FIELD OF INVENTION
The present invention relates to a method of enhancing emissivity of thermal radiation for boiler
radiative surfaces by depositing carbon nano coating.
BACKGROUND OF THE INVENTION
No coating whatsoever is provided in the boiler heat transfer surfaces as of now, to enhance the
thermal radiation. Emissivity of thermal radiation for typical boiler radiative heat surfaces is 0.6-
0.8. Emissivity of thermal radiation for carbon nano tube (CNT) coated boiler radiative heat
surfaces is 0.98-0.99 due to primary material of carbon nano tube (CNT) is carbon.
When fuel burns in a boiler furnace it releases a large amount of energy, which heats up products
of combustion (flue gas) to a very high temperature. This temperature may range from 1500° C to
1600° C in flame core. Though the products of combustion are cooled by super-heaters and
evaporators in furnaces, their temperature at exit of furnace are still in range of 1000-1250° C.
Flame transfers its heat energy to heating surface in furnace by radiation. Because flue gas flows

through the furnace at a low velocity, corrective heat is only a small fraction (about 5%) of the
total heat transferred to the walls in a conventional boiler furnace. Thus, only radiative heat
transfer is considered in furnace.
The emissivity of flame varies both leterally and axially and for heat transfer calculations the
emissivity of radiative heat transfer should be considered.
OBJECTS OF THE INVENTION
1. It is an object of the invention to propose a method of enhancing emissivity of thermal
radiation for boiler radiative surfaces by depositing carbon nano coating, which is capable of
enhancing the emissivity of thermal radiation for boiler and radiative surfaces.
2. Another object of the invention is to propose a method of enhancing emissivity of thermal
radiation for boiler radiative surfaces by depositing carbon nano coating, which can improve
the boiler heat transfer efficiency of pulverized coal fired boilers.
3. A further object of the invention is to propose a method of enhancing emissivity of thermal
radiation for boiler radiative surfaces by depositing carbon nano coating, which is able to
provide a non-sticky effect on the boiler heat transfer surfaces to prevent ash deposition on
the boiler heat transfer surfaces.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figures of the accompanying
drawings in which:
Figure 1 shows the experimental setup to establish the method according to the invention.
Figure 2 shows the internal walls of the tube coated with carbon nano tubes.
Figure 3 shows a graph to compare the emissivity between a plain tube and CNT coated tube.
DETAILED DESCRIPTION OF THE INVENTION
The emissivity of thermal radiation of a typical boiler radiative heat surfaces is 0.6-0.8. After
thorough research and experiment, it has been established that the emissivity of thermal radiation
for boiler radiative heat surfaces can be enhanced to 0.98-0.99 in an extensive spectral range from
O.IJJ. to lOOp.. The absorbity 0.98-0.99 in this said extensive spectral range is achieved to nano-
scale structure of the block coating, demonstrating capability most similar to black body. The
carbon nano tube (CNT) coated thermal radiative heat transfer surfaces of boiler are done by using
various coating techniques. The heat transfer efficiency will be increased when the carbon nano
tube (CNT) coating is applied on boiler radiative heat surfaces.

The emissivity of thermal radiation for carbon nano tube (CNT) coated boiler radiative heat surfaces
is enhanced to 0.98 to 0.99 due to base material of carbon nano tube (CNT) is carbon. Because of
this enhancement of emissivity of thermal radiation for boiler radiative heat surfaces, the efficiency
of the boiler is improved. The carbon nano tube coated thermal radiative heat transfer surfaces of
boiler are developed by using various coating techniques.
Emissivity is unit less dimension. The radiative heat transfer depends on emissivity, heat transfer
surface area in (m2) furnace flame temperature and metal skin temperature. If emissivity increases
in boiler radiative heat transfer surfaces, radiative heat transfer rate will be increased. In the
present invention CNT coating has enhanced the radiative heat transfer rate. First, this has been
established with experimental work, as depicted below.
EXPERIMENT
Figure 1 shows the assembly in which the experiment is carried out. The assembly consists of a
hollow cylinderical stainless steel tube (1) where the inner surface of the tube is coated with a thin
layer of carbon nano tubes by a special deposition technique. A resistive coil (2) made of a high
melting point material is used to transfer / input a thermodynamic equivalent of 5KW energy into
the system primarily by radiative heat transfer. The overall temperature of the system is

maintained by a regulatory supply of water which is made to pass through the cold inlet (3) and
evolves out through the hot zone (4). We assign the temperature at the cold end to be Tl and at
the hot outlet to be T2. The water from the hot outlet is cooled by a condenser assembly (5) and
again fed back to the system through a mortar pump (6) thus completing the closed cycle loop.
The surface temperature of the radiative surface is controlled by a temperature controller (7)
connected to the system. The heat transfer rate of the uncoated as well as the carbon nano tube
coated stainless steel tube (internal coating) is arrived at by calculating the mass flow rate of the
coolant as well as the temperature gradient.
Carbon nano tubes due to their reported high heat absorption rates behave closely to ideal black
bodies and can be employed as candidate materials for boiler plant related. For achieving the
same, the internal walls of the tube in the design shown in Figure 2 are coated with carbon nano
tubes and a performance evaluation of emissivity is made for the uncoated (plain tube) vs the
carbon nano tube coated (tube internal coating) system.
An input power of 5KW is fed to the system, one consisting of a plain tube and the other consisting
of a coating of the inner walls with carbon nano tubes. Because of the normal emissivity range of
most materials in bulk from lies in the range of 0-6-0.8, the heat transfer rate in our experiments
conducted ranged from 3250-4000 KW/m2 with the emissivity ranging from 0.60-0.80. However

the heat rate was greatly enhanced with a coating carbon nano tubes and ranged from 4750-4950
KW/m2 due to the increase in emissivity range to 0.95 to a maximum of 0.99 as shown in Figure 3.
Figure 3 shows a comparison of emissivity between plain tube and CNT coated tube. In view of
these encouraging results, we have used carbon nano tube coating to enhance emissivity of
thermal radiation for boiler radiative surfaces.

WE CLAIM
1. A method of enhancing emissivity of thermal radiation for boiler radiative surfaces by
depositing carbon nano tube coating comprising:
- depositing carbon nano tube coating on boiler radiative surfaces for enhancing the
emissivity of thermal radiation;
characterized in that,
- the emissivity of thermal radiation for carbon nano tube (CUT) coated boiler radiative heat
surfaces enhances from 0.6-0.8 to 0.98-0.99.
2. A method of enhancing emissivity as claimed in claim 1, wherein the coating provides non
sticky effect which prevents ash deposition on the boiler heat transfer surfaces.

The emissivity of thermal radiation for carbon nano tube coated boiler radiative heat surfaces
enhances from 0.6 to 0.8 to 0.98 to 0.99 when carbon nano tube coating is deposited on boiler
radiative surfaces. The coating provides non-sticky effect to prevent ash deposition on the boiler
heat transfer surfaces.