Super-leidenfrost spray cooling: A solution to the problem of controlled high-temperature, high-flux heat extraction

Conference · Mon May 01 04:00:00 EDT 1995

OSTI ID:74179

Edwards, C F; Hahn, D W

Our interest in spray cooling stems from a problem in high-temperature materials synthesis. Specifically, it is the growth of diamond films by flame chemical vapor deposition (CVD). A high velocity jet of premixed C{sub 2}H{sub 2}/O{sub 2}/H{sub 2} is formed into a stagnation point flow over the surface of a molybdenum mandrel causing the formation of a highly strained flame immediately adjacent to the surface. The difficulty that arises is that concomitant with the flux of energetic species to the surface is a large flux of heat which must be removed from the mandrel if control of the growth process is to be maintained. The situation is further complicated by the fact that the deposition surface temperature must be held to a tight tolerance somewhere within the optimal diamond growth range ({approximately}1200 K) and the heat extraction must be made in a one-dimensional fashion to preserve the uniform boundary condition on the flame. Since the cooling surface temperature is fixed near the saturation condition by the phase change of the droplets, and the heat flux into the mandrel is imposed by the flame, the only way to achieve a desired deposition surface temperature is to vary the thermal resistance of the mandrel itself. Since the cooling surface is isothermal, uniform temperature at the deposition surface will only result if the heat flux through the mandrel is uniform, that is, if the sides of the mandrel are effectively adiabatic and the flame is uniform over the mandrel surface. If either of these conditions is not met, the deposition surface temperature cannot be made uniform using this method. These limitations could be overcome if it were possible to carry out the spray cooling process without being tied to the isothermal boundary condition inherent in phase-cooling. Such a solution exists for spray cooling above the Leidenfrost temperature; that is the subject of this paper -- super-Leidenfrost spray cooling.

• Research Organization: Sandia National Labs., Livermore, CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 74179
• Report Number(s): SAND--95-8551C; CONF-9505212--1; ON: DE95010758
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
42 ENGINEERING
CHEMICAL VAPOR DEPOSITION
DIAMONDS
DROPLETS
FORCED CONVECTION
HEAT FLUX
MOLYBDENUM
SPRAY COOLING