• Energy Research

Data availability: No data was used for the research described in the article. Supplementary data available online at: https://www.sciencedirect.com/science/article/pii/S2451904923000653?via%3Dihub#s0125 (2MB). The present work demonstrates a modified chemical synthesis route (chemical, hydrothermal methods, and sonication) for fabricating n-hexacosane-impregnated graphene nanosheets (GrPCM) nanocomposite, exhibiting enhanced thermal stability in energy storage. The exfoliation of the graphene sheet during the hydrothermal and sonication process increases the surface area that can absorb n-hexacosane, improving the impregnation and interaction between them. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy were used to examine the morphological and structural characteristics of the GrPCM nanocomposite. The findings demonstrate the loading of n-hexacoreferesane PCM materials into porous nanosheet structures without any chemical reactions. Thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and infrared thermography (IR) were used to measure the latent heat, mass loss, thermal conductivity, and stability of as-synthesized GrPCM nanocomposites. The melting and solidification of GrPCM nanocomposite were observed at 57.11 ◦C with a latent heat of 154.61 J/g and 49.28 ◦C with a latent heat of 147.58 J/g, respectively. The GrPCM nanocomposites showed a thermal conductivity of 12.63 W/m K, which is enhanced compared to that of pure PCM materials of around 0.26 W/m K. Thermal performance measurements using infrared thermography revealed a significant increase in the nanocomposite's thermal conductivity over n-hexacosane, which was attributed to the reduced graphene nanosheet. Further, to study the heat transfer between fluid and different nanocomposites, the GrPCM nanocomposites were investigated inside a thermal storage tank. The experimental results were found in agreement with the COMSOL simulation and confirms GrPCM3 to be an excellent composite material for efficient heat transfer processes.

In this paper, we report an experimental and Computational Fluid Dynamics (CFD) investigation on the overall heat transfer coefficient, friction factor and effectiveness of a tube equipped with classic and variable twisted tape inserts. Constant (Y = 4.0) and variable pitch twisted inserts (Y = 4-3-4) made of Stainless Steel and Aluminium were used during the experiments due to their ease in machinability. Resistance thermometers were used to measure temperature of the working fluid at the inlet and outlet of the test section. It was observed that the twisted tape in the tube imposes the turbulence in the fluid and enhances the heat transfer due to swirling flow. The results showed that the overall heat transfer coefficient and effectiveness of aluminium variable pitch twisted tape were higher than stainless steel inserts. The experimental data obtained were validated using Computational Fluid Dynamics (CFD) simulations. The constant pitch inserts for aluminium and stainless steel showed an enhancement of 67.54% and 66.65% as compared to plain tube. Whereas aluminium variable pitch inserts showed an enhancement of overall heat transfer coefficient by 18.15% as compared to constant pitch insert and stainless-steel variable pitch insert showed enhancement of 15.25% as compared to constant pitch insert.

Data availability: Data will be made available on request. Acknowledgment: The work is done as part of the collaboration between Pandit Deendayal Energy University and the Heat Pipe and Thermal Management Research Group at Brunel University London, UK. The multi-objective optimization study of the combined Brayton and inverse Brayton cycle is carried out with the aim to maximize specific work output and minimize thermal efficiency using an evolutionary heat transfer search optimization algorithm. The design variation considers the top cycle pressure ratio and bottom cycle expansion pressure. From the results of the multi-objective optimization, multiple optimal solutions for the objective functions are presented using a Pareto optimal curve. Further, five optimal points (A) – (E) from the Pareto curve are selected, and a sensitivity analysis on the objective functions is performed. The conflicting nature between the objective functions is observed, and with any attempt to increase the thermal efficiency, the system’s specific work output decreases and vice versa. The proposed system can produce a maximum specific work output of 497 kJ/kg with a thermal efficiency of 44 %. For the system to be operated at a maximum thermal efficiency of 50 %, it can produce specific work output of 464 kJ/kg. Additionally, the effects of the inlet air temperature, the turbine inlet gas temperature, the exhaust gas temperature from the heat exchanger, turbine efficiency, and compressor efficiency on the specific work output and thermal efficiency are studied and presented. The findings of the study should help users to select the operating parameters based on the need as multiple solutions are presented for the system. Finally, the distribution of the design variables during the optimization is identified and presented.

Data availability: No data was used for the research described in the article. Acknowledgement: The work was done as part of the collaboration between Pandit Deendayal Energy University and the Heat Pipe and Thermal Management Research Group at Brunel University London, UK. This study presents the energy-economic analysis and optimization of a shell and tube heat exchanger. A water-water, segmental baffled shell and tube heat exchanger was designed using the Kern method and analysed by performing energy and economic modelling. The analysis is carried out considering the design variables on the shell side i.e. baffle cut, baffle spacing, shell diameter and tube side variables i.e. tube layout, tube outside diameter, number of tube passes and number of tubes. The multi-objective heat transfer search algorithm was used to optimize the heat exchanger for minimum total cost and maximum heat exchanger efficiency. Multiple optimal solutions were presented using the Pareto optimal curve. TOPSIS selection criteria was used to identify the optimum operating condition. Within the given bounds of the variables, the shell and tube heat exchanger can be operated at a minimum cost of 72,000 $/year resulting in 16.4 % efficiency, or, it can be operated at a maximum efficiency of 81.6 % with a total cost of 275,000 $/year. The scattered distribution of shell diameter, baffle spacing, number of tube passes and number of tubes between the lower and upper bound represent their substantial role in optimizing the heat exchanger performance. The number of tubes and tube passes showed the maximum variation in efficiency, while significantly less impact was observed when the tube layout was altered.

Data availability: No data was used for the research described in the article. The primary objective of the current study is to demonstrate the multi-objective, ecological optimization of an irreversible Stirling cycle-based cryogenic refrigerator. The novelty of the work lies in the ecological optimization of the system, where irreversibilities are considered during the study and the thermal reservoirs have finite energy. The heat source and heat sink exchange energy with the working fluid and respective thermodynamic processes are carried out. The aim is to maximize the ecological objective function and the ecological coefficient of performance, and the effect of design variables on the objective function is investigated. The heat sink capacitance rate, temperature ratio, heat source, and sink capacitance rates, and effectiveness of the hot and cold side heat exchangers are regarded as the design variables. A heat transfer search algorithm is used to optimize the objective functions, and multiple optimal solutions are presented using the Pareto optimal curve. The multi-criteria decision technique TOPSIS is employed to select the ideal solution. For an ideal point selected through TOPSIS, the system works at an optimum ECF and ECOP of 787 W and 5.9, respectively. The ECOP of the system for the current study is 1.81 times and 4.03 times higher than the existing literature. However, the maximum ECF of 1797 W and maximum COP of 17.2 can be obtained for the given constraints of design variables.

Data availability: No data was used for the research described in the article. Shell and tube heat exchanger is a pivotal equipment used in industries for heat transfer. Any effort to minimize the irreversibility in the heat exchanger will enhance the performance and leads to energy optimization and cost savings. In the current study, a water to water, segmental baffled shell and tube heat exchanger was considered for an investigation and designed using the Kern method. Exergy analysis and advanced exergy analysis was carried out to understand the performance of the heat exchanger and to determine the possibility of reducing irreversibilities. The results of the exergy analysis showed that the system has 684.6 kW of exergy destruction. Advanced exergy analysis was carried out through endogenous and exogenous modes and subsequently performed for avoidable and unavoidable components. Majority of the exergy destruction in the heat exchanger is avoidable. The results showed that 97.5 % of the total exergy destruction is of endogenous avoidable type. The system can be improved by changing the system configuration, design variables, mass flow rates, materials, and many other parameters. Subsequently, the exergy destruction in the pumps is unavoidable and no further design improvements are required. The work is done as part of the collaboration between Pandit Deendayal Energy University, India and the Heat Pipe and Thermal Management Research Group (HPTM) at Brunel University London, UK. The HPTM's part was partially funded from the European Union’s H2020 programme iWAYS under grant agreement numbers 958274).

This article presents the results of an experimental study of multiphase flows focusing on the influence of convective condensation of atmospheric water vapour on heat and mass transfer. The primary emphasis is on developing a laboratory setup capable of directly measuring the condensation rate of atmospheric water vapour on a water surface. Such an approach provides the opportunity to obtain more precise and reliable data on convective condensation and its impact on the water balance under various conditions. The experimental results revealed a nonlinear relationship between the condensation rate and the moisture excess, which differs from the linear relationship described by Dalton's law. This deviation was thoroughly examined, and a linear relationship between downward molecular flows and the forces induced by differences in relative humidity concentrations in the convective layer was proposed. The estimated average values of the condensation rate obtained in the experiments were 0.017 L/m²·hour, which, according to estimations, accounts for the condensation flux of water from the atmosphere to the ocean, consistent with the precipitation-evaporation balance in the land-ocean water balance. This information helps to more accurately determine the role of convective condensation in the water balance, contributing to refining assessments of water balance components in various watersheds. The results of this study have practical significance for hydrologists, climatologists, and experts in thermohydraulics and energy engineering. The proposed approaches and methods for measuring convective condensation of atmospheric water vapour can be applicable in various engineering systems and technologies to enhance the efficiency and accuracy of water balance calculations and forecasts.

In this work, the refrigerant R1233zd(E) (A1 ASHRAE safety code) is investigated for the possible substitution of refrigerant R161 (A2 ASHRAE safety code) in a cascade refrigeration system. The high-temperature circuit refrigerant R1233zd(E) is evaluated with the low-temperature circuit refrigerants R41 and R170 for thermo-economic consideration. A comparative analysis of the refrigerant combination R41-R1233zd(E) and R170-R1233zd(E) presents exergy efficiency and total plant cost as evaluation criteria. Pareto solutions are obtained for the thermo-economic objectives for each pair of refrigerants. A decision-making method is adopted to identify the best result from the Pareto solutions obtained. The effects of operating variables such as evaporator temperature, condenser temperature, LTC condensing temperature, and temperature difference of cascade condenser are evaluated. The sensitivity of the operating variables on thermo-economic objectives is also evaluated. The comparative results reveal that for the same total cost rate of the system (68,615 $/year), the exergy efficiencies of the CRS are 63.08% (R170-R161), 64.04% (R41-R161), 64.93% (R170-R1233zd(E)), and 65.81% (R41-R1233zd(E)). Also, the R1233zd(E) based CRS operates with a lower total cost rate than the R161-based system.