Hi Prithviraj,
You are right that there isn't a MA-MA heat exchanger. We have to get a bit creative here. Just an idea, you'll have to try it and see if it works.
I would assume you are trying to cool down the moist hydrogen and water condensation can occur. If this is not the case, leave a comment; it would be easier actually :p
The workaround I have in mind is to use a 2P-MA heat exchanger, and use two Interface (2P-G) blocks to go between the 2P & G domains. You will need to attached a two-phase property block to the 2P part so it's air, and you'll need REFPROP or Coolprop to get the air thermodynamic properties. If you have access to either software, you can use the twoPhaseFluidTables command to get the properties into Simscape (see: https://www.mathworks.com/help/simscape/ref/twophasefluidtables.html ).
Not super elegant, but I feel it may work.
