Heat Exchanger: Glossary of Terms and Definitions

We are “Teplo-Polis,” specialists in heat exchange, and we are pleased to present to you our new guide: “Heat Exchanger: Glossary of Terms and Definitions.” In this manual, we explain the basic concepts and terms in the field of heat exchange in simple and understandable language.

Recognizing the complexity of mastering specialized terminology, we have developed this glossary as an intuitively understandable tool for end-users.

Heat exchanger: a device for transferring thermal energy from one medium to another. According to design features, heat exchangers are divided into shell-and-tube and plate heat exchangers.

Key elements of a tubular heat exchanger: tubes and tube bundle, tube sheet, shell, cover, tube bundle gaskets, etc.

• Tubes: pipelines through which substances pass in the heat exchanger. They can be made of various materials to enhance heat transfer efficiency while minimizing corrosion.
• Tube sheet: a plate that supports the positioning of tubes in the heat exchanger. It can be fixed, floating, or stationary.
• Shell: an element that serves as a protective casing for each heat exchanger.
• Cover: a cap that is attached to the end of the heat exchanger, especially in bonnet assemblies.
• Tube bundle gasket: located between two surfaces of the heat exchanger, plays an important role in preventing fluid leaks, maintaining system integrity.

Air cooler: Air coolers use ambient air to cool liquids used in processes such as lubrication. They are also known as “finned coolers,” representing a form of heat exchanger with increased heat exchange surface.

Heat exchanger: A device that transfers thermal energy from one medium to another.

Key elements of a plate heat exchanger: heat exchanger frame (fixed plate, movable plate, upper and lower guides), heat transfer plates, rubber seals (gaskets), tie rods, etc.

• Frame of a plate heat exchanger: consists of a movable and fixed plate, upper and lower guides, and a rear post.
•  Heat transfer plates: flat corrugated stainless steel sheets of various sizes through which the heat exchange process occurs without mixing the fluids.
•  Rubber seals: ensure the tightness of the heat exchanger and guide the movement of fluids (without mixing) inside the heat exchanger through their channels.
• Tie rods: tighten the plate bundle of the heat exchanger.

Working pressure: denotes the standard pressure at which the heat exchanger operates during normal operation.

Atmospheric air: The term denotes the air saturating the surrounding environment.

Ambient parameters: Characteristics such as temperature, pressure, humidity, and the presence of suspended particles specific to a given environment.

Axial fans: Used to move gas streams (air) using an electric motor and a rotating blade shaft.

Bar: A metric unit of pressure measurement.

Condensers: Condensers cool gaseous substances to their dew point and transform them into liquids.

Hot water storage tank (HWST): A vessel for storing hot water used to balance daily water consumption in heating systems and create a reserve of replenishment water. In industrial settings, it is installed when the ratio of hot water supply thermal load to heating is less than 0.2. Tanks can be top and bottom, open (without pressure, safer) and closed (maintaining pressure). They differ in operating mode: variable temperature and constant volume or constant temperature and variable volume. They can function as accumulators or capacity water heaters.

Water heater: A device for heating water using steam, hot water, or other heat carriers. There are storage and tankless types. They are used for hot water supply, heating, heating feed water for boilers, and other purposes. Typically, these are surface water heaters that transfer heat through a heating surface, and less commonly, contact heaters where water comes into direct contact with steam or hot gases.

Installation dimensions: Include height, width, and depth with insulation, cladding, and structural support elements, excluding protruding components such as instruments and pipes.

Boiler boundaries: Defined by shut-off devices such as feed, safety, drain valves, and valves that separate the internal parts of the boiler from attached pipelines. Without shut-off devices, the boundaries are the first flanged or welded connections from the boiler.

Test pressure: Excess pressure used during hydraulic testing of thermal installations and networks to check their strength and tightness.

Allowed pressure: The maximum excess pressure determined after technical evaluation or control calculation for strength.

Working pressure: The maximum excess pressure at the inlet of the thermal installation or its element, calculated taking into account the working pressure of pipelines and their resistance, as well as hydrostatic pressure.

Closed heating system: A water system that uses water only as a heat carrier without consuming it from the network. Hot water is heated in heat exchangers to the required temperature. Heat exchangers are located in central or individual heating substations. The system operates in a closed loop: water, after giving off heat, returns to the source for reheating. The heat source is usually a CHP plant, where water is heated and then distributed through the heating networks. The supply of heat transfer fluid is regulated to compensate for leaks. Temperature control provides heat supply according to needs, with additional boilers used at maximum loads. The system allows separate regulation of heat supply for heating and hot water, optimizing expenses and ensuring high-quality hot water due to the proximity of heat exchangers to consumers. The main drawback is the complexity of management due to the fragmentation of heating substations.

Individual heating substation: A heating substation is an automated complex of equipment for preparing a heat transfer fluid, designed in a compact form and assembled in factory conditions using components from leading manufacturers. It is intended for connecting heating systems of a single building or its part. It is often located in basement premises. To increase reliability and serviceability, it should be placed on the first floor of the building with natural lighting. Building heating systems connect individual heating substations to heating networks using mixing units such as elevators or mixing pumps, which should be noiseless, or through surface heat exchangers. At all connection points, the higher temperature of the heat transfer fluid coming from the heat sources of the heating system is reduced to the required value. Hot water supply systems are connected via water heaters according to a scheme determined based on the ratio of heat consumption for hot water supply to the consumption for building heating and the presence of accumulator tanks.

Source of thermal energy (heat): A heat-generating energy installation or combination thereof, where the heat transfer fluid is heated by transferring heat from burned fuel, as well as by electric heating or other, including non-traditional, methods, participating in supplying heat to consumers.

Preservation: A set of actions aimed at protecting thermal energy installations and networks during their temporary shutdown or long-term storage from corrosion and other external influences, according to technical documents.

Water-heating boiler: A device where fuel is burned to heat water under pressure, which is then used as a heat transfer medium outside the boiler.

Steam boiler: An apparatus where fuel combustion leads to the generation of steam under pressure, used externally.

Boiler economizer: Equipment for heating a heat transfer fluid using exhaust gases from other devices.

Boiler room: A complex of interconnected thermal installations in specialized buildings or premises, including boilers and water heaters for heat production.

Open water heating system: A system where network water is used for hot water supply to consumers.

Energy efficiency indicator: A value reflecting the efficiency of energy resource utilization according to state standards, important for assessing and improving energy conservation.

Safety valves: Devices for protecting boilers and pipelines from pressure differentials, automatically regulating the discharge of excess medium.

Network water: Water prepared for use in heating systems, purified from various types of impurities.

Heat consumption system: The aggregate of thermal installations and networks to meet heat load requirements.

Heat supply system: An integrated network of heat sources and consumers to meet heat needs.

Stationary boiler: A boiler installed on a permanent basis.

District heating network: A structure for the production and distribution of thermal energy, including various sections from production to consumption metering.

District heating networks ensure efficient distribution of thermal energy, resource utilization optimization, and control over heat consumption.

Thermal energy installation: An energy installation designed for the production or transformation, transmission, storage, distribution, or consumption of thermal energy and heat carrier. Thermal installations can be classified as follows:

1.     Heat-generating energy installations:

• Auxiliary equipment for boiler installations (smoke extractors, pumps, fans, deaerators, feed tanks, condensate tanks, separators, etc.)
• Pipelines and fittings
• Steam and water heating boiler installations
• Heat pumps
• Heat generators
• Non-traditional heat-generating energy installations

2.     Accumulator tanks
3.     Heat-consuming energy installations:

• Heat substations
• Heating, ventilation, air conditioning, and hot water supply systems
• Units for air heating, ventilation, and conditioning systems
• Hot water supply systems

4.     Technological energy installations:

• Heat exchange apparatus
• Drying installations
• Evaporation installations
• Rectification installations
• Installations for thermal and moisture treatment of reinforced concrete products
• Steam hammers
• Steam pumps

5. Condensate collection and return systems.

Heat pump: a device that transfers heat from a low-temperature heat source (such as air, ground, or water) to a higher temperature level for heating purposes. Thermodynamically, a heat pump is similar to a refrigeration machine. However, while the main purpose of a refrigeration machine is to produce cold by extracting heat from a volume through the evaporator, and the condenser releases heat to the surroundings, the situation is reversed in a heat pump. The condenser is a heat exchanger that releases heat to the consumer, while the evaporator is a heat exchanger that utilizes low-grade heat: secondary energy resources and/or non-traditional renewable energy sources.

Heat substation: A complex of devices located in a separate room, consisting of elements of thermal energy installations that provide the connection of these installations to the district heating network, their operability, control over heat consumption modes, transformation, and regulation of the parameters of the heat carrier. The main tasks of a heat substation include:

• Transformation of the type and parameters of the heat carrier.
• Control and regulation of the parameters of the heat carrier.
• Distribution of the heat carrier to heat consumption systems.
• Disconnection of heat consumption systems.
• Filling and replenishment of heat consumption systems.
• Protection of local heat consumption systems from emergency increases in the parameters of the heat carrier.
• Accounting for heat carrier and heat consumption expenditures.

Types of heat substations: heat substations differ in the number and type of connected heat consumption systems, the individual characteristics of which determine the thermal scheme and characteristics of the substation equipment, as well as the type of installation and features of equipment placement in the substation room. The following types of heat substations are distinguished:

• Central heat substation (CHS). Used to serve a group of consumers (buildings, industrial facilities). It is often located in a standalone structure but can be placed in the basement or technical room of one of the buildings.
• Individual heat substation (IHS). Used to serve a single consumer (building or its part). Typically located in the basement or technical room of the building, but due to the characteristics of the serviced building, it may be placed in a standalone structure.
• Block heat substation (BHS), also known as a modular block. Manufactured in factory conditions and supplied for installation as ready-made blocks. It can consist of one or several blocks. The equipment of the blocks is mounted very compactly, usually on one frame. It is typically used when space-saving is necessary, in confined conditions. Depending on the nature and number of connected consumers, BHS can be classified as either IHS or CHS.

Heat sources and thermal energy transport systems: Heat-generating enterprises such as boiler houses and thermal power plants serve as heat sources, connecting to heat-consuming installations (HCIs) via district heating networks. These networks are divided into primary trunk lines, connecting HCIs to heat-generating enterprises, and secondary lines, which connect HCIs to end consumers. The section of the district heating network directly connecting HCIs and primary heat networks is called a heat input.

Primary networks: can reach lengths of over 10 km, using steel pipes up to 1400 mm, and sometimes interconnected into a single network to enhance reliability.

Secondary networks: are typically shorter (up to 500 meters) and may use both steel and polymer pipes to reduce corrosion.

Water supply networks serve as the source of water for both cold and hot water supply systems.

Hot water supply system (HWSS): provides consumers with hot water and can be of closed or open type. Sometimes used for additional heating of premises in residential buildings.

Heating system: ensures the maintenance of the required temperature in premises, with various connection schemes to heat sources.

Ventilation system: aimed at heating the outdoor air to create optimal indoor air conditions, may also be integrated with heating systems.

Cold water supply system: does not utilize thermal energy but is important for maintaining pressure in the water supply of multi-story buildings.

Heat-generating energy installation (HGEI): produces thermal energy for various needs.

Building thermal insulation: characteristics of structures that limit heat exchange between the interior and exterior spaces of a building.

Heat-consuming energy installation (HCEI): utilizes heat and heat carriers for heating, ventilation, air conditioning, hot water supply, and technological processes.

Central Heating Plant (CHP): a node connecting local heating systems to urban networks, managing heating, ventilation, and water supply systems in buildings.

Heat Carrier of a Heat Power Plant: a medium that carries heat in heat power plants.

Thermodynamic Cycle of a Heat Power Plant: a sequence of processes returning the working substance to its initial state after a cycle of plant operation.

Direct Thermodynamic Cycle of a Heat Power Plant: a thermodynamic cycle of a heat power plant in which a portion of the heat supplied to the working substance is converted into useful work.

Reverse Thermodynamic Cycle of a Heat Power Plant: a thermodynamic cycle of a heat power plant in which heat is transferred from a less heated body to a more heated one at the expense of work done.

Thermoelectric Generator: a device for direct conversion of heat into electrical energy using thermoelectric phenomena.

Magnetohydrodynamic Generator (MHD Generator): a device in which the energy of an electrically conducting fluid moving in a magnetic field is directly converted into electrical energy.

Thermal Power Plant (TPP): a plant designed to convert heat into mechanical or electrical energy using a direct thermodynamic cycle.

Steam Turbine Plant: a plant designed to convert steam energy into mechanical energy, including a steam turbine and auxiliary equipment.

Combined Cycle Gas Turbine Plant (CCGT Plant): a plant designed for simultaneous conversion of energy from two working fluids – steam and gas, into mechanical energy.

Steam Turbine Power Station: a thermal power station with steam turbine plants.

Condensing Power Station (CPS): a steam turbine power station designed for electricity generation.

Combined Heat and Power Plant (CHP Plant): a type of condensing power station with the ability to extract heat energy from steam after it is used to generate electricity. The distinctive feature of CHP plants is the use of steam turbines, which allow for the regulation of the amount of steam extracted. CHP plants can operate on two schedules: thermal, where electrical load depends on thermal load, and electrical, where electrical load is independent of thermal load, especially in summer. Cogeneration in CHP plants increases the overall efficiency up to 80% (compared to 30% for CPS), although this does not always indicate high cost-effectiveness. The efficiency of CHP plants also depends on the proximity to heat consumers, as long-distance heat transfer is economically impractical.

According to the connection of boilers and turbines: CHP plants can be either block-type, where boilers and turbines are connected in pairs, usually with an electrical power of 100–300 MW, or non-block type with cross-connections, allowing steam from any boiler to be directed to any turbine. This requires the installation of large steam pipelines and uniform parameters for all equipment.

According to the type of steam-generating installations: CHP plants can have steam boilers, combined-cycle gas turbine and gas turbine installations, as well as nuclear reactors. These installations can use various types of fuel, such as coal, fuel oil, gas.

Features: CHP plants are often built and modernized over many years, leading to the emergence of stations with a variety of equipment.

Gas Turbine Power Station (GTPS): a thermal power station with gas turbine installations.

Air-Accumulating Gas Turbine Power Station: a thermal power station with air-accumulating gas turbine units.

Combined Cycle Gas and Steam Power Station (CCGT Power Station): a thermal power station with combined-cycle gas turbine units.

Magnetohydrodynamic Power Plant (MHD Power Plant): a plant designed to produce electrical energy, with the main component being a magnetohydrodynamic generator.

Solar Power Station (Solar Power Plant): a power station designed to produce electrical energy by converting solar radiation into heat.

Geothermal Power Station: a power station designed to convert the Earth’s deep heat into electrical energy.

Heat Supply Station: a complex of installations designed to produce heat for heating purposes.

Heat Recovery Boiler Plant: a plant with a stationary recovery boiler.

Water Heating System: a heating system where water is the heat carrier.

Steam Heating System: a heating system where steam is the heat carrier.

Heat Balance: a quantitative characteristic of heat production, consumption, and losses.

For any type of boiler, the heat balance equation holds true:

Qin = Q1 + Q2 + Q3 + Q4 + Q5 + Q6

where Qin – heat input to the boiler unit along with the fuel; Q1 – useful heat used for heating or hot water production; Q2 – heat loss with flue gases leaving the boiler; Q3 – heat loss due to chemical incompleteness of fuel combustion; Q4 – heat loss due to mechanical incompleteness of fuel combustion; Q5 – heat loss due to dissipation into the surrounding environment; Q6 – heat loss with slag removed from the boiler furnace.

Heat Balances of Heat Exchange Equipment: heat calculation starts with determining the heat load of the apparatus and the flow rate of the heating or cooling heat carrier. Heat load is the amount of heat transferred from the hot heat carrier to the cold one.

Obviously: Q = Qhot = Qcold

Qгор=Gгор*С*(t1+t2),where Gгор-​ is the flow rate of the hot heat transfer fluid, kg/s;  is the average specific heat capacity of the hot heat transfer fluid, J/(kg °C); (for gas, c=cp​); t1 and t2 are the initial and final temperatures of the hot heat transfer fluid, °C.

Heat Load of the District Heating System: the total amount of heat received from heat sources, equal to the sum of heat requirements of heat receivers and losses in heat networks per unit of time.

Heat Load Profile of the District Heating System: the variation over time of the heat load of the district heating system.

Specific Fuel Consumption for Electricity Generation: the amount of fuel consumed per unit of electricity generated.

Specific Fuel Consumption for Heat Generation: the amount of fuel consumed per unit of heat generated.

Thermal Efficiency Coefficient: the ratio of the thermal power of turbine extractions to the maximum power of heat sources.

Counterflow Configuration: a scenario in which the primary heat transfer fluid moves in the direction opposite to the movement of the cooling or heating medium, which maximizes heat exchange efficiency and reduces the temperature of the outlet flow.

Crossflow Installation: the organization of heat exchange in which primary and secondary heat transfer fluids intersect at right angles, providing optimal conditions for heat transfer, applicable, for example, in plate heat exchangers.

Structural Pressure: often referred to as the maximum allowable working pressure, plays a key role in determining the structural parameters of heat exchangers, ensuring their stability against maximum pressures during operation.

Dew Point: determines atmospheric conditions at which gas transitions into a liquid state, depending on pressure and other factors of the surrounding environment.

Economizer: a type of heat exchanger that optimizes energy usage by recovering heat from exhaust gases, for example, from boilers, for preheating processes in the system.

Enhanced Fins: developed using complex surface geometries to increase the contact area between mediums, thereby increasing the rate of heat transfer, which is critically important when working with gaseous substances due to their comparatively low thermal conductivity compared to liquids.

Ribbed Tubes: Also known as “fins” or “extended surfaces,” ribbed tubes increase the surface area on the heat transfer side participating in the heat exchange process. They are most commonly used when gas is present.

Air Coolers, or “Fan Coolers”: represent a specific design of heat exchangers that use ambient air to dissipate heat from the system.

Flue Gases: Gases discharged into the atmosphere through a chimney (combustion product), which is a common occurrence in boilers and large power stations.

Fouling: characterized by the accumulation of undesirable deposits inside the heat exchanger, resulting from sedimentation, scaling, fouling by process fluids, or even biological growth, which can reduce operational efficiency.

Gas Coolers: remove excess heat from a gas stream, for example, cooling CO2 in a refrigeration system. Gas-liquid heat exchangers, or “Condensers,” specialize in transferring heat from gases to liquid mediums, crucial in condensation processes.

Heat Transfer Rate: measures the amount of heat transferred per unit of time, for example, joules per second. Important for assessing and optimizing heat exchanger performance.

Modular Design: The concept of constructing equipment from a standard set of basic blocks. A heat exchanger design in which elements (modules) can be easily removed. This facilitates servicing and repairing the heat exchanger. For example, steam air heaters are well-suited for modular design.

OFAF: Oil Forced Air Forced, air-cooled. OFAF coolers use forced air and oil movement to enhance heat dissipation in oil-based transformers.

OFWF: Oil Forced Water Forced, water-cooled. OFWF coolers use forced air and water movement to enhance heat dissipation in oil-based transformers.

Pass Configuration in Heat Exchangers (single-pass, double-pass, four-pass): indicates the number of times the fluid passes through the tube bundle, affecting heat transfer efficiency and fluid dynamics.

Parallel Flow Distribution: where the primary medium moves in the same direction as the cooling or heating medium, exiting the tubes at one end, typically used in high temperature differences between the mediums.

Heater: Raises the temperature of gas or liquid before it is fed into another process, optimizing operational efficiency and energy utilization.

Process Stream: Describes all substances flowing through process equipment, which can be liquid or gas.

Temperature Range: The temperature difference of a liquid (or gas) as it passes through a heat exchanger, crucial for performance analysis.

Reboilers: Heat exchangers within a rectification column designed to vaporize liquid at the column’s bottom.

Removable Bundle: When a tube bundle can be removed for maintenance or cleaning.

Shell and Tube Heat Exchanger Assembly: Involves a tube bundle within a shell, facilitating heat exchange between the fluid in the shell and the fluid in the tubes.

Shell Assembly: The assembly in which the tube bundle is housed in a shell and tube heat exchanger.

Shell-side: Refers to the part of a shell and tube heat exchanger where the fluid flows over the tubes (as opposed to the tube-side, where the fluid flows inside the tubes).

Single Tube Heat Exchanger: Contains a single tube within the structure, rather than multiple tubes, applicable in various cooling and heating applications, including air coolers, air heaters, CACA coolers, CACW coolers, or steam air heaters.

U-Tube Heat Exchangers: Named for their U-shaped tube configuration, popular in the chemical industry but with limited applications, especially in the presence of fouling.

Test Pressure: A test checking for leaks that may occur at the joints of a heat exchanger, above both the working and design pressures.

Thermosyphon: A high thermal conductivity device consisting of sealed tubes containing refrigerants, allowing heat transfer without the need for pumps and fans.

Transformers Water Coolers: A type of shell and tube heat exchanger incorporating a double wall. They are used to control the temperature of transformers in high ambient temperature conditions.

If you have any further questions or need to clarify details regarding heat exchange devices, our team at “Teplo-Polis” is always ready to provide professional support and consultations. We are focused on providing customized solutions tailored to the needs of each client, and we guarantee the high quality of our products and services.

We offer a wide range of heat exchangers, including standard and custom-made models, capable of meeting diverse heat transfer requirements. Whether you need a heat exchanger for industrial applications, heating, ventilation, and air conditioning systems, or specialized processes, our specialists will help you find the optimal solution.

In addition to manufacturing and supplying heat exchangers, we also offer maintenance and repair services, ensuring the long-term operability and efficiency of your equipment.

For more information, technical consultations, or discussing your specific requirements, contact “Teplo-Polis”. You can reach us by phone or fill out the feedback form on our website. Our team of experts will be happy to assist you in choosing the perfect solution for your heat exchange needs.