Fluid-heating device

A vehicle fluid-heating device for heating fluid comprising:

• a heater unit configured to have a heater and a heating portion, the heating portion being formed so as to cover a surrounding of an outer surface of the heater;
• and
• a tank configured to accommodate the heater unit, wherein the heating portion includes
• an inner heat exchange surface formed on an inner surface of a through hole penetrating through an inner side of the heater, the inner heat exchange surface being configured to perform heat exchange with the fluid, and
• an outer heat exchange surface formed on an outer-wall portion of an outer side of the heater, the outer heat exchange surface being configured to perform heat exchange with the fluid,
• a heat transfer area of the outer-wall portion is larger than a heat transfer area of the through hole,
• the outer-wall portion has outer circumferential fins, the outer circumferential fins being configured to project towards an outer circumference,
• the tank has a top surface, the top surface being configured to close an opening portion for inserting the heater unit,
• the outer circumferential fins are provided so as to extend substantially parallel to the top surface,
• the through hole forms an inner circumferential flow channel, the inner circumferential flow channel being configured such that the fluid flows therethrough,
• the outer-wall portion providing an outer circumferential flow channel, the outer circumferential flow channel being configured such that the fluid flows between the outer-wall portion and an inner wall of the tank,
• the inner circumferential and the outer circumferential flow channels being configured to permit fluid to flow from the inner circumferential flow channel to the outer circumferential flow channel continuously, and
• a flow channel area of the outer circumferential flow channel is larger than a flow channel area of the inner circumferential flow channel.