Subsea unit with conduction and convection cooling

1. A subsea unit comprising: a housing containing a dielectric liquid;

a first heat generating component; and

a second heat generating component, wherein the first heat generating component is arranged in thermal conductive connection with the housing,

wherein the second heat generating component is arranged at a distance from a lateral side wall of the housing,

wherein the first heat generating component is arranged in thermal conductive connection with the lateral side wall of the housing.

2. The subsea unit of claim 1 , wherein said subsea unit is a pressure compensated subsea unit, the housing being entirely filled with the dielectric liquid.

3. The subsea unit of claim 1 , wherein the first heat generating component has a higher heat loss than the second heat generating component.

4. The subsea unit of claim 1 , further comprising a first heat sink arranged in thermal conductive connection with the first heat generating component.

5. The subsea unit of claim 4 , wherein the first heat sink is arranged in thermal conductive connection with the housing.

6. The subsea unit of claim 1 , further comprising a first flow directing structure arranged along the sidewall of the housing for guiding the dielectric liquid vertically.

7. The subsea unit of claim 6 , wherein the first heat generating component is arranged between the sidewall of the housing and the first flow directing structure.

8. The subsea unit of claim 6 , further comprising a first heat sink arranged in thermal conductive connection with the first heat generating component, wherein the first heat sink is arranged between the sidewall of the housing and the first flow directing structure.

9. The subsea unit of claim 8 , wherein the first heat generating component is arranged on the inner side of the first flow directing structure, the inner side of the first flow directing structure being the side of the first flow directing structure that faces the centre of the housing.

10. The subsea unit of claim 6 , further comprising a second flow directing structure arranged along a top wall of the housing for guiding the dielectric liquid horizontally.

11. The subsea unit of claim 10 , wherein the first flow directing structure is connected to the second flow directing structure.

12. The subsea unit of claim 10 comprising a second heat sink arranged in thermal conductive connection with the top wall of the housing.

13. The subsea unit of claim 10 comprising a flow restriction arrangement for preventing dielectric liquid guided by the second flow directing structure from flowing backwards and mixing with dielectric liquid guided by the first flow directing structure.

14. A subsea unit arrangement comprising: a main subsea unit, configured in accordance with claim 1 ; and

a subordinate subsea unit arranged inside said main subsea unit; wherein said subordinate subsea unit comprises:

a housing containing a dielectric liquid;

a first heat generating component; and a second heat generating component, wherein the first heat generating component is arranged in thermal conductive connection with the housing, wherein the second heat generating component is arranged at a distance from a lateral side wall of the housing, wherein the first heat generating component is arranged in thermal conductive connection with the side wall of the housing.

15. A method of cooling heat generating components contained in a housing of a subsea unit comprising the steps of:

providing a housing; arranging a first heat generating component in thermal conductive connection with a lateral side wall of the housing;

arranging a second heat generating component at a distance from the lateral side wall of the housing;

filling the housing with a dielectric liquid so that the heat generating components are immersed in the dielectric liquid;

arranging the subsea unit under the sea water surface, preferably on the seabed, so that the housing is cooled by the sea water; and

supplying electric power to the heat generating components so that the first heat generating component heats up the dielectric liquid and thus a convective flow of the dielectric liquid is created within the housing, cooling also the second heat generating component.

16. The subsea unit of claim 2 , wherein the first heat generating component has a higher heat loss than the second heat generating component.

17. The subsea unit of claim 2 comprising a first heat sink arranged in thermal conductive connection with the first heat generating component.

18. The subsea unit of claim 3 comprising a first heat sink arranged in thermal conductive connection with the first heat generating component.

19. The subsea unit of claim 1 , wherein a side wall insulator is arranged to insulate said side wall apart from where the first heat generating component is arranged in thermal conductive connection with the lateral side wall.

20. The subsea unit arrangement of claim 14 , wherein a side wall insulator is arranged to insulate said side wall apart from where the first heat generating component is arranged in thermal conductive connection with the side wall.