Swasti Sundar Mondal

Maintaining both maximum temperature and temperature uniformity within the desirable limit is a crucial issue for high C-rating Li-ion batteries of electric vehicles, which can be achieved by the properly designed battery thermal management system (BTMS). In this research, three new designs of liquid-cooled micro-channeled BTMS are suggested for cylindrical batteries to address the issue of temperature variations and uneven temperature distribution. Using 3D numerical simulation, we investigate the impacts of volume flowrate and the usage of mono/hybrid nanofluids with varying concentrations on the thermal performance of the battery pack at a high C-rate by utilizing a two-phase mixture model. Effects on maximum temperature, temperature uniformity, pumping power, and heat transfer coefficient to pressure drop ratio are investigated. Results demonstrate that the effectiveness of heat transmission and temperature uniformity of the battery pack are positively impacted by an increase in nanoparticle concentration in nanofluid and volume flow rate. Even at high C-rates (5 C), the proposed design can effectively reduce both cell temperature and thermal gradient of the 21700-type cylindrical cell. Design 3 is the most favorable BTMS for Li-ion cylindrical battery in terms of both maximum temperature and temperature uniformity (maximum temperature of 304.72 K and temperature difference of 4.7 K).

A simplified 2D axisymmetric computational fluid dynamics simulation of oxy-coal combustion is performed to address the influence of swirl strength and the combustion environment on the flow field and combustion characteristics. A quantitative analysis of the internal recirculation zone length and flame length under various operating conditions is studied by employing developed numerical models. The influence of char-CO₂ and char-H₂O gasification reactions on the species consumption and temperature profile is also studied through numerical modelling. The swirl strength considerably influences both the flow field and temperature profile inside the furnace. At higher swirl strength, radially dispersed shorter flames are obtained due to spreading of the secondary stream. Results showed that the flame shifted towards the burner at higher oxygen content due to rapid devolatilisation at higher flame temperature. The ignition of pulverised coal particles is enhanced at higher oxygen concentration due to increased stoichiometry near the burner. Oxy-35% O₂ has 300 K higher flame temperature than oxy-21% O₂. Endothermic gasification reactions significantly influence the temperature profile in the furnace. CO₂-char gasification reaction has a more pronounced influence than the H₂O-char gasification reaction. The consideration of gasification reactions has resulted in an approximately 5% reduction in peak temperature.

Oxy-coal combustion is the most promising technology for the reduction of greenhouse gases from pulverized coal-fired power plants. Oxy-coal combustion employs recirculated flue gas mainly consisting of CO₂ and water vapor as a diluent. Thus, the pulverized coal particles are surrounded and burned under steam rich atmosphere. The addition of H₂O would have a significant impact on the combustion characteristics of oxy-coal combustion. The chemical and physical properties of steam are different than the CO₂, replacement of CO₂ with steam will alter heat capacity, gasification, and radiation properties considerably. The present article numerically compares ideal dry recycle oxy-coal combustion (0% H₂O) with wet recycle oxy-coal (10-50% H₂O) and oxy-steam combustion (H₂O replaces whole CO₂ from oxidant) in terms of flow field, temperature distribution, oxidizer distribution, radiative heat transfer, char consumption, and species concentration. Higher flame temperatures under enriched steam oxy-coal combustion cases were found due to lower volume heat capacity of H₂O than CO₂. Steam enrichment also enhanced char gasification reaction, which has affected temperature distribution and incident radiation profile inside the combustion chamber. Peak temperature obtained under oxy-steam case is around 10% higher than ideal dry recycle case (0% H₂O) and 2-5% higher than the wet oxy-coal combustion cases having 50-10% H₂O in the oxidizer.

In the present article, CFD simulation of various oxy-fuel combustion cases has been performed to find out the influences of oxy-fuel combustion environment on temperature distribution, char consumption, radiative properties and temporal variation of particle phase variables such as particle temperature, volatile and char mass fraction. The oxy-fuel combustion cases are obtained by varying O₂ and CO₂ concentrations while keeping the total volume flow rate constant. Four oxy-fuel cases are considered in the present work having oxygen concentration 21%, 25%, 30%, and 35%. The present article also investigates the influence of char gasification reactions on temperature distribution, species concentration and temporal profile of particle char mass fraction. The predicted temperature distribution and radiative properties under oxy-fuel cases are compared with the corresponding values obtained under air-fired combustion as for retrofit existing power plants comparable values are desirable. The oxy-30 case having 30% oxygen has almost identical temperature and radiative profiles. With an increase in oxygen concentration in oxy-fuel cases leads to an increased peak temperature and surface incident radiation due to the rise in local stoichiometry, which results in enhanced reaction kinetics and burning rate. The peak temperature obtained in oxy-25, oxy-30 and oxy-35 cases is around 10%, 18%, and 24% higher than the oxy-21 case. Reduced char burnout time is obtained due to the presence of gasification reactions.

Carbon capture and storage employing oxy-fuel combustion is one of the most promising options to reduce greenhouse gas emission. For the transition from conventional air-fired combustion to oxy-fuel combustion, there is a necessity of detailed investigation of various phenomena that occur during oxy-fuel combustion. Numerical modeling of oxy-fuel combustion process can serve the purpose effectively and efficiently. The current paper presents a thorough numerical investigation of the combustion process of pulverized coal under oxy-fuel conditions. The influence of inlet temperature and pressure of feed gas is investigated in the present study. Computational fluid dynamics simulation is performed for the test facility located at the Institute of Heat and Mass Transfer at Aachen University. The numerical results obtained employing various Reynolds Averaged Navier Stokes (RANS) models have been compared with measured data. The results showed that the strength and axial dispersion of the internal recirculation zone (IRZ) are enhanced at higher inlet temperature. The combustion of volatile matter present in coal shifts near the burner which results in shorter flames at higher inlet temperature. The flame temperature increased by ~9% with increase in inlet feed gas temperature from 313 to 800 K. Inlet feed gas pressure of 10.0 bar has ~38% increment and ~32% reduction in IRZ length and flame length, respectively, than the base case.