International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 1- February 2016
CFD Analysis of a Heat Pipe with Different
Lengths and Various Wick Structures
Ch.Naveenkumar#1, R.Vijay Krishna*2, A.Madhuri#3 , K.Vidya*4
#1
Assistant Professor, Mechanical Department, NRI INSTITUTE OF TECHNOLOGY, Agiripalli,
Krishna District, Andhra Pradesh, India.
*2
Associate Professor, Mechanical Department, NRI INSTITUTE OF TECHNOLOGY, Agiripalli,
Krishna District, Andhra Pradesh, India.
#3
Assistant Professor, Mechanical Department, NRI INSTITUTE OF TECHNOLOGY, Agiripalli,
Krishna District, Andhra Pradesh, India.
*4Associate Professor, Mechanical Department, NRI INSTITUTE OF TECHNOLOGY, Agiripalli,
Krishna District, Andhra Pradesh, India
Abstract — Heap pipe is a device that utilizes the
evaporative heat transfer in the evaporator and
condensation heat transfer in the condenser. In this
paper the performance of heat pipe with various
wick structures, lengths and different working fluids
are used to study the change of various parameters
like temperature gradient, heat transfer rate
variation. In this circular heat pipe with various
wick thickness of 0.7mm, 1mm, 1.3mm are taken.
The wick shapes like sintered , v-groove, screen
covered groove are used, stainless steel is used as
the heat pipe material and copper granulates is used
for wick material, different lengths of heat pipe
190mm, 200mm are taken and ethanol, methanol
and aqueous methanol are used as the working
fluids. The simulation work runs on CFD by using
CFX and results are analysed for better working
fluid , better wick thickness and het pipe lengths. The
results yield from the simulation that ethanol has
high temperature gradient at 1.3mm for 200mm long
heat pipe are able to enhance the heat pipe
performance.
Keywords — Heat pipe with CFD analysis, Heat
pipe, Heat transfer in heat pipe.
I. INTRODUCTION
Heat pipe operates on a closed two-phase
cycle and only pure liquid and vapour are present in
the cycle. The working fluid remains at saturation
conditions as long as the operating temperature is
between the triple point and the critical state. As
typical heat pipe consists of three sections: an
evaporator or heat addition section, an adiabatic
section, and a condenser or heat rejection section.
When heat is added to the evaporator section of the
heat pipe, the heat is transferred through the shell
and reaches the liquid. When the liquid in the
evaporator section receives enough thermal energy,
the liquid vaporizes. The vapor carries the thermal
energy through the adiabatic section to the
condenser section, where the vapour is condensed
ISSN: 2231-5381
into the liquid and releases and releases the latent
heat of vaporization.
For a heat pipe to be functional, the liquid
in the evaporator must be sufficient to be vaporized.
There are a number of limitations to affect the
return of the working fluid. When the pumping
pressure produced by the surface tension cannot
overcome the summation of the total pressures, the
heat transport occurring in the heat pipe reaches a
limit known as the capillary limit. There are several
other limitations disconnecting the return of the
working fluid from the evaporator to the condenser
or from the condenser to the evaporator. Among
these are the boiling limit, sonic limit, entrainment
limit, and viscous limit.
Based on the structure, a heat pipe
typically consists of a sealed container charged with
a working fluid. Heat pipe is capable of creating its
own capillary pressure at the evaporator end. This
would cause a continuous flow of liquid in the wick
and replenish the liquid at the evaporator zone. Heat
flow through evaporator section and condenser
section assumed to be adiabatic. Due to this reason
the vapour experiences a negligible temperature drop.
Generally heat pipes exhibit thermal characteristics
that are even better than a solid conductor of the
same dimension.
As per wick structure, the working fluid
travels from the condenser section to the evaporator
section. The working fluid should be evenly
distributed over the evaporator section. In order to
provide a proper flow path with low flow resistance,
an open porous structure with high permeability is
desirable. This is to ensure that the working fluid
returns from the condenser to the evaporator.
II. MODELLING OF HEAT PIPE
A. Work specification
Heat pipe material
: Stainless steel.
Wick material
: Copper granulates
Wick thickness
: 0.7mm, 1mm, 1.3mm.
Wick structures
: Sintered, V-groove,
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 1- February 2016
Screen groove.
: Ethanol, Methanol,
Aqueous Methanol
Lengths of Heat pipes : 190mm, 200mm.
Outer diameter
: 9 mm.
Thickness of Heat pipe
Material
: 1.5mm
A. Contours of a heat pipe:
Working fluids
B. Mesh files of Heat pip:
Fig. 5 Contour of a heat pipe with Ethanol as
working fluid.
Fig. 1 Heat pipe with dimensions
Fig. 2 Heat pipe with sintered wick with working
fluid inside
Fig. 6 Contour of a heat pipe with Methanol as a
working fluid.
Fig. 3 Heat pipe with Screen groove wick
Fig. 7 Contour of a heat pipe with Aqueous
methanol as working fluid.
Fig.4 V-groove heat pipe with working fluid.
IV. RESULTS AND DISCUSSIONS
Finally the comparison tables as below. The
tablesg gives that the average out flow temperatures
and the temperature gradient(ΔT). Inlet flow
temperatures are 340K as mentioned in input data.
III. INPUT DATA
Working fluid velocity: 0.1 m/s
Working fluid inlet temperature: 290 K
Evaporator section temperature: 340 K
Compensator section temperature: 293 K
Working fluid fill ration in a heat pipe: 40% of
its volume.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 1- February 2016
A. Results for 190mm length Heat pipe
TABLE 1Temperature gradients for 0.7 mm Wick thicknes
for all working fluids and for all wick shapes.
Wick
thickness
Working
fluid
Type of
wick
Tout
ΔT(K)
(K)
0.7 mm
Ethanol
Sintered
307.92
32.08
0.7 mm
Methanol
Sintered
308.18
31.82
0.7 mm
Aqueous
Methanol
Sintered
308.94
31.06
0.7 mm
Ethanol
V-Groove
308.52
31.48
0.7 mm
Methanol
V-Groove
309.27
30.73
0.7 mm
0.7 mm
0.7 mm
0.7 mm
Aqueous
Methanol
V-Groove
Screen
groove
Ethanol
Screen
groove
Methanol
Aqueous
Methanol
Screen
groove
307.84
306.91
307.82
307.98
TABLE 3 ΔT for 1.3mm wick for all working fluids and for
all wick structures
Working
fluid
Type of
wick
Tout
(K)
1.3 mm
Ethanol
Sintered
301.19
38.81
1.3 mm
Methanol
Sintered
302.92
37.08
1.3 mm
Aqueous
Methanol
Sintered
304.28
35.72
1.3 mm
Ethanol
V-Groove
300.90
39.09
1.3 mm
Methanol
V-Groove
302.52
37.48
1.3 mm
Aqueous
Methanol
V-Groove
302.99
37.08
1.3 mm
Ethanol
Screen
groove
300.69
39.31
1.3 mm
Methanol
Screen
groove
301.92
38.08
1.3 mm
Aqueous
Methanol
Screen
groove
302.75
37.25
30.16
33.08
32.18
32.02
TABLE 2 ΔT for 1 mm wick for all working fluids and for all
wick structures.
ΔT(K)
Wick
thickness
B. Results for 200mm Length heat pipe
TABLE 4 ΔT for 0.7mm wick for all working fluids
and for all wick structures.
ΔT(K)
Wick
thickness
Working
fluid
Type of
wick
Tout
(K)
0.7 mm
Ethanol
Sintered
302.47
37.53
0.7 mm
Methanol
Sintered
307.82
32.18
0.7 mm
Aqueous
Methanol
Sintered
308.27
31.73
303.21 36.79
0.7 mm
Ethanol
V-Groove
306.81
33.19
V-Groove
304.14 35.86
0.7 mm
Methanol
V-Groove
308.01
31.99
Aqueous
Methanol
V-Groove
304.92 35.08
0.7 mm
Aqueous
Methanol
V-Groove
308.98
31.02
1 mm
Ethanol
Screen
groove
301.90 38.10
0.7 mm
Ethanol
Screen
groove
306.42
33.58
1 mm
Methanol
Screen
groove
304.23 35.77
0.7 mm
Methanol
Screen
groove
307.25
32.75
1 mm
Aqueous
Methanol
Screen
groove
304.98 35.02
0.7 mm
Aqueous
Methanol
Screen
groove
308.79
31.21
Wick
thickness
Type of
wick
Ethanol
Sintered
305.45 34.55
1 mm
Methanol
Sintered
307.29 32.71
1 mm
Aqueous
Methanol
Sintered
307.84 32.16
1 mm
Ethanol
V-Groove
1 mm
Methanol
1 mm
1mm
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Tout
(K)
ΔT(K)
Working
fluid
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 1- February 2016
TABLE 5 ΔT for 1mm wick for all working fluids and for all
wick structures.
A. Graphs
Graphs for 190mm length heat pipe:
ΔT
Wick
thickne
ss
Working
fluid
Type of
wick
Tout
(K)
1mm
Ethanol
Sintered
304.52 35.48
1 mm
Methanol
Sintered
306.18 33.82
1 mm
Aqueous
Methanol
Sintered
306.99 33.01
1 mm
Ethanol
V-Groove
303.10 36.90
1 mm
Methanol
V-Groove
303.23 36.77
1 mm
Aqueous
Methanol
V-Groove
304.76 35.24
1 mm
Ethanol
Screen
groove
301.62 38.38
1 mm
Methanol
Screen
groove
302.24 37.76
1 mm
Aqueous
Methanol
Screen
groove
303.88 36.12
(K)
Fig. 8 Variation of temperature gradients for
different working fluids for 0.7mm wick for all
wick structures.
TABLE 6 ΔT for 1.3mm wick for all working fluids
and for all wick structures.
Working
fluids
Wick
structure
1.3 mm
Ethanol
Sintered
300.85 39.15
1.3 mm
Methanol
Sintered
301.72 38.28
1.3 mm
Aqueous
Methanol
Sintered
303.18 36.82
1.3 mm
Ethanol
V-Groove
298.67 41.33
1.3 mm
Methanol
V-Groove
301.48 38.52
1.3 mm
Aqueous
Methanol
V-Groove
301.64 38.36
1.3 mm
Ethanol
Screen
groove
299.89 42.11
1.3 mm
Methanol
Screen
groove
301.38 38.62
1.3 mm
Aqueous
Methanol
Screen
groove
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Tout
(K)
ΔT
(K)
Wick
thickness
301.96 38.04
Fig. 9 Variation of temperature gradient for
different working fluids for 1mm wick for all
wick structures.
Fig. 10 Variation of temperature gradient for
different working fluids for 1.3mm wick for all wick
structures.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 1- February 2016
V. CONCLUSION
B. Graphs for 200mm length heat pipe
From the results and discussions we seen that
ethanol has a highest heat transfer gradient
among all the working fluids.
Out of three wick shapes screen groove covered
wick perform best when compared to sinter and
V-groove wicks.
When compared to wick thickness 1.3mm wick
thickness wick perforce is good.
The heat pipe with 200mm length can have
more temperature gradient due to its grater
length it has a more heat transfer surface area.
Ethanol used as a working fluid the cost of the
working fluid is less.
Fig. 11 Variation of temperature gradient with 0.7mm wick
for all working fluids and wick structures.
Fig. 12 Variation of temperature gradient with 1mm wick for
all working fluids and for all wick structures.
VI. REFERENCES
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Enhancement of thermal performance in a sintered miniature
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[2] HANLON M A, MA H B. Evaporation heat
transfer in
sintered porous media [J]. Transactions-American Society of
Mechanical Engineers. Journal of Heat Transfer, 2003,
125(4): 644−652.
[3] Grover, G. M., et al., Structures of very high thermal
conductance, Journal of Applied Physics, 35 (1964), 10, pp.
1990
[4] Banjerd Saengchandr and Nitin, V. Afzulpurkar., A novel
approach for cooling electronics using combined heat pipe
thermoelectric module, American J. of Engineering and
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[5] Busse C.A. (1992). Heat Pipe Science, Advances
in Heat Pipe Science and Technology, Proc. of
8th Int.
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Publishers
[6] Li T.H. and Hua C.S. (1987). Heat Pipe Design
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Fig. 13 Variation of temperature gradient with 1.3mm wick for
all working fluids and for all wick structures.
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