Publications

Natural ventilation is considered the first suggestion for COVID-19 prevention in buildings by the World Health Organization (WHO). Solar chimney’s viability in aged care centers or similar facilities was analyzed numerically and theoretically. A new solar chimney design was proposed to reduce the cross-infection risk of COVID-19 based on an airflow path through window, ceiling vent, attic, and then chimney cavity. Solar chimney performance, quantified by the natural ventilation rate, presented power function with window area, ceiling vent area, cavity height, and solar radiation. The ceiling vent is suggested to be closer to the corridor to enhance the performance and ventilation coverage of the room. A cavity gap of 1.0 m is recommended to balance the ventilation performance and construction cost. A theoretical model was also developed for aged care centers with multiple rooms and a joint attic. Its predictions obey reasonably well with the numerical results. Solar chimney’s viability in aged care center is confirmed as a 7.22 air change per hour (ACH) ventilation can be achieved even under a low solar radiation intensity of 200 W/m2, where its performance fulfills the minimal ventilation requirement (i.e., 6 ACH) suggested by the WHO for airborne infection isolation rooms. This study offers a new design and a guideline for the future implementation of solar chimney in aged care centers or similar facilities.

A type of smart window using thermochromic glazing (TCG) is a promising technology for green buildings owing to the self-regulating feature and low-maintenance need. Its most important feature, thermo-optical properties that regulate the blockage of solar heat, is directly linked to the variation of surface temperatures. However, challenges from the inhomogeneity of thermo-optical properties, the coupled solar radiation and natural convection, and varying outdoor conditions all seriously hinder the understanding of its mechanism. In this paper, a validated Computational Fluid Dynamics (CFD) model achieves the simulation of inhomogeneous tinting of TCG by defining the thermo-optical properties of each finite volume according to the surface temperature. Solar radiation and natural convection at outdoor, indoor and the cavity are solved to reflect glazing temperature more accurately. The case studies compared six different switching temperatures in the range of 20 ∼ 42.5 °C with a transition gradient of 10 °C. Averaged meteorological data for both summer and winter, sunny days and cloudy days are selected to present realistic climate impacts. The result reveals the overall saving in transmitted solar radiation in summer and heating penalties in winter. It suggests the best switching temperatures for each climate condition. With the seasonal operation, the highest saving in solar heat gain is 20.9% when adopting a switching temperature of 25–35 °C, while the lowest saving can be negative, meaning TCG is not suitable for those climate zones. The proposed evaluation criteria help to quantify the applicability of TCG with the input of the summer/winter day ratio and sunny/cloudy ratio. The best region to apply TCG is where summer days are longer and winter solar radiation is significantly lower. The in-depth understanding of this temperature-sensitive process benefits the optimization of TCG in buildings, especially for its seasonal operation needs.

Although a combination of various (or types of) solar chimneys (SCs) can overcome the limitations of a solo system, the interactions, designing factors and overall performance in one building are still not known. Therefore, a combined wall and roof SCs were investigated both numerically and theoretically through this study. After being coupled with a roof SC, the performance of the wall SC is generally enhanced, which is quite stable when the designs of the roof solar chimney keep changing. The optimal designs of the wall SC are basically the same with those without coupling a roof SC. Furthermore, the window area shows an obvious impact on the roof SC but not the wall SC. Solar radiation offers an obviously positive effect on both the wall SC and the overall performance, while its impacts on the roof SC are relatively less obvious. The optimized design of the combined system can be achieved with specific designs, such as possibly big absorption walls for both chimneys, a big window, an appropriate level of cavity gap and air inlet height for the wall SC, a relatively small cavity gap for the roof SC, and a closer wall and roof SCs. A theoretical model is also developed to predict the airflow rates through both the wall and roof SCs. A coefficient, namely α, is proposed to describe the percentage of the airflow from the window to the wall SC. The predictions based on fixed α obey well with those numerical results.

High-performance silicon carbide (SiC) aerogels with excellent high-temperature resistance and high porosity are highly desirable in the fields of thermal insulation and adsorption. However, constructing a super-elastic SiC aerogel and controlling its properties is still a significant challenge. To better regulate its properties, it is necessary to clarify its reaction and growth mechanism. Here, we propose an in-situ reactive growth strategy to prepare super-elastic SiC aerogels. The obtained aerogels can withstand 80 % deformation and exhibit an ultra-low thermal conductivity of 0.024 W·m−1 K−1. Furthermore, the aerogel shows a superior electromagnetic wave (EMW) absorption performance with a minimum refection loss (RLmin) value of – 40.7 dB. More importantly, we reveal the mechanism of the reaction and growth of SiC crystal. The growth process of SiC crystal can be divided into three stages: pyrolysis, nucleation and growth. Based on understanding the growth mechanism, we can further regulate the structures of SiC crystals by controlling the sintering time, including sea urchin-like, nanorod-like, nanowire-like and slub-like shapes. This study provides a new idea for preparing super-elastic SiC aerogel and regulating its structure.

Solar chimneys as cost-effective renewable energy systems offer significant energy saving in buildings through the enhanced natural ventilation. Previous studies have focused on the fluid dynamics of the solar chimney itself. Still, few studies were found in the literature on its assessment on the energy performance in buildings, such as addressing how many percentages of energy can be saved based on it in buildings. This is mainly due to the relevant challenges of the assessment methods, such as absent functions, modeling accuracy, experimental validation, and the capability of addressing many influencing factors. To overcome the constraints, five typical energy assessment methods were critically reviewed through this review, including hydrostatic pressure, thermal network, zonal model, theoretical/empirical models, and computational fluid dynamics (CFD) modeling. This is the first review paper specified for the energy assessment methods of solar chimneys. The major influencing factors of solar chimney include configuration, installation conditions, material usage, and environment. The current energy assessments for solar chimneys are primarily based on the thermal network and zonal model (or the combination) but not CFD modeling. The current challenge for hydrostatic pressure analysis is its applications in multiple chambers, especially with those large openings (e.g., doors and windows). The thermal network could overcome this challenge, but its modeling accuracy and generality still require effort. Due to many influencing factors, a single assessment method may not be viable for practical implementation. Future research on energy assessment could be in several directions, such as a combined zonal and CFD modeling, the validity and uncertainty of those energy assessments in practical building applications, and detailed and comprehensive experimental tests for the validation.

The maximum gas temperature below the ceiling is an important parameter for tunnel safety. The present study analyzed the characteristics of the maximum excess ceiling gas temperature driven by double fire sources in a naturally ventilated tunnel. A series of reduced-scale tunnel fire experiments were carried out with different fire separation distances and heat release rates. Theoretical analysis based on the equivalent virtual origin was also undertaken. The results showed that there exists only one peak gas temperature when the two fire plumes are merged before reaching the ceiling, while two peak gas temperatures can be observed for when the two fire plumes are completely separated. The maximum excess gas temperature below the tunnel ceiling gradually decreases with an increasing fire separation distance in the plume merging region (S < Scp). When the fire separation distance increases further (S > Scp), the effect of the fire separation distance on the maximum gas temperature below the ceiling is very limited. Furthermore, a model using an equivalent fire source was proposed to predict the maximum excess gas temperature below the ceiling, considering different plume merging states. The present study benefits to the understanding of the maximum excess gas temperature characteristics of the smoke flow driven by double fires with an equal heat release rate in naturally ventilated tunnels.

Energy dissipation piers comprised of concrete filled steel tubular (CFST) columns and steel shear links can exhibit good seismic performance by reasonable collaborative optimization design of columns and links. Considering the time and economic costs of experiments and fine element analysis (FEA), an efficient and accurate numerical model is critical to investigate the hysteretic behavior of energy dissipation piers under earthquake action. Therefore, a hysteretic constitutive law for steel shear links is first proposed including the theoretical shear force-deformation skeleton curve and the unloading and reloading rules during hysteretic loading. Next, a hysteretic spring model is developed for efficiently simulating the hysteretic mechanical behavior of steel shear links, which is validated to have good accuracy with comparison to fine FEA and experimental results. Then, a simplified hybrid model consisting of the self-developed spring model and fiber beam model and two multi-scale FEA models with different levels of refinement are established for nonlinear analysis of energy dissipation piers, respectively. The comparison of numerical and test results confirms that the innovative fiber beam-spring hybrid model can accurately describe the hysteretic performance of energy dissipation piers, especially the detailed mechanical behavior of steel shear links and column feet, which provides an efficient numerical tool for analysing the collaborative working mechanism of energy dissipation piers and similar energy dissipation structures.

Tunnel fires are usually accompanied with major casualties and properties losses, and multiple fires in a tunnel may cause intense burning behavior like fire merging, which could be more destructive and hazardous. Therefore, the characteristics and hazards of multiple pool fires in a tunnel were investigated under natural ventilation in this study through a series of experiments. Experimental results showed that the characteristics of one-dimensional fire arrays were different from those of square fire arrays in open space. Due to the extra heat feedbacks (e.g. from adjacent fire sources, tunnel wall and hot smoke), the burning rate was found being enhanced. When there is more than one fire source, it was observed that the flames deflect towards the center of one-dimensional fire arrays, leading to flame merging when fire spacing decrease to some extent, which would result in the increased hazards of the heptane fires. An empirical model was developed to predict the global dimensionless average burning rates based on modified fire area ratio, which characterizes the fuel load and incorporated fire spacing, fire number and the fuel pan size. The research results in this paper provide a theoretical guide on understanding the behaviors of multiple fire resources in tunnels.

The increased demand for cladding in high-rise buildings has prompted engineers to explore alternative products utilizing recycled materials. However, ensuring fire compliance in these alternative claddings, which are predominantly composed of low-volume polymer-based composites, poses a critical challenge. Traditional experimental methods for fire evaluation are costly, time consuming, and environmentally impactful. Considering this, a numerical approach was proposed for evaluating the fire performance of glass-polymer composite materials, which contain a high proportion of recycled glass and a lower percentage of rigid polyurethane. A cone calorimeter test was simulated using Computational Fluid Dynamics (CFD) software to investigate the flammability of the novel glass–polymer composite material. This validated numerical model was employed to assess the combustibility of the glass–polyurethane composite materials and identify influential parameters using the Design of Experiments (DoE) method. Statistical analysis revealed that three material properties, namely, the heat of combustion, the absorption coefficient, and the heat of reaction, significantly influenced the peak heat release rate (pHRR) of the glass–polyurethane composite materials compared to other properties. Based on these findings, an empirical equation was proposed that demonstrates a reasonable correlation with the pHRR of low-polymer recycled glass composite materials. The outcomes of this study hold considerable importance for understanding and predicting the combustibility behaviour of low-polymer–glass composites. By providing a validated numerical model and identifying critical material properties, this research contributes to the development of sustainable fire safety solutions for buildings, enabling the use of recycled materials and reducing reliance on conventional claddings.

Temperature fluctuations pose a critical challenge for infrastructure, necessitating functional concrete to protect structures and promote sustainability. Self-heating concrete and phase change material (PCM) concrete are closely linked to thermal energy, with the former focused on heat generation and the latter on heat storage. This study aims to explore the self-heating performance of modified PCM concrete. Carbon-based materials, chosen for their low electrical resistance and high thermal conductivity, are incorporated to enhance the PCM concrete. Carbon black (CB), carbon nanotubes (CNT), and carbon fibres (CF) with various dimensions and scales, are combined to achieve optimal performance. Materials below a threshold yield minimal change, as they fail to establish the crucial conductive circuit. The self-heating behaviour becomes pronounced with increased in materials, reaching an optimal temperature rise up to 31.2 °C in one hour. However, the group with the highest content of materials experiences a reduced final temperature of 23.9 °C and an increased electrical conductivity of 40 Ω. CB and CNT show different efficiency improvements, and the ideal combination is proposed as 0.3 % CNT and 0.75 % CB. Inorganic hydrated salt-based PCM reduces electrical conductivity by 12 % – 35 % in its liquid state due to free ions, potentially enhancing self-heating capability, though its impact is less significant compared to carbon materials. Overall, the optimum group demonstrates significant self-heating behaviour, high efficiency, and low material cost. Models and electrical impedance results validate these observations and provide novel insight into the self-heating performance of PCM mortar with hybrid carbon-based materials.