Friction and mechanical energy loss

1978 ◽  
Vol 16 (3) ◽  
pp. 173-175
Author(s):  
Kenneth Flowers
Keyword(s):  
Energy Loss ◽  
Mechanical Energy ◽  
Mechanical Energy Loss

scholarly journals Determination of Mechanical Energy Loss in Steady Flow by Means of Dissipation Power

2017 ◽  
Vol 64 (2) ◽  
pp. 73-85 ◽  
Author(s):  
Wojciech Artichowicz ◽  
Jerzy M. Sawicki
Keyword(s):  
Energy Loss ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Mechanical Energy ◽  
Turbulent Viscosity ◽  
Viscosity Coefficient ◽  
Mechanical Energy Loss ◽  
Different Types ◽  
Loss Determination

Abstract When systems of simple geometry like pipes or regular channels are considered, the mechanical energy loss of the fluid flow can be expressed by local and longitudinal empirical energy loss coefficients. However, in the case of large spatially distributed objects, there are no simple approaches to this task. In practice, general recommendations addressing different types of objects are used, but they usually provide very coarse estimates of energy loss. In this work, a new methodology for determination of mechanical energy loss in steady flowis proposed. This methodology is based on the observation that the magnitude of the power of energy dissipation in turbulent flow can be determined using the averaged flow velocity and turbulent viscosity coefficient. To highlight this possibility, an analysis of the magnitudes of the power of the main and fluctuating components of turbulent flow is presented. The correctness of the method is verified using an example of laminar and turbulent flows in a circular pipe. The results obtained show clearly that the proposed methodology can be used for mechanical energy loss determination in flow objects. This methodology can be used as a basis for mechanical energy loss determination in different types of flow objects.

scholarly journals Entropy Generation for Negative Frictional Pressure Drop in Vertical Slug and Churn Flows

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 156
Author(s):  
Lei Liu ◽  
Dongxu Liu ◽  
Na Huang
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Energy Loss ◽  
Entropy Generation ◽  
Mechanical Energy ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Pressure Drops ◽  
Frictional Pressure Drop ◽  
Mechanical Energy Loss

It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility.

Analysis of Heat, Mass, and Momentum Transfer in the Rain Zone of Counterflow Cooling Towers

1999 ◽  
Vol 121 (4) ◽  
pp. 751-755 ◽  
Author(s):  
E. de Villiers ◽  
D. G. Kro¨ger
Keyword(s):  
Momentum Transfer ◽  
Cooling Tower ◽  
Mechanical Energy ◽  
Performance Evaluations ◽  
Cooling Towers ◽  
Droplet Deformation ◽  
One Dimensional ◽  
Mechanical Energy Loss ◽  
Simplifying Assumptions ◽  
Semi Empirical

The rate of heat, mass, and momentum transfer in the rain zone of three counterflow cooling tower geometries is analyzed using simplifying assumptions and numerical integration. The objective of the analysis is to generate equations for use in a one-dimensional mathematical cooling tower performance evaluations. Droplet deformation is taken into account and momentum transfer is calculated from the air flow’s mechanical energy loss, caused by air-droplet interaction. A comparison of dimensionless semi-empirical equations and experimental data demonstrates the method’s capability to predict the pressure drop in a counterflow rain zone.

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