Analysis of Flow Parameters Influencing Carry-Over Coefficient of Labyrinth Seals

2009 ◽  
Author(s):  
Saikishan Suryanarayanan ◽  
Gerald L. Morrison
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Labyrinth Seals ◽  
Integral Control ◽  
Leakage Model ◽  
Pitch Ratio ◽  
Carry Over

Accurate prediction of the mass flow rate through labyrinth seals is extremely important especially for rotodynamic analysis of turbomachinery. The integral control volume based rotodynamic coefficient prediction programs are no more accurate than the accuracy of the leakage mass flow rate. A leakage flow equation can be developed by comparing the seal to a series of orifices and cavities. An equation of this type usually contains a discharge coefficient and a carry-over coefficient. The carry-over coefficient represents the effectiveness of each cavity to dissipate the kinetic energy entering the cavity and has an effect upon the value of the discharge coefficient for the constriction following that cavity. Therefore, an effective model for the carry-over coefficient must be developed before a leakage model can be obtained. This paper investigates how flow conditions and geometry variations for a smooth shaft operating in straight though tooth on stator rectangular cavity labyrinth seals affect the value of the carry-over coefficient for incompressible flow. The effect of Reynolds number, pressure ratio, clearance, number of teeth and shaft speed are considered using computational fluid dynamics. It was found that Reynolds number and clearance to pitch ratio have a major influence on the carry-over coefficient. Models for the same were developed for a generic rectangular tooth on stator labyrinth seal. The carry-over coefficient varied from 1.0 at the lowest clearance/pitch ratio and Reynolds numbers to 1.8 for the largest clearance/pitch ratio and Reynolds number considered. Future studies will investigate how the discharge coefficient is dependent upon the same flow and geometry conditions as well as the carry-over coefficient in order to obtain a complete leakage model.

Thermal and Fluid Dynamic Behavior of a Horizontal Channel With Adiabatic Moving Lower Plate

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Horizontal Channel ◽  
Lower Plate ◽  
Stationary Condition ◽  
Moving Plate ◽  
Plate Velocity

In this study a numerical investigation of mixed convection in air in horizontal parallel walled channels with moving lower plate is carried out. The moving lower plate has a constant velocity and it is adiabatic, whereas the upper one is heated at uniform heat flux. The effects of horizontal channel height, heat flux and moving plate velocity are analyzed. Results in terms of temperature and stream function fields are given and the mass flow rate per unit of length and divided by the dynamic viscosity is reported as a function of Reynolds number based on the moving plate velocity. For stationary condition of lower plate, a typical C–loop inside the horizontal channel is detected. Different flow motions are observed in the channel and the two reservoirs, depending on the heat flux values and the distance between the heated upper stationary plate and lower adiabatic moving plate. The dimensionless induced mass flow rate presents different increase between the Reynolds number lower or greater than 1000.

Aerodynamic Loss Characteristics of a Turbine Blade With Trailing Edge Coolant Ejection: Part 1—Effect of Cut-Back Length, Spanwise Rib Spacing, Free-Stream Reynolds Number, and Chordwise Rib Length on Discharge Coefficients

2000 ◽  
Vol 123 (2) ◽  
pp. 238-248 ◽  
Author(s):  
Oguz Uzol ◽  
Cengiz Camci ◽  
Boris Glezer
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Free Stream ◽  
Cooling System ◽  
Trailing Edge ◽  
Discharge Coefficients ◽  
Reynolds Number Dependency ◽  
Spanwise Rib

The internal fluid mechanics losses generated between the blade plenum chamber and a reference point located just downstream of the trailing edge are investigated for a turbine blade trailing edge cooling system. The discharge coefficient Cd is presented as a function of the free-stream Reynolds number, cut-back length, spanwise rib spacing, and chordwise rib length. The results are presented in a wide range of coolant to free-stream mass flow rate ratios. The losses from the cooling system show strong free-stream Reynolds number dependency, especially at low ejection rates, when they are correlated against the coolant to free-stream pressure ratio. However, when Cd is correlated against a coolant to free-stream mass flow rate ratio, the Reynolds number dependency is eliminated. The current data clearly show that internal viscous losses due to varying rib lengths do not differ significantly. The interaction of the external wall jet in the cutback region with the free-stream fluid is also a strong contributor to the losses. Since the discharge coefficients do not have Reynolds number dependency at high ejection rates, Cd experiments can be performed at a low free-stream Reynolds number. Running a discharge coefficient experiment at low Reynolds number (or even in still air) will sufficiently define the high blowing rate portion of the curve. This approach is extremely time efficient and economical in finding the worst possible Cd value for a given trailing edge coolant system.

scholarly journals Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution

Micromachines ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 323 ◽  
Author(s):  
Jojomon Joseph ◽  
Danish Rehman ◽  
Michel Delanaye ◽  
Gian Luca Morini ◽  
Rabia Nacereddine ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Experimental Studies ◽  
Wire Mesh ◽  
Pressure Losses ◽  
Macro Scale ◽  
Flow Maldistribution

Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).

scholarly journals Effects of Louvered Parameters on Exergetic Performance of Louvered Finned Solar Air Heater

2021 ◽  
Vol 39 (5) ◽  
pp. 1649-1658
Author(s):  
Subhash Chand ◽  
Prabha Chand
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Operating Conditions ◽  
High Mass ◽  
Solar Air Heater ◽  
Air Heater ◽  
Pitch Ratio ◽  
Exergy Performance

The aim of the present study to improve the performance of solar air heater because of low thermo-physical properties of air. In the current work, an attempt has been made to improve the performance of the heater by employing louvered fins to the absorber plate, as it not only enhances heat transfer coefficient but also improve heat transfer area. The effect of exergy performance on the geometrical parameters of louvered fin i.e., louvered angle, louvered pitch and louvered length has been studied and analyzed. The results are compared to plane solar air heater (PSAH) to evaluate the effectiveness of louvered finned solar air heater (LFSAH). The exergy efficiency of LFSAH is comparatively higher for all the operating conditions except for higher mass flow rate where it may even go below that of PSAH; possibly due to the higher pressure drop and more loss of exergy at high mass flow rate. In addition, the results conclude that for louvered parameters viz., louvered angle 20°, fin pitch to louvered pitch ratio 0.75 and louvered length to louvered pitch ratio 1.25, high exergy performance of SAH is obtained as compared to other louvered parameter values.

scholarly journals Exergetic Evaluation of Steel Coaxial Heat Exchangers

2021 ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Circular Ring ◽  
High Mass ◽  
Flow Conditions ◽  
Hydraulic Losses ◽  
Pipe Radius

Abstract Background: A proven option to found buildings are geothermally activated steel pipes. Statics determine their dimensions. Energy improvement research focuses on the radius of inner pipe of such coaxial geothermal probes. Mass flow rate is often constant when optimizing inner pipe dimensions. In contrast, in this study flow conditions in outer pipe are constant (constant Reynolds number) to ensure that they not change during optimization. Aim is to maximize net exergy difference for the desired flow type by changing inner pipe radius (after deduction of hydraulic effort). System technology can be selected based on this optimal design and its associated boundary conditions for mass flow and temperatures.Methods: Thermal calculations based on Hellström are carried out to quantify an influence of changing inner pipe radius on thermal yield. A hydraulic optimization of inner pipe radius is performed. Increasing inner pipe radius results in decreasing hydraulic losses in inner pipe but increases hydraulic losses in outer circular ring. Net exergy difference is a key performance indicator to combine thermal and hydraulic effects. Optimization of net exergy difference is carried out for selected scenarios. All calculations are based on various, but fixed Reynolds numbers in the circular ring (Re = [4e3; 1e4; 1e5]), instead of fixed mass flow rates. This ensures fixed flow conditions and no unnecessary high mass flow rate.Results: Optimal inner radius is approximately as large as outer radius considering thermal results. Reynolds numbers are always bigger in inner pipe, due to the constant Reynolds number in circular ring. Both indicate that from a thermal point of view, a high mass flow rate and a high degree of turbulence are particularly important. Hydraulic optimal inner pipe radius is 54% of outer pipe radius for laminar flow scenarios and 60% for turbulent flow scenarios. Exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains.Conclusions: Design of coaxial geothermal probes should focus on the hydraulic optimum and take energetic optimum as a secondary criterion to maximize net exergy difference.

Study of Gas Flow Through a Stirling Engine Regenerator

2017 ◽  
Author(s):  
E. Rogdakis ◽  
P. Bitsikas ◽  
G. Dogkas
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Small Deviation ◽  
Three Dimensional ◽  
Stirling Engine ◽  
Gas Temperature

In the present work, a three dimensional (3D) Computational Fluid Dynamics (CFD) analysis is applied to a designed small compact regenerator with specific porosity and wire diameter. The regenerator was studied as a part of a Stirling Engine designed in a simple way. The gas temperature along the regenerator followed an approximately linear profile, while the metal temperature showed a small deviation during the engine cycle. The heat transfer coefficient between the gas and the matrix of the regenerator, along with the associate heat transferred were also derived. The heat exchanged in the regenerator is significantly higher to the respective heat in the engine’s heater and cooler. Additionally, the pressure drop and the related energy dissipation are studied. Their variation is largely dependent on both mass flow-rate and working gas velocity. The friction factor coefficient for the designed regenerator is correlated with Reynolds number and an equation of two variables is derived. Finally, the results of the CFD simulation are compared to those produced by a one-dimensional numerical model. These results include gas mass, mass flow-rate and Reynolds number, as well as the heat transferred between the gas and the regenerator matrix. Except for the case of the exchanged heat, the deviation between the two approaches is very small.

scholarly journals Experimental Investigation on Triple Concentric Tube Heat Exchanger with Helical Baffles

2020 ◽  
Vol 6 (11) ◽  
pp. 14-20
Author(s):  
Rohit Kumar Gaur ◽  
Dr. Shashi Kumar Jain ◽  
Dr. Sukul Lomash
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Solid Particles ◽  
Tube Heat Exchanger ◽  
High Heat Transfer

A heat exchanger is a device used to transfer thermal energy between two or more liquids, between a solid surface and a liquid, or between solid particles and a liquid at different temperatures and in thermal contact where shell and tube heat exchangers contain a large number of tubes packed in a jacket whose axes are parallel to those of the shell. Heat transfer occurs when one fluid flows into the pipes while the other flows out of the pipes through the jacket. In industry, three-tube heat exchanger tubes are used as condensers, evaporators, sub cooler, heat recovery heat exchangers, etc. The three concentric tube heat exchanger is a constructively modified version of the double concentric tube heat exchanger as an intermediate tube adds some advantages over the double tube heat exchangers in that it is larger tube surface area heat transfer per unit of length.  In the present study, the triple tube heat exchanger is further modified by inserting helical baffle over the surface of one of the tubes and observed turbulence flow which may lead to high heat transfer rates between the fluids of heat exchanger. Further, the Reynolds number, Nusselt number, friction factor of the flow at different mass flow rates of the hot fluid while keeping a constant mass flow rate of cold and normal temperature fluids were calculated. It was found that as the mass flow rate of the fluid increases the Reynolds number increases, the turbulence in the flow will increase which will cause the intermixing of the fluid, higher the rate of intermixing, more will be the heat transfer of the system.  

Numerical Investigation on the Flow Characteristics in a Cover-Plate Pre-Swirl System

2021 ◽  
Author(s):  
Menghua Jian ◽  
Xuesen Yang ◽  
Wei Dong
Keyword(s):  
Reynolds Number ◽  
Numerical Investigation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Circumferential Velocity ◽  
Cover Plate ◽  
Temperature Reduction

Abstract This paper presents a numerical investigation on the flow characteristics in a cover-plate pre-swirl system. The Reynolds-averaged Navier-Stokes equations, coupled with the standard k-ε turbulent model, are adopted and solved. With the inlet total pressure and total temperature being constant, the influences of the temperature reduction and flow resistance by changing pressure ratios and rotational Reynolds numbers were conducted. Flow features in the pre-swirl nozzle, pre-swirl cavity, receiver hole and cover-plate cavity were summarized. The results obtained in this study indicate that the pressure ratio and rotational Reynolds number have a significant influence on the vortex structure of the pre-swirl system. As the air is accelerated by the pre-swirl nozzle, the difference of circumferential velocity between the air and the rotational domain would be reduced, and the static temperature of the air would be decreased. The pressure drop in the pre-swirl system mainly occurs in the pre-swirl nozzle and the pre-swirl cavity. In addition, with the increase of the pressure ratio, the air mass flow rate and the circumferential velocity of the air out of the nozzle increased, thereby leading to an increment in temperature reduction. Moreover, with the increasing of the rotational Reynolds number, the dimensionless mass flow rate and temperature reduction of the pre-swirl system, which are mainly determined by the flow incidence angle of cooling air at the receiver hole, will first increase to a maximum and then decrease.

Study on Total Pressure Losses Characteristics of Rotating Cavity with Radial Inflow of Different Drum Hole Shape

2013 ◽  
Vol 663 ◽  
pp. 483-489
Author(s):  
Bo Ning ◽  
Xiang Luo ◽  
Ye Feng ◽  
Xiao Chen ◽  
Li Jun Wu
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Flow Coefficient ◽  
Hole Shape ◽  
Pressure Losses ◽  
Testing Method ◽  
Rotating Cavity

The pressure losses characteristics of the rotating cavity with radial inflow were investigated by testing method. The rotating cavity with oblong and round drum holes inlet and outlet total pressure under different operational state were tested, the influence of non-dimensional mass flow rate and rotating Reynolds number on rotating cavity with a Radial Inflow of different drum holes were analyzed. The results show that total pressure losses of the rotating cavity increases with the rotating Reynolds number and flow coefficient. Structure with oblong drum holes is superior to structure with round drum holes with lower total pressure losses in the range of the ratio of the flow coefficient and the Reynolds number is less than 0.048.And structure with round drum holes is superior to structure with oblong drum holes with lower total pressure losses in the range of the ratio of the flow coefficient and the Reynolds number is less than 0.048.

Flow Dynamic Behaviors and Characteristics of Two-Stage Viscous Pump in Microchannels

2008 ◽  
Author(s):  
Jianfeng Lu ◽  
Jing Ding
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Small Distance ◽  
Flow Dynamic ◽  
Two Stage ◽  
Dynamic Behaviors ◽  
Viscous Pump ◽  
Identical Type

The flow dynamic behaviors and characteristics of a two-stage viscous pump with two rotating cylinderes in microchannels were numerically studied by laminar model. At low Reynolds numbers, the dimensionless mass flow rate almost keeps constant for similar flow structure in the identical type of pump, and it also has little variation with different types of pump expect for the staggered pump with very small distance between different cylinders. As the Reynolds number increasing, the dimensionless mass flow rate drops because of the vortices evolution, and the distance between different cylinders significantly affects the flow dynamic process. For large distance, two steady vortices appear behind the cylinders, and the flow dynamics of aligned and staggered pump are very similar. For small distance, the flow rate of the staggered pump almost decreases with the distance rising, while the flow rate of the aligned pump has a maximum at a specific distance. Corresponding to the single-stage pump, the mass flow rate of two-stage pump is remarkably enhanced, and the enhanment ratio will increase as Reynolds number droping. Meanwhile, the driving power of two cylinders drops very slowly as the distance decreasing.

Sign in / Sign up

Export Citation Format

Share Document