Jihong Wang

Gaseous pollutant transmission through windows between vertical floors in a multistory building with natural ventilation

Abstract Natural ventilation is an effective strategy to control thermal comfort in buildings, and can be enhanced depending on the window style. The combination of natural ventilation and window can also facilitate the removal or dilution of gaseous pollutants from indoor sources in newly decorated buildings. However, the windows on the same facade may cause gaseous pollutant cross-transmission during single-sided natural ventilation between households on different floors close to the source. Although some research has focused on the pollutant cross-transmission in buildings, the simplification of windows into rectangular openings often affects accurate knowledge of pollutant transmission characteristics. Therefore, this investigation explored gaseous pollutant cross-transmission through real windows during single-sided, buoyancy-driven ventilation in a multistory building. Six types of windows were modeled for the indoor pollutant of gaseous formaldehyde (HCHO). Computational fluid dynamics (CFD) was utilized to solve characteristics of pollutant transmission inside and outside the multistory building. The results indicated that the ventilation rates, thermal profiles and pollutant transmission inside and outside the building varied for each window type, although the open window areas were identical. The re-entry ratio of exhausted air entering upper floors and the infection risk of epidemic viruses caused by airborne cross-transmission was sensitive to ventilation rates and window configurations, while the sensitivities for window configurations varied case by case. The comparisons also revealed that the specification of ambient temperature and pollutant release rate ultimately did not affect the evaluation of pollutant cross-transmission using CFD.

Numerical Study of Convection Melting Inside Ice Storage Systems by the Lattice Boltzmann Model

Abstract The internal melt ice-on-coil tank with horizontal pipes is widely used in ice storage systems. The tank’s discharge process is greatly affected by the natural convection process that is caused by melting of the phase change material outside the pipes. To achieve an optimal arrangement of the pipes, a double-population lattice Boltzmann model was developed to simulate the transient solid-liquid phase change behavior in a section of an internal-melt ice-on-coil thermal storage tank with nine aligned built-in horizontal pipes. The evolutions in the phase change interface and melting rate was illustrated with different pipe shapes and pipe connections. Based on the melting rate, the whole melting process was divided into three stages: sharp decrease stage, continuous decrease stage, and snail-melting stage. The numerical results showed that a high melting rate was obtained by preferentially assigning the high-temperature pipes to the upper part of the tank, while a stable melting rate could be obtained when high-temperature pipes were preferentially assigned to the bottom part of the tank.

Numerical and analytical investigations of heat transfer for a finned tube heat exchanger with ice slurry as cooling medium

Using ice slurry as cooling medium in HVAC systems has potential due to its high energy capacity. In order to investigate heat transfer characteristics in finned tube cross-flow heat exchangers with ice slurry as a cooling medium, a numerical method with volume of fluid model and an analytical method are applied. The composition of ice slurry considered for analysis is a carrier fluid (9 wt% sodium chloride solution) and ice crystals with mass fraction at 5%–35%. Results from the proposed methods are primarily validated via comparing with the experimental data from the published literature. Both the numerical and analytical results reveal that the ice crystals have a positive effect on heat transfer of the heat exchanger. Heat transfer rate of the heat exchanger increases with the inlet ice mass fraction rising, and then it will reach a relative stable value. It is also found that the heat transfer rate almost increases linearly with the air inlet temperature. In addition, the numerical results of the airflow temperature field reveal that extending the width of the fins at the downstream direction of the airflow is favorable to the heat exchanging performance of the ice slurry finned tube heat exchanger. Finally, it is beneficial for the analytical method to obtain reliable results when the ice mass fraction difference between the ice slurry inlet and outlet remains no more than 8%.