We claim the ornamental design for a heat exchanger, as shown and described.
Cross-reference is made to U.S. patent application Ser. No. 14,331,578 entitled “Heat Exchanger Coil for a Recreational Vehicle,” which is filed on the same day as the present application and is expressly incorporated herein by reference.
FIG. 1 is a perspective view of a heat exchanger showing our new design;
FIG. 2 is a top plan view;
FIG. 3 is a bottom plan view;
FIG. 4 is a front elevation view;
FIG. 5 is a rear elevation view;
FIG. 6 is a first side elevation view; and,
FIG. 7 is a second side elevation view.
The features shown in broken lines depict environmental subject matter only and form no part of claim design.