Field of the Invention
The present invention relates to a hollow fiber membrane module and, more particularly, to a hollow fiber membrane module which removes a region, into which a fluid flowing outside a hollow fiber membrane bundle has difficulty in permeating, so that the fluid uniformly flows and thus, even if hollow flow membranes are highly integrated, performance of the hollow fiber membrane module may be maximized. 
The hollow fiber membrane module may be a water exchange module, a heat exchange module, a gas separation module or a water treatment module. 
Description of the Related Art
In general, a fuel cell refers to a power generation-type cell which produces electricity by bonding hydrogen and oxygen.  The fuel cell may continuously produce electricity as long as hydrogen and oxygen are supplied, differently from general chemical cells, such as batteries or storage batteries, and have no heat loss, thus having efficiency twice that of an internal combustion engine.  Further, the fuel cell converts chemical energy, generated by bonding hydrogen and oxygen, directly into electrical energy and thus discharges few pollutants.  Therefore, the fuel cell is advantageous in that it is eco-friendly and reduces worries about resource depletion owing to increase in energy consumption.  Fuel cells may be generally classified into a polymer electrolyte membrane fuel cell (PEMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), an alkaline fuel cell (AFC), etc.  according to kinds of electrolytes used.  The respective fuel cells are basically operated by the same principle, but kinds of fuels used, operating temperatures, catalysts, electrolytes, etc.,  of the respective fuel cells are different.  Thereamong, it is known that the PEMFC is operated at a low temperature, as compared to other fuel cells, has high power density, is small-sized, and may thus be promising as small mounting-type power generation equipment but also transportation systems. 
One of important factors to improve performance of the PEMFC is to supply moisture of a designated amount or more to a polymer electrolyte membrane or a proton exchange membrane (PEM) of a membrane-electrolyte assembly (MEA) so as to maintain a desired water content.  The reason for this is that, when the PEM is dried, power generation efficiently is rapidly decreased.  In order to humidify the PEM, 1) a bubbler humidification method in which moisture is supplied by filling a pressure vessel with water and then causing target gas to pass through a diffuser, 2) a direct injection method in which an amount of supply moisture necessary for fuel cell reaction is calculated and then moisture is supplied directly to a gas flow pipe through a solenoid valve, and 3) a humidification membrane method in which moisture is supplied to a gas fluidized bed using a polymeric separation membrane.  Thereamong, the humidification membrane method, in which vapor is fed to gas supplied to a polymer electrolyte membrane using a membrane selectively transmitting only vapor included in exhaust gas so as to humidify the polymer electrolyte membrane, is advantageous in that a humidifier may be lightweight and small. 
As selectively permeable membranes used in the humidification membrane method, hollow fiber membranes in which, if a module is formed, a transmission area per unit volume is large, are preferably used.  That is, if a humidifier is manufactured using the hollow fiber membranes, high integration of the hollow fiber membranes having a large contact surface area is achieved and a fuel cell may be sufficiently humidified at a small capacity, a low-cost material may be used, and moisture and heat included in unreacted gas of a high temperature discharged from the fuel cell may be collected and reused through the humidifier. 
However, in the case of a humidifier using hollow fiber membranes, in order to increase the capacity of the humidifier, many hollow fiber membranes are integrated.  Here, a gas flow at the outside of the hollow fiber membranes is not uniform throughout the inside of the humidifier due to resistance of the highly integrated hollow fiber membranes. 
In order to solve such a problem, the thickness of a hollow fiber membrane bundle is restricted or the hollow fiber membrane bundle is divided.  However, in this case, another problem, i.e., a limit on mounting of the hollow fiber membranes in a confined space, may be caused.