1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
160
EXPERIMENTAL INVESTIGATION OF CONVECTION HEAT TRANSFER
FOR LAMINAR FLOW IN AN INCLINED ANNULUS
Jawdat A. Yakoob*
, Ehsan F. Abbas**
Assist. Professor, Refrigeration and Air Conditioning Engineering Department,
Kirkuk Technical College, Iraq
ABSTRACT
The present paper investigate convection heat transfer for laminar flow in an inclined
concentrated with 54mm outside diameter and 800 mm length pipe. The pipe was exposed to
constant heat flux of 529 W/m2
by other internal tube which was an electric element with 6.3 mm
diameter and 600mm length. The pipe kit was rotated by ten declination angles, which were varied
from (0O
to 90O
) by 10O
for each step. Results showed that the effect of declination angle was
proportioned inversely with the value of heat transfer coefficient, where the maximum reduction in
value of heat transfer coefficient was obtained in vertical position, which was about 6.596%.
Reynolds number was also varied inversely with declination angle from 1750 to 1700. The
comparison between experimental results and correlation relation results, showed that both results
closed to each other up to declination angle value equal to (40o
).
Keywords: Convection Heat Transfer, Laminar Flow, Inclined Annulus.
Nomenclature
A : Area (m2
)
c : Specific heat capacity (J/kg.o
C)
D: Inside diameter of the pipe (m)
d : Outside diameter of the tube (m)
h: Heat transfer coefficient (W/m2
.o
C)
k: Thermal conductivity of air (W/m.o
C)
Q: Heat transfer (W)
r : Radius (m)
T: Temperature (o
C)
U: Velocity (m/s)
V: Volume (m3
)
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 4, April (2014), pp. 160-168
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IJMET
© I A E M E

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
161
Greek Symbols
θ: Angle of inclination (degree)
ߩ: Density of air (kg/m3
)
߬ : Time (s)
ߤ : Dynamic viscosity (N.s/m2
)
Dimensionless Groups.
Nu: Nusselt number,
௛.஽
௞
Pr: Prandtl number,
ఓ.௖
௞
Re: Reynolds number
௎೘.஽
ఓ
Subscripts
b : bulk
i : inlet
o : outlet
s :surface
w : wall
1, 2, 3, 4 : sequence of thermocouples on the electric element.
INTRODUCTION
In the study of thermodynamic the average heat transfer coefficient (݄ത) is used in calculating
the amount of convection heat transfer between a moving fluid and a solid. This is the most
important factor for evaluating convective heat loss or gain. The symbol (݄ത) is necessary for heat
transfer design calculation and widely used in thermal manufacturing processes, oil and gas flow
processes and air conditioning system[1]. Laminar flow heat transfer in annular pipe is encountered
in a wide variety of engineering applications as chemical vapor deposition reactor in the semi
conductor manufacturing industry[2]. Many theoretical and experimental investigations have been
performed to study the effect of an inclined annular pipe on the coefficient of heat transfer.
Mohammed A.[3], studied natural convection heat transfer in a vertical concentric annulus, the
results showed an increase in the natural convection with an increase in heat flux which leaded to an
improve in the heat transfer process. Salim K. T.[4] developed an experimental study for heat
transfer enhancement by laminar forced convection from horizontal and inclined tube with constant
heat flux, using two types of porous media. The results showed that the dimensionless temperature
distribution was decreased with an increase in dimensionless channel length for all cases by changing
Peclet number, heat flux and inclination angle. Shkarah J. A. et. al [5] investigated analytical study
of combined convection heat transfer for flow in a horizontal annulus, the obtained results for
velocity and temperature profile revealed that, the secondary flow created by natural convection has
a significant effect on heat transfer process. Kelvin C. S. et al.[6] studied unsteady heat transfer in
annular pipe by using dimensional analysis and commercial CFD codes provided by ANSYS CFX.
The results are compared with other similar cases found, they were in the vicinity of good
agreement. Mohammed A. A. et al.[7] carried out an experimental investigation on natural
convection heat transfer in an inclined circular cylinder. An empirical equation of average Nusselt
number as a function of Rayliegh number was deduced for each angle of inclination.
The purpose of this paper is to study the effect of an inclined annular pipe on the coefficient
of heat transfer in laminar flow experimentally.

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
162
EXPERIMENTAL APPARATUS
The used apparatus consists of a copper pipe of (54mm) outside diameter, (2mm) wall
thickness and (800mm) length, it was insulated with glass wool layer of (5mm) thick to avoid heat
loss to the surrounding. An electric element of (6.3mm) diameter, (82 ) electric resistance and
(600mm) length inserted into the pipe and supported at its center by two screws as shown in Fig.(1).
This kit was placed on a wood base designed to rotate the kit properly and adjusted at required
inclined angle value. Air was forced by centrifugal blower with flow rate of (0.6 m3
/s) connected to
the copper pipe by (54mm) diameter flexible rubber hose with 1m length. The apparatus provided
with 8 channel temperature data logger type Pico (TC-08) for temperature recording at 8 selected
location inside copper pipe with K-type thermocouples as shown in Fig. (1). A variac power supply
used to control supplied voltage to the electric element. Fig.(2) shows the photographic configuration
of actual apparatus test components.
Fig(1): Schematic diagram for pipe kit
Fig (2): Photographic of test apparatus

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
163
EXPERIMENTAL PROCEDURE
To achieve the experiments with working condition as illustrated in table (1), the following
procedures were followed:
a. The test apparatus prepared to insure the well performance of all components.
b. Adjusting the pipe kit at required inclined angle.
c. The supply power to the electric element was switched on, and it was adjusted by variac to
obtain constant required heat flux, then it was left in operation action for a period until the
surface temperature of electric element, annular space and internal surface of the pipe were
reached to steady state which was about (45 min.) then power supply was switched off.
d. The blower was switched on after the air flow rate was adjusted at a required amount by
throttle valve and digital anemometer was used to obtain the required amount of air flow rate.
This procedure was continued until the difference between input and output air temperature
reached to (0o
C).
e. During each experiment, at all selected temperature recording position the temperature
recorded by data logger for each interval time about of (30 sec), together with the potential
voltage and current input through the electric element by ammeter.
f. The procedures (b to f) were repeated by varying inclination angle from horizontal to vertical
status by (10o
) for each step.
Table (1): working conditions
Supplied voltage
24V AC
Current rate
0.3 A
Time of steady state
1200 sec.
Period of single test
1700 sec.
Heat flux
592 W/m2
Air velocity
0.6 m/sec.
Electric element surface temperature at
steady state condition
180°‫ܥ‬
CALCULATION OF DATA REDUCTION
To analyze the obtained value of heat coefficient, the following steps were done in each test.
During cooling process for the electric element for a period of (1700 sec.). A set of surface
temperatures of the electric element which were chosen from the recording data used to calculate the
average surface temperatures as follow:
ܶ௦
ഥ ൌ
்భା்మା்యା்ర
ସ
…………...………..(1)

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
164
The bulk temperature of air inside copper pipe is calculated as:
ܶ௕ ൌ
்೔ା்೚
ଶ
…………………….(2)
where the weight of the electric element is too light with respect to the surface area, this mean
that the conduction resistance was little compared with the convection resistance at the surface.
Therefore the lumped- capacity analyze law is suitable for the solution of this cases, where this law
assume that the internal resistance of the body can be neglected when compared with external
resistance[8]. Thus
ܳ ൌ ݄‫ܣ‬௦ሺܶ െ ܶ௕ሻ ൌ െܿߩܸ
ௗ்
ௗఛ
…….(3)
The initial condition is taken to be
ܶ ൌ ܶ௦
ഥ at ߬ ൌ 0
So that the solution of eq.(3) after integration will be as follow:
ln ቂ
்ି்್
்ೞഥ ି்್
ቃ ൌ െ ቂ
௛஺ೞ
ఘ௖௏
ቃ ߬ ……...…………(4)
Let ݉ ൌ ቂ
௛஺ೞ
ఘ௖௏
ቃ
ln ቂ
்ି்್
்ೞഥ ି்್
ቃ ൌ െ݉߬ ……………...….(5)
The value of m was calculated by two methods [9], the first method was done by applying
eq.(5) which suggest that a plot of െ ln ቂ
்ି்್
்ೞഥ ି்್
ቃ against t should yield a straight line of slope m. and in
the second method, the value of m was calculated by mean slope value as follow:
݉ ൌ
ି ∑ ୪୬൤
೅ష೅್
೅ೞതതതതష೅್
൨
∑ ௧
………………….(6)
The value of heat transfer coefficient calculated by applying following relation:
݄ ൌ
ఘ௖௏
஺ೞ
ൈ ݉ ………………….(7)
RESULTS AND DISCUSSION
From a set of data were obtained from ten tests with different declination angle of pipe by
changing the declination angle of the kit from (θ=0O
to θ=90O
). The value of (h) in all tests were
obtained by analyzing the data according to equations (6 and 7). The results of the numerical solution
were indicated that the value of (h) related inversely with an increase in the value of declination
angle, these values which were arranged between maximum value (5.055 w/m2
.o
C) at θ=0O
and
minimum value (4.721 w/m2
.o
C) at θ=90O
as shown in Fig.(3). Therefore the reduction ratio of (h)
for the former values was about of (6.6%). Since this reduction ratio is too small, so that this function
can be neglected especially in laminar flow. This fact emphasized by [1], where they were worked in

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
165
similar case, but in different pipe diameters. To compare the results of present steady by using
correlation which was used by [1], as
ܰ‫ݑ‬஽
തതതതതത ൌ 0.182ܴ݁஽
଴.଺ଷ
ܲ‫ݎ‬
భ
య ……………...(8)
where,
ܴ݁஽ ൌ
௎೘஽
ఓ
……………….(9)
and
‫ܦ‬ ൌ ሺ‫ܦ‬௜ െ ݀ሻ ...……………..(10)
The correlation value of heat transfer coefficient calculated by
݄ത ൌ
ே௨ವതതതതതതത௞
஽
…………………(11)
Properties of air are evaluated at bulk temperature (ܶ௕) . By applying equations (8 to 11). The
results showed that the flow regime of air in all tests was laminar in which were the values of Re
arranged between (1750 to 1700) when the pipe kit varied from the horizontal to vertical status as
shown in Fig.(4). The results which were obtained from applying equations (8 to 11) indicated that
the values of average heat transfer coefficient were not affected essentially with declination angle as
shown in Fig.(3). Table (2) shows that the amount of reduction in values of average heat transfer
coefficient for each of experimental test and empirical relation. The maximum reduction in value of
average heat transfer coefficient obtained by experimental test at vertical status with (6.596%), but
the calculated values of reduction in empirical relation was too small. Particularly in vertical status
which was approximately about of (0.19988%). The results of each of the experimental tests and
correlation relation were closed to gather up to 40O
.
Fig (3): Relation between heat transfer coefficient and declination angle
4
4.5
5
5.5
6
0 10 20 30 40 50 60 70 80 90
h(W/m2.oC)
θ (Degree)
Experimental Values Emperical Values

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
166
Fig(4): Relation between Reynolds number and declination angle
Table (2): Value of (m) at each pipe kit position status
θ (Dgree) ܶ௦ሺԨሻ ܶ௕ሺԨሻ ݉ ൌ
െ ∑ ln ቂ
ܶ െ ܶ௕
ܶ௦ െ ܶ௕
ቃ
∑ ߬
ሺ‫ݏ‬ିଵ
ሻ
0 180.49 16.83 0.003761
10 180.65 17.06 0.00375
20 180.52 17.24 0.003736
30 180.28 16.92 0.003724
40 180.25 16.57 0.003708
50 180.20 16.41 0.003691
60 180.28 16.91 0.003667
70 180.61 17.16 0.003642
80 180.43 17.19 0.003588
90 180.32 17.14 0.003513
1500
1600
1700
1800
0 10 20 30 40 50 60 70 80 90
Re
θ (Dgree)

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
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Table (3): Reduction in values of heat transfer coefficient
CONCLUSION
The experimental result of present study showed a limited effect of declination angle on the
average heat transfer coefficient in laminar flow inside two concerted pipe.
REFERENCES
[1] Manobar K. and Ramroop K.,A comparison of correlation for heating from Inclined pipes,
International Journal of Engineering (IJE), Volume (4), Issue (4), Oct. 2010, pp.268-278.
[2] Ismael K.A., Hussain I.Y. and Mohammed A.A., Experimental investigation of laminar
mixed convection in an inclined annular, Journal of Engineering, Volume (12), No.1, March
2006, pp.181-198.
[3] Mohammed A.A., Natural convection heat transfer in a vertical concentric annulus, Journal
of Engineering, Volume (13) No. 2, June, 2007, pp.1417- 1425.
[4] Salim T.K., An experimental study for heat transfer enhancement by laminar forced
convection from horizontal and inclined tube heated with constant heat flux, using two types
of porous media, Tikrit Journal of Engineering and Sciences, Volume (15), Issue (2), June,
2008, pp.15-36.
[5] Shkarah A.J., Hasan M.I. and Eraebee I. K., Analytical study of combined convection heat
transfer for flow in horizontal annulus, Thi-Qar University Journal for Engineering Sciences,
Volume (2), No. (2), May, 2011, pp.26-40.
θ (Dgree) Experimental test Correlation Relation
0 0 0
10 0.294% 0
20 0.684% 0.0199%
30 0.998% 0.0199%
40 1.421% 0.0497%
50 1.862% 0.0497%
60 2.503% 0.0596%
70 3.160% 0.1988%
80 4.598% 0.1988%
90 6.596% 0.1988%

9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 160-168 © IAEME
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[6] Kelvin H.C., Yousif A.A. and Andrew C., Unsteady heat transfer in an annular pipe, Part II:
Swirling laminar flow, IIUM Engineering Journal, Volume (12), No. (6), 2011, Special Issue
in Science and Ethics, pp.79-95.
[7] Mohammed A.A., Mashkour M.A. and Ahmed R.S., Natural convection heat transfer in an
inclined circular cylinder, Journal of Engineering, Volume (17), No.(4), August 2011,
pp.659-674.
[8] Holman J. P., Heat transfer, 8th
edition, McGraw-Hill, 1997, pp.142-143.
[9] Mehrabian M.A., Heat transfer and pressure drop characteristics of cross flow of air over a
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[13] S.K. Dhakad, Pankaj Sonkusare, Pravin Kumar Singh and Dr. Lokesh Bajpai, “Prediction of
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(IJMET), Volume 4, Issue 4, 2013, pp. 259 - 265, ISSN Print: 0976 – 6340, ISSN Online:
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