Heat transfer tube including a groove portion having a spiral shape extending continuously and a rib portion extending continuously and protruding inward by the groove portion

A heat transfer tube for a boiler, an interior of the heat transfer tube being configured to have a heating medium flow therethrough, the heat transfer tube comprising:

• a groove portion that is defined on an inner circumferential surface and has a spiral shape extending continuously toward a tube axis direction;
• and
• a rib portion that extends continuously and protrudes inward in a radial direction by the groove portion of the spiral shape,
• wherein, a height [mm] of the rib portion in the radial direction is defined as Hr, an interval [mm] of the rib portion in the tube axis direction is defined as Pr, the number of the rib portion in a cross section which is taken perpendicularly to the tube axis direction is defined as Nr, and a wetted perimeter length [mm] of the cross section which is taken perpendicularly to the tube axis direction is defined as L,
• wherein the height Hr [mm] of the rib portion, the interval Pr [mm] of the rib portion, the number Nr of the rib portion and the wetted perimeter length L [mm] satisfy “(Pr·Nr)/Hr>1.25L+55”, and
• wherein the interior of the heat transfer tube has a supercritical pressure.

A heat transfer tube for a boiler, an interior of the heat transfer tube being configured to have a heating medium flow therethrough, the heat transfer tube comprising:

• a groove portion that is defined on an inner circumferential surface and has a spiral shape extending continuously toward a tube axis direction;
• and
• a rib portion that extends continuously and protrudes inward in a radial direction by the groove portion of the spiral shape,
• wherein, a height [mm] of the rib portion in the radial direction is defined as Hr, an interval [mm] of the rib portion in the tube axis direction is defined as Pr, a width [mm] of the rib portion in a circumferential direction of the inner circumferential surface is defined as Wr, the number of the rib portion in a cross section which is taken perpendicularly to the tube axis direction is defined as Nr, a wetted perimeter length [mm] of the cross section which is taken perpendicularly to the tube axis direction is defined as L, a width [mm] of the groove portion in the tube axis direction of a cross section which is taken along the tube axis direction is defined as Wg, and a tube outer diameter [mm] is defined as D,
• wherein the width Wg [mm] of the groove portion, the height Hr [mm] of the rib portion, and the tube outer diameter D [mm] satisfy “Wg/(Hr·D)>0.40”,
• wherein the height Hr [mm] of the rib portion, the interval Pr [mm] of the rib portion, the width Wr [mm] of the rib portion, the number Nr of the rib portion and the wetted perimeter length L [mm] satisfy “(Pr·Nr)/(Hr·Wr)>0.40L+9.0” and
• wherein the interior of the heat transfer tube has a supercritical pressure.