List of variables

The boiling point is only relevant for the condensation side.

The boiling point is only relevant for the condensation side.

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

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

This is the total number of flown-through tubes without dummy tubes or tie-rods.

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).

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

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 class is determined by the inlet pressure.

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 class is determined by the inlet pressure.

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 class is determined by the inlet pressure.

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 class is determined by the inlet pressure.

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).

Theoretical heat exchanger area, which is required to transfer the demanded heat.

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

Theoretical bundle length, which is required to transfer the demanded heat.

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. 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.

Name of the exchanger type selected in the library

For condensation this is the maximum flow velocity of the steam.

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 see Variable 57 - Bundle-shell distance) 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 overdesign is the ratio of final heat transfer area and required heat transfer area in %.

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 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

Desired shell-side velocity

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

s. Variable 287 – Linear coefficient of thermal expansion of tube

Tube-side volume flow

For the cooling medium it is the volume flow at mean temperature of the medium (ϑ_e,i + ϑ_a,i )/2 and at tube-side inlet pressure P_i.

For superheated steam it is the volume flow at inlet of the condenser at inlet temperature ϑ_e,i and inlet pressure P_i.

You cannot enter the volume flow. It is calculated by the mass flow and the density of the medium and is only shown for documentation.

Shell-side volume flow

For the cooling medium it is the volume flow at mean temperature of the medium (ϑ_e,a + ϑ_a,a )/2 and at shell-side inlet pressure P_a.

For superheated steam it is the volume flow at inlet of the condenser at inlet temperature ϑ_e,a  and inlet pressure P_a.

You cannot enter the volume flow. It is calculated by the mass flow and the density of the medium and is only shown for documentation.