Heat exchanger, oxygenator, and method of manufacturing a heat exchanger

A method of manufacturing a heat exchanger including multiple hollow fiber membranes that each have a hollow portion through which a heat medium passes, and exhibiting a shape of a cylinder body as a whole shape disposed over a cylinder member, the method comprising:

• winding each of the hollow fiber membranes around a central axis of the cylinder following a path which is tilted at a tilt angle θ with respect to the central axis of the cylinder body while simultaneously tensioning the hollow fiber membranes in a pulled state wherein the hollow fiber membrane is stretched in a longitudinal direction of the hollow fiber membrane at a stretching rate of each of the hollow fiber membranes ranging from 0.5% to 3%, wherein tilt angle θ with respect to the central axis of the cylinder body of each of the hollow fiber membranes ranges from 22° to smaller than 67°, and wherein a constituent material of each of the hollow fiber membranes has a Young's modulus E of 2.6 GPa or smaller;
• and
• fixing the hollow fiber membranes as opposing ends of the cylinder member to maintain the stretching of the hollow fiber membranes.