|
Ta (Ambient Temperature) - Ambient Temperature, also Low Ambient. In heat trace design, Ta
refers to the surrounding air temperature on the coldest day where
the heat traced equipment is located. See also Delta T (il T) .
Temperature Controller … An automatic switching device which cycles
an electric heat tracing circuit on and off so that the required Tp
will be maintained regardless of Ta.
Delta T (ΔT) - Temperature difference. Usually used to describe the difference
between the required pipe/vessel temperature (Tp) and the
anticipated low ambient temperature (Ta). Therefore, ΔT will usually
equal (Tp-Ta).
For example, to maintain a pipe temperature (Tp) of 40°F in an area
where the ambient temperature (Ta) can drop to -20°F, the goal of
heat tracing is to maintain a temperature difference (ΔT) of 60°F.
Freeze Protection - A heat tracing application. Usually refers to
maintaining pipe temperatures at slightly above freezing
(Tp = 40°F - 50°F). Freeze protection design is simply a
matter of selecting a heater to offset the heat loss
through the thermal insulation. Freeze protection
systems are characterized by relatively low heat
delivery and by the fact that their use is generally
seasonal during cold weather months. "Freeze protection"
is sometimes used to describe moderate temperature
maintenance applications (Tp = 90°F or less).
For more information:
http://www.thermon.com/us/pipefreeze.aspx
Heat Loss - The rate at which process equipment heat flows to a cooler ambient,
stated in either watts or BTU/hour. The purpose of heat tracing is
to replace that heat lost through the thermal insulation in order to
maintain a desired temperature difference (ilT or Delta T).
Therefore, the first step in heat tracing system design is to
calculate the heat loss. Heat loss calculations always involve three
factors:
1) ilT (Delta T) or(Tp - Ta)
2) Nominal Pipe Size or Vessel Dimensions 3) Type & Thickness of
Thermal Insulation
Nothing can prevent the eventual flow of heat to any area of
lower temperature. If there are two adjacent areas having different
temperatures, the warmer will continue losing heat to the cooler
until both are the same temperature. Then both areas have reached
thermal equilibrium. The loss of heat can be restricted to a
measurable and predictable degree by use of thermal insulation. But
the heat loss process cannot be eliminated. However, it is possible
to determine exactly how much heat is being lost for a given
application. Once this is known, it is only a matter of replacing
that amount of heat to offset the amount being lost.
Conduction - By far the most efficient heating method of the three is conduction. Conductive heating acknowledges the fact that heat will follow the path of least resistance in seeking lower temperature areas and that air is a very effective thermal insulation. Conductive heating involves placing the object to be heated in contact with the heat source, thereby eliminating any air barrier between the two. The object being heated in this fashion can be referred to as a "heat sink" because it will practically drain the heat from the source. A good example could be a piece of ice in a container of hot water. Thermon heat transfer cements offer the optimum conductive heating arrangement by eliminating air spaces and replacing them with a highly conductive thermal bridge between the heat source and the object to be heated. Heat flow always follows the path of least resistance.
Heat Transfer - Heat always flows (is transferred) from an area of higher temperature to an area of lower temperature. Heat will also follow the path of least resistance in seeking areas of lower temperature. Thermon uses this natural phenomenon to our (and the customer's) advantage. Thermon's specialty is taking heat from a higher temperature source and putting it into a specified lower temperature object with as little waste of heat as possible.
Convection - Convection heating makes use of the fact that heat rises. It represents a more efficient use of the available heat than does radiant heating. Cooking over a fire is the most obvious example of convection heating.
Radiation - The least efficient means of transferring heat. Radiation is most often used for space heating of closed areas. Warming an object by placing it next to a fire would be an example of radiant heating. The vast majority of the heat is lost to the atmosphere.
Watts Per Foot - When determining the heat loss characteristics of a tank, we usually just determine the total surface area and the corresponding total watt requirement to do the heating job. This is due to the rather rectangular cross section of most tanks; 20' diameter by 20' long is a typical tank measurement. Piping, on the other hand, is usually long enough so that the diameter is just a fraction of the length; 2" diameter by 200' long is a typical pipe measurement. We, therefore, find it convenient to refer to a pipe's heat loss characteristics in terms of "watts per foot." Watts per foot is merely the total watt requirement divided by the length of the pipe in feet.
Power - Wattage can be compared to the flood in progress. The damage the flood does will be directly related to the speed of the flow and the force behind it. Wattage is also a product of the force (voltage) multiplied by the current (amps).
Due to the mathematical relationships between these different values, knowledge of any two will enable someone to determine the other two. For this we use the "power circle" which is another interpretation of Ohm's law.
Amperage - Amperage, or current, kills. A fraction of an amp flowing through your body can kill you. Being next to a high voltage source is similar to standing next to a dammed lake. The potential force is there but potential is unjust speculation.
Resistance - Measured in ohms (W), resistance is a measurable property in every physical object. Electrical insulations have high resistance which resist current flow. Electrical conductors have low resistance and allow free current flow.
Resistance is a quality, not a force. Every physical object has a relative level of electrical resistance. Those having a high level of resistance are called insulators. Those with a low level of resistance are called conductors.
Weather Barrier - Metal or plastic material, sometimes sealed with mastic, used to protect thermal insulation from external moisture. Thermal insulation must be dry to slow heat loss properly.
Wattage - A value used to measure and describe work produced by forcing voltage across a resistance in order to induce current. As an example, light bulbs are rated by watt output. The higher the wattage, the hotter and brighter the bulb. Wattage is the product when voltage is multiplied by amperage (current).
Voltage - Power supply. A potential force which can be connected to a load in order to produce heat, light or motion.
Tp - Pipe Temperature, Process Temperature & Maintenance Temperature - In heat trace design, Tp refers to the required temperature for the contents of piping/vessels. (See also Delta T [~T]).
Thermal lnsulation - Material containing tiny air pockets and which acts as a
barrier against heat migration. Dry, properly installed
thermal insulation will slow (but not eliminate) process
system heat loss by approximately 85%. Moist thermal
insulation will render any heat tracing system
inoperative. Heat tracing designed for freeze protection
or process maintenance will usually be unable to dry wet
insulation because of the relatively low heat output of
the tracing.
Thermal insulation inadequacies (wetness, improper
installation, removal for valve maintenance, etc.)
account for the vast majority of heat tracing problems.
Dry, properly installed and maintained thermal
insulation is absolutely essential for proper heat
tracing design and performance.
For More Information:
http://www.thermon.com/us/products.aspx?prodid=13
Self-Regulating Heating Cable - Any heating cable providing a watt output
which increases as temperatures fall and
decreases as temperatures rise.
Self-regulating heating cables use a carbon
matrix heating element with variable
resistance.
For More
Information:
http://www.thermon.com/us/selfreg.aspx
Series Constant Watt Heating Cable - A heating cable which includes a
single heating element. Any
break in the element will cause
the entire cable to fail.
Circuit length has a direct
effect on the watt/foot output.
The resistance of each
individual heating circuit
length must be considered for
each pipe length, heat loss and
operating voltage.
Series cables fall into two
basic types:
1) Flexible, plastic-jacketed
cable for longer tracing
circuits (generally 1000' to
5000').
2) Semi-rigid, metal jacketed,
mineral insulated (MI) cables
for high temperature service. (Tp
to 800°F, maximum exposure
temperatures to 11 OO°F).
For More Information:
http://www.thermon.com/us/seriesconstant.aspx
Power-Limiting Heating Cable - A parallel
resistance heating
cable that will
reduce its power
output as
temperatures rise
but does not have
the high in-rush
currents associated
with self-regulating
heating cables.
These cables are
capable of
delivering high
watt-per-foot heat
outputs.
For more
information:
http://www.thermon.com/us/powerlimit.aspx
Parallel Constant Watt Heating Cable - A heating cable which includes a continuous series of short,
independent heating circuits. Localized damage can result in only
partial loss of heating. Watt-per-foot output is relatively
unchanged by variations in circuit length up to several hundred
feet. Known as "cut-to-Iength," parallel cables are easy to size
because circuit lengths (Within limits) do not have to be
considered.
For more information:
http://www.thermon.com/us/parallelconstant.aspx
Constant Watt Heating Cables - Any heating cable providing a watt output which is unaffected by
temperature changes. Constant watt heating cables use alloy heating
elemems with a fixed resistance.
>
For more information:
http://www.thermon.com/us/parallelconstant.aspx
Current - Measured in amps, current results when voltage is applied across a resistance. For a given voltage, current will increase as resistance decreases or vice-versa. The result of current flow through a resistance is to produce heat and light.
Circuit Breaker - An automatic switching device which will disconnect a circuit in the event of excessive current (amps). Usually caused by a short circuit, excessive amperage can lead to personnel and equipment hazards.
Circuit - A complete electrical system consisting of a voltage supply and an electrical load connected by electrical conductors. A complete circuit is necessary for current flow. Any break in an electrical circuit, intentional or accidental, will interrupt current flow.
Electric Heat Tracing for Freeze Protection and Temperature Maintenance - Tracing means following a path or progression that has already been
established. The term "heat tracing" may have come from engineers
who had to indicate on drawings which pipes require heating.
The purpose of heat tracing is to ensure that the contents of the
tank and! or piping are available for use even under the most
extreme ambient conditions.
Thermon specializes in applying heat to the place where it is needed
and nowhere else. Any heat that goes into the atmosphere represents
wasted energy. Heat tracing on a piping drawing could be represented
by the dotted line following the path of the pipe (see figures
below). Thermon's art lies in applying the necessary amount of heat
(no more) to the appropriate location (nowhere else).
For more information:
http://www.thermon.com/us/pipefreeze.aspx
http://www.thermon.com/us/pipetemp.aspx
|