The invention claimed is:1. A shrinking device for a liquid cooling system, comprising:a housing having a chamber therein, wherein a coolant flows through the chamber;at least one shrinking bag having an open end and a closed end, the closed end being inserted into the chamber, and the shrinking bag being in communication with outside atmosphere through a vent hole;a sealing member provided at the open end of the shrinking bag and mounted to the housing, wherein the sealing member is provided with the vent hole such that the shrinking bag is in communication with outside atmosphere through the vent hole; anda sleeve sealingly connected to the housing and to the sealing member, and wherein the shrinking bag is disposed into the chamber through the sleeve.2. The shrinking device for the liquid cooling system according to claim 1, wherein an end face of the open end of the shrinking bag is provided with a sealing flange which abuts against an end face of the sleeve.3. The shrinking device for the liquid cooling system according to claim 1, wherein the sleeve and the sealing member are sealingly connected through screw thread.4. The shrinking device for the liquid cooling system according to claim 1, wherein the housing has a cylindrical shape, and the shrinking bag extends along the length of the housing.5. The shrinking device for the liquid cooling system according to claim 1, wherein the sealing member has a protruded tube, wherein the vent hole extends through the protruded tube, and the protruded tube is inserted into the open end of the shrinking bag.6. A liquid cooling system, comprising:a heat exchanger radiator through which a coolant dissipates heat;a cooling block, wherein the liquid cooling system absorbs heat through the cooling block and transfers the heat to the heat exchanger radiator; anda shrinking device, comprising:a housing having a chamber therein, wherein coolant flows through the chamber;wherein the coolant flows through the chamber, and the housing is in fluid communication with both the heat exchanger radiator and the cooling block;at least one shrinking bag having an open end and a closed end, the closed end being inserted into the chamber, and the shrinking bag being in communication with outside atmosphere through a vent hole;a sealing member provided at the open end of the shrinking bag and mounted to the housing, wherein the sealing member is provided with the vent hole such that the shrinking bag is in communication with outside atmosphere through the vent hole; anda sleeve sealingly connected to the housing and to the sealing member, and wherein the shrinking bag is disposed into the chamber through the sleeve.7. The liquid cooling system according to claim 6, wherein an end face of the open end of the shrinking bag is provided with a sealing flange which abuts against an end face of the sleeve.8. The shrinking device for the liquid cooling system according to claim 7, wherein the sleeve and the sealing member are sealingly connected through screw thread.9. The liquid cooling system according to claim 6, wherein the housing has a cylindrical shape, and the shrinking bag extends along the length of the housing.10. The liquid cooling system according to claim 6, wherein the sealing member has a protruded tube, wherein the vent hole extends through the protruded tube, and the protruded tube is inserted into the open end of the shrinking bag.11. The liquid cooling system according to claim 6, wherein the housing is disposed onto the heat exchanger radiator and is integrally formed with the heat exchanger radiator.12. The liquid cooling system according to claim 11, wherein the housing is arranged along one side of the heat exchanger radiator in a width direction of the heat exchanger radiator.13. The liquid cooling system according to claim 6, wherein a coolant passage is provided on one side of the heat exchanger radiator in a width direction thereof, and the housing is in fluid communication with the coolant passage through a separate connection tube.14. The liquid cooling system according to claim 6, wherein a coolant inlet pipe and a coolant outlet pipe are provided between the heat exchanger radiator and the cooling block, wherein the housing is in fluid communication with the coolant inlet pipe or the coolant outlet pipe through a separate connection tube.15. The liquid cooling system according to claim 6, wherein the housing is disposed within the cooling block.16. The liquid cooling system according to claim 14, wherein the housing comprises a connection portion in fluid communication with the water pump.
