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Urban high-rise buildings and dense street canyons significantly disrupt synchronised wind flows, potentially exacerbating urban heat island effect. Fortunately, urban heat island effect can be mitigated by the green infrastructure in cities, particularly through the presence of roadside trees and green walls. However, the combined mechanisms of tree resistance, shading effects, and cooling effect, along with sensible thermal buoyancy flows within canyon ventilation and pollution dispersion, remain undisclosed. This study employs refined computational fluid dynamics numerical simulations to analyse airflow and pollutant dispersion within urban street canyons. Air exchange rate and pollutant retention time are employed to evaluate ventilation and pollutant dispersion, respectively, inside the street canyons. In scenarios with leeward green wall layout, higher tree canopy spread and trunk height lead to a shift in high pollutant concentrations from the region near the windward side to that near the leeward side of the typical canyon (H/W = 1). Conversely, in deep canyons (H/W = 5), most pollutants are retained near the bottom leeward side. Moreover, differences in pollutant dispersion between typical and deep canyons increase with with rising tree canopy spread. Additionally, higher tree canopy spread and trunk height values result in longer pollutant retention time, which are unfavourable for pollutant removal, and particularly limiting pollutant dispersion as street canyon depth increases. Similarly, increasing tree canopy spread reduces the difference in air exchange rate between windward and leeward green wall layout patterns. Regarding Richardson number variations —indicating thermal buoyancy effects—lower Richardson number values lead to reduced differences in pollutant retention time between typical and deep canyons. Furthermore, ventilation performance of the windward green pattern surpasses that of the leeward pattern. This research provides valuable insights for implementing green infrastructure to locally mitigate urban air pollution. • Resistance, shading, and transpiration effect of green infrastructure were revealed. • Canyon ventilation was complicated by green infrastructure. • Pollutant dispersion and purification were modified by green infrastructure. • Air exchange in canyons were determined in combined wind-buoyancy setting. • Present modelling research could facilitate the layout of green infrastructure. [ABSTRACT FROM AUTHOR]

• Cleanroom with the secondary return system was modeled with airflow and energy network. • The air change rate has a notable influence on the mean age of air globally and locally. • The air change rate has a small effect on contaminant removal effectiveness and air change efficiency. • Promotion of return air volume in the occupied area could reduce local pollutant concentration levels; • Computational fluid dynamics procedure was validated by the on-site measurements. Improving air quality in occupied area has always been the core focus of ventilation design in cleanrooms. A 10,000 class pharmaceutical cleanroom, with secondary return system, was firstly introduced. Full computational fluid dynamics procedure validated by on-site measurements was then applied to model such cleanroom airflow and particle transport. Energy balance of this ventilation system was also analyzed. Details of room airflow and contaminant fields for the specific zone (above the device and around the human body) were subsequently analyzed concerning the effect of delivering ventilation flow rate and return air volume. Representative parameters, mean age of air, contaminant removal effectiveness, and air change efficiency at the occupied zone and the whole space were evaluated. Results demonstrate that promotion of the return air volume in the occupied area could appropriately reduce pollutant concentration level. Moreover, an increase in ACH (air change rate per hour) did not always shorten the local age of air near the equipment. For a large ACH, it not only will raise the dust around the machine again, it will also cause uncomfortable flow draft. Additionally, when ACH = 20 h −1 and 25 h −1 were achieved respectively, the age of air was reduced by 32% and 21.4% in the whole room and further done by 31.1% and 23.5% in the occupied zone; with identical changes, room air change efficiency (RACE) was achieved at 49.3 % and 50.4 %, respectively. It shows that the increase of ACH seems to have little effect on the air change efficiency. When ACH increases from 15 h−1 to 20 h−1, the efficiency of pollutant removal at the occupied zone will not be significantly improved ( ε = 1.78). [ABSTRACT FROM AUTHOR]

The prompt and accurate identification of transient pollution sources in urban regions is imperative for effective pollutant control and the mitigation to public health risks. Depending on sparse concentration distributions, multiple pollution sources identification is inherently complex and difficult, particularly when the pollutant sources exhibit time-varying release rates and are located in urban environments subject to dynamic wind flows. In this research, two niche-based Particle Swarm Optimization (PSO) algorithms, Niche-DPSO (niche pso for dynamic systems) and RSNM-DPSO (ranged subgroup pso with nelder mead for dynamic systems), were simultaneously proposed, aiming to localize multiple pollution sources under the background of unsteady wind flow fields. The MUST experiment, characterized by its complex layout replete with densely arranged obstacles, was adopted as the application scenario. Computational Fluid Dynamics (CFD) was employed to simulate the release of pollutant concentration at (−25.8 m, 0 m, 1.6 m) and (24.2 m, 41.6 m, 1.6 m), with flow velocities ranges from 1.8 to 7.6 m/s. Representative performance-influencing factors, including niche radius, population size, sensor response time, and sensor errors, were systematically evaluated. The results suggested that both Niche-DPSO and RSNM-DPSO algorithms were generally effective in positioning multiple pollution sources. Comparative analysis revealed that Niche-DPSO consistently outperformed RSNM-DPSO in terms of localization success rates, achieving a peak performance of approximately 98 %. Furthermore, Niche-DPSO could maintain its robust performance even under time-spatial-varying environmental and operational conditions, albeit at the expense of requiring more search steps and longer CPU processing time. • Two specialized algorithms were proposed for locating multiple pollution sources. • A CFD model was established and verified for application in the MUST experiment. • The algorithms' performance was rigorously evaluated in the simulation scenario. • Key performance factors were identified, and a sensitivity analysis was conducted. [ABSTRACT FROM AUTHOR]

Abstract The air flow and pollutant dispersion within a group of street canyons ventilated merely by thermal buoyancy force induced by heated building surfaces are examined by CFD model using SST k - ω turbulence model for different urban skyline configurations. Pollutants emitted from the bottom of street canyon roughly mimic the traffic exhaust releasing. Numerical results are validated well with former theoretical results on thermal boundary flow adjacent to a heated vertical wall. The air exchange rate per hour (ACH) and pollutant retention time are adopted to evaluate the canyon ventilation performance. An exponential relationship could be established between the pollutant retention time and the thermal boundary flow rate. A semi-empirical formula is proposed by using the theoretical results of thermal boundary layer and two empirical constants derived from the present simulation results, which could be used to evaluate the ventilation performance at the urban design. As the convergence flow at the street canyon roof decays from urban rim to urban center, the pollutant retention time differs from canyon to canyon. The " protuberant " skyline configuration is found more effectively in purifying the street canyons at urban edge, in contrast, the " concave " skyline configuration shows higher purification efficiency at urban center. Present research could benefit for design purpose and environmental impact assessment. Highlights • Canyon dispersion was modelled under the regime of pure buoyancy driven flows. • Theoretical evaluation on the air exchange rate at canyon roof was presented. • Air exchange rates were of linear relationships with thermal boundary flow rates. • Thermal plume merging was a key pattern for near-ground level pollutant dilution. • Pollutant retention time reduces exponentially with the increase of boundary flow rate. [ABSTRACT FROM AUTHOR]

In urban areas, especially in valleys, challenges from heat and pollution are common. The situation worsens due to temperature inversions, where warm air traps pollutants. A new study employed multi-scale computational fluid dynamics (CFD) to assess ventilation in valley cities, specifically during temperature inversions and calm winds. Parameters like air change rate (ACH), local mean age of air (LMAA), and purging flow rate (PFR) were used to gauge street canyon ventilation efficiency. Factors such as atmospheric stability, city-slope positioning, and surface materials are altered to analyze impacts on urban heat island (UHI) intensity and air quality. Results indicated that katabatic winds had varied effects on pollution in different city regions, influenced by atmospheric conditions. Higher temperature lapse rates led to enhanced pollutant removal near slopes due to vortex interactions, but distant regions experienced thicker inversion layers, limiting pollutant dispersion. Conversely, anabatic winds improved ventilation with distance. Under inversion conditions, slope-city distance and surface materials played roles. For katabatic winds, city positioning significantly reduced UHI intensity, lowering LMAA by around 440s. Anabatic winds' UHI impacts ranked as atmospheric conditions, city location, and surface materials. A neutral atmosphere reduced UHI by 4.5K, but increased distance between city and slopes strengthened UHI by 4.04K. Ventilation efficiency was mainly tied to atmospheric conditions, while city location impacted pollution mitigation. This research aids in understanding air quality and airflow patterns during extreme weather events, aiding urban canyon design in valleys, especially with recurring heatwaves. In urban areas located within valley region, thermal and pollutant islands could become worsen due to temperature inversions, and even warm air traps pollutants. A multi-scale computational fluid dynamics (CFD) code was adopted to evaluate the ventilation in valley cities, specifically during temperature inversions and calm winds. Parameters like air change rate (ACH), local mean age of air (LMAA), and purging flow rate (PFR) were used to gauge street canyon ventilation efficiency. Factors such as atmospheric stability, city-slope positioning, and surface materials are altered to analyze impacts on urban heat island (UHI) intensity and air quality. [Display omitted] • Urban flows, slope dynamics, and ranked factors affect valley city's heat island and air quality. • Diode promoting/inhibiting effects of slope winds on pollutant emissions are observed for valley city. • For katabatic winds, the dominant factors are city position, temperature lapse rate. • For anabatic wind, underlying surfaces material will play an important role. • The adaptation of valley city in extreme weather could be enhanced in the future. [ABSTRACT FROM AUTHOR]

Achieving a healthy and comfortable indoor air environment has long been an objective of human endeavors. For a novel ventilation system, the wall-attached multidirectional jet pattern, the mathematical model describing the jet trajectory, temperature and velocity changes was first proposed to predict airflow attachment and separation moments from walls, covering a densimetric Froude number range from 0.5 to 4.0. Subsequently, this mathematical model was solved using a comprehensive numerical methodology and validated by full-scale experiments, which demonstrated that this established model could accurately depict the wall-attached multidirectional jet flow, with controllable errors — 16.4% for jet trajectory and 8.2% errors for jet axis temperature — when maintaining a supply velocity of 0.2 m/s. Also, the flow characteristics within a room featuring internal heat sources were analyzed, varying air supply velocities from 0.1 to 0.8 m/s and jet angles from 0° to 60°. Finally, this flow pattern of the wall-attached multidirectional jet was further confirmed and reproduced through CFD modelling which illustrated temperature stratification ranging from 18.1 °C to 25.2 °C, similar to the pattern observed in displacement ventilation. Present research could be valuable for the development of wall-attached multidirectional jet and the establishment of a healthy indoor air environment in practical applications. • A novel air supply pattern, the wall attached multidirectional jet, was proposed. • The mathematical model describing a novel ventilation pattern was formulated. • The novel ventilation pattern was confirmed by full scale experimental rig system. • Present novel ventilation pattern was fully favored for virus transmission control. • Novel jet flows can create healthy and comfortable indoor air patterns. [ABSTRACT FROM AUTHOR]

During the sunny days with very weak wind, thermal buoyancy forces will play a crucial role in the airflow and urban thermal environment. The merging effect of urban building plumes is particularly investigated by the use of unsteady Reynolds-averaged Navier Stokes (URANS) methodology. After testing against benchmark theoretical results, the SST k - ω model showing better performance in capturing the near wall processes and it was adopted to simulate the urban turbulent flows. The airflow patterns and temperature fields are analyzed for seven urban sizes ranging from 3 to 10 rows of buildings and six aspect ratios ranging from 0.5 to 3.0. The merging of thermal plumes induces a horizontal convergence flow, resulting in stagnant region at the urban center. A typical urban heat island temperature distribution with a peak value at the urban center is then found. Additionally, with the increase of urban size, the averaged velocity with the canyon decreases and averaged temperature increases. The average velocity within the street canyon decreases monotonously and the vortices number increases with the aspect ratio (building height H to the street width W ). The average temperature also increases with aspect ratio, except when the aspect ratio increases from 2.0 to 2.5, where the flow structure within the street canyon changes from a three vortices structure into a four vortices structure. This research could provide a new idea about how urban heat island is formed and the relation between its intensity with urban size and geometry. [ABSTRACT FROM AUTHOR]

The opening location plays an important role of buildings’ environment and natural ventilation effectiveness. Present research investigated three categories of ventilation configurations: single-sided ventilation with an opening on the windward wall; single-sided ventilation with an opening on the leeward wall and cross ventilation with two openings. The velocity distribution and pressure distribution as well as the pressure coefficient are presented to analyze the representative fluid dynamic characteristics of these three configurations. Numerical results indicate that cross ventilation could achieve the best ventilation performance, and the situation for opening on the leeward wall is better than that on the windward wall. According to these results, the study gives some guidance for building design on natural ventilation and provides some useful ideas as well as approach and methodology for the development of energy-efficient buildings. [ABSTRACT FROM AUTHOR]

With the increasing refrigeration demand in medical field, a portable and non-toxic refrigeration box is proposed and developed in the present work. Regarding of operating stability and size minimization, thermoelectric cooler (TEC) does well in it compared with traditional cooler devices such as compressors and heat pipes. This paper aimed at obtaining the optimal cooling performance of the thermoelectric refrigeration box system. Three groups of experiments comprised of 17 working conditions were conducted, depending on the full scale experiments. The temperature of hot and cold sides, internal temperature of the refrigeration box, refrigeration capacity and coefficient of performance were investigated, concerning on the influences of the voltages on the TEC. Furthermore, theoretical analysis was developed to demonstrate there exists an appropriate electrical voltage range for the semiconductors, hot side fans and cold side fans, where cooling capacity and COP (coefficient and performance) could reach their optimal values. Afterwards, experimental system has sound operating status. Optimal performance of TEC will be enhanced further by our detailed numerical and experimental investigations. [ABSTRACT FROM AUTHOR]

A comprehensive investigation and review about the free vent boundary conditions are conducted regarding of natural convections inside an open cavity with one side horizontal opening, aiming to abandon the extended computational domain through imposing suitable pressure and momentum boundary conditions on the free ventilated ports. The main differences among Type A , Type C and Type D BCs are the definitions and assumptions on the free port boundary pressures. The physical governing equations for the present investigation are solved numerically for a wide range of thermal Rayleigh number and enclosure aspect ratio to identify the applicability of the four categories of free port boundary conditions. The simulation results show that, with the flow intensity increasing in the region near free opening, Type D BCs , Type C BCs and Type A BCs would take turns being the most effective and suitable BCs to achieve the flow solutions approaching to the reference ones. Regarding of the computational stability, authors-proposed free vent port boundary conditions ( Type D BCs ) achieve the best performance. In addition, it is found that enclosure ventilation rate is a more suitable and convincing criterion than heat transfer rate to validate the accuracy of the numerical methods. [ABSTRACT FROM AUTHOR]

• Wind decay and pollutant purification were simultaneously caused by roadside trees. • Ventilation in the street canyons was complicated by the non-uniform buildings and trees. • Pollution spread and reduction was altered by the joint effects of vegetation and buildings. • Ventilation exchange and pollutant dispersion in the street canyons have been evaluated. • Delicate Modelling research could benefit the guidelines and planting of roadside trees. A refined CFD research was reported, concerning on the individual characteristics of different roadside tree planting and street canyon with non-uniformity of buildings. In this work, airflow field and pollutant dispersion were simulated by the use of a full three-dimensional simulations. Ventilation air exchange rate (ACH) and net escape velocity (NEV) were, respectively applied to assess ventilation exchange and pollutant dispersion in the street canyons. Numerical results show that the airflow patterns within the street canyon varies significantly with canopy leaf area density (LAD) and trunk height (Htb), whereas the distribution of pollutants at pedestrian level in the street canyon is mainly determined by the symmetrical inverse vortex structure of the street canyon. Promotions of LAD and Htb of the road trees simultaneously reduce the wind velocity, ACH and NEV of the street canyon, deteriorating the ventilation exchange conditions as well as the pollutant dispersion performance. As the value of the Htb becomes larger, NEV of the step-up canyon is approximately approaching to that of the step-down canyon. In addition, as the value of standard deviation (σ H) of the street canyon increases, the vortex structure of the canyon disappears and promotes the diffusion of pollutants inside canyons. As σ H further increases, ACH of the step-down canyon also boosts, indicating better ventilation performance of street canyon, whereas the step-up canyon only tops the best ventilation performance at the value of σ H = 33.3%. The best dispersion of pollutants is observed at σ H = 16.7% in the step-down canyon while in the step-up canyon the dispersion of pollutants becomes better continuously with increasing σ H. In particular, as σ H = 66.7% was maintained, the dispersion of pollutants is better in the step-up canyon compared to the street canyon without trees. At the same time, the difference between the NEV of the step-down canyon and the step-up canyon increases as σ H increases, which indicates that the difference in pollutant dispersion performance between adjacent street canyons becomes greater. This research provides a theoretical reference for urban design and vegetation planning in urban areas to improve the habitat. [ABSTRACT FROM AUTHOR]

A multi-objective optimization based on thermoelectric heat exchanger module (TEHEM) is presented for application in CPU cooler. The thermoelectric heat exchanger module coupling multi-parameters is used as a novel method to solve the heat dissipation. Assuming that thermal-power consumption and physical properties of thermoelectric material are known, the optimal operating conditions covering with working current and hot-side thermal resistance are derived analytically from previous module. By combining the surface temperature of CPU and input power with a weight factor as the multi-objective function, the optimization is again implemented. Simultaneously, the multi-objective optimization is compared with the surface temperature of CPU and input power as the single-objective function. Finally, the optimal conditions are investigated to get a balance between the surface temperature and the input power. The simulation results show the optimal variables for single objective function are not suitable multi objective function sometimes. It is indispensable to consider the relative importance of objective values when it comes to practical demand. In addition, the optimal operating conditions depend on intensities of these operating parameters. [ABSTRACT FROM AUTHOR]

The definition and governing equation of probability density function (PDF) have been implemented in the present work. The procedure is applied to the backward time identification of the pollutant probability density function history and finally the maximal probability density of airborne pollutant source location in a two-dimensional slot ventilated building enclosure contained with two solid blocks. Steady-state airflow field, sensor location, boundary conditions, thermo-physical properties and geometric characteristics should be known in prior. Spatial probability density function history has been computed under four ventilation modes, i.e., mixed ventilation (MV), displacement ventilation (DV), mixed ventilation with top ceiling outlet (MVS), and displacement ventilation with left side outlet (DVS). Effects of pollutant source location and alarming sensor on the accuracy of the probability density function have been disclosed. The pollutant sources will be more easily identified for the concentrated pollutant strips, where pollutant diffusion is efficient compared with the pollutant source at outlet. Particularly, the good agreement of the probability density function identified source location with the true situation fully shows that adjoint probability density function method is more competitive in the engineering applications involving with complicated convective fluid flows. [ABSTRACT FROM AUTHOR]

In the present work, an open-type thermoelectric heating system with multiple channels was developed. A mathematical model of heat transfer, based on one-dimensional treatment of thermal and electric power, is conducted. The heating coefficient and production are both correlated in terms of temperature difference, thermal conductivity, electric resistance and electric current. The looped air circulation was designed to simultaneously recycle heat and enhance heater system performance. Experimental investigations were conducted to identify thermal performance of the thermoelectric heater. Effects of airflow rates through the heating side and cooling side, temperatures of heating side and cooling side on the performance were investigated. The heating coefficient was calculated upon that surface temperatures of hot and cold sides were recorded. The results show that the average heating coefficient of the thermoelectric heating system could reach to 1.3, which is greater than that of a typical electric heater with heating coefficient of less than one. The optimal isolation thickness for this thermoelectric heater, i.e., 14 mm, is confirmed by the experimental rig system. Generally, heating coefficient was found to increase first and decrease afterwards when the current was continuously increasing. Analytical and experimental results demonstrate that the optimum performance of the thermoelectric heat recovery heater strongly depends on the intensities of these operating parameters. [ABSTRACT FROM AUTHOR]

Decreasing the building energy consumption and improving thermal comfort through optimization of heating, ventilation and air conditioning (HVAC) control systems are becoming increasingly significant due to global energy crisis, carbon emission and requirement of high life quality for people. Therefore, evaluation on building energy efficiency and human thermal comfort is extremely necessary. In the present work, energy conservation performance of one passive school building and classroom thermal comfort enhancement will be simultaneously investigated. Energy performance of single reference classroom under six design points and whole school building with two scenarios have been numerically investigated concerning the effects of different indoor set-point temperatures, pre-ventilation, sun-shading system, and the efficiency of the heat recovery facility. Numerical results demonstrate that heating and cooling demands heavily depend on indoor set-point temperature, occupancy and heat recovery rate. Building energy performance analysis illuminates that the optimized control systems for HVAC and sun-shading systems show an expectedly energy efficient performance. In addition, classroom thermal comfort indicated by the recommended thermal range and comfort zone has been numerically and experimentally presented. [ABSTRACT FROM AUTHOR]

In the present study, a thermoelectric mini cooler coupling with a micro thermosiphon cooling system has been proposed for the purpose of CPU cooling. A mathematical model of heat transfer, depending on one-dimensional treatment of thermal and electric power, is firstly established for the thermoelectric module. Analytical results demonstrate the relationship between the maximal COP (Coefficient of Performance) and Q c with the figure of merit. Full-scale experiments have been conducted to investigate the effect of thermoelectric operating voltage, power input of heat source, and thermoelectric module number on the performance of the cooling system. Experimental results indicated that the cooling production increases with promotion of thermoelectric operating voltage. Surface temperature of CPU heat source linearly increases with increasing of power input, and its maximum value reached 70 °C as the prototype CPU power input was equivalent to 84 W. Insulation between air and heat source surface can prevent the condensate water due to low surface temperature. In addition, thermal performance of this cooling system could be enhanced when the total dimension of thermoelectric module matched well with the dimension of CPU. This research could benefit the design of thermal dissipation of electronic chips and CPU units. [ABSTRACT FROM AUTHOR]

Periodic vortex shedding from the building can induce pumping ventilation (PV) and promote the ventilation rate of single-sided ventilation with well-arranged open windows. The present study aims to investigate the influence of sheltering conditions (presence of upwind and/or downwind buildings) on pumping ventilation using wind tunnel experiments. Different building gap aspect ratios and sheltering conditions were considered as main influencing factors. The mean streamwise velocity and velocity fluctuation around the target building were measured. The oscillation frequency of pumping ventilation was obtained from the time history of window center velocity. The effective ventilation rate was utilized to quantify the ventilation effectiveness of pumping ventilation through constant-injection tracer gas method. The experimental results show that the influence of upwind building on the mean velocity and velocity fluctuation are much more significant than that of downwind building. The presence of upwind or downwind building can reduce the pumping ventilation frequency compared with the isolated case. The downwind building has larger reduction effect on PV frequency of the target building compared with the upwind building. Increase of gap aspect ratio could linearly promote the PV frequency. Sheltering could promote the effective ventilation rate of pumping ventilation compared with the isolated case and the ventilation rate could be overall the highest when sheltered by both upwind and downwind building. Upwind building has much larger effect on the concentration fluctuation inside the target building than downwind building. The findings of this study may help to better understand pumping ventilation mechanism in urban areas. • Wind tunnel experiments on pumping ventilation were conducted with reduced scale models. • The influence of upwind building on the velocity was more significant than downwind building. • Downwind building had larger reduction effect on PV frequency than upwind building. • Sheltering promoted the ventilation rate of pumping ventilation compared with isolated one. • This study may help to understand pumping ventilation mechanism in urban areas. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat recovery facility operating with heat pump unit and mechanical ventilation system. [•] School building energy and classroom environment jointly solved by theory and CFD. [•] Classroom thermal comfort and IAQ influenced by the heat recovery ventilation. [•] Heat pump energy conservation correlated by heat recovery efficiency and indoor/outdoor air. [•] Classroom environment and school energy simultaneously achieved by the heat recovery ventilation. [Copyright &y& Elsevier]

Abstract: The recently-built school buildings have adopted novel heat recovery ventilator and air conditioning system. Heat recovery efficiency of the heat recovery facility and energy conservation ratio of the air conditioning unit were analytically modeled, taking the ventilation networks into account. Following that, school classroom displacement ventilation and its thermal stratification and indoor air quality indicated by the CO2 concentration have been numerically modeled concerning the effects of delivering ventilation flow rate and supplying air temperature. Numerical results indicate that the promotion of mechanical ventilation rate can simultaneously boost the dilution of indoor air pollutants and the non-uniformity of indoor thermal and pollutant distributions. Subsequent energy performance analysis demonstrates that classroom energy demands for ventilation and cooling could be reduced with the promotion of heat recovery efficiency of the ventilation facility, and the energy conservation ratio of the air conditioning unit decreases with the increasing temperatures of supplying air. Fitting correlations of heat recovery ventilation and cooling energy conservation have been presented. [Copyright &y& Elsevier]

Natural ventilation nowadays has been paid great concerns due to its zero carbon emission and good performance on the human health. In engineering applications, cross ventilation driven by winds has been frequently restricted in building clustered cities. Instead, single-sided natural ventilation becomes an alternative mode in wind driven natural ventilation strategies for clustered urban buildings. This research has reviewed the former published researches on single-sided natural ventilation in terms of the classification, features, influence factors, investigation methodologies and evaluation indices/parameters. Existing researches on a novel ventilation mechanism of single-sided natural ventilation—"pumping ventilation" have been comprehensively reviewed, which could be a promising ventilation strategy of single-sided natural ventilation. This critical review demonstrates that single-sided ventilation has raised increasing concerns of researchers. In current and future investigations, different methodologies and other advanced technologies should be coupled together to promote the predicting capability of single-sided ventilation. This review could facilitate the fundamental researches and engineering applications of natural ventilation in modern urban buildings. [ABSTRACT FROM AUTHOR]

• Modern cities could be vulnerable to radionuclides and other airborne pollutants;. • Urban ventilation capacity could be reduced or enhanced by the urban skylines;. • Increase of inhomogeneity of adjacent buildings reduced the age of air in the canyons;. • Retention became longer in well-ventilated regions, and it shrank in poorly-ventilated regions;. • Built array morphology essentially affects the dispersion of radionuclides in urban blocks. In the present work, a parametric CFD research of an urban block model was conducted to investigate the effects of street aspect ratio and urban skyline on their ventilation and radionuclide dispersion within such urban blocks. Representative ventilation indicators, including velocity ratio (V R), age of air (τ P), retention time (τ c) and atmospheric dispersion factor (A D F), were introduced here to evaluate urban blocks ventilation and radionuclide dispersion. Our numerical results indicated that the street aspect ratio has a dominant impact on the air age of the main street canyons. The age of air in the canyon increased with the expansion of its street aspect ratio. When remarkable downwash and weak wind regions were observed around the higher buildings, the age of air on the windward side of a higher building became small, whereas it prolonged on the leeward side. Similarly, canyon retention time increased positively with the street aspect ratio. There was also a longer canyon retention time on the windward side of higher buildings. Reversely, short canyon retention time was found on the leeward side. Additionally, mechanical disturbance of buildings and the rugged underlying surface primarily influence the radionuclides dispersion in the urban region, whereas wind wake flows heavily affect the radionuclides dispersion in the downstream of urban blocks. This research has provided a theoretical reference for the ventilation and far-field pollutant dispersion in urban blocks located near mining or industrial areas. [ABSTRACT FROM AUTHOR]

Abstract: The backward time modeling of diffusion–convection pollutant dispersions has been developed with quasi-reversibility method in this work. The procedure is applied to the backward time identification of the contaminant release history and source location in a three-dimensional slot ventilated building enclosure. Spatial distributions of pollutant concentrations are known in priori. The effects of supplying air velocity, pollutant source location, pollutant diffusivity property, and pollutant release time on the accuracy of the pollutant dispersion history recovery have been investigated. Numerical results demonstrate that the accuracy of the pollutant dispersion history recovery can be enhanced with different approaches and measures, including the promotion of room ventilation rate, the shrinkage of distance between the pollutant source and supplying air port, and the reduction of pollutant diffusivity. The facilitated implementations of boundary conditions and the improved generality of quasi-reversibility methods make the pollutant source history identifications of less computational efforts. Particularly, the good agreement of the backward time identified source location with the true situation fully shows that quasi-reversibility method is more competitive in the engineering applications involving with convective fluid flows. [Copyright &y& Elsevier]

Abstract: Combined natural convective heat and moisture transports in a moist-air-filled enclosure with four free vent ports are numerically investigated. Four situations of ambient air states, hot and humid (I), hot and arid (II), cold and arid (III), and cold and humid (IV), are taken into consideration. Convective transports of semi-enclosed air, heat and moisture are respectively analyzed using the contours of streamfunction, heatfunction and massfunction, in addition to the isotherms and iso-concentrations. Overall convective heat transfer rate (Nu) and moisture transfer rate (Sh) of the internal concentrated heat and moisture source have been correlated with the thermal Rayleigh number respectively within the domain of the heat transfer driven flows and that of moisture transfer driven flows. When different initial convective flow conditions were imposed in the cases (I) and (IV), dual steady flow states of semi-enclosed heat and moisture convection are observed, and heat and moisture transport potentials can be enhanced or inhibited depending on the flow solution branches. These results can be adopted to guide the design of natural ventilation in the humid regions. [Copyright &y& Elsevier]

Abstract: Slot ventilated enclosure flows have been simulated, respectively in displacement ventilation and mixed ventilation covering from the forced convection dominated flow to the natural convection dominated flow. Direct convection simulation together with the turbulent streamlines and turbulent heatlines demonstrate that the enclosure flow pattern, indoor thermal level and heat transfer potential will depend on the interactions of external forced flow and thermal buoyancy driven flows, i.e., Reynolds number and Grashof number. In subsequent inverse convection modeling, the inverse determination of enclosure wall heat flux profiles was conducted by the use of adjoint methodology, in which the direct, sensitivity and adjoint problems are formulated and solved by finite volume method. The effects of the supplying air flow rate, thermal source strength, ventilation mode, flux functional forms, and the measurement errors on the accuracy of inverse turbulent convection estimation have been investigated. The inverse solutions of turbulent convections are of low level accuracy as the flow becomes thermal-driven turbulent flows, and they deteriorate as the noise levels increase. This work is of fundamental importance for the room air flow design and measurements involving the turbulent thermal convections. [Copyright &y& Elsevier]

Abstract: Modeling on indoor air quality is performed considering the effect of a new window-type air conditioner, which is a promising way toward compromising energy consumption and residential air environment. Sensitivity analysis of the actual operating situations has been implemented, including the total fresh air supply and the full room air recirculation. The effects of supplying air flow rate, pollutant filtration efficiency, and indoor thermal buoyancy on the airborne pollutant transports are also illustrated. The numerical results demonstrate that the reduction of indoor pollutant levels can be accomplished either by increasing the fresh air ratio, or by increasing filtered removal efficiency, or by increasing the supplying airflow rate, or by decreasing the strength of indoor heating source. The indoor contaminant concentration asymptotically approaches to a small value for the situation of full fresh air supply, which agrees well with the analytical solutions of indoor contaminant concentration under the extreme operations. [Copyright &y& Elsevier]

Abstract: To protect any person from exposure to the toxic and cancerous particles, welding fumes should be removed from region of respiration. In the present work, displacement ventilation system has been established within a high rise-welding hall, where welding processes cause very high welding fume emissions which flow in a thermal up-current from above the welding point to the ceiling. Numerical simulations on the air flow, thermal flow and pollutants have been conducted, showing that displacement ventilation can effectively remove the airborne pollutants from the respiration region and produce the suitable thermal stratification within the large scale industrial building space. Additionally, the personalized ventilation unit is adopted to deliver fresh air to the breathing zone. The spatial distribution of airborne pollutants is affected by the altitude of personalized ventilation annulus, which is numerically investigated to enhance the overall performance of the displacement ventilation and personalized ventilation units. Finally, on site measurements presented in this paper demonstrate the above mentioned numerical investigations. This research will be significant for the ventilation in high rise industrial buildings. [Copyright &y& Elsevier]

Abstract: Thermal transport and transient dispersion of pollutants emitted from two discrete strips within the displacement ventilation enclosure have been modeled numerically. Following the full numerical simulation of turbulent air flows, the inverse determinations of multiple pollutant sources were conducted by the use of quasi reversibility methodology. Direct simulation together with the turbulent streamlines and turbulent heatlines demonstrate that the enclosure flow pattern, enclosure air thermal level and heat transfer potential will depend on the interactions of external forced flow and thermal buoyancy driven flows, i.e., Reynolds number (2×103 ⩽ Re ⩽104) and Grashof number (106 ⩽ Gr ⩽1010). In subsequent forward time and backward time modeling of airborne pollutant transports, temporal evolutions of enclosure average concentration and pollutant exhaust are shown to depend on the supplying velocity (Re), thermal plume (Gr), pollutant diffusivity (0.1⩽ Sc ⩽2), and the pitch between both sources (0.2H ⩽ dPSL = dPSR ⩽0.7H). Reverse time modeling of airborne spread has demonstrated that increasing the spread rate and the concentration sensitivity of airborne pollutants will facilitate the identification of pollutant sources. [Copyright &y& Elsevier]

Abstract: Simultaneous transport of heat and moisture by conjugate natural convection in a partial enclosure with a solid wall is investigated numerically. Moist air motions are driven by the external temperature and concentration differences imposed across enclosures with different ambient moisture conditions. The Prandtl number and Schmidt number used are 0.7 and 0.6, respectively. The fluid, heat and moisture transports through the cavity and solid wall are, respectively, analyzed using the streamlines, heatlines and masslines, and the heat and mass transfer potentials are also explained by the variations of overall Nusselt and Sherwood numbers. The numerical simulations presented here span a wide range of the main parameters (heat and mass diffusion coefficient ratios, solid wall thickness and thermal Rayleigh numbers) in the domain of aiding and opposing buoyancy-driven flows. It is shown that the heat transfer potential, mass transfer potential, and volume flow rate can be promoted or inhibited, depending strongly on the wall materials and size, thermal and moisture Rayleigh numbers. [Copyright &y& Elsevier]

Abstract: With environmental protection and energy source posing as the biggest issue of the global problems, human beings have no choice but to reduce energy consumption. One way to accomplish this is to increase the efficiency of energy consumption and sufficiently exploit the low-grade energy in our lives. Low-grade energy recovery devices are of significance to meet the needs for energy conservation and green environment requirements such as fresh air pre cooling/heating, water heating, drying clothes and humidifying. These devices are also free of motion parts, non-corrosive and environmentally friendly. Various low-grade energy recoveries powered cooling, heating, drying and dehumidifying systems have been tested extensively; however, these systems are not yet ready to compete with the well-known vapor-compression system. The objective of this paper is to provide fundamental knowledge on the low-grade energy usage systems and present a detailed review on the past efforts in the field of low-grade energy recovery and usage subsystems. Lots of attempts have been made by the researchers to improve the performance of the low-grade energy recovery or usage subsystems. It is seen that, for successful operation of such systems, combination of diverse technologies is essential for more effective and multi-purpose applications. [Copyright &y& Elsevier]

Abstract: A numerical implementation of estimating boundary heat fluxes in enclosures is proposed in the present work. Particularly, the flow field is dynamically coupled with the heat convection in the fluid and the heat conduction in the solid domain. An iterative conjugate gradient method is applied such that the gradient of the cost function is introduced when the appropriate sensitivity and adjoint problems are defined. In this approach, no a priori information is needed about the unknown function to be determined. Numerical solutions are obtained for the case of a square enclosure centrally-inserted with a solid block and subjected to an unknown heat flux on one side and to known conditions on the remaining sides. Fluid and heat transports are visualized by the streamlines and heatlines respectively, which are evidently affected by the thermal Rayleigh number, solid body size and thermal conductivity of solid phase, and the functional form of the imposed heat flux. The accuracy of the heat flux profile estimations is shown to depend strongly on the thermal Rayleigh number, body size and relative thermal conductivity of the solid material. Effects of functional form of the unknowns, sensors number and position, and measurement errors on the accuracy of estimation are also investigated. The present work is significant for the flow control simultaneously involving the heat conduction and convection. [Copyright &y& Elsevier]

Abstract: This study aims to investigate multiple flow structures in a three-dimensional chamber with opposed jets. Numerical computations focus on the effect of inlet velocity on the air flow pattern, especially on multiple steady flow characteristics for Reynolds maintaining 105. Three distinct branches of steady-state flows are found for this configuration. A complete study of stability of each branch is performed for varying velocity of the left inlet continuously between 0 and 3. The results are presented by stability diagrams showing the critical parameters corresponding to transition from one steady-state branch to the other state within multiple flow range. In parallel with numerical development, an experimental system was set up where adjustable flow rate was prescribed to produce variation of supplying jets. The corresponding vector flow fields, on a scale model, were measured by a laser-based particle image velocimetry (PIV) system. The multiple flow structures were validated both by numerical simulation and experimental investigation. [Copyright &y& Elsevier]

Abstract: The numerical study presented in this work describes the direct and inverse mixed convection problems in a slot-ventilated enclosure subjected to an unknown heat flux on one side. Particularly, the interaction of internal natural convection with the cold ventilated flow leads to various flow fields depending on the Richardson number, Reynolds number, and the functional form of the imposed boundary heat flux. Fluid and heat transport structures across the enclosure are visualized by the streamlines and heatlines, respectively. Subsequently, an iterative conjugate gradient method is applied such that the gradient of the cost function is introduced when the appropriate sensitivity and adjoint problems are defined for a domain of arbitrary geometries. In this approach, no a priori information is needed about the unknown boundary heat fluxes to be determined. The accuracy of the heat flux profile solutions is shown to depend strongly on the values of Reynolds number and flux functional forms. Effects of measurement errors on the accuracy of estimation are also investigated. The present work is significant for the flow control simultaneously involving the natural convection and forced convection. [Copyright &y& Elsevier]

Abstract: The inverse natural convection problem of estimating the heat source profiles in a porous enclosure is proposed in the present work. The physical model for the momentum conservation equation makes use of the Darcy–Brinkman equation, which allows the no-slip boundary condition on a solid wall to be satisfied. An iterative Fletcher–Reeves conjugate gradient method is applied such that the gradient of the cost function is introduced when the appropriate sensitivity and adjoint problems are defined. Particularly, the pressure-based SIMPLE algorithm is adopted to solve the continuum direct, sensitivity and adjoint problems in unification. Effects of thermal Rayleigh number, Darcy number, heat flux profiles, sensor locations and quantity on the accuracy of inverse solutions are investigated with or without the measurement errors. Additionally, the fluid and heat transport structures in the uniform porous layer are analyzed using the streamlines and heatlines, and the heat transfer potential is also explained by the variation of overall Nusselt number. Noise data solutions are regularized by stopping the iterations with the discrepancy principle of Alifanov, before the high frequency components of the random noises are reproduced. The present method solves inverse strong convection problem satisfactorily without any a priori information about the unknown heat flux to be estimated. [Copyright &y& Elsevier]

• Green roof influenced on the outdoor thermal buoyancy flow distributions in a wide range of H/W. • Aiding and opposing effects were observed as wind and thermal buoyancy simultaneously acted. • A "free air flow region" arose when the leeward green roof deployment was adopted. • Lateral deployment of green roof system performed better than that of rooftop deployment. • Rational design of the green roof system could enhance its cooling capacity. The "thermal effect" of the green roof system on the pollutant dilution process would be analyzed in this research. Different arrangement schemes (on the rooftop, windward side and leeward side) of the green roof system would alter the thermal buoyancy distribution in the street canyon, thus change the overall flow field and pollutant dilution condition Computational Fluid Dynamics (CFD) technique along with the Renormalization Group (RNG) k-ε turbulence model has been adopted for the simulation work. Cases without the green roof system are assumed to be uniformly heated and are prepared for benchmark comparisons. Six aspect ratios (H/W) and ten ranks of unstable thermal stratifications (Rb) are selected to consider the influence of street canyon morphology and thermal buoyancy. Results demonstrate that the lateral deployment of green roof system performs better than the rooftop deployment and the situations without green roof system. In the windward cooling cases, a single vortex is formed in the canyon center and dramatically reduces the pollutant retention time τ when H/W > 1, while in the leeward cooling cases, a "free airflow" region is formed in all the tested aspect ratios expect for H/W = 0.5. The rooftop deployment scheme has negative effects, not just decaying ventilation performance, but also delaying pollutant dispersion period. Present research could benefit the rational design of the green roof system in the urban building clusters, and further enhance its cooling capacity for the built energy conservation. [ABSTRACT FROM AUTHOR]

Abstract: Present work numerically investigates three-dimensional non-linear aerodynamic structures of airflow in a slot-ventilated compartment with three ports. A numerical code based on Reynolds average Navier–Stokes equations and Reynolds stress turbulence model was validated, and successfully conducted for simulating the airflow in the studied room. Numerical results are particularly presented to illustrate the effects of the inlet airflow velocity, enclosure width, supplying ports elevation and Reynolds number on the multiple flow patterns and the associated ventilation flow rate and blowing-axial momentum decay for equal-magnitude opposite jet flows. It is shown that the room airflow rate and the shift of jet flow interface can be promoted or inhibited, depending strongly on the jet velocity, enclosure width and elevation of supplying ports. [Copyright &y& Elsevier]

Abstract: Two-dimensional, double diffusion, natural convection in a rectangular enclosure filled with binary fluid saturating porous media is investigated numerically. Multiple motions are driven by the external temperature and concentration differences imposed across horizontal walls with the simultaneous presence of discrete heat and contaminant sources. The general Brinkman-extended Darcy model is adopted to formulate the fluid flow in the cavity. The fluid, heat and moisture transport through the isotropic porous layer are analyzed using the streamlines, heatlines and masslines, and the heat and mass transfer potentials are also explained by the variations of overall Nusselt and Sherwood numbers. The numerical simulations presented here span a wide range of the main parameters (thermal Rayleigh numbers, strip pitches and Darcy number) in the domain of destabilizing solutal buoyancy forces. It is shown that the heat and mass transfer potential can be promoted or inhibited, depending strongly on the permeability of porous medium, the strip pitch, the thermal and solutal Rayleigh numbers. [Copyright &y& Elsevier]

Abstract: This paper reports a numerical study of double-diffusive convective flow of a binary mixture in a porous enclosure subject to localized heating and salting from one side. The physical model for the momentum conservation equation makes use of the Darcy–Brinkman equation, which allows the no-slip boundary condition on a solid wall to be satisfied. The set of coupled equations is solved using the SIMPLE algorithm. An extensive series of numerical simulations is conducted in the range of , , and , where N, Le, Da and L are the buoyancy ratio, Lewis number, Darcy number and the segment location. Results for a pure viscous fluid and a Darcy (densely packed) porous medium emerge from the present model as limiting cases. Streamlines, heatlines, masslines, isotherms and iso-concentrations are produced for several segment locations to illustrate the flow structure transition from solutal-dominated opposing to thermal dominated and solutal-dominated aiding flows, respectively. The segment location combining with Lewis number is found to influence the buoyancy ratio at which flow transition and flow reversal occurs. The computed overall Nusselt and Sherwood numbers provide guidance for locating the heating and salting segment. [Copyright &y& Elsevier]

Summary: The ability of near infrared spectroscopy (NIRS) to predict vascular compromise in vascular free flaps postoperatively has been assessed, and the extent of regional tissue oxygen saturation (rSO2) after fibular flap transplantation was investigated quantitatively. To validate the sensibility and precision of the technique, the following methods were used. (1) Forearm vessel obstructive tests were conducted in four healthy volunteers. (2) Measurement and analysis of bilateral rSO2 at the mandibular body and ramus were performed in 40 healthy volunteers by NIRS in the morning and afternoon. (3) Measurement and analysis of rSO2 in transplanted fibular flaps for 41 cases with mandibular reconstruction were performed by NIRS at postoperative days 1–6. The results were: NIRS had high sensibility and precision in monitoring rSO2 of living tissues. No significant difference in the values of rSO2 was found across different times or areas in the normal mandible. However, rSO2 in the transplanted fibular flaps was reduced compared to the value on the control side. rSO2 decreased gradually 4–12 hours postoperatively. After that period, rSO2 increased gradually and approached the value of the control side at 20h after the operation. It can be concluded that NIRS is a reliable noninvasive method for monitoring blood circulation in transplanted tissues, particularly for buried flaps. [Copyright &y& Elsevier]

Abstract: This paper reports the results of a numerical study on removal of two contaminants from a three-dimensional enclosure with one inlet, one exhausting port and one returning port. In the formation of the problem, use is made of Reynolds stress model (RSM). The governing equations are solved by means of the SIMPLE algorithm. Lots of cases have been studied for the sensitivity analysis, including more practical cases from the total fresh air supplying to the total recirculation situations. The influence of inlet velocity, fresh air ratio, recirculating air filtered removal efficiency and contaminant property is investigated. The indoor contaminant is studied parametrically as a function of governing dimensionless numbers (Reynolds number and Schmidt number). The results show the above parameters have complex influence to indoor contaminant removal. [Copyright &y& Elsevier]