TRANSIENT HEAT TRANSFER FROM A HORIZONTAL FLAT PLATE IN A POOL OF LIQUID HYDROGEN

Transient heat transfer caused by exponentially increasing heat input (Q = Q(0) exp(t/tau)) to a flat plate in a pool of liquid hydrogen was measured under saturated and subcooled conditions at pressures from 104 to 700 kPa. The exponential period tau was varied from 8 ms to 8 s and the liquid subcoolings from 0 to 8 K. The flat plate heater used was 5 mm in width, 60 mm in length and 0.5 mm in thickness. Transient heat transfer before the inception of boiling for the exponential period shorter than 100 ms was expressed well by the transient conduction heat transfer with no movement of liquid. Incipient boiling heat flux and temperature were higher for shorter period. Transient critical heat flux was higher for shorter exponential period and higher subcooling. No direct transition from non-boiling to nucleate boiling such as first found by some of the authors for transient heat transfer in a pool of liquid nitrogen was observed for liquid hydrogen. An equation for transient critical heat flux was given.