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1 – 10 of over 1000
Article
Publication date: 27 August 2019

Seyed Ali Atyabi, Ebrahim Afshari and Mohammad Yaghoub Abdollahzadeh Jamalabadi

In this paper, a single module of cross-flow membrane humidifier is evaluated as a three-dimensional multiphase model. The purpose of this paper is to analyze the effect of volume…

Abstract

Purpose

In this paper, a single module of cross-flow membrane humidifier is evaluated as a three-dimensional multiphase model. The purpose of this paper is to analyze the effect of volume flow rate, dry temperature, dew point wet temperature and porosity of gas diffusion layer on the humidifier performance.

Design/methodology/approach

In this study, one set of coupled equations are continuity, momentum, species and energy conservation is considered. The numerical code is benchmarked by the comparison of numerical results with experimental data of Hwang et al.

Findings

The results reveal that the transfer rate of water vapor and dew point approach temperature (DPAT) increase by increasing the volume flow rate. Also, it is found that the water recovery ratio (WRR) and relative humidity (RH) decrease with increasing volume flow rate. In addition, all mixed results decrease with increasing dry side temperature especially at high volume flow rates and this trend in high volume flow rates is more sensible. Although the transfer rate of water vapor and DPAT increases with increasing the wet inlet temperature, WRR and RH reduce. Increasing dew point temperature effect is more sensible at the wet side is compared with the dry side. The humidification performance will be enhanced with increasing diffusion layer porosity by increasing the wet inlet dew point temperature, but has no meaningful effect on other operating parameters. The pressure drop along humidifier gas channels increases with rising flow rate, consequently, the required power of membrane humidifier will enhance.

Originality/value

According to previous studies, the three-dimensional numerical multiphase model of cross-flow membrane humidifier has not been developed.

Details

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

Keywords

Article
Publication date: 12 December 2023

Austin R. Colon, David Owen Kazmer, Amy M. Peterson and Jonathan E. Seppala

A main cause of defects within material extrusion (MatEx) additive manufacturing is the nonisothermal condition in the hot end, which causes inconsistent extrusion and polymer…

Abstract

Purpose

A main cause of defects within material extrusion (MatEx) additive manufacturing is the nonisothermal condition in the hot end, which causes inconsistent extrusion and polymer welding. This paper aims to validate a custom hot end design intended to heat the thermoplastic to form a melt prior to the nozzle and to reduce variability in melt temperature. A full 3D temperature verification methodology for hot ends is also presented.

Design/methodology/approach

Infrared (IR) thermography of steady-state extrusion for varying volumetric flow rates, hot end temperature setpoints and nozzle orifice diameters provides data for model validation. A finite-element model is used to predict the temperature of the extrudate. Model tuning demonstrates the effects of different model assumptions on the simulated melt temperature.

Findings

The experimental results show that the measured temperature and variance are functions of volumetric flow rate, temperature setpoint and the nozzle orifice diameter. Convection to the surrounding air is a primary heat transfer mechanism. The custom hot end brings the melt to its setpoint temperature prior to entering the nozzle.

Originality/value

This work provides a full set of steady-state IR thermography data for various parameter settings. It also provides insight into the performance of a custom hot end designed to improve the robustness of melting in MatEx. Finally, it proposes a strategy for modeling such systems that incorporates the metal components and the air around the system.

Details

Rapid Prototyping Journal, vol. 30 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 6 August 2019

Mohammad Haji Mohammadi and Joshua R. Brinkerhoff

Turbomachinery, including pumps, are mainly designed to extract/produce energy from/to the flow. A major challenge in the numerical simulation of turbomachinery is the inlet flow

Abstract

Purpose

Turbomachinery, including pumps, are mainly designed to extract/produce energy from/to the flow. A major challenge in the numerical simulation of turbomachinery is the inlet flow rate, which is routinely treated as a known boundary condition for simulation purposes but is properly a dependent output of the solution. As a consequence, the results from numerical simulations may be erroneous due to the incorrect specification of the discharge flow rate. Moreover, the transient behavior of the pumps in their initial states of startup and final states of shutoff phases has not been studied numerically. This paper aims to develop a coupled procedure for calculating the transient inlet flow rate as a part of the solution via application of the control volume method for linear momentum. Large eddy simulation of a four-blade axial hydraulic pump is carried out to calculate the forces at every time step. The sharp interface immersed boundary method is used to resolve the flow around the complex geometry of the propeller, stator and the pipe casing. The effect of the spurious pressure fluctuations, inherent in the sharp interface immersed boundary method, is damped by local time-averaging of the forces. The developed code is validated by comparing the steady-state volumetric flow rate with the experimental data provided by the pump manufacturer. The instantaneous and time-averaged flow fields are also studied to reveal the flow pattern and turbulence characteristics in the pump flow field.

Design/methodology/approach

The authors use control volume analysis for linear momentum to simulate the discharge rate as part of the solution in a large eddy simulation of an axial hydraulic pump. The linear momentum balance equation is used to update the inlet flow rate. The sharp interface immersed boundary method with dynamic Smagorinsky sub-grid stress model and a proper wall model is used.

Findings

The steady-state volumetric flow rate has been computed and validated by comparing to the flow rate specified by the manufacturer at the simulation conditions, which shows a promising result. The instantaneous and time averaged flow fields are also studied to reveal the flow pattern and turbulence characteristics in the pump flow field.

Originality/value

An approach is proposed for computing the volumetric flow rate as a coupled part of the flow solution, enabling the simulation of turbomachinery at all phases, including the startup/shutdown phase. To the best of the authors’ knowledge, this is the first large eddy simulation of a hydraulic pump to calculate the transient inlet flow rate as a part of the solution rather than specifying it as a fixed boundary condition. The method serves as a numerical framework for simulating problems incorporating complex shapes with moving/stationary parts at all regimes including the transient start-up and shut-down phases.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 2 January 2018

Kazimierz Rup, Lukasz Malinowski and Piotr Sarna

The purpose of this paper is to extend the possibilities of using the earlier developed indirect method of fluid flow rate measurement in circular pipes to the square-section…

Abstract

Purpose

The purpose of this paper is to extend the possibilities of using the earlier developed indirect method of fluid flow rate measurement in circular pipes to the square-section channels with elbows installed.

Design/methodology/approach

The idea of the method is based on selecting such a value of the Reynolds number assumed as a coefficient in fluid flow equations, which fulfills with set accuracy the condition of equality between the measured and computed pressure difference at the end points of the secant of the elbow arch. The numerical calculus takes into consideration the exact geometry of the flow space and the measured temperature of the fluid, on the basis of which its thermo–physical properties are determined. To implement the proposed method in practice, a special test stand was built. The numerical computations were carried out using the software package FLUENT.

Findings

The results of calculations were compared with corresponding results of measurements achieved on the stand, as well as those found in the literature. The comparative analysis of the obtained numerical and experimental results shows a high grade of consistence.

Practical implications

The discussed elbow flow meter, implementing the extended indirect measuring method, can be applied to determine the flow rate of gases, as well as liquids and suspensions.

Originality/value

The indirect method used to measure the volumetric flow rate of the fluid is characterized by high accuracy and repeatability. The high accuracy is possible because of a very realistic mathematical model of the complex flow in the curved duct. The indirect method eliminates the necessity of frequent calibration of the flow meter. The discussed extended indirect measuring method can be applied to determine the flow rate of gases as well as liquids and suspensions. The fluid flow rate measurement based on the method considered in this paper can be particularly useful in newly designed as well as already operated ducts.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 8 January 2018

Mo Jintao, Gu Chaohua, Pan Xiaohong, Zheng Shuiying and Ying Guangyao

For moderate pressure and high pressure gear pumps, the temperature failure problem of bearings is now of considerable concern because of their heavy loads. However, the compact…

124

Abstract

Purpose

For moderate pressure and high pressure gear pumps, the temperature failure problem of bearings is now of considerable concern because of their heavy loads. However, the compact structure and the efficiency consideration make it extremely difficult to improve the bearing cooling. A self-circulating oil bearing system is developed for gear pumps with self-lubricating bearings to solve this problem. The oil is aspirated in from the low pressure chamber of the gear pump and discharged to the same chamber by using the pressure difference in the journal bearing, thus achieving the self-circulation.

Design/methodology/approach

An experiment test rig has been built for the feasibility study. The oil flow rate under different speeds has been recorded. Furthermore, the temperatures of the bearings with or without the oil circulation have been compared. Additionally, the oil flow in the test rig has been simulated using computational fluid dynamics codes.

Findings

The experimental and numerical results agree well. The experimental results indicate that the oil flow rate increases approximately linearly with the speed and the bearing temperature can be lowered successfully. The calculation results indicate that the bearing load capacity is nearly the same. Both the experimental and numerical studies establish that the self-circulating oil bearing system works successfully.

Originality value

As far as the authors know, it is the first time to find that the self-circulation can be built using the pressure difference in the bearing oil film, and this principle can be applied in the cooling and lubrication of the gear pumps to solve the temperature failure problem.

Details

Industrial Lubrication and Tribology, vol. 70 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 21 August 2007

W.B. Wan Nik, M.A. Maleque, F.N. Ani and H.H. Masjuki

The aim of this paper is to investigate hydraulic system performance using vegetable‐based palm oil as hydraulic fluid.

1315

Abstract

Purpose

The aim of this paper is to investigate hydraulic system performance using vegetable‐based palm oil as hydraulic fluid.

Design/methodology/approach

The hydraulic system performance test at different operating conditions, such as pressure, speed and oil ageing, was performed using a Yuken vane pump test rig. The endurance system performance test was also conducted for 200 and 400 h. The effect of speed on flow slip coefficient in discrete and continuous tests was studied. In discrete testing, pressure of 35 and 200 bar and speed of 750 and 1,439 rpm were used in determining flow slip coefficient. The instantaneous data were recorded in a computer using an analog‐to‐digital data acquisition system with respect to time and the parameters stored were reservoir temperature, return line temperature, suction and delivery pressures, instantaneous flow rate, total flow, total running time and torque. The obtained results were interpolated for future prediction of the system performance.

Findings

The experimental and interpolated results showed that slip coefficient decreases with increasing pump speed. The effect of aging condition on volumetric efficiency showed that the efficiency increases with aging period due to increase in oil viscosity.

Practical implications

This vegetable‐based palm oil could be a potentially useful substitute for mineral‐based energy transport media such as hydraulic fluid.

Originality/value

The investigation of hydraulic system performance using palm oil as hydraulic fluid is scarce in the literature. Therefore, the current study is quite new for the hydraulic system performance and it is hoped that it will provide a high value to researchers for further research before it can be used as hydraulic fluid.

Details

Industrial Lubrication and Tribology, vol. 59 no. 5
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 1 May 2000

Phillip Gibson, Donald Rivin and Cyrus Kendrick

Reports on an automated apparatus and test procedure to determine the convective and diffusive gas and vapor transport properties of small pieces of woven and nonwoven fabrics…

Abstract

Reports on an automated apparatus and test procedure to determine the convective and diffusive gas and vapor transport properties of small pieces of woven and nonwoven fabrics, membranes, and foams. The apparatus allows measurement of these properties in the very small quantities typical of material development programs, where the largest sample available may only be 1‐10cm2 in area. The convection/diffusion test method is useful for determining the gas flow resistance property and water vapor diffusion properties from a single experimental run. This eliminates the need for two separate tests, which is the usual procedure. The apparatus may also be used to perform separate tests for the diffusion property or the air permeability property, which may have some advantages when materials exhibit strongly concentration‐dependent transport properties. The convection/diffusion test method is well‐suited for rapid screening and comparison of the properties of a large number of materials with widely‐varying transport properties.

Details

International Journal of Clothing Science and Technology, vol. 12 no. 2
Type: Research Article
ISSN: 0955-6222

Keywords

Article
Publication date: 21 August 2020

Andrej Simeunović and David John Hoelzle

The purpose of this study is to develop nonlinear and linearized models of DW printing dynamics that capture the complexity of DW while remaining integrable into control schemes…

Abstract

Purpose

The purpose of this study is to develop nonlinear and linearized models of DW printing dynamics that capture the complexity of DW while remaining integrable into control schemes. Control of material metering in extrusion-based additive manufacturing modalities, such as positive displacement direct-write (DW), is critical for manufacturing accuracy. However, in DW, transient flows are poorly controlled due to capacitive pressure dynamics – pressure is stored and slowly released over time from the build material and other compliant system elements, adversely impacting flow rate start-ups and stops. Thus far, modeling of these dynamics has ranged from simplistic, potentially omitting key contributors to the observed phenomena, to highly complex, making usage in control schemes difficult.

Design/methodology/approach

The authors present nonlinear and linearized models that seek to both capture the capacitive and nonlinear resistive fluid elements of DW systems and to pose them as ordinary differential equations for integration into control schemes. The authors validate the theoretical study with experimental flow rate and material measurements across a range of extrusion nozzle sizes and materials. The authors explore the contribution of the system and build material bulk modulus to these dynamics.

Findings

The authors show that all tested models accurately describe the measured dynamics, facilitating ease of integration into future control systems. Additionally, the authors show that system bulk modulus may be substantially reduced through appropriate system design. However, the remaining build material bulk modulus is sufficient to require feedback control for accurate material delivery.

Originality/value

This study presents new nonlinear and linear models for DW printing dynamics. The authors show that linear models are sufficient to describe the dynamics, with small errors between nonlinear and linear models. The authors demonstrate control is necessary for accurate material delivery in DW.

Details

Rapid Prototyping Journal, vol. 26 no. 10
Type: Research Article
ISSN: 1355-2546

Keywords

Open Access
Article
Publication date: 5 February 2024

Krištof Kovačič, Jurij Gregorc and Božidar Šarler

This study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN).

Abstract

Purpose

This study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN).

Design/methodology/approach

The physical model is posed in the mixture formulation and copes with the unsteady, incompressible, isothermal, Newtonian, low turbulent two-phase flow. The computational fluid dynamics numerical solution is based on the half-space finite volume discretisation. The geo-reconstruct volume-of-fluid scheme tracks the interphase boundary between the gas and the liquid. To ensure numerical stability in the transition regime and adequately account for turbulent behaviour, the k-ω shear stress transport turbulence model is used. The model is validated by comparison with the experimental measurements on a vertical, downward-positioned GDVN configuration. Three different combinations of air and water volumetric flow rates have been solved numerically in the range of Reynolds numbers for airflow 1,009–2,596 and water 61–133, respectively, at Weber numbers 1.2–6.2.

Findings

The half-space symmetry allows the numerical reconstruction of the dripping, jetting and indication of the whipping mode. The kinetic energy transfer from the gas to the liquid is analysed, and locations with locally increased gas kinetic energy are observed. The calculated jet shapes reasonably well match the experimentally obtained high-speed camera videos.

Practical implications

The model is used for the virtual studies of new GDVN nozzle designs and optimisation of their operation.

Originality/value

To the best of the authors’ knowledge, the developed model numerically reconstructs all three GDVN flow regimes for the first time.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 34 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 December 2000

N. Venkataraman, S. Rangarajan, M.J. Matthewson, B. Harper, A. Safari, S.C. Danforth, G. Wu, N. Langrana, S. Guceri and A. Yardimci

Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of highly loaded polymer systems. The process utilizes particle loaded…

2899

Abstract

Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of highly loaded polymer systems. The process utilizes particle loaded thermoplastic binder feedstock in the form of a filament. The filament acts as both the piston driving the extrusion and also the feedstock being deposited. Filaments can fail during FDC via buckling, when the extrusion pressure needed is higher than the critical buckling load that the filament can support. Compressive elastic modulus determines the load carrying ability of the filament and the viscosity determines the resistance to extrusion (or extrusion pressure). A methodology for characterizing the compressive mechanical properties of FDC filament feedstocks has been developed. It was found that feedstock materials with a ratio (Ea) greater than a critical value (3×105 to 5×105 s‐1) do not buckle during FDC while those with a ratio less than this range buckle.

Details

Rapid Prototyping Journal, vol. 6 no. 4
Type: Research Article
ISSN: 1355-2546

Keywords

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