Abstract
Pool boiling critical heat flux (CHF) at saturated condition was simulated using the hydrogen at the copper cathode in the aqueous solution of sulfuric-acid. The critical current density (CCD) was observed at the cell potential-current density curve, which is analogous to the CHF at the boiling curve. The CHF values calculated by the gas generation rate at the CCD condition showed large discrepancies with the existing CHF values of water boiling system. Meanwhile, the superficial mechanism triggering the CHF and the CCD showed similar characteristics except the size of bubbles. The variation of bubble departure volume with respect to the current density was similar to that of the water vapor but the bubble volume of the present system was 440 times smaller at CCD condition. The critical heat flux value using the present non-heating experiment was corrected accounting for the bubble volumes and the discrepancy with the water CHF was less than 10%. It is concluded that the water CHF condition can be simulated by the non-heating hydrogen evolving system.
Highlights
The nucleate boiling allows larger heat transfer coefficients than the single phase convection
A gas evolving electrode system has upper operational limits so called critical current density (CCD) (Vogt et al, 2004). This limit of the gas generation rate can be roughly elucidated that the vigorous generation of bubble forms the film on the active surface and this gaseous film impedes the convection of the bulk liquid, which is quite similar to the film formation after departure from nucleate boiling (DNB)
The CCD criterion was determined when cell potential was abruptly increased, which is similar to the abrupt temperature increase at the critical heat flux (CHF) condition as the cell potential of the present system is analogous to the superheat of the boiling system
Summary
The nucleate boiling allows larger heat transfer coefficients than the single phase convection. Chung and No (2007) established nucleate boiling limitation model which predicts CHF condition based on dry area fraction studied by Ha and No (1998) As a result, they proposed the heat flux prediction equation from nucleate boiling to a CHF expressed as following relation. A gas evolving electrode system has upper operational limits so called critical current density (CCD) (Vogt et al, 2004) This limit of the gas generation rate can be roughly elucidated that the vigorous generation of bubble forms the film on the active surface and this gaseous film impedes the convection of the bulk liquid, which is quite similar to the film formation after departure from nucleate boiling (DNB).
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