Wave-Coherent Air–Sea Heat Flux

2008 ◽  
Vol 38 (4) ◽  
pp. 788-802 ◽  
Author(s):  
Fabrice Veron ◽  
W. Kendall Melville ◽  
Luc Lenain
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Wave ◽  
Momentum Transfer ◽  
Latent Heat ◽  
Heat Fluxes ◽  
Total Heat ◽  
Research Progress ◽  
Total Heat Flux ◽  
Wave Conditions

Abstract Air–sea fluxes of heat and momentum play a crucial role in weather, climate, and the coupled general circulation of the oceans and atmosphere. Much progress has been made to quantify momentum transfer from the atmosphere to the ocean for a wide range of wind and wave conditions. Yet, despite the fact that global heat budgets are now at the forefront of current research in atmospheric, oceanographic, and climate problems and despite the good research progress in recent years, much remains to be done to better understand and quantify air–sea heat transfer. It is well known that ocean-surface waves may support momentum transfer from the atmosphere to the ocean, but the role of the waves in heat transfer has been ambiguous and poorly understood. Here, evidence is presented that there are surface wave–coherent components of both the sensible and the latent heat fluxes. Presented here are data from three field experiments that show modulations of temperature and humidity at the surface and at 10–14 m above the surface, which are coherent with the surface wave field. The authors show that the phase relationship between temperature and surface displacement is a function of wind speed. At a 10–12-m elevation, a wave-coherent heat transfer of O(1) W m−2 is found, dominated by the latent heat transfer, as well as wave-coherent fractional contributions to the total heat flux (the sum of latent and sensible heat fluxes) of up to 7%. For the wind speeds and wave conditions of these experiments, which encompass the range of global averages, this wave contribution to total heat flux is comparable in magnitude to the atmospheric heat fluxes commonly attributed to the effects of greenhouse gases or aerosols. By analogy with momentum transfer, the authors expect the wave-coherent heat transfer to decay with height over scales on the order of k−1, where k is the characteristic surface wavenumber; therefore, it is also expected that measurements at elevations of O(10) m may underestimate the contribution of the wave-induced heat flux to the atmosphere.

Aero-Thermal Investigation of Tip Leakage Flow in a Film Cooled Industrial Turbine Rotor

2008 ◽  
Author(s):  
S. K. Krishnababu ◽  
H. P. Hodson ◽  
G. D. Booth ◽  
G. D. Lock ◽  
W. N. Dawes
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flow ◽  
Turbine Rotor ◽  
Total Heat ◽  
Leakage Flow ◽  
Total Heat Flux ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow And Heat Transfer

A numerical investigation of the flow and heat transfer characteristics of tip leakage in a typical film cooled industrial gas turbine rotor is presented in this paper. The computations were performed on a rotating domain of a single blade with a clearance gap of 1.28% chord in an engine environment. This standard blade featured two coolant and two dust holes, in a cavity-type tip with a central rib. The computations were performed using CFX 5.6, which was validated for similar flow situations by Krishnababu et al., [18]. These predictions were further verified by comparing the flow and heat transfer characteristics computed in the absence of coolant ejection with computations previously performed in the company (SIEMENS) using standard in-house codes. Turbulence was modelled using the SST k-ω turbulence model. The comparison of calculations performed with and without coolant ejection has shown that the coolant flow partially blocks the tip gap, resulting in a reduction of the amount of mainstream leakage flow. The calculations identified that the main detrimental heat transfer issues were caused by impingement of the hot leakage flow onto the tip. Hence three different modifications (referred as Cases 1 to 3) were made to the standard blade tip in an attempt to reduce the tip gap exit mass flow and the associated impingement heat transfer. The improvements and limitations of the modified geometries, in terms of tip gap exit mass flow, total area of the tip affected by the hot flow and the total heat flux to the tip, are discussed. The main feature of the Case 1 geometry is the removal of the rib and this modification was found to effectively reduce both the total area affected by the hot leakage flow and total heat flux to the tip while maintaining the same leakage mass flow as the standard blade. Case 2 featured a rearrangement of the dust holes in the tip which, in terms of aero-thermal-dynamics, proved to be marginally inferior to Case 1. Case 3, which essentially created a suction-side squealer geometry, was found to be inferior even to the standard cavity tip blade. It was also found that the hot spots which occur in the leading edge region of the standard tip and all modifications contributed significantly to the area affected by the hot tip leakage flow and the total heat flux.

scholarly journals Groundwater flow, heat flux, and permeability inferred from borehole temperature profile in Izu-Oshima volcano, Japan – Implications for subsurface hydrothermal system

2020 ◽  
Author(s):  
Shin'ya Onizawa ◽  
Nobuo Matsushima
Keyword(s):  
Heat Flux ◽  
Groundwater Flow ◽  
Temperature Profile ◽  
Hydrothermal System ◽  
Heat Fluxes ◽  
Total Heat ◽  
Conductive Heat ◽  
Upward Flow ◽  
Total Heat Flux ◽  
Layer Formation

Abstract Groundwater flow velocity as well as conductive and convective heat fluxes were estimated using temperature profile data from a 1000 m–deep borehole in the central part of the Izu-Oshima volcano, Japan. Two depth intervals below groundwater level with upward groundwater flow patterns were examined assuming a one-dimensional vertical steady flow. The groundwater velocity and total heat flux were estimated to be 5.0–5.4×10-10 m/s and 0.54–0.59 W/m2, respectively, for the basement layer (Formation 4). For the shallower layer (Formation 2), both the upward velocity and heat flux were higher, indicating greater contributions of convective mass and heat transfer compared to those in the deeper layer. Furthermore, assuming that the upward flow was buoyancy-driven, vertical permeabilities of 2.8–5.1×10-15 and 1.7–3.1×10-16 m2 , respectively, were estimated for Formations 2 and 4. The temperature patterns of the lava-dominant region (Formation 3), sandwiched between Formations 2 and 4, suggested the occurrence of lateral cooler groundwater inflow in fractures. These results were used for understanding a hydrothermal system beneath the volcano. The total heat flux estimated for Formation 4 (0.54–0.59 W/m2) was nearly three times higher than the conductive heat flux in the northwestern coastal area, suggesting a higher heat supply below the central part of the volcano. A hydrothermal free convection system was inferred in Formations 2 and 3. In Formation 2, buoyancy-driven upward flow was enhanced because of the heat below and the higher permeability. Cooler groundwater was laterally supplied in lava fractures in Formation 3 to compensate for the mass loss by the upward flow at the bottom of Formation 2.

Heat Transfer in Thermal Lattice Boltzmann Equation Method

2012 ◽  
Author(s):  
Like Li ◽  
Renwei Mei ◽  
James F. Klausner
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boltzmann Equation ◽  
Lattice Boltzmann ◽  
Heat Fluxes ◽  
Total Heat ◽  
Lattice Boltzmann Equation ◽  
Thermal Flow ◽  
Total Heat Transfer ◽  
Curved Boundaries

The evaluation of the boundary heat flux and total heat transfer in the lattice Boltzmann equation (LBE) simulations is investigated. The boundary heat fluxes in the discrete velocity directions of the thermal LBE (TLBE) model are obtained directly from the temperature distribution functions at the lattice nodes. With the rectangular lattice uniformly spaced the effective surface area for the discrete heat flux is the unit spacing distance, thus the heat flux integration becomes simply a summation of all the discrete heat fluxes with constant surface areas. The present method for the evaluation of total heat transfer is very efficient and robust for curved boundaries because it does not require the determination of the normal heat flux on the boundary and the surface area. To validate its applicability and accuracy, several numerical tests with analytical solutions are conducted, including 2-dimensional (2D) steady thermal flow in a channel, 1-D transient heat conduction in an inclined semi-infinite solid, 2-D transient conduction inside a circle, and 3-D steady thermal flow in a circular pipe. For straight boundaries perpendicular to one of the discrete velocity vectors, the total heat transfer is second-order accurate. For curved boundaries only first-order accuracy is obtained for the total heat transfer due to the irregularly distributed lattice fractions cut by the curved boundary.

Improved Computation Formula of Thermal Conductivity of Fibrous Porous Materials

2010 ◽  
Vol 152-153 ◽  
pp. 605-612 ◽  
Author(s):  
Peng Cui ◽  
Fu Mei Wang ◽  
Zhi Yong Liang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Porous Materials ◽  
Linear Function ◽  
Permeability Coefficient ◽  
Simulated Data ◽  
The Body ◽  
Total Heat ◽  
Total Heat Flux

For the complexity of convective term, the interior heat transfer is important for the engineering testing of heat conduction of fibrous porous materials. In this paper the heat transfer through the body of fibrous porous materials was simulated with finite volume method. By the simulation, it is found that the total heat flux through the body of fibrous porous materials is a linear function of the thermal conductivity when it is measured by the guarded plate, and some constants in the linear function are related with the thickness and permeability coefficient of the sample. The simulated data are employed to fitting the variation curves of the total heat flux with thermal conductivity, thickness and permeability coefficient, respectively. The improved calculating formula of thermal conductivity for fibrous porous materials is established based on the fitting estimation. Through the experimental, it is demonstrated that the improved calculating formula is more accurate than the original one, which is based on the assumptions of single component continuum material and one dimensional heat transfer.

scholarly journals Heat Fluxes Localization and Abnormal Size Effect Induced by Multi-Body Vibration in Complex Networks

2021 ◽  
Author(s):  
Kezhao Xiong ◽  
Zhengxin Yan ◽  
You Xie ◽  
Yixian Wang ◽  
Chunhua Zeng ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Size Effect ◽  
Complex Networks ◽  
Heat Fluxes ◽  
Total Heat ◽  
Total Heat Flux ◽  
Theoretical Understanding ◽  
Body Vibration ◽  
Multi Body

Abstract Heat conduction in real physical networks such as nanotube/nanowire networks has been attracting more and more attention, but its theoretical understanding is far behind. To open a way to this problem, we present a multi-body vibration model of heat conduction to study how heat is conducted in complex networks, where nodes’degrees satisfy a random distribution and links consist of 1D atom chains with nonlinear springs. Based on this model, we find two interesting phenomenons: (1) The main heat fluxes of network are always localized in a skeleton subnetwork, which may have potential applications in thermal management and thermal concentrators, etc; (2) There exists an abnormal size effect of heat conduction in complex networks, i.e. the total heat flux of network will be enlarged with the increase of atoms on links, which is in contrast to the previous result on a 1D chain. Furthermore, we introduce a transmission diagram to characterize the skeleton of localized heat fluxes and then discover a phase transition of total heat flux in the process of removing links, implying that the control of heat flux can be effective only when the change of network topology is focused on the links within the skeleton. A brief theory is introduced to explain the abnormal size effect.

Aerothermal Investigation of Tip Leakage Flow in a Film Cooled Industrial Turbine Rotor

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
S. K. Krishnababu ◽  
H. P. Hodson ◽  
G. D. Booth ◽  
G. D. Lock ◽  
W. N. Dawes
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flow ◽  
Turbine Rotor ◽  
Total Heat ◽  
Leakage Flow ◽  
Total Heat Flux ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow And Heat Transfer

A numerical investigation of the flow and heat transfer characteristics of tip leakage in a typical film cooled industrial gas turbine rotor is presented in this paper. The computations were performed on a rotating domain of a single blade with a clearance gap of 1.28% chord in an engine environment. This standard blade featured two coolant and two dust holes, in a cavity-type tip with a central rib. The computations were performed using CFX 5.6, which was validated for similar flow situations by Krishnababu et al. (2007, “Aero-Thermal Investigation of Tip Leakage Flow in Axial Flow Turbines: Part I—Effect of Tip Geometry,” ASME Paper No. 2007-GT-27954). These predictions were further verified by comparing the flow and heat transfer characteristics computed in the absence of coolant ejection with computations previously performed in the company (SIEMENS) using standard in-house codes. Turbulence was modeled using the shear-stress transport (SST) k-ω turbulence model. The comparison of calculations performed with and without coolant ejection has shown that the coolant flow partially blocks the tip gap, resulting in a reduction in the amount of mainstream leakage flow. The calculations identified that the main detrimental heat transfer issues were caused by impingement of the hot leakage flow onto the tip. Hence three different modifications (referred as Cases 1–3) were made to the standard blade tip in an attempt to reduce the tip gap exit mass flow and the associated impingement heat transfer. The improvements and limitations of the modified geometries, in terms of tip gap exit mass flow, total area of the tip affected by the hot flow and the total heat flux to the tip, are discussed. The main feature of the Case 1 geometry is the removal of the rib, and this modification was found to effectively reduce both the total area affected by the hot leakage flow and total heat flux to the tip, while maintaining the same leakage mass flow as the standard blade. Case 2 featured a rearrangement of the dust holes in the tip, which, in terms of aerothermal dynamics, proved to be marginally inferior to Case 1. Case 3, which essentially created a suction-side squealer geometry, was found to be inferior even to the standard cavity-tip blade. It was also found that the hot spots, which occur in the leading edge region of the standard tip, and all modifications contributed significantly to the area affected by the hot tip leakage flow and the total heat flux.

scholarly journals Assessing IDDES-Based Wall-Modeled Large-Eddy Simulation (WMLES) for Separated Flows with Heat Transfer

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 246
Author(s):  
Rozie Zangeneh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Heat Fluxes ◽  
Separated Flows ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Isothermal Wall

The Wall-modeled Large-eddy Simulation (WMLES) methods are commonly accompanied with an underprediction of the skin friction and a deviation of the velocity profile. The widely-used Improved Delayed Detached Eddy Simulation (IDDES) method is suggested to improve the prediction of the mean skin friction when it acts as WMLES, as claimed by the original authors. However, the model tested only on flow configurations with no heat transfer. This study takes a systematic approach to assess the performance of the IDDES model for separated flows with heat transfer. Separated flows on an isothermal wall and walls with mild and intense heat fluxes are considered. For the case of the wall with heat flux, the skin friction and Stanton number are underpredicted by the IDDES model however, the underprediction is less significant for the isothermal wall case. The simulations of the cases with intense wall heat transfer reveal an interesting dependence on the heat flux level supplied; as the heat flux increases, the IDDES model declines to predict the accurate skin friction.

Heat Transfer to Supercritical Water in Vertical Annular Channel and 3-Rod Bundle

2009 ◽  
Author(s):  
V. G. Razumovskiy ◽  
Eu. N. Pis’mennyy ◽  
A. Eu. Koloskov ◽  
I. L. Pioro
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Supercritical Water ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Rod Bundle ◽  
Temperature Regimes ◽  
Outside Diameter

The results of heat transfer to supercritical water flowing upward in a vertical annular channel (1-rod channel) and tight 3-rod bundle consisting of the tubes of 5.2-mm outside diameter and 485-mm heated length are presented. The heat-transfer data were obtained at pressures of 22.5, 24.5, and 27.5 MPa, mass flux within the range from 800 to 3000 kg/m2·s, inlet temperature from 125 to 352°C, outlet temperature up to 372°C and heat flux up to 4.6 MW/m2 (heat flux rate up to 2.5 kJ/kg). Temperature regimes of the annular channel and 3-rod bundle were stable and easily reproducible within the whole range of the mass and heat fluxes, even when a deteriorated heat transfer took place. The data resulted from the study could be applicable for a reference estimation of heat transfer in future designs of fuel bundles.

The Effect of Soil on the Summertime Surface Energy Budget of a Humid Subarctic Tundra in Northern Quebec, Canada

2021 ◽  
Vol 22 (10) ◽  
pp. 2547-2564
Author(s):  
Georg Lackner ◽  
Daniel F. Nadeau ◽  
Florent Domine ◽  
Annie-Claude Parent ◽  
Gonzalo Leonardini ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Arctic Region ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

AbstractRising temperatures in the southern Arctic region are leading to shrub expansion and permafrost degradation. The objective of this study is to analyze the surface energy budget (SEB) of a subarctic shrub tundra site that is subject to these changes, on the east coast of Hudson Bay in eastern Canada. We focus on the turbulent heat fluxes, as they have been poorly quantified in this region. This study is based on data collected by a flux tower using the eddy covariance approach and focused on snow-free periods. Furthermore, we compare our results with those from six Fluxnet sites in the Arctic region and analyze the performance of two land surface models, SVS and ISBA, in simulating soil moisture and turbulent heat fluxes. We found that 23% of the net radiation was converted into latent heat flux at our site, 35% was used for sensible heat flux, and about 15% for ground heat flux. These results were surprising considering our site was by far the wettest site among those studied, and most of the net radiation at the other Arctic sites was consumed by the latent heat flux. We attribute this behavior to the high hydraulic conductivity of the soil (littoral and intertidal sediments), typical of what is found in the coastal regions of the eastern Canadian Arctic. Land surface models overestimated the surface water content of those soils but were able to accurately simulate the turbulent heat flux, particularly the sensible heat flux and, to a lesser extent, the latent heat flux.

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