Introduction

The AC program is a package of modules that provides thermal and hydraulic calculation of cross-flow heat exchangers with bare or finned tubes.

The following heat exchanging processes can be calculated with the standard version and the
extensions (*):

·    Heating of air or gases using for example saturated steam

·    Cooling of air or gases using for example brine, water, cooling gas, air or refrigerants

·    Cooling of any medium using gases or liquids

·    Heating or cooling of pools (without a stirrer) or rooms with natural convection (*)

·    Evaporation and condensation of pure substances in the tubes

·    Condensation of pure substances around the tubes

(*) additional modules not included in the standard version

The heat exchanger is assumed to be rectangular bundle of circular or oval tubes with selectable tube pitch and arrangement. The number of passes is specified by the user.

On the tube outside tube bundles of bare tubes, circular fins, corrugated spiral fins, rectangular fins (*) or fin-and-tube plate type can be specified.

On the tube inside the user can select bare tubes, internally finned tubes (*), corrugated tubes (*) or tubes with an internal spiral band (*).

For the shell there are also multiple options in AC:

·          single-pass rectangular shell (register)

·          multi-pass rectangular shell

·          single-pass or multi-pass cylindrical shells (*)

·          no shell at all (convector) (*)

(*) additional modules not included in the standard version

The calculation of single-phase cases is based on the theory presented the VDI Heat Atlas.

When cooling down air or humid gases, condensation of the humid part at the cold wall is considered. The thermal transfer is calculated by using the method of [1] page 108. The amount of water or the humidity is calculated as well. If the wall temperature is below zero or if there is a huge amount of condensed water the program displays warnings.

The calculation of evaporation processes of pure substances is performed according to the VDI Heat Atlas.

[1] Verfahrenstechnische Berechnungsmethoden, part 1, VCH Weinheim

Additionally required calculation methods have been taken from the relevant literature.

The calculation of the pressure drop inside or outside of the tubes is based on the theoretical fundamentals of the VDI Heat Atlas.

The fundamentals for calculation of other heat processes have been taken from the relevant literature.

The program provides several media for which the physical properties can be determined automatically. These media include humid air, flue gas, a common cooling gas (H2N2), refrigerants and water. Property modules specially designed for the user can be integrated into the program. As a matter of principle, this applies also to condensable media. Other media, which are not subject to a phase change, may be specified by the user by entering the required properties.

The material data generator module PROPER can be purchased separately. It provides all physical properties for more than 800 pure substances or user-defined mixtures automatically, both single-phase and two-phase.

The program can draw a true to scale sketch of the tube sheet. The flow direction is presented in two different colors.

The additional option ‘Natural convection ACK’ (not included in the standard package) lets you simulate the behavior of an air cooler while the fans do not move. Therefore, the upward stream of the hot tube bundle is determined and the possible cooling performance and the outlet temperatures of the medium are calculated.