Singh, Shobhana

Sustainable development goals and industry 4.0 push for a holistic plan of action for smart water infrastructure enabling advance digital technologies such as Digital Twins for water networks through an integrated use of machine and physical counterparts. This paper proposes a Digital Twin framework for leakage detection applications in large scale water distribution systems. The framework elucidates digital map generation of the network, hydraulics modelling, calibration and leakage detection model in an integrated manner using python interface. The hydraulic model accounting for spatial and temporal variations of network hydraulics and an optimization formulation for calibration and graph neural networks for leakage identification has been developed. The framework is applied, and results have been demonstrated on a real-life case study of IIT Jodhpur campus water distribution system.

Phase Change Materials (PCMs) are widely used materials in thermal management applications. The passive working, good thermal stability and inherent thermophysical properties make PCM a natural fit for thermal control devices. However, their performance in real working conditions is often different from the behavior measured at lab scale owing to the effects occurring from varied heat sources, length scale, gravity forces, enthalpy and supercooling effects, etc. In this study, a two-dimensional computational fluid dynamic (CFD) model of a PCM-filled square enclosure with constant temperature bottom heating is developed to investigate the impact of reduced gravity on the melting process of PCMs and assess the dynamic characteristics that evolve with time. The control volume-based enthalpy porosity approach is utilized to simulate the melting process of paraffin-based PCM. Numerical simulations are carried out with reduced gravity environments by varying g to 0.2g. The evolution of flow regimes from conductive to convective through the destabilization of conductive state to the onset of Rayleigh-Bénard convection, and chaotic flow is presented in terms of temperature and flow fields. It is found that when the gravity is reduced to 0.2g, the onset of convection delays by ∼ 3 times compared to the time taken by PCM under the standard gravity. In conclusion, the present study has provided valuable insights into the underlying physical phenomenaofPCMmeltinginreducedgravityimportant in developing design strategies for PCM-based thermal energy storage systems that can operate effectively in reduced gravity environments.

Jupiter’s magnetosheath is a natural yet complex laboratory for analyzing compressible plasma turbulence. Recent observations by the Juno mission provide a promising opportunity for the first time to reckon the energy cascade rate in the magnetohydrodynamic scales in the vicinity of Jupiter’s space. In the present work, a two-dimensional model is constructed for a whistler wave that is nonlinearly coupled with a wave magnetic field via ion density perturbation. The dynamics of whistler wave propagating in the direction of the magnetic field are derived within the limit of the two-fluid modeling approach. The magnetic field localization along with magnetic field spectra and spectral slope variations are estimated to realize the turbulence generation and energy cascade from large to small scales in the Jovian magnetosheath region. The simulated magnetic field spectrum in the wave number (in the unit of ion inertial length ρ i ) consists of turbulence in the inertial range with a spectral slope of −1.4 and a spectral knee at k ρ i = 1. Subsequently, the spectral slope increases to −2.6 and the spectrum becomes steeper. The simulated magnetic field spectrum in the wave number is further translated into the frequency domain using the whistler wave dispersion relation and by considering the Taylor frozen-in condition. The analytically estimated magnetic field spectrum slopes, i.e., −1.8 and −4.2 at low and high frequencies are further compared with recent Juno mission observations. The comparison further affirms the existence of Kolmogorov scaling, a spectral knee, and steepening in the spectrum at high frequencies. Furthermore, it is found that the two-fluid model can reasonably simulate the turbulence effects in Jovian magnetosheath in terms of magnetic field spectral distribution in wave number and frequency domains.

Latent thermal energy storage devices can efficiently store surplus thermal energy during off-peak hours. The system's phase change material (PCM) improves energy storage capacity and isothermal properties. Most PCMs have weak thermal conductivity, which hampers heat transfer. Thus, the present analysis involves an insight into the heat transfer characteristics and thermal performance of a vertical tube-in-tank cold storage system. The objective of this investigation is to gain a better understanding of the significance of buoyancy-driven convection within the side bulk region during the discharging of water as PCM in the heat exchanger. A series of experiments are conducted to investigate the effect of varying the initial bulk temperature on the rate of PCM solidification. The effects of three distinct initial bulk temperatures which are 20 °C, 15 °C, and 5 °C on the solidified mass fraction, thermal performance, and heat transfer rate at various radial and axial locations in PCM are examined. It is seen that PCM experienced a varying cooling rate with varying axial height and is found to be the highest in the bottom region. PCM temperature decreases from top to bottom under the cases of 20 °C and 15 °C, respectively. In contrast, a narrow-ranged thermocline layer is observed under 5 °C bulk temperature, making uniform temperature distribution within the bulk. The influence of bulk natural convection prevails in the later stages of the discharging process under 5 °C bulk, whereas it predominantly exists during the initial stages of solidification under bulk temperatures of 20 °C and 15 °C.

The present work aims to investigate dynamic characteristics of Rayleigh–Bénard convection during the solid–liquid phase change process under the influence of variable low-gravity conditions. Low-gravity conditions are crucial to gain physical insights into the complex convection dynamics relevant in terrestrial and space environments that feature diverse gravitational fields. The melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 in a square rigid walled enclosure is analyzed by subjecting it to a fixed temperature difference resulting in a Stefan number Ste ≈ 0.33. The enthalpy porosity method is employed to simulate the solid-liquid phase change process in Rayleigh number range 105

The present work investigates the combined effect of varying gravity and heat flux direction with respect to gravity on the melting dynamics of Phase Change Material. Similar conditions are relevant to applications in space, at different space infrastructures, such as orbiting satellites, as well as various extraterrestrial surface assets, landers, and rovers. The numerical simulations are performed to study the melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 and Stefan number Ste ≈ 0.33 inside a differentially heated square enclosure. The mathematical model employs a control volume-based enthalpy porosity approach to simulate the melting process inside enclosure. The direction of the incoming heat flux relative to the gravity vector is defined in terms of an orientation angle, which is varying circularly with a step of 45°, whereas the gravity level is ranging from the terrestrial surface value g to 0.2g to analyze the melting process over a wide range of Rayleigh number 100 ≤ Ra ≤ 107. The study provides a detailed insight into the attributes of heat transfer, flow dynamics, and energy storage, along with a quantitative analysis of the transition between various melting regimes and temporal fluctuations in the performance parameters. The findings demonstrate that the mutual orientation between the directions of incoming heat flux and gravity, as well as the value of the latter, significantly affect features of the convective motion in the liquid phase, as well as the entire thermally driven heat transfer within the domain. In particular, for the oppositely directed gravity and heat flux, the melted fluid closely resembles Rayleigh-Bénard convection with the presence of multicellular flow structures, while at other orientation angles, except for a co-directed gravity and heat flux case, a circular convective motion of the melted fluid takes place. The results of numerical simulations reveal declining melting rates as the mutual orientation of gravity and heat flux changes from opposite to co-directed and vice versa. The low gravity conditions delay the onset of convection-driven melting, reducing the melting rate significantly.

The present work employs numerical simulations, using Rayleigh-Bénard (RB) convection as a platform, to investigate the influence of different orientations of the gravity vector and heat flux on the melting dynamics of a Phase Change Material (PCM). A paraffin-based PCM with Prandtl number Pr ≈ 71 and Stefan number Ste ≈ 0.33 is utilized to analyze the melting process over a wide range of Rayleigh numbers (102 ≤ Ra ≤ 107). The simulations are conducted in a differentially heated square enclosure, employing the control volume-based enthalpy porosity approach to examine the melting process at various angles between the gravity vector and the incoming heat flux. The results demonstrate that the mutual orientation of the incoming heat flux and gravity significantly affects features of convective motion in the liquid phase and the overall thermally driven heat transfer within the PCM. Specifically, when gravity and heat flux are oppositely directed, the melted fluid exhibits characteristics resembling RB convection, including flow instabilities, bifurcations, structured flow patterns, and chaotic flow behavior. However, a critical orientation angle exists above which melting occurs with a rotational convective motion of the liquid PCM, and the flow remains laminar throughout. In the case of co-directed gravity and heat flux, melting occurs solely through diffusion without the formation of convection currents. This work aims to explore potential changes in flow phenomena, establish criteria for the onset of instabilities, map changes in interface topology, elucidate complexities of nonlinear flow dynamics, and draw comparisons with classical RB systems. In summary, the present study provides comprehensive insights into the dynamics and stability criteria of a phase-change RB system across a broad range of Rayleigh numbers at different mutual orientations between heat flux direction and gravity vector.

Exploring and studying alternative energy options are essential for solving the energy crisis. A thermoelectric (TE) generator is one of the best options available for waste heat recovery. To enhance the performance of the thermoelectric device, it is essential to study the thermoelectric module and analyze the factor affecting the performance of the TE module. In the present work, the influential parameters such as leg length, leg width, load resistance, and temperature on the hot side of the TE module with different combination are numerically investigated. The current numerical work provides the optimal value of the each parameter for efficient working of the TE generator. A 3D model of thermoelectric unicouple is developed to analyze the effect of aforementioned geometric parameters. Moreover, the results of leg length, leg width, load resistance, and temperature on the hot side of the device on the efficiency and power output with constant surface temperature boundary condition are discussed.

The electronic components, instruments, sensors, and other satellite payload subsystems generate significant heat during repeated transient duty cycles. The thermal management of such satellite payload subsystems becomes more challenging under the influence of the microgravity environment. The rapid temperature fluctuations caused due to stringent space environment may lead to the overheating/failure of electronic devices. The phase change materials (PCM) are the natural fit for the thermal control of such satellite subsystems where the heat dissipation is non-continuous. Moreover, during the melting and solidification processes, the PCMs have a tendency to either expand or contract. Designing the containment system for PCM must take both thermal and structural factors into account. Due to the harsh environmental conditions, designing the containment system to accommodate PCM volume change, particularly for space applications, provides extra challenges. Consequently, the present work deliberates two different mass accommodation methods (i.e., an open boundary and a free/movable surface), which takes into account the effect of volume expansion on the melting cycle of PCM. The computational domain consists of an enclosure filled with paraffin-based PCM, and a comprehensive comparative analysis of the PCM melting accommodating volume expansion effects is discussed in the present work.

In an automobile, only one-third of the total fuel energy is used for propulsion, and the remaining two-third is lost to engine coolant and the exhaust as waste. Thermoelectric generators (TEG) demonstrate huge potential in automotive applications by recovering the exhaust waste heat and converting it into direct electric power. TEG helps escalate the engine’s fuel efficiency. However, extracting waste heat from automobile exhaust using TEG manifests practical difficulties attributed to thermoelectric materials, design, and operating conditions. Ineffective configurations and heat exchanger designs lead to non-uniform flow and temperature distribution on the hot and cold sides of TEG, causing undesirable power output, which lowers the entire system’s efficiency. In this study, the flow distribution of exhaust gas through the automotive TEG with pin fin heat exchanger is simulated using Computational Fluid Dynamics (CFD). Improvement in the flow pattern using passive flow distributors such as guide vanes at different angles is analyzed to attain the temperature uniformity through the hot heat exchanger surface. A detailed analysis of flow distribution and its influence on the local and average temperature distribution is presented. Results provide critical design recommendations to improve the flow distribution in an automotive TEG for exhaust waste energy recovery.