Heat of Ablation

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Heat of Ablation

A measure of the effective heat capacity of an ablating material, numerically the heating rate input divided by the mass loss rate which results from ablation. </dd>
In the most general case, heat of ablation is given by

(qc + qr - σεTw4)/m

qc is convective heat transfer in the absence of ablation; qr is radiative heat transfer from hot gases to ablation material; σεTw4 is rate of heat rejection by radiation from external surface of ablation material; and m is rate at which gaseous ablation products are injected into the boundary layer.
Heat of ablation is sometimes evaluated neglecting the heat rejected by radiation and as a result unrealistically high heats of ablation are obtained.
If qr > σεTw4, for moderate values of stream enthalpy hs, heat of ablation is given by

Hv + μ (hs - hw)
where Hs is heat required to cause a unit weight of mass

to be injected into boundary layer; μ is blocking factor with numerical value from about 0.2 to 0.6 depending on material and type of flow; and hw is enthalpy at wall temperature. [[/a>|/a> ]]


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use