Teaching Fluid Mechanics and Thermodynamics Simultaneously through Pipeline Flow Experiments

Rajinder Pal

doi:10.3390/fluids4020103

Abstract

Entropy and entropy generation are abstract and illusive concepts for undergraduate students. In general, students find it difficult to visualize entropy generation in real (irreversible) processes, especially at a mechanistic level. Fluid mechanics laboratory can assist students in making the concepts of entropy and entropy generation more tangible. In flow of real fluids, dissipation of mechanical energy takes place due to friction in fluids. The dissipation of mechanical energy in pipeline flow is reflected in loss of pressure of fluid. The degradation of high quality mechanical energy into low quality frictional heat (internal energy) is simultaneously reflected in the generation of entropy. Thus, experiments involving measurements of pressure gradient as a function of flow rate in pipes offer an opportunity for students to visualize and quantify entropy generation in real processes. In this article, the background in fluid mechanics and thermodynamics relevant to the concepts of mechanical energy dissipation, entropy and entropy generation are reviewed briefly. The link between entropy generation and mechanical energy dissipation in pipe flow experiments is demonstrated both theoretically and experimentally. The rate of entropy generation in pipeline flow of Newtonian fluids is quantified through measurements of pressure gradient as a function of flow rate for a number of test fluids. The factors affecting the rate of entropy generation in pipeline flows are discussed.

Highlights

Fluid mechanics, that is, the study of motion of fluids and forces in fluids, is relatively a less abstract subject as compared with thermodynamics
The experimental data obtained from pipeline flow experiments consist of pressure drop versus flow rate for different diameter pipes
From pressure drop versus flow rate data, friction factor is calculated from Equation (37), re-written as: (

Summary

Introduction

That is, the study of motion of fluids and forces in fluids, is relatively a less abstract subject as compared with thermodynamics. Students find it relatively easy to visualize and understand the motion of fluids and forces in fluids. It is not difficult to convey to the students fluid mechanics concepts such as pressure, pressure distribution, viscosity, velocity distribution, velocity gradient, shear and normal stresses, mechanical energy dissipation and pressure loss in flow of fluids due to friction, etc. Instruments are available to directly measure pressure or pressure drop, flow rate, local velocity, shear and normal stresses, etc. The macroscopic balance of any entity (mass, momentum, energy) over the control volume can be expressed as: Input − Output + Generation = Accumulation (1). It should be noted that the surface integral v →

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