dead zones?

Question

i want to know what is meant by dead zones in heat exchangers and what is the effect of it .Also how can one remove dead zone

Answer 1

Usually, the term 'dead zone' refers to a location where there isn't a good flow of coolant (either the primary or secondary, or sometimes both).

Take a water-to-air heat exchanger for example. Water must pass through some sort of header, distribute to some of the cooling pipes, change direction in the header on the opposite side, pass back through the remaining pipes, and exit through the first header to the drain. Air must pass from one side to the other, often at right angles to the water flow (over the exterior of the pipes).

If there's a spot with a sharp bend in the air path, then the air might have a tendency to recirculate and not be cooled ... this would be a 'dead zone'. Likewise, if there was a spot where the water flow recirculated or 'eddied', you'd have a dead zone there as well.

Another way to have a 'dead zone' is to position the airflow driver (like a fan inlet) too close to the cooler surface, forcing high velocity air through only a protion of the entire exposed piping surface. This leaves the outside edges of the heat exchanger (out past the intake of the fan) as a dead zone.

To reduce the risk of dead zones, try to avoid sharp corners and/or abrupt changes of direction. Also position your elements to allow for best distribution (i.e. not too close together). Finally, understand the flow characteristics of your medium(s).