Jingjing Pei

Experimental study of gaseous and particulate contaminants distribution in an aircraft cabin

Abstract The environment of the aircraft cabin greatly influences the comfort and health of passengers and crew members. Contaminant transport has a strong effect on disease spreading in the cabin environment. To obtain the complex cabin contaminant distribution fields accurately and completely, which is also essential to provide solid and precise data for computational fluid dynamics (CFD) model validation, this paper aimed to investigate and improve the method for simultaneous particle and gaseous contaminant fields measurement. The experiment was conducted in a functional MD-82 aircraft. Sulfur hexafluoride (SF6) was used as tracer gas, and Di-Ethyl-Hexyl-Sebacat (DEHS) was used as particulate contaminant. The whole measurement was completed in a part of the economy-class cabin without heating manikins or occupied with heating manikins. The experimental method, in terms of pollutant source setting, sampling points and schedule, was investigated. Statistical analysis showed that appropriately modified sampling grid was able to provide reasonable data. A small difference in the source locations can lead to a significant difference in cabin contaminant fields. And the relationship between gaseous and particulate pollutant transport was also discussed through tracking behavior analysis.

A hybrid model for investigating transient particle transport in enclosed environments

Abstract It is important to accurately model person-to-person particle transport in mechanical ventilation spaces to create and maintain a healthy indoor environment. The present study introduces a hybrid DES-Lagrangian and RANS-Eulerian model for simulating transient particle transport in enclosed environments; this hybrid model can ensure the accuracy and reduce the computing cost. Our study estimated two key time constants for the model that are important parameters for reducing the computing costs. The two time constants estimated were verified by airflow data from both an office and an aircraft cabin case. This study also conducted experiments in the first-class cabin of an MD-82 commercial airliner with heated manikins to validate the hybrid model. A pulse particle source was applied at the mouth of an index manikin to simulate a cough. The particle concentrations versus time were measured at the breathing zone of the other manikins. The trend of particle concentrations versus time predicted by the hybrid model agrees with the experimental data. Therefore, the proposed hybrid model can be used for investigating transient particle transport in enclosed environments.

Ozone reaction with clothing and its initiated VOC emissions in an environmental chamber

Human health is adversely affected by ozone and the volatile organic compounds (VOCs) produced from its reactions in the indoor environment. Hence, it is important to characterize the ozone-initiated reactive chemistry under indoor conditions and study the influence of different factors on these reactions. This investigation studied the ozone reactions with clothing through a series of experiments conducted in an environmental chamber under various conditions. The study found that the ozone reactions with a soiled (human-worn) T-shirt consumed ozone and generated VOCs. The ozone removal rate and deposition velocity for the T-shirt increased with the increasing soiling level and air change rate, decreased at high ozone concentrations, and were relatively unaffected by the humidity. The deposition velocity for the soiled T-shirt ranged from 0.15 to 0.29 cm/s. The ozone-initiated VOC emissions included C6-C10 straight-chain saturated aldehydes, acetone, and 4-OPA (4-oxopentanal). The VOC emissions were generally higher at higher ozone, humidity, soiling of T-shirt, and air change rate. The total molar yield was approximately 0.5 in most cases, which means that for every two moles of ozone removed by the T-shirt surface, one mole of VOCs was produced.

A modified tracer-gas decay model for ventilation rate measurements in long and narrow spaces

Ventilation is essential to the health and comfort of occupants in enclosed spaces. However, it is difficult to accurately measure the ventilation rates in large, long, and narrow spaces such as aircraft cabins and train compartments. This study has proposed a modified tracer-gas-concentration decay method that combines the multi-zone technique with the genetic algorithm to determine ventilation rate in such spaces. To validate the proposed method, the investigation utilized both the modified decay method and the traditional decay method to numerically measure the ventilation rate in an MD-82 aircraft cabin by computational fluid dynamics technique. The results showed that the modified tracer-gas-concentration decay method can significantly improve the accuracy and reliability of the ventilation rate measurements in such a large, long, and narrow space. The modified tracer-gas-concentration decay method was also used to experimentally measure the ventilation rate in an actual MD-82 aircraft cabin. Although no exact ventilation rate could be measured, but compared with the traditional tracer-gas-concentration decay method, the ventilation rate determined by the modified method was much closer to that obtained by the constant tracer-gas-concentration method, which is considered to be the most accurate measurement.

Evaluation of filter media performance: Correlation between high and low challenge concentration tests for toluene and formaldehyde (ASHRAE RP-1557)

To guide the selection of gas phase filtration media in the air cleaning devices, it is important to understand and estimate the media performance under usage concentrations. Filters for improving indoor air quality are typically subject to low volatile organic compounds (VOCs) concentration levels (e.g., ∼50 ppb), while the current standard tests per ASHRAE 145.1 (ANSI/ASHRAE 2008). are performed at relatively high challenge concentrations (∼1–100 ppm level). The primary objective of this study was to determine if media that perform well at the high concentration test condition would also perform well under the low concentration. The secondary objective was to investigate if and how existing models of filtration by media bed can be applied to extrapolate the results from the high concentration tests to the low concentration condition. Experiments and simulations were carried out at both high concentrations (100 ppm for toluene and 1 ppm for formaldehyde) and low concentrations (0.05 ppm for toluene and formaldehyde) for six selected filtration media. The results show that (1) the high concentration test data were able to differentiate the relative performance among the media at the low concentration properly, confirming the validity of using ASHRAE 145.1 (ANSI/ASHRAE 2008) for relative performance comparison; (2) significant initial breakthrough observed at high concentration tests of large pellet media was not present at the low concentration tests, indicating the dependency of the adsorption capability of the sorbent media on the concentration level as well as the possible “by-pass” effects (i.e., not all the VOC molecules in the air stream had the same chance to contact with the sorbent media); and (3) existing models need to be improved by incorporating the concentration dependency of the partition coefficient and the by-pass effect in order to predict the breakthrough curve at low concentrations properly. Such an improved model was proposed, evaluated with the measured data, and was found to be promising for physical sorbent, but requires further development for chemical, catalytic sorbent and large pellet sorbent. The study provides previously unavailable experimental data and new insight into the behavior of the filtration media for volatile organic compounds as well as evidence in support of the application of ASHRAE Standard 145.1 (ANSI/ASHRAE 2008) for media performance evaluation.

The effect of air change rate and temperature on phthalate concentration in house dust

Semi-volatile organic compounds (SVOCs) are one of the main indoor pollutant categories. Six phthalates (dimethyl phthalate (DMP), diethyl phthalate (DEP), di(isobutyl) phthalate (DiBP), di(nbutyl) phthalate (DnBP), butyl benzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP)) in house dust samples were measured in forty residential apartments in Tianjin and Urumqi in four seasons throughout a year. The measured DEHP dust-phase concentration is in the range: 11.9-699.9 μg/g; and showed obvious differences in different seasons, and the maximum can be 2 times higher than minimum. The DiBP and DnBP showed similar phenomenon. The corresponding gas-phase concentration is estimated considering the influencing factors of indoor temperature, air change rate, particle concentration. Then the dust-gas partition coefficient Kd under different season was obtained through the measured dust-phase concentration and estimated gas-phase concentration. From winter to summer, because the increased temperature leads to higher emission rate, the gas-phase concentration is obviously high in spite of the higher air change rate in summer. The estimated DEHP gas-phase concentration showed obvious differences in different seasons, and the maximum can be about 2 times higher than minimum. The DiBP and DnBP showed similar phenomenon. The lower dust-phase concentration in summer is observed due to the temperature-dependency of the dust-gas partition coefficient. Therefore temperature has the greatest impact on the dust concentration, not influence via emission rate, but influences the partition coefficient Kd.