A heat exchanger includes a cooling plate having a heat collection surface for fixing against an object to be cooled, an opposed heat transfer surface which may be provided with fins, and a cooling chamber over the heat transfer surface, the cooling chamber having an inlet port and an outlet port for circulating a fluid through the cooling chamber via a flow path between the ports. A flow distributor in the flow path forms a plurality of inlet channels communicating with the inlet port, a plurality of outlet channels alternating with the inlet channels and communicating with the outlet port, and a plurality of flow surfaces which are spaced from the heat transfer surface by gaps. The inlet channels communicate with the gaps so that a fluid entering the inlet channels via the inlet port will flow through the gaps, into the outlet channels, and out of the chamber via the outlet port. The gaps are dimensioned to increase fluid velocity and promote mixing of the fluid, thereby improving heat transfer.