Membrane humidifier for fuel cell

A membrane humidifier for a fuel cell, the membrane humidifier comprising:

• a first hollow fiber membrane bundle including first hollow fiber membranes having a first humidification performance;
• a second hollow fiber membrane bundle including second hollow fiber membranes having a humidification performance relatively lower than the first humidification performance, the first hollow fiber membrane bundle being arranged on one side of a housing of the membrane humidifier and the second hollow fiber membrane bundle being arranged in parallel with the first hollow fiber membrane bundle on the other side of the housing of the membrane humidifier so that the first hollow membrane bundle and the second hollow membrane bundle are in a same chamber of the housing;
• and
• a flow control device, disposed in a dry air inlet the membrane humidifier, that controls the flow direction of dry air introduced into the housing to allow the dry air to pass through one of the first and second hollow fiber membranes according to a power level of a fuel cell stack,
• wherein the first hollow fiber membranes are formed of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, which expand by absorbing water, and the second hollow fiber membranes are formed of polyetherimide or polyphenylsulfone which are less expanded than the sulfonated tetrafluoroethylene based fluoropolymer-copolymer,
• wherein the flow control device further comprises:
• an output detection unit configured to detect a power level of the fuel cell stack,
• a controller configured to output a control signal that controls the flow direction of dry air according to the power level detected by the output detection unit, and
• a flow setting means configured to set the flow direction of dry air according to the control signal applied from the controller, wherein the flow setting means comprises:
• a flow guide rotatably mounted at an inlet portion of the housing to set the path of dry air according to the rotational position of the flow guide, and
• an actuator operably disposed to rotate the flow guide,
• wherein the flow control device is controlled by the controller to allow the dry air to pass through the second hollow fiber membranes when the power level of the fuel cell stack is more than a predetermined reference value and allow the dry air to pass through the first hollow fiber membranes when the power level of the fuel cell stack is less than the reference value.