81a to 81f and a center post portion 82 which connects the radially inner ends of the ribs as shown for example in fig3 the radially outer ends of the ribs 81a and 81b connect with the bulb 36 on opposite sides of the inlet flow area of the conduit 32 and the ribs 81d and 81e also connect with the bulb 36 on opposite sides of the outlet flow area of the conduit 32 as shown in fig7 the upper edges of the ribs taper downwardly toward the post 82 and are spaced from the lower side of the plate 51 the liquid enters the bulb 36 between the ribs 81a and 81b flows through the flow area between the upper edges of the ribs and the plate 51 and flows out of the bulb between the ribs 81d and 81e the flow area between the plate 51 and the upper edges of the ribs is preferably less than the flow area 32a see fig8 of the conduit 32 whereby the velocity of the liquid flow is increased underneath the plate 51 further the relatively large opening of the upper side of the bulb forms a relatively large area of the plate where the liquid cools or draws heat away from.