A water-cooled condenser is a heat exchanger that removes heat from refrigerant vapor and transfers it to the water running through it. Having the refrigerant vapor condensed on the outside of a tube does this. In doing so, the vapor condenses and gives up heat to the water running inside the tube.
A chiller barrel works just the opposite. A chiller barrel is actually a direct expansion evaporator. Chiller barrels evaporate the refrigerant inside the tube. Heat is removed from the water running through the outside shell of the tubes.
The water-cooled condenser is an important component on the high side of an air-conditioning/refrigeration system. The chiller barrel is an important component on the low side of a system.
For condensers, DT is the condensing temperature minus the incoming water temperature. For chillers, DT is the incoming water temperature minus the suction temperature. The greater the DT, the greater the rate of heat exchange in a given time period, usually expressed in BTU’s/Hr.
Velocity is the speed at which a fluid flows. There is an ideal rate of flow through a heat exchanger for any fluid. At this ideal flow rate, the fluid mixes with itself in such a way that it produces maximum heat pick-up. Turbulent flow causes cooler fluid to be constantly moved into contact with the heat surface. If the flow is too slow, a laminar condition may develop. That is a condition in which only the fluid right next to the heat exchange wall is being heated, but beyond this very thin layer, the heat can’t penetrate to the rest of the fluid. But — the velocity must be limited by another condition, pressure drop (DP). DP increases with velocity. After a certain point, the amount of energy expended to overcome DP will be more than any efficiency picked up by increased velocity. High DP and high velocity also produces problems that greatly shorten the life of a heat exchanger. Impingement corrosion and erosion will shorten the life to just a few months, if bad enough.