Heat transfer plate and plate heat exchanger

1. A heat transfer plate comprising:

an edge portion extending along an edge of the heat transfer plate, the edge portion being corrugated so as to comprise alternately arranged ridges and valleys as seen from a first side of the heat transfer plate,

wherein the ridges and the valleys extend perpendicularly to the edge of the heat transfer plate, a first one of the ridges having a top portion extending in a top portion plane, and a first one of the valleys, which is adjacent to the first ridge, having a bottom portion extending in a bottom portion plane,

wherein the top portion of the first ridge and the bottom portion of the first valley are connected by a main flank, the top portion of the first ridge, the bottom portion of the first valley and the main flank ending at an end distance from the edge of the heat transfer plate,

wherein a slope of the main flank in relation to the bottom portion plane as seen from the bottom portion of the first valley varies between a minimum slope and a maximum slope along the top portion of the first ridge and the bottom portion of the first valley, and

wherein a first slope of the main flank at a first distance from the edge of the heat transfer plate is smaller than a second slope of the main flank at a second distance from the edge of the heat transfer plate, the first distance being smaller than the second distance.

2. The heat transfer plate according to claim 1 , wherein said minimum slope corresponds to a minimum angle (αmin) measured between a part of the bottom portion plane extending under the first ridge and the main flank, and said maximum slope corresponds to a maximum angle (αmax) measured between said part of the bottom portion plane and the main flank, said minimum angle (αmin) being at least 3 degrees smaller than said maximum angle (αmax).

3. The heat transfer plate according to claim 2 , wherein said minimum angle (αmin) is smaller than said maximum angle (αmax) by 20 degrees or less.

4. The heat transfer plate according to claim 1 , wherein the slope of the main flank is constant between a third distance and a fourth distance from the edge of the heat transfer plate, the fourth distance being larger than the third distance and the third distance being larger than the first distance.

5. The heat transfer plate according to claim 4 , wherein a difference between the fourth distance and the third distance corresponds to 0-85% of the end distance.

6. The heat transfer plate according to claim 4 , wherein the slope of the main flank is continuously decreasing from the third distance towards the edge of the heat transfer plate.

7. The heat transfer plate according to claim 1 , wherein the top portion plane and the bottom portion plane are parallel to a center extension plane of the heat transfer plate.

8. The heat transfer plate according to claim 1 , wherein the slope of the main flank at said end distance is said maximum slope.

9. The heat transfer plate according to claim 1 , wherein the first ridge and the first valley extend from the edge of the heat transfer plate.

10. The heat transfer plate according to claim 1 , wherein the slope of the main flank at the edge of the heat transfer plate is said minimum slope.

11. A plate heat exchanger comprising the heat transfer plate according to claim 1 .