Operation

Start KOND by ‘Programs’ / ‘Heat ‘ / ‘KOND Shell and tube condensers for pure vapours.

In this menu you can determine the network paths for a network installation of KOND. KOND basic data (tubes, pitches, shells) and the tubesheet library.

After starting the program, the ‘Selection of basic data‘ mask appears.

In this mask user-specific company standards and variables of series as well as the media can be selected.

The conception of the KOND program is, that only few mouse clicks are needed to select type and basic design of the heat exchanger as well as tube-side and shell-side medium. Only seven values (temperatures, pressures, mass flows resp. performance) have to be entered to generate a tubesheet and design a heat exchanger.

Before starting the calculation the type and the general layout should be known if possible. To specify this, the ‘Basic data selection’ dialog box is provided. Furthermore, standard values for dimensions of tube and shell can be used to meet variables of series or company standards for design of the heat exchanger.

The following basic data can be specified:

Several standard tubes according to DIN standards are given.

The description 25 x 2, Shell-Bu. 12, Bend R 37 means:

Tube outside diameter 25 mm

Wall thickness 2 mm

Minimum distance bundle-shell 12 mm (This distance is not underrun when the shell is completely tubed. This value can be modified in the input mask afterwards. If you have selected 'TEMA Standard' in the 'Selection of basic data', the minimum bundle-shell distance is calculated according to TEMA and cannot be overwritten anymore.

If you want to change the value, you have to deactivate the 'TEMA standard' option in the 'Selection of basic data' first.)

Bending radius for U-tube 37 mm

The description refers to the smallest bending radius possible. The tube outside diameter, the wall thickness and the tube material essentially determines this radius.
Bending radii for some tubes made from C steel and CrNi steels

If the tubes closest to the exchanger center are bent crosswise or the passes are separated by separating baffles in the bonnets you should enter the pass lane width instead of the bending radius.

The pass lane width is the clearance between the tubes of two passes. The bending radius calculates the pass lane width:

Pass lane width = 2 x bending radius - tube outside diameter

Bending radius or pass lane width are only required for two or multiple tube side passes.

DR 13.5 x 0.7 – 26°/0.8 means:

·         DR corrugated tube or KDR cross- corrugated tube

·         Tube outside diameter 13.5 mm

·         Wall thickness 0.7 mm

·         Corrugation angle φ = 26°

·         Corrugation depth h = 0.8 mm

With corrugated tubes, the minimum bundle-shell distance is set to 12 mm by default. This value can be modified in the input mask afterwards.

Distance and arrangement of tubes in the tube bundle.

The crosswise pitch, the longitudinal pitch and the pitch angle determine the arrangement of the tubes in the tube bundle.

The crosswise tube pitch is the center-to-center distance of two adjacent tubes in a tube row, crosswise to the flow direction. The longitudinal tube pitch is the center-to-center distance of two adjacent tubes in flow direction.

Crosswise pitch and longitudinal pitch are depending from the pitch angle. There are four frequently used tube pitches. The most frequently used pitch is the 60° tube pitch.

32 x 60° means:

Crosswise tube pitch 32 mm

Pitch angle 60°

Tube pitch

a) Triangle pitches 60° and 30°

With the triangle pitches you can achieve the highest tube density in the shell. This means, in a shell with a triangle tube pitch there can be 15% more tubes than in a shell with a square tube pitch. Additionally, with triangle pitches the heat transfer is better than with square pitches. This means the same area has a better thermal performance than with a square tube pitch.

Disadvantages of triangle pitches:

No mechanical cleansing of the outer side of the tubes is possible and the pressure drop is higher than with square pitches.

b)  Square pitches 45° and 90°

A square pitch should be used for all heat exchangers with expected greater shell-side fouling.

The 45° pitch leads to a better heat transfer with laminar flow due to better turbulences. If the pressure drop is the limiting element of the heat exchanger the 90° pitch should be used for turbulent flow.

Conversion of pitches

With the 60° pitch, the crosswise tube pitch should be about 1.25 to 1.5 times the tube outside diameter.

By means of using the 'conversion of tube pitch' the crosswise pitch of the according 30°, 45° und 90° pitch can be calculated.

Here you may select the tube material and the according thermal conductivity. The unit of the thermal conductivity is [W/(m·K)].

To save a new material and its thermal conductivity, simply enter your data in the fields 'Tube material' and 'Thermal conductivity' and then press the 'Save' button.

Under shell diameter a lot of shells are predefined in accordance to DIN standards 2448 and 2458 for seamless and welded tubes.

273 x 6.3 Dist. Baffles 100 means:

·         Outside shell diameter 273 mm

·         Wall thickness 6.3 mm

·         Minimum baffle pitch 100 mm (This pitch is not underrun when the heat exchanger is designed. This value can be modified in the input mask afterwards.)

The minimum baffle pitch should not underrun 20% of the inside diameter of the shell, but be at least 50 mm.

If you have chosen ‘Free input / design’ for the shell the program automatically selects a shell from the list of shells during calculation of the heat exchanger. The selection criterion is the desired flow velocity in the tubes. The program tries not to exceed the desired velocity in the tubes when the shell is completely tubed. The desired velocity is an upper limit for the velocity in the tubes.

The shell may be changed by selecting either a new shell in the ‚basic data selection‘ or by entering the wall thickness and the shell outside diameter in the WTS input mask. You can also enter the number of tubes in the WTS input mask. The program selects the shell from the database, in which all the tubes fit in. As the shell is always filled completely, the entered number of tubes might not be the same as the calculated number of tubes.

To make the program select the next larger shell, it is sufficient to increase the number of tubes slightly. Tod have a smaller shell, you have to decrease the number of tubes significantly.

If the option Default values is deactivated and you enter a number of tubes, the program determines the shell that is perfectly sized to fit the number of tubes you have entered. Usually this is not a standard shell, this means it has to be custom made.

By the bundle type you define the design of the tube-side end head. Together with the option ‘Tema standard’ the calculation of the tubesheet is adjusted to the values of TEMA standard.

The installation position is important only for condensation processes because due to the type of installation of the heat exchanger different correlations have to be used for the thermal calculation.

The desired velocity in the tubes determines the selection of the shell diameter if ‘Free input / design’ has been chosen under shell diameter.

The program tries not to exceed the desired tube-side velocity and selects an appropriate shell from the list of shells under ‘shell diameter’.

If a shell has been selected under ‘shell diameter’ the tube-side velocity is fixed so that indicating a desired tube-side velocity makes no sense and is deactivated therefore.

The user can modify the value for the desired tube-side velocity at any time by mouse-click on the value field.

Typical values for tube-side velocity:

(From: Walter Wagner, Wärmeübertrager)

The velocity is limited due to cavitation and erosion.

To avoid erosion at the inlet and outlet region, the product ρ·v² should also be put into consideration. This dynamic pressure considers also the influence of the fluid mass

The desired shell-side velocity serves for determination of the distance of the segmental baffles. If the option ‘Tema standard’ has been selected the resulting value is checked according to Tema standard and corrected if necessary.

The user can modify the value for the desired velocity in the tubes at any time by mouse-click on the value field.

Typical values for shell-side velocity are:

The velocity is limited due to vibration, cavitation and erosion.

To avoid erosion at the inlet and outlet region, the product r·v² should also be put into consideration. This dynamic pressure considers also the influence of the fluid mass.

¹⁾ velocity means velocity in nozzle

²⁾ velocity means velocity in first tube row

For all other gases and vapors, including all nominally saturated vapors and for liquid vapor mixtures, impingement protection is required.

The tube-side and shell-side media are selected by mouse-click in the pull-down-menu. At the condenstaion side only media that can be condensed are shown. The physical state of the media ‘liquid or gas’ which is important for calculation of the heat transfer is set automatically. The values for the desired tube-side and shell-side velocities are adjusted to the physical state.

If ‘Free input‘, ‘Refrigerants (without change of phase, ‘Proper’ or ‘STAB’ has been selected, the physical state has to be indicated by the user. Then, the values for the desired tube-side and shell-side velocities are adjusted to the physical state.

If ‘Free input‘ has been selected the properties have to be entered manually (see section ‘Manual input of properties’).

The standard version of the KOND package provides several property modules:

This list can be extended by further property modules which are not included in the basic package. The material data compiler PROPER (not included in the basic package) allows free selection of the components and their mixtures included in the library. Furthermore, the free input of properties is possible with the SDAT module. If both media have been preselected with the menu item ‘Basic data‘ the properties are calculated automatically by the corresponding modules (e.g. water, air, natural gas).

Condensation can take place tube-side or shell-side. No subcooling of the condensate is calculated for horizontal condensers with shell-side condensation. The temperature of the condensate is set to a value 0.5°C lesser than the boiling temperature.

With this option you can design multi-tube heat exchangers (without baffles). In contrast to a double pipe heat exchanger, consisting of one outer and one inner tube, a tube bundle is assumed with the option ‘Shell without baffles’!

The option ‘TEMA Standard’ ensures that the dimensions specified according to TEMA are kept in the calculation. The TEMA module is activated automatically and dimensions according to the TEMA code appear in the KOND user interface. For example, by selecting the bundle type the bundle-shell distance is determined according to the TEMA code.

By default WTS calculates segmental baffles. The window size should range from 15% to 40% of the shell diameter.

Baffle spacing

The program calculates the baffle spacing to meet the requirements of the desired shell-side flow velocity of the medium. At first, the inlet baffle spacing is set equal to the baffle spacing (see Give inlet baffle spacing).

The baffle distance can be adjusted in the KOND input mask.

The option 'No-tubes-in-window' creates a tubesheet without tubes in the window zones. (see Segmental baffles)

Application:

·         Avoiding of tube vibrations.

The unsupported tube length is reduced to the baffle distance. The unsupported tube length in the window zone is twice the baffle distance

·         Significant reduction of pressure drop in window zones

With the option ‘Corrugated tubes‘ heat transfer and pressure loss for flow in single or crosswise corrugated tubes can be calculated. 21 different types of tubes of Messrs. HDE GmbH, Menden, with diameters ranging from 13,5 to 28 mm can be selected in a pull-down-menu after clicking the option ‘Corrugated tubes’.

With the button ‘Tubesheet library‘ the values of a tubesheet created by yourself can be transferred from your tubesheet library into the program.

After pressing this button a table is displayed where you have to mark the tubesheet by mouse-click.

Transferring tubesheet data

To transfer the values of the tubesheet click ‘Load Tubesheet’. With ‘Finish editing (ESC)’ you return to the ‘Basic data‘ menu. Variables selected before such as diameters of tube and shell are overwritten by the data transfer.

>> Please note that creating, editing and saving of the tubesheet in the tubesheet library is only possible in the SPIE module.

After selection of basic data is completed confirm your selection by ‘OK’. The next selection box appears:

Already here, it is possible to specify the system data (temperatures, pressures, mass flows resp. thermal performance).

You may also enter these values in the KOND basic mask.

TIP: Conversion of units

A click on the unit or a double click on the input field the conversion of units is activated.

Enter the values in the unit you have at hand; e.g., mass flow in kg/h. The value is immediately converted in all other displayed units. The unit with the activated checkbox is displayed on the mask and will be used for the documentation.

Please confirm your input with 'ENTER'.

On the KOND user interface the user controls the run of the calculation. From here it is possible to switch to any other module.

The KOND user surface contains all input variables required to calculate a heat exchanger. These input values also appear in the input masks of the selected chapters. They can be entered or modified there as well because all chapters are linked with each other.

To switch to the user interfaces of the single modules click on ‘ATLAS’ / ‘Chapter’. KOND provides a special ‘Basic input‘ menu which can be found in the menu bar of the input mask.

Input mask and ‘Basic input‘ menu

With this menu item you return to the ‘Selection of basic data‘ dialog box. Later entries or modifications made with this menu item during calculation may lead to calculation errors. If basic data have to be modified, please restart KOND, select the new basic data, enter the values and restart the calculation.

For output of specification sheets to MS EXCEL click the menu item ‘Specification sheet‘. MS EXCEL has to be installed before activating this item.

You can choose between German, English or French in the 'Language' menu.

The KUDO module creates an abridged documentation with the performance characteristics and only a few geometrical data like outside diameter of the shell and tube length. Geometrical data documentation is reduced to outside diameter of the shell.

If a tubesheet is loaded from the tubesheet library it is always locked, i.e. the geometrical variables of the heat exchanger are fixed and it can be neither overwritten in the input mask nor recalculated by the program. The fields concerned are marked in on the input mask.

If modification of those variables is desired click the menu item ‘Tubesheet lock / unlock’ to unlock the tubesheet for editing.

The ‘Default values’ are activated if this menu item is ticked. Click ‘Default values’ to deactivate the option or to re-activate it.

If the option is activated KOND uses preselected dimensions and default shells for the design of a heat exchanger. For example, if the user enters a new number of tubes during the optimization, KOND selects the shell which just has enough space for this number of tubes.

If the function is deactivated and a new number of tubes is entered, KOND calculates the exact inside shell diameter resulting from this number of tubes. If the option is activated again, the heat exchanger is automatically recalculated. KOND uses again preselected default shells for the calculation.

The tubesheet is displayed in the graphics window. Changes in the input mask are presented in the graphics dynamically.

Before entering the shell nozzle the inlet baffle spacing is set equal to the baffle spacing. After having entered the nozzle diameters the program checks if the distance tubesheet to first baffle is greater than the nozzle diameter plus a run-out length depending on nozzle diameter and shell diameter. If this is the case, the inlet baffle spacing is increased automatically.

Thus you can avoid that the first or the last baffle is below the inlet or outlet nozzle. The increase of the distance is considered for calculating the heat transfer coefficient. This may result in a correction of the required length or of the overdesign.

You can also enter the inlet baffle spacing as long as it is greater than the baffle spacing or greater than the nozzle diameter plus run-out length. Smaller values are not accepted by default!

If you activate the option ‚Give inlet spacing‘, every positive value is accepted even if it is smaller than the nozzle diameter. Then, the baffle spacing is always calculated and cannot be entered (the input field is locked). The baffle spacing can then be changed by entering the number of baffles.

If ‘Free input‘ has been selected in ‘Basic data‘ for one of the media, the properties of this medium have to be entered manually. This is possible with the SDAT module. After entering the inlet and outlet temperature and the pressure on the WTS mask the SDAT module is activated. Pressure and mean temperature have already been transferred.

Required data:

Liquids and gases (single-phase media)

For calculating the heat transfer and the pressure drop, properties at mean temperature and at wall temperature are required. At first start of SDAT the wall temperature is unknown. Please enter only the properties at mean temperature at first. As soon as the data input is complete, the program switches automatically back to the KOND mask. After the wall temperature has been calculated please switch to the SDAT module by clicking on the according tab strip and complete the properties at wall temperature.

If you do not enter the properties at wall temperature, the values are replaced by the values at mean temperature for calculating the pressure drop and the heat transfer. Then the accuracy of the calculation decreases.

>> Especially with viscous media like oils greater errors might occur.

Condensation of pure substances

When condensing pure substances, the properties of the vapor and the properties of the condensate at condensation temperature are required.

As soon as the data input is complete, the program switches automatically back to the KOND mask.

If you have selected ‘Free input’ for both exchanger sides two SDAT modules are created.

KOND input mask (heat balance)

The first value block contains the information about the quantities, pressures and temperatures of both media. The best way for the medium to be condensed is, to enter the condensation pressure first. For the standard medium water the boiling temperature is displayed now. Complete your inputs by entering the remaining temperatures, shell-side as well as tube-side.

In most cases the mass flows and temperatures are already known, which means that the heat balance is fixed. However, the exact temperatures or quantities are specified only by the properties used in the program, i. e. the last temperature or quantity which remains to be entered is calculated by the program to complete the heat balance.

Fouling resistances for water in shell and tube heat exchangers (m²K/W)

© Springer Verlag Berlin Heidelberg 2013

© Springer Verlag Berlin Heidelberg 2013

© Springer Verlag Berlin Heidelberg 2013

© Springer Verlag Berlin Heidelberg 2006

If no standard dimensions, i.e. no default variables for the tube-side and shell-side dimensions have been specified, all data required for the calculation of the tube area have to be entered. For this the second value block in the KOND input / output mask is provided.

KOND input mask (geometry)

The tube sheet is generated for one shell-side pass automatically.

Usually, heat exchangers are designed based on fixed standard dimensions. This applies e.g. to the shell diameter, the tube pitch and tube dimensions, the type of the tube-side head and other values specified by a standard (e.g. TEMA).

Additionally, the tube-side and shell-side velocities have to be considered. The shell-side velocity and the TEMA standard determine the baffle pitch. The input of these values into the menu item ‘Basic data selection‘ of the ‘Basic input‘ menu leads to an exchanger designed according to industrial standards.

>> Immediately after specification of the thermal performance the calculation of the exchanger starts.

By default, KOND uses shells which are saved in the data base and can be selected in the ‘Selection of basic data’ form. If you want to use a shell differing from these default values, you need to deactivate the option ‘default values’ in the ‘Basic Input’ menu. Then you can enter the inside diameter of the shell.

The calculation ends as soon as the length of the exchanger is determined. This is the required length. A standard length (final length) has to be defined now. With this length the exchanger is calculated again and a new required length is determined. The difference between the two lengths shows the ‘reserve‘ of the design.

Usually, the difference between final size and required size is expressed by a ‘substitute fouling rate’. But this is not very specific.

The ‘length reserve‘ is directly proportional to the area and represents a tangible measure of the reserve.

After having entered the nozzle diameters on the cooling side the pressure drop of the cooling medium is calculated.

>> The pressure drop on the condensing side is not calculated.

The calculation can be directed by modification of the corresponding variables. The quality of the calculation can be enhanced e.g. by a ‘parameter study’ informing how the exchanger responds when the process parameters are modified.