Fluid Flow 2

Fluid Flow 2

1. Work

   • W = F*S
   • Energy is a body's capacity to do work
   • Power is the rate of doing work

2. 1st Law of Thermodynamics

   • Energy cannot be created, nor destroyed - only converted between forms
   • Q + W = E(2) - E(1)
     • Heat transfer and work done are equal to the change in overall energy of a system
     • E = U + 0.5*m*v^2 + m*g*z
       • Overall energy (E) is equal to the sum of the Internal Energy (U), the kinetic energy and the potential energy 
   • Conservation of Mass
     • Input - Output = Accumulation
       • dM/dt = rho*A*v
         • Mass flow rate = density * area of flow * flow velocity
         • dM/dt (In) = dM/dt (Out)
           • ONLY VALID FOR STEADY STATE SYSTEMS
           • Steady state will occur unless: - density changes - control volume changes size

3. Bernoulli's Equation

   • P(1)/rho*g + V(1)^2/2g + z(1) = P(2)/rho*g + V(2)^2/2g + z(2)
     • The total energy of the flow, assuming ZERO friction at the boundary, no temperature and no density changes, will be CONSTANT
   • Methods of Measuring Flow Velocity
     • Pitot Tubes
       • Work on the principle that: Stagnation head = velocity head + pressure head
       • P(1)/rho + v^2/2 = P(2)/rho
         • Hence dp/rho = v^2/2
     • Pitot-Static Tube
       • Height difference between static fluid and stagnant fluid equals velocity head
       • rho*v^2/2 = h(m)*g*(rho(m)/rho -1)
     • Venturimeter
       • Measures velocity by constricting flow and applying Bernoulli's
         • dP is measured with a manometer
       • Q(actual) / Q(ideal) = discharge coefficient
     • Orifice Plates

4. Conservation of Momentum

   • For fluid flow between two sections of a pipe
     • P(1)*A(1) - P(2)*A(2) = Rate of change of momentum