of a boundary-layer suction system for turbulent trailing-edge noise reduction of wind turbines

Abstract The present work introduces a method for the design of a boundary-layer suction system for turbulent trailing-edge noise reduction of wind turbines. Since the latter hitherto has been primarily assessed in a two-dimensional framework, the paper is meant to point out whether the predicted improvements carry over to wind turbine flow. Since the processes of trailing-edge noise reduction and effective power alteration are intimately bound together, great emphasis is put on an accurate prediction of pump power requirement, the latter being based on a detailed suction hardware system implying pressure losses across each component. An exemplarily performed design reveals that, within a certain design regime, trailing-edge noise reduction is accompanied by an enhancement of rotor power. However, as of a distinct cross-over point at which the pump power requirement exactly compensates the amelioration of aerodynamic power, a trade-off between aeroacoustics and aerodynamics arises. The method bases on fully-resolved URANS computations and is applied to the generic NREL 5 MW turbine.

Numerical investigation on heat transfer enhancement of solar air heater using sinusoidal corrugations on absorber plate

This paper presents the effect of sinusoidal profiled absorber plate on augmented heat transfer and corresponding thermo-hydraulic performance of solar air heater using three dimensional Computational Fluid Dynamics (CFD) simulation for the flow Reynolds number ranging between 4,000 and 24,000. The effect of variation of design parameters of corrugated absorber plate such as the non-dimensional wavelength and aspect ratio on the thermo-hydraulic performance is brought out. The aspect ratio is varied between 1.5 and 4.0 while the normalized wavelength is varied between 1.0 and 6.0. The study reveals that the presence of sinusoidal corrugations provides increased flow disturbances leading to considerable enhancement in heat transfer. It is found that the use of lower values of non-dimensional wavelength and aspect ratio leads to higher thermal efficiency. The average increase in thermal efficiency is about 12.5% as compared to the base model for the configuration having an aspect ratio of 1.5 and non-dimensional wavelength of 1.0. In terms of effective efficiency, the sinusoidal corrugations are found to be highly effective at lower flow rate conditions and generally have a relatively narrow useful operating range of flow Reynolds number. The aspect ratio and non-dimensional wavelength have significant influence on the effective efficiency. The pumping power requirement is generally found to be relatively higher as compared to the base model owing to increased flow obstruction by the corrugations.

Mixing and pumping by pairs of helices in a viscous fluid.

Here, we study the fluid dynamics of a pair of rigid helices rotating at a constant velocity, tethered at their bases, in a viscous fluid. Our computations use a regularized Stokeslet framework, both with and without a bounding plane, so we are able to discern precisely what flow features are unaccounted for in studies that ignore the surface from which the helices emanate. We examine how the spacing and phase difference between identical rotating helices affects their pumping ability, axial thrust, and power requirements. We also find that optimal mixing of the fluid around two helices is achieved when they rotate in opposite phase, and that the mixing is enhanced as the distance between the helices decreases.

Analytical investigation of solar air heater with jet impingement using energy and exergy analysis

In this present work an exergy efficiency of the single pass double duct jet plate solar air heater (SPDDJPSAH) is analytically investigated. The analysis is carried out for different mass flow rate m = 0.002–0.023 kg/s, stream wise pitch ratio X/Dh = 0.435–1.739, span wise pitch ratio Y/Dh = 0.435–0.869 and jet diameter ratio Dj/Dh = 0.043–0.109. The overall performance of solar air heaters is effectively evaluated by the exergy analysis by considering both the useful energy gain and subsequent pumping power requirement. Results show that SPDDJPSAH has been enhancing the effective efficiency by 21.2% and exergy efficiency by 22.4% when compared with Single Pass Single Duct Jet Plate Solar Air Heater (SPSDJPSAH). The effects of mass flow rate and jet plate design parameters on the exergy efficiency have been presented. The optimized values of stream wise pitch ratio X/Dh = 1.739, span wise pitch ratio Y/Dh = 0.869 and jet diameter ratio Dj/Dh = 0.065 are identified at the mass flow rate of 0.0035 kg/s and yields the maximum exergy efficiency of 4.36%. Design plots are also prepared in order to identify the optimum values of jet plate design parameters to achieve the desired temperature rise. Using the analytical results, the correlations have been developed for predicting the exergy efficiency in terms of Reynolds number and jet plate design variables.

Experimental and numerical studies of helium-cooled modular divertors with multiple jets

As part of the US-Japan PHENIX program, the helium-cooled modular divertor with multiple jets (HEMJ) and a simpler “flat” variant were experimentally studied in a closed helium loop with a redesigned test chamber at coolant inlet temperatures as great as 425 °C, incident heat fluxes as great as 2.2 MW/m2 and prototypical inlet pressures of ∼10 MPa. The data were used to develop correlations for the average Nusselt number and loss coefficient for a range of mass flow rates; these correlations were used in turn to predict the thermal-hydraulic performance of a single divertor module at prototypical conditions.The experimental results suggest that a flat jet array with six holes surrounding one central hole, all of the same diameter, can provide similar average heat transfer coefficients as the HEMJ divertor, albeit with higher pumping power requirements. Because of its smaller cooled surface area, however, this design has lower maximum allowable heat fluxes compared with the HEMJ divertor. Nevertheless, the flat variant could potentially simplify manufacturing and reduce the costs required to fabricate O(106) “finger” modules.

Computational fluid dynamics analysis of a V-rib with gap roughened solar air heater

A CFD analysis of a solar air heater has been carried out using V-shaped ribs as artificial roughness on the absorber plate. The relative roughness pitch, P/e = 6-12, Reynolds number of 3800-18000, relative roughness height, e/D = = 0.042, and angle of attack, ? = 30?-75?, have been selected as design variables of V-shaped rib for analysis. The ANSYS FLUENT 15.0 with renormalization group k-? turbulence model is selected for the analysis of computational domain of solar air heater. The enhancement of Nusselt number and friction factor with Reynolds number for different values of a relative roughness pitch are presented and discussed by CFD analysis. The effect of angle of attack and Reynolds number on enhancement of Nusselt number and friction factor is also presented. The optimum value of rib configuration based on constant pumping power requirement has been derived using thermohydraulic performance parameter and has been found maximum at angle of attack of 60? and P/e = 10.