Water heat exchanger

A water heat exchanger comprising:

• a first layer and a second layer that are stacked upon each other and that exchange heat between a first fluid and a second fluid, wherein the first fluid is water,
• the second fluid is a refrigerant,
• the first layer comprises first flow paths disposed in a plurality of rows and through which the first fluid flows,
• the second layer comprises second flow paths disposed in a plurality of rows and through which the second fluid flows,
• when the first layer is viewed in a stacking direction of the first layer and the second layer, each of the first flow paths extends from one end portion to another end portion of the first layer in a direction crossing an arrangement direction of the first flow paths,
• when the second layer is viewed in the stacking direction, each of the second flow paths extends from one end portion to another end portion of the second layer in a direction crossing an arrangement direction of the second flow paths, and
• the first flow paths are disposed such that, when the first fluid is heated by the second fluid, a flow-path cross-sectional area of a first-fluid outlet vicinity is larger than a first flow-path cross-sectional area of a first upstream-side portion disposed upstream of the first-fluid outlet vicinity.