Two-zone Chamber Research Articles

Modeling transient particle transport in transient indoor airflow by fast fluid dynamics with the Markov chain method

It is crucial to accurately and efficiently predict transient particle transport in indoor environments to improve air distribution design and reduce health risks. For steady-state indoor airflow, fast fluid dynamics (FFD) + Markov chain model increased the calculation speed by around seven times compared to computational fluid dynamics (CFD) + Eulerian model and CFD + Lagrangian model, while achieving the same level of accuracy. However, the indoor airflow could be transient, if there were human behaviors involved like coughing or sneezing and air was supplied periodically. Therefore, this study developed an FFD + Markov chain model solver for predicting transient particle transport in transient indoor airflow. This investigation used two cases, transient particle transport in a ventilated two-zone chamber and a chamber with periodic air supplies, for validation. Case 1 had experimental data for validation and the results showed that the predicted particle concentration by FFD + Markov chain model matched well with the experimental data. Besides, it had similar accuracy as the CFD + Eulerian model. In the second case, the prediction by large eddy simulation (LES) was used for validating the FFD. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The computational time of the FFD + Markov chain model was 7.8 times less than that of the CFD + Eulerian model.

Characterizing transport and deposition of particulate pollutants in a two-zone chamber using a Markov chain model combined with computational fluid dynamics

• Markov chain model combined with CFD for multi-zone space proposed. • Exposure levels and deposition rates of particulate pollutants analyzed. • Proposed model may be of practical use for obtaining real-time predictions. Understanding the distribution and spread of indoor airborne contaminants between rooms in a multi-zone space is crucial for protecting human health and indoor environmental control. Predicting the transmission of suddenly released particulate pollutants from one room to another in a rapid and precise manner is important for reducing or even eliminating the risk of cross contamination between occupants. In this study, we developed a modified Markov chain model that considers the effect of gravity to predict the dispersion and deposition of aerosol particles in a two-zone chamber. To perform particle phase simulations, the proposed model couples the data obtained from a steady-state flow field using the computational fluid dynamics (CFD) software Fluent with some codes that we developed in the MATLAB environment. Two examples based on previously reported experimental data were used to validate the proposed model. The results indicate that the proposed model is suitable for modeling the dynamic processes where airborne particles are released from constant and pulsed contaminant sources in multi-zone spaces with reasonable accuracy and computational efficiency. After analyzing particle exposure in the two-zone chamber, we found that the accumulated exposure level in the zone with the constant contaminant source always had a higher rate of increase than the other zones. However, the accumulated exposure level for the pulsed (instantaneous) source was inversely proportional to the air exchange rate for all zones. Compared with traditional CFD models and multi-zone models, our proposed model can balance the accuracy and efficiency when predicting the spread of particulate contaminants in multi-zone spaces by choosing appropriate grid resolution (s).

Integrated gas dynamic computational modelling and thermodynamic combustion diagnostics of multicylinder four-stroke spark ignition engine using compressed natural gas as a fuel

A comprehensive computational simulation model has been developed to describe the performance, efficiency and emission characteristics of the four-stroke multi-cylinder spark ignition engine which uses compressed natural gas as a fuel. This model performs an integrated simulation of thermodynamic, gas dynamic, and chemical kinetics of the whole engine system coupling with intake and exhaust manifolds. The thermodynamic combustion process is modelled by using the turbulent flame propagation process with a two-zone chamber (burned and unburned). Gas dynamics in the manifold system are modelled by using unsteady compressible hyperbolic partial differential equations. These equations contain heat transfer, friction, area change in pipe and empirical constants, which are used to determine boundary conditions at pipe junctions, valves and open ends. These equations are transferred into a set of ordinary differential equations by applying the method of characteristics and are solved by the finite difference method. Regarding exhaust emissions, nitric oxide concentrations have been predicted by using the rate kinetic model in the power cycle and along the exhaust pipes. Carbon monoxide is computed under the chemical equilibrium condition and then the empirical adjustment is made for kinetic behaviours based upon experimental results. Finally, predicted results of this model have been compared with experimental results and are found to be compatible. The parametric studies have been conducted with the equivalence ratio and the engine RPM, to predict engine performance. Also, the variations of pressure, temperature, and gas compositions in the exhaust system have been studied.

Experimental and numerical study on particle distribution in a two-zone chamber

Better understanding of aerosol dynamics is an important step for improving personal exposure assessments in indoor environments. Although the limitation of the assumptions in a well-mixed model is well known, there has been very little research reported in the published literature on the discrepancy of exposure assessments between numerical models which take account of gravitational effects and the well-mixed model. A new Eulerian-type drift-flux model has been developed to simulate particle dispersion and personal exposure in a two-zone geometry, which accounts for the drift velocity resulting from gravitational settling and diffusion. To validate the numerical model, a small-scale chamber was fabricated. The airflow characteristics and particle concentrations were measured by a phase Doppler Anemometer. Both simulated airflow and concentration profiles agree well with the experimental results. A strong inhomogeneous concentration was observed experimentally for 10 μm aerosols. The computational model was further applied to study a simple hypothetical, yet more realistic scenario. The aim was to explore different levels of exposure predicted by the new model and the well-mixed model. Aerosols are initially uniformly distributed in one zone and subsequently transported and dispersed to an adjacent zone through an opening. Owing to the significant difference in the rates of transport and dispersion between aerosols and gases, inferred from the results, the well-mixed model tends to overpredict the concentration in the source zone, and under-predict the concentration in the exposed zone. The results are very useful to illustrate that the well-mixed assumption must be applied cautiously for exposure assessments as such an ideal condition may not be applied for coarse particles.

A study of heat-pipe heat recovery for natural ventilation

The performance of four types of heat-pipe heat recovery unit for naturally ventilated buildings was determined in terms of effectiveness and pressure drop. The effectiveness of the heat recovery units was tested in a two-zone chamber. The pressure loss characteristics of the heat recovery units were determined using computational fluid dynamics (CFD) and experimental measurement. CFD was also used to evaluate the performance of a solar chimney for heat recovery in naturally ventilated buildings.

Airborne particles in a ventilated room: Prediction and measurement

A study of air movement and aerosol particle distribution and migration in a ventilated two-zone chamber is presented. The comparisons of average particle concentration decay between numerical results and measured data are generally satisfactory and acceptable. It can be concluded that the particle distribution and migration are mainly influenced by the airflow pattern and ventilation rates.

Measurement and simulation of air flow in a two-zone chamber with heat-pipe heat recovery

SYNOPSIS The performance of a heat-pipe heat recovery unit was tested in a two-zone chamber with a horizontal partition. Air velocity was found to have a significant effect on the effectiveness of heat recovery. The effectiveness decreased with increasing air velocity. Simulation of air flow was carried out for the test chamber under natural ventilation conditions. It was shown that a heat-pipe heat exchanger can be used to reclaim exhaust heat in naturally-ventilated buildings to effect energy conservation.

Determination of effectiveness of heat-pipe heat recovery for naturally-ventilated buildings

The performance of three types of heat-pipe heat recovery unit for naturally-ventilated buildings was tested in a two-zone chamber with a horizontal partition. Air velocity was found to have a significant influence on the effectiveness of heat recovery. The effectiveness decreased with increasing air velocity. The effectiveness was also affected by the shape of fins and pipe arrangement. The pressure loss characteristics of heat recovery units were determined using computational fluid dynamics (CFD). It was found that at low velocities for natural ventilation the pressure loss coefficient decreased with increasing air velocity but the total pressure loss increased with the velocity.

Modelling and measurement of airflow and aerosol particle distribution in a ventilated two-zone chamber

A CFD analysis of air movement and aerosol particle deposition and distribution in a ventilated two-zone system with a small interzonal opening is presented. The comparisons of average particle concentrations in both zones between computations and experiments are generally satisfactory and acceptable. It is concluded that particle deposition and migration are mainly influenced by the particle properties, the ventilation conditions and the airflow patterns in the two zones. Small particles have a greater influence on the indoor air quality than do the large particles.