Kern Method Heat Exchanger
- Kern method heat exchangers
- PPT - Heat exchanger design KERN METHOD PowerPoint Presentation, free download - ID:340152
- Kern method heat exchanger hose
- Kern method heat exchange rates
• The principal components of an STHE are: • shell; shell cover; • tubes; tubesheet; • baffles; and nozzles. • Other components include tie-rods and spacers, pass partition plates, impingement plate, longitudinal baffle, sealing strips, supports, and foundation. ahnazari Types of Shells By: Dr. ahnazari Fixed tube sheet By: Dr. ahnazari U-Tube STHE By: Dr. ahnazari Floating Head STHE TEMA S By: Dr. ahnazari Floating Head STHE TEMA T By: Dr. ahnazari Cross Baffles • Baffles serve two purposes: • Divert (direct) the flow across the bundle to obtain a higher heat transfer coefficient. • Support the tubes for structural rigidity, preventing tube vibration and sagging. • When the tube bundle employs baffles, • the heat transfer coefficient is higher than the coefficient for undisturbed flow around tubes without baffles. • For a baffled heat exchanger the higher heat transfer coefficients result from the increased turbulence. • the velocity of fluid fluctuates because of the constricted area between adjacent tubes across the bundle.
Kern method heat exchangers
The correction factor is a function of the fluid temperatures and the number of tube and shell passes and is correlated as a function of two dimensionless temperature ratios Kern developed a relationship applicable to any heat exchanger with an even number of passes and generated temperature correction factor plots; plots for other arrangements are available in the TEMA standards. The correction factor Ft for a 1-2 heat exchanger which has 1 shell pass and 2 or more even number of tube passes can be determined from the chart in the Appendix VIII and is given by: The overall heat transfer coefficient U is the sum of several individual resistances as follows: The combined fouling coefficient hf can be defined as follows: The individual heat transfer coefficients depend on the nature of the heat transfer process, the stream properties and the heat transfer surface arrangements. The heat exchanger layout depends on the heat transfer area (HTA) so an initial estimate is required based on a trial value of the OHTC.
There are several software design and rating packages available, including AspenBJAC, HTFS and CC-THERM, which enable the designer to study the effects of the many interacting design parameters and achieve an optimum thermal design. These packages are supported by extensive component physical property databases and thermodynamic models. It must be stressed that software convergence and optimisation routines will not necessarily achieve a practical and economic design without the designer forcing parameters in an intuitive way. It is recommended that the design be checked by running the model in the rating mode. It is the intention of this paper to provide the basic information and fundamentals in a concise format to achieve this objective. The paper is structured on Chemstations CC-THERM software which enables design and rating to be carried out within a total process model using CHEMCAD steady state modelling software. However the principles involved are applicable to any software design process.
By: Dr. ahnazari Tube Layout & Flow Structure A Real Use of Wetted Perimeter!
PPT - Heat exchanger design KERN METHOD PowerPoint Presentation, free download - ID:340152
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Kern method heat exchanger hose
• Overall Heat Transfer coefficient. • Hydraulic Analysis of Tube side. • Hydraulic Analysis of Shell side. ahnazari Fluid Allocation: Tube Side • Tube side is preferred under these circumstances: • The higher velocities will reduce buildup • Mechanical cleaning is also much more practical for tubes than for shells. • Corrosive fluids are usually best in tubes • Tubes are cheaper to fabricate from exotic materials • This is also true for very high temperature fluids requiring alloy construction • Toxic fluids to increase containment • Streams with low flow rates to obtain increased velocities and turbulence • High pressure streams since tubes are less expensive to build strong. • Streams with a low allowable pressure drop By: Dr. ahnazari Fluid Allocation: Shell Side • Shell side is preferred under these circumstances: • Viscous fluids go on the shell side, since this will usually improve the rate of heat transfer. • On the other hand, placing them on the tube side will usually lead to lower pressure drops.
ahnazari Types of Baffle Plates: Segmental Cut Baffles • The single and double segmental baffles are most frequently used. • They divert the flow most effectively across the tubes. • The baffle spacing must be chosen with care. • Optimal baffle spacing is somewhere between 40% - 60% of the shell diameter. • Baffle cut of 25%-35% is usually recommended. Double Segmental Baffles Triple Segmental Baffles By: Dr. ahnazari Types of Baffle Plates The triple segmental baffles are used for low pressure applications. ahnazari Types of Baffle Plates By: Dr. ahnazari Types of Baffle Plates Disc and ring baffles are composed of alternating outer rings and inner discs, which direct the flow radially across the tube field. § The potential bundle-to-shell bypass stream is eliminated § This baffle type is very effective in pressure drop to heat transfer conversion By: Dr. ahnazari Therm-Hydraulic Analysis of Heat Exchanger • Initial Decisions. • Tube side Thermal Analysis. • Thermal analysis for Shell side.
Kern method heat exchange rates
CHEMCAD is used to establish the steady state mass and energy balances across the heat exchanger and typical values of the OHTC are shown in the Attachments. A quick calculation method XLTHERM is also available to assist this procedure. The fouling factors chosen can have a significant effect on the design and again typical values are shown in the Attachments. hhhhh fofi fofif += () () LWorTTCWttCwTAUQ 21)s(p12)t(plm === () ()()()tT tTlntTtTT 1221 1221lm = TFT mtm = ()()tt TTR 12 21 = ()()tT ttS 11 12 = h1 h1 xk1 h1 h1 U1 foofii++++= Design and Rating of Shell and Tube Heat Exchangers PAGE 6 OF 30 MNL 032A Issued 29 August 08, Prepared by J. 2 Heat Transfer Model Selection The heat transfer model selection is determined by the heat transfer process (sensible, condensing, boiling), the surface geometry (tube-side, shell-side), the flow regime (laminar, turbulent, stratifying, annular), and the surface orientation (vertical, horizontal). A heat transfer model selection flow chart is presented in the Appendix IV to assist in this procedure.
In the Attachments a Design Aid is presented which includes key information for data entry and a shortcut calculation method in Excel to allow an independent check to be made on the results from software calculations. Detailed mechanical design and construction involving tube sheet layouts, thicknesses, clearances, tube supports and thermal expansion are not considered but the thermal design must be consistent with the practical requirements. Source references are not indicated in the main text as this paper should be considered as a general guidance note for common applications and is not intended to cover specialist or critical applications. Sources for this paper have been acknowledged where possible. The symbols, where appropriate, are defined in the main text. The equations presented require the use of a consistent set of units unless stated otherwise. Design and Rating of Shell and Tube Heat Exchangers PAGE 4 OF 30 MNL 032A Issued 29 August 08, Prepared by J. Edwards of P & I Design Ltd, Teesside, UK 2.
0 Fundamentals The basic layout for a countercurrent shell and tube heat exchanger together with the associated heat curve for a condensing process generated from CHEMCAD are shown below: Design and Rating of Shell and Tube Heat Exchangers PAGE 5 OF 30 MNL 032A Issued 29 August 08, Prepared by J.
