Ablation enthalpy

One other temperature that has found some utility, in ablation studies using a plasma jet, has been referred to as the calorimetric temperature. The enthalpy of the stream of hot gas is determined with a calorimeter and the known heat content of the gas makes possible a calculation of the original temperature of the gas. 

In an ablating system, the change in the enthalpy of the coolant, i,w - iic, includes the effective heat of ablation, the heat absorbed by phase change, and the chemical processes that take place in the char, if present. In evaporating systems, ilw - ilc includes the heat of vaporization. 

Gaseous products formed by material ablation are injected into the hot boundary layer. In diffusing through this high temperature region, they absorb heat by sensible temperature rise. The boundary layer is thus increased in thickness, and its original enthalpy or temperature is lowered. Consequently, less heat is transferred from the environment to the ablating surface. 

These pyrolytic species are injected into the adjacent hot boundary layer, and they effectively lower the enthalpy (heat content) of the environment. In this manner, less heat is convected to the ablating surface. 

Spalling. This is only possible for brittle materials. In this case the energy required to ablate an unit of volume is much smaller than the binding enthalpy between the ions (see Sect. 2.1) or the latent heat of melting. 

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