SU Series Steam-to-Liquid Heat Exchangers

Steam in the Shell, Liquid in the Tubes

The SU takes steam on the shell side and heats liquid passing through a removable U-tube bundle. Steam condenses at essentially constant temperature, which makes the water side the controlling resistance and means the unit is sized on tube-side velocity and pressure drop rather than on anything happening in the steam.

Why the U-tube geometry matters here. Saturated steam meeting cold water is a large temperature difference by definition, and startup makes it abrupt. Each tube in a U-bundle is anchored at one end and free at the bend, so it expands independently and no differential load reaches the shell or the tubesheet. A fixed tubesheet unit on the same duty would need an expansion joint.

Condensate has to leave as fast as it forms. This is the single most common cause of an SU that appears to have lost capacity. When condensate cannot drain it floods the shell from the bottom up and progressively covers surface. Performance falls, the approach widens, and every symptom points at fouling. Check the trap, the back pressure and the drain leg before anyone pulls the bundle.

Pass count sets the tube-side velocity. Two-pass is standard; four and six pass arrangements raise velocity where the flow rate alone would leave the tubes laminar. Each additional pass buys heat transfer at the cost of pressure drop, and the part number records which arrangement a given unit carries.

Reading the part number. A catalogue number such as 5-260-04-060-011 encodes the series group, the shell diameter, the shell length and the pass and connection arrangement. The older SU45-2 style designation describes the same unit. Both forms appear on nameplates, and either one is enough for us to identify what you have.