Chapter-04: Heat Exhanger

Solution

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The effectiveness of a heat exchanger can also be measured by heat transfer area for a given quantity of heat transferred. Out of given types of HEs, least area is of counter flowi.e. highly effective and maximum area in parallel HE i.e. least effective (from economical point ow view).

Betweeen shell and tube and cross-flow,shell and tube is more effective than cross-flow. So out of all four types, the correct sequence is -

The Process of Manufacturing Heat Exchangers

Heat exchangers are an integral component of industrial processes, transferring thermal energy from one fluid stream to another. The design and manufacturing of heat exchangers are critical to ensure optimal performance, reliability, and safety. Below, we go over the design and manufacturing processes of heat exchangers, as well as the verification and testing procedures heat exchanger manufacturers perform.

Thermal Design Process (During Bid Stage)

The design starts with the customer providing a process datasheet (typically formatted to TEMA, API 660, or API 661), containing detailed process information &#; flow rates, inlet and outlet temperatures, operating pressures, densities, viscosities, specific heats, thermal conductivities, and fouling factors.  If the process stream(s) undergoes a phase change (eg, gas condensing to liquid, or liquid evaporating to gas), then we also need heat-release and process property curves (data points).  

Ideally, the customer will also advise the desired TEMA type (AEU, NEN, etc), design pressures and temperatures, allowable pressure drops, corrosion allowances, and material selection (eg, carbon steel, 304 stainless steel, duplex, etc.).

Our thermal designers and estimators perform complete reviews of all customer-provided requirements, including the scope of supply, material requisitions (MR), inspection & test plans (ITP), vendor documentation requirements (VDR), datasheets, drawings, and customer specifications, in addition to industry specifications and ASME Code.  

Altex Industries&#; thermal design engineers then use HTRI to thermally size and optimize the shell & tube or air-cooled heat exchanger to maximize performance and minimize cost.  Considerations at the thermal design stage include &#; velocities, pressure drops, vibration, leakage streams, and constructability.  We size nozzles to stay within TEMA rho-v^2 limitations and add impingement plates or impingement rods when necessary to protect the tubes at the shell inlet nozzle.  

A preliminary mechanical design is completed (typically via Compress) to generate a bill of material (BOM) that includes material grades, thicknesses, diameters, lengths, and flange & bolting details.  This is required by the estimator to source material costs and generate accurate pricing.

Detailed Engineering and Design Process (Post Award)

Once we receive a customer purchase order (PO), a Project Manager and Altex job number are assigned, and the project is formally handed over from the Commercial Operations sales team to our Project Management and Engineering teams.

The Engineering Team, with support from other departments (QC, Supply-Chain, Manufacturing, Projects, and Sales) performs a complete review of the scope to capture and incorporate details into the design for material purchase, fabrication, and testing.

Detailed mechanical engineering is performed via Compress, Nozzle-Pro, and other software, and complete detailed drawings are generated in 2D via AutoCAD or in 3D with Solidworks.  Issued-for-approval (IFA) drawings and calculations are submitted to the client for review and mark-ups.  Once the approval process is completed, issued-for-construction (IFC) drawings are distributed to our Supply Chain team for material purchase, and to our shop for fabrication.  

The Manufacturing Process

Heat exchangers are manufactured from basic material shapes that undergo forming, machining, and welding processes to fabricate them into the major components.  Channel and shell cylinders are typically rolled and welded plates (greater than 24-inch diameter) or pipe (24-inch or less diameter).  Tube sheets can be plates or forgings depending on thickness, which are then machined and drilled.  Flanges are usually hot forged rings that are then machined and drilled.  Baffles are plate materials, cut into circles before being machined and drilled.  Tubes (seamless and welded variants) come in various standard diameters and gauges (thicknesses) and can be bent (into U-tubes) and cut to length as needed.  

Generally, shell & tube heat exchanger fabrication is split into four functional areas &#; machining and drilling operations, welding operations, bundle assembly, and final assembly and testing.  

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The machine-shop machines and drills baffles, tubesheets, and flanges.  

The bundle shop assembles the tubesheets, baffles, tubes, skid-bars, seal-strips, and impingement plates/rods into completed bundles (AEU, BEU, AES, BES), or near-complete assemblies for fixed bundles (NEN, AEL, BEM).  

The welding shop performs submerged-arc welding (SAW) on longitudinal and circumferential seams of the shell and channel cylinders.  The welding shop also locates and fits nozzles into the shell and channel cylinders.  They also fit and weld saddles, pass-plates, lifting-lugs, and other pressure-boundary attachments.

The assembly and testing shop does the final assembly of the exchanger, pushing the bundle into the shell, and bolting up the channel and other body flanges.  

Testing and Shipping Preparation

Altex Quality Control (QC) Department monitors and measures quality indicators throughout the manufacturing process to ensure the finished heat exchanger meets customer, industry (ASME, ABSA, etc), and Altex quality requirements.  Typical testing includes visual examination (VE/VT), magnetic particle (MPI), liquid penetrant inspection (LPI, aka dye-particle examination), ultrasonic testing (UT), and radiographic testing (UT).

When fabrication is complete and the exchanger has been fully assembled,  hydro testing (pressure testing via water) is performed to prove the heat exchanger can safely withstand the design and operating pressure requirements of the application.  The exchanger is then drained and dried, typically using shop air, but drying equipment and/or nitrogen may be used to achieve a specific dew point.

Depending on customer timing for installation and startup, requirements may dictate that additional protection of the exchanger is needed for short or long-term storage.  Poly-wrap and/or skidding/crating, and nitrogen purge (aka nitrogen blanket) are often added to Altex&#;s scope.  

Final Transportation and On-Site Inspections

Once the heat exchanger has passed all verification and testing procedures, it can be transported to the final location where it will be installed. During transportation, the heat exchanger must be carefully handled to prevent damage to flanged sealing surfaces, exposed tubes (in case of bundles), and fins (air coolers).  Often, operational and spare parts like gaskets and bolting are included or shipped loose.

3rd party on-site inspections and field crews typically perform inspection and installation and are responsible to ensure the heat exchanger is installed correctly and is operating safely and efficiently. This may involve checking for leaks, verifying the fluid flow rates and temperature differences, and monitoring the overall performance of the heat exchanger.

Speak With Altex, Canada&#;s Leading Heat Exchanger Manufacturer to Design the Perfect Exchanger

If you need a heat exchanger, it&#;s important to work with a reliable and experienced manufacturer like Altex. Altex Industries has been designing and manufacturing heat exchangers for years and has the expertise and capabilities to create custom heat exchangers that meet your specific requirements.

We have a heat exchanger for whatever your industrial process is -, refining, SAGD, petrochemical, pulp & paper, or power generation &#; Altex will provide a solution that meets your needs. With modern and fully equipped manufacturing facilities and a team of experienced engineers and technicians, Altex can deliver high-quality heat exchangers that are reliable, efficient, and safe. Get in touch with us today to learn more.

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