Chapter 8

Question 1

Laminar Flow

Answer 1

A flow regime characterized by high momentum diffusion and low momentum convection. When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow.

Question 2

Transitional Flow

Answer 2

The process of a laminar flow becoming turbulent is known as laminar-turbulent transition. This is an extraordinarily complicated process which at present is not fully understood.

Question 3

Turbulent Flow

Answer 3

A flow regime characterized by chaotic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time.

Question 4

Enterance Length

Answer 4

The entrance length is the length in a tube or duct after an obstruction until the flow velocity profile is fully developed. A fluid need some length to fully develop the velocity profile after passing through components like bends, valves, pumps, turbines or similar.

Question 5

Fully Developed Flow

Answer 5

Is when the viscous effects due to the shear stress between the fluid particles and pipe wall create a fully developed velocity profile for a fluid as it travels through the length of a straight pipe. The velocity of the fluid for a fully developed flow will be at its fastest at the center line of the pipe

Question 6

Wall Shear Stress

Answer 6

The shear stress in the layer of fluid next to the wall of a pipe.

Question 7

Poiseuille’s law

Answer 7

In the case of smooth flow (laminar flow), the volume flowrate is given by the pressure difference divided by the viscous resistance. This resistance depends linearly upon the viscosity and the length, but the fourth power dependence upon the radius is dramatically different.

Question 8

Friction Factor

Question 9

turbulent shear stress

Question 10

major loss

Answer 10

Head loss for laminar or turbulent pipe flow can be written in terms of the friction factor. (For major losses)

Question 11

minor loss

Answer 11

Head loss for laminar or turbulent pipe flow can be written in terms of the loss coefficients. (For minor losses)

Question 12

relative roughness

Answer 12

The ratio between absolute roughness an pipe or duct diameter - is important when calculating pressure loss in ducts or pipes with the Colebrook Equation. Relative roughness can be expressed as

r = k / dh (1)

where

r = relative roughness

k = roughness of duct, pipe or tube surface (m, ft)

dh = hydraulic diameter (m, ft)

Question 13

moody chart

Answer 13

Is a graph in non-dimensional form that relates the Darcy-Weisbach friction factor f_D, Reynolds number Re, and relative roughness(e/D) for fully developed flow in a circular pipe. It can be used for working out pressure drop or flow rate down such a pipe.

Question 14

colebrook formula

Answer 14

The friction coefficients used to calculate pressure loss (or major loss) in ducts, tubes and pipes can be calculated with the Colebrook equation

1 / λ1/2 = -2 log [2.51 / (Re λ1/2) + (k / dh) / 3.72]

where

λ = Darcy-Weisbach friction coefficient

Re = Reynolds Number

k = roughness of duct, pipe or tube surface (m, ft)

dh = hydraulic diameter (m, ft)

The Colebrook equation is only valid at turbulent flow conditions.

Question 15

loss coefficient

Answer 15

used for minor losses

K_L=

Question 16

hydraulic diameter

Answer 16

Is simply the diameter of the tube. Annulus. Square duct. Rectangular duct (fully filled). The velocity for the flow in the Reynolds equation is based on the actual cross section area of the duct or pipe. The hydraulic diameter is also used to calculate pressure loss in ducts or pipes. The hydraulic diameter is not the same as the geometrical equivalent diameter of a non-circular duct or pipe.

Question 17

multiple pipe systems

Answer 17

sum of the flows in = sum of the flows out

Question 18

orifice meter

Answer 18

is a device used for measuring flow rate, for reducing pressure or for restricting flow. (Consists of a flat orifice plate with a circular hole drilled in it. There is a pressure tap upstream from the orifice plate and another just downstream. There are in general three methods for placing the taps. The coefficient of a meter depends on the position of the taps.)

Question 19

nozzle meter

Answer 19

Used for determining fluid’s flowrate through pipes.

Question 20

Venturi meter

Answer 20

Flow measurement instruments which use a converging section of pipe to give an increase in the flow velocity and a corresponding pressure drop from which the flowrate can be deduced.