at one end and is communicated at the other to the liquid outlet opening 9 by way of suction pipes 36 and horizontal structure 37 suction pump 15 operates to suck in bubbles that are produced on and floating over the heat sinks 3 to heat exchanger 11 together with liquid coolant heat exchanger 11 cools down the coolant and recirculates it into the housing 5 through feed pump 12 and supply pipe 38 the effect of agitation is therefore produced by the upward flows of liquid from the surface of each heat sink disfavoring the tendency of liquid to produce film boiling in preferred embodiments the inside pressure of the cooling chamber 10 is adaptively controlled so that it is maintained at an optimum condition for nucleate boiling variants of the pressure regulating system are shown in fig8 through 14 in fig8 the pressure regulating system includes a feed pump 40 a constant flow valve 41 and a flow sensor 42 all of which are connected in series from a reservoir 47 to the inlet opening of a cooling chamber 43 which is identical in construction to those shown in fig1 and 7 reservoir 47 receives coolant from heat exchanger 46 to accommodate fluctuations that vary as a function of the temperature of the heated working fluid to the outlet opening of the cooling chamber 43 is connected a flow sensor 44 whose outlet is coupled to a suction pump 45 a heat exchanger 46 and reservoir 47 are connected in series to the output of pump 45 cooled working fluid in the reservoir 47 is drained by feed pump 40 to constant flow valve 41 in which it is regulated so that a desired volume of coolant is supplied therefrom to cooling chamber 43 flow.