Spray evaporation of ammonia was tested using spray nozzles distributing liquid ammonia downward onto a horizontal, 3-2-3 triangular-pitch, 1.25 pitch ratio, plain-tube bundle composed of stainless-steel tubes of 19 mm (0.75 in.) diameter. The saturation temperature test range was from -23°C to 10°C, and the heat flux range from 3.2 to 35 kW/m2. The effects of heat flux, saturation temperature, spray flow rate, nozzle height, and nozzle type (standard-angle or wide-angle) were investigated. The spray evaporation heat transfer performance was compared with that of pool boiling, as well as spray evaporation on square-pitch tube bundle and single tube.