scholarly journals Daytime Heat Transfer Processes Related to Slope Flows and Turbulent Convection in an Idealized Mountain Valley

2010 ◽  
Vol 67 (11) ◽  
pp. 3739-3756 ◽  
Author(s):  
Stefano Serafin ◽  
Dino Zardi
Keyword(s):  
Heat Transfer ◽  
Ground Surface ◽  
Turbulent Convection ◽  
Mountain Valley ◽  
Transfer Processes ◽  
Slope Winds ◽  
Large Eddy ◽  
Thermally Driven ◽  
Slope Wind ◽  
The Impact

Abstract The mechanisms governing the daytime development of thermally driven circulations along the transverse axis of idealized two-dimensional valleys are investigated by means of large-eddy simulations. In particular, the impact of slope winds and turbulent convection on the heat transfer from the vicinity of the ground surface to the core of the valley atmosphere is examined. The interaction between top-down heating produced by compensating subsidence in the valley core and bottom-up heating due to turbulent convection is described. Finally, an evaluation of the depth of the atmospheric layer affected by the slope wind system is provided.

scholarly journals Evolution of Late Wintertime Thermally Driven Local Flows and Temperature Fields over Far-Western Nepal

2016 ◽  
Vol 21 (1) ◽  
pp. 35-47
Author(s):  
Ram P. Regmi ◽  
Sangeeta Maharjan
Keyword(s):  
Thermal Environment ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Valley Wind ◽  
Plain Area ◽  
Slope Winds ◽  
Thermally Driven ◽  
Slope Wind ◽  
Wrf Modeling ◽  
Southern Plain

Atmospheric processes over the Himalayan complex terrain are yet to be studied extensively. Only a few significant researches are reported from this region and the Far-Western Region (FWR) of Nepal still remains untouched. Thus, the present study was conceived to understand the meteorological flow characteristics and thermal environment over the region and associated areas during the late wintertime with the application of the state-of-the-art-of Weather Research and Forecasting (WRF) Modeling System. The study revealed that the northern mountainous region developed strong down slope wind during the night and morning times, which sweeps out the southern plain area of Nepal and may reach just beyond the border. The wind over the plain was very shallow whose depth was just about 100 m. The down slope winds over the southern slope of the Daijee and Nandhaur mountain ranges were significantly enhanced by the subsidence of the southerly wind that prevails above 1 km height above the mean sea level. Close to the noon time a very gentle southerly valley wind from the southern plain replaced the nighttime down slope. Very shallow but strong surface inversion builds up over the plain that breaks up in the late morning. The depth of the mixed layer and the valley wind may reach up to 1km in the afternoon. The thermal environment over the FWR of Nepal was fairly hot that may remain around 35°C in the afternoon around the Mahendranagar area whereas the temperature during the nighttime may go as low as 23°C. The study revealed that, contrary to the general perception, temperature over plain areas of Nepal was significantly higher than further southern areas belonging to India. The meteorological flow fields over the FWR of Nepal executed diurnal periodicity with little day-to-day variation during the late wintertime.Journal of Institute of Science and TechnologyVolume 21, Issue 1, August 2016, page: 35-47

Large-Eddy Simulations of Heat Transfer Within a Multi-Perforation Synthetic Jets Configuration

2019 ◽  
Author(s):  
Soizic Esnault ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Synthetic Jets ◽  
Large Eddy Simulations ◽  
Heated Plate ◽  
Piston Displacement ◽  
Large Eddy ◽  
Grazing Flow ◽  
The Impact ◽  
Ejection Phase

Abstract Synthetic jets are produced by devices that enable a suction phase followed by an ejection phase. The resulting mean mass budget is hence null and no addition of mass in the system is required. These particular jets have especially been considered for some years for flow control applications. They also display features that can become of interest to enhance heat exchanges, for example for wall cooling issues. Synthetic jets can be generated through different mechanisms, such as acoustics by making use of a Helmholtz resonator or through the motion of a piston as in an experience mounted at Institut Pprime in France. The objective of this specific experiment is to understand how synthetic jets can enhance heat transfer in a multi-perforated configuration. As a complement to this experimental set up, Large-Eddy Simulations are produced and analysed in the present document to investigate the flow behavior as well as the impact of the synthetic jets on wall heat transfer. The experimental system considered here consists in a perforated heated plate, each perforation being above a cavity where a piston is used to control the synthetic jets. Placed in a wind tunnel test section, the device can be studied with a grazing flow and multiple operating points are available. The one considered here implies a grazing flow velocity of 12.8 m.s−1, corresponding to a Mach number around 0.04, and a piston displacement of 22 mm peak-to-peak at a frequency of 12.8 Hz. These two latter parameters lead to a jet Reynolds number of about 830. A good agreement is found between numerical results and experimental data. The simulations are then used to provide a detailed understanding of the flow. Two main behaviours are found, depending on the considered mid-period. During the ejection phase, the flow transitions to turbulence and the formation of characteristic structures is observed; the plate is efficiently cooled. During the suction phase the main flow is stabilised; the heat enhancement is particularly efficient in the hole wakes but not between them, leading to a heterogeneous temperature field.

scholarly journals Large Eddy Simulations with Conjugate Heat Transfer (CHT) modeling of Internal Combustion Engines (ICEs)

2019 ◽  
Vol 74 ◽  
pp. 51 ◽  
Author(s):  
Angela Wu ◽  
Seunghwan Keum ◽  
Volker Sick
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Wall Temperature ◽  
Conjugate Heat Transfer ◽  
Internal Combustion Engines ◽  
Internal Combustion ◽  
Large Eddy Simulations ◽  
Temperature Fields ◽  
Large Eddy ◽  
The Impact

In this study, the effects of the thermal boundary conditions at the engine walls on the predictions of Large-Eddy Simulations (LES) of a motored Internal Combustion Engine (ICE) were examined. Two thermal boundary condition cases were simulated. One case used a fixed, uniform wall temperature, which is typically used in conventional LES modeling of ICEs. The second case utilized a Conjugate Heat Transfer (CHT) modeling approach to obtain temporally and spatially varying wall temperature. The CHT approach solves the coupled heat transfer problem between fluid and solid domains. The CHT case included the solid valves, piston, cylinder head, cylinder liner, valve seats, and spark plug geometries. The simulations were validated with measured bulk flow, near-wall flow, surface temperature, and surface heat flux. The LES quality of both simulations was also discussed. The CHT results show substantial spatial, temporal, and cyclic variability of the wall heat transfer. The surface temperature dynamics obtained from the CHT model compared well with measurements during the compression stroke, but the absolute magnitude was 5 K (or 1.4%) off and the prediction of the drop in temperature after top dead center suffered from temporal resolution limitations. Differences in the predicted flow and temperature fields between the uniform surface temperature and CHT simulations show the impact of the surface temperature on bulk behavior.

Study of Impact of Gas Cooler Cooling Circuit on Heat Transfer Performance

2012 ◽  
Vol 236-237 ◽  
pp. 224-229
Author(s):  
Bing Qiang He ◽  
Chun Ling Liao
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Heat Transfer Performance ◽  
Experimental Tests ◽  
Transfer Performance ◽  
Cell Type ◽  
Cooling Circuit ◽  
Transfer Processes ◽  
The Impact ◽  
Side Flow

Experimental study on the structure and characteristics of cooling circuit of full-aluminum parallel flow gas cooler. The experimental tests on the built cell-type and ternary GCMCPF are conducted. In the heat transfer processes of the cooler with different circuit structures, the impact of CO2 refrigerant side flow resistance and the mass flow on the heat transfer performance of gas cooler is measured. The results show that the ternary type GCMCPF structure can enhance the heat transfer for CO2 fluid at the weak heat transfer area in the cell-type GCMCPF. Within a certain range of mass flow, the former heat transfer is 1.5 times the later one, and the structural sizes of GCMCPF can be reduced in the same requirements for heat transfer.

scholarly journals Heat Transfer in the Ducts of the Cooling Systems of Traction Motors

2018 ◽  
Vol 7 (4.3) ◽  
pp. 315
Author(s):  
A А. Aleksahin ◽  
A V Panchu ◽  
L A. Parkhomenko ◽  
H V. Bilovol
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Nuclear Power ◽  
Power Plants ◽  
Cooling System ◽  
Transfer Processes ◽  
New Energy ◽  
Working Media ◽  
Artificial Heat ◽  
The Impact

Requirements for increasing thermal efficiency heat exchangers, which lead to energy saving, material and reduction cost, and as a result of reducing the impact on the environment, led to the development and use of various methods of increasing heat transfer. These methods are called intensification of heat transfer processes. Intensification of heat and mass transfer processes is of great importance for making progress in improving the existing and creation of new energy and heat-exchange equipment. Among the ways of intensifying heat transfer, the swirling of flows of working media is one of the simplest and most common methods and is widely used in energy-intensive channels of nuclear power plants, heat exchangers, aeronautical and rocket and space equipment, chemical industry and other technical devices. We have proposed formulas to determine the cooling air velocity necessary to ensure the required temperature condition of the traction motor assemblies. Decrease in the power of fans in the cooling system using the artificial heat transfer intensification in the ducts was estimated based on the generalization of the results of calculations.  

scholarly journals A Method of Experimental Studies of Heat Transfer Processes between Adjacent Facilities

2018 ◽  
Vol 7 (4.3) ◽  
pp. 288 ◽  
Author(s):  
Vadym Nizhnyk ◽  
Stanislav Shchipets ◽  
Olexandr Tarasenko ◽  
Vitalii Kropyvnytskyi ◽  
Bogdan Medvid
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Test Specimen ◽  
Experimental Studies ◽  
Ground Surface ◽  
Heat Radiation ◽  
Lower Edge ◽  
Specimen Type ◽  
Transfer Processes ◽  
Window Opening

A method of experimental studies of heat transfer processes between adjacent facilities during fire was developed. Equipment necessary for the experimental studies was determined. A new specimen type for studies was created in order to perform experimental studies. Configuration of the specimen for the studies allows simulation of a building fragment with filler structures which is affected by heat radiation emitted by fire. Points of placement of the specimens for studies relative to the heat flux source when conducting experimental studies were substantiated. It was revealed that height of the specimen installation shall be determined so that the test specimen is located below the flame tip in order to take into account the most severe impact of heat radiation coming from the fire bed and to exclude any possibility of irradiation from the ground surface. It was proposed that the test specimens are placed at the level of the lower edge of the window opening of the building fragment at the distances of2 m,4 mand6 mfrom the building fragment. The sequence of conduction of experimental studies of heat transfer processes between adjacent facilities during fire was developed. 

A Simulative Study on the Impact of Physical Property Parametersupon Flow and Heat Transfer in Annular Space

2012 ◽  
Vol 516-517 ◽  
pp. 858-865
Author(s):  
Qun Hui Lu ◽  
Yang Yan Zheng ◽  
Biao Yuan
Keyword(s):  
Heat Transfer ◽  
Physical Property ◽  
Annular Space ◽  
Forced Circulation ◽  
Viscosity Change ◽  
Transfer Processes ◽  
Flow And Heat Transfer ◽  
Model Sets ◽  
Property Model ◽  
The Impact

Through finite volume method, this study establishes a steady state flow and heat transfer model of a single phase flow flowing vertically upward in annular space. The model sets the inner cylinder of the annular space as a heating body with fixed heat generation rate. Flow and heat transfer boundary layers are set between the flow and the inner cylinder wall, in order to give more accurate description of momentum and heat coupling and transfer processes between the fluid and the solid near the wall. Compared with the constant physical property model, the variable physical property model, in which the fluid density, heat transfer coefficient, and viscosity change along with the temperature, has relatively lower heat transfer capacity and a little bit lower interface shear stress between the fluid and the solid heat transfer surfaces. Through the comparison between Re and Ri of the constant physical property model and the variable physical properties model, it can be concluded that the physical property changes of the fluid have gradually lower impact on flow and heat transfer processes along with the acceleration of the forced circulation of the fluid.

Large Eddy Simulation of Heat Transfer Within a Multi-Perforation Synthetic Jets Configuration

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Soizic Esnault ◽  
Florent Duchaine ◽  
Laurent Gicquel ◽  
Stéphane Moreau
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Wind Tunnel Test ◽  
Synthetic Jets ◽  
Heated Plate ◽  
Piston Displacement ◽  
Large Eddy ◽  
Grazing Flow ◽  
The Impact ◽  
Ejection Phase

Abstract Synthetic jets are produced by devices that enable a suction phase followed by an ejection phase. The resulting mean mass budget is hence null and no addition of mass in the system is required. These particular jets have especially been considered for some years for flow control applications. They also display features that can become of interest to enhance heat exchanges, for example, for wall cooling issues. Synthetic jets can be generated through different mechanisms, such as acoustics by making use of a Helmholtz resonator or through the motion of a piston as in an experience mounted at Institut Pprime in France. The objective of this specific experiment is to understand how synthetic jets can enhance heat transfer in a multi-perforated configuration. As a complement to this experimental setup, large-eddy simulations are produced and analyzed in the present document to investigate the flow behavior as well as the impact of the synthetic jets on wall heat transfer. The experimental system considered here consists in a perforated heated plate, each perforation being above a cavity where a piston is used to control the synthetic jets. Placed in a wind tunnel test section, the device can be studied with a grazing flow and multiple operating points are available. The one considered here implies a grazing flow velocity of 12.8 m s−1, corresponding to a Mach number around 0.04, and a piston displacement of 22 mm peak-to-peak at a frequency of 12.8 Hz. These two latter parameters lead to a jet Reynolds number of about 830. A good agreement is found between numerical results and experimental data. The simulations are then used to provide a detailed understanding of the flow. Two main behaviors are found, depending on the considered mid-period. During the ejection phase, the flow transitions to turbulence and the formation of characteristic structures are observed; the plate is efficiently cooled. During the suction phase, the main flow is stabilized; the heat enhancement is particularly efficient in the hole wakes but not between them, leading to a heterogeneous temperature field.

Large-Eddy Simulation for Turbine Heat Transfer

2013 ◽  
Author(s):  
Gorazd Medic ◽  
Jongwook Joo ◽  
Ivana Milanovic ◽  
Om Sharma
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Large Scale ◽  
Leading Edge ◽  
Pressure Side ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
The Impact ◽  
Side Flow

Heat transfer in a high-pressure turbine configuration (from an experiment documented in [1–2]) has been analyzed by means of large-eddy simulation. Blair’s large-scale rotating rig consists of a first stator, a rotor and an exit stator. Flow and heat transfer in the first stator are assessed for two configurations — with and without the presence of turbulence generating grid. A particular challenge here is that turbulence grid generates fairly high levels of inlet turbulence with turbulence intensity (TU) of about 10% just upstream of leading edge; this in turn moves the transition location upstream in a dramatic fashion. As far as the rotor blade is concerned, the flow and heat transfer is also analyzed experimentally for a range of incidence angles assessing the pressure side heat transfer increase at negative incidence angles. Several challenging aspects relevant to flow in the rotor are also considered — the three-dimensionality of pressure side flow separation at negative incidence, the impact of upstream stator wakes, as well as the role of surface roughness.

Effects of Domain-Size on Large-Eddy Simulation for a Forced-Convection Flow in a Pipe With Circumferentially-Varying Heat Flux

2020 ◽  
Author(s):  
Yasuo Hattori ◽  
Hitoshi Suto ◽  
Keisuke Nakao ◽  
Yuma Hasebe ◽  
Shuji Ishihara
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Large Scale ◽  
Heated Surface ◽  
Practical Interest ◽  
Domain Size ◽  
Large Eddy Simulations ◽  
Streamwise Direction ◽  
Transfer Processes ◽  
Large Eddy

Abstract We performed large-eddy simulations by using an open source CFD code, OpenFOAM to examine the performance of large-eddy simulations for examining turbulence heat-transfer processes of forced-convection in a pipe with non-homogeneous thermal boundary conditions; an accurate description of such processes is of practical interest of nuclear engineering. Special attention was paid to the domain size in the streamwise direction, which must be closely related to the turbulence processes with super structures. Three domain sizes were used: the size was varied from 5R to 100R, where R is the radius of the pipe. The turbulence intensities of temperature fluctuations near the heated surface strongly depended on the domain size. This was because that the turbulence intensities were closely related to large-scale fluid motions, the scale of which is much larger than 25R, and such large-scale fluid motions interfered in the dynamics of turbulence heat transfer processes near the heated surface. This indicates that the large-eddy simulations for estimating the turbulence heat-transfer rate in the pipe must require the large domain size in the streamwise direction with well resolved grids to capture turbulence eddies near the heated surface.

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