Browsing by Author "Rai, Aakash Chand"

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Effect of Air-Curtains on Labyrinth Seal Performance
(ASME, 2016-09) Rai, Aakash Chand
Labyrinth 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.
Effectiveness of plants for passive removal of particulate matter is low in the indoor environment
(Elsevier, 2022-08) Rai, Aakash Chand
Particulate 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).
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 Sankar
Indoor 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.
End-user perspective of low-cost sensors for outdoor air pollution monitoring
(Elsevier, 2017-12) Rai, Aakash Chand
Low-cost sensor technology can potentially revolutionise the area of air pollution monitoring by providing high-density spatiotemporal pollution data. Such data can be utilised for supplementing traditional pollution monitoring, improving exposure estimates, and raising community awareness about air pollution. However, data quality remains a major concern that hinders the widespread adoption of low-cost sensor technology. Unreliable data may mislead unsuspecting users and potentially lead to alarming consequences such as reporting acceptable air pollutant levels when they are above the limits deemed safe for human health. This article provides scientific guidance to the end-users for effectively deploying low-cost sensors for monitoring air pollution and people's exposure, while ensuring reasonable data quality. We review the performance characteristics of several low-cost particle and gas monitoring sensors and provide recommendations to end-users for making proper sensor selection by summarizing the capabilities and limitations of such sensors. The challenges, best practices, and future outlook for effectively deploying low-cost sensors, and maintaining data quality are also discussed. For data quality assurance, a two-stage sensor calibration process is recommended, which includes laboratory calibration under controlled conditions by the manufacturer supplemented with routine calibration checks performed by the end-user under final deployment conditions. For large sensor networks where routine calibration checks are impractical, statistical techniques for data quality assurance should be utilised. Further advancements and adoption of sophisticated mathematical and statistical techniques for sensor calibration, fault detection, and data quality assurance can indeed help to realise the promised benefits of a low-cost air pollution sensor network.
Energy performance of phase change materials integrated into brick masonry walls for cooling load management in residential buildings
(Elsevier, 2021-07) Rai, Aakash Chand
Energy 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
Impact of global warming on heating and cooling degree days in major Indian cities
(Elsevier, 2021-08) Rai, Aakash Chand
Global 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.
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 Chand
Volatile 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.
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 Chand
Residential 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.
Numerical modeling of particle generation from ozone reactions with human-worn clothing in indoor environments
(Elsevier, 2015-02) Rai, Aakash Chand
Ozone-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.
Numerical modeling of volatile organic compound emissions from ozone reactions with human-worn clothing in an aircraft cabin
(Taylor & Francis, 2014-11) Rai, Aakash Chand
Volatile 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.
Ozone reaction with clothing and its initiated particle generation in an environmental chamber
(Elsevier, 2013-10) Rai, Aakash Chand
Ozone-initiated chemistry in indoor air can produce sub-micron particles, which are potentially harmful for human health. Occupants in indoor spaces constitute potential sites for particle generation through ozone reactions with human skin and clothing. This investigation conducted chamber experiments to examine particle generation from ozone reactions with clothing (a T-shirt) under different indoor conditions. We studied the effect of various factors such as ozone concentration, relative humidity, soiling levels of T-shirt with human skin oils, and air change rate on particle generation. The results showed that ozone reactions with the T-shirt generated sub-micron particles, which were enhanced by the soiling of the T-shirt with human skin oils. In these reactions, a burst of ultrafine particles was observed about one hour after ozone injection, and then the particles grew to larger sizes. The particle generation from the ozone reactions with the soiled T-shirt was significantly affected by the different factors studied and these reactions were identified as another potential source for indoor ultrafine particles.
Ozone reaction with clothing and its initiated VOC emissions in an environmental chamber
(Wiley, 2013-07-10) Rai, Aakash Chand
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.
Parametric analysis and optimization of a latent heat thermal energy storage system for concentrated solar power plants under realistic operating conditions
(Elsevier, 2021-08) Srinivasan, P.; Rai, Aakash Chand
High-temperature latent heat thermal energy storage (LHTES) systems are currently being considered for integration into concentrated solar power (CSP) plants; however, the challenge is to properly design the LHTES system under real-world operating conditions. Thus, this numerical investigation studied the effects of the LHTES system's design parameters on its performance under periodic steady-state with charging and discharging ‘cutoff’ temperatures to mimic its real-world operation. The study found that with the incorporation of cutoff temperatures, the system's specific energy and storage effectiveness decreased by 74% and 68%, respectively, due to lower useful charging and discharging times. Furthermore, the study demonstrated that the system's useful charging and discharging time could be augmented by increasing the shell radius (R) or length (L) of the system, or by decreasing the system's tube radius (ro) or the velocity of the heat transfer fluid (um) that flows through the system. The system's geometrical parameters (R, L, and ro) and um also substantially influenced its performance, but in a different manner than their influence on charging-discharging times. For example, increasing R deteriorated the system's performance substantially. Thus, we proposed optimized designs that achieved high charging-discharging times as well as good performance levels, using the response surface methodology.
Performance assessment of residential building envelopes enhanced with phase change materials
(Elsevier, 2020-02) Rai, Aakash Chand
Residential buildings in India account for ~22% of the national electricity consumption, of which one-third is used for space cooling; however, they are rarely constructed with energy-efficiency considerations. This presents an opportunity for reducing the energy consumption and associated greenhouse gas (GHG) emissions by design and construction of energy-efficient houses. Therefore, this investigation assessed the potential of PCM-enhanced building envelopes for reducing the cooling energy requirements of residential buildings in Delhi (capital of India). Through numerical simulations, we studied the impact of key PCM design parameters such as its thickness, position, melting point temperature and latent heat capacity on the proposed energy benefits, and compared them with those obtained with insulation-enhanced envelopes. We found that, applying a PCM layer on the roof reduced the summer heat gain by 12.6%–36.2%, whereas an insulation layer of the same thickness reduced heat gains by 41.0%–71.4% over the baseline construction. PCM-enhanced walls were also found to reduce the heat gain by 10.4%–26.6%, while insulated walls led to a heat gain reduction of 32.4%–64.0%. By extrapolating these results to city-scale, it appears that PCM/insulation-enhanced envelopes could reduce Delhi's annual electricity consumption and GHG emissions by 0.3%–1.5% and 0.2%–1.0%, respectively.
Phytoremediation of Airborne Particulate Matter in Indoor Environments
(SINTFF, 2021) Rai, Aakash Chand
This 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.
Simulations of ozone distributions in an aircraft cabin using computational fluid dynamics
(Elsevier, 2012-07) Rai, Aakash Chand
Ozone is a major pollutant of indoor air. Many studies have demonstrated the adverse health effect of ozone and the byproducts generated as a result of ozone-initiated reactive chemistry in an indoor environment. This study developed a Computational Fluid Dynamics (CFD) model to predict the ozone distribution in an aircraft cabin. The model was used to simulate the distribution of ozone in an aircraft cabin mockup for the following cases: (1) empty cabin; (2) cabin with seats; (3) cabin with soiled T-shirts; (4) occupied cabin with simple human geometry; and (5) occupied cabin with detailed human geometry. The agreement was generally good between the CFD results and the available experimental data. The ozone removal rate, deposition velocity, retention ratio, and breathing zone levels were well predicted in those cases. The CFD model predicted breathing zone ozone concentration to be 77–99% of the average cabin ozone concentration depending on the seat location. The ozone concentration at the breathing zone in the cabin environment can better assess the health risk to passengers and can be used to develop strategies for a healthier cabin environment.