An apparatus includes a reservoir to hold a volume of liquid, a port to inject a flow of gas into a lower portion of the reservoir, and a structure to transform the flow of gas into one or more streams of bubbles in said liquid. The reservoir has a port for injecting the gas into a lower region of the volume of liquid and has a top opening to release the injected gas therefrom. The apparatus includes one or more active electronic or optical devices located in the reservoir or located physically adjacent and in thermal contact with the reservoir such that the volume of the liquid is able to absorb part of heat produced by the one of more electronic or optical devices.