The thermal management system or perhaps more correctly the Battery Thermal Management System (BTMS) encompasses the control and temperature regulation of a battery system to ensure optimal performance, reliability, and lifetime. Hence it is everything from the cell to the heat rejection to the environment.
This means we need to consider the cell requirements, other sources of heat flux, the transport medium, heat exchange, sensing, control and use cycles.
Within the Thermal section we cover the heat generation within a cell and look at the absolute temperature limits. Up to and including cell to cooling interfaces.
When we consider the battery thermal management system we need to start with the basics and look at the heat sources and paths in a battery pack. We don’t have to minimise all of these sources of heat, but it is important that we carefully consider them all.
It is important to calculate
- thermal gradients within a cell
- total heat generated
- thermal gradients across the pack
Thermal Conduction and Temperature Gradients
Whatever the cell format and however we cool it there will be a temperature gradient. This is described by Fourier’s Law of Conduction. An empirical law stating that the rate of heat flow is directly proportional to the temperature gradient and the area of heat transfer, and inversely proportional to the thickness of the material.
Cell to Cell Temperature Gradient
With any cooling system design it is important to consider the cell to cell temperature gradient.
The thermal management system is unlikely to be just concerning the battery pack. Hence it is important to think about the complete system and all of the connections. Those connections can be heat exchange (coolant pipes), mechanical, electrical or control signals.
See also: Refrigerant based Cooling, Heat Generation in a Cell, Performance Analysis of an Integrated BEV Thermal Management