Coaxial heat exchanger and circuit having a coaxial heat exchanger

A thermodynamic circuit comprising:

• a coaxial heat exchanger, the coaxial heat exchanger comprising:
• an inner tube with a tube axis, a tube wall, an outer face and an inner face, wherein the inner tube has a flow-through cross-sectional area and wherein fins are formed on the outer face of the inner tube, having a fin height measured from the tube wall of the inner tube as far as an undeformed tip of the fins, and having an outer tube, which is arranged coaxially to the inner tube, having a tube wall, an outer face and an inner face, wherein projections are formed on the inner face of the outer tube, which projections protrude substantially in a radial direction from the tube wall of the outer tube and continuously extend axially parallel or helically along the inner face of the outer tube, wherein the projections of the outer tube enclose an angle of at least 60° with the fins on the outer face of the inner tube and are connected thereto, whereby a plurality of adjacently running channels which can be flowed through in parallel are formed between the tube wall of the outer tube and the tips of the fins of the inner tube, each of which channels has a cross-sectional area measured transversely to a direction of flow and a channel height measured from the tube wall of the outer tube as far as the undeformed tips of the fins of the inner tube, wherein adjacent channels are separated from one another in each case by a projection of the cuter tube and wherein a ratio of a flow-through cross-sectional area of the inner tube to a sum of the cross-sectional areas of all of the channels is at least 0.5 and at most 5;
• wherein the thermodynamic circuit is configured such that the coaxial heat exchanger can be operated as an evaporator in a first operating period and can be operated as a condenser in a second operating period, and the evaporating or the condensing takes place in the channels of the coaxial heat exchanger.