Xist
Xist models all shell-and-tube heat exchangers. A fully incremental program, Xist contains HTRI’s latest pointwise methods for predicting condensing, boiling, and single-phase heat transfer and pressure drop. The methods are based on extensive shellside and tubeside condensation, boiling, and single-phase data.
Process Specifications
Xist handles the following process conditions:
- single-phase
- all shell styles
- vertical and horizontal shell orientations
- shellside and tubeside
- condensation
- all shell styles available for horizontal units
- shellside and tubeside
- vertical downflow condensation in single shellpass or tubepass
- tubeside inclined condensation
- pure fluids and multicomponent mixtures
- superheated, saturated, or partially condensed at inlets
- subcooled, or partially or totally condensed at outlets
- vertical intube reflux condensation
- boiling
- all shell styles available for horizontal units
- shellside and tubeside
- vertical upflow boiling in single shellpass or tubepass
- vertical intube falling film
- pure fluids and multicomponent mixtures
- subcooled, saturated, or partially vaporized at inlets
- superheated, or partially or totally vaporized at outlets
- two-phase no phase change (e.g., glycol injection)
- all shell styles
- vertical and horizontal shell orientations
- shellside and tubeside
Geometry Specifications
Xist accommodates the following geometries:
- TEMA E, F, G, H, J, K, and X shells
- horizontal, vertical, and inclined shells
- piping for horizontal and vertical thermosiphons and kettle reboilers
- one to sixteen tubepasses
- fixed and variable baffle spacing
- plain or low-finned tubes in fixed tubesheet with or without twisted-tape inserts, U-tube, or floating-head bundles
- continuous fins in pure crossflow or no-tubes-in-windows (NTIW) bundles
- segmental, double-segmental, segmental with no-tubes-in-window (NTIW) baffles, RODbaffles®, helical baffles, EMbaffles™, Square One grid baffles, and no baffles
- vertical and horizontal cut baffles
- kettles, thermosiphons, falling film evaporators, flooded evaporators, and tubeside reflux condensers
You can enter all details of the shell construction. Default values based on TEMA standards and common industrial practice are available.
Calculation Modes
Xist operates in rating, simulation, and design modes, automatically screening all cases for flow-induced mechanical and acoustic vibration problems.
Rating
You define exchanger geometry and specify process conditions. Xist calculates the expected heat transfer coefficients and pressure drops, compares these calculations to the required heat duty, and reports the difference as under- or overdesign.
Simulation
You define exchanger geometry and specify partial process conditions. Xist calculates expected exchanger performance and missing process conditions for zero overdesign, as well as heat transfer coefficients, pressure drops, and heat duty.
Design
Xist contains two distinct design options: program and user-specified.
In the program (or classic) mode, you define partial exchanger geometry and enough process conditions for Xist to calculate the required heat duty. Xist designs the missing geometry, expected heat transfer coefficients, and pressure drops.
In the user-specified (or grid) design mode, you have complete control over which geometry is varied and over what range each geometric parameter is varied. The program runs all possible permutations and automatically selects the best available design. The program can set the shell style, shell diameter, tube length, tubepasses, baffle spacing, baffle style, tube diameter, and tube pitch.
Special Calculations
- Thermosiphons: Xist calculates the expected pressure drops in the inlet and outlet piping.
- Flooded evaporators: Xist calculates the conditions required to keep the top of the bundle in wet-wall boiling
- Kettle reboilers: Xist calculates the internal recirculation rate. Either entrainment or kettle diameter can be specified, and Xist calculates the missing value.
- Exchanger trains: Xist handles trains of exchangers in series and parallel. Permitted process conditions include
- both fluids in series throughout the exchanger train
- one fluid in series and the other in parallel
- the same or separate parallel fluids in each shell
- Flow regime maps generated for two-phase fluids
- Automatic screening for flow-induced acoustic and mechanical tube vibration
Each exchanger in the series can be a different type; exchanger trains are not limited to identical shells. Parallel trains are considered to be identical.
Calculation Methods
The calculation methods in Xist are the result of HTRI’s latest research. Xist employs a 3D incrementation scheme to model shell-and-tube heat exchangers. The geometry (shell style, baffle spacing, tubepasses, baffle style) divides the exchanger into small increments containing crossflow or window flow and a single tubepass. Localized methods and fluid properties are used to predict the heat transfer and pressure drop in each increment. Incremental techniques allow accurate prediction of shell-and-tube heat exchangers with complex geometry and hydraulics.
Special Features
- Integrated graphical tube layout tool
- Unique 3D kettle reboiler circulation model
- Trains of exchangers modeled with identical or unique geometry in each shell
- Setting plan calculations/drawing for plant layout
