MTS Water Quality User Manual

Heat Exchanger Care and
Water Quality Guide

l

015-164-000 C

Copyright information © 2005 MTS Systems Corporation. All rights reserved.

Trademark information MTS is a registered trademarks of MTS Systems Corporation.

DTE and SHC are registered trademarks of Mobil Corporation.
Molykote is a registered trademark of Dow Chemical Corporation.

Contact information MTS Systems Corporation

14000 Technology Drive
Eden Prairie, Minnesota 55344-2290 USA
Toll Free Phone: [phone] (within the U.S. or Canada)
Phone: [phone] (outside the U.S. or Canada)
Fax: [phone]
E-mail: [e-mail]
http://www.mts.com

Publication information

Manual Part Number Publication Date

015-164-000 A June, 1996
015-164-000 B June, 1996
015-164-000 C June, 2005

Content

Heat Exchanger Care 5

What is a heat exchanger? 5
What are the major components of my heat exchanger? 6
What ambient conditions are required? 8
What is the life expectancy of my heat exchanger? 10
What causes heat exchanger failure? 10
How can I prevent heat exchanger failure? 11
Mechanical failure with chemically induced corrosion 13
How do I know when I have a heat exchanger failure? 14
How can I improve the life of my heat exchanger? 15
What regular heat exchanger maintenance is required? 16
How do I remove corrosion? 20
How do I remove water from the hydraulic fluid after a heat exchanger failure? 20
How do I know when to replace my heat exchanger? 20

Troubleshooting 22

Heat Exchanger Care and Water Quality Guide Content

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Content

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Heat Exchanger Care and Water Quality Guide

Heat Exchanger Care

MTS hydraulic power units (HPUs) are equipped with heat exchangers that are
designed to remove 100% of the HPUs heat load.

Heat exchangers usually provide a long service life with little required
maintenance because they have very few or no moving parts. Often, however , the
heat exchanger is a neglected component of the HPU until it fails. A heat
exchanger failure can result in a costly and time-consuming cleanup, especially
when your cooling water supply is mixed with hydraulic fluid. Proper
maintenance is therefore essential to maintaining a long life for your heat
exchanger. The information that is provided below will help you get the longest
possible service from your heat exchanger.

What is a heat exchanger?

A heat exchanger is a mechanical device that is used to transfer heat from one
medium to another. The amount of heat transferred is directly proportional to the
temperature difference between the hydraulic fluid and the cooling medium.
MTS uses two types of heat exchangers: hydraulic fluid-to-water or hydraulic
fluid-to-air.

Hydraulic fluid-to-

water

Hydraulic fluid-to-water heat exchangers are used in an HPU when an ample
cooling water supply is available. Hydraulic fluid-to-water heat exchangers, also
referred to as oil coolers, use heat transfer to cool the hot hydraulic fluid in the
HPU by passing it over or through a conductor that separates the hydraulic fluid
from the cooling water.

The two most common designs are the plate design, and the shell and tube
design.

Plate design In the plate design, the hot hydraulic fluid passes between a series of copper-

coated, corrugated stainless steel plates. The herring bone design of the
corrugations in the plates increases the turbulence in the fluid to maximize the
transfer of heat. Cooling water passes between altenating plates to effect the heat
transfer.

Shell and tube design In this design, the hot hydraulic fluid circulates through the shell and over the

outside surface of a bundle of tubes. Baffles direct the hydraulic fluid through the
shell side of the unit at right angles to the tube bundle. Cooling water passes
through the inside of the tubes and the heat is exchanged from the hot hydraulic
fluid to the cool water. Heat is removed from the water by passing it through a
cooling tower or an evaporation pond.

Shell and tube hydraulic fluid-to-water heat exchangers are available in many
design variations. The straight tube design with a fixed tube bundle is used by
MTS. These units are available with various baffle arrangements to create single
or multiple pass heat exchangers. Multiple pass designs use less water and can be
used more efficiently and at less cost when colder circulating water is available.
The tubes are accessible from either end for cleaning.

Hydraulic fluid-to-air Hydraulic fluid-to-air heat exchangers, also referred to as air coolers, are similar

to the cooling system in an automobile. Hydraulic fluid-to-air heat exchangers
are used in locations that do not have a sufficient water supply for cooling.
Hydraulic fluid passes through a radiator while air is blown over the tubes and
cooling fins to remove the heat.

Heat Exchanger Care and Water Quality Guide Heat Exchanger Care

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What are the major components of my heat exchanger?

Hydraulic fluid-to-

water

Plate design The plate design hydraulic fluid-to-water heat exchanger has no moving parts. It

consists of a series of corrugated stainless steel plates brazed together. The
direction of the herring bone design of the plates alternates to provide maximum
turbulence and therefore maximum cooling efficiency. The plates are brazed
together to provide strength and a compact package.

Fluid In

Plates

Water Out

Water In

Fluid Out

Cutaway View of a Plate Design Hydraulic Fluid-to-Water Heat Exchanger

Shell and tube design A shell and tube design hydraulic fluid-to-water heat exchanger has no moving

parts. It is composed of an outer shell, tubes, tube sheets, baffles (or fins), hubs
and bonnets:

Cool Fluid Out

Hub

Hot Fluid In

Shell

Baffles or Fins

Cooling Tubes

Tube Sheet

Mounting Bracket

Cooling Water In

End Bonnet

Cooling Water Out

Optional Zinc Anode

Cutaway View of a Shell and Tube Design Hydraulic Fluid-to-Water Heat Exchanger

Heat Exchanger Care

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Heat Exchanger Care and Water Quality Guide

• Shell–the shell is a seamless, nonferrous tube, usually made of brass. Both

ends are welded into the hubs. The shell encloses the baffles or fins very
closely to prevent any bypassing and ineffective flow areas.

• Tubes–straight, seamless, nonferrous tubes are usually made from copper, a

copper-nickel alloy or stainless steel.

• Tube sheets–brass tube sheets hold the cooling tubes in place. Tube sheets

are bonded to the inside of the hubs.

• Baffles or fins–brass baffles or fins provide a contact area for dissipating

heat. The hot hydraulic fluid flows around the baffles (fins), while the
cooling water flows through the tubes.

• Hubs–forged brass hubs are used to connect the shell with the end bonnets.

Vents and drains are located on the underside of the hubs.

• Bonnets–cast iron bonnets provide an unrestricted connection for cooling

water flow. Renewable zinc anodes may be attached in the bonnet to prevent
electrolytic damage.

Hydraulic fluid-to-air A hydraulic fluid-to-air heat exchanger is composed of a motor and fan, tubes,

fins and a cabinet.

Tubes and Fins

Fluid In/Out Connection*

* Hot Fluid In/Cool Fluid Out connections vary between models

Cutaway View of a Hydraulic Fluid-to-Air Heat Exchanger

Motor and Fan

Fluid In/Out Connection*

Fluid In/Out

Connection*

Heat Exchanger Care and Water Quality Guide Heat Exchanger Care

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What ambient conditions are required?

Operating

temperatures

Water-cooled heat exchangers used in HPUs, operate at a minimum ambient
temperature of 4°C (40°F) and a maximum ambient temperature of 40°C
(104°F).

Air-cooled heat exchangers operate effectively up to an ambient temperatures of
37°C (98°F).

A nameplate specifying operating pressures and temperatures is attached to each
heat exchanger by the manufacturer. The MTS Hydraulic Power Supply Product
Manual provided with your test system contains specific information on the fluid
temperatures and cooling water requirements for your HPU.

The Air-Cooler to SilentFlo® HPU Integration Product Information manual
provides system integration requirements for

MTS Air-Coolers used with

MTS Series 505 SilentFlo™ Hydraulic Power Units.

Environment

Heat exchangers should not be located in a corrosive atmosphere, as rapid
deterioration of the brass casing, cooling element, fan and motor (hydraulic fluid­to-air units only) may take place, resulting in a shortened operating life and
unnecessary replacement costs.

Water quality Water chemistry for hydraulic fluid-to-water heat exchangers, is critical for a

successful heat exchange system. Generally speaking, municipal drinking water
that is pollution free, bacteriologically safe, and has a neutral pH is perfectly
acceptable for hydraulic fluid-to-water heat exchangers.

Cooling tower water and natural water sources, such as wells, rivers, or ponds,
must be free of pollutants and treated to reduce contaminants to the same levels
as municipal drinking water.

Softened or distilled water may not be suitable as a cooling liquid because
although most of the minerals have been removed there is a higher than desirable
level of carbon dioxide and oxygen present in the water. High levels of carbon
dioxide and oxygen will act to decrease the protective layer of minerals that form
on the surface of the tube, and increase the formation of copper oxide.

If the source of cooling water is a cooling tower, the presence of contaminants
that are corrosive to metals will vary over time. Contaminants must be controlled
to the levels listed in the following table. Ideally, the pH level should be
maintained in the 6.5–8.0 range for most applications. Chlorine should be used to
limit the growth of microbiological organisms that are generated by protein
decay. You must be careful not to use excessive amounts of chlorine. The
chloride concentration in the cooling water must be kept to less than 5 ppm.

The following table lists the acceptable levels of common compounds allowed in
the cooling water supply:

Heat Exchanger Care

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Heat Exchanger Care and Water Quality Guide