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Tema Standards
This type of construction can be specified where a close approach temperature is required and when the flow rate permits the use of one half of the shell at a time . In heat recovery applications , or where the application calls for increased thermal length to achieve effective overall heat transfer , shells can be installed with the flows in series . TEMA G and H : These shell designs are most suitable for phase change applications where the bypass around the longitudinal plate and counter-current flow is less important than even flow distribution . In this type of shell , the longitudinal plate offers better flow distribution in vapor streams and helps to flush out non-condensables . They are frequently specified for use in horizontal thermosiphon reboilers and total condensers . A G-type is used for cases with small pressure drop at the shell side . The H-type is similar to F-type but in larger units . TEMA J : J-type shells are typically specified for phase change duties where significantly reduced shell side pressure drops are required . They are commonly used in stacked sets with the single nozzles used as the inlet and outlet . A J-type shell is usually used in cases where the maximum allowable pressure drop is greater than that with an E-Type shell . It is also utilized when tube vibration is a problem . TEMA K : This type is used for flooded evaporation of shell side fluids . The TEMA K shell , also termed a “ Kettle Reboiler ,” is specified when the shell side stream will undergo vaporization . The liquid level of a K shell design should just cover the tube bundle , which fills the smaller diameter end of the shell . This liquid level is controlled by the liquid flowing over a weir at the far end of the entrance nozzle . The expanded shell area serves to facilitate vapor disengagement for boiling liquid in the bottom of the shell . U-bundles are typically used with K shell designs . K shells are expensive for high pressure vaporization due to shell diameter and the required wall thickness . A K-type is employed only for reboilers to supply a large disengagement space to minimize shell-side fluid carryover . TEMA X : This shell , also known as a crossflow shell , is most commonly used in vapor condensing applications , though it can also be used effectively in low pressure gas cooling or heating . It produces a very low shell-side pressure drop , and is therefore most suitable for vacuum service condensing . In order to ensure adequate distribution of vapours , X shell designs typically feature an area free of tubes along the top of the exchanger . It is also typical to design X shell condensers with a flow area at the bottom of the tube bundle to allow free condensate flow to the exit nozzle . Careful attention to the effective removal of non-condensables is vital for X shell constructions . X-type is appropriate when the maximum shell side pressure drop is exceeded by all combinations of other shell types . Please refer to Table 1 for a summary of the TEMA shell types advantages and disadvantages .
TEMA Shell Types Advantages & Disadvantages Shell Type Advantages Disadvantages
E
F
G
H
J
K
X
Very common and predictable . All types of channels and heads can be fitted
Counterflow possible with two tube passes . Compact and effective if all welded baffle is used
Equivalent to nearly two E-shells in series with respect to approach to true counterflow . Can have low pressure drop if up & down flow
Used for phase changes . Very low pressure drop . As G-shell type regarding counterflow
Used for phase changes . Very low pressure drop
Low pressure drop . Used for production of ‘ dry ’ vapor
It produces a very low shell side pressure drop
Table 1 : TEMA shell types advantages – disadvantage summary ( Source : Mihir ’ s Handbook of Chemical Process Engineering ).
Conclusion This article has highlighted the TEMA types for S & T exchangers with pros & cons for major types . Having selected the TEMA type and allocation of the process fluids to shell and tube sides , the process engineer still needs to properly specify pressure drops , temperature profile and properties for the process fluids on both the shell and tube side . The engineer then needs to optimize the thermal design for the exchanger . This topic will be covered in a future article .
About the author
Mihir M . Patel is a chemical engineer and project management professional ( PMP ® ) from PMI , USA , as well as a TUV SUD certified functional safety professional . He has been practicing chemical engineering for over 36 years in the chemical process Industry . Patel now shares his knowledge and experience through the format of published handbooks and training courses for chemical engineers .
Single pass tubes must be used if counterflow is required
Removable bundle prone to leakage across longitudinal baffles edges
As for F-shell type
Ineffective for large sensible heat change
As H-shell type .
As H-shell type . Local concentration gradients may reduce LMTD with multi components
Careful attention to the effective removal of non-condensables is important . Also , due to nature of design , ends up with an almost square construction www . heat-exchanger-world . com Heat Exchanger World May 2023
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