Heat Fluxes In Excess Research Articles

Numerical study on the influence of foamed copper on flow boiling characteristics

Traditional heat dissipation materials can no longer withstand the overheating phenomenon caused by excessive heat flux, metal foam materials provide new solutions for chip heat dissipation and air conditioning due to the superior structural characteristics. In this paper, the tetradecahedron model of the foamed copper was constructed to simulate the heat transfer characteristics of the filled foamed copper channel in the boiling flow process to explore the influence of the foamed copper structure parameters and filling length on the heat transfer characteristics. By changing the filling length of the foamed copper, the polynomial fitting function is solved to the optimum filling ratio of 0.6, and the gas phase rate and the working fluid outlet temperature are both at the optimum value ; Introducing the heat transfer influence factor i, it is obtained that it increases with the increase of PPI and decreases with the increase of ε.

Experimental Characterization of Two-Phase Cooling of Power Electronics in Thermosiphon and Forced Convection Modes

Abstract In this paper, we present the results of an experimental study involving low thermal resistance cooling of high heat flux power electronics in a forced convection mode, as well as in a thermosiphon (buoyancy-driven) mode. The force-fed manifold microchannel cooling concept was utilized to substantially improve the cooling performance. In our design, the heat sink was integrated with the simulated heat source, through a single solder layer and substrate, thus reducing the total thermal resistance. The system was characterized and tested experimentally in two different configurations: the passive (buoyancy-driven) loop and the forced convection loop. Parametric studies were conducted to examine the role of different controlling parameters. It was demonstrated that the thermosiphon loop can handle heat fluxes in excess of 200 W/cm2 with a cooling thermal resistance of 0.225 (K cm2)/W for the novel cooling concept and moderate fluctuations in temperature. In the forced convection mode, a more uniform temperature distribution was achieved, while the heat removal performance was also substantially enhanced, with a corresponding heat flux capacity of up to 500 W/cm2 and a thermal resistance of 0.125 (K cm2)/W. A detailed characterization leading to these significant results, a comparison between the performance between the two configurations, and a flow visualization in both configurations are discussed in this paper.

A two-phase mathematical model to describe the dissolution of corium crust by molten steel

This paper deals with the study of dissolution phenomena in corium crust, in a severe accident. In case of an In-Vessel Retention (IVR) strategy, it is expected that the corium pool will be surrounded by an oxide crust, which will be in contact with molten steel from the top, and along the sides. CORDEB experiments have shown that this crust becomes permeable, having an impact on the thickness of molten steel layer above it. A thin molten steel layer atop crust may lead to an excessive heat flux to the Reactor Pressure Vessel (RPV), resulting in a rupture or melt-through. Corium being a mixture of (U,Zr,O) atoms, undergoes a quaternary interaction with Fe atoms. Such an interaction plays an important role in the stability (or not) of the crust. A thermochemical study of this quaternary system shows that it can be reduced to a pseudo-binary in each phase: (U,Zr)+O in the oxide phase and (U,Zr)+Fe in the metal phase. Therefore, in this paper, dissolution of a binary two-phase porous region by liquid, is studied by means of an up-scaled mathematical model. The model is derived by volume averaging transport equations – Mass, Momentum and Specie – over a Representative Elementary Volume (REV). Final system of Partial Differential Equations (PDEs) is closed by deriving empirical relations for the effective diffusivities and for the mass transfer coefficients. Model is solved numerically to study the progress of dissolution, facilitating, molten steel filtration through the two-phase region. A qualitative comparison has also been made with CORDEB experiment. Results without convection show that the model is able to demonstrate the creation of liquid metal channels similar to the ones observed in the CORDEB findings. Further, the result with pressure gradient driven convection shows the possibility of complete crust dissolution, which is due to the convection enhanced dissolution in the corium crust.

Drag and Heat Flux Reduction using Counterflow Jet and Spike - Analysis of their Equivalence for a Blunt Cone Geometry at Mach 8

This study aims to explore equivalence between active and passive flow control techniques in reducing the wave drag and surface heat flux over a blunt cone model kept in Mach 8 stream. Computational investigations were carried out by using finite volume-based compressible flow solver. Throughout the study, the solution of governing equations is sought by assuming two dimensional-axisymmetric nature of the flowfield. Both counter flow-stagnation point injection and forward facing-physical spike are considered to mitigate the excess drag and heat flux experienced by a blunt body representing the nose cone section of a hypersonic vehicle. Eventually, based on identified drag reductions, the present study proposes equivalence cases between these two methods. It is shown that a pointed spike of L/D=1 provides almost the same drag reduction as the counterflow injection jet with a pressure ratio of 8.25. Similarly, other equivalence cases are identified and the physics behind them is explored. The identified equivalence is expected to help the designers in effectively replacing one technique with another according to the requirement. Equivalence matrix is presented for different spike cases in terms of injection ratios of counterflow injection.

Comparative oceanographic eddy variability during climate change in the Agulhas Current and Somali Coastal Current Large Marine Ecosystems

Twenty years (1993–2012) of satellite altimetry dataset, through maps of absolute dynamic topography and their derived geostrophic velocities, as well as monthly climatological maps of windstress and windstress-curl have been used to assess the oceanic variability in the western Indian Ocean region (WIO). We have performed a comparative study between the Agulhas Current Large Marine Ecosystem (ACLME) and the Somali Coastal Current Large Marine Ecosystem (SCCLME) during the current time period when significant levels of climate change related variability have been documented. In the WIO region, climate variability, and/or change are impacting the atmospheric and oceanic circulation, e.g: excessive sea surface warming and consequent air-sea heat flux exchanges in the SCCLME; and broadening and weakening of the Agulhas Current, with potential negative implication on Agulhas leakage, in the ACLME. The latter being caused by an acceleration of the mesoscale eddy field in response to changing atmospheric wind forcing conditions. Therefore, eddies need to be properly quantified, characterized and monitored if their contribution on climate is to be assessed. While four hotspot regions of enhanced mesoscale variability have been identified in the combined Agulhas Somali Currents Large Marine Ecosystem (ASCLME), the main focus of this study has been in the ACLME and in the SCCLME. The results suggest that the levels of variability in these two LMEs are controlled by different physical processes: seasonality appears to be important in the SCCLME, but conversely less important in the Agulhas LME. The census conducted on the eddy field revealed that more eddies have been formed in the ACLME than in Somali Coastal Current. The eddy mean properties have shown that the eddies in the ACLME are smaller in diameter, and higher in amplitude than those in the SCCLME. In addition, the eddies in the ACLME are maintained as coherent structures longer; have been more strongly nonlinear; and have propagated longer distances from their origins than those in the SCCLME. These indicate that the eddies in the ACLME have relatively much stronger implication on the overall retention and transport of hydrographic properties (e.g. heat and salt). Therefore, they could have stronger influence on oceanic lateral fluxes and ocean-atmosphere flux exchanges, thus may influence more strongly the environmental conditions (both in the ocean and atmosphere) in the combined ASCLME, than those in the SCCLME. Time-evolution of the eddies mean properties suggests that inter-annual changes, may have influenced the eddy field differently in the ACLME and the SCCLME: moderate correlation r = 0.6, p = 0.05 has been found between time and eddy mean radius in the ACLME, and also r = 0.6, p = 0.05 was found between time and EKE in the SCCLME. Therefore, eddy size (for the Agulhas LME) and energy content (for Somali LME) could serve as potential indicators of change in oceanographic conditions over time in these LMEs.

On finite element analysis of material removal rate in microwave drilling of borosilicate glass

Abstract In the present work, microwave drilling of borosilicate glass has been investigated at 2.45 GHz using experimental and simulation tools. Microholes were produced on glass (Thickness = 1.3 mm) using a graphite concentrator (Diameter = 500 µm) at different dielectric velocity (0.2 ms−1, 1.0 ms−1, 1.8 ms−1, 2.6 ms−1). Effect of power and dielectric velocity has been studied on material removal rate. A model of the same was developed using the finite element method. Experimental results were found in reasonable agreement with the simulation results. Study on distribution of input microwave energy during microwave drilling indicated that maximum usable energy is utilized in heating the workpiece, whereas, rest of the usable energy is absorbed by the dielectric and concentrator. Material removal rate increases with increase in power but also attracts defects like crack around the hole. It was observed that increase in dielectric velocity up to 1 ms−1 improves material removal rate due to the efficient flushing of glass residue. However, further increase in dielectric velocity decreases the material removal rate due to the loss of excess heat flux from the machining zone.

Explaining the Zonal Asymmetry in the Air‐Sea Net Heat Flux Climatology Over the Antarctic Circumpolar Current

AbstractSurface heating occurs over the streamline of the Antarctic Circumpolar Current (ACC) and balances the heat transport associated with the global meridional overturning circulation. With a combination of ocean assimilation model output, objectively analyzed products, and atmospheric reanalysis, this paper investigates the mechanism of climatological surface cooling in the Pacific sector with zonal asymmetry. The poleward shift of the ACC path in the Pacific with barotropic potential vorticity conservation was found to account for this cooling. The southward transport of warm/wet surface waters encounters relatively cold/dry air at high latitudes, causing strong turbulent heat fluxes. Sensible heat flux related to the sea‐air heat convection plays an equivalent role alongside the sea surface evaporative latent heat flux, both of which dominate the surface cooling in the Pacific sector. Solar radiation decreases with a poleward meandering of the ACC, which aggravates the cooling process. A significant seasonal cycle of the ensemble mean net surface heat flux (Qnet) is demonstrated, that is, approximately half‐year heating (cooling) during austral warm (cool) seasons. The estimated magnitude of Qnet over the ACC is approximately 20 W m−2 by averaging 10 heat flux climatologies and 4 W m−2 in an ocean state estimate model. However, efforts are still needed to reduce the excess heat flux over the sea surface in the Southern Ocean for the heat flux products.

Optimization design for plasma configuration at the CFETR

Equilibrium is essential in the design of the Chinese Fusion Engineering Test Reactor (CFETR). It is based on the principle underlying various physical and engineering issues, such as vertical instability, core plasma physics, divertor physics and design, etc. Built on the 0-D parameters with elongation κ∼2.0 using the equilibrium code TEQ, series of equilibria with different lower triangularity (range of 0.3–0.8) were constructed. Through iterations with the divertor and blanket structures, we optimized the plasma shape, including, in particular, the position of the X-point, hence obtaining the first acceptable single-null plasma with δ = 0.418. This optimal ITER-like equilibrium has in turn served as the starting point for various other design works. Besides the standard divertor configuration, the quasi-snowflake-plus (QSF+) divertor configurations with different total plasma currents have also been produced, which aimed at controlling excessive heat flux load on the divertor target. The results indicate that the poloidal field (PF) coil system has the capacity to sustain the shape of the QSF+; however, the PF coil system will continue to be optimized with particular attention of the divertor coil.

Coupling Ocean Currents and Waves with Wind Stress over the Gulf Stream

This study provides the first detailed analysis of oceanic and atmospheric responses to the current-stress, wave-stress, and wave-current-stress interactions around the Gulf Stream using a high-resolution three-way coupled regional modeling system. In general, our results highlight the substantial impact of coupling currents and/or waves with wind stress on the air–sea fluxes over the Gulf Stream. The stress and the curl of the stress are crucial to mixed-layer energy budgets and sea surface temperature. In the wave-current-stress coupled experiment, wind stress increased by 15% over the Gulf Stream. Alternating positive and negative bands of changes of Ekman-related vertical velocity appeared in response to the changes of the wind stress curl along the Gulf Stream, with magnitudes exceeding 0.3 m/day (the 95th percentile). The response of wind stress and its curl to the wave-current-stress coupling was not a linear combination of responses to the wave-stress coupling and the current-stress coupling because the ocean and wave induced changes in the atmosphere showed substantial feedback on the ocean. Changes of a latent heat flux in excess of 20 W/m2 and a sensible heat flux in excess of 5 W/m2 were found over the Gulf Stream in all coupled experiments. Sensitivity tests show that sea surface temperature (SST) induced difference of air–sea humidity is a major contributor to latent heat flux (LHF) change. Validation is challenging because most satellite observations lack the spatial resolution to resolve the current-induced changes in wind stress curls and heat fluxes. Scatterometer observations can be used to examine the changes in wind stress across the Gulf Stream. The conversion of model data to equivalent neutral winds is highly dependent on the physics considered in the air–sea turbulent fluxes, as well as air–sea temperature differences. This sensitivity is shown to be large enough that satellite observations of winds can be used to test the flux parameterizations in coupled models.

A coupled ocean-atmosphere downscaled climate projection for the peninsular Florida region

Abstract A downscaled projection over the Peninsular Florida (PF) region is conducted with a Regional Climate Model (RCM) at 10 km grid spacing that incorporates interactive coupling between the atmosphere and ocean components of the climate system. This is first such application of a coupled ocean-atmosphere model for climate projection over the PF region. The RCM is shown to display reasonable fidelity in simulating the mean current climate and exhibits higher variability both in the ocean and in the atmosphere than the large-scale global model (Community Climate System Model version 4 [CCSM4]), which is used to drive the RCM. There are several features of the regional climate that RCM displays as an improvement over CCSM4: upper ocean thermal stratification, surface eddy kinetic energy of the ocean, volume flux through the Yucatan Channel, and terrestrial rainfall over PF. The projected mean hydroclimatic change over the period 2041–2060 relative to 1986–2005 over PF shows significant difference between RCM and CCSM4, with the RCM becoming significantly drier and CCSM4 moderately wetter. Furthermore, over the ocean surface, especially over the West Florida Shelf (WFS), RCM displays a wetter and a warmer surface climate compared to the CCSM4 simulation. Our analysis of the model output indicates that improved resolution of ocean bathymetry in the RCM plays a significant role in the response of the projected changes in surface heat flux, clouds, upper ocean circulations and upper ocean stratification, which manifests with some of the largest differences from the CCSM4 projections, especially over the shallower parts of the ocean around PF. This contrast is most apparent between WFS and PF in the RCM simulation, which suggests that a future warm climate would likely produce more rain over WFS at the expense of corresponding reduction over PF, contrary to the absence of any such gradient in the CCSM4 simulation. Furthermore, in the RCM simulation, the warming of the sub-surface ocean in the future climate is owed to the combined influence of excess atmospheric heat flux directed towards the ocean from the atmosphere and the advective heat flux convergence with the relative slowing of the Loop Current in the future climate. The study demonstrates that such RCMs with coupled ocean-atmosphere interactions are necessary to downscale the global climate models to project the surface hydro-climate over regions like PF that have mesoscale features in the ocean, which can influence the terrestrial climate.

Vertical Feedback Mechanism of Winter Arctic Amplification and Sea Ice Loss

Sea ice reduction is accelerating in the Barents and Kara Seas. Several mechanisms are proposed to explain the accelerated loss of Arctic sea ice, which remains to be controversial. In the present study, detailed physical mechanism of sea ice reduction in winter (December–February) is identified from the daily ERA interim reanalysis data. Downward longwave radiation is an essential element for sea ice reduction, but can primarily be sustained by excessive upward heat flux from the sea surface exposed to air in the region of sea ice loss. The increased turbulent heat flux is used to increase air temperature and specific humidity in the lower troposphere, which in turn increases downward longwave radiation. This feedback process is clearly observed in the Barents and Kara Seas in the reanalysis data. A quantitative assessment reveals that this feedback process is being amplified at the rate of ~8.9% every year during 1979–2016. Availability of excessive heat flux is necessary for the maintenance of this feedback process; a similar mechanism of sea ice loss is expected to take place over the sea-ice covered polar region, when sea ice is not fully recovered in winter.

Design to Validation of a New Heat Flux Source with Uncertainty Analysis

High-speed, transient aerothermal studies produce excessive temperatures and heat fluxes in laboratory, ground, and flight-test experiments. Experiments are performed for 1) understanding the response of test vehicles under various induced thermal environments, 2) verifying computational codes and input parameters, and 3) evaluating thermophysical and mechanical characteristics of new materials. In addition to these rationales, the reconstruction of the surface heat flux from in-depth or backside instrumentation is an important inverse application. Recent research has led to an alternative view of inverse heat conduction based on calibration principles performed in the frequency domain leading to a novel “parameter-free” inverse heat conduction measurement equation. The final mathematical framework reveals that the resolution of a first-kind Volterra integral equation for the surface heat flux prediction contains only experimental data sets. This type of mathematical formulation is highly ill posed. This paper focuses on the design, fabrication, and preliminary test campaign of a new electrical heating cell for producing a verifiable heat flux source. The feasibility investigation demonstrates the merits of system through modeling, experimental design, and transient uncertainty propagation. Validation studies are presented, leading to favorable outcomes. Slug calorimetry, composed of a pure copper, is used in the validation campaign.

Response of unsaturated soils to heating of geothermal energy pile

Geothermal energy piles (GEPs) are an environmentally friendly heat exchange technology that dualizes the role of structural foundation pile for load support and in meeting the building heating/cooling need. Energy loops made from high-density polyethylene which allow heat carrier fluid circulation, are fitted into the pile foundation elements to extract or inject and store heat energy in the soil surrounding the pile. This paper reports the results of a numerical study investigating the response of an energy pile embedded in unsaturated soils (sand, silt and clay) to natural thermal recovery, after heat injection process. It was found that the increase in soil saturation, duration of heating operation i.e. intermittent (8 or 16 h heating) or continuous mode, magnitude of the heat injection rates influences the temperature changes in the soil surrounding the pile, consequently impacting on the system performance. Similarly, it was observed that temperature at all location approached initial state in a duration equal to about twice that of the heating time. In addition, it was found that imposing excessive heat flux on the pile results in the drying up of the surrounding soil leading to lower thermal conductivity thus decreasing the overall GEP system performance.

Effect of stoichiometric mixture fraction on soot fraction and emission spectra with application to oxy-combustion

Many proposed oxy-combustion concepts for carbon capture incorporate the recycling of flue gas which is used as a dilution gas to aid in the control of temperature and heat flux. Improvements in efficiency may be realized by significantly reducing the recycle flue gas (RFG), however, in application, care must be taken to avoid excessive radiant heat flux and gas temperature. One of the features oxy-combustion, unlike air-fired combustion, is that the oxygen and dilution gases are initially separated. RFG can, for example, be strategically blended with either the fuel stream, or oxidizer stream, or both, which affects the stoichiometric mixture fraction, Zst. In this work, the effects of the amount of dilution, or RFG, and Zst on soot fraction are experimentally investigated in a laminar coflow flame. Carbon dioxide is employed as the dilution gas to simulate the recycling of dry flue gas. Soot fraction and temperature are quantitatively determined by a flame image processing technique. In addition, the visible and near-IR emission spectra are given. When dilution, or RFG, is reduced, while holding Zst constant, soot formation and thermal radiation increase due to higher temperature. However, high temperature flames with reduced or zero soot are achieved by increasing Zst via the combination of fuel dilution and oxygen enrichment. This study highlights the inherent flexibility of oxy-fuel combustion, which offers the opportunity to control flame temperature and gas volume while independently controlling soot formation and radiant heat transfer.

Embedded Two-Phase Cooling of High Flux Electronics Via Press-Fit and Bonded FEEDS Coolers

The increasing heat densities in electronic components and focus on energy efficiency have motivated utilization of embedded two-phase cooling, which reduces system-level thermal resistance and pumping power. To achieve maximum benefit, high heat fluxes and vapor qualities should be achieved simultaneously. While many researchers have achieved heat fluxes in excess of 1 kW/cm2, vapor qualities are often below 10%, requiring a significantly large amount of energy spent on subcooling or pumping power, which minimizes the benefit of using two-phase thermal transport. In this work, we describe our recent work with cooling devices utilizing film evaporation with an enhanced fluid delivery system (FEEDS). The design, calibration, and experimental testing of a press-fit and bonded FEEDS test section are detailed here. Heat transfer and pressure drop performance was characterized and discussed. With the press-fit Si test chip, heat fluxes in excess of 1 kW/cm2 were obtained at vapor qualities approaching 45% and a coefficient of performance (COP) approaching 1400. With the bonded SiC test chip, heat fluxes in excess of 1 kW/cm2 were achieved at a vapor quality of 85% and heat densities approaching 490 W/cm3.

SST biases over the Northwest Pacific and possible causes in CMIP5 models

In this paper, the features and possible causes of sea surface temperature (SST) biases over the Northwest Pacific are investigated based on a mixed-layer heat budget analysis in 21 coupled general circulation models (CGCMs) from phase 5 of the Coupled Model Inter-comparison Project (CMIP5). Most CMIP5 models show cold SST biases throughout the year over the Northwest Pacific. The largest biases appear during summer, and the smallest biases occur during winter. These cold SST biases are seen at the basin scale and are mainly located in the inner region of the low and mid-latitudes. According to the mixed-layer heat budget analysis, overestimation of upward net sea surface heat fluxes associated with atmospheric processes are primarily responsible for the cold SST biases. Among the different components of surface heat fluxes, overestimated upward latent heat fluxes induced by the excessively strong surface winds contribute the most to the cold SST biases during the spring, autumn, and winter seasons. Conversely, during the summer, overestimated upward latent heat fluxes and underestimated downward solar radiations at the sea surface are equally important. Further analysis suggests that the overly strong surface winds over the Northwest Pacific during winter and spring are associated with excessive precipitation over the Maritime Continent region, whereas those occurring during summer and autumn are associated with the excessive northward extension of the intertropical convergence zone (ITCZ). The excessive precipitation over the Maritime Continent region and the biases in the simulated ITCZ induce anomalous northeasterlies, which are in favor of enhancing low-level winds over the North Pacific. The enhanced surface wind increases the sea surface evaporation, which contributes to the excessive upward latent heat fluxes. Thus, the SST over the Northwest Pacific cools.

Hotspot Thermal Management via Thin-Film Evaporation—Part II: Modeling

We developed a unified semianalytical thermal–fluidic model for hotspot (HS) thermal management via thin-film evaporation from well-defined silicon micropillar wicks. The capillary pressure generated at a receding liquid meniscus is matched with the flow resistance of the micropillar wick to estimate the dryout heat flux. In addition to modeling the fluidic transport within the porous wick structure, the thermal transport was modeled by solving the 3-D heat diffusion equation. The model prediction for the capillary-limited dryout heat flux agrees within ±20% accuracy with our experiments for the range of heat fluxes reported in this paper. Our comprehensive thermal–fluidic model shows that ultrahigh heat fluxes in excess of 10 kW/cm2 can be dissipated from a $640 \times 620~\mu \text{m}^{2}$ HS area via thin-film evaporation from microstructured surfaces by carefully selecting the thickness and thermal conductivity of the substrate. Furthermore, our results show that there is a global optimum pillar diameter-to-spacing ratio for a given micropillar wick thickness and spreading radius that maximizes the capillary-limited dryout heat flux. The physical insights gained from this paper can be used to improve and optimize the design of wicking structures for extreme heat flux thermal management.

β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after separation and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a $\beta$-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The $\beta$-distribution yields important hints for the development of a turbulence model.

3D Thermal Analysis for CFETR Pre-Superheated Water-Cooled Blanket

Initial China Fusion Engineering Test Reactor (CFETR), blanket design, includes water-cooled ceramic breeder (WCCB) blanket operating in pre-superheated regime. This condition allows efficient cooling; however it requires accurate control and analysis to avoid zones with excessive heat flux. Analysis of the coolant flow and heat transfer in CFETR Pre-Superheated Blanket was performed using ANSYS CFX and included: 3D coolant flow analysis, external volumetric and surface heating effect, and two-phase wall boiling. ASIPP CAD Model imported directly into ANSYS Workbench Design Modeler as a STEP file. Fluid volume is created using Design Modeler Fill operation, and converting Inlet and Outlet surfaces. Meshing was performed using CFX method available within the framework of the ANSYS mesh generator. Application of tetrahedral elements for meshing of the internal regions allowed automatic mesh generation. Advanced sizing functions were used with automatic mesh inflation depending on wall proximity and curvature. Conjugated heat transfer analysis was performed including solution of heat transfer equations in solid and liquid parts, and solution of the flow equations in the liquid parts. Coolant flow in that was assumed turbulent and was resolved using Reynolds averaged Navier-Stokes equations with Shear Stress Transport turbulence model. RPI model for wall driven boiling is used. Inhomogeneous two-phase flow is resolved solving two sets of momentum and energy equations for liquid and steam. Results showed ability of the model to simulate two-phase boiling flow in complex configuration.

Evaluation of the Regional Climate Model over the Loess Plateau of China

ABSTRACTThis paper presents an evaluation study of the Regional Climate Model version 4.3 (RegCM4.3) over the Loess Plateau in northern China, which is a semi‐arid region characterized by complex topography. During recent years, a series of reforestation programmes have been implemented across the region that might influence the local climate in complex ways. To better understand the local climate, the RegCM4.3 was applied to simulate the present‐day conditions over the Loess Plateau. The simulation was carried out from 1990 to 2009 at the 50‐km horizontal resolution, with lateral boundary conditions taken from the ECMWF‐Interim reanalysis. A series of climate variables and processes were evaluated during the winter and summer seasons, such as 2‐m air temperature, precipitation, wind circulation, surface energy balance, full moisture budget, and cloud radiative forcing (CRF). The possible origins of the simulation bias and the physical linkages with other model processes were examined.In general, RegCM4.3 is able to reproduce both the spatial and temporal features of the regional climate over the Loess Plateau. However, there are still biases in some meteorological variables including precipitation and 2‐m air temperature. In particular, the model tends to produce cold biases during winter and underestimate precipitation during summer. Further analyses indicates that the cold biases in winter may have resulted from the deficiency of the downward longwave radiation fluxes, excessive ground heat fluxes, and negative temperature advection by the seasonal mean circulation. These processes are primarily triggered by deficiencies in CRF and excessive northwesterlies over the plateau. The underestimated precipitation during summer is associated with a weak southerly monsoon in the model. A full moisture budget analysis reveals that the dry bias in this region can be mainly attributed to model deficiency in moisture advection and convergence, and to a lesser extent to that in surface evaporation.