A fluid heat exchanger assembly cools an electronic device with a cooling fluid supplied from a heat extractor (R, F) to an upper portion of a housing. A refrigerant is disposed in a lower portion of the housing for liquid-to-vapor transformation. A partition divides the upper portion of the housing from the lower portion and flow interrupters are disposed in the upper portion for interrupting thermal boundary layer to enhance thermal heat transfer to the flow of liquid coolant through the coolant passage of the upper portion in response to heat transferred by an electronic device to the lower portion of the housing.