The role of urban development in the formation of a “heat island”

2021 ◽  
pp. 4-14
Author(s):  
Виктория Дмитриевна Мешкова ◽  
Александр Анатольевич Дектерев ◽  
Кирилл Юрьевич Литвинцев ◽  
Сергей Анатольевич Филимонов ◽  
Андрей Анатольевич Гаврилов
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Solar Radiation ◽  
Urban Development ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Convective Motion ◽  
Surface Velocity ◽  
Heat Island ◽  
Near Surface

Для оценки роли городской застройки в формировании “острова тепла” и исследования его влияния на распространение загрязняющих веществ разработана микромасштабная математическая модель городской среды. В качестве модельной задачи рассматривалось локальное влияние городской застройки микрорайона г. Красноярска. Установлено, что наибольший вклад в формирование “острова тепла” вносят наружные стены зданий и их верхние конструкции - крыши. При учете теплообмена наблюдаются рост средней скорости воздушного потока внутри квартала и уменьшение низкоскоростных областей более чем на 0.5 м/с. Также выявлено, что при учете теплообмена наблюдается заброс загрязняющих веществ, поступающих от дороги, на б´ольшую высоту, чем без него. Разработанная математическая модель позволяет комплексно подойти к исследованию гидродинамики и прогнозированию экологической обстановки урбанизированных территорий Introduction. The configuration of modern micro districts leads to the formation of zones with low velocity, in which the accumulation of pollutants occurs. On the other hand, during the construction of cities, the surface of the Earth is covered with materials that actively absorb solar radiation, which leads to the formation of an urban heat island. Our work is devoted to the study of the local influence of urban development on the spread of pollutants, which takes into account the above mentioned factors. Mathematical model. For solving our problems we developed the microscale mathematical model based on the Reynolds-averaged Navier-Stokes equations for incompressible flows with variable density. For the correct calculation of the temperature on the surface of buildings, we used a model of conjugate heat transfer with a one-dimensional equation of thermal conductivity. As a model problem, we considered the Krasnoyarsk area with dense development and the presence of a highrise building for two seasons: winter and summer. The source of emission of pollutants was traffic. Results. The results of the calculations show a significant decrease in velocity around buildings. On the contrary, solar radiation leads to the intensification of free convective motion, especially in the surface area. That can double the near-surface velocity compared to the solution that does not account for the heat transfer. Conclusions. The developed mathematical model allows a comprehensive approach to solving hydrodynamic problems of prediction the ecological situation of cities

Development of High Order LES Solver for Heat Transfer Applications Based on the Open Source OpenFOAM Framework

2015 ◽  
Author(s):  
Luca Mangani ◽  
David Roos Launchbury ◽  
Ernesto Casartelli ◽  
Giulio Romanelli
Keyword(s):  
Heat Transfer ◽  
Open Source ◽  
Gas Turbines ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Order ◽  
Computational Time

The computation of heat transfer phenomena in gas turbines plays a key role in the continuous quest to increase performance and life of both component and machine. In order to assess different cooling approaches computational fluid dynamics (CFD) is a fundamental tool. Until now the task has often been carried out with RANS simulations, mainly due to the relatively short computational time. The clear drawback of this approach is in terms of accuracy, especially in those situations where averaged turbulence-structures are not able to capture the flow physics, thus under or overestimating the local heat transfer. The present work shows the development of a new explicit high-order incompressible solver for time-dependent flows based on the open source C++ Toolbox OpenFOAM framework. As such, the solver is enabled to compute the spatially filtered Navier-Stokes equations applied in large eddy simulations for incompressible flows. An overview of the development methods is provided, presenting numerical and algorithmic details. The solver is verified using the method of manufactured solutions, and a series of numerical experiments is performed to show third-order accuracy in time and low temporal error levels. Typical cooling devices in turbomachinery applications are then investigated, such as the flow over a turbulator geometry involving heated walls and a film cooling application. The performance of various sub-grid-scale models are tested, such as static Smagorinsky, dynamic Lagrangian, dynamic one-equation turbulence models, dynamic Smagorinsky, WALE and sigma-model. Good results were obtained in all cases with variations among the individual models.

Convective Motion and Heat Transfer in a Slowly Rotating Fluid Quasi-Sphere With Uniform Heat Source and Axial Gravity

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Gerardo Anguiano-Orozco ◽  
Ruben Avila ◽  
Syed Shoaib Raza
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Transfer Rate ◽  
Rotation Rate ◽  
Transfer Rate ◽  
Stokes Equations ◽  
Convective Motion ◽  
Maximum Temperature ◽  
Rotating Fluid ◽  
Uniform Heat

The laminar natural convection of a rotating fluid quasi-sphere in the presence of an axial gravity field and uniform heat source is presented. The influence of the Rayleigh number Ra and the Taylor number Ta on the flow pattern and heat transfer rate from the fluid quasi-sphere is discussed. The governing nonsteady, three-dimensional Navier–Stokes equations for an incompressible fluid, formulated in a Cartesian coordinate system, have been numerically solved by using the h/p spectral element method. It is shown that for a given Ta number, as the Ra number is increased, the heat transfer on the northern hemisphere is enhanced whereas the average Nusselt number on the southern hemisphere is reduced. On the other hand for a given Ra number, as the Ta number is increased, the heat transfer is a function of the convective motion intensity. It has been found that for low and high Ra numbers the heat transfer rate slightly depends on the rotation rate. However at intermediate Ra numbers, the net effect of an increased rotation rate is a reduction of the heat transfer through the wall, hence an increase of the maximum temperature of the fluid sphere is observed. We show that the net effect of the Coriolis force is to damp the convective motion and to allow a redistribution of the vorticity field.

Finite Analytic Solution of Convective Heat Transfer for Tube Arrays in Crossflow: Part I—Flow Field Analysis

1989 ◽  
Vol 111 (3) ◽  
pp. 633-640 ◽  
Author(s):  
Tzong-Shyan Wung ◽  
Ching Jen Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Analytic Solution ◽  
Stokes Equations ◽  
Convective Motion ◽  
Field Analysis ◽  
Analytic Method ◽  
Finite Analytic Method ◽  
Tube Arrays ◽  
Local Analytic Solution

The convective motion in two types of tube array is solved numerically by the Finite Analytic Method. The Finite Analytic Method utilizes the local analytic solution of governing differential equations in obtaining its discretized algebraic representation. Both in-line tube arrays and staggered tube arrays with longitudinal and transverse pitches of 2 are studied. The geometries are expressed in boundary-fitted coordinates on which the Navier–Stokes equations and energy equation are solved. Solutions for Reynolds numbers of 40, 120, 400, and 800 are obtained. Differences in stream function, vorticity function, and location of separation and reattachment for flow past in-line tube arrays and staggered tube array are predicted and compared. The zone of separation for both arrays tends to increase with increasing Reynolds number. The predicted results on flow field and heat transfer are shown to agree with available experimental measurements.

Heat Transfer of Coupled Fluid Flow Within a Channel With a Permeable Base

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Rosemarie Mohais ◽  
Balswaroop Bhatt
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Effective Means ◽  
Reynolds Numbers ◽  
Model Systems ◽  
Surface Velocity ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Small Reynolds Numbers

We examine the heat transfer in a Newtonian fluid confined within a channel with a lower permeable wall. The upper wall of the channel is impermeable and driven by an accelerating surface velocity. Through a similarity solution, the Navier–Stokes equations are reduced to a fourth-order differential equation; the analytical solutions of which determined for small Reynolds numbers show dependence of the temperature and heat transfer profiles on the slip parameter based on the properties of the porous channel base. For larger Reynolds numbers, numerical solutions for three main groups of solutions show that the Reynolds number strongly influences the heat transfer profile. However, the slip conditions associated with the porous base of the channel can be used to alter these heat transfer profiles for large Reynolds numbers. The presence of a porous base in a channel can thus serve as an effective means of reducing or enhancing heat transfer performance in model systems.

Numerical Simulation of Solar Radiation and Conjugate Heat Transfer through Cabin Seat Textile

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Yijie Zhang ◽  
Juhong Jia
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Conjugate Heat Transfer ◽  
Radiative Heat ◽  
Stokes Equations ◽  
Thermal Environment ◽  
Heat Radiation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Lower Temperature

AbstractThe solar radiation and the conjugate heat transfer through the cabin seat fabric were investigated numerically with a focus on a comparative analysis of various fabric solar reflectance or reflectivity (SR) and inlet cooling air velocity. For this purpose, 3D compressible Reynolds-averaged Navier–Stokes equations with the low Reynolds number turbulence model were utilized to simulate the airflow in the cabin. The discrete ordinate radiation model was adopted to describe the solar radiation. The conjugate heat transfer between the airflow and the fabric seats was included. The airflow temperature, radiative heat flux, and radiative heat transfer through the fabrics in a fixed cross section were studied. The results demonstrate that the increase in fabric SR leads to the increase in energy reflected to the atmosphere, which will bring about a lower temperature on the seat fabric. The decrease in emissivity and the energy absorbed results in the lower heat transfer and heat radiation and leads to the improvement of the cabin thermal environment. The high-temperature gradient near the seat causes the forced air circulation and is beneficial for the improvement of the thermal comfort. However, the cooling effect is not so obvious near the cabin seats when the inflow speed is increased.

scholarly journals Modelling of thermal regimes in the air cooling channel of the titanium reduction apparatus

2021 ◽  
pp. 39-51
Author(s):  
T. O. Karasev ◽  
◽  
A. V. Perminov ◽  
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Titanium Sponge ◽  
External Boundary ◽  
Air Cooling ◽  
Cooling Channel

Numerical modeling of thermophysical processes in the air cooling channel of titanium sponge reduction apparatus is performed. The cooling channel is an area bounded by a retort filled with liquid magnesium and the apparatus wall, on which heating elements are mounted. Air flows inside the channel, cooling the retort. A mathematical model is constructed based on unsteady Navier-Stokes equations in axisymmetric formulation using a k-ω SST turbulence model. The model takes into account the radiation heat transfer between the retort and reactor walls. Four variants of thermal boundary conditions are considered. The aim of this work is to create a mathematical model of conjugate heat transfer in an air channel. Based on this model, the temperature conditions of the retort wall are calculated and the profiles of the heat transfer coefficient along the retort wall for a wide interval of air flow rates are obtained. It is shown that temperature distributions along the retort are heterogeneous and strongly depend both on external boundary conditions and on the cooling intensity. Heat transfer coefficient distributions from its outer wall for different retort heating conditions are plotted and an empirical formula for calculating the profile of this coefficient is proposed.

Dynamic Simulation and Analysis of the Process of Cold-Storage Plate Release Cool in Refrigerator Vehicle

2013 ◽  
Vol 732-733 ◽  
pp. 589-592
Author(s):  
Xiao Yan Li ◽  
Shi Qiang Du ◽  
Yue Ming Li
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Solar Radiation ◽  
Dynamic Simulation ◽  
Cold Storage ◽  
Transfer Process ◽  
Heat Transfer Process ◽  
Cool Time ◽  
Radiation Time ◽  
Variation Rule

This paper presents a mathematical model for simulating the heat transfer process in a cold-storage plate that can be used in the refrigerator vehicle. The numerical method studied was an enthalpy method. Variation rule between process of release cool and influenced factors were obtained. The effect of solar radiation time was investigated in discharging process. Both increasing the number of cold-storage plate and improving sealed performance of door and compartment can extend release cool time. The results show that according to the different breath heat of goods, reasonable arrangement of number of cold-storage plate can meet cold demand in the transport; solar radiation also has influence to the process of cold-storage plate release cool, with considering cold load caused by solar radiation, release cool time is shortened by 13%.

Influence of trees on the energy consumption of a social housing in mid-western Brazil

2019 ◽  
pp. 53-65
Author(s):  
Renata Domingos ◽  
Emeli Guarda ◽  
Elaise Gabriel ◽  
João Sanches
Keyword(s):  
Energy Consumption ◽  
Solar Radiation ◽  
Thermal Comfort ◽  
Air Conditioning ◽  
Computational Simulation ◽  
Building Energy ◽  
General Idea ◽  
Heat Island ◽  
Study Region ◽  
Ample Evidence

In the last decades, many studies have shown ample evidence that the existence of trees and vegetation around buildings can contribute to reduce the demand for energy by cooling and heating. The use of green areas in the urban environment as an effective strategy in reducing the cooling load of buildings has attracted much attention, though there is a lack of quantitative actions to apply the general idea to a specific building or location. Due to the large-scale construction of high buildings, large amounts of solar radiation are reflected and stored in the canyons of the streets. This causes higher air temperature and surface temperature in city areas compared to the rural environment and, consequently, deteriorates the urban heat island effect. The constant high temperatures lead to more air conditioning demand time, which results in a significant increase in building energy consumption. In general, the shade of the trees reduces the building energy demand for air conditioning, reducing solar radiation on the walls and roofs. The increase of urban green spaces has been extensively accepted as effective in mitigating the effects of heat island and reducing energy use in buildings. However, by influencing temperatures, especially extreme, it is likely that trees also affect human health, an important economic variable of interest. Since human behavior has a major influence on maintaining environmental quality, today's urban problems such as air and water pollution, floods, excessive noise, cause serious damage to the physical and mental health of the population. By minimizing these problems, vegetation (especially trees) is generally known to provide a range of ecosystem services such as rainwater reduction, air pollution mitigation, noise reduction, etc. This study focuses on the functions of temperature regulation, improvement of external thermal comfort and cooling energy reduction, so it aims to evaluate the influence of trees on the energy consumption of a house in the mid-western Brazil, located at latitude 15 ° S, in the center of South America. The methodology adopted was computer simulation, analyzing two scenarios that deal with issues such as the influence of vegetation and tree shade on the energy consumption of a building. In this way, the methodological procedures were divided into three stages: climatic contextualization of the study region; definition of a basic dwelling, of the thermophysical properties; computational simulation for quantification of energy consumption for the four facade orientations. The results show that the façades orientated to north, east and south, without the insertion of arboreal shading, obtained higher values of annual energy consumption. With the adoption of shading, the facades obtained a consumption reduction of around 7,4%. It is concluded that shading vegetation can bring significant climatic contribution to the interior of built environments and, consequently, reduction in energy consumption, promoting improvements in the thermal comfort conditions of users.

Sign in / Sign up

Export Citation Format

Share Document