Momentum Transport
Tips for Test & Exam
Tip 1 : Please approach TP with an open mind. Get rid of all preconceived notions. Please talk to me to solve your problems / misunderstandings. The more you talk to me the more I can help
Tip 2: when to use equations of change and when to use shell balance?
The answer is: the choice is yours unless the question specifies the method. Given choice, I would prefer using equations of change. of course you need to justify when cancelling terms
Tip 3: Always assign r to the radial coordinate and z to the axial coordinate in cylindrical systems
Tip 4: if pressure not known, do not assume, Check if Bernoulli equation can be used to find it
Tip 5 : If you are taking 40 minutes or less for the microscopic momentum balance problem, the remaining 80 minutes should be enough for the other 3 problems
Tip 6: checking dimensional consistency of equations will help avoid errors
Tip 7: Pressure in the macroscopic momentum balance equation should be gauge pressure
Tip 8: particle Re is Dp*V*rho / mu
Dp is particle diameter, whereas rho and mu are fluid properties
Tip 9: For inclined planes and pipes, Learn to determine the component of gravity force acting on the flow
Tip 10: Practice TP, Never study
Mechanisms
Molecular Transport
viscous forces due to velocity gradients in flow
Pressure forces
Convective Transport
Caused by Bulk flow by
Pressure gradient
Gravity
Important Concepts
Skin friction loss is the frictional force exerted by fluid on the wall of a pipe (Ff-s). This is same as frictional loss calculated from Moody chart
Drag is the frictional force for external flow
Drag Coefficient
Momentum Transport = Molecular Momentum Transport + Convective Momentum Transport
The three levels of study of TP are related to each other
Velocity gradients in a flow are confined to a thin layer near the wall. This layer is called Boundary layer. by solving equations of change for this layer skin frictional loss can be calculated
Microscopic Balance
Methods
Shell balance
Equations of Change
Macroscopic Variables
Internal flow
Friction
External flow
Drag
Macroscopic balance
Mass balance
Momentum balance
Meachanical energy balance