Modeling of an isolated liquid hydrogen droplet evaporation and combustion

摘要

In this model, diffusive governing equations of Liquid Hydrogen (LH) evaporation and combustion were solved. The simulation reveals that, there exists a critical radius (a(cri)) where radiation heat is equal to conduction heat (Q(rad) = Q(cond)) and a(cri) is a function of ambient temperature during LH droplet evaporation process. Under pure evaporation condition, for large liquid hydrogen droplets (a a(cri)) radiation heat is dominant at a given environment temperature, but as liquid droplet size decreases, radiation heat becomes insignificant and thermal conduction will be dominant for liquid evaporation. When LH droplet is burned in a cold environment (T-infinity = 300 K), there are two films above the LH surface, Film I is from LH surface to flame front within which a dense hydrogen gas cloud is formed; Film II is from flame front to the free stream where oxygen is diffused inward to react with hydrogen. The flame front is located about 95 times of the droplet radius (r(f) = 95a) and the flame temperature could rise up to 2077 K. When an LH droplet is immersed in a hot environment (T-infinity = 2050 K), the flame front is located at a similar distance to the LH droplet (r(f)/a = 114) and flame temperature could go up to 3769 K.