ENG 103 Fluid Mechanics

Mid-Term Exam

Section I. Concept Problems [25%]

1. [5 points] Continuum means that the fluid properties vary continuously in time. Is this statement correct or not? If not, justify your answer.

2. [5 points] Write down three flow lines.

3. [5 points] Which velocity is used in the control volume flow term, absolute flow velocity or relative flow velocity when they are different?

4. [5 points] There are four laws of mechanics that are relevant to fluid mechanics. Write down at least three of them.

5. [5 points] Energy per unit mass includes the internal energy, kinetic energy, and potential energy.   However, we usually do not compute or require the internal energy explicitly when we solve a steady and 1-D energy equation. What is the reason for this?

Section II. Equation Problems [75%]

Problem 1. [25%] Gate AB in figure is 1.2 m long and 0.8 m into the paper. Neglecting atmospheric pressure, compute the force F on the gate (10%) and its center of pressure position X that is a distance measured from A (15%). 

Problem 2. [25%] Water enters and leaves the 6 cm diameter pipe bend in figure at an average velocity of 8.5 m/s. The horizontal force to support the bend against momentum change is 300 N.

(a)  Find the angle 。(15%)

(b)  Determine the vertical force on the bend. The positive sign of the force directs upward. (10%)

Problem 3. [25%] The long pipe in figure is filled with water at 20 °C. When valve A is closed, p1 − p2 = 75 kpa. When the value is open and water flows at the same speed in the pipe at 500 h/m3, p1 − p2 = 160 kpa. What is the friction head loss between 1 and 2, in m?