as to be converted into low pressure liquid gas mixture and a great deal of heat will be generated along with this process the role of the gathering apparatus 15 is to collect water and nitrogen gas and transports them into the liquid gas separator 16 while the role of the liquid gas separator 16 is to separate the mixture of water and nitrogen gas formed during the test the separated nitrogen gas is discharged under security condition whereas the separated water flows into the water tank 5 through the connecting pipeline 17 the cooling system 18 and the recycling manifold 19 so as to be recycled in one embodiment of the invention the cooling system 18 comprises a cooling column a plate type heat exchanger a recycling pump valves and pipelines because energy generated in the test is absorbed by water which acts as the experiment medium resulting in temperature rising the cooling system 18 is used to cool the water recycled in the test and decrease its temperature and plays a role in stabilizing the liquid flow in other embodiments other known technology may also be employed for the cooling system 18 because the controlling to the nitrogen gas displacement of liquid nitrogen equipments is achieved by using the power transmitting system and the flow distributing system of the liquid.