energies
Article
Performance Characteristics of PTC Elements for an
Electric Vehicle Heating System
Yoon Hyuk Shin 1 , Seung Ku Ahn 2 and Sung Chul Kim 3, *
1
2
3
*
Green Car Power System R&D Division, Korea Automotive Technology Institute, 74 Yongjung-ri,
Pungse-myun, Dongnam-gu, Chonan-si, Chungnam 330-912, Korea; [email protected]
R&D Center, 67-2 Sangdaewon-dong, Jungwon-gu, Seongnam-si, Kyeonggi 462-120, Korea;
[email protected]
School of Mechanical Engineering, Yeungnam University, 280 Daehak-ro, Gyeongsan-si,
Gyeongbuk 712-749, Korea
Correspondence: [email protected]; Tel.: +82-53-810-2572; Fax: +82-53-810-4627
Academic Editors: Samuel Gendebien and Vincent Lemort
Received: 6 July 2016; Accepted: 30 September 2016; Published: 11 October 2016
Abstract: A high-voltage positive temperature coefficient (PTC) heater has a simple structure and a
swift response. Therefore, for cabin heating in electric vehicles (EVs), such heaters are used either on
their own or with a heat pump system. In this study, the sintering process in the manufacturing of
PTC elements for an EV heating system was improved to enhance surface uniformity. The electrode
production process entailing thin-film sputtering deposition was applied to ensure the high heating
performance of PTC elements and reduce the electrode thickness. The allowable voltage and
surface heat temperature of the high-voltage PTC elements with thin-film electrodes were 800 V
and 172 ◦ C, respectively. The electrode layer thickness was uniform at approximately 3.8 µm or
less, approximately 69% less electrode materials were required compared to that before process
improvement. Furthermore, a heater for the EV heating system was manufactured using the
developed high-voltage PTC elements to verify performance and reliability.
Keywords: performance characteristics; positive temperature coefficient (PTC) element; screen printing;
sputtering; electric vehicle; high voltage
1. Introduction
The automobile industry is striving to replace internal combustion engine vehicles with
environmentally friendly electric vehicles (EVs) to address global energy depletion and environmental
pollution. The one-charge driving range of EVs must be improved to boost EV use by reducing battery
power consumption, which requires the development of a highly efficient EV heating system [1,2].
Apart from powering the vehicle engine, the EV heating system accounts for the majority of
energy consumption; therefore, some recent studies have applied high-efficiency heat pumps for
heating to improve the driving range of EVs [3–5]. The performance of heat pump systems tends to
deteriorate at low temperatures and in open air. A high-voltage positive temperature coefficient (PTC)
heater has a simple structure and a swift response; hence, for cabin heating in EVs, such heaters have
been used on their own or with a heat pump system [6–8].
The PTC element used in a high-voltage heater is an electric heat source that ensures safety
by not exceeding the design temperature. It is universally used in vehicle heating systems.
Moreover, to maximize the advantages of the PTC elements’ swift response, securing the performance
and reliability of the high-voltage PTC element by considering the driving environment and the
characteristics of repeated operations is becoming increasingly crucial as air heaters that directly heat
the air flowing into the vehicle are being actively adopted for EV heating.
Energies 2016, 9, 813; doi:10.3390/en9100813
www.mdpi.com/journal/energies
Energies 2016, 9, 813
Energies 2016, 9, 813 2 of 9
2 of 9 Cen and Wang [9] investigated the current PTC element manufacturing process and developed Cen
and Wang [9] investigated the current PTC element manufacturing process and developed
PTC elements with enhanced heating performance and durability. The raw material composition of PTC
elements with enhanced heating performance and durability. The raw material composition of any
any element
PTC element strongly influences PTC characteristics such as temperature and resistance. PTC
strongly
influences
PTC characteristics
such as temperature
and resistance.
Accordingly,
Accordingly, a uniform mixture can element
ensure performance.
stable element performance. Therefore, the physical a
uniform mixture
can ensure
stable
Therefore,
the physical
mixture
process
mixture process and the forming equipment’s compressive force, which ensures adequate and uniform and
the forming equipment’s compressive force, which ensures adequate and uniform density and
density and time inside are
the crucial
furnace, crucial and must [10].
be improved optimizes
theoptimizes sintering the timesintering inside the
furnace,
andare must
be improved
Moreover,[10]. the
Moreover, the PTC heating elements must ensure surface flatness for ease of packaging. PTC
heating elements must ensure surface flatness for ease of packaging.
In particular,
particular, the
the electrode production process, which is on
based on existing screen methods,
printing In
electrode
production
process,
which
is based
existing
screen printing
methods, must be toimproved to element
ensure PTC element and
performance and electrical and to must
be improved
ensure PTC
performance
electrical durability
and todurability reduce electrode
reduce electrode material cost. The physical and material characteristics of the electrode part of the material
cost. The physical and material characteristics of the electrode part of the PTC element, which
PTC element, which is different
a structure connecting different materials, strongly affect and
the reliability;
element’s is
a structure
connecting
materials,
strongly
affect the
element’s
performance
performance and reliability; improving this Furthermore,
process is the most difficult. Furthermore, screen improving
this
process
is the most
difficult.
screen
printing
consumes
the electrode
printing consumes the electrode material, which is expensive, and material,
which is expensive,
and
producing
a uniform
electrode producing a layer on the uniform electrode element’s surface
layer on the element’s surface is difficult. is
difficult.
Therefore, this improved the sintering process
process in
in the
the PTC
PTC element
element manufacturing
manufacturing to
to Therefore,
this study study improved
the sintering
enhance surface uniformity. The electrode production process entailing thin‐film sputtering enhance surface uniformity. The electrode production process entailing thin-film sputtering deposition
deposition was applied to ensure the heating performance of the PTC elements and to reduce the was
applied to ensure the heating performance of the PTC elements and to reduce the amount of
amount of electrode material required. In addition, a heater an EV system using
was electrode
material
required.
In addition,
a heater
for an EV
heatingfor system
washeating manufactured
manufactured using the developed high‐voltage PTC elements to verify their performance. the
developed high-voltage PTC elements to verify their performance.
2.
Fabrication of PTC Element
2. Fabrication of PTC Element The
by forming
a structure
The PTC
PTC element
element was
was manufactured
manufactured by forming a structure stacked
stacked with
with electrode
electrode layers
layers to
to transmit
ceramic
materials
(Figure
1). TheThe technical
development
of the
transmit power
power to
to semiconductive
semiconductive ceramic materials (Figure 1). technical development of key
the processes
for the element, namely sintering and electrode production, are detailed herein.
key processes for the element, namely sintering and electrode production, are detailed herein. Figure 1. Schematic of the positive temperature coefficient (PTC) element manufacturing process. Figure 1. Schematic of the positive temperature coefficient (PTC) element manufacturing process.
2.1. Sintering 2.1. Sintering
The outer component of the PTC element for heating was manufactured from a compound The outer component of the PTC element for heating was manufactured from a compound
containing barium titanate (BaTiO3), additional raw materials, and binder using a press device. containing barium titanate (BaTiO3 ), additional raw materials, and binder using a press device.
Subsequently, the component was sintered in a furnace of at least 1300 °C to combine the Subsequently, the component was sintered in a furnace of at least 1300 ◦ C to combine the compounds
compounds and increase its rigidity. The surface flatness of the plate‐type element may deteriorate and increase its rigidity. The surface flatness of the plate-type element may deteriorate because of
because of thermal deformation. However, the PTC elements for heaters must smoothly conduct thermal deformation. However, the PTC elements for heaters must smoothly conduct heat through
heat through contact. Therefore, the temperature distribution uniformity of each PTC element must contact. Therefore, the temperature distribution uniformity of each PTC element must be ensured
be ensured inside the furnace to enhance the surface flatness of the PTC elements during sintering. inside the furnace to enhance the surface flatness of the PTC elements during sintering. Appropriate
Appropriate plates were used for layering inside the furnace (Figure 2) to minimize the distortion plates were used for layering inside the furnace (Figure 2) to minimize the distortion of the PTC
of the PTC element during sintering. Silicon carbide (SiC), which has a high thermal conductivity, element during sintering. Silicon carbide (SiC), which has a high thermal conductivity, was used as
was used as the material for the base plate to enhance the temperature distribution uniformity the material for the base plate to enhance the temperature distribution uniformity within the furnace.
within the furnace. The SiC base plate also minimized bending and thickness variations by further equalizing the PTC element’s sintering temperature distribution. Energies 2016, 9, 813
3 of 9
The SiC base plate also minimized bending and thickness variations by further equalizing the PTC
element’s
sintering temperature distribution.
Energies 2016, 9, 813 3 of 9 Energies 2016, 9, 813 3 of 9 Figure 2. Schematic of the PTC element sintering process. Figure
2. Schematic of the PTC element sintering process. Figure 2. Schematic of the PTC element sintering process. After sintering, the flatness and thickness variations of the PTC elements were measured After
the
flatness
andand thickness
variations
of the PTC
elements
were measured
(Figure 3).
After sintering,
sintering, the flatness thickness variations of the PTC elements were measured (Figure 3). Table 1 lists the characteristics for each sintering process and the corresponding Table
1 lists
characteristics
each sinteringfor process
the corresponding
measurement
results.
(Figure 3). the
Table 1 lists the for
characteristics each and
sintering process and the corresponding measurement results. When SiC was used as the base plate material, thickness variation reduced by When
SiC was used as the base plate material, thickness variation reduced by approximately 60%
measurement results. When SiC was used as the base plate material, thickness variation reduced by approximately 60% compared with that obtained when aluminum oxide (Al2O3) was used; this compared
with that
when
aluminum
oxide when (Al2 O3aluminum ) was used;oxide this result
of this the
approximately 60% obtained
compared with that obtained (Al2Ois3) indicative
was used; result is indicative of the enhanced flatness of the PTC elements. enhanced
flatness of the PTC elements.
result is indicative of the enhanced flatness of the PTC elements. Figure 3. Measuring PTC element thickness. Figure 3. Measuring PTC element thickness. Figure 3. Measuring PTC element thickness.
Table 1. Specifications of the conventional and improved positive temperature coefficient (PTC) Table 1. Specifications of the conventional and improved positive temperature coefficient (PTC) element sintering processes. Table
1. Specifications of the conventional and improved positive temperature coefficient (PTC) element
element sintering processes. sintering processes.
Specifications of Sintering Process Parameter Specifications of Sintering Process Conventional
Method
Improved Method
Parameter Specifications
of Sintering
Process
Conventional
Method
Improved Method
Parameter
Sintering temperature (°C) 1310 1310 Conventional1310 Method
Improved1310 Method
Sintering temperature (°C) Base plate Al2O3 SiC ◦
Base plate ( C)
SiC Sintering temperature
1310Al2O3 1310
Thermal conductivity (W/m∙K) 25.0 77.5 Base plate
Al2 O325.0 SiC77.5 Thermal conductivity (W/m∙K) Thickness variation of the PTC element (mm)
0.05 Thermal conductivity (W/m·K)
25.0 0.15 77.5
Thickness variation of the PTC element (mm)
0.15 0.05 3
Size of the PTC element (mm
) 28.5 × 12.9 × 2.1 (length × width × thickness) Thickness
variation of the PTC element (mm)
0.15
0.05
3
Size of the PTC element (mm ) 28.5 × 12.9 × 2.1 (length × width × thickness) 28.5
× 12.9 × 2.1 (length × width × thickness)
Size of the PTC element (mm3 )
2.2. Electrode Production 2.2. Electrode Production 2.2. Electrode
Production
Producing electrodes on the element surface is the most critical procedure in the Producing electrodes on the element surface is the most critical procedure in the manufacturing of PTC elements for heaters. To enhance element performance by improving contact Producing electrodes on the element surface is the most critical procedure in the manufacturing
manufacturing of PTC elements for heaters. To enhance element performance by improving contact between materials to reduce the cost of the base materials in the electrode layer, this study of
PTC elements
for and heaters.
To enhance
element
performance
by improving
contact between
materials
between materials and to reduce the cost of the base materials in the electrode layer, this study actively applied the sputtering method instead of the existing screen printing method as shown in and to reduce the cost of the base materials in the electrode layer, this study actively applied the
actively applied the sputtering method instead of the existing screen printing method as shown in Figure 4. Table 2 details the specifications of the sputtering equipment. The electrode layer inputs sputtering
method instead of the existing screen printing method as shown in Figure 4. Table 2 details
Figure 4. Table 2 details the specifications of the sputtering equipment. The electrode layer inputs electric energy into the PTC element. The performance and durability of the electrode is dependent the
specifications of the sputtering equipment. The electrode layer inputs electric energy into the PTC
electric energy into the PTC element. The performance and durability of the electrode is dependent on the characteristics of its core because of
it the
is formed at is
the surface, where heater’s thermal element.
The performance
and
durability
electrode
dependent
on thethe characteristics
of its
on the characteristics of its core because it is formed at the surface, where the heater’s thermal energy is released. Electrode layers must be adequately thick (at least 10 μm) to withstand the energy is released. Electrode layers must be adequately thick (at least 10 μm) to withstand the voltage induced during screen printing. The characteristics of electrode layers composed of metallic voltage induced during screen printing. The characteristics of electrode layers composed of metallic materials (e.g., Ag and Al) differ from those composed of ceramic materials (e.g., BaTiO3). materials (e.g., Ag and Al) differ from those composed of ceramic materials (e.g., BaTiO3). Energies 2016, 9, 813
4 of 9
core because it is formed at the surface, where the heater’s thermal energy is released. Electrode layers
must be adequately thick (at least 10 µm) to withstand the voltage induced during screen printing.
The characteristics of electrode layers composed of metallic materials (e.g., Ag and Al) differ from
thoseEnergies 2016, 9, 813 composed of ceramic materials (e.g., BaTiO3 ).
4 of 9 Energies 2016, 9, 813 4 of 9 Figure 4. Schematic of the improved electrode patterning method. Figure 4. Schematic of the improved electrode patterning method.
Figure 4. Schematic of the improved electrode patterning method. Table 2. Specifications of the thin‐film deposition (sputtering) equipment. Table 2. Specifications of the thin-film deposition (sputtering) equipment.
3) Chamber size (m
3015 × 2450 × 3700 (width × height × depth) Table 2. Specifications of the thin‐film deposition (sputtering) equipment. Substrate rotation 28 axes (80 rpm) 3015 × 2450 × 3700
(width × height × depth)
Chamber size (m3 )3
Chamber size (m ) 3015 × 2450 × 3700 (width × height × depth) Substrate
rotation
28 axes (80 rpm)
Pump Cryo pump (22 inch) 2ea Substrate rotation Pump
Cryo28 axes (80 rpm) pump (22
Cathode power (kW) 20 inch) 2ea
Pump Cryo pump (22 inch) 2ea Cathode
power (kW)
20
Input voltage (V) DC 380 Input voltage (V)
DC 380
Cathode power (kW) 20 Vacuum gauge (Torr) 1 × 10
–760 −−6
6 –760
Vacuum
gauge (Torr)
1 × 10
Input voltage (V) DC 380 Vacuum gauge (Torr) 1 × 10−6–760 Figure 5 presents the cross‐sections of the PTC elements manufactured through the existing Figure
presents
the cross-sections
of sputtering the PTC elements
through
existing
screen
screen 5
printing method and the new method. manufactured
Compared with screen the
printing, the Figure 5 presents the cross‐sections of the PTC elements manufactured through the existing printing
method
and the
new sputtering
method.use Compared
with screen
printing,
thecontact sputtering
sputtering method reduced electrode material by approximately 69%. Moreover, screen printing method and the new sputtering method. Compared with screen printing, the uniformity of the electrode improved. method
reduced electrode material use by approximately 69%. Moreover, contact uniformity of the
sputtering method reduced electrode material use by approximately 69%. Moreover, contact electrode
improved.
uniformity of the electrode improved. (a) (b)
Figure 5. Electrode thickness of PTC elements fabricated through (a) screen printing and (b) sputtering. (a) (b)
Figure 5. Electrode thickness of PTC elements fabricated through (a) screen printing and (b) sputtering. 3. Performance Characteristics of the PTC Element Figure
5. Electrode thickness of PTC elements fabricated through (a) screen printing and (b) sputtering.
The variations in the resistance of the high‐voltage PTC element prototypes manufactured 3. Performance Characteristics of the PTC Element 3. Performance
Characteristics of the PTC Element
through both electrode production processes were measured as a function of temperature by using The variations in the resistance of the high‐voltage PTC element prototypes manufactured the experimental devices shown in Figure 6. The resulting characteristic curves are presented in The
variations in the resistance of the high-voltage PTC element prototypes manufactured
through both electrode production processes were measured as a function of temperature by using Figure 7 and summarized in Table 3. The temperature at which resistance sharply increases is called the both
experimental devices shown processes
in Figure 6. The measured
resulting characteristic curves are presented through
electrode
production
were
as a function
of temperature
byin using
the switching temperature or the Curie temperature (Tc). It is the most representative parameter of Figure 7 and summarized in Table 3. The temperature at which resistance sharply increases is called the experimental
devices
shown
in
Figure
6.
The
resulting
characteristic
curves
are
presented
any temperature‐resistance characteristic curve and is generally defined as the temperature at in
the switching temperature or the Curie temperature (T
c). It is the most representative parameter of Figure
7 andthe summarized
intwo Table
3. The
at
whichor resistance
sharply
is called
which resistance is times the temperature
minimum resistance the resistance at increases
the reference any temperature‐resistance characteristic curve and is generally defined as the temperature at the switching
temperature
or
the
Curie
temperature
(T
).
It
is
the
most
representative
parameter
temperature (25 °C). The operating Tc range during sputtering (~175 °C) is almost equal to that of
c
which the resistance is two times the minimum resistance or the resistance at the reference during screen printing, which indicates curve
that proposed approach can realize the operation range any temperature-resistance
characteristic
and is generally
defined
as the
temperature
at which
temperature (25 °C). The operating Tc range during sputtering (~175 °C) is almost equal to that required for EV heating. Moreover, the resistance
temperature‐resistance characteristics of the prototype the resistance
is
two
times
the
minimum
or
the
resistance
at
the
reference
temperature
during screen printing, which indicates that proposed approach can realize the operation range ◦ C) is3) fabricated through sputtering (prototypes C and (~175
D in Table are similar those fabricated (25 ◦ C).
The operating
Tc range
during
sputtering
almost
equalto toof that
screen
required for EV heating. Moreover, the temperature‐resistance characteristics the during
prototype through screen printing (prototypes A and B). fabricated through sputtering (prototypes C and D in Table 3) are similar to those fabricated through screen printing (prototypes A and B). Energies 2016, 9, 813
5 of 9
printing, which indicates that proposed approach can realize the operation range required for EV
heating. Moreover, the temperature-resistance characteristics of the prototype fabricated through
sputtering (prototypes C and D in Table 3) are similar to those fabricated through screen printing
(prototypes
A and B).
Energies 2016, 9, 813 5 of 9 Energies 2016, 9, 813 5 of 9 Figure 6. Measuring the temperature‐resistance characteristics of the PTC elements. Figure
6. Measuring the temperature-resistance characteristics of the PTC elements.
Figure 6. Measuring the temperature‐resistance characteristics of the PTC elements. Figure 7. Temperature‐resistance characteristics of high‐voltage PTC element prototypes Figure 7. Temperature‐resistance characteristics of high‐voltage PTC element prototypes manufactured through screen printing and sputtering. Figure
7. Temperature-resistance
characteristics of high-voltage PTC element prototypes manufactured
manufactured through screen printing and sputtering. through screen printing and sputtering.
Table 3. Temperature‐resistance characteristics of the PTC elements fabricated through screen Table 3. Temperature‐resistance characteristics of the PTC elements fabricated through screen printing and sputtering. Tableprinting and sputtering. 3. Temperature-resistance characteristics of the PTC elements fabricated through screen printing
and sputtering.
Screen‐Printed Electrode Layer Thin‐Film Electrode Layer
Parameter Screen‐Printed Electrode Layer Thin‐Film Electrode Layer
A
B
C D Parameter A
B
C D Layer
Screen-Printed
Electrode3.25 Layer
Thin-Film
Electrode
Initial resistance (kΩ) 3.00 3.32 2.98 Parameter
Initial resistance (kΩ) 3.00 3.25 3.32 2.98 Minimum resistance value (kΩ) 0.89 0.76 A 0.77 B0.79 C
D
Minimum resistance value (kΩ) 0.77 0.79 0.89 0.76 Maximum resistance value (kΩ) 4564 4784 4775 4450 Initial resistance (kΩ)
3.004564 3.25
3.32
2.98
Maximum resistance value (kΩ) 4784 4775 4450 Tc (°C) value (kΩ)
175 Minimum resistance
0.77
0.79
0.89
0.76
Tc (°C) 175 Maximum resistance value (kΩ)
4564
4784
4775
4450
A device to estimate the allowable voltage and heat‐generating temperature was fabricated ◦
T to ( C)
175 temperature was fabricated A device estimate allowable voltage and heat‐generating (Figure 8) to cexamine the the improvements in surface solidity, electrode layer contact, and PTC (Figure 8) to examine the improvements in surface solidity, electrode layer contact, and PTC element surface uniformity resulting from the thin‐film electrode production process. Power element surface uniformity resulting from the thin‐film electrode production process. Power sockets in contact with both sides of the PTC element were inserted within the Al contact tube and A
device to estimate the allowable voltage and heat-generating temperature was fabricated
sockets in contact with both sides of the PTC element were inserted within the Al contact tube and connected to the power supplier to permit power. (Figure 8) to examine the improvements in surface solidity, electrode layer contact, and PTC element
connected to the power supplier to permit power. surface uniformity resulting from the thin-film electrode production process. Power sockets in contact
with both sides of the PTC element were inserted within the Al contact tube and connected to the
power supplier to permit power.
Energies 2016, 9, 813
6 of 9
Energies 2016, 9, 813 6 of 9 Figure 8. Schematic of the device estimating the allowable voltage and heat‐generating temperature Figure 8. Schematic of the device estimating the allowable voltage and heat-generating temperature of
of the high‐voltage PTC element prototype. the high-voltage PTC element prototype.
The allowable voltage was estimated at room temperature (25 ± 1 °C). Voltages of 800 and 850 The allowable voltage was estimated at room temperature (25 ± 1 ◦ C). Voltages of 800 and 850 V
V were applied for more than 300 s. The results are summarized in Table 4. At the reference voltage were
applied for more than 300 s. The results are summarized in Table 4. At the reference voltage of
of 800 V, the high‐voltage PTC element prototypes did not exhibit any damages that could be seen 800
V, the
element prototypes
not exhibit
any than damages
could be that seen the with
with the high-voltage
naked eye. PTC
Furthermore, resistance did
variation was less 10%, that
confirming theprototypes meet the performance requirements for use in EV heaters. naked eye. Furthermore, resistance variation was less than 10%, confirming that the prototypes
A performance
contact thermometer was used to measure the element’s surface heat temperature at room meet the
requirements
for use
in EV heaters.
temperature and 330 or 350 V. The results are summarized in Table 5. The measured surface heat Table 4. Allowable voltage for the PTC element prototype for both electrode production processes.
temperatures were approximately 170 °C, which is the target temperature at 300 V for use in EV heaters. Screen-Printed Electrode Layer
Thin-Film Electrode Layer
Table 4. Allowable voltage for the PTC element prototype for both electrode production processes. Parameter
A
Parameter Initial
resistance (kΩ)
Input 800 V
Initial resistance (kΩ) Resistance
after voltage
withstanding test (kΩ)
Input 800 V Resistance after voltage Input 850 V
withstanding test (kΩ) Test duration (s)Input 850 V Test duration (s) B
Screen‐Printed Electrode Layer
3.00 A
3.25 B
3.29 3.00 3.43 3.25 3.29 3.34
3.61 3.43 3.34 3.61 300
300 C
D
Thin‐Film Electrode Layer
3.32 C 2.98 D
3.47 3.32 3.152.98 3.47 3.52
3.223.15 3.52 3.22 A contact thermometer
was used to measure the element’s surface heat temperature at room
Table 5. Surface temperature estimations for the PTC element prototypes. temperature and 330 or 350 V. The results are summarized in Table 5. The measured surface heat
temperatures were
approximately 170 ◦ C, which is the targetPrototype temperature at 300 V for use in EV heaters.
Parameter A
B
C
D Input voltage (V) 330 350 330 350 330 350 330 350 Table 5. Surface temperature estimations for the PTC element prototypes.
Surface temperature (°C) 172.1 178.3 173.9 179.4 171.2 178.6 172.4 179.2 Parameter
4. Performance and Reliability of the PTC Heater A
Input voltage (V)
4.1. Heating Performance ◦
Surface temperature ( C)
330
172.1
350
178.3
330
173.9
Prototype
B
C
350
179.4
330
171.2
D
350
178.6
330
172.4
350
179.2
An electric heater was manufactured to evaluate the performance of the developed PTC element as a heating system. Figure 9 presents the schematic design and a photograph of the test 4. Performance and Reliability of the PTC Heater
device used to measure the heating capacity, efficiency, and pressure drop of the high‐voltage heater. The temperature of the inlet and outlet air from the wind tunnel device was measured at 4.1.
Heating Performance
24 different locations using a ±0.1 °C–resolution T‐type thermocouple. Temperature and An electric
was manufactured
to evaluate
the performance
the
developed
PTC element
pressure data heater
were collected using a data logger (Gantner) under of
the following experimental asconditions: input power voltage of 330 V, inlet air temperature of 0 °C, and inlet air flow rate of a heating system. Figure 9 presents the schematic design and a photograph of the test device used to
measure
the heating capacity, efficiency, and pressure drop of the high-voltage heater. The temperature
300 kg/h. These factors mirror the characteristics of the air volume exiting a vehicle’s Heating, of Ventilation and Air Conditioning (HVAC) system blower during winter. the inlet and outlet air from the wind tunnel device was measured at 24 different locations using a
±0.1 ◦ C–resolution T-type thermocouple. Temperature and pressure data were collected using a data
logger (Gantner) under the following experimental conditions: input power voltage of 330 V, inlet air
temperature of 0 ◦ C, and inlet air flow rate of 300 kg/h. These factors mirror the characteristics of
the air volume exiting a vehicle’s Heating, Ventilation and Air Conditioning (HVAC) system blower
during winter.
Energies 2016, 9, 813
Energies 2016, 9, 813 7 of 9
7 of 9 (a)
(b)
Figure 9. Schematic fabricated for evaluating heating
heating Figure 9.
Schematic of of the the test test equipment equipment and and prototype prototype heater heater fabricated
for evaluating
performance. (a) Schematic diagram of the test equipment [5]; (b) Prototype heater. performance. (a) Schematic diagram of the test equipment [5]; (b) Prototype heater.
Heat transfer by air, power consumption, and pressure drop were measured by evaluating Heat transfer by air, power consumption, and pressure drop were measured by evaluating the
the performance of the four high‐voltage prototype heaters. Efficiency was defined as the ratio performance of the four high-voltage prototype heaters. Efficiency was defined as the ratio of the
of the heating capacity of the heater to its power consumption (Equation (1)). The results are heating capacity of the heater to its power consumption (Equation (1)). The results are summarized in
summarized in Table 6. The heating capacity and efficiency were on average 4.63 kW and 0.952, Table 6. The heating capacity and efficiency were on average 4.63 kW and 0.952, respectively, thereby
respectively, thereby meeting the performance requirements for use as electric heaters in EV meeting the performance requirements for use as electric heaters in EV heating systems. The pressure
heating systems. The pressure drop was 82.8 Pa on average, which is acceptable. drop was 82.8 Pa on average, which is acceptable.
C  m  (T  T )
η  CPP× m. × ( Too − Ti )
i
V I
η=
(1) (1)
V×I
Table 6. Results of heating performance experiments.
Table 6. Results of heating performance experiments. Parameter Prototype Heater Prototype
Heater
Parameter
A
A
B
Input voltage (V) 331.3 Input voltage (V)
331.3
330.8
Input current (A) 14.7 Input current (A)
14.7
14.7
Power consumption (kW) 4.86 4.85
Power consumption (kW)
4.86
Heating capacity (kW) 4.61 4.59
Heating capacity (kW)
4.61
Pressure drop (Pa)
83.4
Pressure drop (Pa) 83.4 82.4
Energy
efficiency
0.944
0.946
Energy efficiency 0.944 B
C
330.8 331.3
14.7 14.6
4.85 4.85
4.59 4.68
82.9
82.4 0.964
0.946 C
D
331.3 330.9
14.6 14.7
4.85 4.86
4.68 4.63
82.9 82.6
0.953
0.964 D 330.9 14.7 4.86 4.63 82.6 0.953 Energies 2016, 9, 813
8 of 9
4.2. Reliability
Vibration and thermal shock test reliability tests were conducted in compliance with the relevant
test conditions for PTC heaters (IEC60068-2-6 and IEC60068-2-14, respectively). Tables 7 and 8 present
the heating performance results before and after the vibration and thermal shock reliability tests,
respectively. After the vibration and thermal shock tests, the heating performance of the prototype
heaters decreased by a maximum of 6.1% and 5.3%, respectively, which is much less than that allowed
(10%). Moreover, after the reliability tests, the overall performance of the prototype heater reduced by
only 5%. Overall, these results prove the high reliability of the developed prototypes.
Table 7. Prototype characteristics before and after the vibration test.
PTC Heater
Parameter
Input voltage (V)
Input current (A)
Power consumption (kW)
Heating capacity (kW)
Pressure drop (Pa)
Energy efficiency
Before
After
A
B
A0
B0
331.3
14.7
4.86
4.61
83.4
0.944
330.8
14.7
4.85
4.59
82.4
0.946
330.3
14.6
4.82
4.35
83.7
0.903
329.9
14.7
4.84
4.31
83.5
0.890
Table 8. Prototype characteristics before and after the thermal shock test.
PTC heater
Parameter
Input voltage (V)
Input current (A)
Power consumption (kW)
Heating capacity (kW)
Pressure drop (Pa)
Energy efficiency
Before
After
A
B
A0
B0
331.3
14.6
4.85
4.68
82.9
0.964
330.9
14.7
4.86
4.63
82.6
0.953
330.3
14.7
4.85
4.43
84.0
0.913
330.4
14.6
4.84
4.45
83.1
0.918
5. Conclusions
This study improved the sintering process to enhance surface uniformity in the manufacturing
process of PTC elements for use in EV heating systems. An electrode production process using
thin-film sputtering deposition was applied to ensure the heating performance of PTC elements and
reduce electrode material use. In addition, a heater for an EV heating system was manufactured using
the developed high-voltage PTC elements to verify their performance. The study conclusions are
as follows:
(1) The proposed method realized an electrode layer of uniform thickness not exceeding 3.8 µm
and reduced electrode material use by approximately 69%.
(2) The allowable voltage and surface heat temperature of the high-voltage PTC elements
developed with the thin-film electrode were 800 V and 172 ◦ C, respectively, which is adequate for use
in high-voltage heaters.
(3) The results of vibration and thermal shock testing were within the standard range, confirming
that the developed heater was adequately reliable for use in EV vehicles.
Acknowledgments: This study was performed as a part of the Energy Technology Development project sponsored
by the Ministry of Trade, Industry and Energy and was supported by the 2016 Yeungnam University Research
Grant. In addition, support from E-Gun Technology is greatly appreciated.
Energies 2016, 9, 813
9 of 9
Author Contributions: Sung Chul Kim and Yoon Hyuk Shin organized the overall experimental evaluations
and result analysis. Seung Ku Ahn commented on the results and conclusions. All the authors also reviewed
the manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
Nomenclature
Cp
I
.
m
Tc
Ti
To
V
η
specific heat of air (J/kg·K)
current (A)
mass flow rate of air (kg/s)
Curie temperature (◦ C)
inlet air temperature (◦ C)
outlet air temperature (◦ C)
input voltage (V)
energy efficiency
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