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.

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.

Internal Flow Losses: A Fresh Look at Old Concepts

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Bastian Schmandt ◽  
Heinz Herwig
Keyword(s):  
Flow Field ◽  
Entropy Generation ◽  
Mechanical Energy ◽  
Internal Flow ◽  
Second Law Of Thermodynamics ◽  
Head Loss ◽  
Local Entropy ◽  
Flow Losses ◽  
Loss Coefficients ◽  
Local Entropy Generation

Losses in a flow field due to single conduit components often are characterized by experimentally determined head loss coefficients K. These coefficients are defined and determined with the pressure as the critical quantity. A thermodynamic definition, given here as an alternative, is closer to the physics of flow losses, however. This definition is based upon the dissipation of mechanical energy as main quantity. With the second law of thermodynamics this dissipation can be linked to the local entropy generation in the flow field. For various conduit components K values are determined and physically interpreted by determining the entropy generation in the component as well as upstream and downstream of it. It turns out that most of the losses occur downstream of the components what carefully has to be taken into account when several components are combined in a flow network.

Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 797-800 ◽  
Author(s):  
W. W. Lin ◽  
D. J. Lee
Keyword(s):  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Spanwise Direction ◽  
Minimum Entropy ◽  
Tube Heat Exchanger ◽  
Second Law Analysis ◽  
Minimum Entropy Generation

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

scholarly journals Second Law Analysis for the Experimental Performances of a Cold Heat Exchanger of a Stirling Refrigeration Machine

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 215 ◽  
Author(s):  
Steve Djetel-Gothe ◽  
François Lanzetta ◽  
Sylvie Bégot
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Mass Flow ◽  
Hydraulic Diameter ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Water Mixture ◽  
Fluid Friction ◽  
Refrigeration Machine

The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate N S , the irreversibility distribution ratio ϕ and the Bejan number B e | N S based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K < TC < 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and B e | N S → 1 and ϕ → 0 for mass flow rates m ˙ → 0.1 kg.s−1.

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Mohammad Shanbghazani ◽  
Vahid Heidarpoor ◽  
Marc A. Rosen ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Local Entropy ◽  
Fluid Friction ◽  
Local Entropy Generation

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

Entropy generation and second law analysis of pulsed impinging jet

2015 ◽  
Vol 25 (5) ◽  
pp. 1089-1106 ◽  
Author(s):  
Kazem Esmailpour ◽  
Behnam Bozorgmehr ◽  
Seyed Mostafa Hosseinalipour ◽  
Arun S. Mujumdar
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Entropy Generation ◽  
Impinging Jet ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Pulsation Frequency ◽  
Content Type ◽  
Thermal Entropy ◽  
Plate Distance

Purpose – The purpose of this paper is to examine entropy generation rate in the flow and temperature field due pulsed impinging jet on to a flat plate. Heat transfer of pulsed impinging jets has been investigated by many researchers. Entropy generation is one of the parameters related to the second law of thermodynamics which must be analyzed in processes with heat transfer and fluid flow in order to design efficient systems. Effect of velocity profile parameters and various nozzle to plate distances on viscous and thermal entropy generation are investigated. Design/methodology/approach – In this study, the flow and temperature field of a pulsed turbulent impinging jet are simulated numerically by the finite volume method with appropriate boundary conditions. Then, flow and temperature results are used to calculate the rate of entropy generation due to heat transfer and viscous dissipation. Findings – Results show that maximum viscous and thermal entropy generation occurs in the lowest nozzle to plate distance and entropy generation decreases as the nozzle to plate distance increases. Entropy generation in the two early phase of a period in the most frequencies is more than steady state whereas a completely opposite behavior happens in the two latter phase. Increase in the pulsation frequency and amplitude leads to enhancement in entropy generation because of larger temperature and velocity gradients. This phenomenon appears second and even third peaks in entropy generation plots in higher pulsation frequency and amplitude. Research limitations/implications – The predictions may be extended to include various pulsation signal shape, multiple jet configuration, the radiation effect and phase difference between jets. Practical implications – The results of this paper are a valuable source of information for active control of transport phenomena in impinging jet configurations which is used in different industrial applications such as cooling, heating and drying processes. Originality/value – In this paper the entropy generation of pulsed impinging jet was studied for the first time and a comprehensive discussion on numerical results is provided.

scholarly journals CFD Prediction of Airfoil Drag in Viscous Flow Using the Entropy Generation Method

2018 ◽  
Vol 2018 ◽  
pp. 1-15
Author(s):  
Wei Wang ◽  
Jun Wang ◽  
Hui Liu ◽  
Bo-yan Jiang
Keyword(s):  
Flow Field ◽  
Viscous Flow ◽  
Turbulent Flows ◽  
Entropy Generation ◽  
Aerodynamic Force ◽  
Pressure Coefficient ◽  
Generation Rate ◽  
Momentum Balance ◽  
Entropy Generation Rate ◽  
Prediction Approach

A new aerodynamic force of drag prediction approach was developed to compute the airfoil drag via entropy generation rate in the flow field. According to the momentum balance, entropy generation and its relationship to drag were derived for viscous flow. Model equations for the calculation of the local entropy generation in turbulent flows were presented by extending the RANS procedure to the entropy balance equation. The accuracy of algorithm and programs was assessed by simulating the pressure coefficient distribution and dragging coefficient of different airfoils under different Reynolds number at different attack angle. Numerical data shows that the total entropy generation rate in the flow field and the drag coefficient of the airfoil can be related by linear equation, which indicates that the total drag could be resolved into entropy generation based on its physical mechanism of energy loss.

scholarly journals Numerical Investigation of Flow Field and Energy Loss in a Centrifugal Pump as Turbine

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Jingze Li ◽  
Dongrong Meng ◽  
Xun Qiao
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Energy Loss ◽  
Entropy Generation ◽  
Flow Separation ◽  
Guide Vane ◽  
Great Influence ◽  
Internal Flow ◽  
Asymmetric Structure ◽  
Centrifugal Pumps

Centrifugal pumps as turbine (PAT) are widely used in petrochemical and water conservancy industries. The research on the internal flow field and energy loss of PAT is of great significance to improve the performance and efficiency of PAT. In this paper, experimental and numerical simulation methods are used to study the energy loss and flow field. The results show that the numerical simulation method can accurately simulate the internal flow field of PAT. And the entropy generation theory is applied to visualize the internal energy loss of PAT through the comparison of total pressure loss and entropy generation. The highest energy loss among PAT components is the guide vane. The loss in the guide vane is mainly caused by the flow separation caused by the wake of the guide vane and the asymmetric structure of the volute. The losses in the impeller are mainly due to flow separation and wake. Besides, the unsteady simulation results show that rotor-stator interaction has a great influence on the gap between the impeller and the guide vane. The research results provide a reference for the design of the PAT. This study is beneficial to studying the dynamic and static interference and PAT vibration to improve the stability of the PAT.

Thermo-Fluiddynamic Numerical Simulation and Entropy Generation Maps of an Ultra-Micro-Turbogas Compressor Wheel

2010 ◽  
Author(s):  
Giovanni Pierandrei ◽  
Enrico Sciubba
Keyword(s):  
Numerical Simulation ◽  
Entropy Generation ◽  
Electrical Power ◽  
Entropy Generation Rate ◽  
Inlet Temperature ◽  
Vaneless Diffuser ◽  
Turbulent Structures ◽  
Accurate Analysis ◽  
Compressor Wheel ◽  
Fine Mesh

The present study was designed to gain deeper insight of the thermofluiddynamic fields in a compressor wheel. The compressor is part of an ultra-micro-turbogroup developed by the University of Roma 1, co-funded within the frame of a National Research Project, conceived as a portable energy conversion system delivering electricity to a broad range of small devices, for medical, military or emergency use. The expected electrical power output is 400 watts. The turbogroup, fuelled by natural gas, has a single-shaft configuration and is coupled with a reversible electric motor-generator, granting a more compact overall system, encapsulated in a relatively small self-contained assembly. The compressor wheel has an outlet diameter of 38 mm, spins at 175,000 rpm and delivers the fluid to the vaneless diffuser endowed with a static pressure of 155 kPa. The mass flow rate is 0.02 kg/s, and the total inlet temperature is 300 K and the total temperature of the flowing out fluid is about 400 K. The rotor, featuring 6 full- and 6 splitter blades, is coupled with a vaneless diffuser followed by a toroidal volute that collects the almost purely radial fluid at diffuser exit and delivers it to the regenerator. The numerical simulation based upon the k-ε turbulent model has been run within the commercial software Fluent®, on a very fine mesh constructed on a geometry obtained from a commercial turbocharger manufacturer. A critical analysis has been performed on the turbulent structures that evolve within the rotor channel, to better understand the dissipative mechanisms. To this goal, the thermal and viscous entropy generation rate, have been computed on the converged solution of the thermal-fluiddynamic field, and their maps have been inspected to study the development of turbulent structures. The results of this study confirm that an accurate analysis of the local entropy generation rates provides useful hints on how to introduce design improvements and to achieve a higher stage efficiency.

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.

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