Department of Mechanical Engineering

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P91 steel weld joint was prepared using the shielded metal arc welding process and four different conditions of weld consumable that provide the different levels of diffusible hydrogen in deposited metal. In the present research, the effects of diffusible hydrogen content on the flexural strength, lower critical stress, and tensile strength of P91 steel welds were also determined with respect to different electrode conditions. To investigate the effect of diffusible hydrogen on multipass welding, top and root side flexural tests were performed. The residual stresses (axial stress and transverse stress) were also measured using the blind hole drilling method for different conditions of welding consumable. The peak value of residual stresses was measured at the center of the weld fusion zone. The maximum value of transverse stress was measured to be 355 MPa for case II (6.21 mL/100 g of diffusible hydrogen), while the maximum axial stress was about 218 MPa for case IV (12.43 mL/100 g of diffusible hydrogen). A three-dimensional finite element simulation was also performed to predict the residual stress distribution and thermal profile along the welded joint. The experimentally determined residual stresses correlated well with the numerically estimated residual stresses. The diffusible hydrogen content was not observed to have any significant effect on the residual stresses. The corrected residual stress values were also predicted by considering the plasticity-induced error. However, the flexural performance of the welded joint was affected by the diffusible hydrogen content. The top and root flexural strength was measured to be optimum for the low level of diffusible hydrogen content, and the values decreased with an increase in diffusible hydrogen content. © 2018, The Minerals, Metals & Materials Society and ASM International.

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Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science

Effect of Weld Consumable Conditioning on the Diffusible Hydrogen and Subsequent Residual Stress and Flexural Strength of Multipass Welded P91 Steels

Vortex generators (VGs) are the most commonly investigated enhancement methods in the field of improved heat exchangers. The aim of present work is to study the effect of VGs in a fin-and-tube heat exchanger (FTHE) with herringbone fin shape. The delta winglet VG design with length (s) and height (H) is selected based on previous studies. The investigated VG design is simple and considered realistic from the manufacturing point of view. The combined enhancement with herringbone fin and the VG is evaluated by simulating the conjugate heat transfer and the air flow. The structured mesh is created for both solid and fluid domains to solve the model numerically using a coupled open source solver in OpenFOAM. The influence of flow condition on the performance enhancement is studied by changing the Reynolds number in a range Re=1354–6157. The study showed that VGs not only increase the heat transfer in the herringbone fin but also decrease the pressure drop. The highest and longest investigated VG design is found to perform the best because of its ability to delay the flow detachment from the tube, to feed high kinetic energy flow to the recirculation zone and to create longitudinal vortices in the downstream region from the VG. The fin with VG design s=0.5D and H=0.6Fp enhances the overall performance by 5.23% in comparison to the fin without VG. The results demonstrated the usefulness of VGs for the performance enhancement in connection with a herringbone fin design. © 2017 Elsevier Ltd

International Journal of Heat and Mass Transfer

Fin-and-tube heat exchanger enhancement with a combined herringbone and vortex generator design

Flight dynamic analysis and estimation of handling quality parameters have become important aspects in the design and development of helicopters. This paper presents a detailed analysis of the procedure for estimating the handling quality parameters such as quickness parameter, bandwidth and phase delay. The flight dynamic model used in this study considers rigid flap model for blade structural dynamics, three states dynamic inflow for inflow calculation and modified ONERA dynamic stall model for sectional aerodynamic loads calculation. The applicability of open loop linearized (uncoupled, and coupled) and nonlinear flight dynamic models in estimating the handling quality parameters is studied. For linearized models, only pulse input is used, whereas in the nonlinear model, two different types of input, namely pulse and step inputs, are used to estimate the attitude quickness parameters. The bandwidth and phase delay are calculated from the frequency responses of helicopter attitude in pitch and roll axes, which are obtained from the time response of nonlinear flight dynamic model for the harmonic excitation of cyclic pitch input. The results show that the attitude quickness parameter depends on the duration of input pulse and the nonlinear open system provides attitude quickness parameter which is different from that of the linearised system. In addition, it is noted that linearized flight dynamic models (8x8) cannot be used for bandwidthphase delay calculations, due to their lower order nature. Copyright © 2018 by author(s).

44th European Rotorcraft Forum 2018, ERF 2018

Estimation of handling quality parameters of a rotorcraft using open-loop linearized and nonlinear flight dynamic models

The objective of the present work is to study the heat transfer distribution in the helical coil flow boiling system. Infrared thermal imaging technique is used to measure the local wall temperature. The wall temperature is measured across the circumference and in axial direction along the length of a helical coil. The literature showing circumferential heat transfer distribution in a helical coil during flow boiling process is scarce. The present work compares the wall temperature and heat transfer coefficient distribution on the inner side and the outer side of helical coils at different diameter ratios and density ratios. In the present study, the experimental databank (containing total 400 heat transfer coefficient data points) includes the data not only from the present experimental study but also from the literature. The data bank includes the subcooled and the saturated flow boiling data. The data includes two fluids namely water and R123. Data covers the range of parameters namely a density ratio of 30–1600, a mass flux of 100–1300 kg/m2 s, a heat flux of 2–640 kW/m2, an exit quality of −0.5 to 1 and a coil to tube diameter ratio of 14–58. Ten empirical correlations which include well referred correlations of straight tubes and available correlations of helical coils are evaluated with the databank. The study concluded that the circumferential wall temperature variation in helical coils decreases with increase in a diameter ratio and with decrease in a density ratio. The circumferential averaged heat transfer coefficient during a saturated flow boiling in a helical coil is same as a straight tube. A correlation is suggested to measure the circumferential average heat transfer coefficient in helical coils. © 2017 Elsevier Ltd

Heat transfer distribution in helical coil flow boiling system

Vision based techniques for kinematic identification of an industrial robot and other devices

Solar thermal resources can be effectively utilized to meet the refrigeration and air-conditioning demands for both household and industrial purposes. Considerable fraction of total available electricity is consumed by the conventional vapor compression refrigeration systems (VCRS) during the summer season in countries with tropical climate. The leakage of VCRS refrigerants in the atmosphere has also been identified as one of the major contributors toward ozone layer depletion and hence global warming. The utilization of solar thermal energy for obtaining refrigeration and air-conditioning is the key to address these issues concerning high electricity demand as well as the environmental pollution. Solar thermal energy, being one of the leading resources of green energy, can reduce the carbon footprint considerably, when used for sorption cooling process. The advantages of using sorption cooling systems powered by solar thermal energy over VCRS are twofold when we consider environmental issues. Sorption-based solar thermal cooling reduces the electricity demand for cooling to a large extent, which in turn reduces usage of fossil fuels to produce this electricity, and thus leads to low-carbon footprint. Also, the refrigerants used for sorption cooling are less prone to cause ozone layer depletion. Although sorption-based refrigeration systems driven by solar thermal energy are mature technologies, wide acceptability of such cooling system is yet to be achieved. Two major limitations of sorption-based solar thermal cooling are relatively low coefficient of performance (COP), and large volume requirement. Other than these two limitations, the intermittent nature of solar thermal resource and heat exchanger and control mechanism design complicacies also pose considerable challenge. Sorption cooling technology can be broadly classified base on absorption and adsorption processes. Absorption is a volumetric phenomenon where a substance of one state gets absorbed in another substance in a different state with or without having chemical reaction, such as liquid being absorbed by solid or gas being absorbed by liquid. On the other hand, adsorption is a surface phenomenon due to physical bonding forces such as Van der walls forces between a solid surface and adjacent fluid or due to chemical bonding between the two. The discussion in this chapter is attributed to Water–Lithium Bromide-based absorption cooling systems. The discussion emphasizes on fundamental concepts of absorption refrigeration cycle, starting with simplest intermittent vapor absorption refrigeration system and gradually elaborating toward the operating principles of commercially used chillers at the end. Cycle analysis of most commonly used single-effect absorption chillers is discussed in a detailed manner along with the background knowledge of how to determine pertinent thermodynamic properties at the inlet and outlet of individual components. Finally, methods and design criteria that can improve the system performance are discussed. © 2018, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Water–Lithium Bromide Absorption Chillers for Solar Cooling

Quality of casting products can be significantly improved by controlling the crystal growth rate. Both dendritic and equiaxed grain structures depend strongly on crystal growth rate along the crystallographic direction. Uncontrolled solidification processes may lead to the formation of porous and columnar material with an extremely non-homogeneous composition distribution. These undesirable micro-structures can be avoided by adopting an optimal cooling rate (K/s) during the crystal growth. The present work focuses on determining suitable cooling curves to obtain desired unidirectional crystal growth rates, by implementing a semi-analytical model. Here, we defined cooling curve as the time history of temperature evolution at the cold boundary. The proposed semi-analytical heat transfer model is diffusion driven and accounts for shrinkage effect during solidification. The proposed model is found capable of predicting cooling curves for prescribed interface velocities. The model is self-sufficient in validating itself by means of solving inverse and forward problems. The cooling curve prediction by the model is validated by using it as the transient boundary condition for an existing enthalpy updating scheme-based numerical model. The proposed model is also applied to empirical data reported in literature, to validate the model against experimental results. All the validations showcased excellent fit. The proposed model will facilitate controlled unidirectional crystal growth rate by providing cooling rate (K/s) as an input for the experiments involving directional solidification. © 2018, The Minerals, Metals & Materials Society and ASM International.

Prediction of Cooling Curves for Controlled Unidirectional Solidification Under the Influence of Shrinkage: A Semi-analytical Approach

Over the past few decades, considerable research efforts have been devoted to improve the usage of renewable energy resources. Till date, major energy demands have been addressed by fossil fuels, and the limited resource of these precious fuels is continuously depleting at an alarming rate. Increase in the energy demands, deficiency of fossil fuels, and influence of pollution on the environment have forced us to opt for renewable energy resources. Solar energy is a natural source of energy that is not depleted by its use. It is a promising option for replacing conventional energy resources partially or totally, but it is transient, intermittent, and unpredictable in nature. Because of this sporadic nature of solar energy across a given interval of hours, days, and season, various practical problems arise. Variable DNI causes power plants to shut down for few hours of the day or to run at part load most of the time. This creates a demand for an effective subsystem which is capable of storing energy when available solar energy overshoots the demand during the interval of radiant sunshine, and to make it accessible during night or season. A similar problem arises for waste heat recovery systems where accessibility of waste heat and usage period are not the same, and thus creates a need for thermal energy storage (TES) for energy conservation. TES has tempted a lot of researchers to improve its high energy storage capacity and efficiency. If solar energy system is not run with TES, a considerable section of energy demand has to depend on conventional resources which in result reduce the annual solar fraction. TES helps to reduce dependency over conventional resource by minimizing energy waste. TES is mainly described by the parameters like capacity, power, efficiency, storage period, charge and discharge time, and cost. There are different storage mechanisms by which energy can be stored: sensible, latent, and chemical reactions. In sensible-type storage, energy is stored by increasing the temperature of solid or liquid storage media (e.g., sand-rock minerals, concrete, oils, and liquid sodium). These materials have excellent thermal conductivity and are cheaper, but due to low heat capacity, it increases system size. In latent-type storage, energy is stored/released during phase change; thus, it has higher storage capacity than sensible, but suffers from the issue of low thermal conductivity. As the solid–liquid phase change process of pure or eutectic substances is isothermal in nature, it is beneficial for the application having limitations with working temperature. In chemical-type TES, heat is absorbed/released due to breakdown or formation of chemical bonds. The technology is not much developed and has limited application due to possibility of degradation over time and chemical instability. TES can also be classified as active and passive depending upon the solid or liquid energy storage medium. Active TES is further classified as direct active and indirect active depending on whether the storage fluid and the heat transfer fluid (HTF) are same or some other HTF is required to extract heat from solar field. The discussion in this chapter includes basic heat transfer models, along with experimental studies by different research groups on various TES. Finally, methods and design criteria that can improve the system performance are discussed. © 2018, Springer Nature Singapore Pte Ltd.

Solar Thermal Energy Storage

The present work focuses on developing a 2-D axisymmetric numerical model to study the dynamic behaviour of charging and discharging cycle for an elementary latent heat storage unit with simple geometry. The domain under consideration consists of a pipe of negligible thickness carrying heat transfer fluid (HTF), while being surrounded by latent heat storage medium or the phase change material (PCM). The PCM domain is considered to be 2-D axisymmetric and heat transfer mechanism is diffusion dominated. On the other hand, 1-D model is considered for the flow of HTF through the pipe. The heat transfer models in the PCM and HTF is coupled through the energy balance at the pipe wall. A fully implicit Finite Volume model is developed to obtain the evolution of temperature in PCM and HTF domain along with extent of melting/solidification in the PCM domain. Simulations are performed for charging and discharging of PCM domain considering pure PCM and PCM-Graphite composite with enhanced thermal conductivity. © 2018 by the authors of the abstracts.

International Conference on Computational Methods for Thermal Problems

Numerical analysis of latent heat thermal energy storage (Lhtes) performance: A 2-D axisymmetric approach

An electricity consumer paying residential tariff and is willing to become a producer of power through photovoltaic (PV) panels is termed as a solar prosumer. The demand for distributed deployment of solar energy through such panels in Europe, USA and Japan arose due to the residential rooftop sector. In contrast, large scale power plants led the solar power growth in India. This article presents some of the efforts made to generate awareness regarding roof top PV plants in India and addresses the reasons behind the Indian residential (and even commercial) electricity consumers' unwillingness to become solar prosumers. In the recent times, the concept of adding energy storage capacity to solar panels is referred to as 'prosumage', still uneconomical at large. Going off-grid is a possible option in the Europe and USA, if an inexpensive storage option is provided to take care of intermittency of solar energy. An unreliable grid is one of the reasons for seeking energy storage in the Indian context. In addition there exists a significant captive power generation capacity through diesel generator sets, wind, biomass and other energy sources. Hybridization of solar with such sources can be a way forward to meet the goals of the solar mission. © 2017 IEEE.

Proceedings of 2017 IEEE International Conference on Technological Advancements in Power and Energy: Exploring Energy Solutions for an Intelligent Power Grid, TAP Energy 2017