Performance Model for Optically Driven Micropumps With Carbon Opacified Aerogel Membranes

2013 ◽  
Author(s):  
Yen-Lin Han
Keyword(s):  
Rarefied Gas ◽  
Carbon Aerogel ◽  
Performance Model ◽  
Operating Conditions ◽  
Thermal Creep ◽  
Maximum Pressure ◽  
Membrane Thickness ◽  
Carbon Particles ◽  
Knudsen Compressors ◽  
Highly Porous

Aerogel, a highly porous material with less than several percent of solids, has been utilized in applications requiring high precision thermal managements due to its extremely low thermal conductivity. Combining the advantages of high porosities and low thermal conductivities, aerogels were used as thermal creep membranes in Knudsen Compressors, micro/meso-scale pumps/compressors with no moving parts. Heating one side of the thermal creep membrane to create a temperature gradient, a Knudsen Compressor is operated based on the rarefied gas phenomenon of thermal creep to create flows and to induce a pressure gradient from the cold side to the hot side of the membrane. Adding carbon particles in silica aerogels creates an optically thick, opacified carbon aerogel that can absorb radiation energies to heat up one side of the aerogel membrane in a Knudsen Compressor to create thermal creep flows. An analytical model was developed to predict the temperature profile inside of the carbon opacified aerogel thermal creep membrane for the Knudsen Compressor. Applying this temperature model, pressure ratios achieved by the optically heated Knudsen Compressors for given operating conditions were also studied and correlations between the membrane thickness and the maximum pressure increase were determined.

Computational Studies on the Effects of Non-Linear Temperature Functions in Thermal Creep Membranes of Radiantly Driven Knudsen Compressors

2015 ◽  
Author(s):  
Yen-Lin Han
Keyword(s):  
Distribution Function ◽  
Temperature Distribution ◽  
Rarefied Gas ◽  
Experimental Studies ◽  
Radiation Energy ◽  
Thermal Creep ◽  
Maximum Pressure ◽  
Linear Temperature ◽  
Non Linear ◽  
Knudsen Compressors

Employing rarefied gas phenomenon of thermal creep (also known as thermal transpiration), Knudsen Compressor is a micro/meso-scale gas compressor/pump without moving parts. Driven by a temperature difference, gas molecules moved from the cold side of the thermal creep channel, which has a size less than the molecular mean free path, to the hot side of the channel. To utilize its low thermal conductivity and nanometer range size pores, carbon opacified aerogel membranes, treated as a bundle of thermal creep channels, were used in prior experimental studies of radiantly driven Knudsen Compressors. By absorbing the radiation energy, a temperature gradient will develop inside of a carbon opacified aerogel membrane to drive thermal creep flows. Analytical studies of the radiation energy absorbed by a carbon opacified aerogel membrane were performed and the resulting non-linear temperature distribution function within the carbon opacified aerogel thermal creep membrane was identified previously. This paper presents DSMC (Direct Simulation Monte Carlo) simulation studies that incorporate the previously reported non-linear temperature distribution function to investigate the performance of the radiantly driven Knudsen Compressor with a carbon opacified aerogel membrane. Cases with different connector temperatures for a closed system Knudsen Compressor were studied to observe the maximum pressure differences. Comparison of results indicates that radiantly driven Knudsen Compressor with a carbon opacified aerogel membrane could achieve a larger pressure gradient than what is predicted by the theoretical model reported by Muntz et al.

Characterization of a Radiantly Driven Multistage Knudsen Compressor

2003 ◽  
Author(s):  
M. Young ◽  
Y. L. Han ◽  
E. P. Muntz ◽  
G. Shiflett
Keyword(s):  
Steady State ◽  
Atmospheric Pressure ◽  
Maximum Flow ◽  
Performance Model ◽  
Experimental Results ◽  
Maximum Pressure ◽  
Flow Rates ◽  
Micro Scale ◽  
Knudsen Compressors

Knudsen Compressors are meso/micro scale gas compressors/pumps based on thermal transpiration or thermal creep. The design of radiantly driven Knudsen Compressors is discussed, along with a model that was developed to understand their performance. Experimental pumping performances for Knudsen Compressors with one, two, five, and fifteen stage, radiantly driven cascades are also discussed. Temperature measurements across the transpiration membranes, for various pressures of Nitrogen, were obtained and compared to those predicted by the performance model. The results agree with the model to within 15% consistently under predicting the measured hot side temperature of the transpiration membrane. The pump-down curves, steady-state maximum pressure differences, and maximum flow rates produced by a single stage Knudsen Compressor were obtained. A variety of configurations were studied at pressures from 500 mTorr to atmospheric pressure. The experimental results agreed with the performance model’s predictions to within 20%.

Simulation Studies of Micro-Scale Gas Pumps Driven by Isolated Heating Elements Induced Thermal Creep Flows

2009 ◽  
Author(s):  
Yen-Lin Han
Keyword(s):  
Temperature Gradient ◽  
Rarefied Gas ◽  
Pressure Ratio ◽  
Direct Simulation Monte Carlo ◽  
Thermal Creep ◽  
Heating Element ◽  
Maximum Pressure ◽  
Monte Carlo Simulation Technique ◽  
Micro Scale ◽  
Heating Mechanism

The Knudsen Pump (or Knudsen Compressor) is an unconventional micro-scale gas pump driven by the rarefied gas phenomenon of thermal creep, which is commonly induced by applying a temperature gradient along the wall of thermal creep channels. Previous experimental and simulation results have demonstrated satisfactory performances for Knudsen Pumps using the “linear wall temperature” heating concept. Employing a different heating mechanism, the present work used an isolated heating element placed in front of but not in direct contact with the thermal creep channel. The thermal creep flow was then induced by this isolated heating element instead of the direct temperature gradient along the thermal creep channel wall. Using the DSMC (Direct Simulation Monte Carlo) simulation technique, cases with various heaters’ sizes and operating pressures were studied here to investigate the limitation of thermal creep flows induced by an isolated heater. The maximum pressure ratio in the simulation domain was found to be varied with the heater sizes. This preliminary study of the “isolated heater” heating mechanism is proven to be viable for driving the thermal creep flows and be used in Knudsen Pumps.

Impact of Operating Conditions and Design Parameters on Gas Turbine Hot Section Creep Life

2010 ◽  
Author(s):  
S. Eshati ◽  
M. F. Abdul Ghafir ◽  
P. Laskaridis ◽  
Y. G. Li
Keyword(s):  
Gas Turbines ◽  
Performance Model ◽  
Operating Conditions ◽  
Creep Model ◽  
Design Parameters ◽  
Gas Temperature ◽  
Creep Life ◽  
Cooling Effectiveness ◽  
Radial Temperature ◽  
The Impact

This paper investigates the relationship between design parameters and creep life consumption of stationary gas turbines using a physics based life model. A representative thermodynamic performance model is used to simulate engine performance. The output from the performance model is used as an input to the physics based model. The model consists of blade sizing model which sizes the HPT blade using the constant nozzle method, mechanical stress model which performs the stress analysis, thermal model which performs thermal analysis by considering the radial distribution of gas temperature, and creep model which using the Larson-miller parameter to calculate the lowest blade creep life. The effect of different parameters including radial temperature distortion factor (RTDF), material properties, cooling effectiveness and turbine entry temperatures (TET) is investigated. The results show that different design parameter combined with a change in operating conditions can significantly affect the creep life of the HPT blade and the location along the span of the blade where the failure could occur. Using lower RTDF the lowest creep life is located at the lower section of the span, whereas at higher RTDF the lowest creep life is located at the upper side of the span. It also shows that at different cooling effectiveness and TET for both materials the lowest blade creep life is located between the mid and the tip of the span. The physics based model was found to be simple and useful tool to investigate the impact of the above parameters on creep life.

Heat transfer characteristic modelling and the effect of operating conditions on re-cooled cycle for a scramjet

2011 ◽  
Vol 115 (1164) ◽  
pp. 83-90 ◽  
Author(s):  
W. Bao ◽  
J. Qin ◽  
W. X. Zhou
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Transfer Characteristic ◽  
Cooling Capacity ◽  
Sensitivity Study ◽  
Performance Model ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Fuel Flow ◽  
Temperature And Pressure

Abstract A re-cooled cycle has been proposed for a regeneratively cooled scramjet to reduce the hydrogen fuel flow for cooling. Upon the completion of the first cooling, fuel can be used for secondary cooling by transferring the enthalpy from fuel to work. Fuel heat sink (cooling capacity) is thus repeatedly used and fuel heat sink is indirectly increased. Instead of carrying excess fuel for cooling or seeking for any new coolant, the cooling fuel flow is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. A performance model considering flow and heat transfer is build. A model sensitivity study of inlet temperature and pressure reveals that, for given exterior heating condition and cooling panel size, fuel heat sink can be obviously increased at moderate inlet temperature and pressure. Simultaneously the low-temperature heat transfer deterioration and Mach number constrains can also be avoided.

Adaptation Application to Engine Modelling

2007 ◽  
Author(s):  
Jude Iyinbor
Keyword(s):  
Measurement Data ◽  
Engine Performance ◽  
Performance Model ◽  
Operating Conditions ◽  
Adaptation Process ◽  
Design Point ◽  
Component Map ◽  
Important Measurement ◽  
Unknown Component ◽  
Selection Of

The optimisation of engine performance by predictive means can help save cost and reduce environmental pollution. This can be achieved by developing a performance model which depicts the operating conditions of a given engine. Such models can also be used for diagnostic and prognostic purposes. Creating such models requires a method that can cope with the lack of component parameters and some important measurement data. This kind of method is said to be adaptive since it predicts unknown component parameters that match available target measurement data. In this paper an industrial aeroderivative gas turbine has been modelled at design and off-design points using an adaptation approach. At design point, a sensitivity analysis has been used to evaluate the relationships between the available target performance parameters and the unknown component parameters. This ensured the proper selection of parameters for the adaptation process which led to a minimisation of the adaptation error and a comprehensive prediction of the unknown component and available target parameters. At off-design point, the adaptation process predicted component map scaling factors necessary to match available off-design point performance data.

A Fully Coupled Approach for the Integration of 3D-CFD Component Simulation in Overall Engine Performance Analysis

2017 ◽  
Author(s):  
C. Klein ◽  
S. Reitenbach ◽  
D. Schoenweitz ◽  
F. Wolters
Keyword(s):  
Performance Analysis ◽  
Boundary Conditions ◽  
Progress Monitoring ◽  
Cfd Simulation ◽  
System Simulation ◽  
Pressure Ratio ◽  
Performance Model ◽  
Operating Conditions ◽  
Operating Characteristics ◽  
Design Environment

Due to a high degree of complexity and computational effort, overall system simulations of jet engines are typically performed as 0-dimensional thermodynamic performance analysis. Within these simulations and especially in the early cycle design phase, the usage of generic component characteristics is common practice. Of course these characteristics often cannot account for true engine component geometries and operating characteristics which may cause serious deviations between simulated and actual component and overall system performance. This leads to the approach of multi-fidelity simulation, often referred to as zooming, where single components of the thermodynamic cycle model are replaced by higher-order procedures. Hereby the consideration of actual component geometries and performance in an overall system context is enabled and global optimization goals may be considered in the engine design process. The purpose of this study is to present a fully automated approach for the integration of a 3D-CFD component simulation into a thermodynamic overall system simulation. As a use case, a 0D-performance model of the IAE-V2527 engine is combined with a CFD model of the appropriate fan component. The methodology is based on the DLR in-house performance synthesis and preliminary design environment GTlab combined with the DLR in-house CFD solver TRACE. Both, the performance calculation as well as the CFD simulation are part of a fully automated process chain within the GTlab environment. The exchange of boundary conditions between the different fidelity levels is accomplished by operating both simulation procedures on a central data model which is one of the essential parts of GTlab. Furthermore iteration management, progress monitoring as well as error handling are part of the GTlab process control environment. Based on the CFD results comprising fan efficiency, pressure ratio and mass flow, a map scaling methodology as it is commonly used for engine condition monitoring purposes is applied within the performance simulation. Hereby the operating behavior of the CFD fan model can be easily transferred into the overall system simulation which consequently leads to a divergent operating characteristic of the fan module. For this reason, all other engine components will see a shift in their operating conditions even in case of otherwise constant boundary conditions. The described simulation procedure is carried out for characteristic operating conditions of the engine.

Effect of Operating Parameters on the DMFC Performance

2004 ◽  
Vol 2 (2) ◽  
pp. 81-85 ◽  
Author(s):  
Guo-Bin Jung ◽  
Ay Su ◽  
Cheng-Hsin Tu ◽  
Fang-Bor Weng
Keyword(s):  
Concentration Polarization ◽  
Solution Concentration ◽  
Open Circuit ◽  
Methanol Solution ◽  
Operating Conditions ◽  
Cell Performance ◽  
Membrane Electrode ◽  
Membrane Thickness ◽  
Methanol Crossover ◽  
Cell Temperature

Methanol crossover largely affects the efficiency of power generation in the direct methanol fuel cell. As the methanol crosses over through the membrane, the methanol oxidizes at the cathode, resulting in low fuel utilization and in a serious overpotential loss. In this study, the commercial membrane electrode assemblies (MEAs) are investigated with different operating conditions such as membrane thickness, cell temperature, and methanol solution concentration. The effects of these parameters on methanol crossover and power density are studied. With the same membrane, increasing the cell temperature promotes the cell performance as expected, and the lower methanol concentration causes the concentration polarization effects, thus resulting in lower cell performance. Although higher methanol solution concentration can overcome the concentration polarization, a serious methanol crossover decreases the cell performance at high cell temperature. In this study, the open circuit voltage (OCV) is inversely proportional to methanol solution concentration, and is proportional to membrane thickness and cell temperature. Although increasing membrane thickness lowers the degree of methanol crossover, on the other hand, the ohmic resistance increases simultaneously. Therefore, the cell performance using Nafion 117 as membrane is lower than that of Nafion 112. In addition, the performance of the MEA made in our laboratory is higher than the commercial product, indicating the capability of manufacturing MEA is acceptable.

scholarly journals Closed-loop control of a dual-fuel engine working with different combustion modes using in-cylinder pressure feedback

2019 ◽  
Vol 21 (3) ◽  
pp. 484-496 ◽  
Author(s):  
Carlos Guardiola ◽  
Benjamín Pla ◽  
Pau Bares ◽  
Alvin Barbier
Keyword(s):  
Closed Loop ◽  
Combustion Engine ◽  
Fuel Combustion ◽  
Operating Conditions ◽  
Dual Fuel ◽  
Maximum Pressure ◽  
Cylinder Pressure ◽  
Pressure Derivative ◽  
Combustion Modes ◽  
Dual Fuel Combustion

This work presents a closed-loop combustion control concept using in-cylinder pressure as a feedback in a dual-fuel combustion engine. At low load, reactivity controlled compression ignition combustion was used while a diffusive dual-fuel combustion was performed at higher loads. The aim of the presented controller is to maintain the indicated mean effective pressure and the combustion phasing at a target value, and to keep the maximum pressure derivative under a limit to avoid engine damage in all the combustion modes by cyclically adapting the injection settings. Various tests were performed at steady-state conditions showing good abilities to fulfil the expected operating conditions but also to reject disturbances such as intake pressure or exhaust gas recirculation variations. Finally, the proposed control strategy was tested during a load transient resulting in a combustion switching-mode and the results exhibited the closed-loop potential for controlling such combustion concept.

An Experimental Analysis of Misalignment Effects on Hydrodynamic Plain Journal Bearing Performances

2001 ◽  
Vol 124 (2) ◽  
pp. 313-319 ◽  
Author(s):  
J. Bouyer ◽  
M. Fillon
Keyword(s):  
Film Thickness ◽  
Journal Bearing ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Maximum Pressure ◽  
Minimum Film Thickness ◽  
Oil Flow ◽  
Hydrodynamic Effects

The present study deals with the experimental determination of the performance of a 100 mm diameter plain journal bearing submitted to a misalignment torque. Hydrodynamic pressure and temperature fields in the mid-plane of the bearing, temperatures in two axial directions, oil flow rate, and minimum film thickness, were all measured for various operating conditions and misalignment torques. Tests were carried out for rotational speeds ranging from 1500 to 4000 rpm with a maximum static load of 9000 N and a misalignment torque varying from 0 to 70 N.m. The bearing performances were greatly affected by the misalignment. The maximum pressure in the mid-plane decreased by 20 percent for the largest misalignment torque while the minimum film thickness was reduced by 80 percent. The misalignment caused more significant changes in bearing performance when the rotational speed or load was low. The hydrodynamic effects were then relatively small and the bearing offered less resistance to the misalignment.

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