arXiv subjects

Piyush Mani Tripathi

Publications and source records attributed to Piyush Mani Tripathi.

3 recordsLinked to original sources

arXiv2024

Multi-Physics Numerical Analysis of Single-phase Immersion Cooling for Thermal Management of Li-Ion Batteries

Battery thermal management systems (BTMSs) are critical for efficient and safe operation of lithium-ion batteries (LIBs), especially for fast charging/discharging applications that generate significant heating within the cell. Forced immersion cooling, where a dielectric fluid flows in direct contact with the LIB cells, is an effective cooling approach. But because of its complex nature, a thorough understanding of the underlying physics - including the coupled electrochemical, thermal, fluid, and mechanical effects - is required before immersion cooling will see wide adoption into commercial systems. In this work, to investigate the performance of a LIB subjected to forced immersion cooling, we develop a fully coupled modeling approach that solves the detailed electrochemical model in conjunction with the thermal-fluid transport models for both the cell and fluid domain. After calculating the electrochemical and thermal responses, we also estimate the mechanical stresses within the cell generated due to the ion diffusion and temperature rise that impact reliability. To assess the effectiveness of forced immersion cooling, we evaluate several different configurations for a cylindrical 18650 battery cell under varying cell discharge rates. We compare forced immersion cooling for two liquids (deionized water and mineral oil) at three different fluid mass flow rates. The results highlight the strong cross-coupling of the electrochemical and heat transfer phenomena. By comparing results across fluids and flow rates, we define a new metric that can be used to compare the cooling capacity considering different flow parameters. Overall, this study provides insights that will be useful in the design of immersion cooling-based BTMSs including, for example, the selection of forced immersion cooling specifications, such that the temperature is controlled without significant capacity loss.

physics.flu-dyn↗

arXiv2021

Effect of wall roughness on heat transfer in the supercritical water flow

This paper discusses the numerical investigation of the wall roughness effect on the supercritical water flow susceptible to heat transfer deterioration (HTD). The simulation was carried in the vertical circular pipe using the SST k-omega turbulence model for different sets of heat flux (220kW/m2 & 1810kW/m2) and mass flow rate (0.0106kg/s &0.022kg/s) at a maximum pressure of 25.3MPa. The presence of roughness was incorporated as a uniform sand-grain roughness on the heated wall. As a result, HTD recuperated gradually as the roughness height (Ks) was increased. The mitigation of HTD is a direct consequence of the increase in turbulent kinetic energy (TKE). In contrast, the delay in the onset of HTD is due to the decrease in the dominant forces (buoyancy or acceleration effects) responsible for HTD occurrence. An equivalent thermal resistance model was proposed to elucidate the same. Additionally, the heat transfer coefficient reduces (HTDn) near the outlet at higher roughness values where HTD has completely recovered. This is attributed to the high specific heat value around the pseudocritical temperature. In the end, the efficacy of the roughness was analyzed using two methods: entropy generation and thermal performance factor. Both techniques suggest that the use of rough pipe is beneficial. However, the first method recommends using a Ks value greater than the critical roughness height (Ksc): as the total entropy generation was found to peak at Ksc because of the thermal conductivity variation with temperature. The study revealed high sensitivity of maximum wall temperature and HTD onset to roughness presence. In addition, contrary to usual HTD, a new type of heat transfer impairment (HTDn) can occur without any loss of TKE.

physics.flu-dyn↗

arXiv2020

Novel two-phase method for supercritical water flow

The current resurgence in the phase diagram study beyond the critical point has questioned the conventional belief of supercritical fluid as a single phase with varying properties. On the same line, a novel two-phase approach has been proposed to study the supercritical flow with heat transfer deterioration (HTD) phenomena. The Volume of Fluid (VOF) multiphase model has been used to analyze the flow, and the simulation result reasonably predicts the wall temperature peaks. Moreover, the velocity and turbulent kinetic energy profiles for different axial locations explain the occurrence of HTD, and it is on par with the pre-existing numerical method. Besides, the quantitative analysis presented in the paper expounds on qualitative understanding. The parametric study of the thermophysical properties revealed that the density variation is the primary cause of HTD in supercritical flows. So banking on this conclusion, the propounded study focuses on the forces generated due to the density variation. This technique equips us with a holistic picture of the supercritical flows. It leads to the inference that for no HTD effects to be present, buoyancy and inertia forces have to be of comparable magnitude throughout the flow. In addition, the pseudo phase change model outclasses the existing research by rendering us the volume fraction data. Mapping of this variable reveals a sudden jump in the lighter phase's thickness near the wall at the site of HTD, which is also reflected as a maximum in the nondimensional two-phase thickness (P) plot. Nevertheless, this observation is only restricted to HTD caused by buoyancy. In the end, a theoretical expression has been conceptualized for computing the two-phase thickness (h) value, which can serve as a fundamental length scale in supercritical flows as it marks the region of highest property gradient near the wall.

physics.flu-dyn↗