Stepwise turndown by closing heat exchanger passageways responsive to measured flow

A plate type heat exchanger apparatus comprising in combination:

• a plurality of elongated metallic plates disposed in spaced relationship defining a plurality of elongated platelike passages in spaces therebetween;
• said plurality of passages including a first group of passages and a second group of passages, the passages of said first group being disposed in alternate relationship with said second group so as to be in heat exchange relationship therewith;
• end means extending between said plates along the periphery thereof defining the width and length of said passages;
• first inlet header communicating with said first group of passages;
• first outlet means for removing fluid from said first group of passages;
• a second header means having associated therewith a sparger means for introducing a vapor into said second group of passages and sparging a liquid into said vapor, said second header means being divided into means to separately communicate with at least two fractions of the total number of passages in said second group of passages;
• second outlet means for removing spent refrigerant from said second group of passages;
• means to measure the flow of liquid to said second inlet header;
• and
• means to shut off flow through a uniformly spaced fraction of the total number of passages in said second group of passages responsive to a signal generated by said means to measure flow.