Figure 3: Enthalpy
Wheel Supply to Turbine & Cathode
On the fresh air side (Station 1 to 2), the air is cooled (sensible
cooling) and humidified (latent heating).
On the exhaust side (Station 3 to 4) the air is heated (sensible heating) and
dehumidified (latent cooling). Note that
sensible heat is transferred in the enthalpy wheel from fresh (Station 1) to
exhaust (Station 4) while latent heat is transferred from exhaust (Station 3) to
fresh (Station 2). Thus, the heat of
compression (sensible) is recovered in the turbine while the humidity (latent)
is recovered in the fuel cell. No energy
is rejected to the atmosphere.
The enthalpy wheel conditions the cathode fresh air as shown in Figure 4. This data is presented as fuel cell inlet relative humidity referenced to the fuel cell operating temperature. Note that at full power (50 kW), hot day conditions, the fresh supply to the fuel cell is at or above the specified minimum of 60% RH. Here, the humidifier/condenser function operates at a minimum 53% effective. At the same time the recuperator function returns 65% of the heat of compression to the turbine. This experiment illustrates the following advantage of the enthalpy wheel system:
Figure 4:
Relative Humidity at Cathode Inlet
This experiment illustrates the following advantage of the enthalpy wheel system:
1) Well humidified reactant even at hot day conditions
2) Increased turbine temperature ratio and power extraction
3) Water independence
4) No external heat rejection
5)
Very light, compact physical size (combines aftercooler humidifier and
condenser function)
6) No freezing problems (no liquid water)
7) Minimum pressure drop (14” H20 or 0.036 atm/at full power)
8) Minimum motor power (30 watts)
9) Minimum cross leakage (<2%)
