BITS Faculty Publications
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Item Modeling VOC emisssions from ozone reactions with human-worn clothing in an aircraft cabin(International Conference on Indoor Air Quality and Climate, 2014) Rai, Aakash ChandVolatile Organic Compounds (VOCs) are indoor air pollutants with many adverse health effects for humans. Ozone reactions with human surfaces (skin, hair, and clothing) are an important source of VOCs in the indoor air, especially in aircraft cabins due to typically high ozone concentrations and occupant densities. Therefore, it is important to study the ozone-initiated VOC emissions from its reactions with passengers in an aircraft cabin and assess their resulting exposure. This investigation developed empirical models for computing the emissions of some major VOCs such as acetone, 4-oxopentanal (4-OPA), nonanal, and decanal from ozone reactions with human-worn clothing. The empirical models were used to compute the contributions of human surfaces to those VOCs in an aircraft cabin mockup under different environmental conditions. The computed results were then compared with their corresponding experimental data obtained in the mockup. The models can provide rough estimates of the ozone-initiated VOCs.Item Phytoremediation of Airborne Particulate Matter in Indoor Environments(SINTFF, 2021) Rai, Aakash ChandThis research is motivated by the urgent need to protect people from the adverse health effects of PM2.5 (particles smaller than 2.5 μm in size) exposure by using potted plants as air filters in indoor environments. We quantified the ability of three different plant species for removing airborne particles by conducting experiments in an environmentcontrolled chamber. The plants selected were Christmas plant (Araucaria heterophylla, a needleleaved plant), Ficus plant (Ficus retusa, a small-leaved plant), and Croton plant (Codiaeum variegatum, a broad-leaved plant). The particle deposition velocities ranged from (32.4±10.6 to 41.0±10.8) cm/h for the Christmas plant, (0.6±1.6 to 2.53±3.27) cm/h for the Ficus plant, and (−0.09±3.8 to 6.07±6.28) cm/h for the Croton plant, depending on the particle size. On extrapolating those results to a small residential room, we found that 35–44 Christmas plants (the most effective species) would be required for reducing the steady-state PM2.5 concentration by 10% at an air exchange rate of 0.5 h−1.Item A Multi-model and Multi-scenario Assessment of the Impact of Climate Change on the Heating and Cooling Load Components of an Archetypical Residential Room in Major Indian Cities(ARXIV, 2023-07) Rai, Aakash ChandResidential heating and cooling currently account for approximately 7% of electricity consumption of India. A warming climate will increase residential cooling requirements, while heating needs will decrease which is an alarming consequence for India, which has predominantly cooling requirements. Thus, to reduce the energy and carbon footprint of Indian building sector, it is essential to assess the impact of climate change on future heating and cooling needs and develop energy-efficiency solutions. This research evaluated the effect of climate change on the heating and cooling energy needs of an archetypical residential room in India, covering all climate zones. We developed a novel approach to quantify the heating and cooling load components (walls, windows, etc.) for identifying building elements to be targeted for improving energy efficiency. Our median climate model predicted that the cooling energy demand of the room archetype would increase by 23-155% by the 2090s compared to the 1990s, depending on the city and emission scenario. Walls and windows account for over 60% of the cooling needs and should be the prime targets for energy-efficiency measures. We also predict between 45-100% reductions in the heating requirements of the archetype room by the 2090s. Walls contribute over 67% to heating needs and should be targeted for heating energy reductions.Item Effects of Indoor Plants on Occupants’ Emotional-State, Performance, and Perceived Comfort in an Open-Plan Seating Space(SSRN, 2023-09) Rai, Aakash Chand; Dasgupta, Mani SankarIndoor plants are a reliable means of introducing nature connection indoors, which can positively affect occupants’ well-being. To better understand the effectiveness of indoor plants on occupants’ well-being (perceived comfort, emotional state, and performance), we conducted a between-subjects study in a simulated open-plan seating space. Subjective questionnaires queried the occupants regarding their perception of indoor climate, sick building syndrome (SBS) symptoms, emotional state, self-assessed performance, and overall satisfaction with the space with and without indoor plants. The participants also undertook a cognitive task targeting working memory (operation Span). Participants in the group with plants (WP) rated the room to have better aesthetics (p = 0.004, r = 0.27), felt slightly cooler (p = 0.05, r = 0.18), and perceived less air dryness (p = 0.05, r = 0.18) than the group without-plant (WoP). Differences noted between the two groups’ perception of air quality, SBS symptoms, and their subjectively or objectively assessed task performance were not significant. The WP group had enhanced positive emotions (p < 0.0001 to 0.02, |r| = 0.21–0.45) and reduced negative emotions (p = 0.05, |r| = 0.18). Overall, our findings indicate that potted indoor plants positively impacted aesthetics, perceived thermal comfort, and mood in a simulated open-plan seating space.Item Effectiveness of plants for passive removal of particulate matter is low in the indoor environment(Elsevier, 2022-08) Rai, Aakash ChandParticulate air pollution is a major health concern and is responsible for about one in nine premature deaths worldwide. Significant exposure to particulate matter (PM) may happen indoors because people spend a large fraction of their time inside buildings. Indoor plants have been suggested as a potential solution for removing PM; however, their effectiveness has not been well characterized. We quantified the ability of eleven different plant species to remove airborne PM through experiments conducted in an environmental chamber. By introducing PM into the chamber and measuring its removal rate with and without the plants, we estimated plants’ deposition velocities and clean air delivery rates (CADRs).Item Effect of Air-Curtains on Labyrinth Seal Performance(ASME, 2016-09) Rai, Aakash ChandLabyrinth seals are used in many key sealing locations in gas turbines to control various leakage flows, e.g., to control the secondary air-flow from the compressor (bypassing the combustor), the turbine inter-stage leakages and blade tip leakages. This study was performed to assess the improvement in the performance of a labyrinth seal by using an air-curtain (cross-flow jet(s)) from the stator. Detailed parametric studies were performed to study the effect of the air-curtain jet pressure, location, and the number of jets on the seal performance with respect to the leakage flow. The analysis was done using 2-dimensional axisymmetric CFD simulations. It was found that in the case of a labyrinth seal with a flat stator (without a honeycomb attached to the stator) the air-curtain design can reduce the seal leakage by about 30% over the baseline seal design without air-curtains. This reduction happened because the air-curtain jet deflected the main seal jet away from the seal clearance. A similar conclusion was also obtained in case of a labyrinth seal with a honeycombed stator. Furthermore, our parametric studies with different air-curtain designs parameters implemented over a honeycombed labyrinth seal showed that the air-curtain jet pressure, location, and the number of jets were crucial factors governing the seal leakage. Amongst the air-curtain designs studied, it was found that implementing three air-curtains in the 1st pocket gave the maximum leakage reduction (by about 50%) over the baseline design.Item Numerical modeling of volatile organic compound emissions from ozone reactions with human-worn clothing in an aircraft cabin(Taylor & Francis, 2014-11) Rai, Aakash ChandVolatile organic compounds are indoor air pollutants with many adverse health effects for humans. Ozone reactions with human surfaces (skin, hair, and clothing) are an important source of volatile organic compounds in the indoor air, especially in aircraft cabins because of their typically high ozone concentrations and occupant densities. Therefore, it is important to study the ozone-initiated volatile organic compound emissions from ozone reactions with passengers in an aircraft cabin and assess their resulting exposure. This investigation developed empirical models for computing the emissions of several major volatile organic compounds, including acetone, 4-oxopentanal, nonanal, and decanal, from ozone reactions with human-worn clothing. The empirical models were used to compute the contributions of human surfaces to these volatile organic compounds in an aircraft cabin mockup under different environmental conditions. The computed results were then compared with the corresponding experimental data obtained in the mockup. The models can provide rough estimates of ozone-initiated volatile organic compound concentrations. The empirical models were integrated into a computational fluid dynamics analysis, and the results showed that the levels of ozone-initiated volatile organic compounds were significantly enhanced in the breathing zones of the passengers. Therefore, to accurately assess passenger exposure to volatile organic compounds, their concentrations in the breathing zones should be used.Item Impact of global warming on heating and cooling degree days in major Indian cities(Elsevier, 2021-08) Rai, Aakash ChandGlobal warming induced rise in ambient temperatures would significantly impact the space heating and cooling (H/C) energy requirements in buildings. This investigation assessed the impact of global warming on space H/C energy requirements in eight major Indian cities covering all of the county’s climate zones. By using historical weather records and general circulation model outputs, we quantified the historical (1969–2017) and future (2018–2100) trends in annual mean temperatures together with heating and cooling degree days (HDDs and CDDs), which are well-known metrics for quantifying buildings’ H/C requirements. The investigation demonstrated that annual temperatures would be higher by 0.1–1.1 °C in the 2020 s, by 0.6–2.8 °C in the 2050 s, and by 1.0–4.6 °C in the 2080 s, depending on the city and the emission scenario. Due to rising temperatures, CDDs would also increase by 2.9–22.9% in the 2020 s, by 8.3–54.1% in the 2050 s, and by 11.89–83.0% in the 2080 s; thus, increasing the cooling requirements by a similar amount. In contrast, HDDs would decrease by 8.1–30.3% in the 2020 s, by 17.6–83.3% in the 2050 s, and by 19.3–97.1% in the 2080 s, thereby reducing the heating requirements.Item Numerical modeling of particle generation from ozone reactions with human-worn clothing in indoor environments(Elsevier, 2015-02) Rai, Aakash ChandOzone-terpene reactions are important sources of indoor ultrafine particles (UFPs), a potential health hazard for human beings. Humans themselves act as possible sites for ozone-initiated particle generation through reactions with squalene (a terpene) that is present in their skin, hair, and clothing. This investigation developed a numerical model to probe particle generation from ozone reactions with clothing worn by humans. The model was based on particle generation measured in an environmental chamber as well as physical formulations of particle nucleation, condensational growth, and deposition. In five out of the six test cases, the model was able to predict particle size distributions reasonably well. The failure in the remaining case demonstrated the fundamental limitations of nucleation models. The model that was developed was used to predict particle generation under various building and airliner cabin conditions. These predictions indicate that ozone reactions with human-worn clothing could be an important source of UFPs in densely occupied classrooms and airliner cabins. Those reactions could account for about 40% of the total UFPs measured on a Boeing 737-700 flight. The model predictions at this stage are indicative and should be improved further.Item Energy performance of phase change materials integrated into brick masonry walls for cooling load management in residential buildings(Elsevier, 2021-07) Rai, Aakash ChandEnergy demand for space cooling in residential buildings is projected to witness rapid growth, primarily fueled by increasing household incomes in developing countries. To manage this ever-increasing cooling demand, integration of phase change materials (PCMs) in building walls is a potential solution that can reduce the buildings’ cooling energy consumption and peak cooling loads. However, to attain the proposed benefits from PCM integration, it is crucial to appropriately select PCM parameters such as its phase-change temperature and positioning in the wall. Thus, this investigation studied the energy performance of PCM integrated brick masonry walls for cooling load management in residential buildings under periodic steady-state conditions to identify the parameters that govern its performance and develop simple design guidelines. The research found that regardless of the amount of latent heat stored by the PCM, the daily heat gains and cooling loads were equal for wall configurations having equal thermal resistances under identical boundary conditions. Furthermore, even with the application of night ventilation, adding a PCM layer to a well-insulated wall did not reduce its cooling load; thus, PCM integration was ineffective in reducing the cooling load. However, the latent heat stored by the PCM reduced the fluctuations in the hourly heat gains and cooling loads; thus, PCM integration was found suitable for peak load management. For the PCM's proper utilization, its recommended position is on the inner side of the wall with sufficient insulation shielding it from outdoor conditions, and its melting temperature should be close to the indoor set-point temperature