These modifications can affect all phases (vapor, liquid, single-phase, two-phase) and both the default (simple) and detailed piping input options; they do not affect sudden contraction/expansion losses from/to a distillation column. The pressure drop for all other contractions increases for both single- and two-phase flows. For all expansions except a column connection, the pressure drop decreases for two-phase flow, leading to a pressure gain in most cases. The pressure drop for a T-junction either decreases (if a dividing junction) or increases (if a combining junction) for two-phase flows. For single-phase flows, the change in predictions is small. The infinite range of possible piping element combinations makes it impossible to generalize on the impact that these new methods have on the overall circulation rate and outlet vapor fraction, but most cases are expected to see differences of less than 10%.

Additional reading: TPF-10, TPF-11, and TPF-12. Design Manual updates in progress.

5.    Liquid holdup model for vertical upflow in piping

The two-phase static head pressure drop calculation for vertical (upflow) piping elements has been modified to better capture the effects of liquid holdup. The old method overpredicted measured pressure drop, and this updated method is expected to provide better results for thermosiphon circulation calculations. The method change involves a modification to the calculation of the vapor volume fraction, R_v. The new method leads to a slight mean increase (3.5%) in predicted circulation rate and a slight mean decrease (3.2%) in predicted outlet vapor quality. The modified method, in general, leads to lower two-phase pressure drop values and seems to improve the prediction of several outlying thermosiphon circulation rates previously overpredicted by a factor of ~3 but are now within 15%.

Additional reading: TPF-14. Design Manual updates in progress.

6.    Fair map eliminated for vertical upflow piping

The Fair flow regime map, previously used to determine the flow condition of adiabatic upflow in vertical piping elements, was determined to be unsuitable for this application. All references to the Fair flow regime map in the relevant piping reports have been removed. The Dukler flow regime map is used exclusively for this purpose since it adequately represents vertical adiabatic upflow. The Fair flow regime map is still used for two-phase upflow in vertical tubes.

Additional reading: TPF-15. Design Manual updates in progress.

7.    Liquid holdup model for vertical downflow in piping

Xist previously used the same liquid holdup model for two-phase upflow and downflow in vertical piping. Research indicates that vertical upflow and downflow have very different two-phase characteristics and that pressure recovery due to static head gain in downflow tends to be much smaller than the pressure loss due to static head for vertical upflow. HTRI proprietary data indicate that the homogeneous model is more appropriate in predicting static head for two-phase vertical downflow, ensuring consistency with our downflow calculations for boiling intube applications. The impact of this change is expected to be negligible because downward two-phase flow in vertical piping is rare.

Additional reading: TPF-16. Design Manual updates in progress.

8.    Neotiss boiling tube option

The Neotiss boiling tube option in Xist, Xjpe^®, and Xhpe is based on proprietary fin geometry on the outside tube surface. On the Geometry/Tubes panel, the HPT Thermo-B option activates the proprietary geometry and boiling methods to simulate the heat transfer and pressure drop with the “rolled-over” low-finned structure commercially available from Neotiss, Inc. The tube enhances nucleate boiling compared to plain and traditional low-finned structures. It is suitable for consideration for pure components in low-fouling applications, especially for low heat fluxes. With the HPT Thermo-B option, the user should select None or HPT Microfin Type 2 option for the inside surface.

Additional reading: BX-17-TR. Design Manual updates in progress.

9.    Micro-finned Neotiss tubes for single-phase and condensing

Two intube micro-fin options in Xist, Xjpe, and Xhpe are based on Neotiss fin geometry. On the Geometry/Tubes panel, an HPT Microfin Type 2 option is available on the Tube internals drop-down menu. With these options selected, proprietary methods are activated to simulate the heat transfer and pressure drop for these commercially available geometries. HPT Microfin Type 2 provides enhanced condensing performance. These geometry options are available for plain, HPT low-finned, and HPT Thermo-B tube types.

Additional reading: HTRI report and Design Manual updates in progress.

10.  Airside recirculation warning in Xace^®

A runtime message reports probable hot air recirculation (HAR) due to wind or no-wind conditions. The recirculation-analysis is activated for cases specified with a single bay, no chimney, and ground clearance. The probability of hot air recirculation is expressed as either low or high. Low probability is reported in an Informative message, and high probability in a Warning.

Additional reading: AC-17. Design Manual updates in progress.

11.  Single-phase vapor crossflow heat transfer methods for low-finned tubes

An improved j-factor correlation for single-phase vapor crossflow has been implemented for tubes. The new correlation changes the heat transfer coefficient for vapor only and boiling cases. Condensing cases are not affected. This correlation applies to X shells, NTIW, kettle, and Xace cases only. For vapor only cases, the heat transfer coefficients are approximately 30 to 50% lower for inline bundles and 10 to 20% lower for staggered bundles, compared to previous versions. For boiling cases, the changes in the heat transfer coefficient are negligible. For condensing cases, a heat transfer multiplier is recommended for inline low-finned bundles as described in TT-15.

Additional reading: S-SS-3-24. Design Manual updates in progress.

12.  Air-cooler header pressure drop and flow maldistribution

An option for calculating both flow maldistribution and pressure loss in headers has been implemented in Xace for liquid only cases. When the option is selected, the program calculates header pressure drop and a maldistribution parameter for both the inlet and outlet headers. Header maldistribution is defined as the relative variation in mass flow rate down the tubes in the header. This method assumes nozzles are equal in size and equally spaced across inlet/outlet headers. If any Reynolds number in any section is below 10000, the program issues a warning message stating that there is uncertainty in the applicable method. A new line in the tubeside nozzle section of the Final Results reports the maldistribution parameter. The calculations are not performed for turnaround headers.

Additional reading: AC-18. Design Manual updates in progress.

13 and 14. Shellside boiling methods

Changes to shellside boiling methods in Version 8 have been implemented:

• Convective + nucleate option (on the Methods panel) now ensures a smooth transition to convective-only boiling when vaporization duty is insignificant (less than 10% of the total duty).
• Convective-only option (on the Methods panel) now considers convective, thin film, and natural convection coefficients. Previous versions included only the convective coefficient.
• Two-phase, no-phase change option (on the Process Conditions panel) applies only to convective boiling and now includes a lower limit for convective boiling so that it cannot be lower than the sensible liquid coefficient.
• Pure crossflow exchangers (kettle and X shells) includes a lower limit for the sum of the convective coefficients (convective, thin film, and natural convection) so that their combined value cannot be lower than the sensible liquid coefficient.

For cases where the nucleate boiling coefficient is dominant, the change in the calculated heat transfer coefficient is negligible. For cases where the convective or natural convection coefficient is dominant, the change in the heat transfer coefficient is small.

Additional reading: Q 15-1 and TT-4. Design Manual updates in progress.

15.  General cooling water fouling

For the generalized cooling water fouling option, the software requires four individual indices (acidity, total alkalinity, calcium hardness, and total dissolved solids) to calculate the saturation index (SI). A new input field allows direct specification of SI, with a default value of 6 and within a range of 3 – 10. If all four indices are specified, users can override the default or any specified value as long as the new value stays within the given limits.

Additional reading: Q 11-4. Design Manual updates in progress.

16.  Shellside thermal stratification

A new runtime message alerts users to potentially significant thermal stratification. This warning message is limited to horizontal shells with vertical-cut baffles. The message is generated if all four of the following conditions are met.

• if Re < 200
• if Ri > 0.01
• if Ri Pr > 2000
• if the relative error in the shellside coefficient can be more than 20%

Additional reading: S-SS-3-29. Design Manual updates in progress.

17.  Improved incremental explicit delta-factor method

An improved explicit delta-factor method in Xist more accurately captures the effect of ineffective and effective stream remixing in each segmental baffle space. In general, the delta factor is increased for cases with previously low delta factors. The increases are greater for exchangers with many baffles, large shellside temperature ranges, close temperature approaches, and viscous liquids. These changes affect all TEMA types except kettles and X shells.

Additional reading: Design Manual changes in progress.

18.  Bypass sealing devices in Xist and Xhpe

Unless specified by the user, the number of bypass sealing devices in exchangers with segmental baffles (single, double, or NTIW) or no baffles (X shells or K shells) is calculated in accordance with API Standard 660. Per the API standard, the number of seal strips and passlane seal rods should be identical, and no sealing devices are applied to kettles. The most noticeable change in seal strip and seal rod numbers occurs for bundles with a small overlap distance between baffle cuts, for units with rotated triangular tube patterns, and for kettles. In these cases, the change in the number of sealing devices can impact shellside heat transfer and pressure drop results by as much as 10 – 30% due to the modified stream analysis. For most geometries, the expected difference in heat transfer and pressure drop is between 2 – 7%.

19.  Shellside condensate cooling

For shellside condenser cases with horizontal shells and an inlet weight fraction vapor less than 0.05, the condensing contribution is low, effectively causing the condenser to behave as a condensate cooler. The new model trends with the liquid-only heat transfer calculation for a smoother transition to the subcooled predictions. For some cases, the changes can be greater than 10% when compared to previous versions, but new results should be similar in liquid-only cases.

Additional reading: Design Manual updates in progress.

20.  Momentum gain for thermosiphon inlet header

The calculation of momentum pressure gain for inlet headers is limited based on the same criteria used for momentum pressure drop calculations in the outlet header. This modification has a negligible effect on overall results except for the rare case in which the inlet nozzle velocity is unreasonably high.