scholarly journals Brownian Motion and Thermophoretic Effects in Mini Channels with Various Heights

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1965
Author(s):  
Zainab Al Hajaj ◽  
Mohamad Ziad Saghir
Keyword(s):  
Aspect Ratio ◽  
Heat Removal ◽  
Major Effect ◽  
Working Fluid ◽  
Flow Rates ◽  
Pressure Drops ◽  
Optimum Configuration ◽  
Mini Channels ◽  
Flow Through ◽  
The One

Flow-through mini channels have received tremendous interest from researchers over a long period. However, the study of flow between the channel and on top of the channel has received little to no attention. In the present paper, different parameters have been used to investigate this heat enhancement. The height of 10 mini channels has been varied, allowing the corresponding aspect ratio to vary from 3 to 6, 9, and 12. When the aspect ratio is 12, flow circulates through the mini channel only, and when the aspect ratio is less than 12, flow is distributed between the one circulating inside the channel and moving on top of the channel. Different flow rates are studied corresponding to a Reynolds number varying from 250 to 1250 if water is the working fluid. Brownian and thermophoresis effects are taken into consideration to investigate the nanoparticle sedimentation. Results revealed that the optimum configuration, if one needs to take into consideration the friction factor, is 12. If one ignores the pressure drops, then the optimum configuration is when the aspect ratio is equal to 6. This means that the flow interaction between the one circulating in the channel and above the channel plays a major effect in heat removal.

Novel Lightweight Metal Foam Heat Exchangers

2001 ◽  
Author(s):  
David P. Haack ◽  
Kenneth R. Butcher ◽  
T. Kim ◽  
T. J. Lu
Keyword(s):  
Heat Exchange ◽  
Pore Size ◽  
Heat Exchangers ◽  
Metal Foam ◽  
Heat Removal ◽  
Random Orientation ◽  
Flow Rates ◽  
Small Pore ◽  
Complex Heat Exchange ◽  
Flow Through

Abstract An overview of open cell metal foam materials with application to advanced heat exchange devices is presented. The metal foam materials considered consist of interconnected cells in a random orientation. Metal foam materials, manufacture and fabrication into complex heat exchange components are described. Experiments with flat foam panels brazed to copper sheets shows increasing heat removal effectiveness with decreasing product pore size at equivalent coolant flow rates. However, the high-pressure drop associated with flow through small pore-size material makes the use of larger pore size material more attractive.

Numerical Comparison of Static and Rotordynamic Characteristics for a Grooved-Stator/Smooth-Rotor and a Smooth-Stator/Grooved-Rotor Liquid Annular Seals

2019 ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Working Fluid ◽  
Leakage Flow ◽  
Frequency Range ◽  
Flow Rates ◽  
Pressure Drops ◽  
Force Coefficients ◽  
Operation Conditions ◽  
Annular Seal ◽  
Positive Direct ◽  
Annular Seals

Abstract Liquid annular seals with parallelly-grooved stator or rotor are used as replacements for smooth plain seals in centrifugal pumps to reduce leakage and break up contaminants within the working fluid. Parallelly-grooved liquid annular seals have advantages of less leakage and smaller possibility of abrasion when the seal rotor-stator rubs in comparison to smooth plain seals. This paper deals with the static and rotordynamic characteristics of parallelly-grooved liquid annular seals, which are limited in the literature. Numerical results of leakage flow rates, drag powers and rotordynamic force coefficients were presented and compared for a grooved-stator/smooth-rotor (GS-SR) liquid annular seal and a smooth-stator/grooved-rotor (SS-GR) liquid annular seal, utilizing a modified transient CFD-based perturbation approach based on the multiple-frequency elliptical-orbit rotor whirling model. Both liquid annular seals have identical seal axial length, rotor diameter, sealing clearance, groove number and geometry. The present transient CFD-based perturbation method was adequately validated based on the published experiment data of leakage flow rates and frequency-independent rotordynamic force coefficients for the GS-SR and SS-GR liquid annular seals at various pressure drops with differential inlet preswirl ratios. Simulations were performed at three pressure drops (4.14 bar, 6.21 bar, 8.27 bar), three rotational speeds (2 krpm, 4 krpm, 6 krpm) and three inlet preswirl ratios (0, 0.5, 1.0), applying a wide rotor whirling frequency range up to 200 Hz, to analyze and compare the influences of operation conditions on the static and rotordynamic characteristics for both the GS-SR and SS-GR liquid annular seals. Results show that the present two liquid annular seals possess similar sealing capability, and the SS-GR seal produces a slightly larger (∼ 2–10%) drag power loss than the GS-SR seal. For small rotor whirling motion around a centered position, both seals have the identical direct force coefficients and the equal-magnitude opposite-sign cross-coupling force coefficients in the orthogonal directions x and y. For all operation conditions, both the GS-SR and SS-GR liquid annular seals possess negative direct stiffness K and positive direct damping C. The GS-SR seal produces purely positive Ceff throughout the whirling frequency range for all operation conditions, while Ceff for the SS-GR seal shows a significant decrease and transitions to negative value at the crossover frequency fco with increasing rotational speed and inlet preswirl. From a rotordynamic viewpoint, the GS-SR liquid annular seal is a better seal concept for pumps.

Effect of Protuberances in the Heat Transfer Enhancement in Mini-Channels

2021 ◽  
Author(s):  
Ariel Cruz Diaz ◽  
Gerardo Carbajal
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Heat Removal ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Mini Channels

Abstract This study presents the effects of adding an array of protrusions in a microchannel for heat transfer enhancement. The presence of mini-channels increases the overall heat transfer area and boosts the mixing development near the solid-fluid interaction; therefore, it can remove more heat than conventional mini-channels without protuberances. A numerical study proved that protuberances in a mini-channel increase the heat transfer performance by disturbing the relative fluid motion near the solid wall. The numerical simulation was performed with three different protuberances arrays: aligned, staggered, and angular. Each array consists of a thin flat plate with a hemispherical shape; the working fluid and the solid materials were water and copper. The study also includes the effect of different Reynolds numbers: 1,000, 1,500, and 2,000. Three heat inputs were applied in the numerical simulation; these were 1W, 3W, and 5W. The study was compared with a simple microchannel with non-protuberances to analyze the microchannel performance regarding heat removal and pressure drop. For heat transfer performance, the best array was the staggering array with a maximum heat removal increase of 5.26 percent. In terms of pressure drop performance, the best array was the aligned array, with a maximum increase of 34.73 percent.

Forced Convection Boiling in Microchannels for Improved Heat Transfer

2006 ◽  
Author(s):  
Thomas B. Baummer ◽  
Ebrahim Al-Hajri ◽  
Michael M. Ohadi ◽  
Serguei V. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Surface Areas ◽  
Feed Pressure ◽  
Wide Range

This paper presents experimental results from research investigating the heat transfer capabilities of microchannel surfaces using a novel force-fed boiling and evaporation technique. The evaporative surfaces being investigated consist of a series of parallel, high-aspect ratio, open topped microchannels. The different sample surfaces vary in channel density, channel aspect ratio, and channel width and have heat transfer surface areas up to ten times their nominal surface areas. Liquid enters the channels of the evaporative surface from above through a developed system of feed channels. This method organizes a liquid-vapor circulation at the boiling surface that results in dissipation of very high heat fluxes in the boiling/thin film evaporation mode. By using the force-fed boiling technique, nominal area heat transfer rates of 100,000 W/m2-K have been achieved with HFE-7100 as the working fluid [1]. In force-fed boiling, the many very short microchannels are working in parallel; therefore the feed pressure and pumping power are very low. This technique may prove valuable to a wide range of heat transfer applications, particularly for heat removal at high heat flux surfaces.

scholarly journals PENGARUH DEBIT TERHADAP UNJUK KERJA ALAT PENUKAR KALOR DAN PENURUNAN SUHU RUANGAN

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Mirmanto Mirmanto ◽  
I Made Adi Sayoga ◽  
Zulkarnain Zulkarnain
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Room Temperature ◽  
Rapid Development ◽  
Volumetric Flow Rate ◽  
Working Fluid ◽  
Flow Rates ◽  
Pressure Drops ◽  
Growth Industry ◽  
Pipe Heat

ABSTRACTDue to population growth, industry advance and rapid development, fresh and comfortable air may be difficult to get. Conditioning the air to get comfort environment may be a basic demand for people, but the prices of the device and its operation for this purpose are expensive. This research tries to solve this problem but it is just only to know the capability of the heat exchanger  to transfer/ absorb heat and is not to cool the room to be below the ambient temperature. The working fluid used was clean water and the heat exchangers employed were parallel and serpentine which were made of copper pipes with a diameter of 1/4 inch and 1/2 inch (for the header). The volumetric flow rates used were 300 ml/minutes, 400 ml/minutes and 500 ml/minutes. While the heat that should be absorbed by the water from the room is 50 W, 100 W and 150 W. The results show that the effect of volumetric flow rate on heat exchanger performance and room temperature is insignificant. From the pressure drop results, the parallel pipe heat exchanger has lower pressure drops while the serpentine has higher pressure drops. 

scholarly journals Pipe Network Design and Analysis: An Example with WaterCAD

2021 ◽  
Author(s):  
Shiblu Sarker
Keyword(s):  
Water Systems ◽  
Water Utilities ◽  
Pipe Network ◽  
Flow Rates ◽  
Pressure Drops ◽  
Specialized Software ◽  
Hydraulic Design ◽  
Flow Through ◽  
The Common ◽  
The Individual

Pipe network analysis is the analysis of the fluid flow through a network that containing several interconnected branches of pipes and their components. The common analysis of pipe network often demonstrates to determine the flow rates and pressure drops in the individual components of the pipe network. Water utilities typically use specialized software to solve these issues automatically. Municipal water systems frequently route water through a water supply network to reach a large number of users. In this paper we aim to demonstrate the use of WaterCAD software to solve hydraulic design parameter of an example pipe network problem.

Oxygen Transport in Salmon Spawning Gravels

1980 ◽  
Vol 37 (2) ◽  
pp. 155-162 ◽  
Author(s):  
R. A. Johnson
Keyword(s):  
Oxygen Transport ◽  
Flow Resistance ◽  
Head Loss ◽  
Flow Through Porous Media ◽  
Air Entrapment ◽  
Flow Rates ◽  
Pressure Drops ◽  
Salmon Eggs ◽  
Flow Through ◽  
Media Data

The importance of understanding transport characteristics of flow through gravel media is discussed from the viewpoint of salmonid enhancement programs. A summary of the important features of the incubation process with respect to mass transport is provided along with applicable theories describing flow through porous media. Data obtained from experiments described herein are used to assess the accuracy of existing correlations for predicting pressure drops across gravel substrates. It is found that available hydraulic relations can be used to predict flow velocity magnitudes in gravel media with an accuracy of ± 50% over a twofold range of flow rates, providing one measurement of head loss is available at one flow rate. An adaptation of the Carman–Kozeny equation is found to be suitable for calculating the influence of fines on permeability. The importance of air entrapment on flow resistance is confirmed experimentally and modeled using available correlations. Lastly, the applications of these results for calculating oxygen transport to incubating salmon eggs and minimum water flows in hatcheries are discussed.Key words: Salmon enhancement, oxygen transport, permeability, gravel, incubation, hatcheries

scholarly journals Simulation of the Flow Through Porous Layers Composed of Converging-Diverging Capillary Fissures or Tubes

2018 ◽  
Vol 23 (1) ◽  
pp. 161-185 ◽  
Author(s):  
A. Walicka
Keyword(s):  
Porous Medium ◽  
Power Law ◽  
Analytical Method ◽  
Algebraic Equations ◽  
Governing Equations ◽  
Flow Rates ◽  
Pressure Drops ◽  
Porous Layers ◽  
Linear Algebraic Equations ◽  
Flow Through

AbstractIn this paper, a porous medium is modelled by a network of converging-diverging capillaries which may be considered as fissures or tubes. This model makes it necessary to consider flows through capillary fissures or tubes. Therefore an analytical method for deriving the relationships between pressure drops, volumetric flow rates and velocities for the following fluids: Newtonian, polar, power-law, pseudoplastic (DeHaven and Sisko types) and Shulmanian, was developed. Next, considerations on the models of pore network for Newtonian and non-Newtonian fluids were presented. The models, similar to the schemes of central finite differences may provide a good basis for transforming the governing equations of a flow through the porous medium into a set of linear or quasi-linear algebraic equations. It was shown that the some coefficients in these algebraic equations depend on the kind of the capillary convergence.

scholarly journals An experimental investigations of the single phase fluid flow through mini pipes with circular cross section

2020 ◽  
Vol XXIII (2) ◽  
pp. 25-31
Author(s):  
Avram Elena Rita
Keyword(s):  
Fluid Flow ◽  
Cross Sections ◽  
Circular Cross Section ◽  
Experimental Results ◽  
Working Fluid ◽  
Total Hardness ◽  
Experimental Investigations ◽  
Turbulent Friction ◽  
Pressure Drops ◽  
Flow Through

The experimental investigation that has been conducted on the fluid flow in mini pipes with circular cross-sections are presented in this paper. The working fluid is water and its main physical-chemical analysis (pH, total hardness, electrical conductivity) were carried out. The liquid flow through mini pipes of 1, 2 and 3 mm diameter with simulated pressure drops from 1.01 to 61 bar is investigated and the experimental results are presented. The laminar and turbulent friction factor f at different pressure drop values, the transition from the laminar to turbulent flow, the effect of relative roughness, and the boundary-layer thickness, δ, are computed and studied. The experimental results are presented, discussed and analysed, according to the theoretical principles.

Boiling Heat Transfer in Microtubes at High Flow Rates

2010 ◽  
Author(s):  
Mehmed Rafet O¨zdemir ◽  
Ali Kos¸ar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Removal ◽  
High Flow ◽  
High Mass ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Mass Fluxes ◽  
Boiling Heat Transfer Coefficient

Boiling heat transfer is an important heat removal mechanism for cooling applications in micro scale and finds many applications. Many studies were conducted to shed light on boiling heat transfer in microchannels. They were concentrated on saturation boiling at low mass fluxes (G<1000 kg/m2s). In the current study, the emphasis is on high mass fluxes unlike in the literature. Thus, the current study addresses to the lack of information about boiling heat transfer at high flow rates and aims at presenting necessary experimental data. For this, an experimental study was conducted at high flow rates in microtubes. The microtube sizes were used as 250 micrometers. Deionized water was used as working fluid, and the test section was heated by Joule heating. Mass flux was changed from 1000 kg/m2s to 7500 kg/m2s, and heat transfer coefficients and qualities were deduced from local temperature measurements. The effects of mass velocity and quality on boiling heat transfer coefficient were investigated.

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