Department of Mechanical engineering

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Analysis of Critical Success Factors to Design E-waste Collection Policy in India: A Fuzzy DEMATEL Approach
(Springer, 2021-09) Dasgupta, Mani Sankar; Routroy, Srikanta
The design of an e-waste collection policy is challenging, especially for a country like India, where the economy is a developing state, and there is a large diversity in socio-economic factors. The e-waste collection policy impacts the various stakeholders such as the manufacturer, the raw material producers, the assemblers, the retailers, the generator (households and bulk consumers), the scrap dealers, the smelters, the recyclers, and the regulators. The design of an e-waste collection policy needs to consider the appropriate set of Critical Success Factors (CSFs), which will maximise the e-waste collection providing business sustainability to the stakeholders while satisfying the environmental regulations in the operating locations. Twenty-three CSFs identified and categorised in six implication dimensions for the e-waste collection policy framework based on a literature survey and experts committee view. The fuzzy DEMATEL approach is employed to analyse the CSFs to design an e-waste collection policy in India from a comprehensive perspective. Cause and effect interrelationship is established among the CSFs, and also their impacts are evaluated to segregate the CSFs into cause group (prominent influencing and independent) and effect group (influenced and dependent). The CSFs such as technology involvement, green practices, environmental program, certification and licensing, public ethics and stakeholder's awareness for circular economy are prominent influencing CSFs for e-waste collection policy in India. The current study is expected to provide a platform for policymakers to design the e-waste collection policy.
ANN controller trained with steady state input-output data for a heat exchanger
(NISCAIR, 2021-05) Dasgupta, Mani Sankar
This paper discusses the design and implementation of an Artificial Neural Network (ANN) based adaptive controller for a heat exchanger. The control strategy chosen is that of explicit nonlinear model predictive control. The nonlinear inverse model of the plant is identified from steady state input-output data by off-line training of a multilayered neural network through error back propagation. For performance enhancement, manipulation of training data and on-line parameter updating are tried. Single pass of derivative of error measure across the plant, on-line gave an excellent performance for regulatory as well as servo problem. The proposed cont roller is found to be successful over a wide operating range. The results are compared with that of an optimized PID controller.
Annual energy and economic performance assessment of transcritical R744 supermarket refrigeration systems powered by an organic Rankine cycle
(Elsevier, 2023-08) Dasgupta, Mani Sankar
In this work the annual and economic performance of a transcritical R744 booster supermarket refrigeration system integrated with an organic Rankine cycle (ORC) was investigated. The results were compared to those of a conventional R744 booster supermarket refrigeration system (i.e. without ORC) in nine different locations worldwide. The benefits from overfeeding the medium temperature (MT) evaporators were also studied. It was found that the ORC can be used at outdoor temperatures above 27 °C. Also, it was observed that the proposed systems offer energy savings from 6 % to 16 % in warm and hot locations, such as New Delhi (India), Phoenix (USA), Bangkok (Thailand) and Riyadh (Saudi Arabia). The payback period of the additional investment associated with the ORC was equal to about 3.5 years in Athens (Greece) and less than 1.5 years in New Delhi, Phoenix, Bangkok and Riyadh.
Assessment of Alumina Nanofluid as a Coolant in Double Pipe Gas Cooler for Trans-critical CO2 Refrigeration Cycle
(Elsevier, 2017-03) Dasgupta, Mani Sankar
In this study, the performance of an alumina nanofluid cooled double pipe gas cooler for trans-critical CO2 refrigeration cycle is theoretically compared to that of water cooled gas cooler. Equal pumping power comparison criterion is adopted besides conventional equal Reynolds number comparison base. Nanofluid is loaded with 0.5%, 1.5% and 2.5% of particle volume fraction under turbulent flow conditions. Drastic variation of thermal and transport properties of CO2 in the vicinity of pseudo critical temperature is taken care of by employing an appropriate discretization technique. Effect of gas cooler pressure, Reynolds number, pumping power and nanoparticle volume fraction on COP of refrigeration system, gas cooler overall conductance, effectiveness and its capacity has been studied. Results indicate that at equal Reynolds number comparison, performance for alumina nanofluid cooled system is better than that of water cooled system. On the other hand, at equal pumping power comparison basis, the performance of water cooled system is superior. Even at equal mass flow rate comparison criterion, the performance of nanofluid cooled system degrades with increase in particle volume fraction. This study is expected to help to assess the nanofluid as a coolant before expensive experimentation.
Assessment of benefits of employing natural refrigerants in seafood cold chain in India
(IIR, 2022) Dasgupta, Mani Sankar
In 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.
Assessment of risk propagation in an e-waste collection system using Bayesian networks
(Springer, 2025-03) Routroy, Srikanta; Dasgupta, Mani Sankar
The widespread use of electrical and electronic devices has become integral to modern life, transforming communication and day-to-day work; however, this has led to a significant challenge in effectively managing the growing volume of electronic waste (e-waste). Effective e-waste management faces a substantial challenge as the collection rates remain low, primarily due to inadequate collection systems and socioeconomic disparities. The present study investigates the assessment of various prominent risks affecting the e-waste collection system. It aims to examine the e-waste collection risk propagation categorized into social, environmental, economic, technical, and policy aspects. The Bayesian network approach is utilized to address a range of potential risks. The key findings indicate inconsistencies in the data collected on e-waste, including information such as collection date and time, location, and technical details. These inconsistencies are observed both between users or customers and e-waste collection agencies, as well as among the country's administration officials. In improving the e-waste collection system, the pivotal factors contributing to improvement were found to be technical and social risks. The insights of this study provide valuable information for policymakers to make informed decisions about promoting sustainable e-waste management practices.
A bibliometric analysis of circular economy concept in E-waste research during the period 2008–2020
(Elsevier, 2021) Routroy, Srikanta; Dasgupta, Mani Sankar
This paper provides an overview of standard literature publications during 2008–2020 on e-waste linked circular economy concept using bibliometric analysis. It presents key topic of waste to wealth and reduction of an environmental hazard. As applied in e-waste management, the concept of circular economy has received considerable attention among the research community over the past few decades. The Scopus database is utilized to retrieve the peer-reviewed articles from 2008 to 2020. A total of 326 publications were identified to focus on e-waste and circular economy. The parameters examined are document type, year wise and journal wise distribution, top authors, top citation and keywords. After that, VOSviewer software is used to visualize the current trends as well as the recent hotspots. It is observed that the topic of a circular economy is encircled by various issues such as e-waste, reuse, recycle, and sustainability in a density map of frequency of appearance of keywords. A few factors are also identified for improved e-waste management and for achieving the sustainable development goals of 2030 though minimized utilization of natural resources.
CFD Modeling of a Scroll Work Recovery Expander for Trans-critical CO2 Refrigeration System
(Elsevier, 2017-03) Dasgupta, Mani Sankar
Fluid flow characteristics of CO2, as a refrigerant in a scroll work recovery expander is investigated using CFD approach. A 2D simulation is carried out, adopting dynamic mesh in Ansys environment (FLUENT) and turbulent flow in the scroll expander is modeled using PISO algorithm. Changing behavior of CO2 during suction, expansion and exhaust process in a scroll involute are captured at four rotation angles. Study is carried out for a commercially available geometry. Pressure and velocity distribution of CO2 along the involute profile for the trans-critical expansion process is presented. It is observed that the leakage space can be further optimized to reduce the internal leakage of CO2 which can increase the overall efficiency of the scroll expander.
CFD supported thermodynamic analysis of a CO2 pressure exchanger based refrigeration system for supermarkets
(Elsevier, 2023-04) Dasgupta, Mani Sankar
This manuscript presents a method to thermodynamically model a pressure exchanger device. CFD-based model of a rotary energy recovery device used in desalination process is developed and validated with published experimental data with a maximum deviation of 5.19%. The dimensionality of the validated model was reduced to investigate the potential of the pressure exchanger device operating with CO2 as the working fluid. Based on the data obtained from several numerical experiments, two correlations were developed, by means of non-linear regression analysis, for estimating the pressure lift generated by the device as a function of inlet velocity of high pressure fluid (0.5 – 3 m/s), rotor speed (500 – 3000 rpm), receiver pressure (25 – 40 bar) and gas-cooler pressure (90 – 120 bar). The correlations were found to be within acceptable error margin. The pressure lift generated by the pressure exchanger was found to be directly proportional to the inlet velocity of the high pressure fluid and inverse proportionality to the rotor speed. The developed correlations are used to evaluate the thermodynamic performance of a multi evaporator supermarket refrigeration system integrated with pressure exchanger to a conventional parallel compression system and a published multi-ejector system in the ambient temperature range of 30 to 40°C. The pressure exchanger based system was found to outperform the parallel compression as well as the multi-ejector system and demonstrate significant energy savings.
Classical nucleation theory based simulations of non-equilibrium condensation of carbon dioxide inside converging-diverging nozzles
(Begell House, 2021) Dasgupta, Mani Sankar; Yadav, Shyam Sunder
In the current work, we perform numerical simulations of the phase change process of Carbon Dioxide inside three different converging diverging nozzles, the experimental data on which is available in open literature. The simulations are performed with the classical nucleation theory based non-equilibrium phase change solver available in Ansys CFX with the thermophysical properties of CO2 obtained from NIST Refprop. We focus on the supercooling levels attained by the fluid and the distribution of the liquid mass fraction of CO2 during its high speed expansion inside the nozzles. The nozzle shape, expansion rate and fluid inlet conditions have a strong influence on the supercooling levels and the maximum liquid mass fractions obtained inside the nozzles. The results show much lower supercooling levels attained by CO2 (~ 2K) inside the Claudio Lettieri nozzle, the inlet state for which is near to the critical point. The supercooling attained by the vapor inside the Gyarmathy nozzle is around 22.5 K, the inlet state for which is far from the critical point. The case with the Nakagawa nozzle fails to converge properly.
CO2 heat pump for waste heat recovery and utilization in dairy industry with ammonia based refrigeration
(Elsevier, 2017-06) Dasgupta, Mani Sankar
Based on field data from a medium scale ammonia based milk refrigeration plant located in northern India, a trans-critical CO2 heat pump system with IHX is conceptualized for waste heat utilization. The waste heat is utilized to pre-heating the boiler feed water and thereby reduces energy consumption. A thermodynamic model of the refrigeration system is built and simulated for year-round field data. In this study, the condenser of the ammonia based refrigeration system is coupled with the evaporator of the proposed CO2 heat pump which is maintained at 20 °C year-round. The heat pump delivers heat at about 70 °C to pre-heat the boiler feed water drawn from underground source and is available in temperature range of 25 °C to 29 °C year-round. Thus, the CO2 heat pump performance is essentially independent of variation in ambient temperature. We reported reduction in CO2 emission and reduction in total energy cost by approximately 45.7% and 33.8% respectively. Economic analysis shows the payback period (PBP) is about 40 months.
Comparative analysis of a few novel multi-evaporator CO2-NH3 cascade refrigeration system for seafood processing & storageAnalyse comparative de quelques nouveaux systèmes frigorifiques au CO2-NH3 en cascade à évaporateurs multiples pour le traitement et le stockage des fruits de mer
(Elsevier, 2021-11) Dasgupta, Mani Sankar
Three novel CO2-NH3 multi-evaporator cascade refrigeration systems (CRS) are proposed and evaluated for application in seafood processing for high ambient. The CRSs have evaporators both above and below the cascade temperature and are intended to replace a multi evaporator NH3 system. They exploit the comparatively superior thermo-physical properties of CO2 in the low temperature evaporators while NH3 in the high temperature condenser keep the overall operating pressure low. Thermodynamic models of the CRSs for a single evaporator are validated against published literature. CRS1 has an individual compressor for each evaporator while CRS2 & CRS3 incorporate pumped circulation system in CO2 and NH3 circuits, respectively. The CRSs improve the overall efficiency, reduce ammonia charge and contamination hazards from NH3. Suitability of the proposed CRSs are established for a wide range of tropical ambient and also for cooling demands in other prominent seafood processing and storage applications like fish fillets and shrimp/prawn. CRS1 is found to give the highest COP advantage of about 11.5% in surimi processing where the foremost cooling load is at a high temperature evaporator. While CRS3 is found gainful for fish fillet & shrimp/prawn industry where the major cooling load is at low temperature evaporator. COP advantage of 16.5% & 20.3%, respectively are observed for fish fillet & shrimp/prawn processing. Dealing with surimi in climate condition of Mumbai (India), CRS1, showed a maximum 8.3% reduction in Annual average energy consumption (AAEC), while for fish fillets and shrimp/prawn CRS3 showed maximum AAEC reduction which is 7.5% & 13.2%, respectively.
Comparative Assessment of Low-GWP Based Refrigerating Plants Operating in Hot Climates
(Elsevier, 2017-03) Dasgupta, Mani Sankar
Carbon dioxide (CO2 or R744) and HFO-1234ze(E) are two promising alternatives to the currently employed high-GWP working fluids for food retail applications. In this paper, two indirect refrigeration systems using respectively R1234ze(E) and CO2 as the primary and the secondary fluid, a R744 booster configuration with parallel compression and a R744 booster solution with R290 dedicated mechanical sub-cooling are theoretically compared with a R404A multiplex direct expansion refrigerating system (baseline). The latter serves both the LT and the MT load. All the evaluated configurations are supposed to be for commercial refrigeration technologies. The results in terms of COP reveal that both the investigated “CO2 only” configurations have the best performance at low outdoor temperatures. On the other hand, the indirect solutions can outperform all the selected refrigerating plants at the extreme climatic conditions. In comparison with the baseline, a maximum reduction in annual electricity consumption by 6.4% and 8.9% is observed for R1234ze(E) and CO2 based systems, respectively.
Comparative investigation of low GWP pure fluids as potential refrigerant options for a cascade system in seafood application
(Springer, 2022-10) Dasgupta, Mani Sankar
The world is conscious about contribution to global warming from refrigeration and air-conditioning sector. A search is ongoing for energy-efficient refrigeration systems and environment-friendly refrigerants. Cascade refrigeration system (CRS) has been recognized as a prospective technology to improve energy efficiency while meeting multi-target temperatures. This study investigates various environment-friendly refrigerants for seafood processing and storage application having multi-target temperature in a warm climate. Fourteen potential low GWP pure fluids and one popularly used blend are identified as refrigerants based on literature survey. Out of these, six refrigerants (R41, R170, R1270, R404A, CO2, and N2O) were earmarked for the low-temperature circuit and ten (R152a, R161, RE170, R290, R1270, R1225ye(Z), R1234yf, R1234ze(E), R1243zf, and NH3) for the high-temperature circuit of the CRS. Suitable modelling and simulation techniques were employed to investigate the performance parameters namely COP, annual energy consumption, total equivalent warming impact, compressor volumetric displacement, compressor discharge temperature, and compression ratio. The refrigerant pair RE170-R1270 showed the best overall COP and also the lowest total equivalent CO2 emission for the application. NH3-CO2, the most studied refrigerant pair in literature, showed marginally lower COP; however, it has the lowest compressor volumetric displacement leading to a compact system with the minimum refrigerant charge. NH3 exhibited a higher compressor discharge temperature in all CRS, which can provide an opportunity for heat recovery. The study is expected to help the policy makers to frame regulations to encourage the use of sustainable refrigerants in the near future
Comparative study of cycle modification strategies for trans-critical CO2 refrigeration cycle for warm climatic conditions
(Elsevier, 2016-03) Dasgupta, Mani Sankar
This paper presents a comparative study of performance of six prominent modifications on the basic trans-critical CO2 refrigeration system to investigate their suitability to high ambient temperature application (35–55 °C). To explore the application in chiller, domestic refrigeration and air cooling the evaporator temperature chosen are −10 °C, 0 °C and 10 °C respectively. In general the cycle modifications have a positive effect on the overall COP of the system. However, to comprehend practicability of these modifications for three application areas, a few other parameters which affect design and operation are also included in the study. These are compressor discharge pressure and temperature, mass flow rate, interstage pressure for multi-stage operation and exergy destruction. Effect of real time constraints like approach temperature, pressure drop in gas cooler, compressors efficieny, degree of superheat, expanders efficiency and effectivenesss of intermediate heat exchanger are also incorporated. Interrelation between these parameters are brought out from the study.
Comparative study of Exergetic and Economic analysis of Multi-evaporator NH3 and NH3-CO2 CRS for a Seafood Processing Plant
(Bepress, 2021) Dasgupta, Mani Sankar
In a seafood processing plant, refrigeration is a vital and energy intensive process. In India, NH3 is predominately used to cater to such refrigeration demands. These industrial refrigeration systems have the multi-evaporator configuration with high pressure ratios necessitating adoption of multistage compression. In recent years, owing to excellent and favorable thermo-physical properties of CO2 in low temperature, adoption of NH3-CO2 cascade refrigeration system (CRS) with NH3 in high temperature cycle is gaining worldwide acceptance. In the present work, performance of a conventional NH3 multistage industrial refrigeration system is compared with a proposed NH3-CO2 CRS system in terms of energy, exergy and economic perspectives. Investigation is focused to thermodynamically evaluate and optimize the performance of the proposed cascade configuration with respect to operating parameters. A sensitivity analysis has been performed as well to study the effects of climatic conditions on system performance. The proposed NH3-CO2 CRS showed a maximum benefit of 13.3% in COP, 14% in exergy efficiency and 9% less TEWI compared to the baseline system. The estimated payback period is 25 months.
Comparative study of various supermarket refrigerating systems in European climate context
(IIR, 2018) Dasgupta, Mani Sankar
Due to the enormous carbon footprint of food retail stores the interest in natural working fluids, such as propane (R290) and CO2 (R744), has recently intensified in the commercial refrigeration sector. In this theoretical investigation the performance of various technologies employing low-global warming potential (GWP) refrigerants was compared in an average-size supermarket located in different European cities. It was found that a R744 multi-ejector enhanced parallel compression system consumed from 24.6% in Athens (Greece) to 37.1% in Oslo (Norway) less electricity compared to a R404A direct expansion refrigerating solution (baseline). Also, the results obtained suggested that CO2/R1234ze(E) indirect arrangements perform slightly better than CO2/R290 indirect units. In particular, the former offered, at best, energy savings by 6.9% (in Athens) over the selected baseline. Finally, it was revealed that the solution outfitted with the multi-ejector block features between 36.8% and 50.3% in heating mode and between 3.1% and 18% in air conditioning (AC) mode lower total power input than separated hydrofluorocarbon (HFC) units over the selected range of outdoor temperatures. It could be concluded that highly efficient as well as climate friendly technologies are readily available for the European food retail industry
A comparison of classical nucleation theory and thermal phase change based condensation models
(IOP, 2024) Yadav, Shyam Sunder; Dasgupta, Mani Sankar
In this work, we perform numerical simulations of the condensation process of CO2 inside a converging-diverging nozzle. We use Ansys Fluent for the simulation work. The real gas properties of CO2 are generated in tabular form (including metastable states) using NIST Refprop. We compare the distribution of physical quantities during the high-speed, compressible flow of CO2 inside a nozzle under the Classical Nucleation Theory (CNT) and the Thermal Phase Change (TPC) models. The CNT model is known to be accurate but computationally expensive while the TPC model is computationally cheaper. We observe that the TPC model predicts a knee in the pressure distribution near the throat of the nozzle while CNT predicts a continuous decrease in the pressure. The two solvers predict slightly different temperature, supercooling and liquid mass fraction values in the diverging part of the nozzle. The compressible, phase change simulations under high speed conditions can be performed quickly with the TPC solver. Overall, the TPC based solver appears to be a reliable alternative to the CNT based model.
A comparison of the equilibrium and the droplets based non-equilibrium compressible phase change solvers for condensation of carbon dioxide inside nozzles
(Global Digital Central, 2022) Dasgupta, Mani Sankar; Yadav, Shyam Sundar
In the current work, we simulate the condensation of supercritical CO2 during its high speed flow inside two different converging-diverging nozzles. We use the homogeneous equilibrium method and the classical nucleation theory based non-equilibrium phase change model for this purpose. The simulation results indicate significant influence of the nozzle inlet condition, nozzle shape and the fluid thermophysical behaviour on the nonequilibrium conditions prevailing inside the nozzles. We observe very low, 0.15 K, supercooling for the flow of CO2 inside the Claudio Lettieri nozzle compared to the supercooling of 3 K observed for the Berana nozzle. Very high nucleation rate ( 1035 nucleation per m3 per second) is observed before the throat of the nozzles which remains confined to a very small axial distance. The nucleation rate takes much smaller values ( 107 nucleation per m3 per second) in rest of the nozzle. A maximum of 70 nano meter sized droplets with number densities of the order of 1021 droplets per m3 are predicted inside the nozzles. Liquid mass fraction values between 0.2 to 0.4 are predicted by the solvers inside the nozzles. These results will be useful to the engineering community involved in the design and fabrication of CO2 based systems.
A Comparison of Three Different Flow Solvers For Simulating Steam Condensation Inside a Nozzle
(Springer, 2023-04) Dasgupta, Mani Sankar; Yadav, Shyam Sunder
In 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 nozzle