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Article
Publication date: 1 June 2005

A. Nakayama and F. Kuwahara

To introduce a novel numerical calculation procedure for periodically fully developed heat and fluid flow, which can treat three‐dimensional velocity and temperature fields, using…

685

Abstract

Purpose

To introduce a novel numerical calculation procedure for periodically fully developed heat and fluid flow, which can treat three‐dimensional velocity and temperature fields, using a two‐dimensional storage.

Design/methodology/approach

The three‐dimensional Navier‐Stokes equation and energy equation have been transformed into quasi‐three‐dimensional forms. An appropriate set of explicit periodic boundary conditions have been obtained for thermally fully developed flow through a general three‐dimensional periodic structure, exploiting the volume averaging theory.

Findings

The proposed numerical procedure has been found inexpensive and efficient. Its validity has been proved by comparing the results obtained for a bank of long cylinders in yaw against available experimental data.

Originality/value

Since no explicit sets of periodic boundary conditions of this kind have been reported before, they will be exploited by researchers and practitioners interested in efficient numerical computations of three‐dimensional periodic heat and fluid flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 2 September 2013

Yoshihiro Takebe, Masako Kanai-Pak, Noriaki Kuwahara, Jukai Maeda, Miwa Hirata, Yasuko Kitajima and Jun Ota

– This paper aims to construct a recognition system of nursing activities.

210

Abstract

Purpose

This paper aims to construct a recognition system of nursing activities.

Design/methodology/approach

The authors used accelerometers and radio frequency identification (RFID) tags to ensure patient privacy in practical nursing care environments. The accelerometers were attached to the body of the nurse, and the RFID was attached to apparatuses and objects. In addition, a pattern classification algorithm using a support vector machine and filtering methodology were applied.

Findings

The accuracy using accelerometers and RFID was 73 percent. When the filtering algorithm was applied, the results were 79 percent. The results showed that activities with short execution times or those that resembled others in posture had low recognition accuracy.

Research limitations/implications

Activities requiring only a short period of time tend to be misrecognized.

Practical implications

It is possible to construct a training system for nursing activities with the system that recognizes the sequence of nursing activities and how much time is spent for individual activities.

Originality/value

The originality of the paper is to construct the system that considers the following characteristics of nursing activities: about 13 activities that are fundamental for nurses can be recognized, privacy of the patient is considered, several activities utilizing only part of the body (not whole body) can be recognized, and activities involving and not involving some types of apparatus can be recognized.

Details

Kybernetes, vol. 42 no. 7
Type: Research Article
ISSN: 0368-492X

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Article
Publication date: 8 August 2019

Chunyang Wang, Moghtada Mobedi and Fujio Kuwahara

The purpose of this study is to validate whether the local thermal equilibrium for unsteady state is an appropriate assumption for the porous media with closed pores. It also…

158

Abstract

Purpose

The purpose of this study is to validate whether the local thermal equilibrium for unsteady state is an appropriate assumption for the porous media with closed pores. It also compares the transient temperatures between the pore scale and volume averaged approaches to prove that the volume averaged method is an appropriate technique for the heat transfer in closed-cell porous media. The interfacial heat transfer coefficient for the closed-cell porous media is also discussed in details.

Design/methodology/approach

The governing equations for the pore scale and continuum domains are given. They are solved numerically for the pore scale and volume-averaged domains. The results are compared and discussion was done. The performed discussions and explanations are supported with figure and graphics.

Findings

A local thermal non-equilibrium exits for the closed-cell porous media in which voids are filled with water during the unsteady heat transfer process. Local thermal non-equilibrium condition exists in the cells under high temperature gradient and it disappears when the heat transfer process becomes steady-state. Although a local thermal equilibrium exists in the porous media in which the voids are filled with air, a finite value for heat transfer coefficient is found. The thermal diffusivity of air and solid phase are close to each other and hence a local thermal equilibrium exists.

Research limitations/implications

The study is done only for the closed-cell porous media and for Rayleigh number till 105. Two common working fluids as water and air are considered.

Practical implications

There are many applications of porous media with closed pores particularly in the industry, such as the closed-cell metal foam or the closed cells in porous materials such as foods and plastic-based insulation material. The obtained results are important for transient heat transfer in closed-cell porous materials.

Social implications

The obtained results are important from the transient application of heat transfer in the closed-cell material existing in nature and industry.

Originality/value

The authors’ literature survey shows that it is the first time the closed-cell porous media is discussed from local thermal non-equilibrium point of view and it is proved that the local thermal non-equilibrium can exist in the closed-cell porous media. Hence, two equations as solid and fluid equations should be used for unsteady heat transfer in a closed-cell porous medium.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 11 October 2018

Safa Sabet, Moghtada Mobedi, Murat Barisik and Akira Nakayama

Fluid flow and heat transfer in a dual scale porous media is investigated to determine the interfacial convective heat transfer coefficient, numerically. The studied porous media…

189

Abstract

Purpose

Fluid flow and heat transfer in a dual scale porous media is investigated to determine the interfacial convective heat transfer coefficient, numerically. The studied porous media is a periodic dual scale porous media. It consists of the square rods which are permeable in an aligned arrangement. It is aimed to observe the enhancement of heat transfer through the porous media, which is important for thermal designers, by inserting intra-pores into the square rods. A special attention is given to the roles of size and number of intra-pores on the heat transfer enhancement through the dual scale porous media. The role of intra-pores on the pressure drop of air flow through porous media is also investigated by calculation and comparison of the friction coefficient.

Design/methodology/approach

To calculate the interfacial convective heat transfer coefficient, the governing equations which are continuity, momentum and energy equations are solved to determine velocity, pressure and temperature fields. As the dual scale porous structure is periodic, a representative elementary volume is generated, and the governing equations are numerically solved for the selected representative volume. By using the obtained velocity, pressure and temperature fields and using volume average definition, the volume average of aforementioned parameters is calculated and upscaled. Then, the interfacial convective heat transfer coefficient and the friction coefficient is numerically determined. The interparticle porosity is changed between 0.4 and 0.75, while the intraparticle varies between 0.2 and 0.75 to explore the effect of intra-pore on heat transfer enhancement.

Findings

The obtained Nusselt number values are compared with corresponding mono-scale porous media, and it is found that heat transfer through a porous medium can be enhanced threefold (without the increase of pressure drop) by inserting intraparticle pores in flow direction. For the porous media with low values of interparticle porosity (i.e. = 0.4), an optimum intraparticle porosity exists for which the highest heat transfer enhancement can be achieved. This value was found around 0.3 when the interparticle porosity was 0.4.

Research limitations/implications

The results of the study are interesting, especially from heat transfer enhancement point of view. However, further studies are required. For instance, studies should be performed to analyze the rate of the heat transfer enhancement for different shapes and arrangements of particles and a wider range of porosity. The other important parameter influencing heat transfer enhancement is the direction of pores. In the present study, the intraparticle pores are in flow direction; hence, the enhancement rate of heat transfer for different directions of pores must also be investigated.

Practical implications

The application of dual scale porous media is widely faced in daily life, nature and industry. The flowing of a fluid through a fiber mat, woven fiber bundles, multifilament textile fibers, oil filters and fractured porous media are some examples for the application of the heat and fluid flow through a dual scale porous media. Heat transfer enhancement.

Social implications

The enhancement of heat transfer is a significant topic that gained the attention of researchers in recent years. The importance of topic increases day-by-day because of further demands for downsizing of thermal equipment and heat recovery devices. The aim of thermal designers is to enhance heat transfer rate in thermal devices and to reduce their volume (and/or weight in some applications) by using lower mechanical power for cooling.

Originality/value

The present study might be the first study on determination of thermal transport properties of dual scale porous media yielded interesting results such as considerable enhancement of heat transfer by using proper intraparticle channels in a porous medium.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 11
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 9 September 2019

Marcello Iasiello, Assunta Andreozzi, Nicola Bianco and Kambiz Vafai

Recently, the porous media theory has been successively proposed for many bioengineering applications. The purpose of this paper is to analyze if the porous media theory can be…

195

Abstract

Purpose

Recently, the porous media theory has been successively proposed for many bioengineering applications. The purpose of this paper is to analyze if the porous media theory can be applied to model radiofrequency (RF) cardiac ablation.

Design/methodology/approach

Blood flow, catheter and tissue are modeled. The latter is further divided into a fluid and a solid phase, and porous media equations are used to model them. The heat source term is modeled using the Laplace equation, and the finite element method is used to solve the governing equations under the appropriate boundary conditions and closure coefficients.

Findings

After validation with available literature data, results are shown for different velocities and applied voltages to understand how these parameters affect temperature fields (and necrotic regions).

Research limitations/implications

The model might require further validation with experiments under different conditions after comparisons with available literature. However, this might not be possible due to the experimental complexity.

Practical implications

The improvement in predictions from the model might help the final user, i.e. the surgeon, who uses cardiac ablation to treat arrhythmia.

Originality/value

This is the first time that the porous media theory is applied to RF cardiac ablation. The robustness of the model, in which many variables are taken into account, makes it suitable to better predict temperature fields, and damaged regions, during RF cardiac ablation treatments.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 5
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 December 2005

A. Nakayama, F. Kuwahara and Y. Kamiya

To introduce an efficient two‐dimensional numerical procedure for a three‐dimensional internal flow through a complex passage with a small depth, in which the viscous effects from…

653

Abstract

Purpose

To introduce an efficient two‐dimensional numerical procedure for a three‐dimensional internal flow through a complex passage with a small depth, in which the viscous effects from upper and lower walls are significant.

Design/methodology/approach

A set of two‐dimensional governing equations has been derived by integrating the full three‐dimensional Navier‐Stokes equations over the depth. Then, this set of the governing equations has been discretized using a finite volume method. Simple algorithm and quick scheme are used to solve the resulting discretized equations.

Findings

A numerical experiment conducted to investigate the oscillation mechanism of a feedback fluidic oscillator reveals that the feedback passage plays an important role of transmitting the pressure rise to the control port, which triggers the jet stream to deflect towards the opposite side wall in the reaction region. Comparison of the prediction and experiment substantiates the validity of the present numerical procedure.

Originality/value

The two‐dimensional numerical procedure, proposed in this study, will be used by researchers and practitioners to investigate various kinds of complex passages with a small depth. Especially, those who are interested in fluidic devices may find it extremely convenient to conduct numerical experiments.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 November 2003

N. Massarotti, P. Nithiarasu and A. Carotenuto

In this paper, microscopic and macroscopic approaches to the solution of natural convection in enclosures filled with fluid saturated porous media are investigated. At the…

926

Abstract

In this paper, microscopic and macroscopic approaches to the solution of natural convection in enclosures filled with fluid saturated porous media are investigated. At the microscopic level, the porous medium is represented by different assemblies of cylinders and the Navier‐Stokes equations are assumed to govern the flow. To represent the flow in a macroscopic porous medium approach, the generalised flow model is employed. The characteristic based split scheme is used to solve the conservation equations of both approaches. In addition to the comparison between microscopic and macroscopic approaches of fluid saturated porous enclosures, cavities with interface between fluid saturated porous medium and single phase fluid are also investigated.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 13 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 20 December 2021

Chunyang Wang, Xinghua Zheng, Ting Zhang, Haisheng Chen and Moghtada Mobedi

The purpose of this study is to investigate the applicability of volume average which is extensively used for analyzing the heat and fluid flow (both for single-phase and…

133

Abstract

Purpose

The purpose of this study is to investigate the applicability of volume average which is extensively used for analyzing the heat and fluid flow (both for single-phase and solid/liquid-phase change) in a closed cell porous medium numerically.

Design/methodology/approach

Heat conduction equations for the solid frame and fluid (or phase change material) are solved for pore scale and volume average approaches. The study mainly focuses on the effect of porosity and the number of porous media unit cell on the agreement between the results of the pore scale and volume average approaches.

Findings

It is observed for the lowest porosity values such as 0.3 and the number of porous media unit cell as 4 in heat transfer direction, the results between two approaches may be questionable for the single-phase fluid. By increasing the number of porous media unit cell in heat transfer direction, the agreement between two approaches becomes better. In general, for high porosity values (such as 0.9) the agreement between the results of two approaches is in the acceptable range both for single-phase and solid/liquid-phase change. Two charts on the applicability of volume average method for single-phase and solid/liquid-phase change are presented.

Originality/value

The authors’ literature survey shows that it is the first time the applicability of volume average which is extensively used for analyzing the heat and fluid flow in a closed cell porous medium is investigated numerically.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 4 December 2017

Hasan Celik, Moghtada Mobedi, Oronzio Manca and Unver Ozkol

The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under…

285

Abstract

Purpose

The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer.

Design/methodology/approach

The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method.

Findings

It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01).

Originality/value

To the best of the authors’ knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 12
Type: Research Article
ISSN: 0961-5539

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Book part
Publication date: 17 June 2024

Nassir Ul Haq Wani

The benefits of global trade are primarily attributed to reducing trade distortions between trading partners. The anticipated promise of a progressive diminution in tariffs…

Abstract

The benefits of global trade are primarily attributed to reducing trade distortions between trading partners. The anticipated promise of a progressive diminution in tariffs throughout the globe was, regrettably, steadily superseded by non-tariff measures (NTMs). However, the impact of these NTMs is only sometimes evident since it occurs in various disguises. NTMs significantly influence trade in the SAARC, mandating prompt attention. The question is how much internal trade will expand if NTMs are repealed. Based on statistics from 2015 to 2020, the study endeavours to quantify the impact of NTMs on Afghanistan's trade volume within the SAARC region, primarily targeting four export destinations (Bangladesh, India, Pakistan and Sri Lanka). Using trade freedom scores as a proxy for trade distortions, it has been determined that Afghanistan's magnitude of export earnings is significantly lower due to NTMs imposed by its importing trading partners. According to the findings, a 1% rise in tariffs and NTMs applied by importing countries diminishes Afghanistan's exports by 1.23%.

In contrast, the impact of tariffs alone lowers Afghanistan's exports by 1.13%. The incidence of NTMs also devoid actual Afghanistan exports by US$ 5.70 million, equal to a 0.029% loss of Afghanistan's GDP. The calculations also reveal that lowering or eliminating non-tariff barriers has diverse trade growth effects in different trade groupings. The study recommends a serious NTM-oriented trade policy dialogue that is liberal and guarantees regional integration, thereby promoting and ensuring the future of Afghanistan's economic laurels and stability.

Details

Policy Solutions for Economic Growth in a Developing Country
Type: Book
ISBN: 978-1-83753-431-9

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