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1 – 10 of over 1000
Article
Publication date: 6 September 2019

Andreas Diermeier, Dirk Sindersberger, Peter Angele, Richard Kujat and Gareth John Monkman

Ultrasound is a well-established technology in medical science, though many of the conventional measurement systems (hydrophones and radiation force balances [RFBs]) often…

Abstract

Purpose

Ultrasound is a well-established technology in medical science, though many of the conventional measurement systems (hydrophones and radiation force balances [RFBs]) often lack accuracy and tend to be expensive. This is a significant problem where sensors must be considered to be “disposable” because they inevitably come into contact with biological fluids and expense increases dramatically in cases where a large number of sensors in array form are required. This is inevitably the case where ultrasound is to be used for the in vitro growth stimulation of a large plurality of biological samples in tissue engineering. Traditionally only a single excitation frequency is used (typically 1.5 MHz), but future research demands a larger choice of wavelengths for which a single broadband measurement transducer is desirable. Furthermore, because of implementation conditions there can also be large discrepancies between measurements. The purpose of this paper deals with a very cost-effective alternative to expensive RFBs and hydrophones.

Design/methodology/approach

Utilization of cost-effective piezoelectric elements as broadband sensors.

Findings

Very effective results with equivalent (if not better) accuracy than expensive alternatives.

Originality/value

This paper concentrates on how very cost-effective piezoelectric ultrasound transducers can be implemented as sensors for ultrasound power measurements with accuracy as good, if not better than those achievable using radiation force balances or hydrophones.

Article
Publication date: 26 August 2014

Ping Yang and Guangzhen Xing

This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the…

Abstract

Purpose

This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the measurement of first echo current and open-circuit voltage of the driving source.

Design/methodology/approach

The formula for ultrasonic power is derived which has corrected the position of pressure reflection coefficient on the interface of water and steel. The diffraction correction for focusing transducers is evaluated using numerical computation of the Rayleigh integral. One way to estimate the reflection coefficient of focusing beams on heterogeneous interface is also depicted.

Findings

Comparison experiment with radiation force balance method demonstrates that ultrasonic power measurement using self-reciprocity is sound in theory and feasible in practice.

Originality/value

It has a better capability of anti-environmental interference and, thus, can be extended to low-level and high-frequency power measurements.

Details

Sensor Review, vol. 34 no. 4
Type: Research Article
ISSN: 0260-2288

Keywords

Article
Publication date: 30 March 2010

Fahad G. Al‐Amri and Maged A.I. El‐Shaarawi

This paper's aim is to investigate the effect of surface radiation on the developing laminar forced convection flow of a transparent gas between two vertical parallel…

Abstract

Purpose

This paper's aim is to investigate the effect of surface radiation on the developing laminar forced convection flow of a transparent gas between two vertical parallel plates. The walls are heated asymmetrically, this enhances the effect of radiation even with the two walls having low values of emissivity.

Design/methodology/approach

Numerical techniques were used to study the effect of the controlling parameters on wall temperatures, fluid temperature profiles, and Nusslet number.

Findings

The values of the radiation number at which surface radiation can engender symmetric heating (and hence maximum average Nusslet number on the heated wall and maximum reduction in the maximum heated wall temperature are achieved) are obtained. Threshold values of the radiation number at which radiation effects can be neglected are obtained.

Research limitations/implications

Boundary‐layer flow model is used.

Practical implications

The implications include design of high‐temperature gas‐cooled heat exchangers, advanced energy conversion devices, advanced types of power plants, and many others.

Originality/value

Though a number of analyses of internal flows including radiation effect have been made, most have been directed at the simplest case of the prescribed uniform (isothermal) temperature boundary condition. The available literature that deals with the problem with prescribed heat flux at the walls is limited to fully developed flow or specifying the convection coefficient a priori. The lack of both theoretical and experimental data concerning combined forced convection and surface radiation developing flows between two parallel and its practical importance motivated the present work.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 20 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 August 1998

Ahmed Hamza H. Ali, Koki Kishinami, Yutaka Hanaoka and Jun Suzuki

A two‐dimensional numerical study was carried out to investigate laminar forced‐convection heat transfer characteristics of air flow in a two parallel plate channel with…

Abstract

A two‐dimensional numerical study was carried out to investigate laminar forced‐convection heat transfer characteristics of air flow in a two parallel plate channel with offset plates and heated by a radiation heat flux. The SIMPLE method was used for the numerical prediction of the flow and thermal fields. The flow field temperature boundary conditions were obtained by applying the energy balance equation to boundary elements. The ray tracing technique was used to obtain the net absorbed radiation fractions in the boundary elements. The numerical results were validated with measured temperature values and experimentally calculated values of local Nusselt number (Nux), and a reasonable agreement was shown. Then the numerical simulation was used to study effects of design parameters on the convective heat transfer coefficient. It was found that in Re numbers from 650 to 2,550, the optimum spacing of offset plates relative to the nearest channel wall was around one third of the channel height. Also, the optimum offset plates’ numbers can be calculated based on one offset plate length being equal to one and a half times the channel hydraulic diameter. A correlation of average Nusselt number between the flowing air and the offset plates was obtained as follows; —Nu = 1.81 Re 0.352Pr1/3(Dh/l)1/2.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 23 September 2022

Naveen Kumar Battula, Srinu Daravath and Ganesh Kumar Gampa

This paper deals with numerical studies into combined conduction, convection and radiation from a heated vertical electronic board are provided here.

Abstract

Purpose

This paper deals with numerical studies into combined conduction, convection and radiation from a heated vertical electronic board are provided here.

Design/methodology/approach

Here three inbuilt heaters with decrease in their heights were placed in the vertical electronic board. With respect to the non-heat portions, two configurations were studied. The first considers the non-heat portions to be adiabatic, while in the second, they are non-adiabatic. The heat that is produced in three heaters is conducted along the board and is dissipated either from the heater portions alone or from the whole board by convection and radiation. Air is considered as working medium, while the equations of heat transfer and flow of fluid are handled without boundary layer approximations. These equations were further solved using finite volume method with Gauss–Seidel iteration method.

Findings

Results of various comparative studies were discussed to bring out the relevance of thermal conductivity, modified Richardson number and surface emissivity on different heat transfer and flow results concerning this problem.

Originality/value

The optimum values of surface emissivity, thermal conductivity and modified Richardson number have also been notionally explored.

Details

World Journal of Engineering, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1708-5284

Keywords

Article
Publication date: 1 January 2014

Sofen K. Jena, Swarup K. Mahapatra and Amitava Sarkar

The current study aims to address the interaction between participating media radiation with thermo-gravitational convection of an electrically conducting fluid enclosed…

Abstract

Purpose

The current study aims to address the interaction between participating media radiation with thermo-gravitational convection of an electrically conducting fluid enclosed within a tilted enclosure under an externally imposed time-independent uniform magnetic field.

Design/methodology/approach

The differentially heated boundaries of the tilted enclosure are considered to be diffuse, gray and the enclosed fluid is assumed to be absorbing, emitting and isotropically scattering. The Navier-Stokes equations, meant for magneto convection are solved using modified MAC method. Gradient dependent consistent hybrid upwind scheme of second order is used for discretization of the convective terms. Discrete ordinate method, with S8 approximation, is used to model radiative transport equation in the presence of radiatively active medium.

Findings

Effect of uniform magnetic field with different magnitudes and orientations of cavity has been numerically simulated. The effect of participating media radiation has been investigated for different optical thicknesses, emissivities, scattering albedos and Planks number. The results are provided in both graphical and tabular forms. The flow lines, isotherms bring clarity in the understanding of flow behaviour and heat transfer characteristics.

Originality/value

Despite the idealized nature, the present study is quite essential to understand the cumbersome physics of realistic problem.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 9 August 2021

Zongyao Yang, Yong Shan and Jingzhou Zhang

This study aims to investigate the effects of exhaust direction on exhaust plume and helicopter infrared radiation in hover and cruise status.

Abstract

Purpose

This study aims to investigate the effects of exhaust direction on exhaust plume and helicopter infrared radiation in hover and cruise status.

Design/methodology/approach

Four exhaust modes are concerned, and the external flow field and fuselage temperature field are calculated by numerical simulation. The infrared radiation intensity distributions of the four models in hovering and cruising states are computed by the ray-tracing method.

Findings

Under the hover status, the exhaust plume is deflected to flow downward after it exhausts from the nozzle exit, upon the impact of the main-rotor downwash. Besides, the exhaust plume shows a “swirling” movement following the main-rotor rotational direction. The forward-flight flow helps prevent the hot exhaust plume from a collision with the helicopter fuselage generally for the cruise status. In general, the oblique-upward exhaust mode provides moderate infrared radiation intensities in all of the viewing directions, either under the hover or the cruise status. Compared with the hover status, the infrared radiation intensity distribution alters somewhat in cruise.

Originality/value

Illustrating the influences of exhaust direction on plume flow and helicopter infrared radiation and the differences of helicopter infrared radiation under hover and cruise statuses are identified. Finally, an appropriate exhaust mode is proposed to provide a better IR signature distribution.

Details

Aircraft Engineering and Aerospace Technology, vol. 93 no. 10
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 8 August 2016

Mohammad yaghoub Abdollahzadeh Jamalabadi

The purpose of this paper is to find the time dependent thermal creep stress relaxation of a turbine blade and to investigate the effect thermal radiation of the adjacent…

Abstract

Purpose

The purpose of this paper is to find the time dependent thermal creep stress relaxation of a turbine blade and to investigate the effect thermal radiation of the adjacent turbine blades on the temperature distribution of turbine blade and creep relaxation.

Design/methodology/approach

For this analysis, the creep flow behavior of Moly Ascoloy in operational temperature of gas turbine in full scale geometry is studied for various thermal radiation properties. The commercial software is used to pursue a coupled fields analysis for turbine blades in view of the structural force, materials kinematic hardening, and steady-state temperature field.

Findings

During steady-state operation, the thermal stress was found to be decreasing, whereas by considering the thermal radiation this rate was noticed to increase slightly. Also by increase of the distance between stator blades the thermal radiation effect is diminished. Finally, by decrease of the blade distance the failure probability and creep plastic deformation decrease.

Research limitations/implications

This paper describes the effect of thermal radiation in thermal-structural analysis of the gas turbine stator blade made of the super-alloy M-152.

Practical implications

Blade failures in gas turbine engines often lead to loss of all downstream stages and can have a dramatic effect on the availability of the turbine engines. There are many components in a gas turbine engine, but its performance is highly profound to only a few. The majority of these are hotter end rotating components.

Social implications

Three-dimensional finite element thermal and stress analyses of the blade were carried out for the steady-state full-load operation.

Originality/value

In the previous works the thermal radiation effects on creep behavior of the turbine blade have not performed.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 25 October 2021

Akram Mazgar, Khouloud Jarray, Fadhila Hajji and Fayçal Ben Nejma

This paper aims to numerically analyze the effect of non-gray gas radiation on mixed convection in a horizontal circular duct with isothermal partial heating from the…

Abstract

Purpose

This paper aims to numerically analyze the effect of non-gray gas radiation on mixed convection in a horizontal circular duct with isothermal partial heating from the sidewall. The influence of heater location on heat transfer, fluid flow and entropy generation is given and discussed in this study.

Design/methodology/approach

The numerical computation of heat transfer and fluid flow has been developed by the commercial finite element software COMSOL Multiphysics. Radiation code is developed based on the T10 Ray-Tracing method, and the radiative properties of the medium are computed based on the statistical narrow band correlated-k model.

Findings

The obtained results depicted that the radiation considerably contributes to the temperature homogenization of the gas. The findings highlight the impact of the heater location on swirling flow. It is also shown that the laterally heating process provides better energy efficiency than heating from the top of the enclosure.

Originality/value

This study is performed to improve heat transfer and to minimize entropy generation. Therefore, it is conceivable to improve the model design of industrial applications.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 January 2006

H. Bouali and A. Mezrhab

This paper presents a numerical investigation of the interaction of surfaces radiation with developing laminar free convective heat transfer in a divided vertical channel…

Abstract

Purpose

This paper presents a numerical investigation of the interaction of surfaces radiation with developing laminar free convective heat transfer in a divided vertical channel. The influence of the radiation on the heat transfer and on the air flow is studied for various sizes (width and length) of the plate.

Design/methodology/approach

The specifically developed numerical code is based on the utilization of the finite volume method. The SIMPLER algorithm for the pressure‐velocity coupling is adopted. The view factors are determined by using boundary elements to fit the surfaces, an algorithm solving the shadow effect and a Monte Carlo method for the numerical integrations.

Findings

Results obtained show that the radiation: plays a very important role on the paces of the isotherms, especially at Ra≥1,600; increases considerably the average wall Nusselt number; and increases the mass flow rate and the average channel Nusselt number at high Rayleigh numbers. The plate location has a significant effect on the heat transfer only in presence of the radiation exchange. The increase of both length and width of the plate causes a decrease of the heat transfer and the mass flow rate.

Research limitations/implications

The use of the code is limited to the flow that is assumed to be incompressible, laminar and two dimensional. The radiative surfaces are assumed diffuse‐gray.

Practical implications

Natural convection in vertical channels formed by parallel plates has received significant attention because of its interest and importance in industrial applications. Some applications are solar collectors, fire research, electronic cooling, aeronautics, chemical apparatus, building constructions, nuclear engineering, etc.

Originality/value

In comparison to the most of the previous studies on natural convection in partitioned channels, the radiation exchange was neglected. This study takes into account the radiation exchange in a divided channel.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 16 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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