S URFACE G EOMETRY AND H EAT F LUX E FFECT ON T HIN W IRE N UCLEATE P OOL B OILING OF S UBCOOLED W ATER IN M ICROGRAVITY Troy Munro and Andrew Fassmann Mechanical and Aerospace Engineering Utah State University Heng Ban – Faculty Mentor 2011 AIAA Region VI Student Conference 1

N UCLEATE B OILING Characterized by presence of bubbles High heat transfer rates Governed by Newton’s law of cooling Wide range of terrestrial and possible space applications AIAA Region VI Student Conference Photo courtesy of Incropera Boiling regimes for water at 1 atm q” = h(T s – T ∞ ) q” - heat flux h – heat transfer coefficient T s – temperature of surface T ∞ – bulk temperature of fluid Pool Boiling

H EAT F LUX E FFECTS AIAA Region VI Student Conference CHF Nucleate boiling Film boiling Photos courtesy of Incropera

S URFACE G EOMETRY E FFECTS AIAA Region VI Student Conference Photo courtesy of Fukada Photo courtesy of Zhao Photo courtesy of Chyu

M ICROGRAVITY O BSERVATIONS AIAA Region VI Student Conference Photo courtesy of Fukada

O BJECTIVES Investigate the effects of surface geometry, heat flux, and gravity on nucleate boiling by observing: Onset of nucleate boiling characteristics Steady state heat transfer characteristics Bubble dynamics AIAA Region VI Student Conference

E XPERIMENTAL S ETUP AIAA Region VI Student Conference

T RANSIENT W IRE B EHAVIOR AIAA Region VI Student Conference

O NSET OF N UCLEATE B OILING AIAA Region VI Student Conference Steady condition before boiling Range of three wire onset heat flux Average wire temperature below saturation (Bubble dynamic effects on wire temperature)

E FFECTS OF S URFACE G EOMETRY AIAA Region VI Student Conference Single-wireThree-wireFour-wire Minimum Onset Heat Flux 825 kW/m 2 Between 396 and 519 kW/m kW/m 2 Concentrated Surface Area to Total Surface Area 1:11:61:4

S TEADY S TATE H EAT T RANSFER AIAA Region VI Student Conference Efficiency of boiling heat transfer in 1g and 0g are similar More effective area (more active nucleation sites) in microgravity

B UBBLE D YNAMICS - J ETS AIAA Region VI Student Conference TC 1TC 2TC 3TC 4 Distance from wire 1 mm6 mm11 mm16 mm

R ELATIVE B UBBLE A REA A NALYSIS (RBAA) AIAA Region VI Student Conference

H EAT F LUX E FFECT - RBAA AIAA Region VI Student Conference

C ONCLUSIONS The unique twist of three-wires provides a surface geometry that reduces the required heat flux for onset boiling In many instances, steady state heat transfer is enhanced in microgravity in the range of 5-10% As heat flux increases, there is an increased tendency to form jets, which provide convective current normally absent in microgravity

A CKNOWLEDGEMENTS SpaceX Rocky Mountain NASA Space Grant Consortium USU College of Engineering USU Department of Physics USU Undergraduate Research Space Dynamics Lab American Aerospace Advisors National Instruments

Q UESTIONS

F UTURE R ESEARCH AIAA Region VI Student Conference Photo courtesy of Deng 1) Extend input power range up to critical heat flux (wire burnout) 2) Further resolve onset conditions for boiling 3) 2-D Heater: Electric pulses to ‘seed’ the bubbles Bubbles grow as they accept heat Possibility to control amount of cooling CHF

Geometry “Power Level” Input Current (A) Average Power (W) Average Heat Flux (kW/m 2 ) Single Wire Three-Wire Four-Wire