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Article

Erdem Çiftçi and Adnan Sözen

The purpose of this study is to experimentally and numerically scrutinize the heat transfer enhancement in pool boiling and condensation by changing the hydrophilicity or…

Abstract

Purpose

The purpose of this study is to experimentally and numerically scrutinize the heat transfer enhancement in pool boiling and condensation by changing the hydrophilicity or hydrophobicity properties of the working fluid, i.e. by use of nanofluid solution.

Design/methodology/approach

For specifying the effects of nanoparticle concentration on heat transfer properties, two different nanofluid solutions (h-BN/DCM and SiO2/DCM) at three different volumetric concentrations were prepared and tested under different heat flux conditions. Boiling curves, alterations in pressure with heat flux and heat transfer coefficients for both boiling and condensation processes were obtained and viscosity measurements were performed for dichloromethane (DCM) and each working fluid was prepared. In addition, a series of numerical simulations, via computational fluid dynamics approach, was performed for specifying the evaporation–condensation phenomena and temperature and velocity distributions.

Findings

Nanoparticle addition inside the base fluid increased the thermal characteristics of the base fluid significantly. For the experimental results of h-BN/DCM nanofluid, the increment rate in heat transfer coefficient for saturation boiling, after-saturation boiling and condensation processes was found as 27.59%, 14.44% and 15%, respectively.

Originality/value

The novelty of this comparison study is that there is no such experimental and numerical comparison study in literature for DCM fluid, which concentrates on thermal performance enhancement and compares the effect of different kinds of nanoparticles on heat transfer characteristics for boiling–condensation processes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Reza Azadbakhti, Farzad Pourfattah, Abolfazl Ahmadi, Omid Ali Akbari and Davood Toghraie

The purpose of this study is simulation the flow boiling inside a tube in the turbulent flow regime for investigating the effect of using a porous medium in the boiling procedure.

Abstract

Purpose

The purpose of this study is simulation the flow boiling inside a tube in the turbulent flow regime for investigating the effect of using a porous medium in the boiling procedure.

Design/methodology/approach

To ensure the accuracy of the obtained numerical results, the presented results have been compared with the experimental results, and proper coincidence has been achieved. In this study, the phase change phenomenon of boiling has been modeled by using the Eulerian–Eulerian multi-phase Rensselaer Polytechnic Institute (RPI) wall boiling model.

Findings

The obtained results indicate using a porous medium in boiling process is very effective in a way that by using a porous medium inside the tub, the location of changing the liquid to the vapor and the creation of bubbles, changes. By increasing the thermal conductivity of porous medium, the onset of phase changing postpones, which causes the enhancement of heat transfer from the wall to the fluid. Generally, it can be said that using a porous medium in boiling flows, especially in flow with high Reynolds numbers, has a positive effect on heat transfer enhancement. Also, the obtained results revealed that by increasing Reynolds number, the created vapor phase along the tube decreases and by increasing Reynolds number, the Nusselt number enhances.

Originality/value

In present research, by using the computational fluid dynamics, the effect of using a porous medium in the forced boiling of water flow inside a tube has been investigated. The fluid boiling inside the tube has been simulated by using the multi-phase Eulerian RPI wall boiling model, and the effect of thermal conductivity of a porous medium and the Reynolds number on the flow properties, heat transfer and boiling procedure have been investigated.

Details

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

Keywords

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Article

Fabian Krause, Sven Schüttenberg and Udo Fritsching

The purpose of this paper is to describe the development and application of a numerical model for analysis of flow boiling phenomena and heat transfer.

Abstract

Purpose

The purpose of this paper is to describe the development and application of a numerical model for analysis of flow boiling phenomena and heat transfer.

Design/methodology/approach

For flow boiling processes, the fluid and vapour flow regimes in connection with the conjugate heat and mass transfer problem for specimen quenching through the entire boiling curve is modelled. Vaporisation and recondensation, the vapour fraction distribution and vapour movement with respect to the liquid are considered in the calculation of the two‐phase flow and heat transfer process. The derived flow boiling model is based on a mixture model and bubble crowding model approach for two‐phase flow. In addition to the conventional mixture model formulation, here special model implementations have been incorporated that describe: the vapour formation at the superheated solid‐liquid interface, the recondensation process of vapour at the subcooled vapour‐liquid interface, the mass transfer rate in the different boiling phases and the microconvection effect in the nucleate boiling phase resulting from bubble growth and detachment.

Findings

The model prediction results are compared with experimental data for quenching of a circular cylinder, showing good agreement in boiling state and heat transfer coefficient distribution. Simulation and experiments lead to a better understanding of the interaction of incident flow in the boiling state and the resulting heat transfer.

Research limitations/implications

Fluid temperatures in the range of 300‐353 K and specimen wall temperatures up to 1,000 K are considered.

Practical implications

Flow boiling is an efficient heat transfer process occurring in several technical applications. Application background of the model development is in quenching of complex metallic specimen geometries in liquids subject to fast changing heat fluxes.

Originality/value

A general model for the complex two‐phase boiling heat transfer at high wall temperatures and fast flow conditions that can be used in engineering applications does not yet exist. The results provide detailed information describing the non‐uniform phase change during the complete quenching process from film boiling to pure convection.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 20 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Yi Heng, Maka Karalashvili, Adel Mhamdi and Wolfgang Marquardt

The purpose of this paper is to present an efficient algorithm based on a multi‐level adaptive mesh refinement strategy for the solution of ill‐posed inverse heat…

Abstract

Purpose

The purpose of this paper is to present an efficient algorithm based on a multi‐level adaptive mesh refinement strategy for the solution of ill‐posed inverse heat conduction problems arising in pool boiling using few temperature observations.

Design/methodology/approach

The stable solution of the inverse problem is obtained by applying the conjugate gradient method for the normal equation method together with a discrepancy stopping rule. The resulting three‐dimensional direct, adjoin and sensitivity problems are solved numerically by a space‐time finite element method. A multi‐level computational approach, which uses an a posteriori error estimator to adaptively refine the meshes on different levels, is proposed to speed up the entire inverse solution procedure.

Findings

This systematic approach can efficiently solve the large‐scale inverse problem considered without losing necessary detail in the estimated quantities. It is shown that the choice of different termination parameters in the discrepancy stopping conditions for each level is crucial for obtaining a good overall estimation quality. The proposed algorithm has also been applied to real experimental data in pool boiling. It shows high computational efficiency and good estimation quality.

Originality/value

The high efficiency of the approach presented in the paper allows the fast processing of experimental data at many operating conditions along the entire boiling curve, which has been considered previously as computationally intractable. The present study is the authors' first step towards a systematic approach to consider an adaptive mesh refinement for the solution of large‐scale inverse boiling problems.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 21 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Tao Sun, Weizhong Li and Bo Dong

The purpose of this paper is to test the feasibility of lattice Boltzmann method (LBM) for numerical simulation of nucleate boiling and transition boiling. In addition…

Abstract

Purpose

The purpose of this paper is to test the feasibility of lattice Boltzmann method (LBM) for numerical simulation of nucleate boiling and transition boiling. In addition, the processes of nucleate and transition boiling on vertical wall are simulated. The heat transfer mechanism is discussed based on the evolution of temperature field.

Design/methodology/approach

In this paper, nucleate boiling and transition boiling are numerically investigated by LBM. A lattice Boltzmann (LB) multiphase model combining with a LB thermal model is used to predict the phase-change process.

Findings

Numerical results are in good agreement with existing experimental results. Numerical results confirm the feasibility of the hybrid LBM for direct simulations of nucleate and transition boiling. The data exhibit correct parametric dependencies of bubble departure diameter compared with experimental correlation and relevant references.

Research limitations/implications

All the simulations are performed in two-dimensions in this paper. In the future work, the boiling process will be simulated in three-dimensional.

Practical implications

This study demonstrated a potential model that can be applied to the investigation of phase change heat transfer, which is one of the effective techniques for enhance the heat transfer in engineering. The numerical results can be considered as a basic work or a reference for generalizing LB method in the practical application about nucleate boiling and transition boiling.

Originality/value

The hybrid LBM is first used for simulation of nucleate and transition boiling on vertical surface. Heat transfer mechanism during boiling is discussed based on the numerical results.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Farzad Pourfattah, Saeid Yousefi, Omid Ali Akbari, Mahsa Adhampour, Davood Toghraie and Maboud Hekmatifar

The purpose of this paper is to numerically simulate the nanofluid boiling inside a tube in turbulent flow regime and to investigate the effect of adding volume faction of…

Abstract

Purpose

The purpose of this paper is to numerically simulate the nanofluid boiling inside a tube in turbulent flow regime and to investigate the effect of adding volume faction of CuO nanoparticles on the boiling process.

Design/methodology/approach

To make sure the accuracy of the obtained numerical results, the results of this paper have been compared with the experimental results and an acceptable coincidence has been achieved. In the current paper, by Euler–Euler method, the phase change of boiling phenomenon has been modeled. The presented results are the local Nusselt number distribution, temperature distribution of wall, the distribution of volume fraction of vapor phase and fluid temperature at the center of the tube.

Findings

The obtained results indicate that using nanofluid is very effective in the postponement of the boiling process. Hence, by change the amount of volume fraction of nanoparticles in base fluid, the location of phase change and bubble creation are changed. Also, at the Reynolds numbers of 50,000, 100,000 and 150,000 with the volume fraction of 2 per cent, the beginning locations of phase change process are, respectively, 2D, 10D and 13D, and for the volume fraction of 4 per cent, the beginning locations of phase change are 4D, 18D and 19D, respectively. These results indicate that, as the volume fraction of nanoparticles increases, the location of the start of the phase change process is postponed that this issue causes the increment of heat transfer from wall to fluid and the reduction of wall temperature. In general, it can be stated that, in boiling flows, using nanofluid because of the delay in boiling phenomenon has a good effect on heat transfer enhancement of heated walls. Also, the obtained results show that, by increasing Reynolds number, the created vapor phase reduces that leads to increase of the Nusselt number.

Originality/value

The paper investigates the effect of using nanofluid in phase change process of cooling fluid.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Abstract

Purpose

A boiling surface with different initial roughness and under various nanoparticles volume fractions was studied in present work.

Design/methodology/approach

Develop a correlation and sensitivity analysis.

Findings

The results showed that for small (7.3 nm) and much larger (about 2,000 nm) surface roughness, compared to nanoparticle size of around 25 nm, the heat transfer rate of nanofluid diminishes relative to that of base fluid. The results also demonstrated that the boiling heat transfer rate is reduced by increasing the concentration of nanoparticles. For larger boiling surface roughness (480 nm) and nanoparticles volume fractions of less than 0.1 Vol.%, the value of heat transfer increases with the increase of nanoparticles concentration; and for those of more than 0.1 Vol.%, heat transfer rate decreases by adding more nanoparticles, significantly.

Originality/value

Finally, an equation was presented for estimating the wall superheat and the Csf coefficient in terms of mentioned parameters.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Beata Maciejewska and Magdalena Piasecka

The purpose of this paper is to determine the time-dependent heat transfer coefficient during FC-72 flow boiling in a 1.7-mm-deep vertical and asymmetrically heated minichannel.

Abstract

Purpose

The purpose of this paper is to determine the time-dependent heat transfer coefficient during FC-72 flow boiling in a 1.7-mm-deep vertical and asymmetrically heated minichannel.

Design/methodology/approach

The temperature of the minichannel heated wall was recorded continuously with the use of thermocouples. The heat transfer coefficients for the subcooled and saturated boiling regions at the heated wall–fluid contact surface were calculated from the Robin boundary condition. Both the wall and fluid temperatures were obtained from the solution of the inverse nonstationary problems in two adjacent domains: the heated wall and flowing fluid. The FEM with Trefftz-type basis functions was applied to solve the inverse problem.

Findings

The obtained time-dependent heat transfer coefficient in subcooled boiling achieved rather low values, whereas in saturated boiling, the coefficient was the highest at the channel inlet. The boiling curves were plotted to illustrate the results.

Practical implications

The results of experiments are the best source of information for the design of minichannel cooling systems used for thermoregulation of components and heat exchangers. High-tech minichannel heat exchangers are applied in various industrial applications as microelectronics devices, gas turbines, internal combustion engines, nuclear reactors, X-ray sources and organic rankine cycle (ORC) modules.

Originality/value

In the study, the Trefftz functions for the nonstationary Fourier–Kirchhoff equation with the factor describing void fraction were determined and then used to construct the time-dependent basis functions in FEM.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

C. Lea

The success of vapour phase soldering for electronic assemblies has led to the availability of several heat transfer fluids for the purpose. This paper aims to demonstrate…

Abstract

The success of vapour phase soldering for electronic assemblies has led to the availability of several heat transfer fluids for the purpose. This paper aims to demonstrate the significance of the differing properties of fluids, illustrated by measurements on the three most commonly used in the UK. These three, as well as any future fluids, can be judged in terms of (i) vapour temperature and its influence on soldering yields and materials properties; (ii) stability of soldering temperature with time; (iii) heat transfer efficiency; (iv) power requirements and thermal control; (v) rosin solubility and flux wash‐off; (vi) toxicity, especially under thermal stress; (vii) corrosivity and its dependence on process control; and (viii) consumption of fluid.

Details

Soldering & Surface Mount Technology, vol. 1 no. 1
Type: Research Article
ISSN: 0954-0911

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Article

Paul Stark and Udo Fritsching

The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a…

Abstract

Purpose

The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a single submerged water jet. At wall temperatures above the liquid boiling point, the vapor formation process and the interaction of the vapor phase with the developing jet-flow field are included.

Design/methodology/approach

The time-dependent flow and temperature distribution during all occurring boiling phases as well as the local and temporal distribution of the heat transfer coefficient on a flat plate can be simulated.

Findings

The influence of the liquid jet flow rate (10,800=Re_d=32,400) and the nozzle distance to the plate (4=H/d=20) on the transient cooling process are analyzed. This includes the time-dependant positions of the transition regions between the boiling phases on the plate as well as the temperatures at these transition regions. Additionally, the local heat transfer rates are a direct result of the unsteady cooling simulation.

Originality/value

A single model approach is developed and utilized to simulate the unsteady cooling process of a flat plate with an impinging water jet including all occurring boiling phases.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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