Fluid Conditioning

7/29/2019 Fluid Conditioning

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MEL 334

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TERM PAPER :

FLUID CONDITIONING


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FLUID CONDITIONING

Introduction

Fluid conditioning or purification is the removal of contaminants such as air/gases combined

with filtration to remove particulate (solid contaminants) from any fluid. It is a relatively a

straightforward and cost-effective approach to make these fluids suitable for continued use

thus extending their service life and reducing the waste stream. Fluid conditioning is critical in

maintaining proper operation of a hydraulic system. Conditioning means to change the physical

characteristics of fluid. Fluid conditioning is an essential step to ensure reliability of any

hydraulic and lubrication systems since it not only enhances the performance of the fluid, but

also helps in protecting system components, which results in increased productivity. If we take

any fluid water is one of the most commonplace contaminants due to its ubiquitous nature andability to ingress into the system. Given enough time, it will dissolve any organic or inorganic

material. It surrounds foreign particles, such as minerals, entrapping them. Water may be

present in the base fluid in any or all of its three forms: free, emulsified and dissolved, and each

can damage the fluid and the system components.

Aeration of hydraulic and lubrication fluids can be caused by a myriad of reasons including poor

system design, fluid degradation, suction side air leaks, etc. Fluid aeration is undesirable since it

affects the response and control of hydraulic actuators, causes cavitation of valves and pumps,

and results in loss of lubrication film, reduced fluid viscosity, dieseling (adiabatic compression of

air bubbles resulting in thermal degradation of the fluid) and accelerated oxidation of the fluid.

In the case of gas compressors and internal combustion engines, gases from the process are

introduced in the lubrication Fluid causing chemical and physical degradation of the lubricant.

In the case of gas compressors, where hydrocarbons blow by piston rings, the blow by gases

can result in dilution of the fluid, and reduced viscosity and flash point.

There exist various types of conditioning methods which includes mechanical, physio-chemical

separation, or magnetic conditioning each with some advantages and disadvantages. For fluid

conditioning some devices are used in the hydraulic system known as fluid conditioners, such as

filters, heat exchangers, etc. Heat exchangers are used for regulating the temperature offluid. As heat transfer fluids deteriorate over time there is a buildup of VOCs which has an

adverse effect on the flammability of the fluid, lowering the flash and fire points to potentially

unsafe levels. To prevent silting, early component wear, and eventual system failure,

engineered filtration is required. Engineered filtration includes: understanding required micron

rating, application of the beta ratio, maintaining proper ISO code cleanliness levels, filter

location. These filters remove physical contaminants also known as complexes. Filtration


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devices are used to filter particles out of the systems fluid. A filters efficiency is rated with a

beta ratio. The beta ratio is the number of particles upstream from the filter that are larger

than the filters micron rating divided by the number of particles downstream larger than the

filters micron rating.

FLUID CONDITIONING METHODS

Methods commonly employed for the purification of the fluids include

dry air purge coalescence centrifugation absorbent filtration settling (settling tanks) mass transfer vacuum dehydration flash distillation vacuum dehydration.

Methods such as centrifugation and coalescence rely on purely mechanical means, based on

phase separation. Whereas flash distillation vacuum dehydration methods use a more

aggressive approach, employing flash evaporation of the volatile contaminants including water

at temperatures well above those normally found under standard system operating conditions,

and at significantly reduced pressures, the mass transfer vacuum dehydration method, on the

other hand, employs moderate level of vacuum and virtually little or no additional heating. The

technique is referred to as mass transfer because it predominantly relies on the transfer of

water into a steady stream of dry air under moderate vacuum and temperature conditions. The

intent of this paper is to compare and contrast the various technologies employed for removal

of water and other volatile contaminants from hydraulic and lubricating systems, and to

examine the impact of vacuum and temperature on the chemical and physical properties of the

hydraulic and lubricating fluids.

Mechanical separation methods that include settling, coalescence, absorbent filtration, and

centrifugation are limited to the removal of free and emulsified water. Mass transfer and flash

distillation type vacuum dehydrators, on the other hand, remove not only the free water butalso the dissolved water, free / dissolved air and other gases, and lighter hydrocarbons,

solvents and refrigerants. Dry air purge will not remove dissolved air but will strip dissolved

non-environmental gases, lighter hydrocarbons, solvents, and refrigerants, in addition to

free/dissolved water. Following is a brief discussion on each of the commonly used fluid

conditioning method.


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Coalescers

Coalescers remove free water entrained in the oil phase by capturing and coalescing water

droplets into larger droplets and separating them from the oil phase. Specific gravity, viscosity,

and interfacial tension of the fluid are key parameters in the process. Levels as low as 10 ppm

free water can be obtained with influent conditions of 10 % water by weight and an interfacial

tension of 2 dyne/cm and higher. Coalescers tend to disarm (become ineffective) in the

presence of surface-active agents in the fluid. Coalescers also need fine filtration for protection

against fouling by solid contaminants. The process is most effective with low viscosity fluids.

Centrifugal separators

Centrifugal separators utilize the difference in specific gravity between the fluid and the water

for the separation. Industrial centrifuges are designed to generate centrifugal forces on the

order of 3,000 to 10,000 times higher than gravitational force, hence speeding up the

separation of water by the same magnitude as compared with gravitational separation, for

example, in a settling tank. Centrifuges can also remove some emulsified water depending

upon the relative strength of the emulsion vs. the centrifugal force of the separator. Centrifugal

separators do not remove dissolved water. Centrifuges are well suited for applications where

continuous decontamination of fluids with excellent demulsibility (water separating

characteristics) is required.

Water absorbent filters

Water absorbent filters remove free and emulsified water by super absorbent polymers

impregnated in the media of the filter cartridge. The water is absorbed by the polymer, causing

it to swell, and remains trapped in the filtration medium. Super absorbent filters can remove

only a limited volume of water before causing the filter to go into pressure drop induced

bypass. They are not well-suited for removing large volumes of water, but are a convenient

method to maintain dry conditions in systems that dont normally ingest a lot of water. These

filters do not remove dissolved water.

Mass transfer vacuum dehydration

Mass transfer vacuum dehydration type purifiers work on the principle of mass transfer of the

liquid and gaseous contaminants from the oil to a constant stream of dry filtered air under

vacuum. The process, using techniques such as sheet-metal rings, nozzles, spinning disc, etc.

generates a large surface area of the fluid. The vacuum draws ambient air into the chamber,


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expanding the air volume several times consequently decreasing its relative humidity by the

same ratio.

Flash distillation vacuum dehydration

High vacuum / heat purifiers (flash distillation vacuum dehydration) utilize higher vacuum andtemperature conditions inside a chamber to rapidly boil off water and other volatile materials.

Flash distillation type equipment is often operated at vacuum and temperature conditions that

are well within the vapor phase region of the plot for faster removal of water.


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Fluid Conditioning

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