Prototype Testing and Evaluation
5.2 Experiment Setup
The test rig is designed based on two battery cells. Fig. 5.6 shows the experiment schematic. It mainly consists of a test unit, heating/cooling loops, a regulating system, data measurement and acquisition, power supply systems and an environmental controlled chamber. The unit was entirely isolated from the environment by the environmental chamber/freezer, and fluid loops were well insulated to minimise heat loss. Fig. 5.7 demonstrates the in situ experiment in details. Note that a heating block and a fan were used to create a desired summer ambient environment (35 ± 1°C), and a freezer was provided to create different sub-zero temperatures maintaining the chamber environment at -25 ± 2°C, -15 ± 2°C and 0 ± 1°C.
The battery cooling/heating system contains a liquid box, water baths, water pumps, inverter drives and circulating liquid loops (Fig. 5.6). The water bath A provides either heating or cooling to the battery cell by regulating pre-treated liquid coolant at a certain temperature. Water bath B adds another function of simulating battery thermal condition at a controlled temperature examining system transient performance. To note, water bath B only serves to provide a constant initial battery surface temperature at 40°C, 50°C, 60°C, and 70°C since it is difficult to control cartridge heaters to reach to a predetermined temperature. Due to the provision of inverter drive, the water pump can generate different mass flow rates with pre-determined temperatures to simulate different battery working conditions such as acceleration, braking, downhill, uphill, and even start-up condition during cold weather.
The regulating system has two parts: 1) controlling the heat power inputs;
and 2) adjusting liquid coolant flow rate. The power input for the battery cell
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can be regulated via DC power supply, and the flow rate can be changed from inverter drive. DC power supply is provided for cartridge heaters where input voltage (0 – 35 V) can be adjusted accordingly and AC power supply (220 V, 30 – 60 Hz) is used for water pump.
Figure 5.6: Experiment schematic.
Figure 5.7: In situ experiment details.
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The system measurement includes battery power input, battery surface temperature, inlet temperature and outlet temperature of the liquid box, and flow rate of the discharging coolant. The monitored battery surface temperatures can be measured by arranging thermocouples on the back of the plate where channels are constructed such that the thermocouples can be inserted in. Such arrangement is demonstrated in Fig. 5.8.
Figure 5.8: Arrangement of thermocouples on the testing L-shaped heat pipe (T1- T10) and on the back of the plate channels for battery surface temperature measurement (Tb1- Tb7).
5.3 Instrumentation
A list of experimental instruments is demonstrated in Fig. 5.9. Detailed description of each device was made in Table 5.3.
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Figure 5.9: Devices used in experiment.
121 Table 5.3: List of instrumentation
No. Instrument Operating Range Accuracy Comment Quantity
1
Four 10 mm × 100 mm stainless steel cartridge heaters were used to heat up the simulated battery core. DC dual power supply can be adjusted to obtain predetermined power for the battery.
1 circulating bath has a capacity of 6 litres with standard digital controller. It provides precise and stable cooling for laboratory and is ideal for routine applications. The cooling capacity at 0°C, 20°C and -10°C is 140 W, 200 W and 100 W respectively, and the heater wattage is 1600 W. The refrigerant it uses is CFC-free, and the container is made of 304 stainless steel.
2
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The hydraulic gear pump has
specifications of max speed 4000 RPM, 3.75 l/min (flow at 1500 RPM), and 275 bar maximum continuous pressure. The vector control AC frequency inverter converts single phase 230 V input to three phase 230 V for a standard AC induction motor. It has Soft-PWM control with input current of 6.5A and input voltage of 200 –240 V single phase +10 –15% at 50/60 Hz ± 5%. The above devices were used to control the flow rate of the discharged coolant.
The flow rate can be measured from Parker inline flow transmitter and read from DT500 dataTaker. The rotor inside the flow meter, which spins each blade obscures the infra-red signal and then converts it into standard pulse output signal read by DT500 dataTaker. Such digital flow metre can operate at any plane with negligible pressure drop. The maximum working pressure is 20 bar, with maximum 0.1 bar pressure drop at 15 l/min. The pulse output signal for flow is up to 25 l/min, and the calibration is
1
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channels 752 pulses per litre. The digital flow
metre requires 5 V DC power supply, which can be provided by DT500 Datataker. The flow calibration was made by comparing with a standard measuring unit. The uncertainty of the flow measurement is ± 2.1%.
8 RS Thermocouple
(K-type) -200 – 1250 °C ± 2.2 °C or
± 0.75% above 0 °C
Welded tip thermocouples (K-type) have the fastest responding. They are nickel based and can exhibit good corrosion resistance. The standard accuracy is affected by deviations in the alloys (nickel-chromium). However, deviations between thermocouples differ little and a much higher accuracy can be achieved by individual calibration.
Two TC-08 thermocouple data loggers are used to be connected with K-type thermocouples. The measurements are made very fast and accurately, and the high (20-bit) resolution ensures that minute changes in temperature can be detected. The low conversion time (100 ms) of TC-08 indicates that up to 10 temperature measurements can be taken every second.
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9 Pico Thermocouple Data Logger (TC-08)
-270 – 1820 °C
(8 channels) ± 0.2% or ± 0.5 °C 2
124 10 RS Portable Digital
Thermometer (206-3738) -50 – 1000 °C
Accuracy at 0.1°C resolution:
± 0.2% rdg + 1°C @-50 – 199.9°C
All thermocouples were calibrated using the RS portable digital thermometer.
Calibration was done by recording the readings of those 16 K-type
thermocouples connected with
corresponding two TC-08 thermocouple data loggers every 10 °C from -20 °C to 70 °C. A water bath filled with glycol-water mixture was served for providing a stable and constant temperature
environment. The apparent temperature readings were compared with the standard temperature obtained from RS thermometer (Table A.1). The average accuracy of the thermocouples used was
±2.06% or ±0.61°C before calibration (with maximum accuracy of ±8.60% or
±2.01°C; for details, see Appendix A)
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In order to simulate the thermal
environment inside the battery model, an environment controlled chamber/freezer was used with integrated heating (a heating block, a fan, and ISO-TECH DC power supply help create a desired summer ambient environment) and cooling. The temperature inside the
1
125 Channel 4: 8 – 15 V;
Current: 0–3 A or 1 A
chamber will be controlled at 35 ± 1°C representing summer operating
condition. The freezer will be used to create different sub-zero temperatures maintaining the chamber environment at -25 ± 2°C, -15 ± 2°C and 0 ± 1°C for battery preheating test.
13 FLIR Thermal imaging
camera (i7) -20 – 250 °C 0.1 °C
A thermal imaging camera was used to capture surface temperature distribution during experiments
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