Abstract: Disclosed are a method and apparatus for heating a liquid using mechanical vibrations. The liquid is introduced into a cavity (1) in a rotating wheel (2) and expelled into an annular chamber (4) formed by the wheel and the stator (7), passes through a series of outlet apertures (8) and is removed. For this process, the following empirical relationships are preferred: R=1.1614 K/mm; &Dgr;R=1.1614 B/mm; and n=3.8396 K−1.5×106 revs./min, R being the radius of the peripheral cylindrical surface of the wheel, &Dgr;R being the radial dimension of the annular chamber, n the rotation frequency of the wheel, K the number of outlet apertures in the wheel. B is an integer in the rang of 1−K/5. A method and an apparatus for heating a liquid /FIG.