Singh, Shobhana

Packed bed thermal energy storage system is one of the promising solutions to store energy from the renewable power generation plants in the form of thermal energy. The selection of storage material is an important factor for the efficient functioning of the packed bed storage system. In this study, sandstone has been chosen as a storage material because of its good thermophysical properties such as high thermal conductivity, specific heat capacity, and density required for the energy storage in a packed bed, economic viability, and abundantly availability. The aim of the paper is to investigate the thermohydraulic characteristics of the packed bed storage with sandstone rocks as filler material and air as heat transfer fluid. A three-dimensional, dynamic model of a cylindrical packed bed thermal energy storage is developed in Ansys fluent. Transient simulations of the charging phase are carried out with a uniform void fraction of 0.39 and an airflow rate of 0.15?kg/s. Results from the model are compared with the experimental data with a reasonable agreement. The validated model is further used to assess the impact of temperature-dependent thermophysical properties of filler material on the dynamics of the sandstone packed bed energy storage. Results show that there is a significant difference in the performance characteristics when the model uses temperature-dependent properties. The sandstone rock bed with temperature-dependent properties takes a longer charging time, shows a relatively narrow thermocline region and higher pressure drop compared to the case with constant properties.

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.

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.

The heat transfer rate is experimentally investigated in horizontal tubes with constant heat flux boundary condition (UHF). The current study uses a modern-aged technique for contactless temperature measurement by Infra-red camera. Obtained thermal images give the two-dimensional wall temperature distribution. The data interpretation is then used for the visualization of the buoyancy-driven natural convection in laminar and turbulent pipe flow through 2D temperature contours along the length and across the test section diameter. A large variation in tube wall temperature in longitudinal as well as in the circumferential direction of the flow due to the secondary flow is observed for laminar flow under UHF. The heat transfer coefficient (HTC) ratio distribution helps in identifying the convection impact during different regimes. More strength is indicated by the HTC ratio for larger tube diameters.

The ions composition and their densities have been studied for different solar activity periods - along with their diurnal, seasonal and annual variations - for half of the 23rd solar cycle, covering solar minima (1995) to solar maxima (2000) over Indian sector (65–95ᵒE and 5–35ᵒN) at an average altitude of ~500 km. The study has been done by processing the data obtained from in situ measurement made by separate Retarding Potential Analyser (RPA) for electrons and ions, aboard Indian satellite SROSS C2. The plasma density has been found to be rich in O+ ion for all instances of time and showed a direct increase with solar activity. H+ has been observed to be in plenty during night time, especially from moderate to high solar activity period. The difference between H+ and O+ densities widens with increasing value of F10.7. He+ always constitutes a small part of plasma but its density exceeds H+ - during moderate to high solar activity period. O2+ has beenfound to be a minor constituent, even 3-4 folds lesser than He+ density. A positive correlation with solar activity has been found for O2+

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.

In this experimental study, a comprehensive analysis of the flash evaporation of a static liquid pool is conducted. The study investigates the impact of different parameters on the process, including the initial temperature of the water pool ranging from 50 to 85 ◦C and primary pressure between 5 to 50 kPa (abs.) with corresponding superheat levels ranging from 7 to 38 ◦C. The research highlights that superheat is the primary driving force behind flash evaporation operation, and its impact reduces over time. Initially, a high superheat value is present, which affects the temperature drop and evaporated mass evolution throughout the process, along with the initial water pool temperature.

In the present work, the thermal contact resistance in a double fin-and-tube heat exchanger is investigated using multiphysics numerical approach. A three-dimensional (3D) Computational Fluid Dynamic (CFD) model is constructed in commercial software COMSOL Multiphysics® by coupling steady-state conjugate heat transfer and turbulent fluid flow. The impact of contact resistance at the fin and tube interface is analyzed by quantitatively evaluating the thermal-hydraulic characteristics. It is found that contact resistance of 3.3 × 106 Km2/W can reduce the overall performance by approximately 6% when compared without thermal resistance at the contact interface. The developed model can predict the effectiveness of the fin-and-tube heat exchanger design with or without thermal contact resistances. Furthermore, the model can be employed to improve the overall heat exchanger performance used in various applications.

Real-time information on water supply and quality is a crucial asset for planning and managing water resources, infrastructure, and scientific research for sustainable development. In this direction, the innovative concept of smart water infrastructure is progressing. The present paper reports a case study on the demonstration of a `smart graded-water supply grid' on the campus of the Indian Institute of Technology Jodhpur, India. The paper describes the transformation of ∼13 km long water distribution network that supplies drinking water to ∼5,000 inhabitants into smart supply grid by deploying sensors and establishing an IoT-enabled real-time monitoring platform. The data sets of water flow and pressure collected from sensor nodes are analyzed to understand the characteristic diurnal water usage profiles unique to student hostels on the campus. The data show a distinctive consumption profile of student hostels over the weekdays with a maximum peak consumption of 16.38 m3/h. Monitoring of vital quality parameters such as chlorine, pH, and temperature demonstrate acceptable levels thereby ensuring compliance with safety standards. The purpose of the paper is to provide insights from a real-world case and close the knowledge gap between general awareness and the potential of smart water grid in sustainable management of graded-water services.

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.