Home OALib Journal OALib PrePrints Submit Ranking News My Lib FAQ About Us Follow Us+
 Title Keywords Abstract Author All
Search Results: 1 - 10 of 100 matches for " "
 Advances in Materials Science and Engineering , 2012, DOI: 10.1155/2012/523051 Abstract: The surface heat budgets of various pavement surfaces are studied with the aim of mitigating the urban heat island effect. In this study, the thermal characteristics of pavements are examined using data from observations. The net radiation, surface temperature, temperature under the surface, conduction heat flux, and core weight for each experimental surface are recorded, together with the weather conditions at the time of observation. The latent heat flux is estimated from the observed weight of the cores. The surface heat budget under the same weather conditions is examined, and the sensible heat flux from each target surface is calculated. The parameters that influence the surface heat budget, for example, solar reflectance (albedo), evaporative efficiency, heat conductivity, and heat capacity, are examined. On a typical summer day, the maximum reduction in the sensible heat flux from that on a normal asphalt surface is about 150？W/m2 for an asphalt surface with water-retaining material and about 100？W/m2 for a cement concrete surface with water-retaining material, depending on the albedo of each surface. 1. Introduction The purpose of this study is to investigate the urban heat island mitigation effect achieved by conversion from an asphalt pavement surface to another pavement surface for ground surface improvement, which is an established urban heat island mitigation technique. Various kinds of pavements were constructed experimentally for the purpose of investigating their effect on urban heat island mitigation by analyzing the surface heat budget. The urban heat island mitigation effect is discussed from the viewpoint of the sensible heat flux reduction for each pavement. Urban heat island mitigation technologies focus on the improvement of urban surface materials on roads, roofs, and walls. For example, roads and roofs coated with high-reflectance paint are called cool roofs and cool pavements by Akbari et al. [1]. According to their estimates, the annual balances in the saving in cooling cost and the increase in heating cost obtained by introducing cool roofs are $35 million in Los Angeles,$16 million in New York, and $10 million in Chicago. However, fewer studies have been carried out on roads as compared to those on green roofs [2–7], green parks [8–12], and green plantings [13–15]. In Japan, several studies have been carried out to evaluate the performance of pavements designed to have a beneficial environmental impact [16–20]. However, those studies have evaluated each technology separately and discussed only the reduction in surface  Journal of Engineering Science and Technology , 2011, Abstract: A numerical study of the heat and mass transfer through a wall is proposed in this work. The studied wall is submitted to mass and heat convective exchange with the ambient. One of its sides is submitted to a variable solar heat flux. The computer program is used to compare the cases of coupling and no coupling heat and mass transfer through the wall under variable heat flux and ambient temperature. The temperature effect on the moisture diffusion and vice versa is presented for two usual materials. An optimal proposal can be clear from this study based on objectives which are mainly the reductions of energy consumption as it is for winter heating or summer cooling.  地理学报 , 1991, Abstract: In order to clarify the effect of solar radiation on the intensity of urban heat island, we survey the daily data in the year of 1984 of Xinzhuang(rural) and Longhua(urban) and use 154 days as regression samples- The regrassion equation (see Eq. 1) shows that the direct solar radiation has a. positive effect on the intensity of the Shanghai urban heat island but the wind velocity and the cloudiness have a negative effect on it. By using the records provided by satellites and the simultaneous observational data of solar radiation and relative meteorological factors, we analyse several typical cases of Shanghai urban heat island in different seasons.  环境科学学报(英文版) , 2008, Abstract: Urban Heat Island (UHI) is considered as one of the major problems in the 21st century posed to human beings as a result of urbanization and industrialization of human civilization. The large amount of heat generated from urban structures, as they consume and re-radiate solar radiations, and from the anthropogenic heat sources is the main cause of UHI. The two heat sources increase the temperatures of an urban area as compared to its surroundings, which is known as Urban Heat Island Intensity (UHII). The problem is even worse in cities or metropolises with large population and extensive economic activities. The estimated three billion people living in the urban areas in the world are directly exposed to the problem which will be increased significantly in the near future. Due to the severity of the problem, vast research effort has been dedicated and a wide range of literature is available for the subject. The literature available in this area includes the latest research approaches, concepts, methodologies, latest investigation tools and mitigation measures. This study was carried out to review and summarize this research area through an investigation of the most important feature of UHI. It was concluded that the heat re-radiated by the urban structures plays the most important role which should be investigated in details to study urban heating especially the UHI. It was also concluded that the future research should be focused on design and planning parameters for reducing the effects of urban heat island and ultimately live in a better environment.  Physics , 2011, DOI: 10.1103/PhysRevLett.112.040601 Abstract: Consider anomalous energy spread in solid phases, i.e.,$MSD= \int (x -{\langle x \rangle}_E)^2 \rho_E(x,t)dx \propto t^{\beta}$, as induced by a small initial excess energy perturbation distribution$\rho_{E}(x,t=0)$away from equilibrium. The associated total thermal equilibrium heat flux autocorrelation function$C_{JJ}(t)$is shown to obey rigorously the intriguing relation,$d^2 MSD/dt^2 = 2C_{JJ}(t)/(k_BT^2c)$, where$c$is the specific volumetric heat capacity. Its integral assumes a time-local Helfand-moment relation; i.e.$ dMSD/dt|_{t=t_s} = 2/(k_BT^2c)\int_0^{t_s} C_{JJ}(s)ds$, where the chosen cut-off time$t_s$is determined by the maximal signal velocity for heat transfer. Given the premise that the averaged nonequilibrium heat flux is governed by an anomalous heat conductivity, energy diffusion scaling determines a corresponding anomalous thermal conductivity scaling behaviour.  Physics , 2013, DOI: 10.1103/PhysRevLett.112.040601 Abstract: Consider anomalous energy spread in solid phases, i.e.,$MSD= \int (x -{< x >}_E)^2 \rho_E(x,t)dx \propto t^{\beta}$, as induced by a small initial excess energy perturbation distribution$\rho_{E}(x,t=0)$away from equilibrium. The associated total thermal equilibrium heat flux autocorrelation function$C_{JJ}(t)$is shown to obey rigorously the intriguing relation,$d^2 MSD/dt^2 = 2C_{JJ}(t)/(k_BT^2c)$, where$c$is the specific volumetric heat capacity. Its integral assumes a time-local Helfand-moment relation; i.e.$ dMSD/dt|_{t=t_s} = 2/(k_BT^2c)\int_0^{t_s} C_{JJ}(s)ds$, where the chosen cut-off time$t_s$is determined by the maximal signal velocity for heat transfer. Given the premise that the averaged nonequilibrium heat flux is governed by an anomalous heat conductivity, energy diffusion scaling necessarily determines a corresponding anomalous thermal conductivity scaling behavior.  Physics , 2006, Abstract: In this paper we investigate the diffusion of the thermal pulse in Planck Gas. We show that the Fourier diffusion equation gives the speed of diffusion, v > c and breaks the causality of the thermal processes in Planck gas .For hyperbolic heat transport v  大气科学 , 2007, Abstract: The urbanization is a process that the human being changes the local natural surface characteristics widely and dramatically.This process will impact local atmospheric environment greatly.To understand the urbanization's effect on local urban boundary layer will show its great value in urban weather/climate study,urban environmental protection,urban design and construction,urban disaster-prevention,and will help us improve the residential environment and residential quality in urban area.A numerical simulation model is used in this paper to investigate the effect of the inhomogeneity of urban anthropogenic heat source on the exchanges of energy and material between surface and atmospheric system,and its impacts on urban boundary layer structures.To study the anthropogenic heat affecting the urban boundary layer structures,Hangzhou is taken as an example.A new anthropogenic heat source scheme is developed in the regional boundary layer numerical model(RBLM).In this new scheme,the urban anthropogenic heat source is distributed into different model layers.The lower layer heat release is added into the surface energy budget and the upper layer anthropogenic heat release is coupled into the atmosphere energy equations and its vertical distribution is related with the urban building distribution feature,including building height and density and the diurnal change of anthropogenic heat release is included in this scheme.The numerical simulation results show that this scheme can describe the anthropogenic heat release process better than former schemes and the simulated temperatures,wind directions,wind speeds are closer to the observation data.In the former anthropogenic heat release scheme all of the heat is added into the surface,this leads to the increasing of temperature and turbulence energy,and in the daytime this impact will be transported to upper atmosphere due to the strong turbulence and the increase of atmospheric temperature and turbulence is not obvious in lower air layer.The atmospheric instability increases and the boundary layer height increases by 400 m,the vertical speed over urban area is increased and urban heat island density is strengthened.In the nighttime the impact of anthropogenic heat is more obvious than in the daytime without the solar radiation heating.In the cases of the new scheme turbulence energy in lower layers increases by 40% and the atmospheric stability decreases.In general,the simulation results with the new anthropogenic heat release scheme show that the anthropogenic heat affects the urban boundary layer structure more greatly in the nighttime than in the daytime.And this impact is largest in winter,less in spring and autumn and weakest in summer.The reason may depend on that,in the surface energy budget the solar radiation is the main energy source,while anthropogenic heat is an important but not primary source.Compared with the diurnal and seasonal change of solar radiation,the anthropogenic heat release is a  Chia-Hsien Lin Physics , 2015, DOI: 10.1007/s10509-014-1931-x Abstract: A statistical study of 77 solar active regions (ARs) is conducted to investigate the existence of identifiable correlations between the subsurface structural disturbances and the activity level of the active regions. The disturbances examined in this study are$<|\delta \Gamma_1/\Gamma_1|>$,$<|\delta c^2/c^2|>$, and$<|\delta c^2/c^2-\delta \Gamma_1/\Gamma_1|>$. where$\Gamma_1$and$c$are the thermodynamic properties of first adiabatic index and sound speed modified by magnetic field, respectively. The averages are over three depth layers:$0.975-0.98 R_\odot$,$0.98-0.99 R_\odot$and$0.99-0.995 R_\odot$to represent the structural disturbances in that layer. The level of the surface magnetic activity is measured by the Magnetic Activity Index (MAI) of active region and the relative and absolute MAI differences (rdMAI and dMAI) between the active and quiet regions. The eruptivity of each active region is quantified by its Flare Index, total number of coronal mass ejections (CMEs), and total kinetic energy of the CMEs. The existence and level of the correlations are evaluated by scatter plots and correlation coefficients. No definitive correlation can be claimed from the results. While a weak positive trend is visible between dMAI and$<|\delta \Gamma_1/\Gamma_1|>$and$<|\delta c^2/c^2|>$in the layer$0.975-0.98 R_\odot\$, their correlation levels, being approximately 0.6, are not sufficiently high to justify the correlation. Some subsurface disturbances are seen to increase with eruptivity indices among ARs with high eruptivity. The statistical significance of such trend, however, cannot be ascertained due to the small number of very eruptive ARs in our sample.