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1 – 10 of over 1000
Article
Publication date: 20 June 2019

Huijin Xu, Yan Wang and Xingchao Han

Phase change energy storage is an important solution for overcoming human energy crisis. This study aims to present an evaluation for the thermal performances of a phase change…

Abstract

Purpose

Phase change energy storage is an important solution for overcoming human energy crisis. This study aims to present an evaluation for the thermal performances of a phase change material (PCM) and a PCM–metal foam composite. Effects of pore size, pore density, thermal conductivity of solid structure and mushy region on the thermal storage process are examined.

Design/methodology/approach

In this paper, temperature, flow field and solid–liquid interface of a PCM with or without porous media were theoretically assessed. The influences of basic parameters on the melting process were analyzed. A PCM thermal storage device with a metal foam composite is designed and a thermodynamic analysis for it is conducted. The optimal PCM temperature and the optimal HTF temperature in the metal foam-enhanced thermal storage device are derived.

Findings

The results show that the solid–liquid interface of pure PCM is a line area and that of the mixture PCM is a mushy area. The natural convection in the melting liquid is intensive for a PCM without porous medium. The porous medium weakens the natural convection and makes the temperature field, flow field and solid–liquid interface distribution more homogeneous. The metal foam can greatly improve the heat storage rate of a PCM.

Originality/value

Thermal storage rate of a PCM is compared with that of a PCM–metal foam composite. A thermal analysis is performed on the multi-layered parallel-plate thermal storage device with a PCM embedded in a highly conductive porous medium, and an optimal melting temperature is obtained with the exergy optimization. The heat transfer enhancement with metal foams proved to be necessary for the thermal storage application.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 January 2014

Paulas Raja Sekaran, Amir S. Gohardani, Georgios Doulgeris and Riti Singh

– This article aims to investigate a selected number of liquid hydrogen storage tank parameters in a turboelectric distributed propulsion concept.

Abstract

Purpose

This article aims to investigate a selected number of liquid hydrogen storage tank parameters in a turboelectric distributed propulsion concept.

Design/methodology/approach

In this research study, tank structure, tank geometry, tank materials and additional physical phenomenon such as hydrogen boil-off and permeation are considered. A parametric analysis of different insulation foams is also performed throughout the design process of a lightweight liquid hydrogen storage tank.

Findings

Based on the mass of boil-off and foam weight, phenolic foam exhibited better characteristics amongst the five foam insulation materials considered in this particular study.

Practical implications

Liquid hydrogen occupies 4.2 times the volume of jet fuel for the same amount of energy. This suggests that a notable tank size is expected. Nonetheless, as jet fuel weighs 2.9 times more than liquid hydrogen for the same amount of energy, this reduced weight aspect partly compensates for the increased tank size.

Originality/value

In this article, potential insulation materials for liquid hydrogen storage tanks are highlighted and compared utilizing a presented methodology.

Details

Aircraft Engineering and Aerospace Technology: An International Journal, vol. 86 no. 1
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 2 May 2017

Aleksey V. Nenarokomov, Margarita O. Salosina and Oleg M. Alifanov

The presented paper aims to consider algorithm for optimal design of multilayer thermal insulation.

Abstract

Purpose

The presented paper aims to consider algorithm for optimal design of multilayer thermal insulation.

Design/methodology/approach

Developed algorithm is based on a sequential quadratic programming method.

Findings

2D mathematical model of heat transfer in thermal protection was considered in frame of thermal design of spacecraft. The sensitivity functions were used to estimate the Jacobean of the object functions.

Research limitations/implications

Design of distributed parameter systems and shape optimization may be thought of as geometrical inverse problems, in which the positions of free boundaries are determined along with the spatial variables. In such problems, the missing data (i.e. the position of boundaries) are compensated for by the presence of the so-called inverse problem additional conditions. In the case under consideration, such conditions are constrains on the temperature values at the discrete points of the system.

Practical implications

Results are presented how to apply the algorithm suggested for solving a practical problem – thickness sampling for a thermal protection system of advanced solar probe.

Originality/value

The procedure proposed in the paper to solve a design problem is based on the method of quadratic approximation of the initial problem statement as a Lagrange formulation. This has allowed to construct a rather universal algorithm applicable without modification for solving a wide range of thermal design problems.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 16 July 2020

Muhammet Çağrı Ayan, Serap Kiriş, Ahmet Yapici, Muharrem Karaaslan, Oğuzhan Akgöl, Olcay Altıntaş and Emin Ünal

The purpose of this paper is to investigate cotton fabric behavior that is exposed to radar waves between selected operation frequencies as an alternative radar-absorbing material…

Abstract

Purpose

The purpose of this paper is to investigate cotton fabric behavior that is exposed to radar waves between selected operation frequencies as an alternative radar-absorbing material (RAM) response. Cotton fabric biocomposite materials were compared with carbon fabric composite materials, which are good absorbers, in terms of mechanical and electromagnetic (EM) properties for that purpose.

Design/methodology/approach

The laminated composite plates were manufactured by using a vacuum infusion process. The EM tests were experimentally performed with a vector network analyzer to measure reflection, transmission and absorption ability of cotton fabric, carbon fabric and cotton–carbon fabric (side by side) composite plates between 3 and 18 GHz. The tensile and low-velocity impact tests were carried out to compare the mechanical properties of cotton fabric and carbon fabric composite plates. A scanning electron microscope was used for viewing the topographical features of fracture surfaces.

Findings

The cotton fabric composite plate exhibits low mechanical values, but it gives higher EM wave absorption values than the carbon fabric composite plate in certain frequency ranges. Comparing the EM absorption properties of the combination of cotton and carbon composites with those of the carbon composite alone, it appears that the cotton–carbon combination can be considered as a better absorber than the carbon composite in a frequency range from 12 to 18 GHz at Ku band.

Originality/value

This paper shows how cotton, which is a natural and easily supplied low-cost raw material, can be evaluated as a RAM.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 8
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 18 November 2013

Andrew Wright

Wearable electronics is an emerging technology predicted to become a 50B$ industry by 2018. Components and circuits will be highly integrated into clothing and other apparel. One…

Abstract

Purpose

Wearable electronics is an emerging technology predicted to become a 50B$ industry by 2018. Components and circuits will be highly integrated into clothing and other apparel. One crucial factor is the need for highly robust, flexible printed circuit tracks with sufficiently high electrical conductivity. The fact that metal-based tracks tend to suffer from fatigue failure has driven the development of alternative materials. The paper aims to discuss these issues.

Design/methodology/approach

Alternative materials are organic conductors and carbon nanotubes. The latter has a great flexibility and intrinsic strength. While nanotubes can be solubilised and printed using ink-jet techniques, this usually requires polymer additives. The paper has therefore sought to develop a novel solvent-free dry-ink.

Findings

The paper has found that it is possible to directly transfer from a nanotube growth substrate, via a hard print stamp head, onto a flexible rubber substrate and that one loading of the stamp can give many individual prints before exhaustion: the dry-ink stamp face effectively de-layers by a set amount each time a print is made. Many consecutive, highly consistent and uniform prints can be made using this approach. When printed onto natural rubber, the printed tracks are very robust and can be stretched to 100 per cent strain without permanent damage. The electrical conductivity can be improved by a simple alcohol treatment to consolidate the fibers and by iodine doping reaching 38 S · cm−1.

Originality/value

The findings offer an economical way to print highly robust electrically conductive tracks of carbon nanotubes directly onto flexible substrates.

Details

Circuit World, vol. 39 no. 4
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 1 January 2007

M. Grujicic, C.L. Zhao, S.B. Biggers, J.M. Kennedy and D.R. Morgan

Common Aero Vehicles (CAVs) are relatively small‐size, un‐powered, self‐maneuvering vehicles equipped with a variety of weapons and launched from space. One of the major obstacles…

Abstract

Common Aero Vehicles (CAVs) are relatively small‐size, un‐powered, self‐maneuvering vehicles equipped with a variety of weapons and launched from space. One of the major obstacles hampering a full the realization of the CAV concept is a present lack of lightweight, high‐temperature insulation materials which can be used for construction of the CAV’s thermal protection system (TPS). A computational analysis is utilized in the present work to examine the suitability of a carbon‐based, coal‐derived foam for the TPS applications in the CAVs. Toward that end, a model is developed for the high‐temperature effective thermal conductivity of foam‐like materials. In addition, an insulation sizing procedure is devised to determine the minimum insulation thickness needed for thermal protection of the vehicle structure at different sections of a CAV. It is found that the carbon‐based foam material in question can be considered as a suitable TPS insulation material at the leeward side and at selected portions of the windward side of a CAV (specifically the portions which are further away from the vehicle nose).

Details

Multidiscipline Modeling in Materials and Structures, vol. 3 no. 1
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 7 November 2016

Lizhu Liu, Weiliang Li, Weiwei Cui, Xiaorui Zhang and Weng Ling

In this paper, boric acid was loaded on the surface of expandable graphite (EG), polyvinyl alcohol (PVA) and silane coupling agent (KH550) served as a bridge. The purpose of this…

Abstract

Purpose

In this paper, boric acid was loaded on the surface of expandable graphite (EG), polyvinyl alcohol (PVA) and silane coupling agent (KH550) served as a bridge. The purpose of this study was to improve the flame retardant properties of semi-rigid polyurethane, meanwhile, the mechanical properties of the foam got ameliorated.

Design/methodology/approach

PVA was dissolved in hot water. EG was added to this solution. After stirring for 0.5 h at 85°C in ultrasonic agitation, the system was put at room temperature to cool. The silane coupling agent KH550 was added dropwise into the solution system, stirring to fully hydrolyze. Boric acid was added into the system, placing it in an oven at 90°C to dry after filtration. Changing of flame retardant properties and mechanical properties of semi-rigid polyurethane adding modified EG were characterized.

Findings

The flame retardant performance of the foam with EG has been improved, whereas the tensile strength decreased with an increase in the content of EG. After adding modified EG, compared to semi-rigid polyurethane with EG, flame retardant performance and tensile strength of the foam improved.

Research limitations/implications

In the study reported here, the surface of EG was modified by boric acid. The modified EG was added into semi-rigid polyurethane foam. The flame retardant performance and tensile strength of the foam after adding modified EG were discussed. Results of this research could benefit in-depth study of the influence of adding modified EG to semi-rigid polyurethane. The study could promote the application of flame-retardant polyurethane foam.

Originality/value

The flame retardant performance and tensile strength of the semi-rigid polyurethane were improved by adding modified EG. The effects of modified EG on the flame retardant performance and tensile strength of semi-rigid polyurethane were discussed in detail.

Details

Pigment & Resin Technology, vol. 45 no. 6
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 22 June 2012

Salvatore Brischetto and Erasmo Carrera

The purpose of this paper is to consider the static analysis of nanocomposite plates. Nanocomposites consist of a small amount of nanoscale reinforcements which can have an…

Abstract

Purpose

The purpose of this paper is to consider the static analysis of nanocomposite plates. Nanocomposites consist of a small amount of nanoscale reinforcements which can have an observable effect on the macroscale properties of the composites.

Design/methodology/approach

In the present study the reinforcements considered are non‐spherical, high aspect ratio fillers, in particular nanometer‐thin platelets (clays) and nanometer‐diameter cylinders (carbon nanotubes, CNTs). These plates are considered simply supported with a bi‐sinusoidal pressure applied at the top. These conditions allow the solving of the governing equations in a closed form. Four cases are investigated: a single layered plate with CNT reinforcements in elastomeric or thermoplastic polymers, a single layered plate with CNT reinforcements in a polymeric matrix embedding carbon fibers, a sandwich plate with external skins in aluminium alloy and an internal core in silicon foam filled with CNTs and a single layered plate with clay reinforcements in a polymeric matrix. A short review of the most important results in the literature is given to determine the elastic properties of the suggested nanocomposites which will be used in the proposed static analysis. The static response of the plates is obtained by using classical two‐dimensional models such as classical lamination theory (CLT) and first order shear deformation theory (FSDT), and an advanced mixed model based on the Carrera Unified Formulation (CUF) which makes use of a layer‐wise description for both displacement and transverse stress components.

Findings

The paper has two aims: to demonstrate that the use of classical theories, originally developed for traditional plates, is inappropriate to investigate the static response of nanocomposite plates and to quantify the beneficial effect of the nanoreinforcements in terms of static response (displacements and stresses).

Originality/value

In the literature these effects are usually given only in terms of elastic properties such as Young moduli, shear moduli and Poisson ratios, and not in terms of displacements and stresses.

Details

Multidiscipline Modeling in Materials and Structures, vol. 8 no. 1
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 8 August 2016

Zhengfeng Cao, Yanqiu Xia and Xiangyu Ge

The purpose of this paper is to synthesize a new kind of conductive grease which possesses a prominent conductive capacity and good tribological properties.

Abstract

Purpose

The purpose of this paper is to synthesize a new kind of conductive grease which possesses a prominent conductive capacity and good tribological properties.

Design/methodology/approach

A two-step method was used to prepare complex lithium-based grease. Ketjen black (KB), acetylene black (AB) and carbon black (CB) were characterized by transmission electron microscope and used as lubricant additives to prepare conductive greases. Conductive capacity was evaluated by a conductivity meter, a surface volume resistivity meter and a circuit resistance meter. Tribological properties were investigated by a reciprocating friction and wear tester (MFT-R4000). The worn surfaces were analyzed by a scanning electron microscope, Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscope.

Findings

The conductive grease prepared with KB has a prominent conductive capacity at room temperature, 100°C and 150°C. Further, this conductive grease also possesses better tribological properties than AB and KB greases. When the concentration of KB is 1.8 Wt.%, the coefficient of friction and wear width reduced by 11 and 14 per cent, respectively.

Originality/value

This work is a new application of nanometer KB as a lubricant additive in grease, which provides a direction for preparing conductive grease. The conductivity and tribology experiments have been carried out though the variation of experiment conductions.

Details

Industrial Lubrication and Tribology, vol. 68 no. 5
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 26 October 2018

Ajay Kumar Chhabra and Prabal Talukdar

This paper aims to develop a numerical model to investigate coupled conduction radiation heat transfer in a multilayer semi-transparent polymeric foam.

Abstract

Purpose

This paper aims to develop a numerical model to investigate coupled conduction radiation heat transfer in a multilayer semi-transparent polymeric foam.

Design/methodology/approach

The model uses a multi-phase approach in which the radiative transfer is determined by solving the radiative transfer equation explicitly in the whole medium incorporating an interface condition valid in the geometric optics rgime. This is executed by using a combination of ray splitting and a discrete curved ray tracing technique. Both partial photon reflection and total internal reflection at the interface are considered in the present investigation.

Findings

The directional distribution of intensity within the whole medium can be determined, which is used to obtain the detailed temperature profile inside the domain. The performance of the proposed methodology has been tested by simulating the modelled foam at ambient conditions. The results obtained from the simulations are in good agreement with the published results and shows that there is a global non-linearity in the temperature profile in problems where conduction to radiation parameter is small.

Originality/value

Specular nature of radiative transfer at the interface is accounted for in the present analysis. Instead of working with direction integrated quantities (as in the case of P1 approximation), each bundle of rays is treated separately within the whole medium. This model serves as a starting point for a detailed spatially three dimensional study of heat transfer in foams and the mathematical nature of the formulation is such that it may result in an implementation to three-dimensions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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