ARTIFICIAL ROUGHNESS

1. Project on-
ARTIFICIAL ROUGHNESS
IN
SOLAR AIR HEATER

2. Introduction
Solar Energy
Solar energy is radiant light and heat from the Sun that
is harnessed using a range of ever-evolving technologies
such as solar heating, photovoltaics, solar thermal
energy, solar architecture, molten salt power plants and
artificial photosynthesis.

3. Scope: India and the World
India has tremendous scope of generating solar
energy.
The geographical location of the country stands to its
benefit for generating solar energy.
The reason being India is a tropical country and it
receives solar radiation almost throughout the year,
which amounts to 3,000 hours of sunshine.
This is equal to more than 5,000 trillion kWh. Almost
all parts of India receive 4-7 kWh of solar radiation
per sq. metres.

4. This is equivalent to 2,300–3,200 sunshine hours per
year.
Being a non- polluting and free source of energy, that
is sustainable and non- exhaustible, solar energy has
become a powerful source of power supply in the
contemporary world.

5. Types of Solar Energy
Solar energy, which is renewable, widely available and clean,
provides enough energy to meet the world’s annual consumption
needs every 50 minutes. The challenge is to collect a share –
however small – of this heat and radiant energy.
Two major technologies have been developed to harness it:
 Photovoltaic solar technology, which directly converts sunlight
into electricity using panels made of semiconductor cells.
 Solar thermal technology, which captures the sun’s heat.
This heat is used directly or converted into mechanical
energy and in turn electricity, known as concentrated
solar power . This heat is used directly (low-temperature solar
thermal) or converted into mechanical energy and in turn
electricity (concentrated solar power – CSP).

6. Solar Air Heater
 Solar air heating is a solar thermal technology in which the
energy from the sun, insolation, is captured by an absorbing
medium and used to heat air.
 Solar air heating is a renewable energy heating technology
used to heat or condition air for buildings or process heat
applications.
 It is typically the most cost-effective out of all the solar
technologies, especially in commercial and industrial
applications, and it addresses the largest usage of building
energy in heating climates, which is space heating and
industrial process heating.

8.  The objective function of the project is to find out
the relationship between various parameters* with
respect to others by changing the shapes of ribs
accordingly and test their efficient heat transfer.
 Second thing is to review various research papers,
in which different artificial roughness elements are
used to enhance the heat transfer rate with little
penalty of friction.

10. Artificial roughness is basically a heat transfer enhancement
technique by which thermo hydraulic performance of a solar air
heater can be improved.
The thermal efficiency of solar air heater is generally poor due to
low heat transfer coefficient between the absorber plate and the air
flowing in to the duct due to the formation of laminar sub layer on
the absorber plate which acts as heat transferring surface.
So there is a need to break the laminar sub layer. Artificial
roughness, provided on the underside of the absorber plate ,creates
local wall turbulence.

11.  Secondary recirculation flows further enhance the convective heat
transfer.
 Flows from the core to the surface reduce the thickness of boundary
layer and secondary flows from the surface to the core flow
promote mixing.
 Energy for creating turbulence has to come from a blower and
excessive turbulence results in greater power.
 Therefore, it is desirable that the turbulence must be created only in
the region very close to the heat transferring surface, so that the
power requirement may be reduced.

13.  Artificial roughness applied on the absorber plate is the most efficient
method to improve thermal performance of solar air heaters.
 Experimental investigations appropriate to distinct roughness
geometries shows that the enhancement in heat transfer is
accompanied by considerable rise in pumping power.
 Several studies have been carried out to determine the effect of
different roughness element geometries on heat transfer and friction in
solar air heaters.

14. Fig. Ribs shape

17.  Energy in various forms has played an increasingly important
role in worldwide economic progress and industrialization.
 Solar energy is considered a vital energy source to meet the
increased energy demand for sustainable development and to
control the global climate change.
 The freely available solar radiation is infinite, non-polluting
resource of solar energy.
 The easiest way to bestow solar energy is to convert it into
thermal energy by using solar air heaters.
 Among different types of solar thermal systems, solar air heaters
are widely used systems due to lower cost and simplicity in
design.
 Direct as well as diffused solar radiations are absorbed at the
absorber plate and transferred to the air that flows through the
passage underneath the absorbing surface.

18.  The thermal efficiency of solar air heaters is depending on the
useful heat gain by the collector fluid.
As the value of heat transfer coefficient for air is low which
reduces the heat transfer rate and thus increases the heat loss to the
surroundings.
It is believed that the formation of laminar viscous sub-layer over
the heated surface offers thermal resistance to heat transfer.
The methodology of any passive technique of heat transfer
enhancement is directed towards creating disturbance in the flow
by using irregular surfaces.
A popular passive technique of heat transfer enhancement is the
application of artificial roughness on the underside of absorber
plate in the form of ribs, grooves, dimples, winglets, baffles,
twisted tapes, mesh wires, etc.

19. Fig. CAD model for SAH

20. Fig. Actual figure of SAH made in lab

21.  Use of artificially roughened surfaces with different type of
roughness geometries of different shapes, sizes and orientation is
found to be the most effective technique to enhance the heat transfer
rate with little penalty of friction.
 Roughness in the form of ribs and wire matrix were mainly
suggested by different investigators to achieve better thermal
performance.
 Among all, rib roughness was found the best performer as far as
thermal performance is concerned.
 In artificially roughened solar air heaters, there is lot of scope for use
of flow visualization techniques in order to analyse flow and heat
transfer enhancement processes.

22.  In artificially roughened solar air heaters, there is lot of scope for
use of flow visualization techniques in order to analyse flow and
heat transfer enhancement processes.