## Introduction: its wall can create whirling currents in the

Introduction:

Fluids that flow through ducts &
pipes are normally utilized as a part of fluid distribution setups , heating
and cooling applications.
The fluids in these applications are typically constrained by a pump or a fan
to course through a flow
segment.

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But there are things that act as
obstacles to the fluids during their flow inside the pipes & ducts which
are: Friction (causes resistance),pressure drop and head loss and they are
closely related to each other.

For instance, when a fluid flows through
a rough pipe, its wall can create  whirling currents in the fluid which makes
resistance to the flow of the fluid. Pipes with smooth walls like copper, glass
and brass have a little influence on the frictional resistance. But pipes with rough
walls like concrete and steel create bigger whirling currents which will
sometimes significantly affect the frictional resistance. and when the flow
faces obstacles , it will lose its velocity so the pressure becomes low. So is

internal flow has three kinds:

1.      laminar flow (a):

Smooth flow
with organized motion. If it is
overheated, it will make black spots and fouling in the tube or what contains
it.

2.      Turbulent flow(b):

Higher Velocity
with  disturbed motion. Used in heating
and has less fouling and less black spots

3.      Transition flow:

The flow sometimes is laminar and sometimes is
turbulent.

Reynolds Number:

When the fluid is turned from laminar to turbulent, the flow
rely on the forces of inertia and viscosity. The Reynolds number of a flowing
fluid is the inertia force of the fluid which is velocity multiplied by the
diameter divided by the kinematic viscosity .

1

Velocity boundary layer:

The flow region that influences the viscous shear forces that
resulted from fluid viscosity.

Boundary layer region:

The velocity changes  and the viscous effects and the velocity
changes are important.

Irrotational flow
region:

The frictional influences can be ignored and velocity stays
fundamentally constant in the direction of radiu

Application of the internal
flow:

Direct solar water heaters:

They are appliances that give hot water constantly by heating
water using the solar energy and the fluid that is used in the pipes is water. The
whole process starts with linking pipes that bring the cold water to the cylinder
and the solar panels or cells have pipes circle with the cylinder to provide
heating to the whole cylinder and that is how the water gets heated.

·
The
heat capacity of water at 20?C is  4.2
J/(g.K):

When picking a heat transfer fluid inside the pipes, a high
value of specific heat capacity is fundamental because when  the value is high , the fluid energy will be
higher and the fluid will raise in temperature, and the system will be more
efficient.

·
Water is not toxic.

·
Water has a low viscosity so it flows smoothly.2

·
Low cost:

The solar energy is from the sun so it’s free. The water is cheap and
can be free.

·
The availability of the solar energy:

You can take the energy anytime even if the weather is cloudy or at
night because the solar cells store it.

·
The system is green:

It helps the environment because it does not release harmful gases.3

·
The location:

The solar cells needs to be in a place where they are exposed to the sun
so they can absorb the energy like in a roof. The hot water cylinder needs a
suitable location to place it.

·
Water:

It  has a high freezing point and
a low boiling point which means it is harder for it to get hotter .

·
Maintenance:

The pump and the antifreeze needs to be checked every year to make sure
they work perfectly.4

Conclusion:

Direct solar water heaters are good heaters and cheap but the disadvantages

are bad especially if the person who intend to have does not have enough
space

to place the solar panels or cells. The person might not have a roof or
a back

yard and that is a big problem because many people live in hotels with
no water

heating or buildings apartments
and they need hot water in winter especially .

for those kind of people i suggest they use electric water heaters which give

hot water by using
electricity and even though they are  expensive and not so green

to the environment, it is more efficient and
easier to install since the electricity is in

every house and apartment.5

Another suggestion is water
heating by fuels. Even though it is so old and not good for

the environment, the fuels that you can use in
the pipes are many so you have the

choice which do you want to choose and it is
cheap.6