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High solar irradiation, cloud-free dry climate, abundant barren land, and low ambient temperature make the Union Territory of Ladakh, India, suitable for concentrating solar thermal power (CSP) plants. The present study comprehensively analyzes a 5 MW transcritical CO2 Rankine cycle power tower CSP plant. Low ambient temperature of the region allows transcritical operation, which provides high cycle efficiency. The study focuses on five aspects: solar field and thermal energy storage (TES), thermodynamic cycle simulation, turbomachines, and off-design performance analysis. Modeling and optimization of the solar field are undertaken to capture the diurnal and annual variations of direct normal irradiation levels using System Advisor Model open source software. Molten salt TES is integrated to overcome the dynamic variations of solar energy by providing stable operations and additional hours. The effect of storage sizes, starting from no storage to 12 hours, on the solar field size and specifications is also assessed. An in-house algorithm is developed for thermodynamic cycle optimization, exergy analysis, and off-design operations. The turbomachines of the cycle are designed using in-house meanline codes, and 3D CFD simulations are conducted for efficiency estimations. The effects of ambient temperature variations on the low side saturation pressure, cycle efficiency, and power output are evaluated. The proposed plant offers annual optical efficiency of 54.1%, thermal efficiency of 36.5%, and overall efficiency of 19.7%.

This paper investigates the performance of a canister module filled with phase change material (PCM) that is thermally coupled to an axially grooved heat pipe and designed for thermal management of unsteady or cyclic heat loads in spacecraft applications. The PCM canister stores heat from the electronic devices during brief transient peaks and slowly releases this heat to the heat pipe during idle cycle time. A rectangular prism canister module is manufactured and filled with eicosane based on the geometrical parameters obtained from a thermal network model. The performance of this canister is evaluated experimentally, and the thermal network model is validated. Detailed theoretical and experimental evaluation of heat balance for the PCM canister and the heat pipe is carried out. All the required input parameters, including the heat capacity of the heat pipe, for the thermal network model, are theoretically estimated and experimentally evaluated. In general, the difference between predicted and experimental temperature values is observed to be within 3°C, except at the ends. PCM coupled heat pipes result in significant enhancement of the operating time and reduction in the peak temperature. This would be useful in spacecraft applications to reduce the size (and hence the mass) of the thermal radiator.

In this work, a method of focal region flux characterization of Scheffler fixed focus concentrator is presented. Being a fixed focus concentrator, Scheffler dish serves as an ideal focusing unit for on-Sun testing of scaled down high pressure receiver designs under actual boundary conditions. Flux characterization is performed numerically by tracing the ray trajectories from their inception till the focal region and experimentally using point-based heat flux sensors. A circular plate is mounted at the focal region with five water cooled heat flux sensors attached. Four of these sensors are positioned around a diameter of size corresponding to an existing cavity receiver aperture diameter and one sensor is located at the plate centre. These sensors help to obtain the point based flux measurements in the region. Since the dish is not parabolic, a non-Gaussian flux profile is obtained, and spatial averaging of the flux data is performed analytically to obtain an averaged heat flux value. This averaged flux density is then matched with the spatially resolved flux map average value obtained from the numerical analysis. Average thermal power intercepted on the target surface is also measured, which serves as a useful procedure for estimating the radiative power incident on the receiver aperture. Further, as a demonstration exercise of the present fixed focus dish characterization method, a receiver testing methodology with an existing hybrid cavity and tubular design using compressed air is presented.

Sorption-based thermal storage has drawn considerable attention for sustainable and cost-effective thermal management and energy storage. However, the low sorption capacity of sorbents is a long-standing challenge for achieving high-energy-density sorption-based thermal storage. Herein, we demonstrate an ultrahigh-energy/power-density sorption thermal battery (STB) enabled by graphene aerogel (GA)-based composite sorbents for efficient thermal harvesting and storage with record performance. Scalable GA-based composite sorbents with high salt loading are synthesized by confined calcium chloride inside a GA matrix (CaCl2@GA), showing fast sorption kinetics and a large sorption capacity up to 2.89 g·g-1 contributed by the GA matrix and chemisorption-deliquescence-absorption of CaCl2. The STB realizes thermal charging-discharging via the multistep water desorption-sorption of CaCl2@GA sorbent with the humidity from air. Importantly, the lab-scale STB exhibits record energy density of 1580 Wh·kg-1 and power density of 815 W·kg-1 for space heating. Our work offers a promising low-carbon route for efficient thermal energy harvesting, storage, and utilization. ©

This study is aimed towards process design for semi-solid slurry generation of Al–7Si–0.3Mg alloy using cooling slope as a slurry maker, and subsequent isothermal holding to promote globularization of slurry microstructure. The study primarily reports globularization mechanism of cooling slope processed semi-solid slurry of the alloy, and efforts are directed to establish process control by investigating the effect of coarsening during isothermal holding on the shape, size and distribution of primary Al grains. As an outcome of this study, we propose a modified Lifshitz–Slyozov Wagner equation to quantify the effect of coarsening mechanisms prevailing during isothermal holding of the said alloy slurry. The evolution of primary phase morphology due to addition of grain refiner has also been studied and ideal processing condition is identified for the end goal of component development through rheo pressure die casting route.

Significant efforts have been made to develop new platinum anticancer compounds since the discovery of cis-platin; however, non-specific toxicity or loss of efficacy remain some of the major challenges in this area of platinum drug discovery. Newly developed platinum compounds, structurally distinct from the current molecules, imparting efficacy at lower concentrations than the current drugs, and interacting with DNA leading to cell death, may prove beneficial. In the current study, we designed, synthesized, and characterized three phenalenyl based platinum chloride compounds (1, 2, and 3) with the goal that a labile Pt–Cl bond with the planar structure of the phenalenyl moiety would enhance their interaction with DNA, leading to improved efficacy. In addition, it is assumed that the fluorescent properties of these compounds would facilitate mechanistic investigation. The crystal structure of compound 1 demonstrates a perfectly planar structure with a single Pt–Cl bond. In vitro cell viability studies on cancer cell lines, including lung, colorectal, breast, and osteosarcoma, revealed a superior efficacy for compounds 1 and 2, relative to platinum drugs in clinical use. Localization studies utilized the strong fluorescence of compound 3 to investigate the mechanism of action, revealing its interaction with DNA, leading to cell death. This study enriches the arsenal of potential platinum-based anti-cancer therapeutics and provides an easy-to-use tool for the mechanism-of-action studies of these compounds.

Purpose This paper aims to deal with characterisation of the thermal performance of a hybrid tubular and cavity solar thermal receiver. Design/methodology/approach The coupled optical-flow-thermal analysis is carried out on the proposed receiver design. Modelling is performed in two and three dimensions for estimating heat loss by natural convection for an upward-facing cavity. Heat loss obtained in two dimensions by solving coupled continuity, momentum and energy equation inside the cavity domain is compared with the loss obtained using an established Nusselt number correlation for realistic receiver performance prediction. Findings It is found that radiation emission from a heated cavity wall to the ambient is the dominant mode of heat loss from the receiver. The findings recommend that fluid flow path must be designed adjacent to the surface exposed to irradiation of concentrated flux to limit conduction heat loss. Research limitations/implications On-sun experimental tests need to be performed to validate the numerical study. Practical implications Numerical analysis of receivers provides guidelines for effective and efficient solar thermal receiver design. Social implications Pressurised air receivers designed from this method can be integrated with Brayton cycles using air or supercritical carbon-dioxide to run a turbine generating electricity using a solar heat source. Originality/value The present paper proposes a novel method for coupling the flux map from ray-tracing analysis and using it as a heat flux boundary condition for performing coupled flow and heat transfer analysis. This is achieved using affine transformation implemented using extrusion coupling tool from COMSOL Multiphysics software package. Cavity surface natural convection heat transfer coefficient is obtained locally based on the surface temperature distribution.

The quest of automobile industries for weight reduction and enhancement of the mechanical strength of components has been a major incentive for new manufacturing technologies such as thixocasting. It is therefore important that the welded joints of such components exhibit adequate strength and formability. The present investigation is on optimization of process parameters to achieve better weld quality obtained in friction-welded joints of thixocast A356 aluminum alloy. The optimum combination of welding parameters is obtained by using the analysis of the signal-to-noise (S/N) ratio based on the Taguchi method. Joint strength higher than the parent material strength is achieved with an optimum set of friction-welding parameters. In addition, residual stress analysis is carried out both experimentally and numerically. Comparisons between the experimental and numerical residual stresses are in good agreement with each other. The residual stress obtained is of low magnitude and compressive in nature.

The present study discusses the thermodynamic compatibility criteria for the selection of metal hydride pairs for the application in coupled metal hydride based thermal energy storage systems. These are closed systems comprising of two metal hydride beds – a primary bed for energy storage and a secondary bed for hydrogen storage. The performance of a coupled system is analyzed considering Mg2Ni material for energy storage and LaNi5 material for hydrogen storage. A 3-D model is developed and simulated using COMSOL Multiphysics® at charging and discharging temperatures of 300 °C and 230 °C, respectively. The LaNi5 bed used for hydrogen storage is operated close to ambient temperature of 25 °C. The results of the first three consecutive cycles are presented. The thermal storage system achieved a volumetric energy storage density of 156 kWh m−3 at energy storage efficiency of 89.4% during third cycle.

In this study, a computational fluid dynamics (CFD) model is developed to investigate die filling of semi solid slurry as part of rheo pressure die casting (RPDC) system. The die filling cavity corresponds to that of an automobile steering knuckle, and the slurry is made of A356 aluminium alloy. The rheological model used in the CFD simulation is determined experimentally. The results obtained from present numerical model includes flow field of the slurry within the die cavity, viscosity evolution, solid fraction distribution, temperature and pressure distribution during solidification within cavity during die filling stage. The main objective of the study is to determine the gating arrangement, pouring temperature, and injection conditions for desirable microstructure and mechanical properties of the developed component. To study the effect of injection conditions on die filling capability of the said alloy slurry, five injection profiles are studied, with a variation in final injection velocity between 2–3.2 m/s. In order to corroborate the findings of the present study, microstructural morphology and structure-property correlation have been studied, primarily in the form of optical microscopy and macro hardness measurements, by obtaining samples from different locations of the solidified component.

Stand-alone microgrids, also known as remote area power supply systems, are crucial towards providing electricity access to off-the-grid locations/buildings and for communities trying to become 100% dependent on renewables. Design and development of efficient energy storage system remains a key challenge for the stand-alone microgrid technology. Metal hydride based hydrogen-energy storage system, offering long term energy storage at near ambient conditions and additional benefits of thermal and green hydrogen output, have attracted researchers and industrialists worldwide. In this work, LaNi5 (Lanthanum Penta-nickel) based hydrogen-energy storage system for stand-alone microgrid application is studied. An optimization study is performed to find the optimal sizes of hybrid (solar + wind) and wind microgrid components for the requirements of typical Indian village/UK community of 50 households located at various geographical locations, having diverse solar and wind resources availability. The study ensures that the microgrid satisfies the required electric load but is not over-designed, which is achieved by limiting the two performance parameters i.e., unmet load fraction and excess electricity fraction, below 10%. The optimization study is done based on an hourly analysis for a year using the simulation software HOMER. A thermal analysis is carried out to quantify the additional benefit of thermal output from the energy storage system. Comparisons between the performance and thermal output of optimized hybrid and wind microgrids are carried out for the selected locations. Also, green hydrogen produced for energy storage and available for use at the end of the year is quantified. Upon comparing hybrid (solar PV + wind turbine) and wind energy based microgrids, it is observed that hydrogen storage requirement decreases by up to 97% while using hybrid energy source depending on the location. Besides serving electrical load, the microgrid delivers thermal outputs of about 1kWh and 5kWh for Indian and UK locations respectively.

This chapter highlights the multiscale concentrated solar power thrust, which focused on developing new low-cost manufacturable technologies for both high- and moderate-temperature thermal cycles. In the high-temperature range, the focus was on the supercritical carbon dioxide (s-CO2) Brayton cycle. Research involved developing low-cost heliostats coupled with novel bladed receivers and a novel CO2 test loop. A key focus was developing a functional testbed to evaluate and optimize the Brayton cycle as a cost-shared effort with the Indian Institute of Science. The project also investigated developing a novel helical receiver to heat the CO2. Extensive computational modeling of the thermal flow and gradients was conducted to develop the novel CO2 cycle. The program also pursued developing low-cost mirrors, absorbers, and troughs for Rankine cycle solar thermal parabolic trough technology. A new small-scale, positive-displacement organic Rankine cycle expander was developed and tested. Solution-based approaches were considered that promise low-cost manufacturing. Coupled with the heat-collection work were investigations of thermal storage approaches. Specifically, new molten salts were developed capable of much higher-temperature performance with improved thermal conductivity, and a new system was developed for low-temperature Rankine systems.

The goal of this paper is to experimentally study the thermal behavior of a miniature loop heat pipe (LHP) with flat evaporator and correlate the findings with visualization studies of the working fluid within the compensation chamber (CC). A miniature LHP with flat evaporator was fabricated and tested with four working fluids – acetone, methanol, n-pentane and ethanol for various heat inputs till deprime at two different sink temperatures. The CC of the LHP is provided with a glass view port for visualization of the working fluid using a high speed camera. The results show that among the fluids tested, n-pentane has the lowest operating temperature, whereas methanol has the broadest heat load range. Visualization studies with all the four fluids at both sink temperatures reveal that there is no bubble generation in the CC for any heat input level prior to deprime. It was also observed that during deprime, there is explosive nucleation in the CC due to intense heat leak into it, accompanied by a rapid rise in the operating temperature due to cessation of fluid flow in the loop.

In the present paper, we present an experimentally validated 3D multiphase and multiscale solidification model to understand the transport processes involved during slurry generation with a cooling slope. In this process, superheated liquid alloy is poured at the top of the cooling slope and allowed to flow along the slope under the influence of gravity. As the melt flows down the slope, it progressively loses its superheat, starts solidifying at the melt/slope interface with formation of solid crystals, and eventually exits the slope as semisolid slurry. In the present simulation, the three phases considered are the parent melt as the primary phase, and the solid grains and air as secondary phases. The air phase forms a definable air/liquid melt interface as the free surface. After exiting the slope, the slurry fills an isothermal holding bath maintained at the slope exit temperature, which promotes further globularization of microstructure. The outcomes of the present model include prediction of volume fractions of the three different phases considered, grain evolution, grain growth, size, sphericity and distribution of solid grains, temperature field, velocity field, macrosegregation and microsegregation. In addition, the model is found to be capable of making predictions of morphological evolution of primary grains at the onset of isothermal coarsening. The results obtained from the present simulations are validated by performing quantitative image analysis of micrographs of the rapidly oil-quenched semisolid slurry samples, collected from strategic locations along the slope and from the isothermal slurry holding bath.

Heating and cooling systems based on hydrogen sorption in metallic alloys have attracted researchers due to their advantages such as environmental friendliness, ability to utilize low-grade waste or renewable energy, wide operating temperature ranges, and availability of a plethora of alloys to choose from. These heat-operated systems offer a viable alternative to conventional electrically driven HVAC systems. In this paper, a metal hydride-based heating and cooling system (MHHCS) which can cater to the year-round comfort air-conditioning of locations with extreme climatic conditions is proposed. The paper describes the cyclic operation of the MHHCS for application in buildings through the different seasons of a year. The performance of the system is studied using a matched alloy pair of Zr0.82Mm0.09Ti0.09Fe1.4Cr0.6 – LaNi4.6Al0.4 chosen based on thermodynamics and reaction kinetics. This paper discusses the effects of system parameters and operating conditions on the year-round performance of the MHHCS.

This paper presents a theoretical analysis of non-Newtonian (power-law obeying) fluid in a narrow confinement subjected to the combined consequences of interfacial electrokinetics, rheology, and superimposed magnetic field. We devote special attention on the exploitation of magnetic field and power-law exponent, in the development of induced streaming potential and thermofluidic energy transfer characteristics over small scales. In an effort to do so, going beyond the Debye-litickel limit, we first derive an expression for streaming potential by invoking the consequences of strong EDL (electrical double layer) interactions in the narrow fluidic passage and finite conductance of the Stern layer. In particular, we solve thermal energy transport equation with an illustrative case of classical uniform wall heat flux boundary and considering the volumetric heat generation effects due to viscous dissipation as well as Joule heating. Our results demonstrate that the applied magnetic field imparts a retarding influence on the induced streaming potential development, whereas, it results in enhancement of heat transfer rate. Moreover, additional influences of power law index show reduction in heat transfer as well as the streaming potential magnitude. We unveil the optimal combinations of power law index and the magnetic field which lead to the minimization of the global total entropy generation in the system. We believe that theoretical results presented in this research will be useful in the development of novel narrow fluidic energy efficient devices under electrokinetic modulation. (C) 2017 Elsevier Ltd. All rights reserved.

This paper presents an in-depth numerical and thermodynamic study of a two-stage, 2-bed silica gel/water adsorption system for simultaneous generation of cooling power and potable water. The system is air cooled where the ambient temperature remains constant at 36 °C. The first part of this paper investigates the effect of cycle time, chilled water inlet and heat source temperature on system performance viz. specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP). A significant outcome of this study is to show that decrease in heat source temperature not only reduces the specific throughput but also increases the optimum cycle time, whereas COP is relatively insensitive to such alterations. The second part of this paper discusses the estimation of the minimum desorption temperature from the simulated system throughput results as well as from fundamental thermodynamic analysis of a two-stage adsorption cycle. This thermodynamic analysis provides a theoretical limit for minimum desorption temperature and optimal inter-stage pressure for a two-stage adsorption cycle.

For concentrating solar power (CSP) plants to become cost competitive, it is necessary to design systems with significantly higher cycle efficiencies and to innovate cost-effective storage systems and materials. Higher cycle efficiency demands higher operating temperature, which implies that the optical system for the solar receiver needs to be designed for higher concentration ratio. This paper reviews the present technologies for high temperature solar receivers associated with power dish and power tower systems. Significant research and development work required for high temperature storage systems and materials is also discussed. Recently, the supercritical carbon dioxide (s-CO 2 ) Brayton cycle is identified as a potential candidate to realize significantly higher thermal efficiency at high operating temperature and pressure. Recent developments and challenges involved in development of solar receivers and thermal storage systems for such applications are also presented.

Thermal energy storage at high temperature is a challenging research area with typical applications like regenerative heating in steel production plants and auxiliary energy source in solar thermal plants. Honeycomb structures made of ceramics are used as high temperature thermal energy storage units because of their large heat transfer surface area per unit volume, large thermal capacity and good thermal shock resistance. The material properties and geometric parameters of these units determine the storage capacity and heat addition/retrieval rate. A thorough understanding of the thermal response of storage unit at different process conditions is crucial for designing the system.In this work, new compositions of mullite and chromite based ceramic honeycombs were developed for high temperature thermal storage application. An experiment was designed to evaluate the performance of the ceramic honeycomb in the temperature range of 773-1273 K by studying the storing and discharging characteristics in ...

We investigate thermofluidic transport phenomena and entropy generation for combined electroosmotic and pressure-driven flows through narrow confinements, subjected to spatially varying non-uniform magnetic field. Going beyond the Debye-Huckel limit, we consider the size effects of the ionic species (steric effect) to analyse magnetohydrodynamic flow and heat transfer characteristics. We demonstrate that a confluence of the steric interactions with the degree of wall charging (zeta potential) may result in heat transfer enhancement, and overall reduction in entropy generation of the system under appropriate conditions. In particular, it is revealed that a judicious selection of spatially varying magnetic field strength may lead to an augmentation in the heat transfer rate. It is also inferred that incorporating non-uniformity in distribution of the applied magnetic field translates the system to be dominated by the heat transfer irreversibility. The novel scope of the current research lies in the state-of-art design of advanced micromechanical industrial smart-sensors, actuators, and biomedical devices. (C) 2016 Elsevier Ltd. All rights reserved.

Enhancement of energy delivery of a carbon dioxide (CO2) Brayton cycle without compression work liability is achievable using low grade heat for thermal compression. The limitation of the expansion ratios of a single stage adsorption thermal compression is obviated by opting for pressure build up in two stages. Despite the use of a large number of adsorbers, it is shown that, specific work output can be augmented substantially with no undue penalty on the overall cycle efficiency albeit with a marginal shortfall in work output per unit mass of adsorbent. These features are elucidated through an activated carbon based thermal compression of CO2 yet limiting high side pressures to 80 bar and the principal heat source at a temperature equal to or less than 300 degrees C in tandem with another low grade source at 100 degrees C for thermal compression. The net outcome is a substantial reduction in the size of the power block and heat exchangers resulting from enhancement of the expansion ratio and reduction in the mass flow rate in the circuit.

In this work, a novel experimental method for measurement of radiation emitted by supercritical carbon dioxide (s-CO 2 ) at high pressure and high temperature is presented. Due to high pressure conditions, use of conventional spectroscopic methods to measure radiative properties of s-CO 2 is challenging. In the present method, supercritical conditions are created in a shock tube by using carbon dioxide (CO 2 ) as the driven gas. The radiative emission by s-CO 2 is measured using a platinum based thin film sensor. The total emissivity for s-CO 2 is estimated and the value compares favourably with that predicted theoretically using a standard method available in literature. It is estimated that the total emissivity value of supercritical conditions is nearly 0.2 for the conditions studied, implying that s-CO 2 acts as a participating medium for radiation heat transfer. The outcome of this study will have significant impact on the design of heat transfer equipment such as solar thermal receivers and heat exchangers typically used in s-CO 2 based closed Brayton cycle, for which participating medium radiation heat transfer has been neglected traditionally. © 2019 Elsevier Ltd

Diaminocyclohexane-Pt(II)-phenalenyl complexes (1 and 2) showed an appropriate balance between efficacy and toxicity. Compound 2 showed nearly two-fold higher tumour growth inhibition than oxaliplatin in a murine NSCLC tumour model, when a combined drug development approach was used. The fluorescent properties of phenalenone were utilized to understand the mechanistic details of the drug.

A pair of thermodynamically matched hydriding alloys is coupled to function as a thermal battery to store thermal energy and also to simultaneously produce heating/cooling effects. A simulation study is performed on coupled cylindrical reactors using COMSOL Multiphysics® software. This paper presents the thermal performance of dynamically coupled LaNi4.25Al0.75 -LaNi5 pair in which LaNi4.25Al0.75 is used for thermal energy storage at 150 °C. LaNi5 is mainly used for hydrogen storage, but also performs heating or cooling depending on the requirement. Three consecutive cycles consisting of a charging process followed by a discharging process are simulated. Overall system efficiency, specific heating and specific cooling capacities and heating and cooling coefficients of performance are estimated. This study confirms that metal hydride based thermal batteries consisting of suitable hydride pairs can be effectively used for harnessing and storing waste heat in the medium temperature levels of about 150 °C.

Gas-solid chemisorption pairs of ammonia and halide salts have an edge over other pairs for advanced thermal energy storage batteries due to their abundance, easy availability, cost effectiveness, high sorption capacity, and wide operating temperature range. In the present work, thermodynamic analyses of thermal battery systems are performed for various ammonia-halide salt pairs using measured sorption characteristics. The stored thermal energy can also be upgraded by forming a combination of suitable halide salts. A maximum gravimetric energy storage density of 1664 kJ kg−1 is observed for MnCl2 based thermal battery. The degree of heat upgradation can be as high as 43 °C in case of MnCl2–CaCl2 based resorption thermal battery. The first law efficiency is observed to be as high as 0.42 for CaCl2 based thermal battery. The decrease in first law efficiency due to parasitic mass is observed to be in the range of 26–37 % and 57–66% for different CaCl2 and MnCl2 thermal batteries, respectively. It is possible to recover the stored thermal energy in the form of simultaneous heating and cooling effects by using specific combination of salts which enhances the overall efficiency. First law efficiency as high as 0.92 can be achieved with a CaCl2–NaBr resorption thermal battery delivering simultaneous cooling and heating effects at 10 and 55 °C, respectively, while storing thermal energy at 100 °C.

A supercritical carbon dioxide (sCO(2)) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO(2) and single phase operation. Development of a solar receiver capable of delivering sCO(2) at 20 MPa and 700 degrees C is required for implementation of the high efficiency (similar to 50%) solar powered sCO(2) Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used to evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. The resulting body stresses were used to approximate the lifetime performance of the receiver tubes. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. The creep-fatigue analysis displayed the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver. Published by Elsevier Ltd.

Dynamic performance of a single-stage, two-bed, silica gel + water adsorption chiller operating in Bangalore, India is studied. Driving thermal energy is provided directly by an evacuated tube solar collector field. System dynamics are evaluated in the absence of thermal storage, which causes intra-day fluctuations in heat source and evaporator temperatures, which in turn influence the system performance. These dynamics are demonstrated for representative days in the months of April (summer) and December (winter). The focus is on the effect of variation of the collector area and the adsorption cycle time on the system performance. The maximum temperature of heat transfer fluid (water) is limited to 95 degrees C. The cyclic and daily averages of solar coefficient of performance (DACOPsoi) and cooling capacity (DACC) are used as key performance indicators. One of the key aspects of the this study is to show that both of them can be maximized by suitably choosing the collector area and cycle time. Further, it is demonstrated that the solar driven adsorption chiller described here is ideally suited for cascading with an air-cooled R-134a vapour compression refrigeration system (VCRS). The variable throughput obtained from the solar adsorption chiller can help in liquid sub-cooling and hence to cover the deficit in cooling capacity of the VCRS arising due to high ambient temperature. (C) 2016 Elsevier Ltd. All rights reserved.

Solar, thermal power generation by and large uses Rankine cycles with organic working fluids or steam when highly concentrated solar source is used. Brayton cycle is seldom used because the work of compression forms a major fraction of turbine output. We investigate removal of this lacuna by adopting thermal compression using the adsorption route. Here we propose a two source operated cycle with the low temperature source used for thermal compression and the high temperature source to increase the inlet temperature of the working fluid to the turbine. We adopt carbon dioxide as the working fluid in view of its excellent heat transfer properties and environmentally friendly disposition. Activated carbon is used as the adsorbent in the thermal compression process. It is shown that, though the First law thermal efficiency does not show the real merit of the cycle, the exergetic efficiency is substantially high even for low side operating pressures in the range of 15-25 bar. In particular, where the waste heat is available around 100 degrees C and concentrated solar power is available even at 200-300 degrees C, exergetic efficiencies in excess of 25% can be realised. When other advantages such as dispensing with one whole segment of moving parts (compressor) are taken into account, the running costs of such a cycle can be so low that it would be, a viable proposition. However, we appreciate that, large scale use of adsorption compression is associated with huge technological problems for which we propose some remedies. (C) 2016 Elsevier Ltd. All rights reserved.

Brayton power cycles using high temperature, high pressure supercritical carbon dioxide (s-CO2) as the working fluid have been increasingly considered as attractive candidates for solar-thermal power plants. Several configurations of heat exchangers and solar receivers are under investigation, with predicted tube temperatures similar to 1000 K. The inclusion of radiation modeling to capture the effect of absorption bands of s-CO2 and the radiative heat transfer among the equipment surfaces makes the computation costly and time consuming, and is often neglected on the basis of convection being the dominant transport mechanism. In this work, a numerical study has been performed to characterize the heat transfer in simultaneously developing laminar flow of s-CO2 through a circular pipe. The combined effects of convection and radiation are presented by varying the Reynolds number, pipe diameter, length to diameter ratio, wall emissivity and the total wall heat flux. It is shown that neglecting the effects of radiative heat transfer, and in particular the participation of s-CO2 in thermal transport can lead to large errors in predicting wall temperature, and by extension, the component lifetime. The error in wall temperature also leads to erroneous predictions on losses to the environment. The calculations indicate that there is a range of flow conditions over which the design process needs to incorporate radiation modeling. (C) 2016 Elsevier Ltd. All rights reserved.

Single phase performance and appealing thermo-physical properties make supercritical carbon dioxide (s-CO2) a good heat transfer fluid candidate for concentrating solar power (CSP) technologies. The development of a solar receiver capable of delivering s-CO2 at outlet temperatures similar to 973 K is required in order to merge CSP and s-CO2 Brayton cycle technologies. A coupled optical and thermal-fluid modeling effort for a tubular receiver is undertaken to evaluate the direct tubular s-CO2 receiver's thermal performance when exposed to a concentrated solar power input of similar to 0.3-0.5 MW. Ray tracing, using SolTrace, is performed to determine the heat flux profiles on the receiver and computational fluid dynamics (CFD) determines the thermal performance of the receiver under the specified heating conditions. An in-house MATLAB code is developed to couple SolTrace and ANSYS Fluent. CFD modeling is performed using ANSYS Fluent to predict the thermal performance of the receiver by evaluating radiation and convection heat loss mechanisms. Understanding the effects of variation in heliostat aiming strategy and flow configurations on the thermal performance of the receiver was achieved through parametric analyses. A receiver thermal efficiency similar to 85% was predicted and the surface temperatures were observed to be within the allowable limit for the materials under consideration. Published by Elsevier Ltd.

The present study describes about the preparation of semisolid metal (SSM) slurry by using an oblique plate. In this process, A356 aluminum alloy melt partially solidifies while flowing over a bottom cooled oblique plate. Melt flow inertia shears columnar dendrites formed on plate wall into equiaxed/fragmented grains by resulting semisolid slurry at plate exit. Effects of plate length providing required shear and cooling rate enabling necessary solidification are investigated. A 3-phase numerical model vis-a a-vis transport of mass, momentum, energy and species is developed for prediction of velocity, temperature, macrosegregation and solid fraction. Model uses volume of fluid (VOF) for tracking-metal-air-interface and finite volume method (FVM) with enthalpy based phase change algorithm for tracking-solid-liquid-interface within the metal. Darcy model is used for porous mushy zone. Slurry variable viscosity is represented by Oldenburg model. Stokes model incorporates solid phase movement and gravity effect along the flow. Dendrite fragmentation is considered for generation of moving solid phase. Solid movement is handled by coherency point and characteristic diameter of moving grains. Model neglects nucleation and growth kinetics, solidification shrinkage/expansion and thermo-solutal buoyancy. Slurry solid fractions at plate exit are 16%, 22%, and 27% for plate lengths of 200 mm, 250 mm, and 300 mm, respectively. And, are 5%, 22%, and 27% for heat transfer coefficients of 1000 W/m(2)-K, 2000 W/m(2)-K and 2500 W/m(2)-K, respectively. Numerical predictions agree well with experimental results. (C) 2016 Published by Elsevier B.V.

The present work explores the potential of semi-solid heat treatment technique by elucidating its effect on the plastic behavior of 304L SS in hot working domain. To accomplish this objective, hot isothermal compression tests on 304L SS specimens with semi-solid heat treatment and conventional annealing heat treatment have been carried out within a temperature range of 1273-1473 K and strain rates ranging from 0.01 to 1 s(-1). The dynamic flow behavior of this steel in its conventional heat-treated condition and semi-solid heat-treated condition has been characterized in terms of strain hardening, temperature softening, strain rate hardening, and dynamic flow softening. Extensive microstructural investigation has been carried out to corroborate the results obtained from the analysis of flow behavior. Detailed analysis of the results demonstrates that semi-solid heat treatment moderates work hardening, strain rate hardening, and temperature sensitivity of 304L SS, which is favorable for hot deformation. The post-deformation hardness values of semi-solid heat-treated steel and conventionally heat-treated steel were found to remain similar despite the pre-deformation heat treatment conditions. The results obtained demonstrate the potential of semi-solid heat treatment as a pre-deformation heat treatment step to effectively reduce the strength of the material to facilitate easier deformation without affecting the post-deformation properties of the steel.

Supercritical carbon dioxide (sCO2) Brayton cycle-based power plants are being extensively explored as viable alternatives to traditional Rankine based steam power plants. Higher temperatures at the turbine exit in a sCO2 cycle provide better opportunities for heat recuperation, thus improving overall cycle efficiency. Among the various heat exchanger configurations available, compact microchannel heat exchangers commonly known as Printed Circuit Heat Exchangers (PCHE's) are typically used in sCO2 power plants. In the current work, a hybrid approach comprising of a Thermal Resistance Network (TRN) model coupled with a CFD model for estimating local heat transfer and pressure drops is presented for a PCHE core with straight and zigzag channel configurations. Full-scale TRN model is used to optimize the overall stack dimensions based on minimum rate of heat loss from the external surfaces of the PCHE core. The TRN model accounts for the thermo-physical property variations of sCO2 along the channel length to effectively capture the channel pressure drop and heat transfer. This is achieved by discretizing the heat transfer domain comprising of alternatively stacked hot and cold streams into sub-heat exchangers to account for variations in thermophysical properties while calculating the nodal friction factors and local heat transfer coefficients. CFD simulations are performed for a full length of a single stack of hot and cold fluid streams to arrive at corrected heat transfer and pressure drop correlations. Thermo-hydraulic analysis is performed for a range of channel hydraulic diameters and channel mass flow rates for both straight and zig-zag configurations to deduce optimum stack dimensions. The efficacy of the hybrid model is demonstrated with a case study of a counterflow recuperator used in a simple recuperated 1 MW sCO2 Brayton power plant.

The present study reports development and application of a three dimensional phase field (PF) model, to investigate the microstructure evolution mechanism responsible for generation of spheroidal primary Al grains, associated with cooling slope processed semi solid slurry of A356 aluminium alloy. The cooling slope rheoprocessing technique involves solidification of flowing melt on an inclined slope surface, where gravity assisted fluid flow and shearing action between the flowing melt and the slope surface causes formation of near spherical primary solid fragments, and subsequent isothermal globularisation of the evolving primary solid. The present PF model implements a seed density based nucleation model. The seed density requirements to simulate microstructure evolution for different simulation/melt treatment conditions of cooling slope processing have been estimated based on initial experimentation. The simulated micrograph of slope exit state i.e, at the end of cooling slope processing has been used to estimate the number density and average size of constituent α-Al grains of the generated slurry, at slope exit state. The values obtained are fed subsequently as input parameters to simulate post slurry generation isothermal globularisation process. The model predictions are validated experimentally, thus establishing its capability to predict the characteristics of semisolid slurry at different stages of cooling slope rheoprocessing, in terms of solid content (volume fraction), diameter, density, and shape factor (sphericity) of nucleated primary Al grains.

Polygeneration Microgrids (PMG) can be configured to deliver multiple outputs such as, electricity, heat, cold, fuel (hydrogen) and clean water. In an earlier paper the authors presented an analysis of a PMG consisting of solar photovoltaic field, fuel cell, solid state hydrogen storage and electrolyzer using commercial software HOMER. Keeping in mind the fact that battery storage is preferred for stand-alone microgrids, in this paper, the influence of battery storage on the performance of a PMG is presented. An added advantage of solid state hydrogen storage – fuel cell system is the availability heat released during adsorption of metal hydride in addition to that rejected by the fuel cell. A comparison of battery alone versus battery + fuel cell is made.

Polygeneration Microgrids (PMG) are smart energy systems which can be configured for decentralised multiple outputs in the form of electricity, heat, cold, fuel (hydrogen) and drinking water. This paper presents an analysis of a stand-alone PMG, which caters to electrical, thermal and hydrogen loads. The stand-alone PMG consisting of solar photovoltaic field, fuel cell, solid state hydrogen storage and electrolyzer is modelled using commercial software HOMER. An hourly simulation is conducted to analyse its annual performance. A case study is carried out for a typical Indian village of about 50 households needing electrical energy of 100 kWh/day. The by-products of the optimized stand-alone PMG i.e., thermal energy and hydrogen, are quantified.

The objective of this study is to develop a computational model of two-stage silica gel/water adsorption cooling system. Thermal compression is achieved by adsorption, with silica gel (RD type) as the adsorbent and water as the refrigerant. Three dimensional transient heat and mass transfer analysis of adsorption heat exchangers are carried out to derive salient design and performance features. Numerical studies are carried out to evaluate the performance of the beds with respect to key operating parameters. Two different geometric models are considered for the transient study, one having vapor flow only in axial direction through the cylinder, and the other having a thin mesh inserted between the shell and heat exchanger tubes, resulting in a much shorter vapor flow path through the packed bed. Bed temperature distribution, pressure dynamics and the effect of critical depth on uptake of the adsorber heat exchanger are studied numerically. In addition, a parametric study is carried out to determine the significance of silica gel particle diameter on the uptake of the bed. The optimum particle diameter in terms of uptake was found to be 0.8 mm. The effect of ambient temperature on the performance of single-stage and two-stage systems is also studied.

Deprime in a loop heat pipe (LHP) is a phenomenon of drying out of capillary wick due to penetration of vapour into it. The vapour zone thickness increases with the LHP heat input due to the liquid-vapour interface recession into the wick away from the heating zone. An analytical model referred to as zero recession model is first presented to predict the evaporator wall temperature assuming that the capillary wick is always fully saturated with liquid. Experimental results on an LHP with four working fluids (acetone, methanol, n-pentane and ethanol) for a range of heat inputs till deprime are analyzed. The model predictions reveal that there is an additional resistance offered by the vapour zone of the wick to the heat flow. Subsequently, another model referred to as recession model is presented based on minimization of the difference between the predicted and measured evaporator wall temperatures to predict an equivalent vapour blanket thickness inside the wick with the assumption that the vapour zone thickness inside the wick is uniform. The predictions reveal that the equivalent vapour blanket thickness increases with the applied heat input due to the liquid-vapour interface movement away from the heated surface and approaches the wick thickness at a heat input very close to deprime. It was also found that drop in the evaporative heat transfer coefficient is mainly due to the increase in the equivalent vapour blanket thickness in the wick.

Adsorption thermal storage and transformation (ATST) of low-temperature heat is an energy saving technology towards the efficient use of renewable and waste heat. A solid sorption thermal battery (SSTB) is a promising concept for low-grade heat storage, combined cooling and heating, integrated energy storage and energy upgrade. Current progress in SSTB is related to the selection of advanced adsorbents and cycles which are properly adapted to ATST in various climatic zones. This paper mainly addresses such adaptation for China, Russia, and India which are among the top CO2 emitters and partially for Italy and Portugal. First, climatic data for selected cities of these countries were analyzed to specify adsorbents optimal from the thermodynamic point of view. It was found that an innovative sorbent “LiCl inside Multi-Wall Carbon NanoTubes (MWCNT)” is one of the most promising and universal for SSTB operating in several selected climatic conditions. To further elucidate the composite usability, especially, in cooling/(air conditioning) cycles, the experimental dynamic study of methanol sorption on this sorbent was performed. The study included shaping the LiCl/MWCNT composite as grains using polyvinyl alcohol as a binder, and the measurements of methanol sorption/desorption dynamics under conditions of the selected ATST cycle. The dynamics, studied by a Large Temperature Jump method, revealed the fast ad/desorption that led to high specific power and smaller SSTBs. Hence, the selected composite is a promising candidate for SSTB applications in the climatic zones involved.