through circular passages 24 in the direction of arrow 28 and gains heat along its path passages 24 discharge a hotter liquid coolant into outlet header 36 defined by outlet housing 35 which serves to collect the liquid coolant from the circular passages 24 the outlet 32 removes the heated liquid coolant from the outlet header 36 and transfers it to a remotely located air cooled heat exchanger not shown the heat generating element being cooled such as a computer chip 38 is attached to the flat face of the metal block 22 with an intervening layer of thermal grease 23 or the like for increased effectiveness of the heat sink 20 two heat generating elements such as electronic devices 38 may be attached to both flat surfaces of the metal block 22 in order to minimize thermal resistance of the metal block 22 the block thickness 40 represented by dimension u2018 a u2019 is restricted to be no more than 1 1 to 1 4 times the flow passage diameter 42 represented by dimension u2018 d u2019 likewise in order to maintain high heat flux from the concentrated heat source such as electronic device 38 to the cooling fluid in the flow passages 24 the center to center distance 44 represented by dimension u2018 c u2019 of the flow passages should not exceed 1 1 to 1 4 times the flow passage diameter 42 and is more preferably at 1.