IJMEIT// Vol.

04 Issue 10//October//Page No: 1791-1796//ISSN-2348-196x 2016

Experimental Study of Performance of Pin Fin Heat Sink under Forced Convection
Authors
R. Muthukumarn1, R. Rathnasamy2, R. Karthikeyan3
Department of Mechanical Engineering, Annamalai University, Annamalainagar, Tamil Nadu, India
Email: armuthu26@gmail.com
ABSTRACT-
An experimental investigation was performed to study the heat transfer and pressure loss characteristics in
a horizontal rectangular wind tunnel having attachment of cylindrical, grooved cylindrical and perforated
pin fins over a horizontal based pin fin assembly. The experiments covered the rates from 2000-25,000 and
the clearance ratio (C/H) = 0.0. In-line Pin fin arrangements were studied for one constant span wise pitch
(Sx /d=1.2) and three different stream wise pitch (Sy /d = 1.2, 2.4 and 3.6) distance. Nusselt number and
pressure drop were considered as performance parameters. The performance of all the pin fins compared to
each other. The maximum enhancement in Nusselt number corresponds to the grooved cylindrical fin and
the results were matching with previous reports.
Keywords — Pin-fin, duct flow, perforated, Wind Tunnel, Grooved cylindrical, Nusselt number, Reynolds
number.
local Nusselt number and turbulent flow structure
1. INTRODUCTION characteristics in a pin fin channel and their study
This Heat transfer enhancement strategies are revealed that the unsteadiness in the wakes, the shear
classified in two major categories as active and layers formed between the wake and the high speed
passive methods. Active methods required external main stream flow. Sara [7] presented the
power to enhance heat transfer and passive methods characteristics of heat transfer and friction and
do not require external power. One of the most analyzed the convective heat transfer through a
effective methods in heat transfer enhancement is the rectangular channel with pin fins of square cross
use of extended surfaces or fins are example of sectional and attached over a flat surface; the pin fins
passive that are commonly used in various types of were arranged in a staggered manner, with varied
industrial applications such as heat exchanger, clearance ratios C/H. Chang et al. [8] investigated the
furnace design, electronic cooling devices, thermal effects of pin-tip leakages on the end wall heat
regenerators, internal cooling system of gas turbine transfer and entry-to-exit pressure drop
[1]
blades and turbo machines. Shaeri and yaghoubi. performances in the pin–fin channel. They found
Requirement of enhanced heat transfer has been very that the channel pressure drops decrease
much essential in electronic and industrial significantly with moderate heat transfer reductions
components designing because this may cause by opening small gaps between the pin-tips and the
severe overheating problems and occasionally leads channel end wall. Jubran et al. [9] reported on an
to failure of the system. Pin fins are cylinders or experimental investigation to study the effects of
other shaped elements that are attached shroud clearance, optimum inter-fin spacing in both
perpendicular to a wall. Various parameters span wise and stream wise directions. In a study
characterize the pin fins, such as height, shape, performed by Tahat et al. [10] in a channel with
diameter, and height to diameter ratio. Sahin and rectangular cross section equipped with needle fins,
demir, Tahat et al [2, 3]. Metzger et al. [4] and Chyu et the effects of the distance between fins, the space
al. [5] revealed that the pin height-to-diameter ratio, above them and their in-line and staggered
in-line or staggered and fin cross-sectional shape, arrangement on heat transfer were investigated
etc. are crucial parameters in determining the heat experimentally. Shaeri and yaghoubi [11] investigated
transfer and friction factor. Ames et al. [6] studied the thermal performance of three dimensional

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IJMEIT// Vol.04 Issue 10//October//Page No: 1791-1796//ISSN-2348-196x 2016
incompressible laminar flow from heat sinks by data unit. The working an open circuit suction mode
using perforated and solid fins attached on a flat wind tunnel was used for this investigation.
surface are studied numerically. Higher
performances for perforated fins are observed and
effectiveness increased by increasing number of
perforations. sahin and demir [12] Studied heat
transfer enhancement and pressure drop of
perforated pin fins. Enhancement effectiveness
varied between 1.1 and 1.9 depending on the
clearance ratio and inter fin spacing ratio and
optimum design parameters and level were
investigated. Ganesh Murali et al. [13] examined the Fig. 1 Line diagram of Experimental setup
transfer of heat and mass in the radiating type of pin
fin with reference to the array pattern in a A. Wind tunnel:
rectangular channel. The experimental investigation Wind tunnel designed of 19 mm thick plywood and
on the grooved type of flat fin, conducted by Ashish the total length of the tunnel is 2 m with constant
and Anil. [14] signified the forced convection in internal width of 150 mm. centrifugal blower
exposing the characteristics of the heat transfer. supplies air to the test section with required flow rate
Jaideep et al. [15] In this study heat transfer controlled by operating gate valve. The power was
enhancement mechanisms are evaluated for the hot capable of providing a maximum flow rate of 0.242
side of a TEG system generating power from waste Kg/sec. The heated air from the pin fin assembly
heat in automobile exhaust gases. The use of pin fins was passed through an insulated chamber, were
was examined, as they are a common and effective mixing was accomplished by two cardboard
way to increase heat transfer in a channel. Meriam et honeycombs mounted perpendicular to the flow
al. [16] Investigated staggered arrays having a stream, one being relatively low porosity and the
geometry of Sx /d=2.5and H/d=2 it was reported that other of higher porosity. A differential manometer
end wall heat transfer and pressure loss was employed to measure the pressure drop across
measurement. The friction factor is decreasing with calibrated orfice plate to indicate mass flow rate of
increasing spacing. air.
The review of the literature showed a variety of B. Pin-fin assembly:
modifications and the alterations of the fins by It consists of rectangular base having dimensions are
introducing the holes, slits and struts, which 250 mm length, 145 mm width and 25.4 mm
enhanced the heat transfer. Application of thickness. The tested fins and rectangular base plate
perforation and grooves on the fin surface is were made from duralumin because of consideration
justifiable not only because of material saving but of conductivity, machineability and cost.
also due to ease in manufacturing and cost. In the
present work involves experimentally investigated
heat transfer and friction loss characteristics for in
line pin fin array of cylindrical, grooved cylindrical
and perforated fins in a rectangular channel with
considering different geometric and flow parameters.

2. EXPERIMENTAL SETUP
The schematic diagram of the experimental setup is
shown in Fig. 1. This experimental setup consisting Fig. 2 (a) Cylindrical Fin (b) Grooved cylindrical Fin
of a wind tunnel, pin fin assembly, heater unit and (c) Perforated Fin

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The array cylindrical fins diameter 10 mm and Table 1. Experimental Parameters For Pin-Fin and
height 90 mm size, the grooved cylindrical fins Their Values
diameter of 10 mm with height 90 mm size. The
Minimum Maximum
cylindrical fin was subsequently grooves of diameter Parameters
value value
2 mm with height 4 mm sizes are formed over the Spacing of the pin fin [Sx] 12 mm 12 mm
surface by machining. The perforated fins at the 19.5 Spacing of the pin fin [Sy] 12 mm 36 mm
mm from bottom tip of those by a 4 mm diameter Rate of flow [m] (kg/s) 0.069 0.143
drill bit. The values of the relative stream wise pitch Clearance ratio [C/H] 0.0 0.0
(Sy/d = 1.2, 2.4, 3.6) and the relative span pitch (SX/d Fin count [Nxy] 30 48
=1.2) were kept constant. The clearance ratio
Reynolds number [Re] 2000 25000
(C/H=0.0) between the tips of the pin-fins and
Diameter of pin-fin [d]
shroud .the pin fins are attached on the upper surface 10
(mm)
of the base plate. The pin fins can be easily removed Height of pin-fin [H]
90
and replaced with studs made from the same as the (mm)
assembly base. Base plate W x L
145 x 250
(mm*mm)
C. Heater unit
Base plate temperature
The heating unit mainly consisted of an electrical [tb](oC)
50 ±0.25
heater, the heat exchanger was heated uniformly by
plate heater having of 1500 W, the lower horizontal Table 2. Distance Between Pin-Fins and Number of
surface and sides of the heater block were insulated Pin-Fins
thermally with 80 mm thick mineral wool blankets. Sy/d=1.2 Sy/d=2.4 Sy/d=3.6
Configuration
The whole system of heat exchanger base and heater Nx Ny Nt Nx Ny Nt Nx N y Nt
with associate thermal insulation was located in and Cylindrical 6 8 48 6 6 36 6 5 30
protected by a well fitting open top wooden box. Cylindrical
6 8 48 6 6 36 6 5 30
with groove
D. Data unit
The steady state temperature at the rectangular base
plate of the pin fin array are recorded using a set of 3. DATA REDUCTION
nine copper-constant thermocouples embedded and The steady state heat transfer from heated surface
appropriately distributed ,within the rectangular base can be expressed as follows
and average of these readings. The inlet and outlet
air stream in the wind tunnel duct were measured In similar to that followed by Naik et al. [17] and
using eight thermocouples 6 RTD. Section of the Tahat et al. [18] they conducted experiments and fin
channel was measured using U-tube manometer. The arrays are comparable and reported that the heat loss
duration to reach the steady state condition was capabilities of the fin array less than 5%. Although
about 1-2 hours depending upon the experimental in the present operating conditions together with the
conditions. fact that the test section is well insulated and
Geometrical characteristics of the pin fins are given assuming the loss is very minimum, eqn. (1) is given
in Tables as,

The steady state convection heat transfer rate from

test can be given by

Where, is the average temperature at center

location on the base assembly, and are the
air flow temperatures and is the total test surface
area, which can be expressed as,
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5. RESULTS AND DISCUSSIONS
The average convective heat transfer coefficient can In this section result from the experiments for
be calculated by combining eqns. (2) and (3): different pin fins configuration with Reynolds
number are presented for Sx /d=1.2 and Sy /d=1.2,2.4
and 3.6.heat transfer and pressure loss measurements
of various pin-fin geometries have been explored by
Under the present operating conditions together with
carrying out experiments on a test setup that has
the fact that the test section was well insulated, the
been designed.
free flow area is calculated as,
A. Heat transfer rate
Heat transfer rate as function of Reynolds number
The average convection heat transfer coefficient may for different fin types in Fig. 4 it is seen from this
also be presented in terms of average Nusselt figure the heat transfer rate increase in flow
number which can be evaluated from Reynolds number irrespective type of fin. The heat
transfer enhancement in pin fin arrays is achieved by
introducing turbulence (flow re-attachment or delay
The motion of the heat transfer medium can be separation) Fig. 4 shows the pin-fin profile shape
characterized by its Reynolds number (Re) is defined (cylindrical, grooved cylindrical and perforated)
in the conventional way as, influence on heat transfer enhancement. Despite that
the foretold three pin fin profile unique contact
surface area, the grooved cylindrical fins perform
Is the mass flux better than cylindrical and perforated as well. Heat
transfer rate increases with minimizing inter fin
4. COMPARISON WITH OTHER HEAT distance in stream wise direction (Sy /d).The heat
TRANSFER CORRELATIONS transfer is found to be increased in the order of
It is customary to present heat transfer data in terms cylindrical, perforated and grooved cylindrical fin.
of Nusselt number variation against Reynolds
number. For the present work one such plot is given
in Fig. 4 it is clear that the Nusselt numbers arrived
at are increasing with Reynolds number. In order to
validate the data previous work are being compared.
The present results are closer to and higher than the
result of Tahat et al. [14] and Jubran et al. [15] within
the range of experimental conditions.

Fig. 4 Effect of pin-fin shape on Qout for Sx/d=1.2

B. Nusselt number
Fig. 5 shows the variations of Nusselt number with
change in the values of Reynolds number for
different pin-fin geometries. It can be seen from Fig.
5 that the Nusselt is increases with an increase the
value of Reynolds number for all the fin geometries.
Fig. 3 Plot of Nusselt number Vs Reynolds number Figure5 reveal that the Nusselt number of the
(with other correlation) grooved cylindrical geometries is always higher than

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IJMEIT// Vol.04 Issue 10//October//Page No: 1791-1796//ISSN-2348-196x 2016
that of the cylindrical and perforated configuration characteristics was determined. The following
that have the same span wise, stream wise spacing conclusions were drawn from the results of the
and same heat transfer area. present work.
A significant jump in heat transfer is registered pin-
fins for all the values of Reynolds number. Grooved
cylindrical fin geometries out performs compared to
cylindrical and perforated fin geometries. In optimal
stream wise ratio (Sy/d=1.2) to enhance the heat
transfer rate is observed.
The Nusselt number increased with decreasing inter
pin fin space ratio. The highest values of Nusselt
number were obtained for the grooved cylindrical
fin geometries (Sx /d=1.2 and Sy /d=1.2).the values of
Nusselt number for cylindrical and perforated fins lie
Fig. 5 Effect of pin-fin shape on Nu for Sx/d=1.2 very close to each other, irrespective of the change
C. Friction factor in Reynolds number.
Fig. 6 depicts the friction factor as a function of The cylindrical pin fins have smaller pressure drops
Reynolds number, the experimental pressure drop at higher inter fin space ratio (Sy /d) than perforated
over the test section in the fixed duct was measured and grooved cylindrical. The result show that the
under the heated flow conditions. It is not pumping power generally decreases as Sy /d
uncommon that the flow resistance is an important increases.
aspect in heat transfer in order to have minimum Nomenclature
pumping power as constraint. The cylindrical pin A area, m2
fins have smaller pressure drops at higher inter fin C clearance between fin tip and the roof, mm
space ratio (Sy /d) than perforated and grooved Cp specific heat of air, J/kg K
cylindrical. The result show that the pumping power d diameter of the pin-fin, mm
generally decreases as Sy /d increases. f friction factor
G mass flux, kg/m2 s
H height of the pin-fin, mm
K thermal conductivity, W/m K
L length of the base plate, mm
M mass flow rate of air, kg/s
N number of pin-fin
Nu Nusselt number
Q heat transfer rate, W
Re Reynolds number
Fig. 6 Plot of ‘f’ Vs R ynolds numb fo Sx/d=1.2 S spacing, mm
T temperature, C
6. CONCLUSIONS T temperature, K
In this study, convective heat transfer and pressure W width of the base plate, mm
drop in a heat exchanger with different pin-fin arrays
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