Spray cooling with ammonia on micro-structured surfaces

Experiments were performed to investigate spray cooling enhancement on micro-structured surfaces. Surface modification techniques were utilized to obtain micro-scale indentations and protrusions on the heater surfaces. A smooth surface was also tested to have baseline data for comparison. Tests were conducted in a closed loop system with ammonia using RTI's vapor atomized spray nozzles. Thick film resistors, simulating heat source, were mounted onto 1cm x 2cm heaters and heat fluxes up to 500 W/cm(2) (well below critical heat flux (CHF) limit) were removed. Two nozzles each spraying 1 cm(2) of heater area used 96 ml/cm(2)-min (9.7 gal/in(2)-hr) liquid and 13.8 ml/cm(2)-s (11.3 ft(3) /in(2)-hr) vapor flow rate with only 48 kPa (7 psi) pressure drop. Results for micro-structured surfaces with protrusions and indentations offered significant performance enhancement of 115% and 52% increase in heat transfer coefficient over smooth surface respectively.