This section lists some predefined variables that are available to evaluate heat fluxes, sources, and integral quantities used in heat and energy balance. All the variable names begin with the physics interface name (the prefix). By default the Heat Transfer interface prefix is ht, and the Heat Transfer in Shells interface prefix is htlsh. As an example, you can access the variable named tflux using ht.tflux (as long as the physics interface is named ht).