Optimization of the cooling system design for a compact high-power LED luminaire
Using the method of computer modelling, considered in this paper, is the optimization of a passive air system design for cooling the powerful LED luminaire based on heat pipes and cooling rings. Thermal and mass characteristics of the cooling system have been studied for various design parameters: d...
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| Date: | 2020 |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2020
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| Cite this: | Optimization of the cooling system design for a compact high-power LED luminaire / D.V. Pekur, Yu.E. Nikolaenko, V.M. Sorokin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2020. — Т. 23, № 1. — С. 91-101. — Бібліогр.: 49 назв. — англ. |
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| author | Pekur, D.V. Nikolaenko, Yu.E. Sorokin, V.M. |
| author_facet | Pekur, D.V. Nikolaenko, Yu.E. Sorokin, V.M. |
| citation_txt | Optimization of the cooling system design for a compact high-power LED luminaire / D.V. Pekur, Yu.E. Nikolaenko, V.M. Sorokin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2020. — Т. 23, № 1. — С. 91-101. — Бібліогр.: 49 назв. — англ. |
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| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | Using the method of computer modelling, considered in this paper, is the optimization of a passive air system design for cooling the powerful LED luminaire based on heat pipes and cooling rings. Thermal and mass characteristics of the cooling system have been studied for various design parameters: distance between rings, thickness of ring materials, and thermal loads. It has been shown that, to provide a minimal case temperature of the LED source, the optimal distance between cooling rings should be 6 mm, but in this case, the mass of the cooling system is not least. To reduce the luminaire mass, it is reasonable to choose the distance between the cooling rings equal to 8 mm. Then the temperature of the light source increases by only 1.8 °С, or by 2.2%, while the mass of the cooling system reduces by 1357 g, or by 20.5%. At the same time, lowering the ring thickness from 2 to 0.8 mm can, in addition, reduce this mass by 2700 g, or by 48.6%. However, when doing so, the temperature of LED source case is increased by 5.9 °С. The offered cooling system based on heat pipes is capable of providing the thermal resistance 0.131 °С/W when scattering the thermal power 500 W under the maximum temperature of the LED source crystal 135.5 °С. Recommendations for the application of the developed cooling system have been formulated.
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ISSN 1560-8034, 1605-6582 (On-line), SPQEO, 2020. V. 23, N 1. P. 91-101.
© 2020, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
91
Optoelectronics and optoelectronic devices
Optimization of the cooling system design
for a compact high-power LED luminaire
D.V. Pekur1, Yu.E. Nikolaenko2, V.M. Sorokin1
1V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine,
41, prosp. Nauky, 03680 Kyiv, Ukraine,
E-mail: demid.pekur@gmail.com, vsorokin@isp.kiev.ua
2National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”,
37, prosp. Peremohy, 03056 Kyiv, Ukraine,
E-mail: y.nikolaenko@kpi.ua
Abstract. Using the method of computer modelling, considered in this paper is
optimization of a passive air system design for cooling the powerful LED luminaire based
on heat pipes and cooling rings. Thermal and mass characteristics of the cooling system
have been studied for various design parameters: distance between rings, thickness of ring
materials and thermal loads. It has been shown that, to provide a minimal case temperature
of LED source, the optimal distance between cooling rings should be 6 mm, but in this case
the mass of cooling system is not least. To reduce the luminaire mass, it is reasonable to
choose the distance between the cooling rings equal to 8 mm. Then the temperature of light
source increases by only 1.8 °� , or by 2.2%, while the mass of cooling system reduces by
1357 g, or by 20.5%. At the same time, lowering the ring thickness from 2 down to 0.8 mm
can in addition reduce this mass by 2700 g, or by 48.6%. However, when doing so the
temperature of LED source case is increased by 5.9 °� . The offered cooling system based
on heat pipes is capable to provide the thermal resistance 0.131 °� /W when scattering the
thermal power 500 W under the maximum temperature of LED source crystal 135.5 °� .
Recommendations for application of the developed cooling system have been formulated.
Keywords: LED, cooling system, air cooling, heat pipe, optimization.
https://doi.org/10.15407/spqeo23.01.91
PACS 42.72.-g, 52.80.Mg, 85.60.Jb, 92.60.
Manuscript received 16.01.20; revised version received 20.02.20; accepted for publication
18.03.20; published online 23.03.20.
1. Introduction
Currently, LED sources are widely spread in lighting
systems for domestic and industrial consumers [1]. One
of the arguments for using the LED sources is the durable
life span of these sources that can reach 100,000 hours.
As usual, this term means the time of facility operation
up to failure. Another parameter that is often used is the
time of effective operation when device photometric per-
formances are unchanged, i.e., the device characteristics
are kept higher or equal to some definite level. Lowering
the light flux below this level is considered by LED
producers as a life span. To determine this parameter, the
producers perform testing LEDs at various temperatures.
As it is indicated by testing results, the times of keeping
LED characteristics within the limits guaranteed by
producer depend on the LED temperature [2].
Besides, the LED temperature influences on the
light efficiency of LEDs as well as stability of their color
characteristics. Therefore, it is very important to provide
the operation regime for LEDs under the temperatures as
low as possible [3–5] for all the time of their usage.
New generations of LEDs are characterized by
essential growing their power. At the same time, sizes of
separate LEDs decrease or remain at the previous form-
factor.
It results in increasing the density of heat flux
through the case of LEDs, and therefore requirements to
their cooling systems constantly grow.
For instance, the LED matrix CITIZEN CLU058
based on COB technology contains 648 crystals
produced by Nichia company on the board of the sizes
38×38×1.4 mm and possesses the power 526 W [6, 7].
To provide operation temperatures for powerful
LED lighting devices, they more often use the double-
phase heat-transmitting facilities – heat pipes [8–32].
Usage of them allows lowering the thermal resistance of
cooling system and, as a consequence, lowering the
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
92
temperature of LEDs, raising their life span and
stabilizing the electro-optical parameters. The equivalent
heat conductivity can reach more than 10 000 W/(m·°� )
[15, 33], which is considerably higher than that of
homogeneous metal materials used for creation of
cooling systems (aluminum – 240 W/(m·°� ), copper –
400 W/(m·°� )). These performances of the heat pipes
enable to considerably lower the mass of material
necessary to construct these cooling systems.
As to their shape, the heat pipes can be of
cylindrical [11, 12, 15], L-like [16], U-like [15], � -like
[15], flat [28], as well as of other shapes. In some
applications, for example, for internal lighting of
premises with low ceilings as well as for that in cabins of
automobile, marine and city transport, in carriages, etc.,
it is desirable to mount compact LED luminaires with
minimal dimensions along their height. In these LED
luminaires, the most suitable are the cooling systems
with heat pipes of cylindrical or plane shapes with
horizontal or close to it orientation in space.
Development of compact LED luminaires foresees
optimization of complex parameters for the cooling
systems (configuration of arrangement and parameters of
its elements, materials and facilities for heat removal).
The currently known methods to calculate the thermal
parameters of cooling systems, when they use some
simplified analytic expressions, do not enable to optimize
parameters of complex and multi-component systems of
air cooling. Physical modelling [35] can be considered as
the more universal method for such optimization, but it is
characterized by considerable laboriousness and financial
expenses.
The modern method for optimization and designing
the cooling systems is based on application of special
programs for computer modelling and analysis [36–38].
These approaches enable to perform both designing the
cooling systems and their thermal analysis for a relatively
short time.
The aim of this work was to investigate, using the
computer modelling, heat performances of the passive air
cooling system for a compact powerful LED luminaire,
which is based on heat pipes of the cylindrical shape, as
well as optimize the construction parameters of this
cooling system.
To reach this aim, it was necessary to solve the
following tasks:
· to offer a basic version of construction corres-
ponding to the LED luminaire with heat pipes;
· to create computer models of a typical number of
cooling systems with various construction
parameters;
· to carry out the computer modelling for determining
their thermal and mass characteristics;
· to analyze the obtained characteristics;
· to choose the optimal construction parameters of the
cooling system, which could provide the least tem-
perature of LED source under the set value of its
power;
· to formulate recommendations for practical
application of the obtained results when designing
the compact powerful LED luminaires.
2. Construction of the basic version of a compact LED
luminaire
Being aimed at performing investigation, we suggested
the basic construction of the compact powerful LED
luminaire with the passive air cooling system [34]. Its
construction scheme is shown in Fig. 1. The luminaire
consists of a base, LED light source, LED driving
electronic system as well as the cooling system. The LED
source 3 is protected by the light scattering lampshade 4
that can be made as a lens to provide the necessary
distribution of the light flux. The electronic driving
system 1 for this LED is placed within the zone where it
does not prevent propagation of light flow.
The cooling system is assigned to provide operating
thermal conditions inherent to powerful LED sources
during luminaire operation. The authors of this paper
developed a new compact construction for the cooling
system of luminaire. In this cooling system, they use
highly effective double-phase heat-transmitting facilities
– heat pipes, and radiator webbing as an evolved heat-
exchanged surface. The heat pipes 7 are mounted on the
� )
b)
Fig. 1. Bottom (a) and frontal (b) views of the LED luminaire:
1 – LED source driving system, 2 – base, 3 – LED source,
4 – light scatterer, 5 – rings, 6 – air channel, 7 – heat pipes.
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
93
base 2 to provide thermal contact. At the same time, to
ensure luminaire compactness the heat pipes in the
cooling system are oriented in the radial manner, while
the radiator webbing is made in the form of rings 5 and
placed concentrically around the LED source 3 [34].
When using horizontal placing of the luminaire, the
above approach to design and placement of cooling
webbing seems to be the most optimal due to active air
motion through the channels between the rings of cooling
system. As it follows from the results obtained in
[35–37], this placing of cooling webbing enables to use
for heat exchange with ambient air all their area with the
highest efficiency.
Being based on this basic construction version, one
can develop a typical number of LED luminaires that are
distinguished between each other by the amount of heat
pipes and cooling rings as well as construction
parameters of the latter.
The operation principle of the offered cooling
system has been described in [33, 36]. Stating briefly, it
is as follows. After switching on the luminaire and
energizing the LED source 3 (see Fig. 1), the heat flux
from this source is transferred to the heat pipes 7 through
the heat-conducting base 2. Due to the high heat
conductivity of the heat pipes operating in accord with
the closed evaporation-condensation cycle, there
provided is an efficient heat sink from the LED source 3
and transfer to the cooling rings 5. Heat sink from the
ring surface takes place due to free convection of ambient
air. Motion of the latter occurs inside the air channels 6
between the rings of cooling system.
Beforehand, using the method of computer
modelling, we investigated the construction of a similar
LED luminaire where used were 8 copper-water heat
pipes of the diameter 6 mm with the powder porous
capillary structure and 20 cooling rings with the
following chosen but non-optimized parameters: the
ring height – 50 mm, ring thickness – 2 mm, distance
between the rings – 8 mm [36]. Material of the base
and rings – aluminum alloy with the heat conductivity
� = 237 W/(m·°� ). It was shown that for the power of
LED source 500 W this cooling system provides the
temperature of LED semiconductor crystal at the level
139.5 °� , which does not exceed the permissible value of
the crystal operation temperature 140 °� . The total ther-
mal resistance of cooling system reaches 0.131 °� /W.
To reduce the mass and thermal resistance of
cooling system, to improve uniformity of heat fluxes by
the cooling rings, the amount of the latter and their con-
struction parameters can be optimized. Such optimization
performed for definite cooling ring parameters and their
amount can enable obtaining the most optimal luminaire
construction from the viewpoint of lowering the LED
source temperature and luminaire mass.
Defined in this work has been a typical number of
constructive versions for LED cooling systems of
luminaires, performed also the computer modelling of
their thermal and mass characteristics as well as
optimization of cooling system for the set diameter of
luminaire and power of LED light source.
3. Computer modelling of thermal parameters for
the typical number of construction versions for the
cooling system
To choose an optimal design for the luminaire cooling
system, we created a number of models with different
construction parameters (Table 1) and performed their
computer modelling.
When modelling, we took into account the
following requirements that are laid claim to the systems
providing heat operation modes for the LED sources:
· construction should ensure the least thermal
resistance within a wide range of heat powers;
· cooling system should provide such temperature
range of LED operation when the temperature of
p-n junctions in semiconductor crystals does not
exceed 140 °� [6, 7];
· amount of the material used for creation of the
cooling system should be optimized.
For type versions of the cooling system construction
that is analyzed, we created a number of models with
different parameters of the cooling system. With this aim,
we varied the distances between the rings of cooling
system, thickness of the cooling rings and heat load. We
kept unchanged the ring height (50 mm), diameter
(6 mm) and amount (8) of heat pipes, shape and sizes of
the base (regular octagon prism with the side 31 mm and
height 8 mm), dimensions of LED light source
(38×38×1.4 mm), diameter of the largest ring in the
cooling system (516 mm).
Studying the thermal characteristics of these models
was carried out using the analytic module
FlowSimulation SolidWorks from the computer program
SolidWorks.
When creating these computer models, we took into
account the following boundary conditions:
· heat pipes are made of copper, heat carrier
is distilled water, effective heat conductivity of
heat pipes does not depend on temperature and
reaches � ef = 10 000 W/(m·°� );
· all the other construction elements (except heat
pipes) are made of the aluminum alloy, the heat
conductivity coefficient of which does not
depend on temperature, too, and is equal to � =
237 W/(m·°� );
· thermal emission can be neglected;
· ambient medium is air;
· temperature of the ambient medium is equal to
20 °� ;
· atmospheric pressure – 101.325 kPa;
· speed of air movement far from luminaire is close
to zero;
· heat source is uniformly distributed along the
external surface of the model adopted for the LED
light source.
The obtained results of our modelling enable to
determine the temperature in some characteristic points
of the cooling system and to define its suitability for
cooling the powerful LED sources.
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
94
4. Results of the computer modelling and their
analysis
Shown in Fig. 2 are the results of our computer
modelling of the temperature distribution along the
cooling system for the case when the distance between
cooling rings changes from 3 up to 18 mm and the
thickness of each ring is 2 mm. When the outer diameter
of luminaire is kept constant, the change of inter-ring
distance simultaneously varies the amount of rings and
defines the effect on the total area of the heat-conducting
radiator surface. Therefore, this increase in the amount of
rings should result in changing the temperature of LED
source.
In the considered cooling system, the convective
heat exchange with air occurs mainly due to free
convection of air through the channels between the
cooling rings. The area of all the other surfaces taking
part in the heat exchange with air reaches 0.025 up to
0.035 m2, which does not exceed 3.1% of the total area of
the heat-exchanging surface inherent to the considered
cooling system. Shown in Fig. 3 is the dependence of the
area of the total cooling system surface that takes part in
the heat exchange on the distance between cooling rings.
This dependence has a monotonous falling character with
the inflection point corresponding to the distance 8 mm
between cooling rings.
Shown in Fig. 4 is the change of the maximum
temperature inherent to the case of LED source with
changing the distance between rings. As can be seen in
this figure, the dependence of the LED source case on the
distance between cooling rings has its pronounced extre-
mum, which enables to determine the optimum value of
this distance. The minimum value of temperature
inherent to the LED source case is 83.7 °� and reached
for the distance between cooling rings 6 mm (con-
struction version 4). In this case, the area of the cooling
system heat-exchanging surface is equal to 2.63 m2.
When the distance between rings becomes shorter
than 6 mm, the LED source case temperature begins to
increase, despite the growth of total area of cooling
webbing. It is explained by the fact that, for too small
distance between the rings, the hydraulic resistance for
air movement in the channels between rings grows, and
the velocity of air motion through the cooling channels is
lowered, which results in reducing the coefficient of heat
exchange between the ring surface and ambient air.
In the case when cooling rings are placed at the
distance 8 mm one to another (construction version 5),
the amount of rings is decreased by 5 pieces. At the cost
of it, the cooling system heat-exchanging surface area
decreases down to 2.11 m2, which is 24% lower than that
for placing the cooling rings with the step 6 mm (see
Table 1).
Table 1. Typical number of constructive versions for the cooling system of luminaire.
Version
number
Amount of
rings
Distance
between rings,
mm
Ring thickness,
mm
Total ring surface area for heat
exchange (without heat pipes
and base), m2
Total area of heat-
exchanging surface,
m2
1 40 3 2 4.12 4.19
2 33 4 2 3.44 3.52
3 29 5 2 2.95 3.03
4 25 6 2 2.55 2.63
5 20 8 2 2.03 2.11
6 16 10 2 1.69 1.78
7 14 13 2 1.44 1.52
8 10 18 2 1.05 1.13
Table 2. Thermal and mass characteristics of construction versions for the cooling system of LED luminaire, when the ring thickness
is 2 mm.
Number
of version
Maximum temperature
of the LED case, °�
Mass of the cooling
system, g
Temperature change
relatively to the version 4, %
Mass change relatively to the
version 4, %
1 97.2 10682 16.1 61.5
2 88.8 8729 6.1 32.0
3 84.5 7769 1.0 17.5
4 83.7 6613 0.0 0.0
5 85.5 5256 2.2 -20.5
6 89.3 4395 6.7 -33.5
7 95.7 3739 14.3 -43.5
8 105.1 2713 25.6 -59.0
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
95
a
c
e
g
b
d
f
j
Fig. 2. Images of temperature distributions for the LED source heat power 500 W and various distances between the rings, mm:
(a) – 3; (b) – 4; (c) – 5; (d) – 6; (e) – 8; (f) – 10; (g) – 13; (j) – 18.
SPQEO, 2020. V. 23, N 1. P. 91-101.
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96
0 4 8 12 16 20
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
H
ea
t t
ra
ns
fe
r
su
rf
ac
e
ar
ea
, m
2
Spacing of the rings, mm
Fig. 3. Dependence of the total area of cooling system heat-
exchanging surface on the distance between cooling rings.
0 4 8 12 16 20
80
85
90
95
100
105
110
T
em
pe
ra
tu
re
, °
�
Spacing of the rings, mm
Fig. 4. Dependence of the LED source case maximum
temperature on the distance between cooling rings for the heat
power 500 W.
However, this decrease in the amount and surface area of
the rings leads to lowering their mass by 1357 g as well
as increasing the temperature only by 1.8 °� (Table 2).
Although further increasing the distance between
rings and decreasing their amount lowers the cooling
system mass, however, it leads to a sharp increase in the
temperature of LED light source. It can be explained by
reduction of the cooling system total area. For example,
in the case when the distance between cooling rings
reaches 10, 13 and 18 mm (construction versions 6, 7
and 8) the cooling system mass drops by 33.5%, 43.5%
and 59%, respectively, as compared with the version 4,
however, the temperature of LED light source increases
by 6.7%, 14.3% and 25.6% (see Table 2).
Thereof, the most reasonable, from the viewpoint of
practical applications, is the constructive version 5 with
the distance between the rings 8 mm, which provides the
0.5 1.0 1.5 2.0 2.5
80
85
90
95
T
em
pe
ra
tu
re
, °
�
Thickness of the rings, mm
Fig. 5. Dependence of the maximum temperature value inherent
to the LED source case on the ring thickness.
0.5 1.0 1.5 2.0 2.5
2000
3000
4000
5000
6000
W
ei
gh
t o
f c
oo
lin
g
sy
st
em
, g
Thickness of the rings, mm
Fig. 6. Dependence of the cooling system mass on the ring
thickness.
LED source case temperature 85.5 °� and has the worse
mass characteristics than those of the construction
version 4.
Let us analyze the influence of ring thickness on the
luminaire thermal and mass characteristics. The depen-
dences of maximum temperature inherent to the LED
source case and cooling system mass on the ring thick-
ness for their diameter defined at their step 8 mm and
thickness 2 mm are shown in Figs 5 and 6, respectively.
It is worth to note that, on the one hand, when the
ring thickness is decreased the cooling system mass is
decreased to some extent, too, and the width of air
channels increases, which enhances air circulation in
them. On the other hand, when the ring thickness is
decreased, its thermal resistance concerning propagation
of the heat flow from the heat pipe along the ring is
increased, which is related with the negative effect on the
SPQEO, 2020. V. 23, N 1. P. 91-101.
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97
0 100 200 300 400 500 600
0.12
0.13
0.14
0.15
0.16
0.17
0.18
T
he
rm
al
r
es
is
ta
nc
e,
°
�
/W
Power, W
Fig. 7. Thermal resistance of the cooling system for various
powers of the LED source.
Fig. 8. Dependence of the temperature inherent to p-n junction
on power for various values of the coefficients of electrical
power transformation into the thermal one: 1 – 100%, 2 – 95%,
3 – 90%, 4 – 80%, 5 – 70%, 6 – 60%, 7 – 50% as well as the
temperature of the LED case on the power – 8.
temperature of the LED source case. As seen from Fig. 5,
the decease in the ring thickness from 2 down to 0.8 mm
leads to increasing the temperature of LED source case
from 85.5 up to 91.4 °� .
The LED source temperature change by 5.9 °� is
sufficiently low as compared relatively to the overall
temperature drop in the cooling system between the LED
source case and air (65.5–71.4 °� ), but enables to
essentially (by 48.6% or 2700 g) lower the cooling
system mass (Fig. 6).
The important parameter of the cooling system is its
thermal resistance. Since the developed cooling system
with heat pipes can be used in LED luminaires of various
powers inherent to LED sources, then for practical appli-
cation it is desirable to know how the thermal resistance
will change after changing the LED source power. To
answer this question, we performed computer modelling
Fig. 9. Distribution of temperature over the LED luminaire
cooling system when using the copper bars instead of heat
pipes.
of the cooling system thermal parameters for the
construction version 5 when changing the LED source
power from 100 up to 500 W with the step of 50 W.
The cooling system thermal resistance was
determined using the expression (1) described in [27]:
p
tt
R a
thermal
-
= max (1)
where maxt is the maximum temperature of the cooling
system in °� , at – temperature of the ambient medium
in °� , p – thermal power in watts that is scattered.
Adduced in Table 3 are the calculated using the
formula (1) values of the thermal resistance inherent to
the LED luminaire cooling system with 20 rings of the
thickness 2 mm and the distance between them 8 mm,
when the temperature of ambient air is close to 20 °� .
Fig. 7 shows the dynamics of changing the thermal
resistance of the cooling system of this configuration
with the LED source thermal power. As seen from this
figure, this dependence has a monotonically-decaying
character. When the LED source thermal power is
increased, the thermal resistance of cooling system is
decreased. The reason for this behavior is that the
increase in the thermal power raises the temperature of
cooling rings and enhances the speed of air motion in
cooling channels. The growth of air flux increases the
value of coefficient for convective heat exchange
between ring surface and air, which results in lowering
the thermal resistance of cooling system.
The performed calculations show that within the
range of powers for 100 up to 500 W the thermal
resistance of the cooling system decreases from 0.167
down to 0.131 °� /W. This factor of the thermal
resistance enables to use in the LED luminaire design
powerful LEDs and COB-modules with the thermal
package 500 W and to keep the LED case temperature
not higher than 85.5 °� . When doing so, the temperature
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
98
of LED source semiconductor crystals will depend on the
amount of supplied electrical energy transformed into the
thermal one. As usual, the fraction of supplied electrical
energy transformed into the thermal one is higher than
50%.
To determine the temperature of LED
semiconductor crystal junctionT , one can use the
expression (2) for the temperature of crystal p-n junction
on the power and temperature of LED case [27]:
LEDcasejunctionthermalelectricLEDcasejunction RPTT -××h+= ,
(2)
where LEDcaseT is the temperature of LED case, °� ; h –
coefficient of electrical energy transformation into the
thermal one; electricP – total electric power, W;
LEDcasejunctionthermalR - – thermal resistance of the spacing
between the case and p-n junction of LED, °� /W.
Shown in Fig. 8 is the calculation dependence of the
LED crystal temperature on the power for various values
of the coefficient of electrical energy transformation into
the light one within the range 0% up to 50%.
It is seen from Fig. 8 that even under conditions
when all the electric energy is transformed into the
thermal one, the temperature of p-n junction cannot
approach to the permissible operation critical value for
this type of LEDs 140 °� (in Fig. 8, it is shown with the
dashed line).
Besides, to demonstrate the efficiency of the
developed compact cooling system based on heat pipes,
in this work we performed the computer modelling of an
analogous cooling system where instead of heat pipes the
copper bars with the same geometrical sizes were used
(diameter 6 mm, length 250 mm). The copper thermal
conductivity was taken to be 400 W/(m·°� ). In this case,
we used the cooling rings of the thickness 2 mm and
height 50 mm at the distance 8 mm (analog of the
construction version 5). As shown in Fig. 9, the
maximum temperature of the LED source case with the
same power 500 W, when using the copper bars instead
of heat pipes, could be close to 328 °� .
As shown by using additional calculations, to
provide the parameters of heat sink similar to those
typical for the cooling system with heat pipes of the
6-mm diameter, the homogeneous copper bars of the
length 250 mm should have the diameter 30 mm, while
those from aluminum – 39 mm. In this case, the mass of
these bars should be at least 65 and 34 times higher,
respectively, than the mass of heat pipes considered in
the developed cooling system (version 5).
5. Recommendations for practical application of the
developed luminaire
When designing the LED luminaire with a set power for
specific practical applications, first of all, it is necessary
to define what its characteristics are more critical under
these conditions of operation: temperature of the LED
source or the mass of luminaire. In accord with them, it
should be chosen the respective construction version of
luminaire. In the first case, preference should be given to
the construction versions 3 to 5 the most close to the
optimum one from the viewpoint of lowering the
temperature of light source. In the second one – to the
versions 6 to 8 providing the less ring thickness, which
corresponds to a less luminaire mass. However, in this
case, it is necessary to provide the LED source
temperature that does not exceed the maximum
permissible value.
Due to the low height, the developed LED
luminaire can be applied both for lighting the living
spaces with low ceilings and for internal lighting the
cabins, bodies, staterooms and other premises of many
transportations. Specificity of exploitation conditions
inherent to transport vehicles places a demand to the
luminaire producer performing the thermal calculations
for its cooling system to take into account the possible
effects of vibrations, accelerations and shocks on
characteristics of heat pipes [39–46] and, accordingly, of
the whole luminaire.
If it is necessary, in perspective modifications of
LED luminaires for special purposes, one can use LED
sources with the power higher than 500 W. In this case, it
is purposeful to choose larger amount of heat pipes and
rings. Besides, to disperse the high thermal flux over the
whole surface of carrying base, it is reasonable to use
heat-distributing spacers between COB matrix and
carrying base in the form of thin vapor chambers [47–49]
that also operate using the closed evaporation-
condensation cycle for heat transmitting.
6. Conclusions
1. It has been performed optimization of construc-
tion of the passive air cooling system for a compact
powerful LED luminaire, which is based on heat pipes
and cooling rings, by using the updated programs for
computer modelling and analysis. It enables to study the
thermal operation regimes and mass characteristics of the
designed cooling system before producing it.
2. Comparison of the maximum temperature
observed on the body of LED source for various
distances between the rings of cooling system has shown
Table 3. Thermal resistance of the LED cooling system for the construction version 5 under various values of the thermal power.
Power, W 100 150 200 250 300 350 400 450 500
T max, °� 36.7 42.8 48.9 55.0 61.1 67.2 73.3 79.4 85.5
Thermal resistance, °� /W 0.167 0.152 0.145 0.140 0.137 0.135 0.133 0.132 0.131
SPQEO, 2020. V. 23, N 1. P. 91-101.
Pekur D.V., Nikolaenko Yu.E., Sorokin V.M. Optimization of the cooling system design for a compact high-power …
99
that lowering or increasing the distance as compared with
its optimal value 6 mm leads to enhancing the
temperature of the LED source body. With account of the
said above, the most reasonable for practical applications
is the distance between cooling rings equal to 8 mm,
which in comparison 6 mm increases the temperature by
only 1.8 °� (i.e., by 2.2%) for lowering the used material
mass by 1357 g or by 20.5%.
3. Reducing the cooling rings thickness from
2 down to 0.8 mm leads to increasing the LED source
body temperature for its power 500 W by 5.9 °� (6.9%),
however, there reached is an essential gain in the mass of
cooling system, namely: the amount of used material and
mass for producing it is decreased by 2.3–1.8 times.
4. If one uses in the construction of cooling system
for the LED luminaire instead of the heat pipes the
copper bars with the same dimensions, the temperature of
the LED source body will increase up to 328 °� , which is
unallowable from the viewpoint of luminaire operation
reliability. To reach the thermal regimes that are provided
by heat pipes, it would be necessary to 5-fold increase
the diameter of copper bars. Then the mass of these bars
will be 65 times increased.
5. It has been offered recommendations concerning
practical applications of the developed LED luminaire.
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Authors and CV
Demid V. Pekur, Ph.D. student at the
V. Lashkaryov Institute of Semicon-
ductor Physics, NASU. The area of
his scientific interests includes design
of perspective cooling systems for
super-power LEDs and creation of
LED facilities on them.
Scopus Author ID: 57211485091
ORCID: https://orcid.org/0000-0002-
4342-5717
Yurii E. Nikolaenko, Doctor of
Engineering, Leading fellow of the
heat-and-power engineering depart-
ment at the National Technical
University of Ukraine “Igor Sikorsky
Kyiv Polytechnic Institute”. Field of
scientific interests: heat removal from
electronic components by using heat
pipes.
Scopus Author ID: 23393308200
ORCID: http://orcid.org/0000-0002-3036-5305
Viktor M. Sorokin , Professor,
Doctor of Sciences, Corresponding
Member of the National Academy of
Sciences of Ukraine, Head of the
Department of Optoelectronics at the
V. Lashkaryov Institute of Semi-
conductor Physics, NAS of Ukraine.
The author of more than 200 publica-
tions. His research interests include
problems of liquid crystal materials science, lighting
engineering and lighting materials. He organized massive
implementation of LED lighting in Ukraine. He is the
State Prize winner of Ukraine in the field of science and
technology.
Scopus Author ID: 7201463453
ORCID: https://orcid.org/0000-0002-1499-1357
|
| id | nasplib_isofts_kiev_ua-123456789-215655 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-26T19:16:31Z |
| publishDate | 2020 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Pekur, D.V. Nikolaenko, Yu.E. Sorokin, V.M. 2026-03-24T12:17:22Z 2020 Optimization of the cooling system design for a compact high-power LED luminaire / D.V. Pekur, Yu.E. Nikolaenko, V.M. Sorokin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2020. — Т. 23, № 1. — С. 91-101. — Бібліогр.: 49 назв. — англ. 1560-8034 PACS: 42.72.-g, 52.80.Mg, 85.60.Jb, 92.60 https://nasplib.isofts.kiev.ua/handle/123456789/215655 https://doi.org/10.15407/spqeo23.01.091 Using the method of computer modelling, considered in this paper, is the optimization of a passive air system design for cooling the powerful LED luminaire based on heat pipes and cooling rings. Thermal and mass characteristics of the cooling system have been studied for various design parameters: distance between rings, thickness of ring materials, and thermal loads. It has been shown that, to provide a minimal case temperature of the LED source, the optimal distance between cooling rings should be 6 mm, but in this case, the mass of the cooling system is not least. To reduce the luminaire mass, it is reasonable to choose the distance between the cooling rings equal to 8 mm. Then the temperature of the light source increases by only 1.8 °С, or by 2.2%, while the mass of the cooling system reduces by 1357 g, or by 20.5%. At the same time, lowering the ring thickness from 2 to 0.8 mm can, in addition, reduce this mass by 2700 g, or by 48.6%. However, when doing so, the temperature of LED source case is increased by 5.9 °С. The offered cooling system based on heat pipes is capable of providing the thermal resistance 0.131 °С/W when scattering the thermal power 500 W under the maximum temperature of the LED source crystal 135.5 °С. Recommendations for the application of the developed cooling system have been formulated. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Optoelectronics and optoelectronic devices Optimization of the cooling system design for a compact high-power LED luminaire Article published earlier |
| spellingShingle | Optimization of the cooling system design for a compact high-power LED luminaire Pekur, D.V. Nikolaenko, Yu.E. Sorokin, V.M. Optoelectronics and optoelectronic devices |
| title | Optimization of the cooling system design for a compact high-power LED luminaire |
| title_full | Optimization of the cooling system design for a compact high-power LED luminaire |
| title_fullStr | Optimization of the cooling system design for a compact high-power LED luminaire |
| title_full_unstemmed | Optimization of the cooling system design for a compact high-power LED luminaire |
| title_short | Optimization of the cooling system design for a compact high-power LED luminaire |
| title_sort | optimization of the cooling system design for a compact high-power led luminaire |
| topic | Optoelectronics and optoelectronic devices |
| topic_facet | Optoelectronics and optoelectronic devices |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/215655 |
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