Heat transfer sheet for rotary regenerative heat exchanger

A stacked configuration of rotary regenerative heat exchanger sheets, the stacked configuration comprising:

• at least two first heat transfer sheets comprising:
• a first undulating surface formed by first lobes extending along the first heat transfer sheet, the first lobes being parallel to each other and oriented at a first angle relative to a longitudinal direction of flow of hot flue gas through the stacked configuration of rotary heat transfer elements;
• and
• a second undulating surface formed by second lobes extending along the first heat transfer sheet, the second lobes being parallel to each other and oriented at a second angle relative to the longitudinal direction of flow of hot flue gas through the stacked configuration of rotary heat transfer elements, the first angle and second angle being different,
• wherein the first undulating surface and the second undulating surface are laterally adjacent, lateral being generally perpendicular to the longitudinal direction.