Unsteady flow of Williamson fluid under the impact of prescribed surface temperature (PST) and prescribed heat flux (PHF) heating conditions over a stretching surface in a porous enclosure

Sensible heat exchange has important consequences for urban meteorology and related applications. Directional radiometric surface temperatures of urban canopies observed by remote sensing platforms have the potential to inform estimations of urban sensible heat flux. An imaging radiometer viewing the surface from nadir cannot capture the complete urban surface temperature, which is defined as the mean surface temperature over all urban facets in three dimensions, which includes building wall surface temperatures and requires an estimation of urban sensible heat flux. In this study, a numerical microclimate model, Temperatures of Urban Facets in 3-D (TUF-3D), was used to model sensible heat flux as well as radiometric and complete surface temperatures. Model data were applied to parameterize an effective resistance for the calculation of urban sensible heat flux from the radiometric (nadir view) surface temperature. The results showed that sensible heat flux was overestimated during daytime when the radiometric surface temperature was used without the effective resistance that accounts for the impact of wall surface temperature on heat flux. Parameterization of this additional resistance enabled reasonably accurate estimates of urban sensible heat flux from the radiometric surface temperature.

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Analyse De L’impact Du Changement De La Couverture Végétale Sur La Pluie Et La Température De Surface Au Sénégal

European Scientific Journal ESJ ◽

10.19044/esj.2017.v13n29p270 ◽

2017 ◽

Vol 13 (29) ◽

pp. 270

Author(s):

Ibrahima Diba ◽

Moctar Camara

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Vegetation Change ◽

Heat Waves ◽

Sensible Heat Flux ◽

Strong Increase ◽

The North ◽

Model Control ◽

Low Levels ◽

The Impact

This work aims at examining the potential impacts of vegetation change (reforestation) of the Sahel-Sahara interface on the intra-seasonal and interannual variability of the rainfall and surface temperature over Senegal using the RegCM4 model. Two runs were performed from 1990 to 2009 with a spatial resolution of 50 km (0.44 °): the standard version of the RegCM4 model (control version) and the reforested one (named RegCM4_REFORESTATION). The impact of the reforestation is to decrease the surface temperature over Senegal in summer (JJAS). This decrease could be partly due to a decrease of the sensible heat flux over the southern and central Senegal and a strong increase of the latent heat flux. The reforestation also tends to increase the rainfall over the whole country and particularly in the Southwest. This rainfall increase which can also create an evaporative cooling, is consistent with the decrease of the surface temperature. The analysis of the annual cycle over three domains of Senegal shows that the reforestation tends to strengthen the low-levels humidity of the atmosphere from January to December especially during the summer period in the North and in the center of the country. The surface temperature presents two maxima in April-May and October-November and a minimum during the summer. The reforestation has a cooling impact during the whole year (particularly in the summer) and over the center and the northern part of Senegal. At the interannual timescale, the reforestation modifies significantly the rainfall by generally increasing it. However, there are years in which this trend is not respected and this translates into a weak correlation coefficient in the South of the country. This rainfall increase may translates into extreme hydroclimatic events such as floods. This work can be considered as a support for the Senegalese policymakers for the better planning of the management of adverse potential effects (such as floods, drought, heat waves, etc) of the Sahel-Sahara greening effort.

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How Much Do Different Land Models Matter for Climate Simulation? Part I: Climatology and Variability

Journal of Climate ◽

10.1175/2010jcli3177.1 ◽

2010 ◽

Vol 23 (11) ◽

pp. 3120-3134 ◽

Cited By ~ 31

Author(s):

Jiangfeng Wei ◽

Paul A. Dirmeyer ◽

Zhichang Guo ◽

Li Zhang ◽

Vasubandhu Misra

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Latent Heat ◽

General Circulation ◽

Surface Fluxes ◽

Heat Fluxes ◽

Maximum Temperature ◽

Daily Maximum Temperature ◽

Time Step ◽

The Impact

Abstract An atmospheric general circulation model (AGCM) is coupled to three different land surface schemes (LSSs), both individually and in combination (i.e., the LSSs receive the same AGCM forcing each time step and the averaged upward surface fluxes are passed back to the AGCM), to study the uncertainty of simulated climatologies and variabilities caused by different LSSs. This tiling of the LSSs is done to study the uncertainty of simulated mean climate and climate variability caused by variations between LSSs. The three LSSs produce significantly different surface fluxes over most of the land, no matter whether they are coupled individually or in combination. Although the three LSSs receive the same atmospheric forcing in the combined experiment, the inter-LSS spread of latent heat flux can be larger or smaller than the individually coupled experiment, depending mostly on the evaporation regime of the schemes in different regions. Differences in precipitation are the main reason for the different latent heat fluxes over semiarid regions, but for sensible heat flux, the atmospheric differences and LSS differences have comparable contributions. The influence of LSS uncertainties on the simulation of surface temperature is strongest in dry seasons, and its influence on daily maximum temperature is stronger than on minimum temperature. Land–atmosphere interaction can dampen the impact of LSS uncertainties on surface temperature in the tropics, but can strengthen their impact in middle to high latitudes. Variations in the persistence of surface heat fluxes exist among the LSSs, which, however, have little impact on the global pattern of precipitation persistence. The results provide guidance to future diagnosis of model uncertainties related to LSSs.

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Three-dimensional flow of an Oldroyd-B fluid over a bidirectional stretching surface with prescribed surface temperature and prescribed surface heat flux

Journal of Hydrology and Hydromechanics ◽

10.2478/johh-2014-0016 ◽

2014 ◽

Vol 62 (2) ◽

pp. 117-125 ◽

Cited By ~ 16

Author(s):

Tasawar Hayat ◽

Sabir Ali Shehzad ◽

Ahmed Alsaedi

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Surface Heat Flux ◽

Three Dimensional ◽

Surface Heat ◽

Nonlinear Flow ◽

Stretching Surface ◽

Three Dimensional Flow ◽

Dimensional Flow ◽

Bidirectional Stretching

Abstract This paper concentrates on the mathematical modelling for three-dimensional flow of an incompressible Oldroyd- B fluid over a bidirectional stretching surface. Mathematical formulation incorporates the effect of internal heat source/sink. Two cases of heat transfer namely the prescribed surface temperature (PST) and prescribed surface heat flux (PHF) are considered. Computations for the governing nonlinear flow are presented using homotopy analysis method. Comparison of the present analysis is shown with the previous limiting result. The obtained results are discussed by plots of interesting parameters for both PST and PHF cases. We examine that an increase in Prandtl number leads to a reduction in PST and PHF. It is noted that both PST and PHF are increased with an increase in source parameter. Further we have seen that the temperature is an increasing function of ratio parameter

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Biophysical feedback of forest canopy height on land surface temperature over contiguous United States

Environmental Research Letters ◽

10.1088/1748-9326/ac4657 ◽

2021 ◽

Author(s):

Zhijiang Zhang ◽

Xinxin Li ◽

Hongguang Liu

Keyword(s):

United States ◽

Heat Flux ◽

Surface Temperature ◽

Land Surface Temperature ◽

Land Surface ◽

Forest Canopy ◽

Canopy Height ◽

Cooling Effect ◽

Cooling Effects ◽

The Impact

Abstract Forests are considered important to the mitigation of climate change. Biophysical effects of afforestation and deforestation on land surface temperature (LST) have been extensively documented. As a fundamental variable of forest structure, however, few studies have investigated the biophysical feedback of forest canopy height changes on LST at large scale. This study is designed to investigate the impact of forest canopy height changes on local land LST and clarify the biophysical processes controlling LST change from 2003 to 2005 over contiguous United States (CONUS) based on satellite observations. To this end, one satellite-based forest canopy height product is selected, and space-for-time approach together with energy balance equation is applied. Results show that for different forest types, namely evergreen forest (EF), deciduous forest (DF), and mixed forest (MF), taller forests present a net cooling effect (0.056 to 0.448 K) than shorter forests at annual scale. The increase in net radiation and sensible heat flux was less than the increase in the latent heat flux when forest canopy height classes converting from shorter to taller, resulting in annual net cooling effects. Furthermore, the cooling effect of EF is stronger than DF and MF, whether for tall, medium, or short forest canopy height classes. Multiple regression analysis reveals that the changes in biophysical components can effectively explain the LST change during growing season. Our findings provide a new insight for forest management decision in the purpose of mitigating climate warming.

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Investigation of Hierarchically Branched-Microchannel Coolers Fabricated by Deep Reactive Ion Etching for Electronics Cooling Applications

Journal of Heat Transfer ◽

10.1115/1.3001017 ◽

2009 ◽

Vol 131 (5) ◽

Cited By ~ 16

Author(s):

J. P. Calame ◽

D. Park ◽

R. Bass ◽

R. E. Myers ◽

P. N. Safier

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Reactive Ion Etching ◽

Fluid Temperature ◽

Ion Etching ◽

Bulk Fluid ◽

Deep Reactive Ion Etching ◽

Channel Size ◽

The Impact ◽

Resistive Zone

The removal of high heat fluxes from BeO ceramic and GaN-on-SiC semiconductor dies using hierarchically branched-microchannel coolers is investigated, in order to examine the impact of the number of branching levels on performance. The microchannel coolers are made by lithography and deep reactive ion etching of single crystal silicon. The test dies contain a dc-operated resistive zone that approximates the spatially averaged heat flux that would appear in low-temperature cofired ceramic microwave circuit packages and in monolithic microwave integrated circuits. For the particular geometric constraints selected for the study (three source/exhaust channels, ∼5×5 mm2 die footprint, 200 μm deep channels in a 400 μm thick silicon wafer), the optimum performance is achieved with three hierarchical levels of branched-channel size. A heat flux of 1.5 kW/cm2 is removed from the 3.6×4.7 mm2 resistive zone of the BeO-based die, at a surface temperature of 203°C. When attached instead to a high thermal conductivity GaN-on-SiC die with a 1.2×5 mm2 resistive zone, a heat flux of 3.9 kW/cm2 is removed from the resistive zone at 198°C surface temperature. The total water flow rate is 275 ml/min in both situations. The experimental results are found to be in reasonable agreement with finite element simulations based on idealized estimates of convection coefficients within the channels. For the three-channel size configuration, an effective heat transfer coefficient in the range of 12.2–13.4 W/cm2 K (with respect to a 20°C bulk fluid temperature) is inferred to be present on the top of the microchannel cooler, based on simulations and derived values obtained from the experimental data.

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Inverse Analysis of In-Cylinder Gas-Wall Boundary Conditions: Investigation of a Yttria-Stabilized Zirconia Thermal Barrier Coating for Homogeneous Charge Compression Ignition

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4036387 ◽

2017 ◽

Vol 139 (10) ◽

Cited By ~ 5

Author(s):

Ryan O'Donnell ◽

Tommy Powell ◽

Mark Hoffman ◽

Eric Jordan ◽

Zoran Filipi

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Surface Temperature ◽

Homogeneous Charge Compression Ignition ◽

Engine Performance ◽

Ex Situ ◽

Thermal Barrier ◽

Compression Ignition ◽

The Impact ◽

Homogeneous Charge

Thermal barrier coatings (TBCs) applied to in-cylinder surfaces of a low temperature combustion (LTC) engine provide an opportunity for enhanced efficiency via two mechanisms: (i) positive impact on thermodynamic cycle efficiency due to combustion/expansion heat loss reduction, and (ii) enhanced combustion efficiency. Heat released during combustion increases the temperature gradient within the TBC layer, elevating surface temperature over combustion-relevant crank angles. Thorough characterization of this dynamic temperature “swing” at the TBC–gas interface is required to ensure accurate determination of heat transfer and the associated impact(s) on engine performance, emissions, and efficiencies. This paper employs an inverse heat conduction solver based on the sequential function specification method (SFSM) to estimate TBC surface temperature and heat flux profiles using sub-TBC temperature measurements. The authors first assess the robustness of the solution methodology ex situ, utilizing an inert, quiescent environment and a known heat flux boundary condition. The inverse solver is extended in situ to evaluate surface thermal phenomena within a TBC-treated single-cylinder, gasoline-fueled, homogeneous charge compression ignition (HCCI) engine. The resultant analysis provides crank angle resolved TBC surface temperature and heat flux profiles over a host of operational conditions. Insight derived from this work may be correlated with TBC thermophysical properties to determine the impact(s) of material selection on engine performance, emissions, heat transfer, and efficiencies. These efforts will guide next-generation TBC design.

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Impact of nonlinear radiative nanoparticles on an unsteady flow of a Williamson fluid toward a permeable convectively heated shrinking sheet

World Journal of Engineering ◽

10.1108/wje-02-2018-0050 ◽

2018 ◽

Vol 15 (6) ◽

pp. 731-742 ◽

Cited By ~ 1

Author(s):

Aurang Zaib ◽

Rizwan Ul Haq ◽

A.J. Chamkha ◽

M.M. Rashidi

Keyword(s):

Temperature Distribution ◽

Solar Energy ◽

Unsteady Flow ◽

Fluid Velocity ◽

Shrinking Sheet ◽

Suction Parameter ◽

Content Type ◽

Williamson Fluid ◽

The Impact ◽

Accelerating Flow

PurposeThe study aims to numerically examine the impact of nanoparticles on an unsteady flow of a Williamson fluid past a permeable convectively heated shrinking sheet.Design/methodology/approachIn sort of the solution of the governing differential equations, suitable transformation variables are used to get the system of ODEs. The converted equations are then numerically solved via the shooting technique.FindingsThe impacts of such parameters on the velocity profile, temperature distribution and the concentration of nanoparticles are examined through graphs and tables. The results point out that multiple solutions are achieved for certain values of the suction parameter and for decelerating flow, while for accelerating flow, the solution is unique. Further, the non-Newtonian parameter reduces the fluid velocity and boosts the temperature distribution and concentration of nanoparticles in the first solution, while the reverse drift is noticed in the second solution.Practical implicationsThe current results may be used in many applications such as biomedicine, industrial, electronics and solar energy.Originality/valueThe authors think that the current results are new and significant, which are used in many applications such as biomedicine, industrial, electronics and solar energy. The results have not been considered elsewhere.

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Effects of High Frequency Droplet Train Impingement on Spreading-Splashing Transition, Film Hydrodynamics and Heat Transfer

Journal of Heat Transfer ◽

10.1115/1.4032230 ◽

2016 ◽

Vol 138 (2) ◽

Cited By ~ 6

Author(s):

Taolue Zhang ◽

Jorge Alvarado ◽

J. P. Muthusamy ◽

Anoop Kanjirakat ◽

Reza Sadr

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Surface Temperature ◽

Liquid Film ◽

High Frequency ◽

High Heat ◽

High Heat Flux ◽

Droplet Impingement ◽

Dry Out ◽

The Impact

The objective of this study is to investigate the effects of droplet-induced crown propagation regimes (spreading and splashing) on liquid film hydrodynamics and heat transfer. In this work, the effects of high frequency droplet train impingement on spreading-splashing transition, liquid film hydrodynamics and surface heat transfer were investigated experimentally. HFE-7100 droplet train was generated using a piezo-electric droplet generator at a fixed flow rate of 165 mL/h. Optical and IR images were captured at stable droplet impingement conditions to visualize the thermal physical process. The droplet-induced crown propagation transition phenomena from spreading to splashing were observed by increasing the droplet Weber number. The liquid film hydrodynamics induced by droplet train impingement becomes more complex when the surface was heated. Bubbles and micro-scale fingering phenomena were observed outside the impact crater under low heat flux conditions. Dry-out was observed outside the impact craters under high heat flux conditions. IR images of the heater surface show that heat transfer was most effective within the droplet impact crater zone due to high fluid inertia including high radial momentum caused by high-frequency droplet impingement. Time-averaged heat transfer measurements indicate that the heat flux-surface temperature curves are linear at low surface temperature and before the onset of dry-out. However, a sharp increase in surface temperature can be observed when dry-out appears on the heater surface. Results also show that strong splashing (We = 850) is unfavorable for heat transfer at high heat flux conditions due to instabilities of the liquid film, which lead to the onset of dry-out. In summary, the results show that droplet Weber number is a significant factor in the spreading-splashing transition, liquid film hydrodynamics and heat transfer.

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