Submerged Internal Circular Cooler for Vertical Hydro Generators

This is a special fully‑submerged heat exchanger exclusively for vertical‑shaft hydroelectric generators (Francis, Kaplan, pumped‑storage units).

The entire circular / segmented ring‑shaped U‑tube bundle sits directly inside the thrust‑guide bearing oil sump, completely immersed in turbine lube oil.

Cooling medium (river water / raw water) flows inside U‑tubes.

Hot thrust bearing lube oil surrounds outside tube bundle; heat transfer relies mainly on oil natural convection (no external oil pump required).

Core purpose: dissipate huge friction heat from tilting‑pad thrust bearings; maintain thrust pad temperature within safe range 35‑45 °C; prevent babbitt pad melting and unit trip.

Main Structure Forms

(A) Full‑ring integral circular cooler

One complete circular U‑tube bundle, single water inlet & outlet manifold.

Suitable for small‑to‑medium vertical hydro units.

Disadvantage: large outer diameter; hard to lift out through small manholes; requires full oil‑sump draining for overhaul.

(B) Segmented split circular / semi‑ring cooler (dominant for large hydro)

Divided into 2, 3 or 4 independent semi‑ring segments, each segment has separate water inlet/outlet connections.

Key advantage: each segment can be removed individually through existing man‑holes without dismantling large bearing components.

One segment can be isolated for inspection/repair while other segments keep partial cooling during unit standby.

Widely adopted for large‑capacity Francis & pumped‑storage generator thrust bearings.

Main components:

U‑tube heat‑transfer bundle (core)

Upper & lower circular support frames / baffle rings (anti‑vibration restraint)

Inlet‑outlet water manifold headers

Connecting flexible water hoses / hard pipelines penetrating oil‑sump wall

Mounting brackets fixed to bearing housing base

Tube‑to‑header joints (potential high‑leak‑risk location: water‑into‑oil leakage)

Working Principle

Thrust bearing generates massive frictional heat; lube oil temperature rises inside closed oil sump.

Density difference creates natural oil convection: hot oil rises, flows over outer surface of submerged U‑tube bundle, heat transfers to cooling water inside tubes.

Cooler oil sinks back toward thrust pads, forming self‑circulation inside oil tank.

Heated cooling water flows out via manifold and is discharged to tail‑water / cooling water system.

No forced oil circulation pump. Cooling performance highly sensitive to oil‑sump liquid level, tube fouling, and cooling water inlet temperature.