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Bulk and Film Temperature Impacton Heat Transfer Fluids

The transfer of heat is normally from a high temperature to a lower

temperature object. Typically, during normal operation, thermal fluid system

heat transfer takes place by all three means Convection, Conduction, a

Radiation. The first by forced convection of the heating media by a circulatin

pump. Convection is heat transfer by mass motion of the fluid when the

heated fluid is caused to move away from the source of heat, or heater,

carrying energy with it to the source it is targeting to heat. The second b

conduction of the heat from the heating fluid through the tube wall to the

media being heated. Finally, by radiation, from heat being emitted by the

tube wall that was heated by Heat Transfer Fluid to heat up the targeted medi

The flow rate of the Heat Transfer Fluid or media is used for determining th

highest temperature occurring in the heating system. This temperature

occurs in the heater. It is important to maintain a high flow rate by

convection inside the heating tube. This will reduce the difference betwee

the wall/tube Film Temperature and the Bulk Temperature of the Heat Transfe

Fluid while being able to maintain a high heat transfer film coefficient.

The maximum Bulk Temperature is the Heat Transfer Fluids highest avera

temperature and will usually take place at the exit of the fluid heater.

Thermal degradation of the Heat Transfer Fluid will double for every 18F

to 20F increase in the Bulk Fluid Temperature. This could result in the H

Transfer Fluids life being cut in half by operating nearly 20F above the

maximum rated Bulk Temperature. By lowering the temperature similar

degrees would cut the degradation rate of the fluid in half. Therefore, smachanges in temperature can have major impact on the Heat Transfer Fluid

life at elevated temperatures. It is very important to see why accurately

determining the thermal stability limit for a fluid is important, as well as

operating at the appropriate Bulk Temperature of the Heat Transfer Fluid.

Also, Film Temperature is an important aspect of the thermal degradation

rate of the Heat Transfer Fluid. Maximum Film Temperature is the highest

temperature a fluid experiences in the system. Maximum Film Temperatur

normally is found adjacent to the tube wall at the heating surface, and

typically averages 50F (10C) higher than the Bulk Fluid Temperature.

Continued on pa

Volume 1, Issu

May 2

Key Points in this Issue:

I Clearly understand your Fluids

Bulk Operating Temperature and

Maximum Film Temperature.

I Life of Heat Transfer Fluid is cut

in half by operating 18F to 20F

above maximum Bulk Temperature.

I Life of Fluid can possibly be doubled

by operating 18F to 20F below

maximum Bulk Temperature.

I 15 to 25% of Fluid degradation takes

place in the Film Temperature region.

Reducing flow of Heat Transfer Fluid

can overheat and degrade oil as it

surpasses Maximum Film Temperature.

I MultiTherm introduces new

Oxidation Resistant HTF with High

Flash Point and lower Vapor Pressure.

I MultiTherm introduces new

Economical HTF with High Flash

Point and lower Vapor Pressure

I Remember to Conduct Annual Fluid

Analysis on your Heat Transfer fluid.

800-225-7440www.multitherm.com

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3223 Phoenixville Pike, Malvern, PA 19355Phone: 610-408-8361 Fax: 610-408-8365

Email: techinfo@multitherm.comwww.multitherm.com

Bulk and Film Temperature Impacton Heat Transfer Fluids

Continued from pa

In typical systems, between 15 to 25% of the total Heat Transfer Fluid

degradation takes place in the film region. Consider also, if the flow rate

of Heat Transfer Fluid decreases while the heat input remains constant,

both Film and Bulk Temperatures will increase. This also results in less

fluid mass being available to remove the heat transferred to the wall tubinAnd because the film coefficient is almost linear with velocity, the Film

Temperature will increase due to the decreased heat transfer efficiency.

This will result in thermal degradation of the Heat Transfer Fluid as it

reaches and surpasses the Film Temperature of the system.

In conclusion, it is important to understand the correct Bulk Operating

Temperature of your fluid, as well as its maximum Film Temperature.

Operating near or surpassing either condition can result in quicker

degradation of your Heat Transfer Fluid.

For additional technical support call the MultiTherm TechTeam at 800-225-744

The MultiTherm LLC has been a leading supplier of efficient, non-hazardous Heat TransferFluids since 1977. Within a temperature range of -170F (-112C) to 650F (343C), thecompany can successfully and economically accommodate a customers heating orcooling requirements however exacting they may be. Further, MultiTherm providestroubleshooting help and a fluid analysis service to determine the physical and chemicalcondition of the fluid.

MultiTherm IntroducesNew Economical Heat Transfer Oil

MultiTherm is offering a new economical alternative for Heat Transfer

Fluid users. MultiTherm IG-1 is a Group II highly refined, hydro treated

mineral oil designed primarily for use in closed heat transfer systems.

MultiTherm IG-1 is designed for use in operations closed-loop systems

that are equipped with expansion tanks, pressure relief valves and nitroge

blanketing. In properly designed systems it provides trouble-free, long

lasting service to the end user.

MultiTherm IG-1 performs as an excellent Heat Transfer Fluid in numerou

markets looking for an economical alternative for their industrial manufacturi

processes. Common applications for MultiTherm IG-1; heat transfer

equipment used in manufacturing asphalt shingles and roofing compound

road-paving equipment, die-casting industry, paper and particle board marke

MultiTherm IG-1 offers the benefit of excellent thermal conductivity at hig

temperatures; low vapor pressure; and high Flash Point as well as resist

thermal breakdown and long thermal life in closed loop systems.

If you are looking for an economical Heat Transfer Fluid, then you need to

consider MultiTherm IG-1.

MultiTherm IntroducesNew Oxidation Resistant

Heat Transfer Oil

MultiTherm is offering the next generation

of Heat Transfer Fluid for our growing

base of Heat Transfer Fluid users.

MultiTherm OG-1 is a hydrocracked baseoil combined with the latest proprietary

oxidation inhibitor/stabilizer. MultiTherm

OG-1 was designed to meet the rising and

demanding requirements of open-system

liquid phase heat transfer requirements.

MultiTherm OG-1 offers the benefit of

excellent thermal conductivity at high

temperatures; low vapor pressure; and

high Flash Point. The Thermal Stability

from the oxidation resistant benefits reduces

efficiency robbing components such as

coke deposits and particulate build-up.

Finally, the longer oil life will mean less

maintenance; less process downtime, less oil

disposal and reduced environmental waste.

So, if you have an open-loop system or your

expansion tank is open to atmosphere then

MultiTherm OG-1 is the product for you.

Remember to Conduct YourAnnual Fluid Analysis

Develop a Preventive Maintenance

Program for your hot oil heater by annually

conducting a Fluid Analysis on your Heat

Transfer Fluid. MultiTherm TechTeam

can assist you call 800-225-7440.

Newsletters are available via e-mail. If you would liketo receive them electronically, please contact us drop us ane-mail at TechInfo@MultiTherm.com. Please include yourname, company, address, phone numbers and e-mail address.