Fluid Mechanics Integral vs Differential Analysis

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Questions and Answers

What does the integral form of analysis primarily focus on?

  • Overall features of the flow for an entire control volume (correct)
  • Microscopic view of the flow dynamics
  • Flow details at specific points in the system
  • Infinitesimal control volumes in detail

Which approach is associated with analyzing forces on a macroscopic scale?

  • Mathematical modeling
  • Integral analysis (correct)
  • Differential analysis
  • Statistical analysis

What distinguishes differential analysis from integral analysis?

  • Differential analysis applies to microscopic scales (correct)
  • Differential analysis considers the whole system
  • Differential analysis focuses on average properties
  • Differential analysis uses control volumes

What is the primary focus of the differential form of analysis?

<p>Flow details at any or every point (D)</p> Signup and view all the answers

In what scale does integral analysis typically operate?

<p>Macroscopic scale (C)</p> Signup and view all the answers

What type of control volumes does differential analysis utilize?

<p>Infinitesimal control volumes (B)</p> Signup and view all the answers

Which of the following best describes the focus of integral analysis?

<p>The entire flow system interactions (B)</p> Signup and view all the answers

What is the control volume concept primarily associated with?

<p>Overall system performance (D)</p> Signup and view all the answers

What does the pressure force due to a pressure difference at the surfaces of a control volume depend on?

<p>The magnitude of the pressure difference and surface area (B)</p> Signup and view all the answers

In the context of an infinitesimal control volume, what represents the momentum entering the control volume from the x-surface?

<p>Velocity normal to the surface at x (B)</p> Signup and view all the answers

Which direction is NOT explicitly mentioned in the derivation of forces due to pressure?

<p>w - direction (D)</p> Signup and view all the answers

What kind of volume is being analyzed when discussing the derivation of differential form momentum?

<p>Infinitesimal control volume (A)</p> Signup and view all the answers

What is the primary factor that affects the total momentum into the infinitesimal control volume?

<p>Surface area and velocity (A)</p> Signup and view all the answers

What concept is essential for fluid flow analysis?

<p>Infinitesimal control volume (C)</p> Signup and view all the answers

What does the linear momentum balance in differential form represent?

<p>Changes in momentum over an infinitesimal volume (A)</p> Signup and view all the answers

Which equation is referred to as Cauchy’s first equation of motion?

<p>Linear momentum balance equation (D)</p> Signup and view all the answers

How is knowledge of the velocity vector field described in relation to fluid problems?

<p>It is equivalent to solving any fluid problem. (D)</p> Signup and view all the answers

Which statement about control volumes in fluid dynamics is accurate?

<p>Control volumes can be infinitesimal and dynamic. (B)</p> Signup and view all the answers

What does the term τ in the linear momentum balance equation refer to?

<p>Viscous stress tensor (A)</p> Signup and view all the answers

In the context of fluid flow, what is primarily analyzed using the infinitesimal control volume?

<p>Velocity distribution (A)</p> Signup and view all the answers

What does the symbol ∇ represent in the momentum balance formula provided?

<p>Spatial derivative (B)</p> Signup and view all the answers

What does the differential form of linear momentum balance primarily represent?

<p>The flow properties at a point (A)</p> Signup and view all the answers

In the context of linear momentum balance, which of the following forces contributes to net momentum outflow?

<p>Pressure gradient (D)</p> Signup and view all the answers

Which term accounts for the friction between fluid molecules in the momentum balance equation?

<p>Viscous force (A)</p> Signup and view all the answers

How is the concept of body force, such as weight, integrated into the linear momentum balance?

<p>It is added as an external force acting on the control volume (D)</p> Signup and view all the answers

Which equation represents the momentum accumulation rate in the differential form of linear momentum balance?

<p>∂(ρV)/∂t (A)</p> Signup and view all the answers

What happens to the linear momentum balance when considering an infinitesimal control volume?

<p>It retains all forces acting on the volume (B)</p> Signup and view all the answers

Which of the following contributes to the net force acting in the differential form of momentum balance?

<p>Gravity and pressure forces (C)</p> Signup and view all the answers

What do both integral and differential forms of momentum balance represent?

<p>The linear momentum balance (A)</p> Signup and view all the answers

What does the term 'net outflow of momentum' refer to in the context of fluid dynamics?

<p>The difference between momentum entering and leaving a control volume. (A)</p> Signup and view all the answers

In which direction does the net outflow of momentum occur through x-surfaces according to the provided content?

<p>Towards negative x-direction. (C)</p> Signup and view all the answers

Which of the following accurately describes the types of viscous forces acting on a control volume?

<p>Both tensile and compressive forces. (D)</p> Signup and view all the answers

What does the equation involving (!9# 9# ) depict in fluid mechanics?

<p>The momentum density per unit volume. (B)</p> Signup and view all the answers

How are the pressures related when considering the outflow of momentum through different surfaces?

<p>They differ based on the surface orientation. (A)</p> Signup and view all the answers

What is primarily measured during the analysis of viscous forces in a control volume?

<p>The resistance to flow due to viscosity. (D)</p> Signup and view all the answers

What is indicated by the term 'compressive forces' in the context of surface dynamics?

<p>Forces that act perpendicular to the surface area to push inward. (C)</p> Signup and view all the answers

Which expression represents the balance of momentum for fluids exiting a control volume?

<p>Net momentum out equals net momentum in minus external forces. (A)</p> Signup and view all the answers

What form does the compact notation for linear momentum balance take?

<p>h = 8&amp; + 8&quot; + 8# (C)</p> Signup and view all the answers

Which equation represents the Cauchy's Equation of Motion in differential form?

<p>ai - ∇` + ∇ g = 12 ah + ∇ ahh (B)</p> Signup and view all the answers

In the compact notation of linear momentum, what does ∇g represent?

<p>The gradient of momentum flux (A)</p> Signup and view all the answers

Which of the following represents a true statement regarding the linear momentum balance equation?

<p>It includes contributions from various directions in the equation. (A)</p> Signup and view all the answers

How is the gradient in the K-direction represented in the equations?

<p>∇g# = 1&amp; P&amp;&amp; + 1&quot; P#&amp; + 1# P#&amp; (C)</p> Signup and view all the answers

What role does compressibility have in the context of linear momentum balance equations?

<p>It is relevant for both compressible and incompressible flows. (D)</p> Signup and view all the answers

What does the notation a8 represent in the equations?

<p>The acceleration associated with momentum changes (C)</p> Signup and view all the answers

Which part of the linear momentum balance equation specifically addresses external forces?

<p>aF# (D)</p> Signup and view all the answers

What does the term ∇ahh represent in the Cauchy’s Equation of Motion?

<p>Gradient of the specific energy component (B)</p> Signup and view all the answers

Which expression demonstrates the balance of linear momentum along multiple directions in the equations?

<p>aF&amp; + aF&quot; + aF# = a8&amp; + a8&quot; + a8# (D)</p> Signup and view all the answers

Flashcards

Infinitesimal Control Volume

A very small, almost infinitely small, portion of space used to analyze fluid flow.

Differential Form of Linear Momentum Balance

The equation that describes the relationship between forces acting on a fluid, the change in fluid momentum, and the rate of momentum change within the control volume.

Stress

The force per unit area acting on a fluid element.

Normal Stress

The force per unit area acting normal to the fluid element.

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Shear Stress

The force per unit area acting tangential to the fluid element.

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Velocity Vector Field

A vector field that describes the velocity of each fluid particle at any given point in space and time.

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Momentum Flux

The rate of change of momentum of the fluid within the control volume.

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Convective Momentum Flux

The rate of change of momentum of the fluid entering or leaving the control volume.

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Pressure Force

The force acting on a fluid element due to pressure differences in different directions.

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Integral Approach

The overall features of a flow system considered as a whole, like forces acting on the system.

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Differential Approach

Study of flow details at specific points within a system, like pressure or velocity at a given location.

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Control Volume

A fixed region in space through which the fluid flows.

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Integral Analysis

Analyzing fluid flow using integral equations, which consider the entire control volume as a whole.

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Differential Analysis

Analyzing fluid flow using differential equations, which focus on the infinitesimally small control volumes.

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Scale

The size of the region or point of interest in the flow system.

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Integral Scale

A macroscopic scale view of the entire flow system.

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Differential Scale

A microscopic scale view of the flow system, focusing on individual points.

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Momentum Accumulation Rate

The change in momentum of a fluid within a control volume over time, representing the rate of momentum accumulation.

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Study Notes

Fluid Mechanics 2, Chapter 4: Differential Analysis of Fluid Flow

  • Course: KIL 3002, Fluid Mechanics 2, Department of Chemical Engineering, Universiti Malaya
  • This chapter covers the differential analysis of fluid flow.
  • Differential Form of Linear Momentum Balance:
    • Understanding infinitesimal control volumes is crucial for fluid flow analysis.
    • The derivation of the linear momentum balance in differential form from an infinitesimal control volume is a key component.
    • The equation is: ρ(δv/δt) + ρ(v •∇v)=pg - ∇P + ∇•τ
    • This equation is an alternative form of Cauchy's first equation of motion.
  • Motivations:
    • Knowing the velocity vector field is essential to solve fluid problems.
    • Integral form analysis provides an overview of the system's overall features.
    • Differential form analysis provides detailed information at individual points within the flow.
    • Microscopic analysis involves studying the flow at a small scale.
  • Integral and Differential Forms:
    • Both forms, integral and differential, represent the linear momentum balance.
    • The viscous force (friction force) is a key component.
    • Pressure gradient is important in analysis.
  • Derivation from Infinitesimal Control Volume:
    • The derivation considers the momentum change within an infinitesimal control volume.
    • This involves summing up the momentum outflow and inflow and comparing it with the forces imposed on the control volume.
    • External body forces (e.g., weight) and surface forces (e.g., pressure and viscous forces).
  • Derivation of Differential Form:
    • Momentum accumulation rate is crucial to derive the differential form.
    • Consider momentum exchange through control surfaces, including pressure force, viscous force and body force.
  • Differential Form Derivation - Momentum components:
    • The derivation explicitly demonstrates how to calculate momentum accumulation rates in each direction (x, y, z).
    • The key is to evaluate the momentum transfer through surfaces in each direction.
    • Calculations include weight, and the viscous terms
  • Differential Form Derivation - Viscous Force:
    • Viscous forces arise due to the internal friction between fluid molecules.
    • There are two types: shear stress (parallel to surface) and normal stress (perpendicular to surface).
    • Calculations are based on stress terms expressed as tensor values.
  • Differential Form Derivation - Viscous Force - Stress terms:
    • Stress terms are essential in the derivation, given by (Tx)x, (Tx)y,etc
    • Differential form calculations using stress terms are required in different directions.
  • Linear Momentum Balance Overall:
    • The complete form of the linear momentum balance equation in differential form is provided, known as Cauchy's equation of motion.
    • The equation is expressed in terms of the overall linear momentum balance with compact notation.
  • Applications:
    • This analysis is applicable for both compressible and incompressible fluids.
    • It is also valid for Newtonian and non-Newtonian fluids.
    • It can be applied in situations with any symmetry.

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