US Patent 7621320 Internal heat exchanger

In an internal heat exchanger, when a corresponding diameter of a high pressure passage 5a is Ψh, a passage length Lh of the high pressure passage (5a) is so set as to satisfy the relation 9.16/{LN(4.5−Ψh+1.03)}<Lh<46/{LN(4.5−Ψh+1.03)}, and when a corresponding diameter of a low pressure passage 5c is Ψl, a passage length Ll of the low pressure passage 5c is so set as to satisfy the relation 9.16/{LN(0.56×6−Ψl+1.02)}<Ll<46/{LN(0.56×6−Ψl+1.02)}, a passage sectional area Ah of the high pressure passage 5a is so set as to satisfy the relation 100×(0.25×Ψh1.2)−1/(0.04×Ψh+1.7)≧Ah≧100×(500×Ψh1.2)−1(0.04×Ψh+1.7), and a passage sectional area Al of the low pressure passage 5c is so set as to satisfy the relation 1.65/Ψl0.67<Al<626/Ψl0.67.