Modified neural network correlation of refrigerant mass flow rates through adiabatic capillary and short tubes: Extension to CO2 transcritical flow

2009 ◽  
Vol 32 (6) ◽  
pp. 1293-1301 ◽  
Author(s):  
Liang Yang ◽  
Chun-Lu Zhang
Keyword(s):  
Neural Network ◽  
Mass Flow ◽  
Flow Rates ◽  
Transcritical Flow ◽  
Mass Flow Rates

scholarly journals Artificial neural networks trained through deep reinforcement learning discover control strategies for active flow control

2019 ◽  
Vol 865 ◽  
pp. 281-302 ◽  
Author(s):  
Jean Rabault ◽  
Miroslav Kuchta ◽  
Atle Jensen ◽  
Ulysse Réglade ◽  
Nicolas Cerardi
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Reinforcement Learning ◽  
Flow Control ◽  
Mass Flow ◽  
Active Flow Control ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Artificial Neural ◽  
Active Flow

We present the first application of an artificial neural network trained through a deep reinforcement learning agent to perform active flow control. It is shown that, in a two-dimensional simulation of the Kármán vortex street at moderate Reynolds number ($Re=100$), our artificial neural network is able to learn an active control strategy from experimenting with the mass flow rates of two jets on the sides of a cylinder. By interacting with the unsteady wake, the artificial neural network successfully stabilizes the vortex alley and reduces drag by approximately 8 %. This is performed while using small mass flow rates for the actuation, of the order of 0.5 % of the mass flow rate intersecting the cylinder cross-section once a new pseudo-periodic shedding regime is found. This opens the way to a new class of methods for performing active flow control.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Numerical Investigation of Local Cooling Enhancement Using Pin-Finned Channel With Incremental Impingement

2017 ◽  
Author(s):  
Susheel Singh ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Aspect Ratio ◽  
Mass Flow ◽  
Cross Flow ◽  
Surface Cooling ◽  
Local Cooling ◽  
Stagnation Region ◽  
Flow Rates ◽  
Pin Fins ◽  
Mass Flow Rates ◽  
The Impact

Flow and heat transfer in a low aspect ratio pin-finned channel, representative of an internally cooled turbine airfoil, is investigated using Large Eddy Simulations (LES). To achieve greater control of surface cooling distribution, a novel approach has been recently proposed in which coolant is injected incrementally through a series of holes located immediately behind a specially designed cutout region downstream of the pin-fins. Sheltering the coolant injection behind the pin-fins avoids the impact of the cross-flow buildup that deflects the impingement jet and isolates the surface from cooling. The longitudinal and transverse spacing of the pin-fins, arranged in a staggered fashion, is X/D = 1.046 and S/D = 1.625, respectively. The aspect ratio (H/D) of pin-fin channel is 0.5. Due to the presence of the sequential jets in the configuration, the local cooling rates can be controlled by controlling the jet-hole diameter which impacts the jet mass flow rate. Hence, four different hole diameters, denoted as Large (L), Medium (M) , Small (S), Petite (P) are tested for impingement holes, and their effects are studied. Several patterns of the hole-size distributions are studied. It is shown that the peak Nusselt number in the stagnation region below the jet correlates directly with the jet-velocity, while downstream the Nusselt numbers correlate with the total mass flow rates or the average channel velocity. The local cooling parameter defined as (Nu/Nu0)(1-ε) correlates with the jet/channel mass flow rates.

Experimental and Numerical Modeling of Transition Matrix From Momentum to Buoyancy-Driven Flow in a Pressurized Water Reactor

2008 ◽  
Author(s):  
Thomas Ho¨hne ◽  
So¨ren Kliem ◽  
Roman Vaibar
Keyword(s):  
Mass Flow ◽  
Transition Matrix ◽  
Turbulence Models ◽  
Wire Mesh ◽  
Test Facility ◽  
Pressurized Water ◽  
Flow Rates ◽  
Water Reactor ◽  
Ansys Cfx ◽  
Mass Flow Rates

The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the cold leg and downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. This paper presents a matrix of ROCOM experiments in which water with the same or higher density was injected into a cold leg of the reactor model with already established natural circulation conditions at different low mass flow rates. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the cold leg, upper and lower part of the downcomer. A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the CFD software ANSYS CFX. A hybrid mesh with 4 million elements was used for the calculations. The turbulence models usually applied in such cases assume that turbulence is isotropic, whilst buoyancy actually induces anisotropy. Thus, in this paper, higher order turbulence models have been developed and implemented which take into account for that anisotropy. Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy. The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation with lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWR and should be also considered in Pressurized Thermal Shock (PTS) scenarios. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.

Effects of Inlet Mass Flow Distribution and Magnitude on Reactant Distribution for PEM Fuel Cells

2005 ◽  
Vol 3 (1) ◽  
pp. 45-50 ◽  
Author(s):  
M. McGarry ◽  
L. Grega
Keyword(s):  
Fuel Cell ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Flow Distribution ◽  
Pem Fuel Cells ◽  
Local Flow ◽  
Flow Rates ◽  
Large Active Area ◽  
Mass Flow Rates

The mass flow distribution and local flow structures that lead to areas of reactant starvation are explored for a small power large active area PEM fuel cell. A numerical model was created to examine the flow distribution for three different inlet profiles; blunt, partially developed, and fully developed. The different inlet profiles represent the various distances between the blower and the inlet to the fuel cell and the state of flow development. The partially and fully developed inlet profiles were found to have the largest percentage of cells that are deficient, 20% at a flow rate of 6.05 g/s. Three different inlet mass flow rates (stoichs) were also examined for each inlet profile. The largest percent of cells deficient in reactants is 27% and occurs at the highest flow rate of 9.1 g/s (3 stoichs) for the partially and fully developed turbulent profiles. In addition to the uneven flow distribution, flow separation occurs in the front four channels for the blunt inlet profile at all flow rates examined. These areas of flow separation lead to localized reactant deficient areas within a channel.

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