You really need to look into thermofluid science. The system you are describing breaks the laws of thermodynamics if it actually lowered the temperature of the working fluid. If you consider your entire setup (pump, fittings, reservoir, ect.) a system, you have work input (work done by the pump to the fluid) with no energy leaving the system (the boiled liquid stays inside the closed loop). If anything, your liquid will actually gain heat from the energy input by the pump. Also, your not going to lower the pressure enough to boil water with a venturi nozzle.