A compound consisting of a linear saturated C.sub.8-C.sub.24 hydrocarbon-based chain bearing at each end a nitrogen-containing functional group, other than NH.sub.2, is used for the storage of thermal energy. A process for the storage and optionally for the release of thermal energy comprises the contacting of a wall to be cooled with a first heat transfer fluid then of said first heat transfer fluid with a material comprising said compound and optionally the contacting of said material with a second heat transfer fluid then of said second heat transfer fluid with a wall to be heated.

A heat transfer sheet [60,160,260,360] for a rotary regenerative heat exchanger is shaped to include sheet spacing features [59], which provide spacing between adjacent heat transfer sheets [60,160,260,360], and undulation surfaces [68,70] (corrugations) in the sections between the sheet spacing features [59]. The undulation sections [68,70] are constructed of regularly spaced lobes [64,72] extending at an angle with respect to the spacing features [59]. The undulating sections [68,70] impart turbulence in the air or flue gas flowing between the heat transfer sheets [60, 160, 260, 360] to improve heat transfer. The heat transfer sheets [60,160,260,360] may include undulating surfaces that differ in angle of their lobes [64,72].

A heat transfer sheet [60,160,260,360] for a rotary regenerative heat exchanger is shaped to include sheet spacing features [59], which provide spacing between adjacent heat transfer sheets [60,160,260,360], and undulation surfaces [68,70] (corrugations) in the sections between the sheet spacing features [59]. The undulation sections [68,70] are constructed of regularly spaced lobes [64,72] extending at an angle with respect to the spacing features [59]. The undulating sections [68,70] impart turbulence in the air or flue gas flowing between the heat transfer sheets [60, 160, 260, 360] to improve heat transfer. The heat transfer sheets [60,160,260,360] may include undulating surfaces that differ in angle of their lobes [64,72].

A thermalization arrangement at cryogenic temperatures is dislcosed. The arrangement comprises a dielectric substrate layer on which substrate a device/s or component/s are positionable, and a heat sink component is attached on another side of the substrate. The arrangement further comprises a conductive layer between the substrate layer and the heat sink component. A joint between the substrate layer and the conductive layer has minimal phonon thermal boundary resistance. Energy of conductive layer phonons are arranged to be absorbed by electrons. Another joint between the conductive layer and the heat sink component is electrically conductive. The substrate layer and the conductive layer have similar acoustic properties.