Engineering task and calculation objective
The TEMA module checks the design requirements of the TEMA standards for shell-and-tube heat exchangers: permissible clearances between tube bundle and shell depending on TEMA type (fixed tubesheet, U-tube, floating head), minimum and maximum baffle spacings, baffle diameters and hole clearances, minimum number and diameter of tie rods, as well as tube pitch and layout angle. In addition, it checks whether an impingement plate is required at the shell inlet and determines its recommended distance from the nozzle.
These geometry rules are the backbone of every TEMA-compliant design: they ensure that the bundle remains installable, that the baffles support the tubes adequately (vibration and deflection limitation), that bypass streams between bundle and shell are limited, and that the inlet jet does not damage the first tube rows through droplet impact and erosion. The criterion for the impingement plate is based on the dynamic pressure product ρv² of the entering fluid.
In practice, the module is used in preliminary sizing — for instance to determine the bundle diameter and the effective tube lengths for heat transfer and pressure drop calculations from the shell inside diameter and TEMA type — and in design verification before fabrication.
Standard and calculation basis: TEMA Standards
Calculation workflow
- Define TEMA type and main dimensions: From the TEMA type (e.g. BEM, BEU, AES), operating pressure and shell inside diameter follow the permissible diametral clearance between bundle and shell and thus the maximum bundle diameter.
- Determine effective tube lengths: From the real tube length and the thickness of the tubesheets, the free tube length, the effective tube length for heat transfer and the effective flow length for pressure drop are derived — the central input quantities for the thermo-hydraulic design.
- Check impingement plate requirement at the inlet: From the mass flow rate, density and nozzle cross-section, the inlet velocity is calculated and the product ρv² compared with the TEMA limits; if exceeded, an impingement plate (or an enlarged nozzle or distributor dome) must be provided, and its distance to the nozzle is recommended.
- Define baffle spacing: TEMA limits the baffle spacing at the lower end (fabrication, window flow) and at the upper end (maximum unsupported tube length depending on tube diameter and material group Fe or Al/Cu); from this follow the minimum and maximum number of baffles as well as their maximum diameter and the recommended hole diameter.
- Check tie rods and tube pitch: Finally, the minimum number and diameter of the tie rods as a function of the shell diameter, as well as the tube pitch transverse and longitudinal to the flow direction including the layout angle, are checked against the TEMA minimum values.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| TEMA type | T=5 | - |
| Operating pressure | ptotal | Pa |
| Shell inside diameter | Di | m |
| Real length of the tube | Lto | m |
| Thickness of the plates | Lts | m |
| Inside nozzle diameter (inlet) | Dns | m |
| Mass flow at the shell inlet ṁshell | MMantel | kg/s |
| Density of the fluid in the shell inlet | ρ | kg/m³ |
| Impingement plate installed (no / yes) | 1=ja) | – |
| Outside tube diameter | Dra | m |
| Material group (Fe, Al/Cu) Material | 2=Al/Cu) | – |
| Distance between the tubesheet and the 1st baffle (inlet) | Lbi | m |
| Distance between the tubesheet and the 1st baffle (outlet) | Lbo | m |
| Tube pitch (transverse) | s1 | m |
| Pitch angle | Φ | ° |
| Diametral shell-to-tube bundle clearance | Lbb = Di-Db Lbb | m |
| Bundle diameter | Db | m |
| Tube length without plates | Lti | m |
| Effective tube length for heat transfer | Lta | m |
| Effective flow length for pressure loss | Ltt | m |
| Real flow velocity in the nozzle | wn | m/s |
| Maximum allowable flow velocity | wn,max | m/s |
| Recommended distance between impingement plate and nozzle | Lns | m |
| Minimum baffle spacing | Lbc,min | m |
Calculation options
TEMA type
L, M, N (Fixed tubesheet) · U (U-tube bundle) · S (Floating head with backing device) · P (Outside packed floating head) · T (Pull through floating head)
Impingement plate installed (no / yes)
No · Yes
Material group (Fe, Al/Cu) Material
1 · 2
Worked example
For the shell inlet of a shell-and-tube heat exchanger, it is to be checked whether an impingement plate is required per TEMA — a worked example of the ρv² criterion. Water (single-phase, non-corrosive, non-abrasive) enters on the shell side.
Given values
| Inside diameter of inlet nozzle di | 150 mm |
| Shell-side mass flow rate ṁ | 25 kg/s |
| Density of the fluid ρ | 998 kg/m³ |
| TEMA limit ρv² (single-phase, non-corrosive/abrasive) | 2,232 kg/(m·s²) |
Solution
Flow velocity in the nozzle
Nozzle cross-section: A = (π/4) · di² = (π/4) · 0.150² = 0.01767 m²
v = ṁ/(ρ · A) = 25/(998 · 0.01767) = 1.42 m/s
Dynamic pressure product and comparison with the TEMA criterion
ρ · v² = 998 · 1.42² ≈ 2,005 kg/(m·s²)
2,005 < 2,232 kg/(m·s²) (corresponds to 1,500 lb/(ft·s²)) — the limit for non-corrosive, non-abrasive single-phase flow is satisfied.
Assessment
An impingement plate is not required according to the ρv² criterion. However, the margin of about 10% is small: for a future throughput increase or with abrasive components in the fluid (limit then 744 kg/(m·s²)), impingement protection would have to be provided.
Result
| Flow velocity in the nozzle | 1.42 m/s |
| Dynamic pressure product ρv² | ≈ 2,005 kg/(m·s²) |
| Impingement plate required? | No (limit of 2,232 kg/(m·s²) satisfied) |
All values are illustrative. The applicable standard and project-specific boundary conditions remain authoritative.
Frequently asked questions
Why do the permissible bundle-to-shell clearances differ by TEMA type?
The clearance follows from assembly: a fixed tubesheet bundle is welded to the shell and only needs fabrication clearance — the gap is small. A removable floating-head bundle must pass through the shell together with the floating-head flange, so the clearance is correspondingly large. Thermally, a large clearance is disadvantageous because the bypass stream between bundle and shell is not routed past the tubes; this is why sealing strips are provided for large clearances.
When does TEMA require an impingement plate at the shell inlet?
When the dynamic pressure product ρv² in the inlet nozzle exceeds the limits — for non-corrosive, non-abrasive single-phase flow a higher limit applies than for all other fluids; for two-phase flow and saturated vapours, impingement protection must always be provided. The impingement plate protects the first tube rows from erosion and vibration excitation, but narrows the inlet cross-section — therefore the distance between plate and nozzle must remain large enough so that the escape area around the plate does not become the bottleneck.
What limits the maximum baffle spacing?
The maximum permissible unsupported tube length: it is tabulated in TEMA by tube outside diameter and material group (steel or Al/Cu alloys) and prevents excessive sagging and too-low tube natural frequencies. Note that tubes in the window zone are supported only at every second baffle — their free length is twice the baffle spacing. Vibration safety itself is not yet demonstrated by this; a separate analysis (e.g. the RBSA module) is required for that.
What role do the tie rods play?
Tie rods and spacer tubes fix the baffle package in position and spacing — they carry no process loads, but are important for assembly and vibration behaviour: if tie rods are missing or too thin, baffles shift during insertion of the bundle and the supporting effect of the baffles is partially lost. TEMA therefore specifies a minimum number and minimum diameter as a function of the shell diameter.