Loss Coefficients for Periodically Unsteady Flows in Conduit Components: Illustrated for Laminar Flow in a Circular Duct and a 90 Degree Bend

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Bastian Schmandt ◽  
Heinz Herwig
Keyword(s):  
Laminar Flow ◽  
Flow Field ◽  
Numerical Solutions ◽  
Steady Flows ◽  
Circular Duct ◽  
Pipe System ◽  
Second Law Analysis ◽  
Flow Through ◽  
Loss Coefficients ◽  
Laminar Pipe Flow

Losses in a flow through conduit components of a pipe system can be accounted for by head loss coefficients K. They can either be determined experimentally or from numerical solutions of the flow field. The physical interpretation is straight forward when these losses are related to the entropy generation in the flow field. This can be done based on the numerical solutions by the second law analysis (SLA) successfully applied for steady flows in the past. This analysis here is extended to unsteady laminar flow, exemplified by a periodic pulsating mass flow rate with the pulsation amplitude and the frequency as crucial parameters. First the numerical model is validated by comparing it to results for unsteady laminar pipe flow with analytical solutions for this case. Then K-values are determined for the benchmark case of a 90 deg bend with a square cross section which is well-documented for the steady case already. It turns out that time averaged values of K may significantly deviate from the corresponding steady values. The K-values determined for steady flow are a good approximation for the time-averaged values in the unsteady case only for small frequencies and small amplitudes.

Friction and Thermal Characteristics of Laminar Flow of Viscous Oil Through a Circular Tube Having Axial Corrugations and Fitted With Helical Screw-Tape Inserts

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Sujoy Kumar Saha ◽  
Bikram Narayan Swain ◽  
G. L. Dayanidhi
Keyword(s):  
Nusselt Number ◽  
Laminar Flow ◽  
Friction Factor ◽  
Circular Tube ◽  
Thermal Characteristics ◽  
Circular Duct ◽  
Viscous Oil ◽  
Flow Through ◽  
The Individual ◽  
Better Than

The experimental friction factor and Nusselt number data for a laminar flow through a circular duct having axial corrugation and fitted with helical screw-tape inserts have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts, in combination with axial corrugation, perform better than the individual enhancement technique acting alone for laminar flow through a circular duct.

Heat Transfer Enhancement of Laminar Flow Through a Circular Tube Having Wire Coil Inserts and Fitted With Center-Cleared Twisted Tape

2012 ◽  
Vol 4 (3) ◽  
Author(s):  
Sujoy Kumar Saha ◽  
Bikash Kumar Barman ◽  
Soumitra Banerjee
Keyword(s):  
Nusselt Number ◽  
Laminar Flow ◽  
Friction Factor ◽  
Twisted Tape ◽  
Circular Duct ◽  
Twisted Tapes ◽  
Wire Coil ◽  
Flow Through ◽  
The Individual ◽  
Better Than

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having wire coil inserts and fitted with center-cleared twisted tape have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are the center-cleared twisted tapes in combination with wire coil inserts perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of center-clearance.

Laminar Flow Through a Circular Tube Having Transverse Ribs and Twisted Tapes

2015 ◽  
Vol 7 (4) ◽  
Author(s):  
Manvendra Tiwari ◽  
Sujoy Kumar Saha
Keyword(s):  
Nusselt Number ◽  
Laminar Flow ◽  
Friction Factor ◽  
Circular Tube ◽  
Circular Duct ◽  
Viscous Oil ◽  
Twisted Tapes ◽  
Flow Through ◽  
The Individual ◽  
Better Than

The experimental friction factor and Nusselt number data for laminar flow of viscous oil through a circular duct having integral transverse rib roughness and fitted with twisted tapes with oblique teeth have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the twisted tapes with oblique teeth in combination with integral transverse rib roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of fin parameter.

Numerical Solutions of Flow between Rotating Cylinders

1972 ◽  
Vol 14 (6) ◽  
pp. 400-403 ◽  
Author(s):  
B. E. Launder ◽  
W. M. Ying
Keyword(s):  
Laminar Flow ◽  
Finite Difference ◽  
Flow Field ◽  
Newtonian Fluid ◽  
Pressure Field ◽  
Numerical Solutions ◽  
Convective Transport ◽  
Appreciable Effect ◽  
Rotating Cylinders ◽  
The Core

The paper presents solutions of the laminar flow of a Newtonian fluid between cylinders with non-coincident axes, where the core cylinder rotates about its axis. The solutions have been obtained by means of an adapted version of the finite-difference procedure of Gosman et al. (1). The results show that the inclusion of convective transport terms (which in previous analyses have been neglected or included only approximately) may have an appreciable effect upon the flow field and, in particular, upon the pressure field around cylinders.

Loss Coefficients in Laminar Flows: Indispensable for the Design of Micro Flow Systems

2010 ◽  
Author(s):  
H. Herwig ◽  
B. Schmandt ◽  
M.-F. Uth
Keyword(s):  
Numerical Simulation ◽  
Laminar Flow ◽  
Turbulent Flows ◽  
Head Loss ◽  
Laminar Flows ◽  
Second Law ◽  
Second Law Analysis ◽  
Micro Flow ◽  
Loss Coefficients

The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has mainly been applied to fully turbulent flows it is extended here to also cover the laminar flow regime. Specific numbers of K can be determined by integration of the entropy generation field (second law analysis) obtained from a numerical simulation. This general approach is discussed and illustrated for various conduit components.

A Standard Method to Determine Loss Coefficients of Conduit Components Based on the Second Law of Thermodynamics

2012 ◽  
Author(s):  
Bastian Schmandt ◽  
Heinz Herwig
Keyword(s):  
Numerical Simulation ◽  
Laminar Flow ◽  
Flow Field ◽  
Entropy Generation ◽  
Standard Method ◽  
Test Facility ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Gear Pump ◽  
Loss Coefficients

Losses in conduit components of a pipe system can be accounted for by using component specific loss coefficients K. Especially in mini- and micro-systems an exact knowledge of these loss coefficients (which in laminar flow strongly depend on the Reynolds number) is important. Limited space will generally lead to a high loss-contribution of single components compared to the contribution of the straight channels. The determination of K-values of single components based on a numerical simulation using the Second Law Analysis (SLA) has turned out to be a very attractive method. The simulation of the flow field shows the distribution of losses and upstream and downstream lengths of impact (Lu, Ld) where the otherwise fully developed flow is affected by the component. The numerical SLA-Method is introduced as a standard method, illustrated and validated with highly accurate measurements in a 90 deg bend with a square cross section. The local entropy generation rates based on the numerical simulation of the flow field are computed and carefully interpreted. Component specific values of K, Lu are Ld are collected in a table and illustrated by plots of the entropy generation rate distribution along the bend’s centerline. Validation is achieved with experimental results from a test facility exclusively built for this purpose: Laminar flow in a 90 deg bend is induced by a controlled gear pump with polydimethylsiloxanes of different viscosities as working fluids.

Non-isothermal Laminar Flow of Gases through Cooled Tubes

1973 ◽  
Vol 95 (1) ◽  
pp. 85-92 ◽  
Author(s):  
Lloyd H. Back
Keyword(s):  
Laminar Flow ◽  
Numerical Solutions ◽  
Isothermal Flow ◽  
Wall Friction ◽  
Gas Flows ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Flow Equations ◽  
Flow Through ◽  
Good Agreement

Numerical solutions of the laminar-flow equations in differential form are presented for gas flows through cooled tubes. For nearly isothermal flow there is good agreement with available experimental data, as is also found for the case of a large amount of wall cooling. This correspondence along with a check on the satisfaction of the global momentum and energy constraints allowed an appraisal of the effect of wall cooling on flow through tubes. In general, the effect of wall cooling was to decrease the wall friction and the change in pressure along tubes, but the average heat-transfer coefficient did not vary much.

Determination of Loss Coefficients for Micro-Flow Devices: A Method Based on the Second Law Analysis (SLA)

2009 ◽  
Author(s):  
H.-C. Zhang ◽  
B. Schmandt ◽  
H. Herwig
Keyword(s):  
Laminar Flow ◽  
Entropy Production ◽  
Turbulent Flows ◽  
Head Loss ◽  
Second Law ◽  
Second Law Analysis ◽  
Micro Flow ◽  
Loss Coefficients ◽  
Flow Devices

The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has only been applied to fully turbulent flows it is extended here to also cover the laminar flow regime. Specific numbers of K can be determined by integration of the entropy production field (second law analysis). This general approach is discussed and illustrated with the specific example of a conical diffusor.

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