scholarly journals Hydrogen emission in enclosed volume (tunnel for mobility)

2022 ◽  
Vol 334 ◽  
pp. 03004
Author(s):  
Farhad Farajimoghadam ◽  
Matteo Testi ◽  
Luigi Crema
Keyword(s):  
Climate Change ◽  
Fossil Fuel ◽  
Ideal Solution ◽  
Fuel Cell Vehicles ◽  
Great Efficiency ◽  
Flow Rates ◽  
Moving Vehicle ◽  
Hydrogen Emission ◽  
Energy Issue ◽  
Mass Flow Rates

Fuel cell vehicles and trains (FCVs) are seen as a viable alternative to fossil fuel-powered vehicles, with the potential to help the automotive and transport industry grow sustainably. Because of their zero emissions, great efficiency, and diverse hydrogen sources, they are an ideal solution to climate change and the global energy issue. In this study, the simulation of releasing hydrogen from a moving vehicle inside a tunnel has been done. For this purpose, two scenarios have been considered. In the first one, it assumed that hydrogen propagates inside a tunnel without ignition and in the second approach, hydrogen released considered to be combusted. The effect of this combustion on the tunnel and train wall has been investigated. For this goal, two different mass flow rates of hydrogen were considered and results were compared together. Moreover, pressure contours have been shown to represent the overpressure phenomenon and it is resulted that in the area of hydrogen dispersion, there will be high pressure.

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.

scholarly journals Root crops agroforestry for greening the sustainability of green revolution

2018 ◽  
Vol 8 (1) ◽  
pp. 26-37
Author(s):  
Y Widodo ◽  
S Wahyuningsih ◽  
JS Utomo ◽  
A Subagio
Keyword(s):  
Climate Change ◽  
Forest Canopy ◽  
Fossil Fuel ◽  
Agricultural Land ◽  
Green Revolution ◽  
Forest Conversion ◽  
World Population ◽  
Root Crops ◽  
Wide Range ◽  
Agro Forestry

Green revolution started at mid of twentieth century was the answer of anxiousness reminded by Malthusian that food scarcity problems in relation with population growth. In concurrence with exploitation of fossil fuel for agriculture mechanization as well as agrochemicals in the form of inorganic fertilizer and pesticide, green revolution by introducing high yielding varieties of cereals and grains was able to nourish the world population by increasing productivity. Indeed, from beginning of mechanization with fossil fuel based as advised by Rudolf Diesel then Arrhenius would be affected to the release of CO2 to the atmosphere and consequently exaggerating climate change as suffered by current and future generations. Under green revolution based on cereals and grains affected forest conversion into open agricultural land, because both commodities are sun-loving crops, which are hate to the shade. On the other hand, to slow the severity of climate change natural forest must be conserved tightly. Entering third millennium demand of food production with ecologically friendly is stronger. Hence, green revolution needs to be amended into greener perspectives. Thus, implementation of agro-forestry into wide range of agro-ecological zone is urgently innovated. Fortunately, shade tolerant of root crops has significant advantage to be developed under agro-forestry. Under shade of forest canopy at basal forest strata, root crops are able to sequester CO2 to be converted into carbohydrate and other compounds to provide food for the dweller. Back to nature is not only a slogan, with root crops under agro-forestry is a reality; fresh root up to 30 t ha-1 can be harvested yearly as the source of food and renewable fuel as well. This potential is very worthy to improve and greening the existing green revolution to be more sustainable.Int. J. Agril. Res. Innov. & Tech. 8 (1): 26-37, June, 2018

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.

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