Search results

A numerical model of the inclined open thermosyphon has been developed using a finite difference algorithm to solve the vorticity vector potential form of the Navier‐Stokes equations. The model simulates flow in an inclined cylinder whose bottom end is sealed and whose top is connected to uniform temperature reservoir, a configuration typical of evacuated tubular solar absorbers. The solution domain includes the cylinder only without the reservoir; therefore a special set of boundary conditions has been derived for the vector potential at the top end which is a flow‐through surface. Steady flow is simulated at various combinations of Rayleigh number, aspect ratio and mode of heating. An experimental set‐up has also been developed in order to investigate the development of different flow patterns previously predicted by analytical and numerical workers, as well as to observe more closely the behaviour of the fluid at the orifice. Velocity profiles were measured at the orifice using laser doppler anemometry, and compared with predictions from the numerical model.

The limited energy density of batteries generates the need for high-performance power sources for emerging eVTOL applications with radical operational improvement potential over traditional aircraft. This paper aims to evaluate on-design and off-design recuperated turbogenerator performances based on newly developed compression loaded ceramic turbines, the Inside-out Ceramic Turbine (ICT), in order to select the optimum engine configuration for sub-megawatt systems.

System-level thermal engine modeling is combined with electric generators and power electronics performance predictions to obtain the Pareto front between efficiency and power density for a variety of engine designs, both for recuperated and simple cycle turbines. Part load efficiency for those engines are evaluated, and the results are used for an engine selection based on a simplified eVTOL mission capability.

By operating with high turbine inlet temperature, variable output speed and adequately sized recuperator, a turbogenerator provides exceptional efficiency at both nominal power and part load operation for a turbomachine, while maintaining the high power density required for aircraft. In application with a high peak-to-cruise power ratio, such power source would provide eight times the range of battery-electric power pack and an 80% improvement over the state-of-the-art simple cycle turbogenerator.

The implementation of a recuperator would provide additional gains especially important for military and on-demand mobility applications, notably reducing the heat signature and noise of the system. The engine low-pressure ratio reduces its complexity and combined with the fuel savings, the system could significantly reduce operational cost.

Implementation of radically new ICT architecture provides the key element to make a sub-megawatt recuperated turbogenerator viable in terms of power density. The synergetic combination of a recuperator, high temperature turbine and variable speed electric generator provides drastic improvement over simple-cycle turbines, making such a system highly relevant as the power source for future eVTOL applications.

Numerical predictions of laminar and turbulent fluid flow and heat transfer around staggered and in‐line tube banks are shown to agree closely with seven experimental test cases. The steady state Reynolds‐averaged Navier‐Stokes equations are discretised by means of a cell‐centred finite‐volume algorithm. Two‐dimensional results include velocity vectors and streamlines, surface shear stresses, pressure coefficient distributions, temperature contours, local Nusselt number distributions and average convective heat transfer coefficients, and indicate very good agreement with experimental data. It is found that a relatively fine grid is required to be able to predict the surface heat transfer behaviour accurately. Also, three‐dimensional simulations are shown, which are physically consistent. The numerical procedure presented here is robust, accurate and time efficient, making it suitable as a design tool for tube banks in heat exchangers.

A numerical scheme that has already proved to be efficient and accurate for laminar heat transfer is extended for turbulent, axisymmetric heat transfer calculations. The extended scheme is applied to the steady‐state heat transfer of axisymmetric turbulent jets, impinging onto a flat plate. Firstly, the low‐Reynolds version of the standard k‐ε model is employed. As is well known, the classical k‐ε turbulence model fails to predict the heat transfer of impinging jets adequately. A non‐linear k‐ε model, with improved ε‐equation, yields much better results. The numerical treatment of the higher order terms in this model is described. The effect on the heat transfer predictions of a variable turbulent Prandtl number is shown to be small. It is also verified that the energy equation can be simplified, without affecting the results. Results are presented for the flow field and the local Nusselt number profiles on the plate for impinging jets with different distances between the pipe exit and the flat plate.

Supply chain agility (SCA) has recently received considerable attention in the literature and in practice. Despite its popularity, the concept of SCA seems to be vaguely defined and loosely structured. More specifically, definitional ambiguity and conceptual fragmentation have prevented the concept of SCA from reaching its full potential. The time is ripe to address these issues through a systematic literature review.

A review and synthesis of the literature on SCA was undertaken. The authors selected 56 top-tier related articles for further analysis after applying rigorous filtering procedures.

The results of the review confirm that several key themes surround SCA's definition and enablers. In addition, consensus needs to be reached in terms of its performance dimensions and measures. Accordingly, this study constructed an encompassing definition, scrutinized SCA enablers and outcomes and thus developed an original framework for SCA, providing a unique conceptual contribution. Several research directions were also addressed accordingly.

The novelty of this research lies in the selection of highly recognized publications. It also provides an encompassing definition of SCA, consolidates its enablers for better communication and synthesizes its performance implications.

The interaction between mixed convection and thermal radiation in ventilated cavities with gray surfaces has been studied numerically using the Navier‐Stokes equations with the Boussinesq approximation. The effect of thermal radiation on streamlines and isotherms is shown for different values of the governing parameters namely, the Rayleigh number (10³ ≤ Ra ≤ 10⁶), the Reynolds number (50 ≤ Re ≤ 5000) and the surfaces emissivity (0 ≤ ε≤ 1). The geometrical parameters are the aspect ratio of the cavity A = L’/H’ = 2 and the relative height of the openings B = h’/H’ = 1/4. Results of the study show that thermal radiation alters significantly the temperature distribution, the flow fields and the heat transfer across the active walls of the cavities.

The purpose of this paper is to propose a conceptual framework for handling end of life (henceforth EoL) scenarios of solar photovoltaic (solar PV) panels, which includes different options available to businesses and end-users, as well as promoting the collaboration between government and all relevant stakeholders.

This paper adopts purposeful sampling, secondary data and content analysis to develop an appropriate conceptual framework that helps to create awareness of the appropriate options for dealing with the EoL cases of solar PV panels.

From the data analysis, it is revealed that reuse, repair and recycling of solar PV panels can ensure value creation, public-private partnership and a solution for education in sustainability, and thus, prolonging the useful life cycle of the products.

This paper limits the analysis on developing economies and the use of selected literature based on the recycling of solar PV panels.

This paper is an initial attempt to create an awareness by identifying, analyzing and educating the stakeholders to handle appropriately any EoL scenario of solar PV panels.

The earth-sheltered building is an adaptive strategy reducing energy consumption as well as increasing thermal comfort of the residents. Although this idea historically implemented in the city of Yazd, Iran, its effects on thermal comfort have not been studied thoroughly. This paper aims to discuss and analyze energy performance, in terms of parameters such as orientation, underground depth, nocturnal ventilation and its subsequent effects on thermal comfort in earth-sheltered buildings in Yazd.

Using EnergyPlus software, the obtained numeric data are precisely modeled, simulated and analyzed.

Results show that there is a direct relationship between depth of construction and energy consumption savings. The more construction depth of earth-sheltered buildings, the more percentage of energy consumption savings, that is of a higher rate in comparison to the aboveground ones. However, in south orientation, energy saving significantly reduces from depth of 2 m downwards and the annual indoor temperature fluctuation decreases by 50%. This subsequently yields to experiencing indoor thermal comfort for a significant number of days throughout the year. Considering the effects of orientation factor, the south orientation regardless of the depth provides the most desired outcome regarding energy savings.

Simulating the model generalized to the sunken courtyard can approve that the results of this research can be applied to the other models.

With the rapid increase in the consumption of electrical and electronic innovations, responsible management and recycling of electronic waste (e-waste) or waste electrical and electronic equipment (WEEE) has been a significant concern for the governments, stakeholders, researchers and industry practitioners around the world. Consumer awareness, disposal behaviour and perception are chief facets of designing sustainable management strategies. Although researchers have widely studied e-waste over many years, the research focusing on consumer awareness about e-waste recycling has gained momentum recently. This paper aims to systematise the existing literature and explore future research prospects on household e-waste sorting behaviour.

Web of science (WoS) core collection was searched using selected keywords to identify relevant articles published from 2001 to 2021. The search resulted in 1,156 research articles published from 2001 to 2021. After a detailed study, 85 articles were shortlisted for in-depth review. The review was conducted based on global trends, top journals, most prolific authors, most active e-waste research countries, and institutions centring on consumer participation in e-waste disposal and recycling behaviour. The present research has also identified around eleven factors that seem to have a bearing on consumer behaviour towards storage, disposal and recycling of e-waste.

E-waste research has gained increased attention in the last five years. The majority of the studies has focused on motivational factors and ignore the risks associated with handling e-waste. The present study reports the pertinent issue of lack of awareness among the masses about e-waste handling and disposal. Thus, bringing to the fore the lack of awareness programmes and initiatives. The analysis presents the gaps in the literature and future research agendas.

The review article will help in providing an in-depth understanding of consumer behaviour towards storage, disposal and recycling of e-waste and delineates the future direction of research that may be undertaken in this field of study.