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Thermal Fluid Systems Glossary

Balanced system – A system that is arranged whereby each heat consumer has an equally proportional distribution of fluid. This is especially important when one pump supplies flow to the heater and all heat consumers.

Bellow sealed valve – A manual or automatic valve in which the valve stem is attached to a metal bellows to prevent leaks from the process through the valve stem. Valves stems are non-rotating to allow the bellows to compress and expand without rotational distortion.

Blocking vessel – The blocking vessel or cold seal tank is designed to contain the volume of thermal expansion during normal operating temperature fluctuations, thereby keeping the expansion tank relatively cool.

Btu/hr – A BTU (British Thermal Unit) is the amount of heat required to raise one pound of water by one degree Fahrenheit. Btu/hr is the unit of measure that we use to describe the net thermal heat output of our heaters, the gross thermal input of the burner, and the heat consumption of users.

Burner – The device that fires into our heater, regardless of the fuel used.

Cavitation – This is the condition caused by the suction of a pump by air, steam, or thermal fluid vapors entrained in the fluid. The result is pump surging and should be corrected as soon as possible.

Cracking – A serious degradation of the heat transfer fluid. This can be caused by poor heater design, low oil flow, extreme overfiring, or operating above the heat transfer fluid’s temperature limits.

Delta T – The difference between the inlet and outlet temperature of a heater or heat consumer.

Drain (sump) tank – The tank is used to store thermal fluid either before filling the entire system or during maintenance. The volume of the drain tank should be equivalent to the largest volume of fluid between any two shut-off valves. Typically, this is the heater volume, but it could be the volume of a large heat consumer.

Expansion tank – Used to contain the thermal expansion of the heat transfer fluid. It also provides a static head for the primary pump. Since the typical thermal expansion of heat transfer fluid is about 25%, the expansion tank should be sized accordingly.

Filter – A device that removes suspended solids from the heat transfer fluid. It can be designed for the full fluid flow or as a slip stream filter. Filters can be incorporated with or without their own pumps.

Flow meter – When we refer to the “flow meter” on any of our systems, we are speaking of the analog differential pressure gauge mounted on the heater’s instrument bridge. This device also has two independent switches which we use for minimum (50%) and low (95%) flow alarms. In most cases, the design flow rate (100%) is indicated by a differential pressure of 0.30 bar. The flow meters that we use have a range of zero to 0.6 bar differential.

Flow transmitter – A differential pressure device that measures the effective pressure drop across an orifice plate. The output is usually a 4-20 mA signal. Keep in mind that the signal is non-linear and must be “square rooted” to be used properly.

Fuel train – A series of manual and automatic valves, strainers, pressure gauges, pressure regulators, and sometimes temperature switches that safely deliver the fuel to the burner. Fuel trains are regulated by a number of approval agencies and are supplied with gas-type and fuel-oil-type burners.

Fuel/air ratio – The proportion of fuel and combustion air. If a flame is rich, it has too little air. If it is lean, it has too much air. This ratio is more commonly expressed as excess air. All burners should operate with some excess air; however, burners that safely operate with less excess air are more efficient.

Fuel – Any carbon-based gas or liquid that combines with oxygen and an ignition source to supply heat.

Gas & Dirt Separator – The vessel that we use to vent gases to the expansion tank. It is sometimes called a de-aerator. It also acts as the communication vessel between the system and the expansion tank to allow thermal expansion and contraction of the fluid. Since it is constructed like a cyclone, it is designed to trap debris. Therefore, a drain valve is fitted to the bottom for periodic cleaning.

Heat balance – A system is considered “balanced” when heat consumption matches heat output. A detailed heat balance is sometimes used to determine heater output and piping distribution networks.

Heat flux density – The amount of heat in relation to the heating surface area over time. The units are Btu/sq.ft./hr. Heaters with high heat flux densities have smaller heating surface areas and are generally harder on the fluid.

Heater – For our purposes, the heater is the heat exchanger that transfers heat from the burner into the fluid. The terms heater and burner should not be used interchangeably.

Insulation – Any material that reduces heat loss from a hot surface. Our heaters are externally insulated so that skin temperatures are less than 150°F. Hot pipes should also be insulated for personnel protection and to increase efficiency.

Level switch– A float type switch typically located about 6” from the bottom of the expansion tank. A system is considered properly filled when there is just enough oil in the system at ambient temperatures to float (make) this switch.

MAWP – Maximum Allowable Working Pressure. A designation by ASME that determines the maximum pressure with which a heater can be safely operated. Most of the TFS heaters are designed for 150 psi. Other MAWP’s are available upon request.

Mod Motor – Burner’s Modulation Motor. The motor receives a 4-20 MA signal from the main temperature controller and converts this to a mechanical motion. This motion repositions the burner’s combustion air damper and fuel supply values to either increase or decrease the burner’s firing rate as required by the system loading.

Oxidation – The degradation of the heat transfer fluid caused by exposure to the atmosphere (oxygen) at elevated temperatures. Oxidation can be drastically reduced in an open system by the proper design of a blocking vessel and in a closed system by an inert gas blanket (typically nitrogen).

Pigtail assembly – Our designation for the siphon tube, gauge valve, and pressure gauges that we use around pumps and throughout the system where pressure measurements are wanted. These unique assemblies use left and right-hand straight threads so that gauge handles and gauge faces can point in any direction and still be leak-tight.

Pressure drop – Refers to the energy used to move a fluid through a piping network, heater, or heat consumer. It can be expressed in terms of feet, psi, or inches of water.

Primary pump – The main responsibility is to produce the required flow through the heater. It is also employed to provide flow to one or more heat consumers.

Pump head (TDH) – Total Dynamic Head is a term associated with a pump’s ability to provide enough energy to overcome all equipment and piping losses (see pressure drop).

RTD – An RTD (resistance temperature device) or Pt-100 is typically used to measure process temperatures up to 900°F. They use the resistance change of platinum as temperatures vary. The designation Pt-100 indicates a platinum-type temperature probe that measures 100 ohms at 0°C. RTDs are not to be confused with thermocouples (see thermocouple definition), although they are often referred to as thermocouples. RTDs are used almost exclusively on systems designed and supplied by Thermal Fluid Systems, Inc.

Refractory – A material designed to withstand high heat. It is used to protect surfaces from heat damage. In TFS heaters refractory is used in the heater lid (where the burner is mounted) and at the back (bottom) of the heater where the burner flame is directed.

Secondary pump – Responsible for producing the required flow to one or more heat consumers. Secondary pumps are needed when heat consumers require different delta T’s or operating temperatures than would be possible from the primary pump. They are also used when system pressure drops would exceed the capability of the primary pump.

Suction head (NPSH) – Net Positive Suction Head is the pressure required at the suction side of the pump. For primary pumps, this pressure is typically supplied as static pressure by the expansion tank.

Thermocouple – Thermocouples are a type of temperature measuring device that uses the voltage change, measured in mV, caused by dissimilar metals as temperatures vary. There are several types of thermocouples depending on the temperature ranges they are expected to measure. Thermocouples require special wire specific to the thermocouple type including special terminals so as not to corrupt the measured signal from additional dissimilar metal contact. Polarity must also be considered when wiring thermocouples.

Three-way valve – Commonly used to control temperature of a heat consumer. It allows full flow to the user when there is a call for heat and gradually bypasses flow through the bypass port as its temperature approaches the set point. These valves are linear so when the valve is half open the flow is divided equally between the user and the bypass port. If properly balanced, the primary loop will not be affected by flow changes at a heat consumer.

Throttling (pump discharge) – Sometimes required to aid in venting air and vapors and to stop pump cavitation. This is accomplished by closing the discharge valve until the cavitation stops and the discharge pressure stabilizes.

Turndown – A term associated with a burner’s ability to operate below its maximum firing rate. For example, if a burner’s rated capacity is 12,000,000 Btu/hr and it has a 3:1 turndown, it can be expected to operate in its modulation range down to a firing rate of 4,000,000 Btu/hr. Loads below that will cause the burner to operate in an on/off mode. High turndown burners should be used when the actual process load is low compared with the thermal mass of the equipment to be heated or when multiple heat consumers are connected.

Two-way valve – Used to control the temperature of a heat consumer by allowing flow when there is a call for heat and no flow when the temperature is satisfied. Two-way valves are sometimes used when more heat consumption is connected than the heat source can supply. If this is the case, an additional two-way valve is required to bypass flow back to the primary loop so as not to adversely affect flow through the heater.