Method for homogenizing a flow of coolant fluid within a plate heat exchanger, said plate heat exchanger comprising two support end plates (2, 3) on which coolant inlet and outlet connectors (4, 6) and water inlet and outlet connectors (5, 7) are arranged, and a stack of thermal exchange plates interposed between the support end plates (2, 3), among which thermal exchange plates there is defined a plurality of first channels for the passage of a coolant fluid and a plurality of second channels for the passage of water, the second channels alternating with the first channels, wherein through the stack of thermal exchange plates there are formed a coolant inlet manifold fluidically connecting the coolant inlet connector to the first channels, a coolant outlet manifold fluidically connecting the coolant outlet connector to the first channels, a water inlet manifold fluidically connecting the water inlet connector to the second channels, a water outlet manifold fluidically connecting the water outlet connector to the second channels, wherein the coolant fluid is supplied to the coolant inlet connector in form of a liquid/gas mixture, said method being characterized in that upstream of the coolant inlet manifold, between the coolant inlet connector and the coolant inlet manifold, there is a calibrated orifice that receives said liquid/gas mixture and atomizes it in the coolant inlet manifold, wherein the calibrated orifice has a diameter d such that ratio d/D between the diameter d of the calibrated orifice and the average diameter D of the coolant inlet manifold ranges between 0.05 and 0.5, and wherein the calibrated orifice concentrates the entire flow of coolant fluid in an area with a reduced section so as to generate a homogenously mixed spray jet at the outlet of the calibrated orifice, wherein in the spray jet the liquid phase is dispersed in the gaseous phase in droplet form. wherein through the stack of thermal exchange plates there are formed a coolant inlet manifold fluidically connecting the coolant inlet connector to the first channels, a coolant outlet manifold fluidically connecting the coolant outlet connector to the first channels, a water inlet manifold fluidically connecting the water inlet connector to the second channels, a water outlet manifold fluidically connecting the water outlet connector to the second channels, wherein the coolant fluid is supplied to the coolant inlet connector in form of a liquid/gas mixture, said method being characterized in that upstream of the coolant inlet manifold, between the coolant inlet connector and the coolant inlet manifold, there is a calibrated orifice that receives said liquid/gas mixture and atomizes it in the coolant inlet manifold, wherein the calibrated orifice has a diameter d such that ratio d/D between the diameter d of the calibrated orifice and the average diameter D of the coolant inlet manifold ranges between 0.05 and 0.5, and wherein the calibrated orifice concentrates the entire flow of coolant fluid in an area with a reduced section so as to generate a homogenously mixed spray jet at the outlet of the calibrated orifice, wherein in the spray jet the liquid phase is dispersed in the gaseous phase in droplet form.