  This work describes experiments on thermal dynamics of pure H2O excited by
hydrodynamic cavitation, which has been reported to facilitate the spin
conversion of para- and ortho-isomers at water interfaces. Previous
measurements by NMR and capillary methods of excited samples demonstrated
changes of proton density by 12-15%, the surface tension up to 15.7%, which can
be attributed to a non-equilibrium para-/ortho- ratio. Beside these changes, we
also expect a variation of heat capacity. Experiments use a differential
calorimetric approach with two devices: one with an active thermostat for
diathermic measurements, another is fully passive for long-term measurements.
Samples after excitation are degassed at -0.09MPa and thermally equalized in a
water bath. Conducted attempts demonstrated changes in the heat capacity of
experimental samples by 4.17%--5.72% measured in the transient dynamics within
60 min after excitation, which decreases to 2.08% in the steady-state dynamics
90-120 min after excitation. Additionally, we observed occurrence of thermal
fluctuations at the level of 10^-3 C relative temperature on 20-40 min
mesoscale dynamics and a long-term increase of such fluctuations in
experimental samples. Obtained results are reproducible in both devices and are
supported by previously published outcomes on four-photon scattering spectra in
the range from -1.5 to 1.5 cm^-1 and electrochemical reactivity in CO2 and H2O2
pathways. Based on these results, we propose a hypothesis about ongoing spin
conversion process on mesoscopic scales under weak influx of energy caused by
thermal, EM or geomagnetic factors; this enables explaining electrochemical and
thermal anomalies observed in long-term measurements.
