Fluid Heat Transfer Systems

Fluid heat transfer systems circulate thermal fluid through process equipment to maintain an even, consistent temperature profile. They consist of tanks, pipes, pumps, and heating and/or cooling sources. Heating sources for fluid heat transfer systems use electricity, natural gas, propane, fuel oil, and solar power. Cooling sources use air and water. Important specifications include operating temperature, media flow rate, discharge pressure, heater capacity and expansion tank capacity. Media flow rate is the required flow capacity of the pump. Heater capacity, the ability of a device to add heat to the process fluid, is typically measured in kilowatts (kW) or British thermal units per hour (BTU/hr). Some fluid heat transfer systems use national pipe thread (NPT) connectors. Others use 150 lb. or 300 lb. flanges.

Fluid heat transfer systems circulate water, steam, hydrocarbon oils, and glycols. Water is nontoxic and inexpensive, but has a relatively low boiling point and a high freezing point. Water is easy to pump but can become corrosive if its pH levels are not maintained properly. Steam, another medium, is pressurized water vapor. Hydrocarbon oils have a higher viscosity and lower specific heat than water, but require more energy to pump. They are relatively inexpensive and have a low freezing point. Examples include synthetic hydrocarbons, paraffin hydrocarbons, and aromatic refined mineral oils. Ethylene and propylene glycols are highly toxic anti-freeze fluids that deteriorate at high temperatures. They are designed for use in double-walled, closed loop systems and require frequent monitoring to determine whether adjustments or replacements are needed. 

Fluid heat transfer systems are often housed in enclosures that are rated for specific environments. The National Electrical Manufacturers Association (NEMA), a non-profit trade organization, rates enclosures for many types of electrical equipment. Both NEMA 4 and NEMA 12 enclosures are suitable for either indoor or outdoor use. NEMA 4 enclosures can withstand falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water. NEMA 12 enclosures can withstand falling dirt, circulating dust, lint, fibers, and dripping or splashing liquids. NEMA 7 enclosures are only suitable for indoor use, but in hazardous locations classified as Class I, Division 1, Groups A, B, C, or D by the National Fire Protection Association (NFPA). Class I, Division 1 locations are areas in which volatile flammable liquids or flammable gases are handled, processed or used in potentially explosive amounts during normal operations. Class I, Division 2 locations are areas in which these same materials are used, but confined in secure containers or closed systems. Type Z-purge systems are enclosures that allow fluid heat transfers to be used safely in Class 1, Div 2 environments. Type X-purge systems are rated for Class 1, Div 1 environments. 

Fluid heat transfer systems vary in terms of features. Some devices have local control panels with gauges for monitoring temperature and pressure. Others feature remote control panels with digital readouts. Fluid heat transfer systems with emergency alarms alert operators to events such as high temperatures or low coolants levels. Devices that are approved by the American Society of Mechanical Engineers (ASME) comply with that organization’s Boiler and Pressure Vessel Code. Additional features for fluid heat transfer systems include insulated pipes and casters, small wheels fastened to supporting legs to facilitate movement. Skid-mounted fluid heat transfer systems are also available.

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