# Experimental Investigation on Affecting Air Flow against the Maximum Temperature Difference of a Lithium-Ion Battery with Heat Pipe Cooling

^{1}

^{2}

^{*}

## Abstract

**:**

_{max}). All experiments were conducted on lithium nickel manganese cobalt oxide (NMC) pouch battery cells with a 20 Ah capacity in seven series connections at room temperature, under forced and natural convection, at various air velocity values (12.7 m/s, 9.5 m/s, and 6.3 m/s), and with 1C, 2C, 3C, and 4C discharge rates. The results indicated that at the same air velocity, increasing the discharge rate increases the ΔT

_{max}significantly. Forced convection has a higher ΔT

_{max}than natural convection. The ΔT

_{max}was reduced when the air velocity was increased during forced convection.

## 1. Introduction

_{max}and ΔT

_{max}. However, FHPAFs alone cannot handle heat generation at high charge and discharge rates. In this study, cooling performance was enhanced with forced air cooling by an axial fan, and the effect of airflow on the maximum temperature difference of the battery pack (ΔT

_{max}) was investigated.

## 2. Materials and Methods

#### 2.1. Schematic of the Battery Thermal Management System

^{3}/min. An acrylic duct was fabricated to control the direction of airflow through the condenser side of the FHP. One side of the acrylic duct was connected with a flexible duct, which connected with an axial fan. The other side was not connected to anything, so that air velocity will be measured on this side. An acrylic duct was installed at the top of the battery pack and sealed with silicone to prevent air leakage. The airflow rate was adjusted using a silicon-controlled rectifier (SCR).

#### 2.2. Experimental Setup

#### 2.3. Testing Procedure

_{max}, we discharged the battery pack at room temperature (22–23 °C), and the condenser zone was cooled by means of air under different convection conditions, i.e., natural convection and forced convection, at different air velocity values (12.7 m/s, 9.5 m/s, and 6.3 m/s). The battery cells used in this experiment have a maximum discharge at 6C, and for the safety of the experiment, they were not tested at the maximum capacity of the battery. The battery pack with FHPAFs was discharged at 1C, 2C, 3C, and 4C for all different convection conditions. The charge and discharge rates of a battery are governed by C-rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1Ah should provide 1A for one hour. The same battery discharging at 0.5C should provide 500 mA for two hours, and at 2C, it delivers 2A for 30 min. Losses at fast discharges reduce the discharge time, and these losses also affect charge times. In this study, all experiments were tested at discharges of 1C, 2C, 3C, and 4C, so the time for each test was 1 h, 30 min, 20 min, and 15 min, respectively. For protection of the battery cell, the cut-in and cut-off voltages were set at 2.7 V and 4.1 V per cell, or 19.6 V and 28.7 V per battery pack, respectively. Before each test, we charged the battery according to its constant-current mode (CC) and constant-voltage mode (CV). To be specific, the battery was first charged at a constant current of 20 A (i.e., 1C, where C is the rated capacity) until its voltage reached 4.1 V. Charging then proceeded at this constant voltage and finally ended when the battery was fully charged. After charging, the battery pack with FHPAFs was left for a long time to ensure thermal equilibrium with the surroundings at a given room temperature. This was followed by discharging experiments at a constant current, i.e., 20 A (1C), 40 A (2C), 60 A (3C), and 80 A (4C), and seven temperatures on the surface of each battery cell were measured accordingly. The testing procedure flowchart is illustrated in Figure 6.

_{i}(i = 1, 2,…, 7) during the discharge and evaluated their maximum, T

_{max}, and maximum differences, ΔT

_{max}. These variables are defined, respectively, by

_{i,max,}and T

_{i,min}represent the maximum and minimum of the seven temperature measurements, respectively. The control criteria are that the T

_{i,max}must not exceed 50 °C and the ΔT

_{max}must not exceed 5 °C [30]. If the T

_{i,max}exceeds 50 °C, the discharge process will be stopped to prevent battery damage.

## 3. Results and Discussion

#### 3.1. Air Velocity Measurement

_{max}in Experiment 4C discharge rate was close to 50 °C. If the voltage is lower than this, the T

_{max}will be higher than 50 °C, which is the threshold value. The air velocity values were measured at nine points for the purpose of calculating the average value. The air velocity measurement point and air velocity values are shown in Figure 7 and Table 3.

#### 3.2. Cooling Test at 1C Discharge Rate

_{max}occurred at 2780 s, which was T

_{2}, 41.4 °C. The lowest temperature was at 2780 s, which was T

_{5}, 39.0 °C. So, the T

_{max}was 41.4 °C, and the ΔT

_{max}was 2.4 °C. This result is illustrated in Figure 8a,b.

_{1}, 27.8 °C. The lowest temperature was at 2626 s, which was T5, 25.7 °C. At 2626 s, the T

_{max}was 27.8 °C and the ΔT was 2.1 °C. However, the ΔT

_{max}occurred at 2652 s, which was 2.3 °C. The highest and lowest temperatures were 27.8 °C (T

_{1}) and 25.5 °C (T

_{5}), respectively. This result is illustrated in Figure 8c,d.

_{2}, 27.5 °C. The lowest temperature was at 2668 s, which was T

_{5}, 25.2 °C. At 2668 s, the T

_{max}was 27.5 °C and the ΔT was 2.3 °C. However, the ΔT

_{max}occurred at 2686 s, which was 2.4 °C. The highest and lowest temperatures were 27.5 °C (T

_{2}) and 25.1 °C (T

_{5}), respectively. This result is illustrated in Figure 8e,f.

_{max}occurred at 2630 s, which was T

_{2}, 28.4 °C. The lowest temperature was at 2630 s, which was T

_{5}, 26.0 °C. So, the T

_{max}was 28.4 °C, and the ΔT

_{max}was 2.4 °C. This result is illustrated in Figure 8g,h.

#### 3.3. Cooling Test at 2C Discharge Rate

_{1}reached 50.1 °C after discharge proceeded at 1156 s, while the finished time of 2C equals 30 min or 1800 s. The bi-directional power supply was turned off to protect the battery from heat generation. At 1156 s of testing, the highest temperature was 50.1 °C, which was T

_{1}. The lowest temperature was 45.0 °C, which was T

_{7}. So, the T

_{max}was 50.1 °C, and the ΔT was 5.0 °C. However, the ΔT

_{max}occurred at 1150 s, which was 5.1 °C. The highest and lowest temperatures were 49.9 °C (T

_{1}) and 45.2 °C (T

_{4}), respectively. This result is illustrated in Figure 9a,b.

_{max}occurred at 1246 s, which was T

_{1}, 34.6 °C. The lowest temperature was at 1246 s, which was T

_{5}, 27.8 °C. So, the T

_{max}was 34.6 °C, and the ΔT

_{max}was 6.8 °C. This result is illustrated in Figure 9c,d.

_{1}, 36.9 °C. The lowest temperature was at 1262 s, which was T

_{5}, 29.6 °C. At 1262 s, the T

_{max}was 36.9 °C and the ΔT was 7.3 °C. However, the ΔT

_{max}occurred at 1128 s, which was 7.4 °C. The highest and lowest temperatures were 36.8 °C (T

_{2}) and 29.4 °C (T

_{5}), respectively. This result is illustrated in Figure 9e,f.

_{1}, 39.3 °C. The lowest temperature was at 1262 s, which was T

_{5}, 31.4 °C. At 1270 s, the T

_{max}was 39.3 °C and the ΔT was 7.9 °C. However, the ΔT

_{max}occurred at 1150 s, which was 8.0 °C. The highest and lowest temperatures were 39.0 °C (T

_{2}) and 31.0 °C (T

_{5}), respectively. This result is illustrated in Figure 9g,h.

#### 3.4. Cooling Test at 3C Discharge Rate

_{1}reached 50 °C after discharge proceeded for 362 s, while the finished time of 3C equals 20 min or 1200 s. The bi-directional power supply was turned off to protect the battery from heat generation. At 362 s of testing, the highest temperature was 50.0 °C, which was T

_{1}. The lowest temperature was 42.4 °C, which was T

_{4}. So, the T

_{max}was 50.0 °C, and the ΔT

_{max}was 7.6 °C. This result is illustrated in Figure 10a,b.

_{1}, 39.2 °C. The lowest temperature was at 702 s, which was T

_{5}, 31.5 °C. At 702 s, the T

_{max}was 39.2 °C and the ΔT was 7.7 °C. However, the ΔT

_{max}occurred at 576 s, which was 7.8 °C. The highest and lowest temperatures were 39.0 °C (T

_{1}and T

_{2}) and 31.2 °C (T

_{5}), respectively. This result is illustrated in Figure 10c,d.

_{2}, 44.5 °C. The lowest temperature was at 630 s, which was T

_{5}, 33.4 °C. At 630 s, the T

_{max}was 44.5 °C, and the ΔT was 11.1 °C. However, the ΔT

_{max}occurred at 560 s, which was 11.2 °C. The highest and lowest temperatures were 44.4 °C (T

_{2}) and 33.2 °C (T

_{5}), respectively. This result is illustrated in Figure 10e,f.

_{5}, 37.9 °C. At 824 s, the T

_{max}was 48.5 °C, and the ΔT was 10.6 °C. However, the ΔT

_{max}occurred at 550 s, which was 11.4 °C. The highest and lowest temperatures were 47.2 °C (T

_{2}) and 35.8 °C (T

_{5}), respectively. This result is illustrated in Figure 10g,h.

#### 3.5. Cooling Test at 4C Discharge Rate

_{1}reached 50.2 °C after discharge proceeded for 252 s, while the finished time of 4C equals 15 min or 900 s. The bi-directional power supply was turned off to protect the battery from heat generation. At 252 s of testing, the highest temperature was 50.2 °C, which was T

_{1}. The lowest temperature was 41.8 °C, which was T

_{4}. So, the T

_{max}was 50.2 °C, and the ΔT

_{max}was 8.4 °C. This result is illustrated in Figure 11a,b.

_{2}, 43.8 °C. The lowest temperature was at 520 s, which was T

_{4}, 35.3 °C. At 520 s, the T

_{max}was 43.8 °C, and the ΔT was 10.3 °C. However, the ΔT

_{max}occurred at 424 s, which was 10.3 °C. The highest and lowest temperatures were 43.3 °C (T

_{2}) and 33.0 °C (T

_{4}), respectively. This result is illustrated in Figure 11c,d.

_{max}occurred at 538 s, which was T

_{2}, 44.3 °C. The lowest temperature occurred at 538 s, which was T

_{5}, 33.2 °C. At 538 s, the T

_{max}was 44.3 °C, and the ΔT

_{max}was 11.1 °C. This result is illustrated in Figure 11e,f.

_{2}, 49.4 °C. The lowest temperature was at 794 s, which was T

_{5}, 38.7 °C. At 794 s, the T

_{max}was 49.4 °C and the ΔT was 10.7 °C. However, the ΔT

_{max}occurred at 490 s, which was 11.5 °C. The highest and lowest temperatures were 48.0 °C (T

_{2}) and 36.5 °C (T

_{5}), respectively. This result is illustrated in Figure 11g,h.

_{max}also increased. This was because the higher the discharge rate, the more heat was released from the battery. In addition, it was found that when the discharge rate increased, ΔT

_{max}also increased, and ΔT

_{max}under natural convection was better than under forced convection because of the turbulence created during forced convection; each battery cell temperature distribution was not uniform. However, if only the case of forced convection were considered, it was found that increasing the air velocity caused the ΔT

_{max}to decrease.

#### 3.6. Comparison of the Air Velocity with Discharge Rate

_{max}also increased. At an air velocity of 6.3 m/s, the ΔT

_{max}at 1C, 2C, 3C, and 4C discharge rates were 2.4 °C, 8.0 °C, 11.4 °C, and 11.5 °C, respectively. At an air velocity of 9.5 m/s, the ΔT

_{max}at 1C, 2C, 3C, and 4C discharge rates were 2.4 °C, 7.4 °C, 11.2 °C, and 11.1 °C, respectively. At an air velocity of 12.7 m/s, the ΔT

_{max}at 1C, 2C, 3C, and 4C discharge rates were 2.3 °C, 6.8 °C, 7.8 °C, and 10.3 °C, respectively. This result is illustrated in Figure 12.

_{max}significantly. On the other hand, the ΔT

_{max}did not improve. In a 1C discharge rete, ΔT

_{max}was similar. The ΔT

_{max}of the 1C discharge rate without forced convection was 2.4 °C, which equaled the ΔT

_{max}at air velocities of 6.3 m/s and 9.5 m/s. The ΔT

_{max}at an air velocity of 12.7 m/s was 2.3 °C, which was a little better than 2.4 °C. On the other hand, discharge rates at 2C, 3C, and 4C, ΔT

_{max}, were worse than in experiments without forced convection. However, if only the experiments with forced convection were compared, it was found that if the air velocity increased, the ΔT

_{max}improved. This result is illustrated in Figure 13.

## 4. Conclusions and Future Work

#### 4.1. Conclusions

_{max}) is investigated. The NMC pouch battery cells, 20 Ah in seven series connections, were used in this experiment. All experiments were performed at room temperature under different convection conditions, i.e., natural convection and forced convection, at different air velocity values (12.7 m/s, 9.5 m/s, and 6.3 m/s), with 1C, 2C, 3C, and 4C discharge rates. The results are indicated as follows:

- By increasing the discharge rate while the air velocity remains constant, the ΔT
_{max}increases significantly. This is due to the increased heat generated by higher levels of discharging, resulting in a more uniform temperature between batteries. - The ΔT
_{max}under natural convection is lower than under forced convection. Due to the turbulence that forced cooling created, each battery cell temperature distribution was not uniform. - In forced convection, increasing the air velocity has the effect of decreasing the ΔT
_{max}.

#### 4.2. Future Work

^{®}should be used to analyze and confirm the results of experiments. Using CFD simulation software by Ansys

^{®}(Canonsburg, PA, USA), it is possible to determine the appropriate number of heat pipes and aluminum fins, air velocity value, and other factors to improve the cooling performance, especially ΔT

_{max}.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Number of new EV registrations in Thailand [3].

**Figure 4.**Assembling the FHPAFs in the battery pack: (

**a**) filling thermal grease; (

**b**) installation of FHPAFs.

**Figure 7.**The air velocity measurement method: (

**a**) The air velocity measurement point; (

**b**) Air velocity measurement.

**Figure 8.**The T

_{max}and ΔT

_{max}at 1C discharge rate under different convection conditions. (

**a**) The T

_{max}under natural convection. (

**b**) The ΔT

_{max}under natural convection. (

**c**) The T

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**d**) The ΔT

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**e**) The T

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**f**) The ΔT

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**g**) The T

_{max}under forced convection at an air velocity value of 6.3 m/s. (

**h**) The ΔT

_{max}under forced convection at an air velocity value of 6.3 m/s.

**Figure 9.**The T

_{max}and ΔT

_{max}at 2C discharge rate under different convection conditions. (

**a**) The T

_{max}under natural convection. (

**b**) The ΔT

_{max}under natural convection. (

**c**) The T

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**d**) The ΔT

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**e**) The T

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**f**) The ΔT

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**g**) The T

_{max}under forced convection at an air velocity value of 6.3 m/s. (

**h**) The ΔT

_{max}under forced convection at an air velocity value of 6.3 m/s.

**Figure 10.**The T

_{max}and ΔT

_{max}at 3C discharge rate under different convection conditions. (

**a**) The T

_{max}under natural convection. (

**b**) The ΔT

_{max}under natural convection. (

**c**) The T

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**d**) The ΔT

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**e**) The T

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**f**) The ΔT

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**g**) The T

_{max}under forced convection at an air velocity value of 6.3 m/s. (

**h**) The ΔT

_{max}under forced convection at an air velocity value of 6.3 m/s.

**Figure 11.**The T

_{max}and ΔT

_{max}at 4C discharge rate under different convection conditions. (

**a**) The T

_{max}under natural convection. (

**b**) The ΔT

_{max}under natural convection. (

**c**) The T

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**d**) The ΔT

_{max}under forced convection at an air velocity value of 12.7 m/s. (

**e**) The T

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**f**) The ΔT

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**g**) The T

_{max}under forced convection at an air velocity value of 6.3 m/s. (

**h**) The ΔT

_{max}under forced convection at an air velocity value of 6.3 m/s.

**Figure 12.**The ΔT

_{max}at different convection conditions and various discharge rates. (

**a**) The ΔT

_{max}under natural convection. (

**b**) The ΔT

_{max}under forced convection at an air velocity value of 6.3 m/s. (

**c**) The ΔT

_{max}under forced convection at an air velocity value of 9.5 m/s. (

**d**) The ΔT

_{max}under forced convection at an air velocity value of 12.7 m/s.

**Figure 13.**The T

_{max}and ΔT

_{max}at various discharge rates and different convection conditions. (

**a**) The T

_{max}at 1C discharge rate. (

**b**) The ΔT

_{max}at 1C discharge rate. (

**c**) The T

_{max}at 2C discharge rate. (

**d**) The ΔT

_{max}at 2C discharge rate. (

**e**) The T

_{max}at 3C discharge rate. (

**f**) The ΔT

_{max}at 3C discharge rate. (

**g**) The T

_{max}at 4C discharge rate. (

**h**) The ΔT

_{max}at 4C discharge rate.

Detail | Value |
---|---|

Type | Flat heat pipe |

Material | Copper |

Working fluid | Distilled water |

Wick | Sintered |

Length (mm) | 150 |

Width (mm) × Thickness (mm) | 8.0 × 3.0 |

Operating temperature (°C) | 30–120 |

Detail | Value |
---|---|

Cathode | NMC |

Package | pouch |

Capacity (Ah) | 20 |

Nominal voltage (V) | 3.7 |

Maximum voltage (V) | 4.2 |

Minimum voltage (V) | 2.5 |

Internal resistance (mΩ) | 1.5 |

Operating temperature (°C) | −40 to 50 |

Dimensions H × W × T (mm) | 128 × 210 × 7 |

Weight (kg) | 0.345 |

Point Number | SCR Voltage | ||
---|---|---|---|

220 V | 145 V | 120 V | |

1 | 13.2 | 8.9 | 5.6 |

2 | 11.3 | 8.0 | 5.5 |

3 | 11.7 | 8.4 | 5.4 |

4 | 14.0 | 10.9 | 7.1 |

5 | 10.9 | 8.3 | 5.5 |

6 | 10.7 | 6.6 | 4.3 |

7 | 14.3 | 11.3 | 7.9 |

8 | 14.4 | 11.1 | 7.5 |

9 | 13.8 | 11.7 | 8.2 |

Average | 12.7 | 9.5 | 6.3 |

Discharge Rate | Parameter | Air Velocity | Natural Convection | ||
---|---|---|---|---|---|

12.7 m/s | 9.5 m/s | 6.3 m/s | |||

1C | T_{max} (°C) | 27.8 | 27.5 | 28.4 | 41.4 |

ΔT_{max} (°C) | 2.3 | 2.4 | 2.4 | 2.4 | |

2C | T_{max} (°C) | 34.6 | 36.9 | 39.3 | 50.1 * |

ΔT_{max} (°C) | 6.8 | 7.4 | 8.0 | 5.1 * | |

3C | T_{max} (°C) | 39.2 | 44.5 | 48.5 | 50.0 * |

ΔT_{max} (°C) | 7.8 | 11.2 | 11.4 | 7.6 * | |

4C | T_{max} (°C) | 43.8 | 44.3 | 49.4 | 50.2 * |

ΔT_{max} (°C) | 10.3 | 11.1 | 11.5 | 8.4 * |

_{max}exceeded 50 °C.

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© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Anamtawach, C.; Odngam, S.; Sumpavakup, C.
Experimental Investigation on Affecting Air Flow against the Maximum Temperature Difference of a Lithium-Ion Battery with Heat Pipe Cooling. *World Electr. Veh. J.* **2023**, *14*, 306.
https://doi.org/10.3390/wevj14110306

**AMA Style**

Anamtawach C, Odngam S, Sumpavakup C.
Experimental Investigation on Affecting Air Flow against the Maximum Temperature Difference of a Lithium-Ion Battery with Heat Pipe Cooling. *World Electric Vehicle Journal*. 2023; 14(11):306.
https://doi.org/10.3390/wevj14110306

**Chicago/Turabian Style**

Anamtawach, Chokchai, Soontorn Odngam, and Chaiyut Sumpavakup.
2023. "Experimental Investigation on Affecting Air Flow against the Maximum Temperature Difference of a Lithium-Ion Battery with Heat Pipe Cooling" *World Electric Vehicle Journal* 14, no. 11: 306.
https://doi.org/10.3390/wevj14110306