Transport Phenomena in Novel Microstructures for Use in Thermal Separation Processes

2009 ◽  
Author(s):  
Lukas E. Wiesegger ◽  
Ralf P. Knauss ◽  
Thomas Winkler ◽  
Stefan Maikowske ◽  
Ju¨rgen J. Brandner ◽  
...  
Keyword(s):  
Gaseous Phase ◽  
Phase Distribution ◽  
Flow Direction ◽  
Test System ◽  
Operating Conditions ◽  
Low Flow ◽  
Optimum Operating ◽  
Liquid Distribution ◽  
Flow Rates ◽  
Vof Model

In the present work novel microstructures are developed and studied by means of analytical and numerical methods. These microstructures form part of a demonstration microdevice to carry out a distillation without chemical reaction, two for the liquid and gaseous phase distribution/collection, and one for the liquid/gas mass transfer (“μTU-I,-II”). A solution for the 3D velocity field for the velocity component w in flow direction can be given for the rectangular and semicircular microchannel by using a lubrication approximation which gives good realistic values for the Reynolds number at low flow rates comparing to the common 2D approaches. The μTU-I is studied using the CFD code (6.3 FLUENT ® - 3ddp) by the approach of the VOF model. The simulations are performed with the test system methanol/water (distillation). By varying the flow rates of both phases and the contact angle, the condition until the occurrence of flooding of the microunit “μTU-I” is determined. The flooding and the optimum operating conditions of a new optimized configuration “μTU-II” -microunit are also investigated by means of numerical simulation (CFD). It can be shown that longitudinal instability is generated. Based on several concepts for liquid and gaseous phase distribution/collection by the Forschungszentrum Karlsruhe, novel microstructures (“Liquid-Distribution-Collection-Microstructure”, “Vapor-Distribution-Collection-Microstructure”) for both phases are developed, studied and optimized by using CFD. The results of all studies are verified based on the demonstration device in the laboratory.

Unsteady Flow Pattern Characteristics Downstream of a Forward-Curved Blades Centrifugal Fan

2000 ◽  
Vol 123 (2) ◽  
pp. 265-270 ◽  
Author(s):  
Sandra Velarde-Sua´rez ◽  
Rafael Ballesteros-Tajadura ◽  
Carlos Santolaria-Morros ◽  
Jose´ Gonza´lez-Pe´rez
Keyword(s):  
Operating Conditions ◽  
The Other ◽  
Low Flow ◽  
Centrifugal Fan ◽  
Hot Wire ◽  
Measured Velocity ◽  
Flow Rates ◽  
Velocity Fluctuations ◽  
Flow Asymmetry ◽  
Steady Velocity

The results of an experimental investigation of the flow at two exit radial locations of a forward-curved blades centrifugal fan are presented. Hot wire techniques were used to obtain steady velocity components and velocity unsteadiness levels (rms value of the components of velocity fluctuation) for different operating conditions. Globally speaking, the data reveal a strong flow asymmetry, with considerable changes in both magnitude and direction along the different circumferential positions. Particularly, big differences appear between the circumferential positions closer to the volute tongue and the other ones. The periodic character of the velocity signals due to the passing of the blades, clearly observed around the impeller, is missed in the vicinity of the volute tongue, where the main contribution to the velocity fluctuations appears to be random. Based on the measured velocity signals, velocity unsteadiness of the flow is determined analyzing the main contributions as a function of the flow rate and the measurement position. High levels of velocity unsteadiness were observed near the volute tongue, mainly at low flow rates.

scholarly journals Investigation of the Flow Field in the Vicinity of an Axial Flow Fan During Low Flow Rates

2014 ◽  
Author(s):  
Francois G. Louw ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Axial Flow Fan ◽  
Free Vortex ◽  
Flow Rates

Large axial flow fans are used in forced draft air cooled heat exchangers (ACHEs). Previous studies have shown that adverse operating conditions cause certain sectors of the fan, or the fan as a whole to operate at very low flow rates, thereby reducing the cooling effectiveness of the ACHE. The present study is directed towards the experimental and numerical analyses of the flow in the vicinity of an axial flow fan during low flow rates. This is done to obtain the global flow structure up and downstream of the fan. A near-free-vortex fan, designed for specific application in ACHEs, is used for the investigation. Experimental fan testing was conducted in a British Standard 848, type A fan test facility, to obtain the fan characteristic. Both steady-state and time-dependent numerical simulations were performed, depending on the operating condition of the fan, using the Realizable k-ε turbulence model. Good agreement is found between the numerically and experimentally obtained fan characteristic data. Using data from the numerical simulations, the time and circumferentially averaged flow field is presented. At the design flow rate the downstream fan jet mainly moves in the axial and tangential direction, as expected for a free-vortex design criteria, with a small amount of radial flow that can be observed. As the flow rate through the fan is decreased, it is evident that the down-stream fan jet gradually shifts more diagonally outwards, and the region where reverse flow occur between the fan jet and the fan rotational axis increases. At very low flow rates the flow close to the tip reverses through the fan, producing a small recirculation zone as well as swirl at certain locations upstream of the fan.

scholarly journals About the Dependence of Breakthrough Curves on Flow Direction in Column Experiments of Transport across a Sharp Interface Separating Different Porous Materials

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Francesca Giacobbo ◽  
Mauro Giudici ◽  
Mirko Da Ros
Keyword(s):  
Porous Materials ◽  
Flow Direction ◽  
Breakthrough Curves ◽  
Coarse Grained ◽  
Low Flow ◽  
Flow Rates ◽  
Fine Grained ◽  
The Past ◽  
Asymmetric Behaviour ◽  
Flow Through

Conservative transport experiments with layered porous materials (coarse-grained vs. fine-grained) were performed through experimental cylindrical columns to assess the possible occurrence of interface processes at the discontinuity between media with different hydrodynamic and hydrodispersive properties, as proposed by some authors in the past based on modelling and experimental results. The outcomes of the present work show that, under certain conditions, the breakthrough curves (BTCs) obtained for flow through the coarse-grained and then through the fine-grained media (CtF) or vice versa (FtC) can differ. More specifically, an asymmetric behaviour is observed for cases when the ratio between the column and grain diameters is small. Moreover, the discrepancies between CtF and FtC BTCs are enhanced for low flow rates and low quantity of injected solute.

Forty-Seven–Well Case Study: How a Holistic ESP Design for Deep Deviated Wells with Low Flow Rates Achieved Economic Production

2021 ◽  
Author(s):  
Lawrence Camilleri ◽  
Jorge Luis Villalobos ◽  
Pedro Luis Escalona ◽  
Alvaro Correal ◽  
Carlos Reyes ◽  
...  
Keyword(s):  
Historical Review ◽  
Substantial Improvement ◽  
Operating Conditions ◽  
Gas Content ◽  
Low Flow ◽  
Flow Rates ◽  
Artificial Lift ◽  
Electrical Submersible Pumps ◽  
Deviated Wells

Abstract The Shaya wells have vertical depths of 11,000 ft and are heavily depleted. They, therefore, require 10,000 ft of lift to achieve the target drawdown. Electrical submersible pumps (ESPs) were deployed, but because of the low flow rates (80 B/D), produced solids, and high free gas content, initial run lives were uneconomical. This 47-well case study demonstrates how a holistic design and operating procedure achieved both the target drawdown and an economical mean time between failure (MTBF). "Learning from history" was the key method as there was sufficient ESP data to determine the root cause of ESP failures based on a combination of dismantle inspection and failure analysis (DIFA) and operating conditions. Moreover, production testing combined with real-time downhole gauge data enabled inflow characterization with both nodal and pressure transient analysis, thereby establishing the well potential and ensuring that the new proposed design was not only reliable but also achieved the targeted drawdown. An additional requirement was to handle both the current low rates and higher rates associated with future waterflooding. A historical review of 9 wells was conducted, followed by a new ESP design that was proposed and installed in 47 wells, which achieved an MTBF of over 940 days, whereas previous designs in the same wells had an MTBF of only 650 days. This substantial improvement was achieved without compromising drawdown as the wells were produced with a flowing intake pressure of approximately 250 psia at setting depths of 9,500 ft. This result is particularly noteworthy when one considers the harshness of the well conditions and, in particular, bottom-hole temperatures of 240°F, fines migration, deviated wells with doglegs above 2.5°/100ft, intake pressures below bubble point and low productivity indices (PIs) of 0.2 B/D/psi. The high depletion combined with low PIs, which resulted in very low flow rates of as low as 50 B/D, was the most challenging factor of this application. Outflow modeling and wellbore hydraulics were also important considerations to limit solid fallback due to insufficient velocity in the production tubing as well minimize heat rise caused by startup transients, which can be long in low-PI wells. ESPs are traditionally best suited to wells with liquid rates providing sufficient cooling for both the motor and the pump as well as short unloading transients during startup. This success story, therefore, provides an important reference for future ESP applications in very low flow rates in deep wells, which are beyond the recommended application envelope of alternative low flow rate artificial lift solutions such as progressive cavity pumps and sucker rod pumps.

Experimental Investigation of Spray Cooling Heat Transfer on Circular Grooved Surface

2017 ◽  
Author(s):  
Azzam S. Salman ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
Target Surface ◽  
Spray Cooling ◽  
Operating Conditions ◽  
Low Flow ◽  
Inlet Temperature ◽  
Flow Rates

An experimental study was conducted in a closed loop spray cooling system working with deionized water as a cooling medium, to investigate the effects of surface modification on the spray cooling heat transfer enhancement in the single-phase region. Plain copper surface with diameter 1.5 cm and an enhanced surface with circular grooves were tested under different operating conditions. The volumetric flow rate of the coolant ranged from 115 mL/min to 177 mL/min., and the water inlet temperature was kept between 21–23 °C. Also, the distances between the nozzle and the target surface were varied at 8, 10, and 12 mm respectively. The results show that the distance between the nozzle and the target surface did not have a significant effect on the heat transfer performance for the low flow rates, while it has a slight effect on high flow rates for both surfaces. Also, increasing the liquid volumetric flow rate increases the amount of heat removed, and the heat transfer coefficient for both surfaces. Moreover, the maximum enhancement ratios achieved were 23.4% and 31% with volumetric flow rates of 153 mL/min, and 177 mL/min respectively.

scholarly journals Visualisation of flow pattern and measurement of liquid distribution in a random packed column using electrical resistance tomography (ERT)

2021 ◽  
Author(s):  
Nazar Aoda
Keyword(s):  
Flow Pattern ◽  
Flow Rate ◽  
Electrical Resistance ◽  
Packed Column ◽  
Operating Conditions ◽  
Flow Mode ◽  
Electrical Resistance Tomography ◽  
Liquid Distribution ◽  
Flow Rates ◽  
Good Agreement

The aim of this research is to use Electrical Resistance Tomography technique (ERT) to measure factors that affect local mass transfer at various axial locations in a random packed column with diameter 0.3m and bed height 150cm filled with 2 cm plastic spheres. These factors are: liquid maldistribution, velocity profiles, and flow pattern. The system was designed to run in a trickling down-flow mode and a full liquid up-flow mode. Experiments were performed at flow rates of 3, 6, and 9 gpm (or 0.27 x 10⁻², 0.54 x 10⁻² and 0.8 x 10⁻² m³/m² s) and under normal operating conditions of 25C° and atmospheric pressure. The liquid maldistribution factors were measured via ERT technique and the conventional liquid collection method. Both measurements were conducted at various fluid flow rates at different bed heights. The results of ERT were in very good agreement with the conventional method. The standard deviation values were 17% and 21% at flow rates 3 and 6 gpm respectively. The numerical values of velocity for full liquid up flow at 3 gpm were 0.83cm/s, 1.2cm/s, 1.2 cm/s and 1.11 cm/s for different heights of 30, 60 and 90 cm respectively and the numerical values of velocity for trickle down flow at 3 gpm were 16.5 cm/s, 22.5 cm/s and 24 cm/ for different heights of 30, 60 and 90 cm respectively. The values of the liquid maldistribution factor for flow rate 3 gpm were 0.43 (30cm), 0.33(60cm) and 0.30 (90cm) and for flow rate 6 gpm were 0.33(30cm), 0.27(60cm) and 0.22 (90cm). By comparison with findings of many studies conducted on liquid distribution in packed bed column, a good agreement was observed on the relation of Mf and flow rates and bed heights.

scholarly journals Synthesis and Scaling up of Fe3+ by Sol-gel Method Doped on Ceramic Foam for Decolorization of Reactive Red Dyeing Wastewater

2016 ◽  
pp. 47-58
Author(s):  
Pongsak Khaowin ◽  
Prukraya Pongyeela ◽  
Pichayapan Kongpanna ◽  
Juntima Chungsiriporn
Keyword(s):  
Removal Efficiency ◽  
Sol Gel ◽  
Operating Conditions ◽  
Color Removal ◽  
Ceramic Foam ◽  
Optimum Operating ◽  
Disperse Dyes ◽  
Flow Rates ◽  
Gel Method ◽  
Sol Gel Method

Wastewater from the Batiktextile industry contains large amounts of dyestuff together with significant amounts of suspended solids (SS), dispersing agents, salts and trace amounts of me-tals. Since this can lead to severe environmental problems, proper wastewater treatment pro-cesses are essential. The synthesis of Fe3+by sol-gel method doped on a ceramic foam for reac-tive red and disperse dyes removal from synthetic dye wastewater. Inthis research, the effect of color concentration, amount of catalyst and volumetric flow rates for industrial scale were studied.The Fe3+catalyst was prepared by sol-gel method in which 3M of FeCl3was used as a pre-cursor. The synthesized catalyst was characterized by the EDX spectrum from an X-ray spectro-meter. The surface morphology of the catalyst was investigated using a scanning electron microscope (SEM). To determine optimum operating conditions for catalytic testing, variations of disperse and reactive red concentrations (10 to 200 mg L-1) were used. The results indicated that the highest color removal efficiency (up to 96%) was observed when using Fe3+catalyst; 4 piecesper literof solution, and initial pH of 6.0. These conditions were then scaled up for a continuous packed bed column study. It was found that the optimal operating conditions obtained from the mathematical model for reactive red wastewater were: concentration of reactive red in the syn-thetic wastewater20 to 80 mg L-1; amounts of catalyst 432.5 to 1,730 mg and volumetric flow rates of wastewater20 to 200 mL min-1. Up to 84.85% of color removal efficiency was achieved.

Curtiss-Wright Advanced NozzleCheck Valves for Generation III+ Nuclear Power Plants

2017 ◽  
Author(s):  
Haykaz Mkrtchyan ◽  
Ararat Torosyan ◽  
Tsolag Apelian
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Reverse Flow ◽  
Flow Direction ◽  
Fluid Dynamic ◽  
Check Valve ◽  
Operating Conditions ◽  
Low Flow ◽  
Flow Conditions ◽  
Valve Design

Curtiss Wright introduced the first Normally Open NozzleCheck valves to the nuclear power industry nearly 20 years ago. This passive valve design was developed to address reoccurring maintenance and reliability issues often experienced by various check valve types due to low flow conditions. Specifically, premature wear on the hinge pins, bushings and severe seat impact damage had been discovered in several applications while the systems were in steady state operating conditions. Over the last two decades, Curtiss Wright has continued to improve upon the design of the valve, with the latest generation coming most recently in support of the Westinghouse AP1000 design and similar Generation III+ passive reactor requirements. This entirely new valve is designed with minimal stroke, ensuring quick closure under specified reverse flow conditions which no other check valve design could support. Additionally, features such as first in kind test ports, visual inspection points, and the ability to stroke the valve manually or with system fluid in line have resolved many of the shortcomings of previous inline welded flow check valves. Most importantly, advanced test based methodologies and models developed by Curtiss Wright, allow for accurate prediction of NozzleCheck valve performance. This paper presents the development of Curtiss Wright’s advanced Normally Open NozzleCheck Valve for Generation III and III+ nuclear reactor designs. The Valve performance was initially determined by using verified and validated computational fluid dynamic (CFD) methods. The results obtained from the CFD model were then compared to the data gathered from a prototype valve that was built and tested to confirm the performance predictions. Curtiss Wright has fully tested and qualified the Normally Open NozzleCheck valve, which is specifically designed for applications that require a high capacity in the forward flow direction and a closure at low flow rates with short stroke to minimize the hydraulic impact on the system. Paper published with permission.

scholarly journals Study on Characteristics of Heat Transfer and Flow Resistance in Random Porous Foam Metal

2019 ◽  
Vol 128 ◽  
pp. 04010
Author(s):  
Aiqiang Chen ◽  
Sizhong Gu ◽  
El Achkar Georges ◽  
Rachid Bennacer ◽  
Bin Liu
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Homogeneous Model ◽  
Low Flow ◽  
Bottom Plate ◽  
Random Structure ◽  
Plate Temperature ◽  
Inlet Flow ◽  
Flow Rates ◽  
Foam Metal

Porous foam metal has great application prospects in the field of compact heat exchangers. The characteristics of heat transfer and resistance for foam metal with random structure and different porosities (30%, 50%, 70% and 90%) were studied by finite element method in this study. The generated foam structures can be considered as homogeneous model and has better heat exchange capacity at higher inlet flow rate, and the boundary layer can develop well along the flow direction. The open–cell foammetal structure has a uniform heat transfer perpendicular to the flow direction. The bottom plate temperature of the low–porosity structure is more uniform at low flow rates. The intermediate porosities (50% and 70%) at high flow rates has a higher uniformity. As the porosity decreases, the internal pressure increases significantly and the pressure loss also becomes significantly larger. The corresponding optimal porosity is 57%, 66% and 76% at inlet flow rates of 0.001 m/s, 0.01 m/s and 0.1 m/s, respectively.

Experimental and Numerical Study on Hydraulic Performances of a Turbopump With and Without an Inducer

2018 ◽  
Author(s):  
Yanxia Fu ◽  
Meng Fan ◽  
Giovanni Pace ◽  
Dario Valentini ◽  
Angelo Pasini ◽  
...  
Keyword(s):  
Total Pressure ◽  
Pressure Rise ◽  
Hydraulic Performance ◽  
Numerical Results ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Flow Rates ◽  
Lower Flow ◽  
Inlet Duct

The hydraulic performance of a centrifugal turbopump with and without a 3-bladed axial inducer has been studied both experimentally and numerically. A 3D numerical model has been used to simulate the flow through from the inlet to the outlet ducts of the turbopump with and without an inducer using the ANSYS CFX code. The sensitivity of the numerical results has been analyzed with reference to the adopted turbulent flow models, to the length of the input and output ducts included in the simulations, to the reference positions used for the evaluation of the total pressure rise and to the temperature of the operating fluid. The measured and predicted hydraulic performances of the turbopump with and without the inducer have been compared under different operating conditions. As expected, the predicted hydraulic performance of the turbopump is significantly influenced by the lengths of the inlet and outlet ducts, the turbulence models and, at low flow rates, the reference positions of the total pressure rise measurements. The pressure rise coefficients obtained from the simulations using an inlet duct with length of 3 rTi and 10 rTi were significantly lower than the experimental results, while at low flow rates those referring to the inlet duct with length greater than 10 rTi were significantly higher than those obtained for the shorter inlet duct. With reference to the effect of the pressure measurement locations, the difference between the numerical results of the pressure rise coefficient and the experimental values was much higher when the data were obtained at the locations where the transducers was mounted in the experimental tests at lower flow rates. Moreover, the hydraulic performance of the turbopump at lower flow rates can be significantly influenced by the use of the upstream inducer, with a pressure drop of 20% in particular at 60% of the design flow rate.

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