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 or condensing the medium, it is negative.

The heat duty is signed. When heating the medium it is positive, when cooling or condensing the medium, 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. The program does this exit or entrance region correction 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) dependent on temperature

© 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. For U-tubes, only the straight part of the tube is considered. The bend is not considered.

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 bending radius calculates the pass lane width:

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

The pass lane width is required for 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.

Number of tubes, which are flown-through. Blind tubes excluded.

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 first 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 first 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 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))

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 evaporation: Liquid fraction at outlet

Liquid fraction = 0 at total evaporation of the liquid.

For condensation: vapor fraction at outlet

Vapor fraction = 0 at total condensation of the vapor.

It is also possible to enter values greater than 0. For example: For evaporation, a liquid fraction of 0.2 at outlet means that 20% of the mass flow at outlet are still liquid or 80 wt.-% of the liquid is evaporated.

For evaporation: Liquid fraction at outlet

Liquid fraction = 0 at total evaporation of the liquid.

For condensation: vapor fraction at outlet

Vapor fraction = 0 at total condensation of the vapor.

It is also possible to enter values greater than 0. For example: For evaporation a liquid fraction of 0.2 at outlet means that 20% of the mass flow at outlet are still liquid or 80 wt.-% of the liquid is evaporated.

For condensation, this is the maximum velocity of the vapor at tube outlet.

Cross-flow velocity between two baffles.

No shell-side flow velocity will be calculated for shell-side evaporation.

The reference heat flux is the heat flux considered by the reference heat transfer coefficient.

Tube-side evaporation:  Heat transfer coefficients α₀ at tube-side evaporation

Shell-side evaporation:  Heat transfer coefficients α₀ at shell-side evaporation

The reference heat transfer coefficient is the heat transfer coefficient at reference heat flux, a pressure of 10% of the critical pressure and a roughness of the heating area of 1 µm.

Tube-side evaporation:  Heat transfer coefficients α₀ at tube-side evaporation

Shell-side evaporation:  Heat transfer coefficients α₀ at shell-side evaporation

The reference heat transfer coefficient can also be calculated with the HABA module. Select 'menu' - 'chapter' and double-click the HABA module in the alphabetical module list.

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 (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.

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 Basic data first.

Density r [kg/m³] at 20 °C

ã Springer-Verlag Berlin Heidelberg 2013

Specific heat capacity c in J/(kg·K) dependent on temperature