A cooling fan ( 1 ) for cooling an electronic device ( 2 ) is disclosed. The cooling fan ( 1 ) comprises a heat sink ( 5 ) thermally connectable to the electronic device ( 2 ), the heat sink ( 5 ) having a first clearance side ( 6 a, 6 b ) centered relative to a longitudinal axis (L) of the heat sink ( 5 ), and several thermally conductive fan blades ( 13 ) arranged in a circle centered on the longitudinal axis (L). The fan blades ( 13 ) are rotatable relative to the heat sink ( 5 ) about the longitudinal axis (L) by a motor ( 19 ) and each fan blade ( 13 ) has a second clearance side ( 14 ) facing the first clearance side ( 6 a, 6 b ). A clearance space ( 18 ) is provided between the first clearance side ( 6 ) and each second clearance side ( 14 ), the majority of said clearance spaces ( 18 ) having a size of 100 micrometer or less in a direction perpendicular to the first clearance side ( 6 a, 6 b ) and the corresponding second clearance side ( 18 ).
1. A cooling fan for cooling an electronic device, comprising
a heat sink thermally connectable to the electronic device, the heat sink having a first clearance side centered relative to a longitudinal axis of the heat sink, and
several thermally conductive fan blades arranged in a circle centered on the longitudinal axis, the fan blades being rotatable relative to the heat sink about the longitudinal axis by a motor and each fan blade having a second clearance side facing the first clearance side,
characterized in that a clearance space is provided between the first clearance side and each second clearance side, at least a majority of said clearance spaces having a size of 100 micrometer or less in a direction perpendicular to the first clearance side and the corresponding second clearance side, and
wherein the heat sink is a solid right circular cylinder.
2. The cooling fan according to claim 1 , wherein
the first clearance side is a continuous curved side,
the fan blades are arranged around the heat sink as seen along the longitudinal axis, and
the clearance space has a size of 100 micrometer or less in a radial direction perpendicular to the longitudinal axis.
3. The cooling fan according to claim 1 , wherein
the first clearance side is a continuous planar side,
the heat sink and the fan blades are separated along the longitudinal axis, and
the clearance space has a size of 100 micrometer or less in a direction of the longitudinal axis.
4. The cooling fan according to claim 1 , wherein the size of the clearance space is less than 50 micrometer, alternatively less than 30 micrometer or less than 15 micrometer.
5. The cooling fan according to claim 1 , wherein the first clearance side has a first clearance side area and each second clearance side has a second clearance side area, the combined second clearance side area of all the fan blades being from about 10% to about 50% of the first clearance side area.
6. The cooling fan according to a claim 1 , wherein the fan blades have a thermal conductivity of at least 1 watt per meter per kelvin.
7. The cooling fan according to claim 1 , wherein the fan blades are made of a material chosen from the group consisting of glass, ceramics, thermally conductive plastics and metals.
8. The cooling fan according to claim 7 , wherein each of the fan blades is made of aluminum or an aluminum alloy.
9. An assembly comprising, the cooling fan according to claim 1 ; the electronic device thermally connected to the heat sink; and the motor connected to rotate the fan blades relative to the heat sink about the longitudinal axis.