atw - International Journal for Nuclear Power | 06.2021

atw Vol. 66 (2021) | Issue 6 ı November
RESEARCH AND INNOVATION 38
Convection heat transfer is affected
by geometry parameters of enclosure
such as position and area of vents.
There has been limited research
considering such parameters and,
therefore, this found the motivation
behind the present experimental
study. In this present work, cylindrical
heat sources were used, which can be
used to model fuel pins inside a
nuclear reactor or spent fuel inside
spent fuel storage. Heat transfer
through a 2x2 array of heat sources in
square configurations was studied.
Heat transfer between heat sources
and air was tabulated and compared
in different arrangements of the
outlets present on the enclosure. The
results were then plotted showing the
relation between Nusselt number and
modified Rayleigh number.
2 Mathematical Modeling
The equations used for the present
system were:
Q in = P(2.1)
Q out = Q in = V × I(2.2)
Due to small thickness of aluminum
tube, all the heat from the heat source
is conducted to the outer surface.
Q out = Q conduction =Q convection + Q radiation
(2.3)
Q convection = h avg A s (T s,avg – T b )(2.4)
Where, h avg is the average heat
transfer coefficient.
And
For calculating the local heat transfer
coefficients, the following formula
was used.
Q convection = h x A s (T x – T b )(2.5)
Heat losses through radiation can be
calculated by:
(2.6)
ε is 0.04 for Aluminum and σ is
5.67x10 -8 W/m 2 K 4 . Due to small
emissivity of Aluminum and a very low
value of σ, radiation can be neglected
and it can be assumed that all the heat
transfer from the outer surface of heat
sources is via con vection.
The formulae for Nusselt number
and modified Rayleigh number are:
(2.7)
(2.8)
(a)
| Fig. 1.
Thermocouple locations (a) front view of a heat source (b) Top view of the enclosure.
3 Experimental Setup
Four identical sources each having
a diameter of 50.8 mm and a
slenderness ratio of 6.1 were manufactured.
Each of these heat sources
had a rated power of 1000 W. Outer
surface of heat sources was made of
Aluminum. Each of the heat sources
was equipped with four K-type
thermocouples, the positions shown
in Figure 1. In Figure 1(b), the stars
show the thermocouple facing
the flow channel and the triangles
represent the thermocouples on the
opposite side of the flow channel.
The heat sources were placed
inside a wooden enclosure of dimensions
20”x20”x20”. There were three
outlets of same size (4”x2”) in the
enclosure, one at the top and one
each on right top and left top of the
enclosure. For the measurement of
the ambient temperature, a thermocouple
was installed near inner
boundary of the wooden enclosure.
To convert the data provided by the
thermocouples into temperatures,
PANGU data acquisition system was
| Fig. 2.
Experimental setup.
(b)
used. All these components of the
experimental setup are shown in
Figure 2.
In this research work, data
acquisition system was used which
had a calibration uncertainty of 1 °C
and data scatter was observed to be
5.1 °C. Total uncertainty in measurement
of temperature was calculated to
be 4.8 %. Uncertainty in voltage
was 1 % with a full scale reading of
600 V and in current, the uncertainty
was 1.5 % with a full scale reading of
10 A. Anemometer that was used
for the measurement of velocity of air
had an uncertainty of 0.03 m/s.
Also, different dimensions that
were measured e.g., diameter of the
aluminum pipes, length of aluminum
pipes and size of inlet and outlet vents
had an uncertainty of about 2 mm.
Each experiment was repeated thrice
so that the results are reported with
precision and accuracy. Mean values
were shown in the graphs and error
bars were displayed, representing
standard deviation in the results.
4 Results and Discussions
In the experimentation phase, the
outlet configuration was first
optimized to give best heat transfer
and then the further experimentation
was carried out using different heat
fluxes.
4.1 Optimization of Outlets
Configuration
Five cases were studied, each case
differing from the other on the basis of
locations of the outlets’ opening.
In the natural convection case, top
outlet was opened and inlet at the
bottom was opened, but the fan was
remained switched off. Air flowed
freely and naturally from the bottom
and exited through the top outlet. In
other four cases, bottom inlet was
opened with the fan operating at a
Research and Innovation
Experimental Study of Convective Heat Transfer Through Fuel Pins of a Nuclear Power Plant ı Atif Mehmood, Ajmal Shah, Mazhar Iqbal, Ali Riaz, Muhammad Ahsan Kaleem and Abdul Quddus