Dynamic modeling of thermal conditions for hot-water district-heating networks

To investigate the dynamic characteristics of the thermal conditions of hot-water district-heating networks, a dynamic modeling method is proposed with consideration of the heat dissipations in pipes and the characteristic line method is adopted to solve it. Besides, the influences of different errors, space steps and initial values on the convergence of the dynamic model results are analyzed for a model network. Finally, a part of a certain city district-heating system is simulated and the results are compared with the actual operation data in half an hour from 6 secondary heat stations. The results indicate that the relative errors for the supply pressure and temperature in 5 stations are all within 2%, except in one station, where the relative error approaches 4%. So the proposed model and algorithm are validated.

Evaluation of Haney-Type Surface ThermalBoundary Conditions Using a CoupledAtmosphere and Ocean Model

A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition, which linearly connects net downward surface heat fluxQ to air/sea temperature difference ΔT by a relaxation coefficientk. The model was initiated from the National Centers for Environmental Prediction (NCEP) atmospheric observations for 1 December 1977, and from the National Ocean Data Center (NODC) global climatological mean December temperature and salinity fields at 1°x 1° resolution. The time step is 7.5 minutes. We integrated the model for 450 days and obtained a complete model-generated global data set of daily mean downward net surface fluxQ, surface air temperatureT A, and sea surface temperatureT O. Then, we calculated the cross-correlation coefficients (CCC) betweenQ and ΔT. The ensemble mean CCC fields show (a) no correlation betweenQ and ΔT in the equatiorial regions, and (b) evident correlation (CCC≥0.7) betweenQ and ΔT in the middle and high latitudes. Additionally, we did the variance analysis and found that whenk=120 W m?2K?1, the two standard deviations, σQ and σκδT , are quite close in the middle and high latitudes. These results agree quite well with a previous research (Chu et al., 1998) on analyzing the NCEP re-analyzed surface data, except that a smaller value ofk (80 W m?2K?1) was found in the previous study. Key words Air-sea coupled system - Ocean surface fluxes - Surface thermal boundary condition

Experimental Measurements of the Sensitivity of Fiber-optic Bragg Grating Sensors with a Soft Polymeric Coating under Mechanical Loading,Thermal and Magnetic under Cryogenic Conditions

The strain and temperature sensing performance of fiber-optic Bragg gratings （FBGs） with soft polymeric coating, which can be used to sense internal strain in superconducting coils, are evaluated under variable cryogenic field and magnetic field. The response to a temperature and strain change of coated-soft polymeric FBGs is tested by comparing with those of coated-metal FBGs. The results indicate that the coated-soft polymeric FBGs can freely detect temperature and thermal strain, their At variable magnetic field, the tested results indicate accuracy and repeatability are also discussed in detail. that the cross-coupling effects of FBGs with different matrixes are not negligible to measure electromagnetic strain during fast excitation. The present results are expected to be able to provide basis measurements on the strain of pulsed superconducting magnet/cable （cable- around-conduit conductors, cable-in-conduit conductors）, independently or utilized together with other strain measurement methods.

Effect of periodic heat transfer on the transient thermal behavior of a convective-radiative fully wet porous moving trapezoidal fin

A moving trapezoidal profiled convective-radiative porous longitudinal fin wetted in a single-phase fluid is considered in the current article.The periodic variation in the fin base temperature is taken into account along with the temperature sensitive thermal conductivity and convective heat transfer coefficients.The modeled problem,which is resolved into a non-linear partial differential equation(PDE),is made dimensionless and solved by employing the finite difference method(FDM).The results are displayed through graphs and discussed.The effects of amplitude,frequency of oscillation,wet nature,Peclet number,and other relevant quantities on the distribution of temperature through the fin length and with the dimensionless time are investigated.It is deciphered that the periodic heat transfer gives rise to the wavy nature of the fin thermal profile against time.The analysis is beneficial in the design of fin structures for applications like solar collectors,space/airborne applications,and refrigeration industries.

The Effects of Nonuniform Thermal Boundary Condition on Thermal Stress Calculation of Water-Cooled W/Cu Divertors

The thermal boundary condition has very important effects on the accuracy of thermal stress calculation of a water-cooled W/Cu divertor. In this paper, phase-change heat transfer was simulated based on the Euler homogeneous phase model, and local differences of liquid physical properties were considered under one-sided high heating conditions. The steady-state temperature field and thermal stress field under nonuniform thermal boundary conditions were obtained through numerical calculation. By comparison with the case of traditional uniform thermal boundary conditions, the results show that the distribution of thermal stress under nonuniform thermal boundary conditions exhibits tbe same trend as that under uniform thermal boundary conditions, but is larger in value. The maximum difference of maximum von Mises stress is up to 42% under the highest heating conditions. These results provide a valuable reference for the thermal stress caleulat.ion of water-cooled W/Cu divertors.

Unsteady MHD flow over exponentially stretching sheet with slip conditions

The present paper examines the hydromagnetic three-dimensional flow in- duced by a stretched surface. An incompressible material saturates the porous medium. Velocity and thermal slip boundary conditions are considered. Suitable transformations are used to obtain the nonlinear ordinary differential equations. Series solutions of the resulting systems are constructed. The effects of various pertinent parameters on the axial velocity and temperature distributions are analyzed graphically. The skin friction and the Nusselt number are computed numerically and graphically.

Fourth-Order Compact Formulation for the Resolution of Heat Transfer in Natural Convection of Water-Cu Nanofluid in a Square Cavity with a Sinusoidal Boundary Thermal Condition

In the present work, we numerically study the laminar natural convection of a nanofluid confined in a square cavity. The vertical walls are assumed to be insulated, non-conducting, and impermeable to mass transfer. The horizontal walls are differentially heated, and the low is maintained at hot condition (sinusoidal) when the high one is cold. The objective of this work is to develop a new height accurate method for solving heat transfer equations. The new method is a Fourth Order Compact (F.O.C). This work aims to show the interest of the method and understand the effect of the presence of nanofluids in closed square systems on the natural convection mechanism. The numerical simulations are performed for Prandtl number ( ), the Rayleigh numbers varying between and for different volume fractions varies between 0% and 10% for the nanofluid (water + Cu).

A Precursory Signal of June-July Precipitation over the Yangtze River Basin: December-January Tropospheric Temperature over the Tibetan Plateau

The prediction of summer precipitation over the Yangtze River basin(YRB)has long been challenging,especially during June-July(JJ),when the mei-yu generally occurs.This study explores the potential signal for the YRB precipitation in JJ and reveals that the Tibetan Plateau tropospheric temperature(TPTT)in the middle and upper levels during the preceding December-January(DJ)is significantly correlated with JJ YRB precipitation.The close connection between the DJ TPTT anomaly with JJ YRB precipitation may be due to the joint modulation of the DJ ENSO and spring TP soil temperatures.The lagged response to an anomalously cold TPTT during the preceding DJ is a TPTT that is still anomalously cold during the following JJ.The lower TPTT can lead to an anomalous anticyclone to the east of Lake Baikal,an anomalous cyclone at the middle latitudes of East Asia,and an anomalous anticyclone over the western North Pacific.Meanwhile,the East Asian westerly jet shifts southward in response to the meridional thermal gradient caused by the colder troposphere extending from the TP to the east of Lake Baikal.The above-mentioned circulation anomalies constitute the positive anomaly of the East Asia-Pacific pattern,known to be conducive to more precipitation over the YRB.Since the DJ TPTT contains both the land(TP soil temperature)and ocean(ENSO)signals,it has a closer relationship with the JJ precipitation over the YRB than the DJ ENSO alone.Therefore,the preceding DJ TPTT can be considered an alternative predictor of the JJ YRB precipitation.

Temporal and Spatial Distribution Characteristics of Lightning Activity over the Pacific Ocean and Adjacent Land and Its Relationship with AOD and CAPE

Based on LIS/OTD gridded lightning climatology data,ERA5 reanalysis data,and MODIS atmosphere monthly global products,we examined latitudinal and daily variations of lightning activity over land,offshore areas,open sea,and all marine areas(i.e.,the aggregate of open sea and offshore areas)for different seasons over the Pacific Ocean and the adjacent land areas at 65°N-50°S,99°E-78°W,and analysed the relationships of lightning activity with CAPE(Convective Available Potential Energy)and AOD(Aerosol Optical Depth).At any given latitude,the lightning density is the highest over land,followed by offshore areas,all marine areas and the open sea in sequence.The lightning density over land is approximately an order of magnitude greater than that over all marine areas.Lightning activity over land,offshore areas,open sea,and all marine areas varies with season.The diurnal variation of lightning density over land has a single-peak pattern.Over the offshore area,open sea,and all marine areas,lightning densities have two maxima per day.The magnitude of the daily variation in mean lightning density is the largest over land and the smallest over the open sea.The lightning density over the Pacific Ocean and adjacent land areas is significantly and positively correlated with CAPE.The correlation is the strongest over land and the weakest over the open sea.Cloud Base Height(CBH)may affect the efficiency of CAPE conversion to updraft.CAPE has a positive effect on lightning activity and has a greater impact on land than on the ocean.Over the sea,both CAPE and AOD can contribute to lightning activity,but the magnitudes of the influence of CAPE and AOD on lightning activity remain to be determined.Lightning activity over land and sea is a result of the combined action of AOD and CAPE.

Analysis on the Rainstorm Process from June 14 to 15 in 2011

Based on the conventional observational data, NCEP, satellite and radar data, the weather diagnosis and mesoscale analysis of the first rainstorm appearing in Shaoyang City since the flood season from June 14 to 15 in 2011 were carried out. The results showed that this rainstorm occurring in the whole Shaoyang City was an typical rainstorm during the first rainy season, and resulted from the strong development of the mesoscale system generated under extremely favorable weather situation. Guided by the cold advection behind the East Asia trough at 500 hPa, cold air moved southward and met southwest airflow in the northwest of strong subtropical high, so that the junction zone of clod and warm airflow was kept in the middle of Hunan Province. In addition, the stable junction zone of clod and warm airflow as well as extremely vigorous southwest warm and wet airflow made the rainstorm have adequate water vapor, dynamic and thermal conditions, which was extremely beneficial to the stong development of small and medium-scale convection systems. In a word, due to stong water vapor and convergence upward movement, reinforcement of low-level southwest jet, activity of low-level weak cold air, exacerbation of convective unstable stratification, superposition of strong divergence at high levels, and obvious development of vertical vorticity caused by vertical shear of horizontal wind or increase of moist baroclinicity, the rainstorm happened in Shaoyang City.

Finite Element Structural Analysis of Buried Pipelines

This document uses previous results (which we call the first stage), for the development of a computer model based on finite elements under the FEAP programmer, to carry out a structural analysis of a pipeline. For this purpose, we used environmental variables that we believe influence the failure of buried pipelines such as the internal pressure of fluid, the type of support used, the temperature at which the pipelines work, the type of soil and the stiffness of the soil acting on it. Once the model was finalized, analyses were made with each of the variables separately and combined to observe the behavior of the pipeline, finding the most unfavorable case that indicates the main causes that led to its failure.

Human thermal comfort under lateral radiant asymmetries

Occupants’thermal comfort in buildings may be affected by the cool wall and warm wall,which is attributed to the effect of asymmetric radiation.However,the previous majority of the researches on asymmetric radiation were mainly about the comfort limits under thermally neutral condition within 1∼1.5 h but had not considered the effect of exposure duration and the condition beyond neutral.To investigate the human thermal comfort under an asymmetric environment caused by the cool wall and warm wall,forty-four subjects were exposed to neutral air temperature with lateral radiant asymmetries in winter and summer for 3 h.The results indicated that the cool wall caused thermal discomfort easier than the warm wall because the thermal sensation decreased and deviated from neutral with time.Subjects’sensitivity of local parts to asymmetric radiation was affected in the conditions beyond neutral,thus their acceptability to asymmetric radiation decreased.The currently used limits of radiant temperature asymmetry tended to underestimate the local discomfort due to the walls.For the conditions tested,The limits of 5%dissatisfaction in radiant temperature asymmetry were 4.4°C(180 min)and 1.8°C(60 min and 120 min)for the warm wall,and 1.8°C at 60 min for the cool wall.

Misorientation dependent thermal condition-solute field cooperative effect on competitive grain growth in the converging case during directional solidification of a nickel-base superalloy

Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades.In this work,thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples.We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field,and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains.When the unfavorably oriented grain is low misoriented,unfavorably oriented grain dominates grain selection,and the competitive grain growth performs as solute field domination.However,with the increase of unfavorably oriented grain’s misorientation,the grain selection converts into favorably oriented grain domination,and the competitive grain growth changes to thermal condition domination.To explain these abnormal transformation phenomena,we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation(θ_(cm)).According to dynamic equation of dendrite growth,we calculate the critical misorientationθ;to prove this model.The theoretical calculation results agree well with the experimental results.

DIFFERENCES BETWEEN DRY AND WET SUMMER IN THE VERTICAL MOTION ON NORTH SIDE OF QINGHAI-XIZANG PLATEAU AND THE THERMAL IMPACT OF PLATEAU

To better analyse and understand the causes of Northwest China(NW China)arid climate formation,firstly the dry and wet standards were chosen and the yearly dry and wet grades on the north side of Qinghai-Xizang Plateau(hereafter NSQXP)in summers were classified utilizing the rainfall data of five stations over the area in June-August of 1952—1990.Then the differences between the vertical motion over the Qinghai-Xizang Plateau(QXP)and NSQXP in dry and wet summers were comparatively analyzed using the ECMWF's gridded data of June—August of 1979 —1986.Finally the connection between the QXP surface thermal condition and the dry and wet summers on the NSQXP was discussed as well. The main results are the following:(1)the dry and wet standards taking the rainfall standard deviation as criterion are suitable for the arid climate area;(2)the QXP may be,to some extent. responsible for the environment background of Middle Asia,NW China and North China arid climate areas;(3)there are the striking differences between the dominant vertical motion over the QXP and NSQXP in the dry and wet summers of NSQXP:(4)the QXP surface thermal condition is.to a great extent,responsible for the year—to—year variation of NW China arid climate as well.

Changes in thermal comfortable condition in the Qinghai‒Tibet Plateau from 1979 to 2020

Qinghai‒Tibet Plateau(QTP)is one of the most sensitive regions to climate change in the world.As a result,people in the QTP are more likely to be sensitively affected by climate change than those in other regions,particularly in the poverty area.Using the Universal Thermal Climate Index(UTCI)derived from ERA5 and population data,changes in annual thermal comfort condition and population under such condition in the QTP are systematically analyzed.The results reveal that there is considerable regional heterogeneity in the distribution of UTCI and the number of comfortable days(CDs),mainly due to the complex geographic features.In most areas of the QTP,the increase in UTCI leads to an increased number of comfortable days.Spatial distribution and temporal change in the number of comfortable days are found to be principally related to altitude.In areas within altitudes of 3000–4500 m,the number of comfortable days increases by up to 6 d per decade,which is faster than that in higher elevation areas above 4500 m.Results also indicate that thermal comfortable condition has improved in areas of 2500–5000 m(medium to high altitude),particularly in spring and autumn.Further research indicates that population distribution also shows a regional clustering feature,with the majority of residents residing in cities and their vicinities,where a higher number of comfortable days were observed.Most areas with a greater number of comfortable days have experienced a more significant increase in population under thermal comfortable conditions.It implies that climate change more likely has a large influence on population in the QTP.These findings are expected to enhance tourism development and the assessment of the impact on the living environment.The findings can be helpful for optimizing of tourism development and better understanding how climate change affects population distribution.

Numerical simulations on atmospheric stability conditions and urban airflow at five climate zones in China

Due to the quick development of urbanization,it is important to provide a healthy urban environment for the dweller.Previous studies have obtained valuable conclusions of how to improve the urban airflow distribution under isothermal conditions.How to adopt and interpret those conclusions when considering the solar-induced atmospheric stability conditions have not been clarified yet.In this study,the characteristics of atmospheric stability condition and influence of diurnal varying solar-induced thermal effect on urban airflow inside the idealized building arrays were investigated at five cities located at five climate zones in China.Urban energy model,CitySim,was employed to simulate the annual distribution of solar-induced walls’temperatures inside the idealized building arrays.The diurnal varying wall temperatures at the hottest days were set as thermal boundary conditions in computational fluid dynamic(CFD)simulations.With albedo value of 0.5,the possibility of adopting the results from isothermal condition directly ranged from 7%to 11%for the five cities in China throughout the year.The unstable condition ocuppied from 19%to 24%annually and the stable condition of more than 40%annually was observed.Under the diurnal varying solar-induced thermal effect,the spatially-averaged air speeds and airflow patterns were significantly different from the isothermal conditions.The percent of Richardson number under different atmospheric stability conditions annually based on the Citysim simulation results indicated that the atmospheric stability was most likely determined by the local climate characteristics and albedo value rather than the building layouts at the five selected cities in China,but this should be further investigated when the shadow effects of surrounding buildings were considered in simulations.

Comparative analysis of sol-air temperature in typical open and semi-closed courtyard spaces

The building cooling load is calculated in most standards using the sol-air temperature(T_(sol-air)),which depends on the surface properties and the building configuration.This study presents an experimental and numerical analysis to find a relationship between the aspect ratio of the courtyard and the T_(sol-air) at different height levels.Besides,the influence of the surface reflection factor on the T_(sol-air) is analyzed.The results show that the T_(sol-air) inside the courtyard differs compared to the usual outside facade.This difference is increased by increasing the aspect ratio of the courtyard and can reach up to 60°C at low levels of the deep courtyards.It is also found that the courtyard geometry is much more important than the thermal behavior of the materials and the T_(sol-air) within the deep courtyard is less affected by the reflection factor of materials.

A reined global-local approach for evaluation of singular stress ield based on scaled boundary inite element method

A reined global-local approach based on the scaled boundary inite element method（SBFEM） is proposed to improve the accuracy of predicted singular stress ield. The proposed approach is carried out in conjunction with two steps. First, the entire structure is analyzed by employing an arbitrary numerical method. Then, the interested region, which contains stress singularity, is re-solved using the SBFEM by placing the scaling center right at the singular stress point with the boundary conditions evaluated from the irst step imposed along the whole boundary including the side-faces. Beneiting from the semi-analytical nature of the SBFEM, the singular stress ield can be predicted accurately without highly reined meshes. It provides the FEM or other numerical methods with a rather simple and convenient way to improve the accuracy of stress analysis. Numerical examples validate the effectiveness of the proposed approach in dealing with various kinds of problems.

Effects of temperature distribution and level on heat transfer on a rotating free disk

In gas turbine engines,with the existence of the intense forced convection and significant buoyancy effects,temperature distribution and level on turbine or compressor disks affect the heat transfer characteristics strongly.In this paper,numerical simulations were performed to analyze these influences for a free disk,with the laminar and turbulent flow respectively.The influences of temperature distribution on the heat transfer were observed by using incompressible cooling air,and temperature profiles of nth order monomial and polynomial were assumed on the disk.The analysis revealed that the heat transfer for two flow states on the free disk is determined by the exponent n of the monomial profile when specifying the rotating Reynolds number;for an arbitrary polynomial profile,the local Nusselt number can be deduced from results of monomial profiles.To study the effects of temperature level on heat transfer singly,monomial profiles were used and the local Nusselt number of compressible and incompressible cooling air were compared.And both for two flow states,the following conclusions could be drawn: the relative difference of local Nusselt number is mainly controlled by nondimensional local temperature difference,and almost independent of the monomial's coefficient C,exponent n and the rotating Reynolds number.Subsequently,a correction method for heat transfer of the free disk is presented and verified computationally,with which the local Nusselt number,obtained with a uniform and low temperature profile,can be revised by arbitrary distribution and high temperature magnitude.