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Article

Colin F. McDonald, Aristide F. Massardo, Colin Rodgers and Aubrey Stone

This paper seeks to evaluate the potential of heat exchanged aeroengines for future Unmanned Aerial Vehicle (UAV), helicopter, and aircraft propulsion, with emphasis…

Abstract

Purpose

This paper seeks to evaluate the potential of heat exchanged aeroengines for future Unmanned Aerial Vehicle (UAV), helicopter, and aircraft propulsion, with emphasis placed on reduced emissions, lower fuel burn, and less noise.

Design/methodology/approach

Aeroengine performance analyses were carried out covering a wide range of parameters for more complex thermodynamic cycles. This led to the identification of major component features and the establishing of preconceptual aeroengine layout concepts for various types of recuperated and ICR variants.

Findings

Novel aeroengine architectures were identified for heat exchanged turboshaft, turboprop, and turbofan variants covering a wide range of applications. While conceptual in nature, the results of the analyses and design studies generally concluded that heat exchanged engines represent a viable solution to meet demanding defence and commercial aeropropulsion needs in the 2015‐2020 timeframe, but they would require extensive development.

Research limitations/implications

As highlighted in Parts I and II, early development work was focused on the use of recuperation, but this is only practical with compressor pressure ratios up to about 10. For today's aeroengines with pressure ratios up to about 50, improvement in SFC can only be realised by incorporating intercooling and recuperation. The new aeroengine concepts presented are clearly in an embryonic stage, but these should enable gas turbine and heat exchanger specialists to advance the technology by conducting more in‐depth analytical and design studies to establish higher efficiency and “greener” gas turbine aviation propulsion systems.

Originality/value

It is recognised that meeting future environmental and economic requirements will have a profound effect on aeroengine design and operation, and near‐term efforts will be focused on improving conventional simple‐cycle engines. This paper has addressed the longer‐term potential of heat exchanged aeroengines and has discussed novel design concepts. A deployment strategy, aimed at gaining confidence with emphasis placed on assuring engine reliability, has been suggested, with the initial development and flight worthiness test of a small recuperated turboprop engine for UAVs, followed by a larger recuperated turboshaft engine for a military helicopter, and then advancement to a larger and far more complex ICR turbofan engine.

Details

Aircraft Engineering and Aerospace Technology, vol. 80 no. 4
Type: Research Article
ISSN: 0002-2667

Keywords

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Article

Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata and Takehiro Ito

To clarify the physical working principle of refrigeration in basic pulse tube refrigerators (BPTRs).

Abstract

Purpose

To clarify the physical working principle of refrigeration in basic pulse tube refrigerators (BPTRs).

Design/methodology/approach

A numerical simulation was performed. Transient compressible NS equation was solved utilizing the TVD scheme coupled with energy equation.

Findings

The periodic flow and temperature field were obtained. The movement of the gas particles and heat transfer between the gas particles and wall were analyzed. These numerical results explained the mechanism of surface heat pumping (SHP) which is known as the working principle of refrigeration in BPTR.

Research limitations/implications

Pulse tube refrigerator (PTR) is classified into the third generation. BPTR is the first generation. It is needed to clarify the working principle of refrigeration in the second and third generation by analyzing heat and fluid flow in the tube.

Practical implications

A very useful source of information to understand the physical working principle of refrigeration in BPTR.

Originality/value

The mechanism of SHP was shown by analyzing the heat exchange between the gas particles and pulse tube wall.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Roy Botman and Jos van Schijndel

The purpose of this paper is to present a tool for simulating heat sharing opportunities between multiple buildings.

Abstract

Purpose

The purpose of this paper is to present a tool for simulating heat sharing opportunities between multiple buildings.

Design/methodology/approach

The approach is based on a building simulation model, HAMBase, in combination with an analytical programming code using MatLab.

Findings

The tool provides a quick insight in possibilities for district heat sharing. It is able to operate without using too many parameters. From the results, it can be derived that storage tanks provide a great advantage in performance over the direct heat demand and supply method.

Research limitations/implications

The main limitations are as follows: the used models are based on assumptions plus values derived from literature and a verification that is based on energy balance rules; and the MatLab code is verified by checking for possible errors, but is not completely validated.

Originality/value

The main value of the work is that the presented methodology behind the tool is generally applicable and implementable in other models.

Details

Management of Environmental Quality: An International Journal, vol. 28 no. 4
Type: Research Article
ISSN: 1477-7835

Keywords

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Article

Antonio Campo and Yunesky Masip

The purpose of this study is to address one-dimensional, unsteady heat conduction in a large plane wall exchanging heat convection with a nearby fluid under “small time”…

Abstract

Purpose

The purpose of this study is to address one-dimensional, unsteady heat conduction in a large plane wall exchanging heat convection with a nearby fluid under “small time” conditions.

Design/methodology/approach

The Transversal Method of Lines (TMOL) was used to reformulate the unsteady, one-dimensional heat conduction equation in the space coordinate and time into a transformed “quasi-steady”, one-dimensional heat conduction equation in the space coordinate housing the time as an embedded parameter. The resulting ordinary differential equation of second order with heat convection boundary conditions is solved analytically with the method of undetermined coefficients.

Findings

Semi-analytical TMOL dimensionless temperature profiles of compact form with/without regressed terms are obtained for the whole spectrum of Biot number (0 < Bi < ∞) in the “small time” sub-domain. In addition, a new “large time” sub-domain is redefined, that is, setting a smaller critical dimensionless time or critical Fourier number τcr = 0.18.

Originality/value

The computed dimensionless center, surface and mean temperature profiles in the large plane wall accounting for all Biot number (0 < Bi < ∞) in the “small time” sub-domain τ < τcr = 0.18 exhibit excellent quality while carrying reasonable relative errors for engineering applications. The exemplary level of accuracy indicates that the traditional evaluation of the center, surface and mean temperatures with the standard infinite series retaining a large number of terms is no longer necessary.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Motahareh Mokhtari Yazdi, Mohammad Sheikhzadeh and Seyed Ehsan Chavoshi

The purpose of this paper is to identify and evaluate the potential cooling contribution provided by a phase change material cooling vest as part of the total heat exchange

Abstract

Purpose

The purpose of this paper is to identify and evaluate the potential cooling contribution provided by a phase change material cooling vest as part of the total heat exchange mechanism of the body and take in to account the negative side effects of wearing the cooling garments.

Design/methodology/approach

In this study, the three-part system of body-garment-environment has been simulated through the finite element method and the problem of heat exchange between these three parts has been solved with the help of computer modeling.

Findings

The results of this modeling showed that a large percentage of the cooling efficiency of cooling vest was neutralized by the negative effects of the vest that are weight, lack of breathability, and the effects on the thermal conductivity of the skin. Therefore, the net efficiency of the cooling vests resulted in a lower decrease in skin temperature compared to the state that the negative side effects were not included in the model.

Originality/value

Cooling power obtained with the help of cooling garments have been studied in previous studies using either human tests or manikins. But, what has been addressed less in previous studies relates to the negative effects of such equipment on the comfort of body, along with their cooling effect. So it is the first time witch the effect of side effects of such equipments are studied. Also modeling the real performance of cooling garments have not been done yet.

Details

International Journal of Clothing Science and Technology, vol. 27 no. 4
Type: Research Article
ISSN: 0955-6222

Keywords

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Article

S. Spitans and A. Jakovičs

The purpose of this paper is to compare k‐ω shear‐stress transport (SST) and large eddy simulation (LES) turbulence model application effect on numerical computation of…

Abstract

Purpose

The purpose of this paper is to compare k‐ω shear‐stress transport (SST) and large eddy simulation (LES) turbulence model application effect on numerical computation of flow pattern and heat exchange characteristics through the neutron beam window region for European spallation source setup model.

Design/methodology/approach

Transient hydrodynamic and thermal calculations with appropriate heat sources are performed using both turbulence models and typical discrepancies in flow and thermal patterns are discussed, as well as, simulation results are qualitatively compared with experimental data for heat transfer coefficient distribution α at the window surface.

Findings

Contribution of greater k‐energy field obtained with LES calculation leads to prediction of more intensive heat transfer in comparison to k‐ω SST.

Originality/value

The paper illustrates discrepancies of thermal patterns caused by application of k‐ω SST and LES turbulent models.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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Article

Lahcen El Moutaouakil, Zaki Zrikem and Abdelhalim Abdelbaki

A detailed numerical study is conducted on the effect of surface radiation on laminar natural convection in a tall vertical cavity filled with air. The cavity is heated

Abstract

Purpose

A detailed numerical study is conducted on the effect of surface radiation on laminar natural convection in a tall vertical cavity filled with air. The cavity is heated and cooled, through its two vertical walls, by a linear or uniform heat flux q(y) and by a constant cold temperature, respectively. The horizontal walls are considered adiabatic. The paper aims to discuss these issues.

Design/methodology/approach

The radiosity method is employed to calculate the net radiative heat exchanges between elementary surfaces, while the finite volume method is implemented to resolve the governing equations of the fluid flow.

Findings

For each heat flux q(y) (ascending, descending or uniform), the effect of the emissivity ε (0ε1) on the local, average and maximum temperatures of the heated wall is determined as a function of the average Rayleigh number Ram (103Ram 6×104) and the cavity aspect ratio A (10A80). The effect of the coupling on the flow structures, convective and radiative heat transfers is also presented and analyzed. Overall, it is shown that surface radiation significantly reduces the local and average temperatures of the heated wall and therefore reduces the convective heat transfer between the active walls.

Practical implications

The studied configuration is of practical interest in several areas where overheating must be avoided. For this purpose, a simple design tool is developed to estimate the mean and the maximum temperatures of the hot wall in different operating conditions (Ram, A et ε).

Originality/value

The originality lies in the study of the interaction between surface radiation and natural convection in tall cavities submitted to a non-uniform heat flux and a constant cold temperature on the active walls. Also, the development of an original simplified calculation procedure for the hot wall temperatures.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

K.N. Seetharamu, G.A. Quadir, Z.A. Zainal and G.M. Krishnan

Heat exchangers are devices for exchanging energy between two or more fluids. They find applications in various industries like power, process, electronics, refining…

Abstract

Heat exchangers are devices for exchanging energy between two or more fluids. They find applications in various industries like power, process, electronics, refining, cryogenics, chemicals, metals and manufacturing sector. Even though heat exchanger designs have been reported quite extensively, they are generally limited to steady‐state performance, single phase fluids, a few of the many possible flow arrangements and only two fluid heat exchangers. While these designs encompass the majority of the heat exchanger applications, there are some designs, which involve several fluids such as in cryogenics or fault‐tolerant heat exchangers. The governing differential equations for a three‐fluid heat exchanger are written based on the conservation of energy. The finite element method is used to solve the governing differential equations along with the appropriate boundary conditions. The case of a Buoyonet heat exchanger (used for pasteurizing milk) is analysed and the results are compared with the analytical solution available in the literature. The Buoyonet heat exchanger, treated as a three‐fluid heat exchanger is also analysed. The effect of heat loss to the ambient from a parallel flow double pipe heat exchanger is also investigated and the results are compared with those available in the literature. The results are presented both in terms of the temperature distribution along the length of the heat exchanger and the variation of effectiveness with NTU. The methodology presented in this paper can be extended to heat exchangers with any number of streams and any combination of the flow arrangements.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 14 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

K. Svendsen and S.T. Hagen

The purpose of this paper is to describe a model that can be used in the estimation of thermal fatigue limited service life of induction coils.

Abstract

Purpose

The purpose of this paper is to describe a model that can be used in the estimation of thermal fatigue limited service life of induction coils.

Design/methodology/approach

Previous work indicates that the temperature of the cross section of an induction coil can be used to estimate thermal fatigue limited service life. This paper presents a model for estimating these temperatures based on a coupled model. Joule losses modelled in Flux2D are coupled with cooling modelled in Fluent3D. These models are controlled and combined by Python scripts that iterate the heat transfer and temperatures of heat exchange regions between the two domains.

Findings

The combined model is shown to converge nicely. The model is also applied to an optimization problem where a high power loss, copper region is surrounding a wedge‐shaped cooling channel. The point of the wedge was replaced by a radius that was optimized. The optimum was considered where the thermal fatigue service life is maximized, i.e. where the peak deviation from mean temperature in the cross section was at a minimum. The results show that the optimum corner radii are small, typically 0.25‐0.5 mm.

Originality/value

This is the first paper where the full model is presented and used to optimize specific cases.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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Article

Ridha Djebali, Abdallah Jaouabi, Taoufik Naffouti and Said Abboudi

The purpose of this paper is to carry out an in-depth analysis of heat dissipation performance by natural convection phenomenon inside light-emitting diode (LED) lamps…

Abstract

Purpose

The purpose of this paper is to carry out an in-depth analysis of heat dissipation performance by natural convection phenomenon inside light-emitting diode (LED) lamps containing hot pin-fins because of its significant industrial applications.

Design/methodology/approach

The problem is assimilated to heat transfer inside air-filled rectangular cavity with various governing parameters appraised in ranges interesting engineering application and scientific research. The lattice Boltzmann method is used to predict the dynamic and thermal behaviors. Effects of monitoring parameters such as Rayleigh number Ra (103-106), fin length (0-0.25) and its position, pin-fins number (1-8), the tilting-angle (0-180°) and cavity aspect ratio Ar (0.25-4) are carried out.

Findings

The rising behaviors of the dynamic and thermal structures and heat transfer rate (Nu), the heatlines distribution and the irreversibility rate are appraised. It was found that the flow is constantly two contra-rotating symmetric cells. The heat transfer is almost doubled by increasing Ra. A lack of cooling performance was identified between Ar = 0.5 and 0.75. The inclination 45° is the most appropriate cooling case. At constant Ra, the maximum stream-function and the global entropy generation remain almost unchanged by increasing the pin number from 1 to 8 and the entropy generation is of thermal origin for low Ra, so that the fluid friction irreversibility becomes dominant for Ra larger than 105.

Research limitations/implications

Improvements may include three-dimensional complex geometries, accounting for thermal radiation, high unit power and turbulence modelling. Such factors effects will be conducted in the future.

Practical implications

The cooling performance/heat dissipation in LED lamps is a key manufacturing factors, which determines the lifetime of the electronic components. The best design and installation give the opportunity to increase further the product shelf-life.

Originality/value

Both cooling performance, irreversibility rate and enclosure configuration (aspect ratio and inclination) are taken into account. This cooling scheme will give a superior operating mode of the hot components in an era where energy harvesting, storage and consumption is met with considerable attention in the worldwide.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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