Document xj3BQKqEnL82yNJq19E3GRqa0
engineering
HEAT TRANSFER RATA for nu with
a fire-resistant, heat-transfer agent that operates up to 600F. in the liquid phase
0293263
TOWOLDMON0030088 WATER_PCB-00014557
Trade name reg. U. S. PaL Off.
TOWOLDMON0030089 WATER_PCB-00014558
w--^ -- ^
......................... has been used successfully since 1941 as a liquid phase heat transfer
medium at atmospheric pressure and temperatures up to 600F.
The compound, essentially tetrachlorobiphenyl, is a fire-resistant and non
corrosive liquid, which does not crystallize at low temperatures. Handled properly, in
well-designed forced circulation heat exchangers which avoid localized over heating
damage, the fluid gives satisfactory continuous service for many years without
replacement
Most significant, Aroclor 1248 is practically non-flammable. In one in
stallation of record, a ruptured pipe that spewed the hot fluid into gas flames failed
to cause the fluid to ignite.
For general heat transfer, Aroclor 1248 has several other important
qualities: it is highly mobile and can be readily pumped at temperatures as low as 50F.
If cooling is necessary, the heat transfer fluid can be put through a water cooler to be used
as a coolant. . . using this single fluid for both heating and cooling.
i-- .
Aroclor 1248 transfers heat (up to 600F.) as a liquid. This liquid phase
heat transfer makes it unnecessary to use the expensive pressurized equipment required
by a heat transfer medium that operates as a vapor. Aroclor 1248 operates safely and
efficiently with gas-fired, oil-fired, or electrical heat sources. It is used successfully in
the following types of applications ....
0293265
TOWOLDMON0030090 WATER_PCB-00014559
Chemical Processing Equipment, particularly for reacting flammable materials Cooking of Alkyd resins, varnishes, waxes Plastics molding, extruding, calendering Rubber processing Heatingasphalt Food Processing, including potato chip and doughnut frying in vegetable oils Processing titanium, magnesium, other non-ferrous metals Fabrication of magnesium and aluminum honey-comb structures for aircraft Indirect heating in dyestuff manufacture Heatingof corrugating rolls Indirect heating of distillationequipment Saponification of fats Calcining Ovens Impregnation and laminationof fibrous materials
0Z9
I
TOWOLDMON0030091 WATER_PCB-00014560
Appearance Absolute density, g./ml.
Absolute viscosity, centipoises
Thermal Conductivity, Btu./hr.sq. ft./F./ft
Spec. Volume, ml./g.
Practically colorless mobile liquid.
Temperature ''Centigrade Fahrenheit 1.44 30 86 1.41 60 140 1.37 100 212 1.27 200 392 1.17 300 572
112.0 17.5 4.2 0.99 0.47
30 86 60 140 100 212 200 392 300 572
0.0571
30
0.0564
60
0.0555
100
0.0534*
200
0.0512*
300
* Extropolated Data.
86 140 212 392 572
0.696 0.709 0.728 0.787 0.860
30 60 100 200 300
86 140 212 392 572
Table 1
oi^zbl
1 fi h !"' K" fr 1 1
f l:
5
TOWOLDMON0030092 WATER_PCB-00014561
(Table 1, cont.)
Spec. Heat, cal./g./C.
Vapor Pressure, mm. Hg.
Distillation Range, ASTM D-20 Flash Pt., Cleveland Open Cup,
ASTM D 92-45 Fire Pt., Cleveland Open Cup,
ASTM, D 92-45 Pour Pt., ASTM, D-97 Average Coefficient of Expansion
cc./cc./0F.
0.283 0.297 0.326 0.355
0.00037 0.16 2.9 18.0 350.0
Centigrade 50
100 200 300
37.8 100 150 200 300
^Fahrenheit 122 212 392 572
100 212 302 392 572
345-385
652-725
193-196
379-384
None
0.00037 0.00038 0.00041 0.00044 0.00047 0.00052
--
--7
-17.8 to 37.8 37.8 to 93.3 93.3 to 149 149 to 204 204 to 260 260 to 316
--
19.4
0 to 100 100 to 200 200 to 300 300 to 400 400 to 500 500 to 600
PHYSICAL CHARACTERISTICS
of AROCLOR 1248
A complete knowledge erf the physical characteristics of heat transfer media is highly essential to their satisfactory application in a heat exchanger. These physical constants have a major bearing on die equipment design, its mainte nance, and its operation. The following figures and charts give basic physical data on Aroclor 124$.
0293268
TOWOLDMON0030093 WATER_PCB-00014562
TEMPERATURE F.
DENSITY OF AROCLOR 1248
(Top axis, Ibs./cu. ft.; bottom axis, gm./ml.) DENSITY lbs. /cu. tt
0293269
TOWOLDMON0030094 WATER PCB-00014563
VISCOSITY OF AROCLOR 1248
TOWOLDMON0030095 WATER_PCB-00014564
Figure 3
VISCOSITY OF AROCLOR 1248
(Saybolt Universal Seconds)
7:
TEMPERATURE, DEGREES FAHRENHEIT
i3: \ t7i 1 t-:4 j Hi i
j'7 j
j.', I M- |
02^i/7I
5
TOWOLDMON0030096 WATER_PCB-00014565
1
HEAT CAPACITY and Its Relationship to Density
?. ?:' V .
ftg
.-
*1
. .
r;i
$
;S; : V - ;;
fi:-
Systematic errors exist in the various accepted pro cedures for making specific heat determinations. Consequently values may vary depending upon the procedure used. In practical operation, it frequently appears that the values for Aroclor 1248 shown in Figure 4 are somewhat low. Consequently, although these values have been accurately determined, they may be regarded as conservative.
When comparing the specific heat values of Aroclor 1248 with corresponding values for other heat transfer fluids, it is important to note that the density of Aroclor 1248 is much higher relatively than the density of other liquids used for heat transfer. Accord ingly, when comparison of heat capacity is made on a
volume basis (which is most pertinent in equipment design and efficient operation) the heat capacity of Aroclor 1248 shows itself to better advantage than by direct comparison of specific heat values.
Although specific heat values are important, they represent only one of several important constants that enter into the equations for calculating over-all heat transfer efficiency.
Through the use of these conservative heat capacity values, it is possible that equipment engi neered from such data might be slightly "over designed." It may be one of the factors that accounts for the exceptionally good operating performance of a number of highly successful commercial applications.
0293272
r?
TOWOLDMON0030097 WATER_PCB-00014566
SPECIFIC HEAT OF AROCLOR 1248
(Btu. per fl>. per degree F.)
Figure 4
SPECIFIC HEAT 3tu./lb./F.
01'*')273
TOWOLDMON0030098 WATER_PCB-00014567
Temperature c. F.
0 32 10 50 38 100 66 150 93 200 121 250 149 300 177 350 204 400 232 450 260 500 288 550 316 600
HEAT CONTENT of Aroclor 1248
Specific Heat
.269 .272 .280 .288 .295 .303 .311 .319 .327 .335 .343 .351 .359
Heat Content Btu./lb.
0.0 4.85 18.65 32.85 47.43 62.38 77.58 93.48 109.66 126.21 143.17 160.52 178.27
;
!;
i. _________________
0293274
--
TOWOLDMON0030099 WATER_PCB-00014568
I
THERMAL CONDUCTIVITY and VISCOSITY
The thermal conductivity values of Aioclor 1248 are shown in Figure 5. The curve shows this value over Aroclor 1248's operating temperature range, from 50F. to 600F.
As freshly charged into a heat exchanger, Aroclor 1248 has an initial viscosity of 74 (S.U.S.) at 130F. which corresponds to a viscosity of approxi mately 5000 (S.U.S.) at 50F. -- which temperature is assumed for practical purposes to be about the limit at which Aroclor 1248 can be conveniently pumped with a centrifugal pump.
The following table shows a comparison of the initial viscosity and the viscosity after a year's con tinuous service at 600F. in a LaMont forced circu lation heater:
TABLE III
Appearance Specific Gravity, 65 C. Viscosity, S. U. S. at 130F.
Original
Colorless Lipoid 1.410
74.0
After one Year o' service at
600CF.
Dark Brown Liquid
1.418
83.5
Although Aroclor 1248 tends to darken in use, this darkening is not harmful and does not indicate decomposition. In actual use at Monsanto, it has not been found necessary to replace the fluid after seven years of continuous use; additional fluid is only added as necessary to make up spills or leaks.
In Figure 6, the horizontal line indicating vis cosity limit of pumpability at 50F. shows that the rate of viscosity increase based on a year's continuous service should permit Aroclor 1248 to serve approxi mately four years before increased viscosity may inter fere with its pumpability when cold. In practice, Aroclor 1248 has given satisfactory pumpability for much longer periods. A simple S.U.S. viscosity deter mination by the ASTM-D-88 method can be used for periodic checks on the fluid.
oz^75
II
TOWOLDMON0030100 WATER_PCB-00014569
TEMPERATURE f.
THERMAL CONDUCTIVITY OF AROCLOR 1248
(Dotted extension indicates extrapolated data)
TOWOLDMON0030101 WATER_PCB-00014570
EXPECTED MINIMUM SERVICE LIFE IN A FORCED CIRCULATION HEATER
TOWOLDMON0030102 WATER_PCB-00014571
STABILITY
Aroclor 1248 is an extremely stable chemical com pound. Tests over long periods of time have shown that 600F. is a safe maximum temperature for continuous operation in heaters that are properly designed and operated to eliminate intense, localized overheating. At this temperature the fluid is 52F. below the initial temperature of its boiling range, and consequently re mains a liquid.
Near its boiling point Aroclor 1248 tends to dehydrohalogenate to a very slight but measurable degree. If this occurs as a result of accidental over heating, the small amount of HC1 gas evolved tends to pass through the vent tank without harm to the equipment provided that the system is dry.
Experimental observations using ideally-suited heat exchangers operating at a temperature of 650F. with imposed nitrogen pressures of 30 and 70 psig. showed that application of pressure did not prevent this small amount of thermal decomposition, which also occurs when the material is heated above 600CF. at atmospheric pressure.
When heated continuously at 650F. under nitrogen pressure a gradual increase in the viscosity of the fluid occurs indicating that its service life would be limited to about 6 months to one year.
Results of operating at 600F., however, with out imposed nitrogen pressure indicate Aroclor 1248 can be heated continuously at this temperature for about 4 years before any viscosity increase could be expected to interfere with its pumpabilitv at 50F. which is slightly below normal room temperatures.
Provision should be made to prevent water contamination of the system. If the system becomes contaminated with water, any HC1 liberated by local ized overheating may dissolve in the water film which will float on top of Aroclor 1248 in the expansion tank. The acidic solution thus formed can cause corrosion. It is recommended that moisture be eliminated from the expansion tank by installing a moisture trap or by sealing the tank and applying 15 to 30 psig. of nitrogen gas. With exception of the expansion tank, the system should be kept full of Aroclor 1248 at all times to pre vent formation of air pockets where moisture may condense when the system cools off between periods of operation.
Many years of practical operating experience has shown that Aroclor 1248 is virtually non-corrosive to valves, piping, tanks, and jackets made of cast steel, steel, or stainless steel. In actual use, brass valves have been used satisfactorily.
%yV-
i' '
;
0293278
K
TOWOLDMON0030103 WATER_PCB-00014572
SAFETY of OPERATION
Aroclor 1248 can be considered a non-flammable liquid; no fire point is obtained by the Cleveland Open Cup method on heating to its boiling point (650F.). The spontaneous ignition temperature(2) is 1,299F.
In actual use. the following reported accident in a heating system demonstrates the fire resistance of Aroclor 1248 and the freedom it offers from the hazard of fire propagation. An operator's failure to start the circulation pump when the gas heater was on resulted in excessive coil temperatures. The line containing Aroclor 1248 sagged into the fire chamber. A weld rup tured and Aroclor 1248 poured into the red-hot fire chamber in contact with the flame. Dense smoke and fumes arose from the heater but there was no external fire. After the gas flame was cut off, the smoking stopped.
Insurance authorities allow the use of Aroclor 1248 heaters in many locations with a minimum of protection. No fire walls are required to isolate the heaters.
Aroclor 1248 has a low vapor pressure. In sys tems that employ a vented expansion tank, the loss due to evaporation is not measurable. If Aroclor 1248 in the expansion tank would reach a temperature of
266F., the vapor pressure of the fluid would be only 1 mm. of Hg.
SAFETY OF HANDLING
Aroclor 1248 is an inert, unreactive liquid. If it is spilled on the skin, there are no noticeable il! effects. It is advisable, however, to wash the skin with soap and water after contact.
A skin burn resulting from accidental contact with hot Aroclor 1248 should be treated in the normal manner for hot oil burns. Any liquid adhering to the burned area need not be removed immediately unless treatment of the burn demands it. If the bum must be cleaned, soap and water or repeated washings with a vegetable oil (olive oil) may be used.
The vapors emitted by Aroclor 1248 heated to elevated temperatures are injurious on prolonged ex posure and should not be breathed. It is indicated that 2.0 mg. of Aroclor 1248 per cubic meter of air is the maximum safe amount permissable in workrooms. In commercial heat transfer installations, it is presumed that Aroclor 1248 will be used in a closed system free from leaks. Accordingly, their should be little or no opportunity for workers to come in contact with Aroclor 1248 vapors.
0293279
TOWOLDMON0030104 WATER_PCB-00014573
HEATER
The most significant factor to remember when selecting or de signing a heat exchanger for Aroclor 1248 use is this:
Aroclor 1248 transfers heat as a liquid, at the maximum recom mended temperature of 600F. for continuous operation, which is approxi mately 50F. below the boiling point. Consequently, .Aroclor 1248 does not form vapor to accelerate convection circulation. Ordinary fire-tube or water-tube heaters which depend solely upon convection perform satisfactorily only at relatively low temperatures.
When temperatures of 500-600F. are required, a forced circu lation type heater is recommended. A satisfactory type of heater design would consist of a specified number of tubes in parallel, properly orificed to provide a high velocity fluid flow of 8 to 10 feet per second. These should be spaced to permit uniform heat absorption throughout their entire length. A typical construction is shown in Figure 7.
In its fabrication, the heater should be ASME Code all-welded construction, conforming to state and local ordinances. Tube joints, which in an ordinary steam heater would be the expanded type, must be sealwelded to prevent leakage. All connections larger than %" should be flanged connections, since ordinary threaded pipe connection is not suited for Aroclor 1248 service. Spiral-wound stainless steel and asbestos com bination is recommended for sealing joints and plugs.
Drain valves should be installed at all low points on the heater and the valves must conform with ASME requirements for "blow down" valves.
^3^80
TOWOLDMON0030105 WATER_PCB-00014574
Since a heater operating on Aroclor 1248 is completely filled with liquid, costly liquid-level controls and condensate return pipes, fittings, traps, etc. are completely eliminated.
Heaters can be provided with any desired kind of firing. Portable and small size stationary are frequently electrically heated; larger units may be gas- or oil-fired. In installations where an open flame presents a fire hazard, to meet insurance requirements the heater may be installed in a separate build ing with piping carrying the hot Aroclor 1248 to the point of use. Properly constructed transmission pipes may extend for hundreds of feet.
HEATER EFFICIENCY
Forced circulation heaters with integral economizers will show
an efficiency of from 75 to 80%. Heaters of the straight con nector type show efficiencies of 65 to 75%, depending upon the discharge temperatures.
HEATER CAPACITIES
Heaters using Aroclor 1248 (gas- or oil-fired) are available in output capacities ranging from approximately 250,000 Btu. per hour to large units rated over 10 million Btu. per hour. A heat flux density (or heat energy input) of approximately 5,000 Btu. per hour per square foot of tube surface is regarded as satisfactory.
For lower output rate, electrically-heated units are favored, employing watt densities of 12 to 16 watts per square inch.
02S 3281
TOWOLDMON0030106 WATER_PCB-00014575
THE USERS
The "users" or recipients of the heat at the point of processing can be any type of heating pan, platen, jacketed kettle, or coils of steel or stainless steel construction. Ordinary low pressure construction is satisfactory, since the pressure imposed on the Aroclor 1248 seldom exceeds 50 psig. In the user, however, it b important that all-welded construction be used. Threaded connections may allow leakage of the hot fluid. As in the heater, all connections and over should be flanged and all joints sealed with spiral wound stainless steel and asbestos gasket material. Alloy bolts should be used to secure flanges. A typical system with several users is shown in Figure 8.
EIPW*SJO VESSEL
FUEL KMNSKW LEVEL GAUGE
COLO START
STORAGE TAWS 18
TOWOLDMON0030107 WATER_PCB-00014576
THE PUMP
For most systems, cast-steel centrifugal pumps with watercooled stuffing box and bearings are to be preferred. However, high temperature centrifugal pumps with mechanical seals are now available which give excellent performance. In some in stallations, immersion pumps have been used. Whatever type is selected, the pump capacity and pressure head must be sufficient to circulate the volume of fluid at the rate the particular installation demands.
To avoid shaft trouble and leakage at the seals, it is important to provide adequate expansion joints and to support the piping in a manner to avoid stresses on the body of the pump. Direct-connection pumps driven by 1,7.50 rpm. motors are most commonly used. Each pump should be fitted with a positive differential control to switch off the burner in case of pump failure.
When a new system is first put into operation, a slight leakage may be noticed at the pump. It is not advisable to tighten the pump gland, however, until the system has heated up close to the temperature of operation.
PIPING LAYOUT
The most important factors in the piping layout for Aroclor 1248 systems are (a) proper sizing for the required flow rate and (b) minimizing pressure drop. Because the sys tem will undergo temperature changes, adequate expansion joints and loops to relieve expansion and contraction stress are essential.
All pipe lines and connections should be of extra heavy or Schedule 80 welded construction meeting A.S.M.E. require ments. Flanged joints should be used as sparingly as possible to minimize potential leak points.
All valves and controls should be cast steel construction with stainless steel seats. Pipe lines should be well insulated and those exposed to temperatures below 70F. should be steam jacketed.
All high points in the piping system should be provided with vent valves; all low points should have drain connections. Piping should be well anchored at frequent intervals, particu larly near expansion loops, to prevent vibrations.
Figure 9 shows a typical piping diagram that illustrates the important features of an Aroclor 1248 piping system. These may be varied to suit the installation.
THE PIPING AND CONTPOl CIPCUITS
MT0C10R FRO* HtAIES
STEAM Of
yWATER
OUTLET WCTCTtO T1IE COOLER WATER INLET
ATOCLOR TO HEAUR
-XL
---PILOT
XXL-
Ficure 9
L JO
k I
TOWOLDMON0030108 WATEFLPCB-00014577
THE EXPANSION TANK
The expansion tank should be large enough to accom modate about 20% of the total volume of the entire system, including the fluid content of the heater, piping, and all heatusers. Tank should be sized to be %-full when system is cooled to TO'^F. and %-fuIl when system is at maximum operating tem perature. Expansion tank should be fitted with a sight glass at the "full" range and a float-operated low-level switch to shut off burner in case of accidental fluid loss in the system.
The expansion tank should be mounted on a platform high enough to support the liquid reservoir at least six feet higher than the highest point in the piping system.
THE FEED and DRAIN PUMP
To eliminate manual filling and draining of the heating system, it is recommended that a small 2-to-5 gpm. positive displacement pump be installed at some convenient point to pump the Aroclor 1248 into or out of the system.
CONTROLS
Controls for heating systems using Aroclor 1248 should be installed both on the heater itself and on the heat-using units. A wide variety of thermo-operating controls are available and any reliable standard equipment is satisfactory.
Heater controls should be installed to regulate the firing mechanism in direct proportion to the required output. These controls should increase or decrease the heat in-put to main tain the Aroclor 1248 at the operating temperature required by the heat-demand of the user, Small units may be operated satisfactorily by relatively simple "on-off" or "high-low" con trollers; larger units may operate more uniformly if equipped with modulating temperature controls.
User Controls should be installed to regulate the flow of the heat transfer fluid in direct proportion to the heat-con sumption of the heat-using equipment. In a multiple-user sys
tem, separate controls should be installed on each consuming
unit, to assure the proper heat-deliverv.
Safety Controls. In addition to activating controls, the
heater must also be fitted with the proper safety controls to
meet the A.S.M.E. requirements. Safety controls should
include:
1. A high temperature limit control operating at the heater outlet to shut off the burner in the
event of an excessive temperature rise.
2. A suitable low-limit temperature control to
hold the burner at low fire until the Aroclor 1248 in the system reaches a temperature
level of 180 F.
The low limit temperature control is essential because
the viscosity of Aroclor 1248 is rather high at normal room tem
perature. To avoid localized overheating upon start-up, it is not
advisable to apply full heat from the burner until all the fluid
in the system has attained a viscosity that allows good flow and
unimpeded circulation. Cold start-ups require slow up-heats.
Burners should be equipped with automatic ignition
controls and flame failure controls. In wide-range firing opera
tions, an over-fire draft control will increase the economy of
operation. Induced draft fans are another factor which should be
considered as a means of avoiding the expense of high chimneys.
Where they are needed throughout the system, good
quality recording or indicating gauges should be installed.
COOLING EQUIPMENT
Where fast reduction of temperature is required suitable, air- or water-cooling installations may be used. If the cooler is to be a water-type unit, it is suggested that stainless steel tubing be used for the coils to avoid corrosion on the water side. If a cooler is installed in the system, low temperature limit con trols should also be installed to avoid excessive cooling that might raise the viscosity to the point of impeding the circulation in the system.
* **
* *
TOWOLDMON0030109 WATER_PCB-00014578
1
FILTERING EQUIPMENT
When heating systems operated on Aroclor 1248 are run continuously near the maximum temperature of recommended operation (600eF.), it is advisable to provide a filtering device that can be attached to the drain line of the storage tank. In this way discrete particles of dirt that may get into the system can be filtered out periodically. This is an advisable maintenance step since it will eliminate the danger of dirt clogging the valve seats or lodging in parts of the control mechanisms.
A small portable filter such as those manufactured by Honan-Crane Corporation (Lebanon, Ind.) or Sparkler Manufac turing Company (Mundelein, III.) is quite satisfactory.
CONNECTIONS and GASKETS
In a system operated on Aroclor 1248, welded connec tions are preferable; threaded screw connections should be avoided wherever possible. This precaution will minimize leaks with consequent make-up. All connections 1" and over should be of the flanged type fastened with alloy bolts to prevent frozen connections. Steel connectors should be used for all instruments and controls. For gasketing, spiral wound gaskets of corrugated stainless steel and asbestos combination should be used on all flanged connections.
TESTING and CLEANING THE SYSTEM
When a new system has been installed, it is essential to test ihe entire system hydrostatically for leaks, and to wash out all the lines to remove dirt, oil films, or pipe scale. Both the cleaning and the testing can he done with a single operation, such as the following:
Fill the entire system with a water solution containing 5 pounds of soda ash and 5 pounds of caustic soda for cvcrv 1000 pounds (120 gal.) of water used. Thoroughly vent the svs-
tern at all of the highest points in the piping system to assure complete filling . . . then start the circulating pump. With the pump running, the entire system is next inspected for leaks.
Next, turn on the burner at low-fire rate and raise the temperature of the wash solution to 180 "F. This hot wash solu tion should be circulated continuously through the entire system (heater and all users) for at least 24 hours. At regular intervals a portion of the solution should be drained and replaced by fresh water. This partial draining should be continued at regular in tervals until the drainage from the system is clear.
At the end of the 24 hour period, the temperature of the circulating wash solution should be brought up to 240F. and the fire turned off. The whole system should then be drained and all vents in the piping opened. Residual heat will dry the pipes and the heater through the vents, which should remain open until inspection shows that the system is entirely dry. When all traces of water have dried out, the drains and vents are closed.
Aroclor 1248 is then charged into the cleaned, dry sys tem. The circulating pump is started and firing begun at low heat until the Aroclor 1248 has reached a temperature of 250CF. Periodically during this initial up-heating, the lines should be vented every 10-15 minutes for at least two hours to allow any residual moisture or air to escape. After it is certain that all moisture has been eliminated from the system, the entire system should be inspected for leaks with the pump circulating the hot fluid. As a final inspection, the expansion tank should be checked to make sure that the tank is % full. After this, the burner can be set to full-fire and the system brought up to operating tem perature.
When the temperature of operation has been reached all controls should be checked and adjusted so that the burner is regulated for full modulation. When the system is brought to full operating temperature, all pipe lines should be given a final inspection for expansion and bracing.
\
[ f
i i
029328*3
TOWOLDMON0030110 WATER_PCB-00014579
GENERAL RECOMMENDATIONS for Operation and Maintenance
The following recommendations are primarily guides for the manner of using Aroclor 1248 in an operating system. They are supplemental to the equipment manufacturer's own recommendations for operation and maintenance that relate to die heaters or the heat-using installations themselves. The recommendations for start-up, shut-down, precautions in event of power failure, and periodic check-ups on the fluid and equip ment apply as generally accepted practice on all types and sizes of systems. By following these recommendations, the troublefree service life of the heat transfer fluid will be increased.
START-UP
When systems have been shut down for week-ends or over-night and the fluid is cooled to room temperature, follow this start-up procedure:
1. Start the circulating pump and check the expansion tank to make certain the Aroclor 1248 is at the proper cold-start level (Tank should be y<i-full.)
2. Start burner at minimum flame setting and continue full circulation until Aroclor 1248 is heated to 180'F. when measured on the return side of the heater.
3- Turn heater up to full heat.
SHUT-DOWN
The following procedure will eliminate overheating of the fluid when shutting down:
1. Shut off burner completely with circulating pump still oper ating. Continue to run the circulating pump at full head for at least Vz hour to dissipate high residual heat in the com bustion chamber of the burner.
2. Shut off circulating pump at the end of Vz hour and switch off all heater electrical controls.
PRECAUTIONS IN COLD WEATHER
When heat exchanger is exposed to ambient tempera tures below 503F., it is recommended that unit not be shut down. It is recommended that the burner be turned low and the fluid circulated continuously at about 200F. The unit will then be "at ready" for immediate high temperature operation.
PRECAUTIONS IN CASE OF POWER FAILURE
In case of power failure, the burner circuit is interrupted by the heater controls. When power comes on, the circulating pump should first be run for a few minutes to eliminate any vapor pockets that might have been formed by the fluid's being held static in the hot combustion chamber. If there is no knock ing in the piping system, full-fire may be resumed immediately.
PERIODIC CHECK-UPS
The regular maintenance inspection schedule should include the equipment manufacturer's recommendations and also inspection of the heat transfer fluid. The following is a listing of check points.
1. Lubrication of moving parts.
2. Operating fidelity and accuracy of readings of safety controls and temperature limit controls.
3. Inspection of heater tubes, burner, refractory linings.
4. Periodic cleaning of heater surfaces.
5. Inspection of water cooling at the circulating pump.
6. Regular repacking of stuffing boxes according to the manu facturer's recommendations.
7. Semi-annual or annual sampling and analysis of Aroclor 1248.
Under normal operating conditions not affected by fre quent power failures or accidental overheating, when Aroclor 1248 is operated at 600F. it should not be necessary to check on the condition of the fluid more often than once or twice a year.
The analysis for fluid condition is a simple determina tion of viscosity. The information given in Figure 6 serves as a guide to estimate the condition of the fluid, according to vis cosity values. Most users do their own testing; some have the viscosity determination made by an outside laboratory.
Customers can have their fluid tested by Monsanto free of charge. A one-quart sample is required, and sample should be carefully packed to avoid breakage in shipment. Samples should be shipped to:
Monsanto Chemical Company
Organic Chemical Division
Industrial Fluid Sales
St. Louis, Missouri
0293106
TOWOLDMON0030111 WATER_PCB-00014580
Designing or purchasing equipment for a heating system to be operated with Aroclor as a medium to deliver heat into a process requires consideration of heat transfer characteristics of both the user and the heater. The actual heat which can be absorbed by a user, for example, depends upon the over-all heat transfer coefficient, heat transfer area, and a mean ternperature difference between Aroclor and the material being heated. Both overall heat transfer coefficient and mean temperature difference are, in turn, affected by the flow rate of the Aroclor. This inter-relation of flow rate, heat, and temperature is usually solved by a trial and error procedure as covered in standard reference texts. The approach of Granet-3 may be used to minimize or eliminate trial and error.
The following tables and graphs of physical properties and enginecring data are provided as an aid in layout and design calculations for systems to be operated with Aroclor 1248 as a heat transfer fluid in the liquid phase.
Table IV lists properties useful in heat balance calculations by which the flow rate is related to the heat transferred and the temperature change of the Aroclor. This relation is also shown graphically in Figure 10.
The over-all heat transfer coefficient for the heater or user may be estimated by the methods outlined in the texts of McAdams4 or KernS. This is usually done by combining the individual film coefficient of the Aroclor with other coefficients and conductivities to yield the over-all coefficient. Table V contains physical properties of Aroclor as a function of temperature which are needed for calculating the Aroclor film coefficient. Tables VI gives typical film coefficients for Aroclor flowing through a 0.81 inch i.d. tube. These are listed as a function of temperature and flow rate in a tubular heat exchanger. Other tube sizes would, of course, require a correction for the diameter in the Reynolds and Nusselt group of the equation (from McAdams) given at the top of Table VI. Correlations for estimating film coefficients for various material that might be processed by indirect heating may be found in the texts 4 and 5 cited and elsewhere in the literature.
For sizing pipe lines and pumping requirements. Figure 11 shows pressure drop vs. flow rate and pipe size for Aroclor 124S at temperatures over 300F. Above this temperature Aroclor 1248 flows freely like water.
\ 
