Heat exchangers: 50 technical questions and answers
Technical answers to the most frequently asked questions about heat exchangers: from fundamentals and type selection through to specific applications such as SCR systems, pyrolysis plants, paint booths and melamine plants.
Heat exchangers are present in virtually every thermal industrial process. The diversity of types, fluids, operating conditions and regulatory requirements generates a high volume of technical questions. This guide gathers the 50 most frequently asked questions, with a direct answer and a detailed technical explanation for each one.
A — Fundamentals
Basic heat transfer concepts and essential terminology.
What is a heat exchanger and what is it used for?
A heat exchanger is a device that transfers thermal energy between two fluids, gases or solids without mixing them, by exploiting a temperature difference between them.
Industrial applications range from recovering residual heat in combustion gases to cooling process fluids, pasteurisation, distillation, drying, cooling of motors and compressors, or temperature control in chemical reactors.
How does a heat exchanger work?
The two fluids circulate through circuits separated by a conductive wall. Heat flows from the hot fluid to the cold one by convection and conduction, until the thermal equilibrium defined by the design conditions is reached.
The transfer mechanism combines three phenomena: convection from the hot fluid to the wall, conduction through the wall material, and convection from the wall to the cold fluid. The total resistance to heat flow is the sum of these three series resistances, plus fouling resistances on each side.
What is the difference between a heat exchanger and a heat recuperator?
The term heat recuperator is a subset of the term heat exchanger: every recuperator is an exchanger, but not every exchanger is a recuperator.
In industrial contexts, the term heat recuperator is used specifically for exchangers that exploit residual heat from a process — usually hot exhaust gases — to preheat another fluid. Boiler economisers, air preheaters and combustion gas heat exchangers fall into this category.
What materials are commonly used in the construction of heat exchangers?
The most common materials are carbon steel, austenitic stainless steel (304, 316L), aluminium, copper, titanium and cupro-nickel, selected according to the temperature, pressure and chemical aggressiveness of the fluids.
Carbon steel is the standard solution for non-corrosive fluids at moderate temperatures. Stainless steel 316L is used in the presence of chlorides, dilute acids or food-grade fluids. Titanium offers maximum corrosion resistance in marine environments and with oxidising acids. The final material selection must consider chemical resistance, galvanic compatibility, maximum allowable temperature and applicable regulatory requirements.
What is the difference between a direct-contact and an indirect-contact heat exchanger?
In direct contact, the two fluids physically mix (cooling towers, mixing condensers). In indirect contact, a physical wall separates them and mixing is impossible.
Direct contact allows very high transfer coefficients but generates cross-contamination between fluids. For this reason it is only applicable when mixing is acceptable or desirable. In the vast majority of industrial processes, indirect-contact heat exchangers with a metal separating wall are used.
What is the overall heat transfer coefficient (U)?
The coefficient U expresses the amount of heat transferred per unit surface area, per unit time and per degree of temperature difference between the fluids. It is expressed in W/(m²·K).
The value of U synthesises the series resistances of the entire system: hot-fluid convection, wall conductivity, cold-fluid convection and fouling resistances. Typical U values vary enormously: from 5–20 W/(m²·K) in gas-gas exchangers, to 1,000–6,000 W/(m²·K) in steam condensers with water cooling.
What is the pinch point in a heat exchanger?
The pinch point is the minimum temperature difference between the two fluids at any point in the heat exchanger. It determines the required heat transfer surface area and the maximum theoretically achievable thermal recovery.
A small pinch point implies high thermal recovery but requires a very large heat transfer surface and therefore a larger, more expensive unit. A large pinch point allows a more compact unit but with lower energy efficiency. Optimisation is an exercise in balancing the investment in the equipment against the value of the recovered energy.
What is the fouling factor and how does it affect design?
The fouling factor is an additional thermal resistance included in the design to account for the reduction in efficiency caused by the build-up of deposits on the heat transfer surfaces over time.
Limescale deposits, biological fouling, ash or organic residues act as thermal insulators on the heat exchanger surface. The fouling factor forces the designer to oversize the heat transfer surface to guarantee the required thermal duty throughout the useful life of the equipment. Typical values are standardised in TEMA and EN 13445.
B — Types and configurations
Constructive families and criteria for choosing between them.
What are the main types of heat exchangers?
The two main families are tube-type heat exchangers (plain tubes, continuous or helical finned tubes, shell-and-tube, double-pipe coaxial) and plate-type heat exchangers (pillow plate, cross-flow, brazed/welded plates, gasketed plate-and-frame).
The selection between families depends mainly on the fluid types, working pressure, the presence of particles or corrosive compounds, and maintenance and cleaning requirements.
What is the best heat exchanger for viscous or sediment-laden fluids?
For viscous, sticky or sediment-laden fluids, tube-type exchangers (especially shell-and-tube or double-pipe coaxial) and pillow plate exchangers offer the greatest tolerance, thanks to their wide passage surfaces and ease of cleaning.
Conventional gasketed plate-and-frame heat exchangers have very narrow channels (2–5 mm passage) that clog easily. The pillow plate stands out for its wide channels and smooth surfaces that facilitate CIP cleaning, essential in the food and pharmaceutical industries.
When is a helical finned tube heat exchanger preferable to a continuous fin exchanger?
Helical fins are the preferred choice when the gas contains particles, ash or sticky compounds, because the pitch between coil turns is adjustable and the geometry facilitates cleaning. Continuous fins offer greater compactness for clean gases.
In applications with combustion gases from biomass, diesel or exhaust gases containing particles, continuous fins easily clog in the inter-fin spaces. Helical fins allow a wider free passage adapted to the particle size distribution, and are more resistant to vibration induced by gas pulsations.
When is a pillow plate heat exchanger used?
The pillow plate heat exchanger is used in applications involving viscous, sticky or solid-laden fluids, and in heat transfer to granular solids, being an efficient alternative to conventional fluidised beds.
The cushion geometry of the pillow plate is created by inflating two sheets welded at the perimeter and at spot welds, producing heat transfer surfaces with wide and smooth channels. This makes it particularly suitable for the food, chemical and pharmaceutical industries, granular material drying and cooling, and applications requiring CIP or SIP cleaning.
What is the difference between a brazed-plate heat exchanger and a gasketed plate-and-frame exchanger?
Brazed plates form a rigid, joint-free assembly suitable for high pressures and temperatures, but impossible to dismantle for cleaning. Gasketed plate-and-frame exchangers can be dismantled, cleaned and extended, but tolerate lower pressure and temperature.
A brazed-plate heat exchanger can work at pressures up to 40 bar and temperatures up to 350 °C, but can only be cleaned by chemical circulation (CIP). Gasketed exchangers allow each plate to be individually removed for visual inspection, mechanical cleaning and replacement.
When is a shell-and-tube heat exchanger used?
The shell-and-tube heat exchanger is used when high pressures or temperatures are required, when the fluid is viscous or dirty, or when a robust, long-life unit is needed in demanding industrial conditions.
It is the most versatile and widely used type in the petrochemical industry, refineries, chemical industry and steam systems. Its construction allows independent shell-side and tube-side design pressures, material selection for each process side, and various pass configurations to optimise the transfer coefficient. The reference standard for design is TEMA.
What is the difference between parallel flow, counter-flow and cross-flow?
In parallel flow, both fluids move in the same direction; in counter-flow, in opposite directions; in cross-flow, perpendicular to each other. Counter-flow maximises heat transfer and is the thermally most efficient configuration.
In counter-flow configuration, the outlet temperature of the cold fluid can exceed the outlet temperature of the hot fluid — impossible in parallel flow. Cross-flow is typical for compact air-to-air exchangers (HVAC heat recovery, automotive radiators).
When is a cross-flow heat exchanger recommended for air heat recovery?
Cross-flow is the standard solution in ventilation and air conditioning systems where heat needs to be recovered between the extract and supply air streams, without mixing risk, in a compact unit that integrates directly into the air handling unit (AHU).
Cross-flow plate heat recovery units achieve sensible efficiency of 60–85%. In applications where the extract air may contain paint, grease or organic compounds — such as paint booths or industrial kitchens — the installation of upstream capture filters is critical.
What is the difference between a gas-gas, gas-liquid and liquid-liquid heat exchanger?
The designation indicates the pair of fluids exchanging heat. Each pair has very different heat transfer characteristics and requires specific constructive types.
Gas-gas exchangers have the lowest transfer coefficients. Gas-liquid exchangers also show an imbalance: the gas side is limiting, which is why it is finned. In liquid-liquid exchangers, both coefficients are typically high and similar, allowing very compact designs.
C — Selection and design
Process parameters, regulations and engineering criteria for correct selection.
What parameters are needed to size a heat exchanger?
The minimum parameters needed for thermal sizing are: the mass flow rates of both fluids, the inlet and outlet temperatures of each fluid, the working pressures, the physical properties of the fluids (density, specific heat, viscosity, conductivity) and any dimensional or maximum pressure drop constraints.
In addition to thermal parameters, a complete design also requires the chemical composition of the fluids, the presence of suspended particles, applicable regulatory requirements (PED, ATEX) and the environmental conditions of installation.
What heat transfer surface area do I need for my application?
The required heat transfer surface area A is calculated using Q = U · A · ΔTlm, where Q is the required thermal duty, U is the overall heat transfer coefficient and ΔTlm is the log mean temperature difference between the two fluids.
U depends on the exchanger type, fluid flow velocities, surface geometry and fouling factors. For gas-liquid exchangers with fins, typical U values range from 20 to 80 W/(m²·K). For liquid-liquid plate heat exchangers, U can reach 3,000–6,000 W/(m²·K).
Why are fins added to the tubes of a heat exchanger?
Fins extend the heat transfer surface on the gas side, compensating for its low convection coefficient compared to the liquid side. The objective is to balance the thermal resistances on both sides of the wall.
The specific heat capacity of air is approximately 1,214 kJ/(m³·K), while that of water is 4,186 kJ/(m³·K). By adding fins, the effective surface area on the gas side is increased by a factor of 5 to 20, balancing the resistances and fully exploiting the tube surface.
How does fluid viscosity affect heat exchanger design?
The higher the viscosity, the lower the Reynolds number and the lower the convection coefficient. Very viscous fluids require exchangers with wide channels, adapted flow velocities and, often, shell heating to reduce viscosity at start-up.
High viscosity favours the laminar flow regime, where fluid mixing is poor and heat transfer is significantly lower. The optimal design for viscous fluids is usually a shell-and-tube heat exchanger with high-cut-percentage baffles, or a plate heat exchanger with deep corrugation that induces turbulence even at low Reynolds numbers.
When is PED certification required for a heat exchanger?
The Pressure Equipment Directive 2014/68/EU applies to any heat exchanger with a maximum allowable pressure (PS) greater than 0.5 bar gauge.
A heat exchanger in which two fluids circulate constitutes essentially two pressure vessels in one unit. Each circuit must be classified independently according to the Annex II tables of the Directive. For Categories II, III and IV, the involvement of a Notified Body is mandatory.
When is ATEX certification required for a heat exchanger?
The ATEX Directive 2014/34/EU applies when the heat exchanger is installed in a zone classified as having explosion risk due to the presence of explosive atmospheres (flammable gases, vapours, mists or dusts).
The ATEX classification of a heat exchanger depends on the zone category (Zone 0, 1 or 2 for gases; Zone 20, 21 or 22 for dusts), the explosion group of the gas or dust present, and the temperature class. A heat exchanger can be an ignition source through its surface temperature (T-class) if it exceeds the auto-ignition temperature of the surrounding atmosphere.
What materials should be used for corrosive or acidic fluids?
Material selection for corrosive fluids depends on the specific acid or base, concentration, temperature and flow velocity. Common options range from stainless steel 316L through titanium, Hastelloy, Duplex to non-metallic materials (graphite, PTFE, polypropylene).
Hydrochloric acid attacks austenitic stainless steel by pitting corrosion and requires Hastelloy C-276, titanium or nickel alloys. For high-temperature corrosion in combustion gases containing SO₂ or HCl, the cold zones of the heat exchanger (below the acid dew point) require special materials or surface treatments.
How is the acid dew point temperature determined and why is it important in design?
The acid dew point is the temperature at which SO₃ or HCl present in combustion gases condense forming sulphuric or hydrochloric acid on metal surfaces. For combustion gases from sulphur-containing fuels, it typically lies between 120 and 150 °C.
Acid condensation on heat exchanger surfaces causes accelerated corrosion that can destroy the unit within months of operation. Therefore, the design of economisers and heat recuperators for combustion gases must ensure that the minimum wall temperature remains above the acid dew point under all operating conditions.
What heat exchanger is suitable for high-particle-content gases?
For particle-laden gases (fly ash, dust, soot, aerosols), heat exchangers with wide-pitch helical finned tubes, or multi-tube plain-tube designs, are the types offering the greatest resistance to blockage and the easiest cleaning.
The free passage between fins is the critical design parameter in particulate gas applications. Units for high-dust gases must include in-service cleaning systems: steam or air soot blowers, vibration cleaning or gas pulse cleaning.
D — Specific industrial applications
Thermal solutions in concrete processes and sectors, including SCR, pyrolysis, melamine and paint booths.
Is it possible to recover heat from the exhaust of a combustion engine or generator (Filtermist, CHP)?
Yes. The exhaust gases of a gas or diesel engine, the cooling water jacket and the lubrication oil all contain recoverable thermal energy. In combined heat and power (CHP) installations, recovery of this residual heat is the basis for calculating the overall system efficiency.
In a typical internal combustion engine, approximately 30–35% of fuel energy is converted into electricity, 25–30% is lost in exhaust gases (at 400–600 °C), 20–25% is dissipated by the water jacket, and 5–10% by the oil and radiation. In CHP systems, heat recovery exchangers can utilise up to 80–85% of the total fuel energy as useful heat.
What heat exchanger is used to cool engine and compressor oil?
Cooling of engine and compressor oil is typically carried out with compact shell-and-tube exchangers or with demountable gasketed plate-and-frame exchangers, using water or air as the secondary cooling fluid.
Typical oil temperature at the outlet of a screw compressor rotor is 80–100 °C and must be reduced to 40–60 °C before returning to the circuit. A key risk in these units is cross-contamination in the event of an internal leak: oil can contaminate the water circuit or water can contaminate the oil.
What heat recovery solution is suitable for a pyrolysis plant?
Pyrolysis plants generate hot gases rich in hydrocarbons, corrosive compounds and char particles. Heat exchangers for these gases must be of the plain-tube or very wide-pitch fin type, fabricated in materials resistant to acid corrosion and coke deposit formation.
In the pyrolysis of plastics, tyres or biomass, the gases contain hydrocarbon vapour, H₂S, HCl (in the case of PVC), char particles and tar aerosols. Tar condenses at 200–400 °C and adheres to surfaces. Common solutions include vertical plain-tube exchangers (where condensate drains by gravity) and Incoloy or high-alloy stainless steel materials.
How is a heat exchanger integrated into an SCR (Selective Catalytic Reduction) system?
In an SCR system, the heat exchanger is installed downstream of the catalytic reactor to recover thermal energy from the treated gases, or upstream to preheat the gases to the catalyst activation temperature (typically 280–420 °C for TiO₂-V₂O₅ catalysts).
Selective catalytic reduction (SCR) is the standard process for NOₓ removal from industrial combustion gases. When gases arrive at the SCR reactor below the required temperature, a preheating exchanger is installed upstream. When the exchanger operates between 250 and 420 °C in the presence of residual NH₃ (ammonia slip), the possible formation of ammonium bisulphate (ABS) on surfaces must be considered.
What heat exchanger is suitable for SCR (Selective Catalytic Reduction systems)?
A heat exchanger suitable for SCR systems must tolerate gases containing residual NH₃ or urea, temperatures between 200 and 550 °C, possible presence of SO₂ and catalytic particles, and must have wide-passage surfaces to prevent ammonium bisulphate deposit.
Typical technical specifications include: stainless steel 321 or Corten materials for temperatures up to 550 °C; wide-pitch helical fins (>8 mm pitch); design allowing in-service cleaning by steam or hot gas without dismantling the unit. Gas-side pressure drop is a critical parameter, as most SCR systems cannot tolerate additional pressure losses exceeding 100–300 Pa.
What thermal solution is applied in a melamine plant?
In melamine plants, heat exchangers are primarily used to cool the melamine gas (CO₂ and NH₃ at 350–450 °C) at the reactor outlet, to recover the melamine condensation heat, and for the cooling circuits of the purification sections.
Synthesis of melamine from urea generates high-temperature reaction gases rich in vaporised melamine, CO₂ and unreacted NH₃. Melamine sublimes at 354 °C and can deposit on surfaces if the wall temperature falls below the sublimation point. The standard heat exchangers for this application are shell-and-tube designs with large-diameter tubes and 316Ti or 321 stainless steel materials.
How is heat recovery managed in paint booths (paint booth heat recovery)?
In paint booths, heat recovery from the extract air is technically feasible when the extracted air has been correctly filtered to remove paint particles. The recommended type is a cross-flow aluminium or stainless steel plate heat exchanger, with upstream F7–F9 class capture filters.
The standard protocol includes: coarse capture filter (G4) at the air intake, cartridge filter (F7–F9) immediately upstream of the heat exchanger, epoxy-coated aluminium plate cross-flow exchanger, and filter inspection and replacement every 200–400 hours of booth operation. In large automotive paint booths, thermal recovery can reduce heating costs by 40–60% during cold periods.
What pre-filtration is required to protect a heat exchanger in a paint booth?
Protecting the heat exchanger in a paint booth requires at minimum a large-area dry filter of class F7 or higher (EN ISO 16890) installed immediately upstream of the heat exchanger.
Spray paint is extremely adhesive on the cold surfaces of the heat exchanger. Conventional booth capture filters collect coarse paint particles, but fine suspended particles (1–10 µm) easily pass through those filters and deposit on the exchanger fins.
What heat exchanger is used for cooling electrical transformers?
Oil-cooled electrical transformers are typically cooled with oil-to-air finned radiators or with oil-to-water heat exchangers for high-power transformers (ODWF, OFWF).
Power transformers use mineral oil or synthetic ester as the dielectric and heat transfer fluid. For high-power transformers (>100 MVA), oil-to-water forced-flow heat exchangers are used, where oil circulates inside the tubes and cooling water through the shell.
What heat exchanger is suitable for hygienically demanding applications (pharmaceutical, food industry)?
In pharmaceutical and food applications, heat exchangers must meet hygienic design criteria: smooth surfaces without dead corners, finishes Sa 2.5 or Ra ≤ 0.8 µm, materials certified for food contact (AISI 316L, 304), FDA-grade silicone or PTFE gaskets, and compatibility with CIP and SIP.
Reference standards for hygienic design include EHEDG and the 3A Sanitary Standards guidelines. Plate exchangers (pillow plate, demountable plates with FDA gaskets) and double-wall concentric tube exchangers (allowing leak detection through the intermediate space) are the preferred types.
E — Energy efficiency and sustainability
Benefit quantification and economic criteria for heat recovery.
How much fuel can be saved by installing an economiser on a boiler?
As a practical rule of thumb, for every 6 °C rise in feedwater temperature, boiler fuel consumption decreases by approximately 1%. An economiser that raises the temperature by 60 °C can represent savings of 8–10% of annual fuel cost.
The exact saving depends on the initial exhaust gas temperature, the fuel used, the feedwater temperature and the acid dew point that determines the minimum gas cooling limit. On natural gas boilers with exhaust gases at 250 °C and feedwater at 60 °C, a well-designed economiser can recover 4–7% of fuel energy.
What is the typical return on investment for an industrial heat recovery heat exchanger?
In continuously operated installations (>4,000 h/year) with recovered thermal duties of hundreds of kW to MW, the return on investment typically falls between 1 and 3 years, depending on energy cost, recovered duty and equipment cost.
The ROI calculation compares annual energy cost savings against total equipment cost (materials, installation, commissioning, additional maintenance). Projects with the best ROI typically combine high available temperature differential, high gas flow rate, high energy price and a high number of operating hours per year.
How do heat exchangers contribute to CO₂ emission reduction?
Lower fuel consumption translates directly into fewer CO₂ emissions per unit of useful energy produced. In installations subject to emissions trading (EU ETS), every emission reduction has an additional direct economic value.
The emission factor for natural gas is approximately 0.202 kg CO₂/kWh (LHV). Under the EU ETS, with CO₂ prices of 50–80 €/t, a significant heat recovery installation can represent additional savings of tens of thousands of euros per year on top of direct fuel savings.
What is the difference between thermal efficiency and heat exchanger effectiveness (NTU-ε method)?
Thermal efficiency compares the heat actually transferred to an external reference value. The NTU-ε effectiveness compares the heat actually transferred to the maximum theoretically transferable between the two fluids in that specific exchanger.
Effectiveness ε = Q_actual / Q_max is a useful design tool (NTU-ε method) when inlet temperatures are known but outlet temperatures are not. It must not be confused with the overall efficiency of a heat recovery system, which includes conduction losses, load variation and other external factors.
Under what conditions is low-temperature heat recovery economically viable?
Low-temperature heat recovery (40–100 °C) is viable when the available temperature differential is sufficient (>10–15 °C), the flow rate is high, the number of operating hours is large, and there is a productive use for the recovered heat within the same plant or in a nearby circuit.
Applications with the greatest potential include compressor cooling water effluent, steam condensate, extraction gases from refrigeration systems and process wastewater. Using heat pumps in tandem with the recovery heat exchanger can raise the recovered heat temperature to more useful levels, significantly improving the ROI.
F — Installation, maintenance and diagnostics
Problem identification, cleaning methods and operating best practices.
How is excessive fouling detected in an operating heat exchanger?
Operating indicators of excessive fouling include: reduction in cold-fluid outlet temperature, rise in hot-fluid outlet temperature, increase in pressure drop on the affected side, and measurable reduction in transferred thermal duty compared to design values.
Systematic monitoring of these variables enables early fouling detection. Comparing the current U·A value (calculated from in-service flow and temperature measurements) against the design value gives a quantitative estimate of fouling severity. A fall in U·A below 80% of the design value is typically the threshold justifying a shutdown for cleaning.
What cleaning methods are available for industrial heat exchangers?
The main methods include chemical circulation cleaning (CIP), mechanical cleaning using brushes or scrapers (for tubes), high-pressure water washing, compressed air soot blowing (for the gas side), and manual cleaning for dismountable units.
The choice of cleaning method must consider the nature of the deposit, exchanger material compatibility, accessibility and safety requirements. CIP is the most common approach for process exchangers in the chemical and food industries.
What symptoms indicate an internal leak in a heat exchanger (cross-contamination)?
An internal leak manifests as the presence of tracers from fluid A in the circuit of fluid B: colour change, odour, chemical composition change, pH shift or presence of specific tracer compounds. Detection can be confirmed by hydrostatic pressure test or helium leak test.
Cross-contamination is one of the most serious incidents in a heat exchanger, especially when one fluid is toxic, food-grade or dielectric. Common causes include pitting corrosion, mechanical fatigue at tube-to-tubesheet joints (shell-and-tube exchangers), and gasket failure in plate-and-frame exchangers.
When should gaskets be replaced in a gasketed plate-and-frame heat exchanger?
Gaskets should be replaced when they show visible signs of deterioration (cracks, excessive hardness, permanent set), when a hydrostatic test reveals leaks, or preventively when the maximum service life recommended by the manufacturer is reached.
Service life depends mainly on the elastomer material (NBR, EPDM, PTFE, Viton), working temperature and chemical aggressiveness of the fluid. NBR gaskets in hot water may have service lives of 3–5 years, while EPDM gaskets at 120 °C can reach 5–8 years.
How is a hydrostatic pressure test carried out on a heat exchanger?
The hydrostatic test involves filling the circuit under test with water, fully purging all air, gradually applying the test pressure, holding it for a specified period and verifying the absence of leaks and permanent deformation. The applicable test pressure depends on the applicable standard and equipment type; for PED equipment it typically falls between 1.25 and 1.43 times the maximum allowable pressure (PS).
The specific test pressure factor — typically between 1.25 × PS and 1.43 × PS — depends on the equipment type, fluid group, PED category and harmonised standard applied (EN 13445 for pressure vessels, EN 12952 for water-tube boilers, EN 12953 for shell boilers). The exact value must always be verified in the unit's technical documentation. The test must include complete air purging from the circuit, gradual pressure application, continuous recording of pressure and temperature throughout the test, and visual inspection of all joints and flanges. In shell-and-tube heat exchangers, the two circuits are tested independently. For heat exchangers handling toxic or flammable fluids, the hydrostatic test is always preferable to pneumatic testing, as the elastic energy stored in the event of failure is significantly lower.
What vibrations can a gas flow induce in a heat exchanger, and how are they prevented?
Gas flow through a tube bundle can induce mechanical vibrations through Kármán vortex shedding, especially when the vortex shedding frequency coincides with the natural vibration frequency of the tubes. Consequences include mechanical fatigue, fretting wear and, in severe cases, tube failure.
Vortex shedding generates periodic transverse forces on the tubes when gas flows around them above a critical velocity threshold. Preventive measures include: increasing tube rigidity (reducing unsupported span between baffles), changing tube bundle pitch, adding damping elements, or modifying gas velocity.
What is the typical service life of an industrial heat exchanger?
The service life of an industrial heat exchanger depends critically on the materials selected, the actual operating conditions and the maintenance programme applied. There is no universal range: each unit ages according to its specific process environment.
Stainless steel tubular heat exchangers in non-corrosive applications with regular maintenance generally achieve a long service life. The elastomeric gaskets in gasketed plate-and-frame heat exchangers require periodic replacement, while the plate pack itself can last considerably longer if process conditions are not aggressive. Boiler economisers exposed to corrosive gases (biomass, industrial waste streams) age more rapidly if specific design and protection measures are not taken. The factors that most significantly reduce service life are the presence of fluids or contaminants not declared at design stage, excessive fouling without adequate cleaning, and abrupt or frequent thermal cycling. Accurate characterisation of actual process fluids at design stage, selection of materials with appropriate corrosion allowances, and a preventive maintenance programme based on monitoring of operating variables are the elements that most influence real equipment durability.
How do start-stop cycles affect heat exchanger integrity?
Start-stop thermal cycles generate fatigue stresses from differential thermal expansion and contraction between heat exchanger components. In applications with many daily cycles or large temperature gradients during start-up, thermal fatigue sizing is as important as thermal duty sizing.
When the anticipated number of cycles is high (>10,000 cycles in service life), the design must include an expansion bellows in the shell or a floating-head configuration to relieve thermal stresses. Gradual start-up and use of a warm recirculation fluid during shutdown reduce thermal gradients and extend service life.
How can I obtain a custom heat exchanger for my application?
To obtain a custom heat exchanger, you need to provide the supplier technical office with the process data for each fluid (flow rate, inlet and outlet temperatures, pressure, composition and physical properties), dimensional and pressure drop constraints, and applicable regulatory requirements.
An industrial heat exchanger is rarely an off-the-shelf product. The typical process includes: submission of a process data sheet, feasibility study and type selection by the technical team, a technical proposal with thermal calculations and dimensional drawings, client validation, and manufacture with documented inspection. Delivery time from data receipt to shipment must be explicitly agreed with the supplier.