THERMAL MANAGEMENT TECHNIQUES

THERMAL MANAGEMENT TECNIQUES

WHAT IS BTMS?

• BTMS- BATTERY THERMAL MANAGEMENT SYSTEM.
• It plays a vital role in the thermal control of battery thermal behavior.
• These systems are analyzed through a trade-off between performance, weight, size, cost, reliability, safety, and energy consumption.
• For the safe functioning of the battery pack, the BTMS should be installed with the right functions such as cooling, heating, insulation, ventilation.

WHY DO BATTERIES PRODUCE HEAT?

• In a pack, the number of cells are connected in series and parallel connections by different methods.
• These connections at the cell terminals cause more concentration of heat which leads to a rise in temperature at charge-discharge cycles.

• These images will give a brief idea about how the battery pack looks like, how the cell will transmit the current to the load, how cell terminals get heated up, how it transmits the energy to the atmosphere from the cell.
• Due to enthalpy changes, electrochemical reactions a large amount of energy is generated inside the cell.
• Resistive heating is also another factor for the battery because of the cell resistance inside the cell.

WHAT IS ENTHALPY?

• When a chemical reaction takes place, a substance can become warmer or colder.
• As a result, heat is released to the surroundings or absorbed from the surroundings until the temperature is the same again.
• At a constant pressure, the amount of heat is added or removed from the system.
• In simple words, it is the sum of internal energy plus the product of pressure and volume i.e., work done.
• It also accounts for the energy required to combat the atmospheric pressure.

FUNCTIONS THAT ARE TO BE INSTALLED IN BTMS:

COOLING:

• When the battery pack is operated, it not only generates the electricity but also generates heat.
• This heat is to be removed from the battery pack even it reaches to the optimum temperature a cooling function is required in the BTMS.

HEATING:

• In cold climate conditions, the battery pack normal temperature drops below the lower operating temperature.
• For this case, we need to have a heating function, such as a PTC heater, which brings the battery pack temperature to the operational range within a short period of time.

INSULATION:

• Insulation is required to control the extreme weather conditions.
• The temperature difference between outside and inside of the battery pack are having very large ranges.
• To prevent this, we need to have a good insulation where the rise and fall of the battery pack temperature is very slow even the car is parked outdoors.

VENTILATION:

• It is used to exhaust the hazardous gasses from the battery pack.
• By keeping a one-way check wall, these gases are regulated outside of the battery pack with an air system, which reduces the concentration of the fumes inside the battery pack.

HOW TO CALCULATE HEAT DISSIPATED BY THE BATTERY PACK?

• The heat is generated by the internal resistance of the cell that are connected in series and parallel.
• We can estimate the dissipated amount of heat by using:

P=(R*I^²)

• For example, when we consider a battery of 480 cells having a current of 4A and internal resistance of the cell is 30mOhm. The total power to be dissipated is given as:
  • Per cell= 4*4*0.03= 0.48W is for one cell in a battery pack.
  • When we multiply with total no cells = 0.48*480 = 230.4W.

HOW BTMS IS GOING TO FUNCTION IN THE BATTERY PACK?

• The aim of BTMS is used to increase the lifetime of the cells and to manage the temperature levels and distribution.
• The developed BTMS is a combination of thermoelectric cooling, forced air cooling, liquid coolant cooling.
• The thermal management systems are used to increase the longevity of the cells, to maintain the range
• To attain the peak powers even when we use the battery for acceleration, regenerative braking mode, hill climbing.
• The thermal management of batteries can be defined in several types:

2. Immersion cooling.
3. Flexible material mountings.
4. PCM (phase change material cooling).

FINS

• These are the extra projection on the surface of the battery pack.
• These fins provide a natural convection using air as a medium which removes the heat from the battery pack
• When the vehicle is moving the air, which is forced around the battery pack and heat is removed.

IMMERSION COOLING:

• In this type, the battery pack is immersed in a coolant and is well sealed in all directions.
• In this type, the cooling from the battery is taken by the coolant which is present inside the battery casing.
• This improves the power density, and helps in fast charging of the battery, increase in life cycle, thermal runaway can be controlled.

FLEXIBLE MATERIAL MOUNTINGS:

• In this type, the battery is placed in a fixture.
• This fixture is good in resisting the vibrations and damage occurring at the time of usage of the battery pack in the vehicle.
• These materials having some spacing which provides the air to move in and go out easily.

The flexible material is mounted with different types of cooling.

1. Air cooling.
2. Fan cooling.
3. Indirect liquid cooling.
4. Direct liquid cooling.

AIR COOLING:

• The natural air is sent into the walls of the battery pack and between the cells.
• These air media are used to absorb the heat flow which is released by the battery pack.

FAN COOLING:

• in this type of cooling, forced air is made to pass over the battery pack

and the heat is removed from the battery pack.

• The fan is used to force the air.

INDIRECT COOLING METHOD:

• In this type of cooling, the coolant is forced into the pipe type fixture where is removes the heat is removed in a convective mode of heat transfer.
• The circuit is placed in such a way that, maximum heat transfer is made to happen.

DIRECT LIQUID COOLING:

• in this type of cooling, the coolant is made in contact with cells.
• Thus, which it creates more amount of heat to be removed from the cells.
• The coolant should be more viscous, which makes it to easily flow through the cells.
• the coolant is passed through the heat exchanger and compressor and radiator.
• For the better cooling and the temperature of the cells are maintained by condensing the coolant.

PCM (PHASE CHANGE MEMBRANE):

• PCMs, undergo by changing their phase by absorbing or releasing the abundant heat from the battery which is generated at the time of charge and discharge cycles.
• This passive PCM cooling technology maintains the operating temperature of batteries at a relatively constant temperature while these batteries are operated.

• The PCM is made from paraffins, fatty acids, salt hydrate. The most used phase change material is paraffin wax, which has high heat absorption, corrosive resistive, large melting point.
• PCM is sandwiched between two batteries where is connected to a cooling plate where the water is passed between the plates.
• When the PCM is combined with the copper form which creates a composite phase change material that is used for Active PCM cooling.

BENEFITS OF HAVING BTMS:

• BTMS has both hardware and software which takes control over the overall battery pack temperature.
• It is used to maintain the cells at an optimum temperature range.
• Increase the lifetime of the cells by keeping the cells safe and secure.
• To prevent the thermal runaway while the batteries at higher temperature.