Sensing and Modeling Techniques for Micro and Nano Scale Transport

2006 ◽  
Author(s):  
Sung Jin Kim ◽  
Dong-Kwon Kim
Keyword(s):  
Heat Transfer ◽  
Averaging Method ◽  
Thermal Design ◽  
Flow Rates ◽  
Design And Optimization ◽  
Flow And Heat Transfer ◽  
Temperature Distributions ◽  
Modeling Techniques ◽  
Modeling Transport ◽  
Mass Flow Rates

In the present study, three types of micro-sensors developed for experimental investigation of fluid flow and heat transfer in microstructures are introduced. The micro-sensors can be used to measure temperature distributions at the surface of a microstructure and mass flow rates passing through it. It is followed by a description of a method for modeling transport phenomena in microstructures is introduced. The modeling technique, based on the averaging method, is illustrated in thermal design and optimization of a microstructure.

scholarly journals Effects of Temperature on the Flow and Heat Transfer in Gel Fuels: A Numerical Study

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 821
Author(s):  
Qin-Liu Cao ◽  
Wei-Tao Wu ◽  
Wen-He Liao ◽  
Feng Feng ◽  
Mehrdad Massoudi
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Transport System ◽  
Apparent Viscosity ◽  
Thermal Design ◽  
Straight Pipe ◽  
Heating Wall ◽  
Supply Pressure ◽  
Flow And Heat Transfer ◽  
The Mean

In general, rheological properties of gelled fuels change dramatically when temperature changes. In this work, we investigate flow and heat transfer of water-gel in a straight pipe and a tapered injector for non-isothermal conditions, which mimic the situations when gelled fuels are used in propulsion systems. The gel-fluid is modeled as a non-Newtonian fluid, where the viscosity depends on the shear rate and the temperature; a correlation fitted with experimental data is used. For the fully developed flow in a straight pipe with heating, the mean apparent viscosity at the cross section when the temperature is high is only 44% of the case with low temperature; this indicates that it is feasible to control the viscosity of gel fuel by proper thermal design of pipes. For the flow in the typical tapered injector, larger temperature gradients along the radial direction results in a more obvious plug flow; that is, when the fuel is heated the viscosity near the wall is significantly reduced, but the effect is not obvious in the area far away from the wall. Therefore, for the case of the tapered injector, as the temperature of the heating wall increases, the mean apparent viscosity at the outlet decreases first and increases then due to the high viscosity plug formed near the channel center, which encourages further proper design of the injector in future. Furthermore, the layer of low viscosity near the walls plays a role similar to lubrication, thus the supply pressure of the transport system is significantly reduced; the pressure drop for high temperature is only 62% of that of low temperature. It should be noticed that for a propellent system the heating source is almost free; therefore, by introducing a proper thermal design of the transport system, the viscosity of the gelled fuel can be greatly reduced, thus reducing the power input to the supply pressure at a lower cost.

Numerical Study on Flow and Heat Transfer of a Cooled First Stage Vane of a Gas Turbine

2016 ◽  
Author(s):  
Lv Ye ◽  
Zhao Liu ◽  
Xiangyu Wang ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Numerical Study ◽  
Coolant Flow ◽  
The Other ◽  
Edge Region ◽  
Flow Rates ◽  
Flow And Heat Transfer ◽  
Film Cooling Holes

This paper presents a numerical simulation of composite cooling on a first stage vane of a gas turbine, in which gas by fixed composition mixture is adopted. To investigate the flow and heat transfer characteristics, two internal chambers which contain multiple arrays of impingement holes are arranged in the vane, several arrays of pin-fins are arranged in the trailing edge region, and a few arrays of film cooling holes are arranged on the vane surfaces to form the cooling film. The coolant enters through the shroud inlet, and then divided into two parts. One part is transferred into the chamber in the leading edge region, and then after impinging on the target surfaces, it proceeds further to go through the film cooling holes distributed on the vane surface, while the other part enters into the second chamber immediately and then exits to the mainstream in two ways to effectively cool the other sections of the vane. In this study, five different coolant flow rates and six different inlet pressure ratios were investigated. All the cases were performed with the same domain grids and same boundary conditions. It can be concluded that for the internal surfaces, the heat transfer coefficient changes gradually with the coolant flow rate and the inlet total pressure ratio, while for the external surfaces, the average cooling effectiveness increases with the increase of coolant mass flow rates while decreases with the increase of the inlet stagnation pressure ratios within the study range.

Numerical Modeling of Velocity and Temperature Distributions in a Bipolar Plate of PEM Electrolysis Cell With Greatly Improved Flow Uniformity

2009 ◽  
Author(s):  
Jephanya Kasukurthi ◽  
K. M. Veepuri ◽  
Jianhu Nie ◽  
Yitung Chen
Keyword(s):  
Heat Transfer ◽  
Proton Exchange Membrane ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Bipolar Plate ◽  
Proton Exchange ◽  
Electrolysis Cell ◽  
Flow And Heat Transfer ◽  
Temperature Distributions ◽  
Pem Electrolysis

In this present work, finite volume method was used to simulate the three-dimensional water flow and heat transfer in a flow field plate of the proton exchange membrane (PEM) electrolysis cell. The standard k-ε model together with standard wall function method was used to model three-dimensional fluid flow and heat transfer. First, numerical simulations were performed for a basic bipolar plate and it was found that the flow distribution inside the channels in not uniform. The design of the basic bipolar plate has been changed to a new model, which is featured with multiple inlets and multiple outlets. Numerical results show that the flow and temperature distributions for the new design become much homogeneous.

Compact Modeling of Fluid Flow and Heat Transfer in Straight Fin Heat Sinks

2004 ◽  
Vol 126 (2) ◽  
pp. 247-255 ◽  
Author(s):  
Duckjong Kim ◽  
Sung Jin Kim
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Sink ◽  
Volume Averaging ◽  
Thermal Design ◽  
Heat Sinks ◽  
Compact Modeling ◽  
Flow And Heat Transfer

In the present work, a compact modeling method based on a volume-averaging technique is presented. Its application to an analysis of fluid flow and heat transfer in straight fin heat sinks is then analyzed. In this study, the straight fin heat sink is modeled as a porous medium through which fluid flows. The volume-averaged momentum and energy equations for developing flow in these heat sinks are obtained using the local volume-averaging method. The permeability and the interstitial heat transfer coefficient required to solve these equations are determined analytically from forced convective flow between infinite parallel plates. To validate the compact model proposed in this paper, three aluminum straight fin heat sinks having a base size of 101.43mm×101.43mm are tested with an inlet velocity ranging from 0.5 m/s to 2 m/s. In the experimental investigation, the heat sink is heated uniformly at the bottom. The resulting pressure drop across the heat sink and the temperature distribution at its bottom are then measured and are compared with those obtained through the porous medium approach. Upon comparison, the porous medium approach is shown to accurately predict the pressure drop and heat transfer characteristics of straight fin heat sinks. In addition, evidence indicates that the entrance effect should be considered in the thermal design of heat sinks when Re Dh/L>∼O10.

Computational Study on Estimating the Surface Heat Transfer Coefficient of Absorber Tube in Solar Parabolic Trough Collector

2013 ◽  
Vol 446-447 ◽  
pp. 1546-1551
Author(s):  
Harshit Saxena ◽  
Arpit Santoki ◽  
Nimish Awalgaonkar ◽  
Arpan Jivani ◽  
Ganni Gowtham ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Computational Study ◽  
Surface Heat ◽  
Parabolic Trough ◽  
Flow Rates ◽  
Surface Heat Transfer Coefficient ◽  
Mass Flow Rates ◽  
The Given

Solar Parabolic Trough collectors are commonly used to harness the solar power for power generating applications involving high temperatures. In the given paper study we have made use of the SolTrace software which uses the Monte Carlo algorithm for finding out the radiation received on the absorber tube of the collector. The computational study was performed taking into account the solar radiation received at Vellore city in India (12.92oN, 79.13oE) as on 16th February 2013. Further a 3D model of the absorber tube used in the parabolic trough collector was created and meshed with the help of the Ansys Gambit software. The absorber tube which we considered for our study is made up of Stainless Steel AISI 302 material. The meshed model so created was then exported to the Ansys Fluent 6.3 software and simulations were performed for different mass flow rates of the fluid. The fluid which we used in the computational analysis study is Therminol 55. The temperature differences for different mass flow rates of the liquid passing through the absorber tube were found out and based on the temperature rise contours plots so obtained, we have plotted the surface heat transfer coefficient for the absorber tube. We also found out the static temperature contour plot for the fluid flowing through the given absorber tube taking into account the heat flux acting on the absorber tube due to the hourly and daily average solar radiation.

Application of the Transient Heat Transfer Measurement Technique Using TLC in a Network Configuration With Intersecting Circular Passages

2018 ◽  
Author(s):  
Anika Steurer ◽  
Rico Poser ◽  
Jens von Wolfersdorf ◽  
Stefan Retzko
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Mass Flow ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Flow Network ◽  
Mass Flow Rates ◽  
Time Information

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20mm that intersect coplanar at an angle θ = 40°, the innermost in three, the outermost in one intersection level. Two additional non-intersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional RANS simulations using the SST turbulence model. The presented analysis uncouples local heat transfer coefficients from actually measured local temperatures but uses the time information of the thermocouples instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether heat transfer is locally enhanced due to higher mass flow rates or the intersection effects.

Simulation of Flow and Heat Transfer in a Moving Bed Reactor With Cross Flow

2008 ◽  
Author(s):  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Relative Velocity ◽  
Solid Phase ◽  
Cross Flow ◽  
Vertical Direction ◽  
Momentum Equation ◽  
Solid Matrix ◽  
Flow And Heat Transfer ◽  
Temperature Distributions ◽  
Solid Phases

Heat transfer in a porous reactor under cross flow is investigated. The reactor is modeled as a porous bed in which the solid phase is moving horizontally and the flow is forced into the bed in a vertical direction. Equations are time-and-volume averaged and the solid phase is considered to have a constant imposed velocity. Additional drag terms appearing the momentum equation are a function of the relative velocity between the fluid and solid phases. Turbulence equations are also affected by the speed of the solid matrix. Results show temperature distributions for several ratios of the solid to fluid speed.

Numerical Study of Flow and Heat Transfer on a Blade Tip With Different Leakage Reduction Strategies

2003 ◽  
Author(s):  
Sumanta Acharya ◽  
Huitao Yang ◽  
Chander Prakash ◽  
Ron Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Flow Rates ◽  
Leakage Reduction ◽  
Flow And Heat Transfer ◽  
Reduction Strategies ◽  
Blade Tip

Numerical calculations are performed to explore different strategies for reducing tip leakage flow and heat transfer on the GE-E3 High-Pressure-Turbine (HPT) rotor blade. The calculations are performed for a single blade with periodic conditions imposed along the two boundaries in the circumferential-pitch direction. Several leakage reduction strategies are considered, all for a tip-clearance of 1.5% of the blade span, a pressure ratio (ratio of inlet total pressure to exit static pressure) of 1.2, and an inlet turbulence level of 6.1%. The first set of leakage reduction strategies explored include different squealer tip configurations: pressure-side squealer, suction-side squealer, mean-camber line squealer, and pressure plus suction side squealers located either along the edges of the blade or moved inwards. The suction-side squealer is shown to have the lowest heat transfer coefficient distribution and the lowest leakage flow rates. Two tip-desensitization strategies are explored. The first strategy involves a pressure-side winglet shaped to be thickest at the location with the largest pressure difference across the blade. The second strategy involves adding inclined ribs on the blade tip with the ribs normal to the local flow direction. While both strategies lead to reduction in the leakage flow and tip heat transfer rates, the ribbed tip exhibits considerably lower heat transfer coefficients. In comparing the two desensitization schemes with the various squealer tip configurations, the suction side squealer still exhibits the lowest heat transfer coefficient and leakage flow rates.

First and second thermodynamic law analyses applied to a solar dish collector

2014 ◽  
Vol 39 (4) ◽  
Author(s):  
Vahid Madadi ◽  
Touraj Tavakoli ◽  
Amir Rahimi
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Exergy Efficiency ◽  
Exergy Destruction ◽  
Flow Rates ◽  
Energy And Exergy ◽  
Mass Flow Rates

AbstractThe energy and exergy performance of a parabolic dish collector is investigated experimentally and theoretically. The effect of receiver type, inlet temperature and mass flow rate of heat transfer fluid (HTF), receiver temperature, receiver aspect ratio and solar radiation are investigated. To evaluate the effect of the receiver aperture area on the system performance, three aperture diameters are considered. It is deduced that the fully opened receivers have the greatest exergy and thermal efficiency. The cylindrical receiver has greater energy and exergy efficiency than the conical one due to less exergy destruction. It is found that the highest exergy destruction is due to heat transfer between the sun and the receivers and counts for 35 % to 60 % of the total wasted exergy. For three selected receiver aperture diameters, the exergy efficiency is minimum for a specified HTF mass flow rate. High solar radiation allows the system to work at higher HTF inlet temperatures. To use this system in applications that need high temperatures, in cylindrical and conical receivers, the HTF mass flow rates lower than 0.05 and 0.09 kg/s are suggested, respectively. For applications that need higher amounts of energy content, higher HTF mass flow rates than the above mentioned values are recommended.

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