List of variables

For condensation this is the volume flow at the heat exchanger inlet. If there is a fraction of the vapor already condensed (vapor fraction x_i < 1) at the inlet, the volume flow of the vapor-liquid mixture is shown, assuming a homogeneous distribution of liquid and vapor.

For condensation this is the volume flow at the heat exchanger inlet. If there is a fraction of the vapor already condensed (vapor fraction x_i < 1) at the inlet, the volume flow of the vapor-liquid mixture is shown, assuming a homogeneous distribution of liquid and vapor.

The heat duty is signed. When heating the medium it is positive, when cooling the medium or at condensation it is negative.

The heat duty is signed. When heating the medium it is positive, when cooling the medium or at condensation it is negative.

Heat loss of heat exchanger to the surroundings

The heat loss is signed:

( - ) Heat emission from shell to surroundings

( + ) Heat absorption from surroundings

Tube-side heat transfer coefficient for condensing a pure substance

When condensing pure vapors, the tube-side heat transfer coefficient depends, inter alia, on the flow pattern, the film thickness and the value of the vapor shear stress. These parameters are changing along the condensation path and the heat transfer coefficient decreases.

For condensation, we divide the heat exchanger into 10 sections, where 10% of the total amount of vapor are condensing in each section. For every section, the heat transfer coefficient and the required area for condensation are calculated. The value stated in the input mask is the area standardized heat transfer coefficient of the 10 sections.

The standardization is done by the program internally and is not presented in the input mask.

Shell-side heat transfer coefficient for single-phase media in shell-and-tube heat exchangers with segmental baffles (liquids and gases)

The shell-side heat transfer coefficient of a shell and tube heat exchanger with segmental baffles for single-phase media is calculated by means of using the velocity of the medium between two adjacent baffles.

As the distance between the tube sheet and the first baffle (inlet baffle spacing), determined by the size of the nozzle amongst other things, often is greater than the central baffle spacing, the heat transfer coefficient of the entry or exit regions is smaller than the one between the central baffles.

This is taken into account for calculating the mean heat transfer coefficient. This exit or entrance region correction is done by the program internally and you cannot see it in the input mask.

When condensing or evaporating, there is no correction of the heat transfer coefficient based on the entrance or exit region.

Thermal conductivity l in W/(m·K) depending on temperature

Density r [10³ kg/m³] at 20°C

© Springer Verlag Berlin Heidelberg 2013

Description:

Details: Total fouling resistance (shell-side f_a and tube-side f_i)

                   f = f_a+ f_i ·(A_a/A_i)

s. Typical fouling resistances

Theoretical heat exchanger area, which is necessary to transfer the heat duty

Logarithmic mean temperature difference for true counter current flow

Mean temperature of tube-side medium (Inlet temperature + outlet temperature) / 2

Mean temperature of shell-side medium (Inlet temperature + outlet temperature) / 2

For condensation only: Vapor fraction = 1 for pure vapor at inlet.

It is possible to enter values lesser than 1. For example vapor fraction = 0.6 means that 60 wt-% of the medium are in the vapor state and 40 wt-% are already liquid at inlet.

For condensation only: Vapor fraction = 1 for pure vapor at inlet.

It is possible to enter values lesser than 1. For example vapor fraction = 0.6 means that 60 wt-% of the medium are in the vapor state and 40 wt-% are already liquid at inlet.

Absolute pressure of the medium at the inlet of the heat exchanger / tube-side

Absolute pressure of the medium at the inlet of the heat exchanger / shell-side

Distance of tube center to tube center of two adjacent tubes in one row

Distance between two tube rows in flow direction

Clearance of tubes of two tube passes. The pass lane width is calculated by the bending radius:

Pass lane width = 2 · bending radius - tube outside diameter.

The pass lane width is required for 2 and more tube side passes

Theoretical bundle length, which is required for the heat duty demanded. For more heat exchangers in series this is the length of one exchanger.

For condensation this is the maximum velocity of the vapor at tube inlet. When calculating the maximum velocity it is taken into account that the medium might be two-phase (Vapor fraction in x_i < 1).

Number of tube-side passes and tubesheet type number

Ratio of the segment opening height to shell inside diameter in percent

Baffle cut should be 15% to 40% of inside diameter of shell

Distance between the outer tube in the tube-sheet and the shell

Minimum spacing should not be closer than 0.2 of shell ID or 50 mm, which is greater.

Maximum spacing should not be greater than shell ID due to possible tube vibrations.

Inlet baffle spacing is always the same as outlet baffle spacing.

The distance between tube sheet and 1^st baffle is always set greater or equal the spacing of baffles.

When you enter the diameter of shell-side nozzles and the distance between tube sheet and 1^st baffle is smaller than the nozzle diameter, the distance between tube sheet and 1^st baffle is always set greater than the nozzle diameter plus a run-out length depending on the nozzle diameters. This is to avoid having the 1^st baffle below the nozzle.

The final length between the tube sheets. For U-tube heat exchangers, only the straight tube length is considered. The bends are not taken into account.

For more than one exchanger in series, it is the bundle length of one heat exchanger

Total tube-side pressure drop (Pressure drop inlet and outlet nozzle, pressure drop inlet and outlet tubes, friction pressure drop)

For more heat exchangers in series, this is the total pressure drop of all heat exchangers.

Total shell-side pressure drop (Pressure drop inlet and outlet nozzle, pressure drop inlet and outlet tubes, friction pressure drop)

For more heat exchangers in series, this is the total pressure drop of all heat exchangers.
For shell-side condensation, no pressure drop is calculated!

If a nozzle has been selected by nominal width DN, the inside diameter is automatically determined by the class taken from the flange standards. The inlet pressure determines the class.

If a nozzle has been selected by nominal width DN, the inside diameter is automatically determined by the class taken from the flange standards. The inlet pressure determines the class.

If a nozzle has been selected by nominal width DN, the inside diameter is automatically determined by the class taken from the flange standards. The inlet pressure determines the class.

If a nozzle has been selected by nominal width DN, the inside diameter is automatically determined by the class taken from the flange standards. The inlet pressure determines the class.

Correction factor for logarithmic mean temperature difference LMTD. It considers the deviation of the real heat exchanger from the ideal mere counter-current or co-current heat exchanger (Variable 22 - Logarithmic mean temperature difference (LMTD))

If more heat exchangers in series are used, the required bundle length is the length of one heat exchanger while the final heat transfer area is the area of all exchangers in series. The calculated pressure drops are the total pressure drops of all heat exchangers.

s. Typical fouling resistances

s. Typical fouling resistances

Cross flow velocity of medium between the baffles

For condensation, this is the maximum velocity of the vapor. When calculating the maximum velocity, it is taken into account that the medium might be two-phase (Vapor fraction in x_i < 1).

For U-tube heat exchangers, only the straight tube length is considered for calculating the heat transfer area. The bends are not taken into account.

For more than one exchanger in series, it is the total transfer area of all exchangers in series

Minimum distance between the outer tube in the tube sheet and the shell, which is not underrun during calculation of the tube sheet. You may overwrite this value at any time.

The value is set when selecting a tube in the form 'Selection of basic data' (see online help 'tube dimensions'). For the actual bundle-shell distance see Variable 57 - Bundle-shell distance.

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.

When you are designing a shell-and-tube heat exchanger with floating head, there might occur a wide clearance without any tubes between the most outer tubes and the shell (bundle-shell clearance variable 57) due to the construction principle. The bypass flow passing this clearance is not participating in the heat transfer. That's why you place one or more pairs of sealing strips between the edges of the baffles (cross flow zone) to direct the flow back into the bundle. These sealing strips are always placed oppositely in pairs in the bundle.

Sealing strips are not necessary in kettle reboilers and in the case of isothermal condensation.

The fin pitch is the distance of two adjacent fins from fin center to fin center.

Only for internally finned tubes

Only for internally finned tubes

Only for internally finned tubes

Only for internally finned tubes

If the heat exchanger is over-designed or under-designed, this is the real inlet temperature of the tube-side medium.

For condensation, this temperature is not calculated.

If the heat exchanger is over-designed or under-designed, this is the real inlet temperature of the shell-side medium.

For condensation, this temperature is not calculated.

Velocity of medium in the baffle opening (longitudinal flow velocity).

For condensation, this is the maximum velocity of the vapor at the first window. When calculating the maximum velocity, it is taken into account that the medium might be two-phase (Vapor fraction in x_i < 1).

Only for gases: Standard density of shell-side medium at 0 °C and 1.01325 bar

For liquids: No input possible

Only for gases: Standard density of shell-side medium at 0 °C and 1.01325 bar

For liquids: No input possible

Only for gases: Standard density of shell-side medium at 0 °C and 1.01325 bar

For liquids: No input possible

Only for gases: Standard density of shell-side medium at 0 °C and 1.01325 bar

For liquids: No input possible

Name of heat exchanger type selected in tube sheet library

The overdesign is the ratio of final heat transfer area and required heat transfer area in %.

If the heat exchanger is over-designed or under-designed, this is the real outlet temperature of the tube side medium.

For condensation, this temperature is not calculated.

If the heat exchanger is over-designed or under-designed, this is the real outlet temperature of the shell side medium.

For condensation, this temperature is not calculated.

For condensation only:

The vapor fraction equals 0 if the steam is totally condensed. It is possible to enter values greater than 0. For example: Vapor fraction = 0.2, means that 20% of the mass flow is still in the vapor state at the outlet.

For condensation only:

The vapor fraction equals 0 if the steam is totally condensed. It is possible to enter values greater than 0. For example: Vapor fraction = 0.2, means that 20% of the mass flow is still in the vapor state at the outlet.

To avoid damage of the tubes under the inlet nozzle, e.g. by erosion, the product ρ · v² (density and squared velocity) should not exceed some maximum values.

Without impingement plate:

Non-erosive and non-corrosive single-phase media: ρ · v² < 2250

All other liquids and liquids at boiling temperature: ρ · v² < 750

With impingement plate: ρ · v² < 6000

See also 'Desired shell-side velocity'

Tube pattern in the shell

The Re number describes the flow pattern

Re < 2300: Laminar Flow

Re > 10000: Turbulent Flow

2300 < Re < 10000: Transitional area from laminar to turbulent flow

Average linear thermal expansion coefficient β between 20°C and the temperature γ in 10^-6/K