Chemistry Reference
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body. With this setup a relative temperature calibration was performed
with a relative accuracy of the temperature measurement of approximately
30 mK (Schimpf, 2000). The entire instrumentation was mounted on a
boom at the bow of the research vessel (Fig. 4).
4 Estimation of the skin-bulk temperature difference
In closed air circulation mode, no heat exchange between water and air is
present. The relative humidity reaches nearly 100%, and the latent heat
flux vanishes. The temperature in the air space of the facility quickly (ap-
proximately 1 minute) adjusts to the water temperature so that, in addition,
the sensible heat flux is eliminated. Thus no net heat flux at the water sur-
face is present and the bulk temperature is equal to the surface temperature
(see Fig. 5).
Fig. 5.
Schematic of the two operational modes of the wind wave facility to esti-
mate the skin-bulk temperature difference across the thermal sublayer
If the air space of the wind-wave flume is flushed with dry air (relative
humidity approximately 75%), a latent heat flux is established through
evaporation. The surface temperature drops a few tenth of a degree (“cool
skin”) and skin-bulk temperature difference is forced across the thermal
sublayer.
For a duration of 50 minutes every 5 minutes, the air conditioning sys-
tem of the facility is switched between these two conditions. Thus it is
possible to determine an averaged skin-bulk temperature difference every
10 minutes. In the first mode the infrared imager records the bulk tempera-
ture, and in the second mode the surface temperature.
