•We developed a numerical framework incorporating trees in an urban canopy model.•Shade trees have more prominent energy saving potential than urban lawns.•The trade-off between water-energy is a key ...for urban landscape management.•Urban vegetation can significantly alleviate outdoor thermal stress.
The use of urban vegetation in cities is a common landscape planning strategy to alleviate the heat island effect as well as to enhance building energy efficiency. The presence of trees in street canyons can effectively reduce environmental temperature via radiative shading. However, resolving shade trees in urban land surface models presents a major challenge in numerical models, especially in predicting the radiative heat exchange in canyons. In this paper, we develop a new numerical framework by incorporating shade trees into an advanced single-layer urban canopy model. This novel numerical framework is applied to Phoenix metropolitan area to investigate the cooling effect of different urban vegetation types and their potentials in saving building energy. It is found that the cooling effect by shading from trees is more significant than that by evapotranspiration from lawns, leading to a considerable saving of cooling load. In addition, analysis of human thermal comfort shows that urban vegetation plays a crucial role in creating a comfortable living environment, especially for cities located in arid or semi-arid region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An inverse problem for a system of semilinear elliptic equations modeling simultaneously conductive and radiative heat transfer is under consideration. The problem consists in finding the right-hand ...side of the heat transfer equation, in the form of linear combination of given functionals, on the base of prescribed values of these functionals on the solution. The solvability of the problem is proven without any smallness assumptions. It is shown that the set of solutions is homeomorphic to a finite-dimensional compact set, and conditions of uniqueness of solutions are found.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To create a comfortable thermal environment in buildings, building cooling account for a large part of building energy consumption in summer. The spectral radiative properties of radiant cooling ...materials as a passive cooling technology have been extensively studied. However, there are few studies that address the application of radiant cooling materials to building envelopes. This paper proposed a radiative cooling glass composite structure for windows based on existing radiant cooling materials and established a climate adaptive radiant cooling building indoor thermal environment assessment model. This assessment model combines the spectral selectivity of radiative cooling materials with climate characteristics. An indoor thermal environment test system and an ambient climate measurement system are designed under the influence of external windows, and the average error of the assessment model is verified to be no more than 4.83%. Based on this assessment model, three applicability analyses were conducted: Firstly, it is concluded that the daytime indoor temperature with radiative cooling glass (RCG) is 26.43°C lower than that with the ordinary glass. Secondly, RCG can effectively improve the indoor thermal environment for rooms facing each direction, and the indoor temperature is 45.06°C lower than that of ordinary glass in the east and west directions, and 15.05°C lower than that of ordinary glass in the north and south directions. Finally, analysis of the correlation between indoor temperature and outdoor temperature shows that the indoor temperature tends to rise as the outdoor temperature rises. The analysis of the application of RCG in different cities shows that the performance of radiative cooling is relatively weak in areas with high relative humidity.
•This study establishes a model for assessing the thermal environment considering the spectral properties of materials.•Radiative cooling materials are used in building facade applications.•Spectral selectivity of radiative cooling materials is combined with climatic characteristics.•The effect of outdoor environmental parameters on the cooling performance of radiative cooling materials is discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The laser-induced thermocapillary deformation and rupture of liquid layer was investigated.•The experimental technique for measuring profile of the thermocapillary deformation of liquid layer was ...developed.•The optimal function for approximating the thermocapillary deformation was proposed.•The influence of conditions of radiative heat exchange in the system on the layer deformation was investigated numerically.
Characterizing the profile of the laser-induced thermocapillary deformation of a thin liquid layer on a laser absorbing solid is of great fundamental and applied importance. The thermocapillary effect is the basis of several non-contact methods for measuring the physicochemical and thermal properties of liquids and solids, and methods of non-destructive testing in material science and thermal physics. The study of the layer rupturing caused by laser beam heating could contribute to solving the problem of the dry spots formation in thin–film heat exchangers. In this regard, the development of physical and numerical tools to determine the thermocapillary profiles of thin liquid layers is of great interest to researchers. In the present work, we developed a home-made setup to scan a deformed surface of a liquid layer with a laser sheet. Its accuracy was verified by scanning the surface of a solid standard specimen with a given Gaussian profile. By scanning the thermocapillary deformed layers of silicone oil, we found that for the Gaussian distribution of the radiation intensity in the heating laser beam, the thermocapillary deformations are significantly not the Gaussian. A modified Agnesi function, which is characterized by high accuracy and allows defining the surface profile using a minimum of experimental data, is shown to be an optimal function for approximating the thermocapillary deformation. Using Agnesi approximation can significantly reduce the time of the experiment and the processing of results. To validate new experimental data, an axisymmetric numerical model of the thermocapillary convection in a thin liquid layer was developed using commercial software Comsol Multiphysics. It helped calculating the surface profile and the temperature field on the substrate for two boundary conditions of radiative heat exchange in the system corresponding to maximum and minimum radiation heat loss. For the case of the ebonite-silicone oil system, when the laser beam is absorbed by the ebonite surface, it was numerically shown that the difference between the types of boundary conditions becomes noticeable only on very thin layers close to the pseudo-rupture. In general, a comparison of the stationary profiles of the thermocapillary surface deformation and temperature distributions obtained experimentally and numerically for the entire range of the studied layer thicknesses shows satisfactory agreement between the physical and numerical results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Radiation accounts for a significant fraction of the human body and environment heat exchange and strongly impacts thermal comfort and safety. The direct radiative exchange between an individual and ...a source or sink can be quantified using the effective (
f
eff
) and projected radiation area factors (
f
p
). However, these factors have not been quantified for half of the population of the USA with an above-average body mass index (BMI). Here, we address this gap by developing thirty male and thirty female computational manikin models that cover the 1 to 99 percentile variation in height and BMI of adults in the USA. The radiative simulations reveal that the
f
eff
and the
f
p
angular distributions are nearly independent of gender, height, and BMI. Appreciable relative differences from the average models only emerge for manikins with BMI above 80th percentile. However, these differences only occur at low zenith angles and, in absolute terms, are small as compared to variations induced by, for example, the zenith angle increase. We also use the manikin set to evaluate whether the body shape impacts the quality of human representation with several levels of geometrical simplification. We find that the “box/peg” body representation, which is based on the hemispherical
f
p
average, is independent of the body shape. In turn, the
f
p
distributions averaged over the azimuth angle range, representing the rotationally symmetric humans, are only impacted to the same degree as for the anatomical manikins. We also show that the anatomical manikins can be closely approximated by the multi-cylinder and sphere representation, at least from a radiation perspective. The developed anatomical manikin set is freely available and can be used to compute how body shape impacts a variety of external heat transport processes.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We developed a technique for the numerical solution of a nonlinear equation describing the diffusion transfer of radiation energy. The method is based on the introduction of the second time ...derivative with a small parameter into the parabolic equation and an explicit difference scheme. The explicit approximation of the original equation makes it possible to implement an algorithm that is effectively adapted to the architecture of high-performance computing systems. The new scheme provides a second-order resolution of the nonlinearity in time with an acceptable time step. A heuristic algorithm for choosing the parameters of a three-level difference scheme is proposed. Perspective applications of the method are problems in astrophysics, for example, the simulation of a strongly radiating shock wave breakout at the surface of a star at the stage of its evolution known as a supernova explosion.
A mathematical model of a direct-fired continuous strip annealing furnace is developed. The first-principle model uses the heat balance to describe the dynamic behavior of the strip and the rolls. ...The mass and the enthalpy balance are employed to calculate the mass, the composition, and the temperature of the flue gas. The heat conduction equation of the furnace wall is discretized by means of the Galerkin method. Furthermore, the convective and radiative heat transfer interconnect all submodels of the furnace. For the calculation of the radiative heat transfer, the zone method is utilized. Finally, the assembled model is reduced by applying the singular perturbation method. A comparison of simulation results with measurement data from a real plant demonstrates the accuracy of the reduced model. Moreover, due to the moderate computational effort, the model is suitable for real-time applications in control and dynamic optimization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The relevance of the discussed issue is caused by the necessity to reduce the weight and dimensions of high radiation heat exchange systems while improving their energy efficiency. This can be ...achieved by appropriate profiling ribbed elements. Such surfaces are widely used in various fields of modern technology. Therefore, the problems of radiative heat transfer of the developed surfaces are of special scientific and technical interest. The main aim of the study is to obtain a rather simple analytical method from mathematical point of view for calculating the temperature distribution in the ribs of variable cross section in the radiative heat removal from the surface. The methods: use of the proposed linearizing transformation that allows reducing the influence of the nonlinear term in the original differential equation of energy transfer. The results. The authors have proposed the approximate mathematical method based on obtaining lower and upper bounds of the temperature field. This method has an engineering perspective, it is reasonably accurate and at the same time, it is rather simple. In this case, the first two approximations are enough. The calculations given in the article, for trapezoidal ribs may also be used in the particular case for wedge ribs. The found mathematical limits for estimating the upper and lower values of the temperature field allow estimating the coefficient of thermal efficiency for the ribbed surfaces at radial heat exchange.
The relevance of the discussed issue is caused by the necessity to reduce the weight and dimensions of high radiation heat exchange systems while improving their energy efficiency. This can be ...achieved by appropriate profiling ribbed elements. Such surfaces are widely used in various fields of modern technology. Therefore, the problems of radiative heat transfer of the developed surfaces are of special scientific and technical interest. The main aim of the study is to obtain a rather simple analytical method from mathematical point of view for calculating the temperature distribution in the ribs of variable cross section in the radiative heat removal from the surface. The methods: use of the proposed linearizing transformation that allows reducing the influence of the nonlinear term in the original differential equation of energy transfer. The results. The authors have proposed the approximate mathematical method based on obtaining lower and upper bounds of the temperature field. This method has an engineering perspective, it is reasonably accurate and at the same time, it is rather simple. In this case, the first two approximations are enough. The calculations given in the article, for trapezoidal ribs may also be used in the particular case for wedge ribs. The found mathematical limits for estimating the upper and lower values of the temperature field allow estimating the coefficient of thermal efficiency for the ribbed surfaces at radial heat exchange.
