Inlet Restrictor Research Articles

Design and Performance Analysis of Dual Membrane Restrictor for Hydrostatic Bearing

In this paper, a dual membrane restrictor design was proposed to improve the stiffness performance of the compensated hydrostatic bearing. Theoretical models for the proposed dual membrane restrictors were derived. Analysis of these models showed that a high stiffness region could be achieved at the desired loading region through the proper selection of the design parameters. A series of simulations were conducted to study the variations in the design parameters on the stiffness and clearance variations. It was found that the dimensionless membrane stiffness in the inlet restrictor, Kmi*, was the most dominant parameter for the performance of the compensated bearing system. The main advantages of the proposed dual membrane restrictor are the increase in flexibility by providing high stiffness at the desired loading region; and improving the stiffness performance of the bearing system especially at the desired loading region.

Effects of injection mechanism on air-water air lift pump performance

Due to its advantages, the air lift pump has many applications in real life. Therefore, the present study is dealing with the effect of some parameters on the air lift pump performance. The present study is a continuation of a program started years ago by the fluid mechanics group in Faculty of Engineering, Alexandria University. Beginning by validating the obtained results of the experiment set-up by comparing these experimental results with international accepted sets of data. After that the present experiments shed some lights on the inlet injection region of the air lift pump due to the significant effect of its initial conditions on the pump efficiency. Thus the study directed towards investigating the effect of some parameters including the inlet restrictor resistance, the injection direction and the injector riser diameter. The upward injection technique shows higher peak efficiency of 34.7% compared to 29.7% and 28.9% for downward and side injection respectively while the larger injector inner diameter shows maximum water capacity of 928 kg/h. compared to 823 kg/h. water mass flow rate for the smaller inner diameter injector. In all the above experimental tests, flow visualization is used extensively giving a good agreement with well recognized flow pattern map.

Complete suppression of flow boing instability in microchannel heat sinks using a combination of inlet restrictor and flexible dampener

Flow boiling suffers from the issue of instability due to the high rate of bubble generation in confined spaces within microchannel heat sinks. The cyclic changes in flow regimes lead to prolonged periods of dry out due to the backflow of vapour at high heat fluxes. Poor management of excess vapour and the resulting crowding at the outlet plenum drastically deteriorates the thermal and hydraulic performance of microchannel heat sinks. This study incorporates the simple design of a flexible membrane type pulsation dampener at the outlet port to address the aforementioned issues. The flexible dampener expands to accommodate the excess vapour, thereby minimising backflow and dryout within the channels. The heat sink design with the flexible dampener drastically reduces the fluctuations with lower surface temperature and pressure drop in compassion to the baseline case. Next, we combine the flexible dampener design with the inlet restrictor and compared the performance with and without the flexible dampener. The fluctuations/backflow are completely mitigated in this case, however, at the cost of a slight increase in pressure drop. Nonetheless, a quantitative comparison in terms of performance evaluation criteria suggests that the pulsation dampener can largely minimise the pressure drop penalty due to inlet restrictors while ensuring complete suppression of instability.

Combined effect of inlet restrictor and nanostructure on two-phase flow performance of parallel microchannel heat sinks

In this study, the combined effect of nanostructure and inlet restrictor on reducing the instabilities during flow boiling in parallel microchannel heat sinks is investigated experimentally. Four types of microchannel heat sinks are considered; plain microchannel, microchannel with inlet restrictor, nanostructured microchannel, and nanostructured microchannel with inlet restrictor. Different flow regimes such as bubbly flow, slug flow, annular flow, and partial dry out are observed with the variation in applied heat flux and mass flux. The fluctuations in pressure, temperature, and mass flux are characterised in each regime. It is found that the fluctuations increase with power input, which is primarily due to backflow of vapour in the upstream direction of flow. The microchannel with inlet restrictor is more effective in reducing fluctuations and result in less surface temperature compared to the baseline case of plain microchannel without restrictor at the same mass flux. Moreover, if the nanostructured surface is added to the plain microchannel with inlet restrictor, the effectiveness in reducing fluctuations increases at higher heat flux and also produces less surface temperature compared to other types of microchannels.

Modeling of reversal flow and pressure fluctuation in rectangular microchannel

Solving the flow instability in microchannel continues to be a topic of current research. In view of this, the current paper presents an analytical model to predict the pressure fluctuation by the analysis of bubble growth in a rectangular microchannel. To facilitate the analysis, bubble growth in the rectangular microchannel is assumed to be composed of three stages, namely, free growth, partially confined growth and fully confined growth. The interfacial velocity of bubble, being used to investigate the relationship between bubble reversal flow and pressure fluctuation, is determined by solving the conservation equations of the momentum of the liquid column coupled with the equations of the force balance at the bubble interface. The model reveals that when the length of fully confined bubble expands to some extent, the tail interface of bubble will reverse resulting in dramatically pressure increase. Additionally, the dependent factors, including Boiling number, nucleation site position, transverse shape and inlet restrictor, of pressure fluctuation are also analyzed based upon the current model, which denote that a smaller aspect ratio corresponds to a premature pressure fluctuation, and the magnitude of pressure fluctuation increases with the increasing Boiling number, decreases as the position of nucleation site moving downstream of the channel. In addition, the magnitude of pressure fluctuation decreases as the increase of pressure drop multiplier parameter, however, accompanied with the penalty of increasing pressure drop.

Performance of inherently compensated flat pad aerostatic bearings subject to dynamic perturbation forces

The importance of air bearing design is growing in engineering. As the trend to precision and ultra precision manufacture gains pace and the drive to higher quality and more reliable products continues, the advantages which can be gained from applying aerostatic bearings to machine tools, instrumentation and test rigs is becoming more apparent. The inlet restrictor design is significant for air bearings because it affects the static and dynamic performance of the air bearing. For instance pocketed orifice bearings give higher load capacity as compared to inherently compensated orifice type bearings, however inherently compensated orifices, also known as laminar flow restrictors are known to give highly stable air bearing systems (less prone to pneumatic hammer) as compared to pocketed orifice air bearing systems. However, they are not commonly used because of the difficulties encountered in manufacturing and assembly of the orifice designs. This paper aims to analyse the static and dynamic characteristics of inherently compensated orifice based flat pad air bearing system. Based on Reynolds equation and mass conservation equation for incompressible flow, the steady state characteristics are studied while the dynamic state characteristics are performed in a similar manner however, using the above equations for compressible flow. Steady state experiments were also performed for a single orifice air bearing and the results are compared to that obtained from theoretical studies. A technique to ease the assembly of orifices with the air bearing plate has also been discussed so as to make the manufacturing of the inherently compensated bearings more commercially viable. (c) 2012 Elsevier Inc. All rights reserved.

Ledinegg instability in microchannels

The static Ledinegg instability in horizontal microchannels under different flow conditions and fluids pertinent to electronics cooling was studied experimentally and numerically. Two fluids, water at sub-atmospheric pressures and refrigerant HFE-7100, were examined for a range of heat fluxes, mass fluxes, and channel hydraulic diameters. Numerical predictions from the developed pressure gradient model agree well with results from the flow boiling experiments. The model was used to quantify the susceptibility of the system to the Ledinegg instability. A parametric instability study was systematically conducted with varying system pressure, heat flux, inlet subcooling, and channel size with and without inlet restrictor. Increasing system pressure and channel diameter, reducing parallel channel number and channel length, and including an inlet restrictor can enhance the flow stability in microchannels.

The Axisymmetric, Perfectly Flexible Foil Bearing with Porous Inlet Restrictor. (67-Lub-4) : E. J. Barlow and M. Wildmann, pp. 145–152; 8 figs., 4 refs.

The Axisymmetric, Perfectly Flexible Foil Bearing with Porous Inlet Restrictor. (67-Lub-4) : E. J. Barlow and M. Wildmann, pp. 145–152; 8 figs., 4 refs.

The Axisymmetric, Perfectly Flexible Foil Bearing With Porous Inlet Restrictor

The equations for the axisymmetric, perfectly flexible foil bearing are solved for the case of an externally pressurized foil with porous inlet restriction. The results are presented in graphical form for design use. For comparison, results for the axisymmetric, perfectly flexible foil bearing with discrete inlet restrictors are also given.