Applied Thermal Engineering 201 (2022) 117718
Contents lists available at ScienceDirect
Applied Thermal Engineering
journal homepage: www.elsevier.com/locate/apthermeng
Thermal performance of insulated gate bipolar transistor module using
microchannel cooling base plate
Miao Shi a, Xiaoling Yu a, *, Youbo Tan a, Xiaolin Wang b, Xiaotong Zhang c, Jianying Li c
a
School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
School of Engineering, University of Tasmania, Hobart, TAS 7001, Australia
c
State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
IGBT module
Microchannels
Thermal performance
Longitudinal vortex generators
The insulated gate bipolar transistor (IGBT) module cannot meet industrial requirements under high-power
density due to the high junction temperature and non-uniform temperature distribution. To overcome these
problems, two novel microchannel designs (i.e. longitudinal counter-flow microchannel and horizontal counterflow microchannel) were proposed for the base plate cooling of the IGBT module, in this study. A heat transfer
model was developed to investigate the heat transfer performance, pressure drop, temperature distribution of a
full-size IGBT module with the proposed microchannel cooling designs. The results showed that the horizontal
counter-flow microchannel design had better heat transfer performance, lower pressure drop, more uniform
temperature distribution and higher energy efficiency in comparison to the longitudinal counter-flow micro­
channel cooling design. To further improve the heat transfer performance, longitudinal vortex generators was
applied in the horizontal counter-flow microchannel design. It was found that the Nusselt number of the hori­
zontal counter-flow microchannel with longitudinal vortex generators reached 10.86, which increased by 61%
compared with the basic horizontal counter-flow microchannel design.
1. Introduction
With the rapid development of semiconductor manufacturing tech­
nology, insulated gate bipolar transistor (IGBT) modules with higher
capacity have been expected to meet the high-power conversion needs.
However, the gap between the IGBT module power density and indus­
trial needs has been gradually increasing [1,2]. The bottleneck limiting
the power density is heat dissipation in the IGBT module. High voltage
and current produce a large amount of heat which leads to excessive
chip temperature and hence causes serious damage to IGBT modules
[3,4]. The periodic thermal stress caused by the high temperature and
mismatch of the thermal expansion among different materials is the
main source of the interfacial stress, which results in microcracks in the
IGBT module. These microcracks expand along with the bonding inter­
face between the bonding wire and the silicon chip and hence reduce the
electrical/thermal contact [5]. Even if the chip junction temperature is
below the design limit, the increasing temperature also leads to the
linear increase of the on-state and switching power consumption of the
IGBT module. When the cooling capacity cannot meet the heat dissi­
pation requirement, the junction temperature and power consumption
of the chip will form a positive feedback relationship, causing the
junction temperature to continue to rise until a thermal breakdown
occurs [6]. Besides, the switching characteristics of the IGBT module are
also affected by the temperature difference of the chips in the multiple
chip IGBT module, and the uniform chip temperature is conducive to the
module reliability [1]. Therefore, it is important to develop an efficient
cooling method that not only keeps the chip temperature below the limit
but also improves the temperature uniformity of the module.
Indirect liquid cooling has been commonly used in high-power IGBT
modules [7,8]. The liquid cold plate (LCP) is a typical indirect cooling
equipment. It is connected with the module base plate by bolts. The
coolant flows in the LCP and does not contact the module directly
[9–11]. However, the thermal grease between the base plate and the LCP
created an additional interface thermal resistance as the thermal con­
ductivity of the thermal grease is generally 3 W/(m⋅K) much lower than
the thermal conductivity of metals [12].
To improve the cooling effect, direct cooling was then proposed by
researchers. Coolant flows in the IGBT module base plate, and exchanges
heat with the chip directly. Therefore, both the interface thermal
resistance and the conductive thermal resistance of the LCP disappear. It
improves the cooling efficiency and reduces the device dimension. But
* Corresponding author.
E-mail address: xlingyu@mail.xjtu.edu.cn (X. Yu).
https://doi.org/10.1016/j.applthermaleng.2021.117718
Received 4 July 2021; Received in revised form 21 September 2021; Accepted 20 October 2021
Available online 25 October 2021
1359-4311/© 2021 Elsevier Ltd. All rights reserved.
M. Shi et al.
Applied Thermal Engineering 201 (2022) 117718
Nomenclature
average temperature of contact walls (K)
Tcont
Tf
temperature of fluid (K)
average inlet temperature (K)
Tin
Tj
junction temperature of module (K)
average outlet temperature (K)
Tout
Tref
reference temperature (K)
Tw
average temperature of interface (K)
T1,2
transistor 1,2
U
velocity vector (m⋅s− 1)
U1,2,3
parallel units of IGBT modules 1,2 and 3
Ucond0@Tref conduction voltage(V)
Uccref
voltage under reference temperature (V)
USM
capacitor voltage of submodule (V)
V
coolant flow rate (L⋅min− 1)
Wch
width of microchannel (mm)
Win(out) width of inlet(outlet) (mm)
x, y, z
cartesian coordinate system x, y, z
total heat transfer area of the channels (m2)
Ach
cp
constant pressure specific heat (J⋅kg− 1⋅K− 1)
div
divergence operator
diode 1,2
D1,2
Dh
hydraulic diameter (m)
ESW
switching loss (W)
switching loss under reference temperature (W)
ESWref
grad
gradient operator
h
heat transfer coefficient (W⋅m− 2⋅K− 1)
Hch
height of microchannel (mm)
I
current of IGBT module (A)
Iavg
average current (A)
Iref
reference current (A)
Irms
root-mean-square current (A)
coefficient of switching loss
Ki
KSW
coefficient of switching loss (1/℃)
KT1
coefficient of conduction loss (V/℃)
KT2
coefficient of conduction loss (Ω/℃)
Ku
coefficient of switching loss
Lch
length of microchannel (mm)
length of develop section (mm)
Ldevelop
Lin(out)
length of inlet(outlet) (mm)
N
number of microchannels
Nu
Nusselt number
p
pressure (Pa)
Pcond
conduction loss (W)
total inlet pressure (Pa)
pin
pout
total outlet pressure (Pa)
Δp
pressure drop (Pa)
Q
total heat losses of IGBT module (W)
rcond0@Tref conduction resistance (Ω)
Rcap
capacitive thermal resistance (K⋅W− 1)
Rcond
conduction thermal resistance (K⋅W− 1)
Rconv
convection thermal resistance (K⋅W− 1)
Rtotal
total thermal resistance (K⋅W− 1)
Re
Reynold’s number
spacing of microchannel (mm)
Sch
T
temperature (K)
ΔT
temperature difference (K)
Subscripts
ch
f
in
out
s
w
microchannel
fluid
inlet of the base plate
outlet of the base plate
solid
wall
Greek symbols
density (kg⋅m− 3)
λ
thermal conductivity (W⋅m− 1⋅K− 1)
μ
dynamic viscosity (kg⋅m− 1⋅s− 1)
Ф
source term (W⋅m-3)
ρ
Abbreviations
COP
coefficient of performance
DBC
directed bonding copper
H-CFMC horizontal counter-flow microchannel
IGBT
insulated gate bipolar transistor
LCP
liquid cold plate
L-CFMC longitudinal counter-flow microchannel
LVGs
longitudinal vortex generators
the base plate requires far more compact cooling structures, high spe­
cific surface area and flow rates due to its space constraint. Setting fins/
pillars in the base plate can effectively expand the heat transfer area
[13–15], but the temperature uniformity of the coolant in the channel is
poor, and the coolant flowing in the centre of the channel makes little
contribution to the IGBT module cooling. With the progression of
advanced manufacturing technology, the increase of the chip capacity
leads to an exponential growth of heat loss. Therefore, for direct cooling
of high-power density IGBT modules, developing cooling structures with
large heat transfer area, low-pressure drop and good temperature uni­
formity in the restricted volume of the module base plate becomes
essential.
Benefiting from the large specific surface area and good heat transfer
performance, microchannels are the first choice for base plate cooling.
The heat transfer performance of microchannels has been widely studied
[16–18]. In terms of increasing the heat transfer specific surface area,
Jing et al. [19] studied the hydraulic and thermal performance of the
microchannels with the different shapes of channel cross-section. As the
heat transfer specific surface area decreased, both pressure drop and
heat transfer coefficient of the microchannel decreased. Li et al. [20]
studied the heat transfer characteristics and mechanisms of different
cavity arrangements in the microchannel. The results showed that the
heat transfer performance was enhanced with the increase in the num­
ber of cavities. The inner cavity increased the specific surface area and
hence effectively reduced the temperature of the coolant near the wall.
Zhou et al. [21] studied the influence of the shape of the fins on the local
flow velocity and the thermal boundary layer of the microchannel.
Square and fan-shaped fin pillars had the best heat transfer performance
as well as the largest pressure drop. Ma et al. [22] studied the flow and
heat transfer performance of the microchannel with periodically
decreasing flow area. With the increase of the pump power, the heat
transfer performance of the microchannel was improved, and the
maximum temperature of the heat source was effectively reduced.
In terms of improving the temperature uniformity, Tan et al. [23]
optimized the coverage area and flow distribution uniformity of the
coolant in the microchannel. The cobweb-shaped microchannel and
straight-web microchannel were compared in terms of the heat source
temperature difference. Kubos et al. [24] optimized the flow uniformity
of the coolant based on the level set topology optimization method, and
it was useful to improve the temperature uniformity of the heat source.
Longitudinal vortex generators (LVGs) were found useful to improve
both the heat transfer performance and the temperature uniformity as
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Applied Thermal Engineering 201 (2022) 117718
Fig. 1. Detailed features of the IGBT module.
different layouts.
Although the heat transfer performance of microchannels has been
widely studied, there are few studies on the application of the micro­
channels in direct cooling of IGBT module base plates, and the effects of
different microchannel layouts on the chip junction temperature and
module temperature uniformity were unknown. In this paper, the
application of microchannels in the IGBT module base plate was studied
to evaluate the performance of the IGBT module under high power
density. The junction temperature and temperature uniformity of the
IGBT module were evaluated when the microchannels were designed in
the longitudinal and horizontal direction of the base plate. The thermal
and hydraulic performance of the full-size IGBT module using the
counter-flow microchannel base plate was investigated. Finally, the heat
transfer enhancement using LVGs for microchannels was studied.
Table 1
Dimensions of the IGBT module (Units: mm).
No.
1
2
3
4
5
6
7
8
Name
Dimensions
Transistor (T1, T2)
Diode (D1, D2)
Solder 1
Copper 1
Ceramic
Copper 2
Solder 2
Base Plate
Materials
Length
Width
Thickness
13.38
10.65
——
——
38.5
——
——
122
12.58
7.35
——
——
32
——
——
62
0.19
0.2
0.12
0.3
0.38
0.3
0.12
3
Si
Si
SnAgCu
Cu
Al2O3
Cu
SnAgCu
Cu
Table 2
Material properties.
Materials
Si
SnAgCu
Cu
Al2O3
Thermal Grease
Al
2. Structure of IGBT module and microchannel designs
Density
Specific heat
Conductivity
ρ (kg/m3)
cp (J/(kg⋅K))
λ (W/(m⋅K))
2330
7370
8960
3890
2600
2700
700
220
385
880
1200
900
130
57
400
35
3
238
2.1. Structure of IGBT module
Fig. 1(a) and (b) show the structure of a typical commercial IGBT
module which acts as a submodule of Modular Multilevel Converter
(MMC) in a 10 kV distribution network. It consists of three working units
U1, U2 and U3 in parallel. Each working unit includes two transistors (T1,
T2) and two diodes (D1, D2). The full-size 3D model of the IGBT module is
shown in Fig. 1(c), including the transistors, diodes, directed bonding
copper (DBC) substrate, and base plate. As shown in Fig. 1(d), the
components are connected by solder layers. The 3D dimensions and
materials of the chips, solders, DBC substrate and base plate in IGBT
module are provided in Table 1, which are used to establish the full-size
3D heat transfer model of the entire module. The material properties are
listed in Table 2.
they can generate secondary flow to enhance the mixing between the hot
and cold fluids [25–27]. Ali et al. [28] studied the influence of the
structure of LVGs on the flow and heat transfer performance in the
microchannel. The results showed that the LVGs effectively improved
the heat transfer coefficient and pressure drop. Ke et al. [29] showed
that the length and position of the longitudinal vortex strongly affected
the thickness of the thermal boundary layer in the microchannel, thus
affected the heat transfer performance in the microchannel. Zhang et al.
[30] studied the influence of dimensions of LVGs on the heat transfer
performance using the Taguchi method. The results showed that the
length and spacing of LVGs had a great influence on the overall heat
transfer performance in the microchannel. Ebrahimi et al. [31] explored
the heat transfer performance and pressure drop characteristics of LVGs
in different layouts, and compared the average overall efficiency of
2.2. Design of microchannel cooling base plate
Fig. 2(a) shows a widely studied parallel-flow microchannel design.
The coolant flows in the same direction from one side of the micro­
channel to the other side. The coolant temperature rises along the
channel, and the large temperature difference of the coolant between the
upstream and downstream in the microchannel leads to the poor tem­
perature uniformity of the base plate. In order to reduce the temperature
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Applied Thermal Engineering 201 (2022) 117718
Fig. 2. Schematic diagrams of three microchannel layouts.
Fig. 3. Two microchannel designs in the cooling base plate of the IGBT module.
Table 3
Microchannel dimensions (Units: mm).
Microchannel
L-CFMC
H-CFMC
Channel
Development length
Length of inlet/outlet
Width of inlet/outlet
Height
Width
Length
Spacing
Hch
Wch
Lch
Sch
Number
N
Ldevelop
Lin(out)
Win(out)
1
1
0.5
0.5
97.5
38.5
0.4
0.4
42
108
10
10
38.5
97.5
0.5
0.5
Fig. 4. Physical properties of water [32].
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Table 4
Microchannel dimensions and boundary conditions for the model validation [34].
Microchannel parameters
Boundary conditions
Hch
Wch
Lch
Sch
N
Heat flux qw
Tin
Walls
Re
0.2 mm
0.1 mm
10 mm
0.2 mm
10
2 × 106 W/m2
20 ℃
Adiabatic
130 ~ 850
Fig. 5. Schematic diagram of microchannel grid cells.
Fig. 8. The Nu of the L-CFMC and H-CFMC base plates under different Re.
Fig. 6. Grid independence verification.
Fig. 9. Relationship between the pressure drop and flow rate.
CFMC) as shown in Fig. 2(c). This study aims to investigate the cooling
performance of the L-CFMC and H-CFMC applied to the cooling base
plate of the IGBT modules.
Fig. 3(a) and (b) show the detailed design of the L-CFMC and HCFMC adopted in the IGBT module base plate, respectively. Centerlines
of the parallel channels are in the same horizontal plane. The micro­
channels in the L-CFMC and H-CFMC are arranged alternately one by
one, and the fluids flow in the opposite directions in the adjacent two
channels. The thickness of the cooling base plate is 3 mm, and the di­
mensions of the L-CFMC and H-CFMC are detailed in Table 3.
In the IGBT modules with the microchannel cooling base plate, the
heat generated by the transistors and diodes is transmitted sequentially
by conduction to the solder layer, DBC substrate, solder layer and base
plate, as shown in Fig. 1(d). All the heat was then carried away by the
coolant flowing through microchannel within the base plate, as shown in
Fig. 7. Validation of microchannel model.
difference, the counter-flow microchannel was proposed in this study as
shown in Fig. 2(b) and (c). The coolant flows in bi-direction to improve
the temperature uniformity of the base plate. The microchannel can be
designed either along the length of the base plate as shown in Fig. 2(b)
called longitudinal counter-flow microchannel (L-CFMC) or along the
width of the base plate called horizontal counter-flow microchannel (H5
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Fig. 10. Temperature distribution of different modules.
Fig. 3. The coolant is water and its physical properties vary with tem­
peratures, as shown in Fig. 4 [32]. The temperature of the coolant at the
inlet of the base plate is 20 ◦ C.
(1) The fluid flow and heat transfer are in three dimensional and
steady-state.
(2) The flow is incompressible and laminar.
(3) No-slip velocity boundary conditions at all the microchannel
wall.
(4) The heat generation in chips are uniform.
(5) Effects of gravity and other forms of body forces are negligible.
3. Numerical model and model verification
3.1. Numerical model
In order to solve the conjugate heat transfer problem in the full-size
IGBT module with microchannel base plate. A three-dimensional (3D)
heat transfer model is developed based on the following assumptions.
The 3D simulation domain is composed of the entire module, including
the solid domain (transistors, diodes, solders, DBC substrate and
microchannel base plate, see Fig. 1) and the fluid domain (coolant in the
microchannel base plate) (see Fig. 3).
The governing equations of flow and heat transfer in IGBT module
with microchannels are as follows:
Continuity equation:
div(ρf U) = 0
(1)
Momentum equation:
U⋅div(ρf U) = − divp + div(μf ⋅gradU)
Energy equation:
6
(2)
M. Shi et al.
Applied Thermal Engineering 201 (2022) 117718
Fig. 11. Variation of junction temperature and temperature difference of chips. (T1 and T2 represent the transistors, D1 and D2 represents the diodes, and U1, U2, U3
represent the module units).
U⋅div(ρf cp, f T) = div(λf ⋅gradT) (fluid)
div(λs ⋅gradT) = Φ (solid)
(3)
(
ESW = ESWref
(4)
I
Iref
)Ki (
USM
Uccref
) Ku
[
]
1 + KSW (Tj − Tref )
(6)
where I is the current of IGBT module under working condition. Iref,
Uccref and ESWref are the current, the voltage and the switching loss under
reference temperature. USM is the submodule capacitor voltage. Ki, Ku,
and KSW are coefficients in ESW calculation.
The interface conditions between dissimilar solid materials in the
module are connected. In microchannels, the interface conditions be­
tween the solid material and the water are coupled heat transfer sur­
faces, which mean the velocity is zero and the heat is connected on these
surfaces.
The boundary conditions of the heat transfer model of the IGBT
module with microchannel base plates are as follows:
where U is the velocity field of fluid flow, ρf, cp, f, μf, and λf are the
density, specific heat, dynamic viscosity, and thermal conductivity of
the coolant, respectively. λs is the thermal conductivity of the solid. Ф is
the source term. T is the temperature field in the domain.
The IGBT module acts as a submodule of Modular Multilevel Con­
verter (MMC) in a 10 kV distribution network. In this situation, the IGBT
module works under a steady condition. Ф in equation (4) is heat gen­
eration of chips. The heat generated by the transistors and diodes is
composed of the conduction loss Pcond and the switching loss ESW,
calculated by using Formula (5) and Formula (6) respectively [33]. The
heat of T1, T2, D1 and D2 from the module producer are 11.0573 W,
51.3189 W, 17.4182 W and 3.5481 W, respectively.
⃒ ⃒[
⃒ 2 ⃒[
]
⃒ rcond0@T + KT2 (Tj
Pcond = ⃒Iavg ⃒ Ucond0@Tref + KT1 (Tj − Tref ) + ⃒Irms
ref
]
− Tref )
(5)
(1) The flow rate of 0.2–3.5 L/min, and the coolant temperature of
20℃ was set at the inlet of the microchannel base plate.
(2) The pressure at the outlet of the microchannel base plate was set
as 0 Pa.
(3) The heat generation of T1, T2, D1 and D2 was 11.0573 W, 51.3189
W, 17.4182 W and 3.5481 W respectively, and was set in the body
of each chip uniformly.
(4) All external walls of the module (see Fig. 1) were adiabatic.
where Iavg and Irms are the average current and the root-mean-square
current, respectively. Tref is the reference temperature and Tj is the
junction temperature of IGBT module. Ucond0@Tref is the conduction
voltage at Tref, and rcond0@Tref is the conduction resistance at Tref. KT1, KT2
are coefficients in Pcond calculation.
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Applied Thermal Engineering 201 (2022) 117718
Fig. 12. Thermal resistance analysis of the L-CFMC and H-CFMC base plates.
achieved using the COUPLED algorithm. After updating properties of
solids and fluid, the COUPLED algorithm firstly solves coupled equations
comprising the momentum equation and the continuity equations. Then
the energy equation is solved using the current values of the solution
variables. These solving steps are iterated until the convergence criteria
are met.
3.2. Model verification
To verify the numerical heat transfer model of the microchannel
proposed in this paper, a simulation for the parallel-flow microchannels
was conducted and the results were compared with those reported in the
literature [34]. The key parameters of the microchannels and boundary
conditions of the model are the same as those in the literature and listed
in Table 4.
The grid cell size is determined according to the number of grids on
the shortest edge of the microchannel, as shown in Fig. 5. The simulation
results at different grid numbers were shown in Fig. 6. It can be seen that
the simulation results are independent on the grid number when the grid
number on the shortest edge of the microchannel is over 10. Fig. 7 shows
the comparison between the simulation results from the proposed model
and the experimental and simulation results from the literature [34]. It
can be seen that the simulation results in this study agreed well with
both the experimental and simulation results in the literature. This
Fig. 13. COP of the IGBT modules with L-CFMC and H-CFMC.
The solver is the commercial CFD package, FLUENT with the
pressure-based finite volume scheme. The convective and diffusive
terms of the momentum, energy equations spatial discretized using the
second-order upwind scheme, respectively. Pressure-velocity coupling is
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Fig. 14. Dimensions and allocations of LVGs in the microchannel.
Fig. 15. Secondary flow in the microchannel cross-section (x = 14 mm).
comparison results demonstrated that the numerical heat transfer model
proposed in this study can be reliably used to predict the thermal per­
formance of the microchannel.
3.3. Data reduction
The flow and heat transfer characteristics in the IGBT module with
microchannels are analyzed by the following parameters. The pressure
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Applied Thermal Engineering 201 (2022) 117718
Fig. 16. Temperature fields in the central section of the microchannel (y = 0.45 mm).
Fig. 17. Velocity fields in the central section of the microchannel (y = 0.45 mm).
Fig. 18. Comparisons of Nu, Δp and COP of H-CFMC with and without LVGs.
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Applied Thermal Engineering 201 (2022) 117718
drop (Δp) of the fluid in the microchannel can be calculated by (7):
Δp = pin − pout
4.2. Pressure drop
(7)
Rcond =
Tw − Tcont
Q
(10)
Fig. 9 shows the pressure drop of the fluid across the L-CFMC and HCFMC base plates. It can be seen that the flow resistance of the H-CFMC
and L-CFMC base plates increases as the flow rate increases. The pres­
sure drop in the H-CFMC base plate increases much slower compared
with that in the L-CFMC base plate. This is mainly because the channel
length of the H-CFMC base plate is shorter than that in the L-CFMC base
plate. Also, the flow velocity in the H-CFMC base plate is lower than that
in the L-CFMC base plate as the number of the channels in the H-CFMC
base plate is more than that in the L-CFMC base plate. In this study, the
flow velocity in the channels of the H-CFMC base plate is reduced by
61% compared with that of the L-CFMC base plate at the same flow rate,
and the channel length of the H-CFMC base plate is 39% of that of the LCFMC base plate. With the shorter channel length and lower flow ve­
locity in the microchannel, the pressure drop of the fluid in the H-CFMC
base plate is much lower than that in the L-CFMC base plate. As the flow
rate increases, the advantage of the H-CFMC base plate in the pressure
drop becomes more obvious. At the flow rate of 3.5 L/min, the pressure
drops of the L-CFMC and H-CFMC base plates are 56.82 kPa and 9.29
kPa, respectively. The H-CFMC base plate shows a better hydraulic
performance.
Rconv =
Tcont − Tf
Q
(11)
4.3. Junction temperature and the temperature uniformity of the IGBT
module
Tf − Tin
Q
(12)
Heat transfer coefficient (h) and Nusselt number (Nu) are defined by
(8) and (9) respectively:
h=
Q
Ach ΔT
(8)
hDh
λf
(9)
Nu =
where ΔT is the temperature difference, ΔT = Tw − Tf , Tf = Tout2+Tin , Tw is
the average temperature at the interface between the base plate and DBC
substrate. Tf is the arithmetic average coolant temperature at the inlet
and outlet.
In order to characterize the heat transfer performance of the IGBT
module cooling base plate, the conduction thermal resistance Rcond,
convection thermal resistance Rconv, capacitive thermal resistance Rcap,
and total thermal resistance Rtotal are defined as the following, respec­
tively [35]:
Rcap =
Rtotal = Rcond + Rconv + Rcap
The performance and reliability of the module are affected by the
junction temperature of the chips in each unit of the IGBT module. The
temperature uniformity as well as the junction temperature of the chips
should be taken into consideration in the microchannel design. The
small temperature difference between the chips is better for the thermal
stress of the module.
Fig. 10(a) and (b) show the temperature distribution in the IGBT
module with the L-CFMC and H-CFMC base plates at the flow rate of 1.1
L/min, respectively. The temperature distribution of the chips in the
IGBT module with the L-CFMC and H-CFMC base plates is similar. The
maximum temperature differences in the chips in the IGBT modules with
the L-CFMC and H-CFMC base plates are 0.9 ℃ and 0.67 ℃, respec­
tively. Fig. 10(c) shows the temperature distribution of the IGBT module
with the parallel-flow L-CFMC base plate (see Fig. 2 (a)). Compared with
the counter-flow, the temperature difference in the chips in the parallelflow IGBT module is 2.86 ◦ C which indicates the temperature uniformity
of the parallel-flow design is much worse than the counter-flow design.
This is because that the cooling performance of the downstream coolant
becomes weaker as the downstream coolant is heated in a relatively long
flow length in the parallel-flow microchannels.
Fig. 11 shows the junction temperatures of the IGBT module under
different coolant flow rates. When the flow rate is higher than 1.5 L/min,
the junction temperatures and temperature difference in the transistors
and diodes become stable gradually. This indicates that a too high fluid
flow rate is not required for the cooling purpose in the proposed design.
This will save pump power in real applications. When the flow rate is
3.5 L/min, the highest junction temperature of chips in the IGBT mod­
ules with L-CFMC and H-CFMC base plates is 31.3 ℃ and 31.46 ℃,
respectively. The temperature difference in the chips in the IGBT module
with H-CFMC base plate is the smallest, only 0.26 ℃, which is 56.3%
lower than that with L-CFMC base plate. This indicates that the IGBT
module with H-CFMC base plate has better thermal performance.
(13)
where Tcont is the average temperature of the microchannel surfaces.
The cooling coefficient of performance (COP) of the module is
defined by (14):
COP =
Q
ΔpV
(14)
4. Results and discussion
The thermal performance including heat transfer coefficient, pres­
sure drop, chip junction temperature and module temperature unifor­
mity, thermal resistance and COP of the IGBT module with the L-CFMC
and H-CFMC designs was investigated in this section. The performance
enhancement of the H-CFMC using the longitudinal vortex generators
(LVGs) was also evaluated.
4.1. Heat transfer performance
Fig. 8 shows the variation of Nu with Re. As Re increases from 80 to
1200, the Nu increases remarkably in both L-CFMC and H-CFMC base
plates. As Re continues to increase, the increase of Nu in both L-CFMC
and H-CFMC base plates slows down. This is consistent with the con­
ventional heat transfer theory that the larger Re, the smaller the
contribution to the convective heat transfer coefficient. Furthermore, at
the same Re, the Nu in the H-CFMC base plate is higher than that in the LCFMC base plate. This is because the channel length in the H-CFMC
design is shorter than that in the L-CFMC design. Therefore, the ratio of
the region covered with developing flow to the entire flow channel is
larger, which leads to a higher average heat transfer coefficient. Hence,
the Nu is higher in the H-CFMC design compared to the L-CFMC design.
In summary, the IGBT module base plate with the H-CFMC design has
better heat transfer performance than the base plate with the L-CFMC
design.
4.4. Thermal resistance
Fig. 12 shows the thermal resistances (Rcond, Rconv and Rcap) and their
proportion of the two cooling base plates. As the coolant flow rate in­
creases, the total thermal resistances of the two cooling base plates
decrease to below 0.02 K/W. At the same flow rate, the Rtotal of the LCFMC and H-CFMC base plates is nearly the same. At the flow rate of 3.5
11
M. Shi et al.
Applied Thermal Engineering 201 (2022) 117718
L/min, Rtotal of the L-CFMC and H-CFMC base plates is 0.0127 K/W.
As shown in Fig. 12, the thermal resistance was dominated by con­
vection heat transfer. Improving the convective heat transfer would
lower the thermal resistance. As the flow rate increases, Rconv and Rcap of
the two cooling base plates decrease significantly since the heat transfer
coefficient increases as shown in Fig. 8. Rcond does not change signifi­
cantly with the flow rate since it mainly depends on the material
properties. The heat transfer coefficients of the L-CFMC base plate is
lower than the H-CFMC base plate. Therefore, Rconv of the L-CFMC base
plate is always higher than the H-CFMC base plate. At the flow rate of
3.5 L/min, Rconv and Rcond of the L-CFMC base plate account for 59.7%
and 24.1% of Rtotal, respectively, while they are 47.9% and 35.8%,
respectively in the module with the H-CFMC base plate.
equipped in the microchannel can substantially enhance the heat
transfer in the microchannel.
Fig. 18 shows comparisons of Nu, Δp, and COP of the microchannel
with and without LVGs. It is found that the heat transfer performance is
greatly improved by LVGs. However, the pressure drop in the micro­
channel is also significantly increased. At Re = 727, the Nu of the HCFMC base plate with LVGs reaches 10.86, which increased by 61%
compared with that of the H-CFMC base plate without LVGs (Nu = 6.75),
as shown in Fig. 18(a). The pressure drop is also increased by 92%, as
shown in Fig. 18(b). However, the increase of the pressure drop is worth
the cost because the Nu of the microchannel without LVGs can only
reach 7.84 at the same pressure drop. Therefore, the results indicate that
LVGs can effectively enhance the heat transfer performance of the IGBT
module using the H-CFMC base plate.
As shown in Fig. 18(c), when Re changed from 112 to 727, the COP of
the H-CFMC with LVGs is always a little bit less than that of the H-CFMC
without LVGs, however, the temperature rise of the contact wall be­
tween the DBC substrate and the H-CFMC base plate with LVGs
decreased by 30% at Re of 727, as shown in Fig. 17(c). This indicated
that the improvement of the cooling performance of IGBT module
microchannel base plate with LVGs was substantial although the COP
dropped slightly due to an increase in pressure drop. This also implied
that there is a trade-off between the cooling performance and energy
consumption when the LVGs are used in the microchannel.
4.5. Cooling COP
COP is a performance index that indicates the cooling efficiency of
the devices. A larger COP means that the same heat is dissipated with
smaller pump power. As shown in Fig. 13, as the coolant flow rate in­
creases, the COP of the IGBT module decreases. This indicates that the
pump power increases more rapidly than the cooling performance. This
indicates that the selection of the coolant flow rate should be a trade-off
between the COP and temperature rise in the IGBT module. The COP of
the IGBT module with the H-CFMC base plate is higher than the module
with the L-CFMC base plate. This is because the pressure drop in the HCFMC base plate is lower and hence the pump power is smaller. At the
flow rate of 3.5 L/min, the COP of the IGBT module with the H-CFMC
base plate is 461.5, which is about 6 times that of the IGBT module with
the L-CFMC base plate.
5. Conclusions
In this study, a novel counter-flow microchannel base plate was
proposed to enhance the heat transfer of the IGBT module. A heat
transfer model was developed and validated to investigate the thermal
performance of the IGBT module with two different microchannel base
plate designs (e.g. L-CFMC and H-CFMC). Some specific conclusions are
as follows:
4.6. Heat transfer enhancement of LVGs
From the above analyses, it can be seen that the module with the HCFMC base plate has better heat transfer performance, lower pressure
drops and higher COP in comparison to the L-CFMC base plate. In order
to further improve the heat transfer performance of the H-CFMC base
plate, LVGs was proposed to be applied in the microchannel. LVGs can
induce the secondary flow in the microchannel, promote the coolant
mixing and hence enhance the heat transfer in the microchannel. Since
the heat transfer area of the two side walls of the channel is more than 4
times of the top and bottom wall area, LVGs is allocated on the side walls
to achieve better heat transfer enhancement results, as shown in Fig. 14.
Fig. 15 shows the velocity field on the microchannel cross-section at
a position of x = 14 mm under different Re. It can be seen that as the Re
increases, the effect of LVGs inducing the secondary flow in the micro­
channel becomes more obvious, and the mixing of the fluid near the wall
and at the centre of the microchannel is more sufficient. This is bene­
ficial to break the thermal boundary layer of the coolant and thus im­
proves the heat transfer performance of the microchannel. Figs. 16 and
17 show the temperature field and velocity field, respectively, in the
central section of the microchannel with and without LVGs (y = 0.45
mm). At Re = 112, the temperature of the microchannel cross-section
with the LVGs is close to that of the smooth microchannel, the area of
the horseshoe vortex behind the LVGs is smaller. The LVGs have no
significant disturbance to the flow field under this condition. However,
as the Re increases, the horseshoe vortex increases and the LVGs
disturbance to the flow field increases. It gradually enhances the heat
transfer performance. At Re = 420, the reduction of the temperature
using LVGs becomes obvious. It can be seen that the wall temperature of
the microchannel with LVGs is obviously lower than that of the channel
without LVGs. The temperature rise of the contact wall between the DBC
substrate and the H-CFMC base plate with LVGs decreased by 30% at Re
of 727. Furthermore, the wall temperature distribution of the micro­
channel with LVGs is more uniform. The area of horseshoe vortex in the
microchannel increases, therefore the coolant disturbance produced by
LVGs enhances, as Re increases. The above analyses show that LVGs
(1) The heat transfer performance of the H-CFMC base plate is much
better than that of the L-CFMC base plate in the IGBT module. At
Re of 1005, Nu of the H-CFMC base plate is 9.2, which is 33.9%
higher than that of the L-CFMC base plate.
(2) With the advantages of more number of microchannels and
shorter microchannel length, the H-CFMC base plate always
maintains a low-pressure drop at the same flow rate, compared
with the L-CFMC base plate. At the flow rate of 3.5 L/min, the
pressure drops of the L-CFMC and H-CFMC base plates are 56.82
kPa and 9.29 kPa, respectively.
(3) Compared to the IGBT module with the L-CFMC base plate, the
junction temperature of the module with the H-CFMC base plate
is much lower, and the temperature uniformity is better. The
temperature difference of the chips in the IGBT module with the
H-CFMC base plate is 0.26 ℃ at the flow rate of 3.5 L/min.
Meanwhile, the IGBT module with H-CFMC base plate shows
better energy efficiency, and its cooling COP is about 6 times that
of the IGBT module with L-CFMC base plate.
(4) LVGs used in the microchannel plays an increasingly obvious role
in heat transfer enhancement with the increase of Re. At Re =
727, Nu of the H-CFMC base plate with LVGs reaches 10.86 which
is 61% higher than that of the H-CFMC base plate without LVGs.
In summary, the H-CFMC base plate was proved to be a novel method
to enhance the thermal performance of the IGBT module. It can sub­
stantially improve the cooling performance of the IGBT module with low
power consumption.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
12
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Applied Thermal Engineering 201 (2022) 117718
the work reported in this paper.
[16] H.E. Ahmed, B.H. Salman, A.S. Kherbeet, M.I. Ahmed, Optimization of thermal
design of heat sinks: A review, Int. J. Heat Mass Transf. 118 (2018) 129–153.
[17] S. Li, H. Zhang, J. Cheng, X. Li, W. Cai, Z. Li, F. Li, A state-of-the-art overview on
the developing trend of heat transfer enhancement by single-phase flow at micro
scale, Int. J. Heat Mass Transf. 143 (2019) 118476, https://doi.org/10.1016/j.
ijheatmasstransfer.2019.118476.
[18] T. Coşkun, E. Çetkin, Heat Transfer Enhancement in a Microchannel Heat Sink:
Nanofluids and/or Micro Pin Fins, Heat Transfer Eng. 41 (21) (2020) 1818–1828.
[19] D. Jing, L. He, Numerical studies on the hydraulic and thermal performances of
microchannels with different cross-sectional shapes, Int. J. Heat Mass Transf. 143
(2019) 118604, https://doi.org/10.1016/j.ijheatmasstransfer.2019.118604.
[20] F. Li, W. Zhu, H. He, Numerical optimization on microchannel flow and heat
transfer performance based on field synergy principle, Int. J. Heat Mass Transf. 130
(2019) 375–385.
[21] F. Zhou, W. Zhou, C. Zhang, Q. Qiu, D. Yuan, X. Chu, Experimental and numerical
studies on heat transfer enhancement of microchannel heat exchanger embedded
with different shape micropillars, Appl. Therm. Eng. 175 (2020), 115296.
[22] D.D. Ma, G.D. Xia, W. Wang, Y.T. Jia, Y.C. Yang, Study on thermal performance of
microchannel heat sinks with periodic jetting and throttling structures in sidewalls,
Appl. Therm. Eng. 158 (2019) 113764, https://doi.org/10.1016/j.
applthermaleng.2019.113764.
[23] H. Tan, L. Wu, M. Wang, Z. Yang, P. Du, Heat transfer improvement in
microchannel heat sink by topology design and optimization for high heat flux chip
cooling, Int. J. Heat Mass Transf. 129 (2019) 681–689.
[24] S. Kubo, K. Yaji, T. Yamada, K. Izui, S. Nishiwaki, A level set-based topology
optimization method for optimal manifold designs with flow uniformity in platetype microchannel reactors, Struct. Multidiscip. Optim. 55 (2016) 1311–1327.
[25] A. Ebrahimi, F. Rikhtegar, A. Sabaghan, E. Roohi, Heat transfer and entropy
generation in a microchannel with longitudinal vortex generators using nanofluids,
Energy 101 (2016) 190–201.
[26] A. Ebrahimi, B. Naranjani, S. Milani, F. Dadras Javan, Laminar convective heat
transfer of shear-thinning liquids in rectangular channels with longitudinal vortex
generators, Chem. Eng. Sci. 173 (2017) 264–274.
[27] B. Naranjani, E. Roohi, A. Ebrahimi, Thermal and hydraulic performance analysis
of a heat sink with corrugated channels and nanofluids, J. Therm. Anal. Calorim.
(2020).
[28] E. Ali, J. Park, H. Park, Numerical Investigation of Enhanced Heat Transfer in a
Rectangular Channel with Winglets, Heat Transfer Eng. 42 (2021) 695–705.
[29] Z. Ke, C.-L. Chen, K. Li, S. Wang, C.-H. Chen, Vortex dynamics and heat transfer of
longitudinal vortex generators in a rectangular channel, Int. J. Heat Mass Transf.
132 (2019) 871–885.
[30] J.-F. Zhang, L. Jia, W.-W. Yang, J. Taler, P. Oclon, Numerical analysis and
parametric optimization on flow and heat transfer of a microchannel with
longitudinal vortex generators, Int. J. Therm. Sci. 141 (2019) 211–221.
[31] A. Ebrahimi, E. Roohi, S. Kheradmand, Numerical study of liquid flow and heat
transfer in rectangular microchannel with longitudinal vortex generators, Appl.
Therm. Eng. 78 (2015) 576–583.
[32] V. Yadav, K. Baghel, R. Kumar, S.T. Kadam, Numerical investigation of heat
transfer in extended surface microchannels, Int. J. Heat Mass Transf. 93 (2016)
612–622.
[33] Y. Zhang, H. Wang, Z. Wang, F. Blaabjerg, M. Saeedifard, Mission Profile-Based
System-Level Reliability Prediction Method for Modular Multilevel Converters,
IEEE Trans. Power Electron. 35 (2020) 6916–6930.
[34] Y. Zhai, G. Xia, Z. Li, H. Wang, Experimental investigation and empirical
correlations of single and laminar convective heat transfer in microchannel heat
sinks, Exp. Therm Fluid Sci. 83 (2017) 207–214.
[35] L. Chai, G. Xia, L. Wang, M. Zhou, Z. Cui, Heat transfer enhancement in
microchannel heat sinks with periodic expansion–constriction cross-sections, Int. J.
Heat Mass Transf. 62 (2013) 741–751.
Acknowledgements
The authors acknowledge the financial support by the Opening
Project of the State Key Laboratory of Electrical Insulation and Power
Equipment, Xi’an Jiaotong University (No. EIPE20206) and the National
Key Research and Development Program, Xi’an Jiaotong University (No.
2018YFB0905802).
References
[1] H. Luo, F. Iannuzzo, F. Blaabjerg, W. Li, X. He, Effects of uneven temperature of
IGBT and diode on switching characteristics of bridge legs in MW-level power
converters, in: 2016 IEEE 7th International Symposium on Power Electronics for
Distributed Generation Systems (PEDG), IEEE, 2016, pp. 1–7.
[2] N. Iwamuro, T. Laska, I.G.B.T. History, State-of-the-Art, and Future Prospects, IEEE
Trans. Electron Devices 64 (2017) 741–752.
[3] M.H. Mohamed Sathik, P. Sundararajan, F. Sasongko, J. Pou, S. Natarajan,
Comparative Analysis of IGBT Parameters Variation Under Different Accelerated
Aging Tests, IEEE Trans. Electron Devices 67 (2020) 1098–1105.
[4] J. Zhang, X. Du, Y. Wu, Q. Luo, P. Sun, H.-M. Tai, Thermal Parameter Monitoring of
IGBT Module Using Case Temperature, IEEE Trans. Power Electron. 34 (2019)
7942–7956.
[5] Y. Huang, Y. Jia, Y. Luo, F. Xiao, B. Liu, Lifting-Off of Al Bonding Wires in IGBT
Modules Under Power Cycling: Failure Mechanism and Lifetime Model, IEEE J.
Emerging Selected Topics Power Electron. 8 (3) (2020) 3162–3173.
[6] W. Bo, T. Yong, Z. Li, Research on Thermal Failure Mechanism of IGBT Based on
Thermal Balance Analysis, in: in: 2019 3rd International Conference on Electronic
Information Technology and Computer Engineering (EITCE), 2019, pp. 514–518.
[7] I. Aranzabal, I.M. de Alegria, N. Delmonte, P. Cova, I. Kortabarria, Comparison of
the Heat Transfer Capabilities of Conventional Single- and Two-Phase Cooling
Systems for an Electric Vehicle IGBT Power Module, IEEE Trans. Power Electron.
34 (5) (2019) 4185–4194.
[8] C. Qian, A.M. Gheitaghy, J. Fan, H. Tang, B. Sun, H. Ye, G. Zhang, Thermal
Management on IGBT Power Electronic Devices and Modules, IEEE Access 6 (2018)
12868–12884.
[9] Z. Lu, K. Zhang, J. Liu, F. Li, Effect of branching level on the performance of
constructal theory based Y-shaped liquid cooling heat sink, Appl. Therm. Eng. 168
(2020) 114824, https://doi.org/10.1016/j.applthermaleng.2019.114824.
[10] A.A.Y. Al-Waaly, M.C. Paul, P. Dobson, Liquid cooling of non-uniform heat flux of a
chip circuit by subchannels, Appl. Therm. Eng. 115 (2017) 558–574.
[11] L. Sheng, L. Su, H. Zhang, K. Li, Y. Fang, W. Ye, Y. Fang, Numerical investigation on
a lithium ion battery thermal management utilizing a serpentine-channel liquid
cooling plate exchanger, Int. J. Heat Mass Transf. 141 (2019) 658–668.
[12] Y. Zhang, Y.-J. Heo, Y.-R. Son, I. In, K.-H. An, B.-J. Kim, S.-J. Park, Recent
advanced thermal interfacial materials: A review of conducting mechanisms and
parameters of carbon materials, Carbon 142 (2019) 445–460.
[13] J. Lee, S. Ki, D. Seo, J. Kim, Y. Nam, Liquid cooling module incorporating a metal
foam and fin hybrid structure for high power insulated gate bipolar transistors
(IGBTs), Appl. Therm. Eng. 173 (2020) 115230, https://doi.org/10.1016/j.
applthermaleng.2020.115230.
[14] S. Wiriyasart, P. Naphon, Liquid impingement cooling of cold plate heat sink with
different fin configurations: High heat flux applications, Int. J. Heat Mass Transf.
140 (2019) 281–292.
[15] E. Rasouli, V. Narayanan, Single-Phase Cryogenic Flow and Heat Transfer Through
Microscale Pin Fin Heat Sinks, Heat Transfer Eng. 37 (2016) 994–1011.
13