Rothalpy (or trothalpy)
I
XYZ
xyz
O
xyz
\omega
V
w=V-u
Rothalpy of a fluid point
P
I=h0,rel-
| u2 | |
| 2 |
where
u=\omega x r
r=\vec{OP}
h0,rel
P
xyz
h0,rel=h+
| w2 | |
| 2 |
and is known as relative stagnation enthalpy.
Rothalpy can also be defined in terms of absolute stagnation enthalpy:
I=h0-uV\theta
where
V\theta
V
Rothalpy has applications in turbomachinery and study of relative flows in rotating systems.
One such application is that for steady, adiabatic and irreversible flow in a turbomachine, the value of rothalpy across a blade remains constant along a flow streamline:
I=const.
so Euler equation of turbomachinery can be written in terms of rothalpy.
This form of the Euler work equation shows that, for rotating blade rows, the relative stagnation enthalpy is constant through the blades provided the blade speed is constant. In other words,
h0,rel=const.
The function
I
This quantity is commonly called rothalpy, a compound word combining the terms rotation and enthalpy. However, its construction does not conform to the established rules for formation of new words in the English language, namely, that the roots of the new word originate from the same language. The word trothalpy satisfies this requirement as trohos is the Greek root for wheel and enthalpy is to put heat in, whereas rotation is derived from Latin rotare.