APPLICATION

NOTE

March 2004

Bulletin #MMAP004

EIK WATER COOLING

REQUIREMENTS

INTRODUCTION

Water cooled EIK’s operate at high power densities and requires careful attention to the maintenance of adequate water

flow and purity to ensure proper operation and long life. Water with contaminant levels that exceed the purity

requirements will cause corrosion and scaling, this includes ordinary tap water. Unchecked corrosion of the metals in

the EIK coolant passages reduces operating life. Scaling obstructs cooling passages preventing efficient heat transfer

resulting in overheating and permanent damage. Continuous filtering, deionizing and oxygen removal is necessary for

maintaining high water purity.

WATER PURITY REQUIREMENTS

1. Deionized or distilled water

2. Water resistivity shall be maintained at 1 Megohm-cm or higher at 25 °C.

3. Dissolved oxygen should not exceed 0.5 parts per million

4. The particulate matter sized shall not be greater than 50 microns (325 mesh)

Water purity and flow protection must be periodically checked to ensure against excessive degradation. Water can

become contaminated by the cooling system components and from the environment. For example, free oxygen in the

coolant will form copper oxide on the surfaces of the coolant passages, particularly the collector. The oxide compounds

can drastically reduce heat transfer to the water. In extreme cases, heavy oxide deposits can plug up coolant passages

reducing flow. The formation of these oxides is greatly accelerated by elevated temperature within the system.

Corrosion via electrolysis between dissimilar metals may also take place when ions are present in the water and there is

an electric potential across the coolant passages (i.e. as in depressed collector operation). Electrolysis will destroy the

coolant passages.

The presence of either oxidation of electrolysis will result in premature EIK failure.

BASIC SYSTEM DESIGN

Figure 1 shows a typical arrangement of a recirculating cooling system with a purification loop. The main cooling loop

consists of a heat exchanger, water reservoir, particulate filter (10-50 micron), circulation pump, the connection tubing,

valves, pressure gauges, temperature and flow sensing interlocks required to ensure sufficient coolant flow and

temperature whenever the equipment is energized. A nitrogen gas pressurized system as shown is recommended to

reduce oxidation.

The purification loop taps off approximately 10% of the total cooling system flow rate. The purification loop consists of

a purity meter, oxygen, ion and particulate removal cartridges.

Flow and pressure regulating valves should be installed on the inlet lines to the EIK for adjustment of flow rate and

pressure drop. A thermometer interlock should be placed in the inlet line to the EIK and a flow meter interlock should

be placed in the outlet coolant line from the EIK. These interlocks must be wired into the electrical controls, such that

the EIK is completely de-energized in the event of loss of coolant flow or an over temperature condition.

The main circulation pump must be of sufficient size to ensure the flow and pressure throughout the operating range as

specified on the Test Data Sheet. Care must be taken when connecting the coolant lines to the EIK. Be certain that the

flow is in the direction specified. Reversed flow may result in inadequate cooling.

The coolant lines to the EIK inlet and outlet ports should of an insulating flexible material arranged so as to avoid

excessive strain on the coolant ports of the EIK. Many EIK’s are shipped with the collector and body-cooling lines

partially assembled using nylon tubing. Nylon, polypropylene and chlorinated polyvinyl chloride (CPVC) tubing with

adequate wall thickness are acceptable choices for this service.

APPLICATION

NOTE

March 2004

Bulletin #MMAP004

EIK WATER COOLING

REQUIREMENTS

All metallic components within the water system, including other tubing, fittings, pumps and other material that will be

in direct contact with the coolant should be made from copper, nickel, bronze, Monel, Inconel, 304L stainless steel and

347 stainless steel for weld parts to minimize galvanic action. Metals that should not be used in direct contact with the

coolant include steel, cast iron, galvanized iron, aluminum and magnesium. Brass should be used as sparingly as

possible and should be low zinc brass.

PURITY

METER

HEAT

EXCHANGER

AIR REMOVAL VALVE

WITH NITROGEN BLANKET

PRESSURE

STORAGE

TANK

50 MICRON

FILTER

PUMP

OXYGEN

REMOVAL

50 MICRON

FILTER

ION

REMOVAL

FLOW RATE

AND

INTERLOCK

PRESSURE

EIK

PRESSURE

AND INTERLOCK

TEMPERATURE

Figure 1

TYPICAL COOLING SYSTEM WITH PURIFICATION LOOP

Packaged purification systems suitable for this purpose are available from many suppliers; including Barnstead

International (www.barnsteadthermolyne.com) Advice in setting up a cooling system should be obtained from the water

processing manufacturers.