BITS Faculty Publications
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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 Evaluation applicability of trans-critical CO2 refrigeration system using field data of an ammonia based plant(IIR, 2016) Dasgupta, Mani SankarThe study evaluates the potential of a trans-critical CO2 refrigeration system as replacement of an ammonia system in a milk refrigeration plant for a warm climate condition in northern India where the annual range of temperature is 48ºC to -2 ºC. Twenty-four months of field data from the ammonia based plant is collected. An ideal thermodynamic model of the same is built and operated with field data and the performance is compared. A co-relation factor is developed that relates ideal and actual performance encompassing the practical consideration that contribute towards reduction of plant performance from ideal. The performance is next compared with that of hypothetical replacement plant based on CO2 transcritical cycle with booster system, weighing up practical consideration. A few possible COP improvement strategies are also evaluated.Item Fuzzy controller development from information granules for a heat exchanger(NISCAIR, 2000-07) Dasgupta, Mani SankarThis paper discusses the experimental results of on-line fuzzy control of a heat exchanger unit. Fuzzy controllers are a class of model independent controllers. which use common sense logic, expressible in linguistic form and is more amenable to human way of decision-making, A collection of information granules, regarding the process under study, is documented first. Using the some, the steps of formation and justification of the fuzzy look-up table is demonstrated. An efficient fuzzy control is established using multiple look-up tables. These tables are further adapted to accommodate conflicting control demands of 'low overshoot' and 'small rise time', An algorithm for on-line table switching is also proposed.Item Investigation of effect of suction nozzle pressure drop and degree of sub-cooling on co2 transcritical ejector system(Begell House, 2017) Dasgupta, Mani Sankar; Yadav, Shyam SunderA two-phase ejector is often used to improve the performance of a CO2 transcritical refrigeration system, such systems are also, mostly equipped with an internal heat exchanger. Any effect on performance due to suction nozzle pressure drop (SNPD) is generally neglected for theoretical studies using constant pressure mixing model. A few authors, in the recent past, have highlighted the effect of SNPD. A detailed investigation of effect of SNPD as well as sub-cooling on the performance parameters like pressure recovery, ejector efficiency, entrainment ratio and overall COP of the system are presented here. Optimized ejector SNPD values are determined for maximizing COP across a wide range of operating conditions. COP increment upto 4.95% is observed at optimized SNPD condition. Further, the effect of degree of sub-cooling on cycle parameters is studied and optimum degree of sub-cooling for COP improvement for a range of operating conditions is also determined.Item Energetic and economic analysis of trans-critical CO2 booster system for refrigeration in warm climatic condition(Elsevier, 2017-08) Dasgupta, Mani SankarThe performance of five CO2 booster refrigeration systems is analysed and compared in this paper for supermarket application. The investigated configurations include a standard booster system, abbreviated as BC1, a booster system with parallel compressor (BC2), a booster system with flooded low temperature evaporator (BC3), a booster system with work recovery expander (BC4) and a booster with parallel compressor along with flooded low temperature evaporator and work recovery expander (BC5). Annual hourly averaged temperature variations at four prominent cities across the world are taken as case study. Simulation indicates advantage of the proposed system BC5 over BC1 configuration. Work recovery unit is found to have the highest potential in the annual energy savings in BC5, followed by parallel compressor and flooded evaporator. The maximum annual energy savings is found to be 22.16% for BC5 in New Delhi. Economic analysis reveals recovery time of less than four years for the additional investment made in BC5. The slope of recovery time is found steeper at lower tariff compared to that at higher tariff.Item A Comparison of Three Different Flow Solvers For Simulating Steam Condensation Inside a Nozzle(Springer, 2023-04) Dasgupta, Mani Sankar; Yadav, Shyam SunderIn this work the condensation process of steam inside a converging diverging nozzle is simulated, the experiments on which were performed by Moses and Stein [1]. Three different flow solvers are used for this purpose, namely, Ansys Fluent, Ansys CFX and the open source flow solver OpenFOAM. The aim of the current work is to narrow down the choice of the flow solver which can finally be used for simulating non-equilibrium condensation of Carbon Dioxide inside ejectors. The pressure distribution predicted inside the nozzle by the three solvers follow closely the experimental one. However, the location and amount of pressure rise due to the condensation onset are differently predicted by the flow solvers. Only one plateau is observed in the pressure curve experimentally while at least two different plateaus are predicted numerically. For the vapor temperature and supercooling, the three solvers predict similar values before the condensation onset. After start of condensation, Ansys Fluent and OpenFOAM give similar results while Ansys CFX predicts at least 10 degree higher values. Ansys CFX predicts a wider nucleation zone compared to the two other solvers. The highest discrepancy being displayed by the solvers appears in the distribution of droplet diameter and droplet number density. However, the three solvers predict similar trend for the liquid mass fraction distribution inside the nozzleItem Thermodynamic Analysis of a Novel Dual-Ejector Multi-Compressor Transcritical-CO2 Refrigeration System for Supermarket Applications in Warm Climates(Springer, 2023-04) Dasgupta, Mani SankarThe thermodynamic analysis of a novel dual-ejector multistage compressor-based transcritical CO2 booster system for supermarket application in warm climatic conditions is presented in this paper. Dual-ejector flow-pressurization and flow-splitting at higher ambient temperatures are implemented to improve performance. The proposed system is compared with various previously published CO2 systems including B1 (Standard CO2 booster system), B2 (CO2 booster system with parallel compression), B3 (CO2 booster system with flooded LT evaporator), B4 (CO2 booster system with work recovery expander), B5 (CO2 booster system with parallel compression, flooded LT evaporator, work recovery expander) and also with multi-stage ejector systems. The performance of the proposed system is found superior. The COP of the proposed system has been found to be 32% higher than B5 and 26% higher than the multi-ejector systems.Item Evaluating the Effect of Fluid Temperature and Flow Rate on the Pressure Drop Across Direct Flow Evacuated Tubular Collector(Springer, 2023-04) Dasgupta, Mani SankarThe objective of this study is to determine the effect of water temperature and volume flow rate on the pressure drop across an Evacuated Tubular Collector (ETC) with direct flow configuration. The findings are expected to be useful for pump selection and to determine the pumping power required for operating an ETC based solar thermal plant during the day. A detailed mathematical model is developed, utilizing correlations found in previous literature. An experimental investigation was carried out on a Linuo–Ritter CPC1518 ETC solar collector installed in BITS–Pilani, India for water temperature at 25 ℃, 55 ℃ and 85 ℃ and the volume flow rate is varied in the range of 0.4–1.6 m3⁄ℎr with a step of 0.2 m3⁄ℎr. Further, the developed mathematical model is validated with results obtained from the experimental setup within 5% error. Results showed that the pressure drop across the ETC unit becomes lower as the water temperature increases. It was also observed that the pressure drop is a quadratic function of the volume flow rate of water. Hence at higher flow rates, minor changes produce large pressure drop across the ETC unit.Item Effect of Motive Nozzle Exit Position in a R-744 Two-Phase Ejector(Springer, 2022-01) Dasgupta, Mani Sankar; Yadav, Mani SankarEjector expansion transcritical refrigeration systems, in general, have an advantage over conventional transcritical refrigeration systems. In this paper, a CFD-based investigation of transonic flow phenomenon for R-744 inside a three-dimensional model of an ejector is presented. Real-gas thermophysical properties of R-744 such as the density, dynamic viscosity, and thermal conductivity are defined as a function of pressure and temperature based on NIST Refprop. Three different motive nozzle exit positions are investigated. A motive nozzle tip position that is near to the mixing section is found to have higher pressure and lower Mach number due to better mixing.Item Assessment of benefits of employing natural refrigerants in seafood cold chain in India(IIR, 2022) Dasgupta, Mani SankarIn this paper we present a comprehensive assessment of benefits from adoption of suitable natural refrigerants at various stages of seafood cold chain in Indian scenario. This includes cooling demands during fish harvesting, transport of fresh catch, sorting and processing, and long-time storage. For each stage, the cooling demands are estimated and simple refrigeration cycle configurations are simulated to estimate the annual energy consumption and total equivalent warming impact for suitable natural refrigerants from among NH3, CO2, and hydrocarbons such as R170, R290, and R1270. The same is compared with synthetic refrigerants presently used for such application like R22, R134a and R404A etc. Field data from a surimi supply chain in west coastal region and shrimp supply chain in east coastal region of India are used for the study. The results highlight the potential benefits from use of natural refrigerants in seafood sector. Further, the various barriers in terms of technological, economic and policy related are highlighted.