Cooler

Inputs

• Heat to Sink: If selected, use the unit connected via a heat flow as a sink, and transfer as much heat as possible to that unit.
• Heat Duty: Negative heat duty for the amount of energy removed.
• Outlet Temperature: Alternative specification for target outlet temperature.
• Pressure Drop: Optional pressure drop across the cooler (must be ≥ 0).

Use only one of Heat to Sink, Heat Duty or Outlet Temperature, not several.

Outputs

• Heat duty or outlet temperature (matching the chosen specification) together with the cooled outlet stream.

Warnings

• Wrong sign: If the specified outlet temperature of the cooler is higher than the computed inlet temperature.

Details

This unit can connect to other units via a heat flow. This unit can also act as proxy for a more complicated cooling process that either requires or can deliver work.

Heat integration

This unit can act as a heat source for other units. This can be done in one of two ways:

• If either Heat Duty or Outlet Temperature specification is used, the amount of heat removed in the Cooler is fully specified.

  • A unit connected to the Cooler via a heat flow can select the Heat from Source option.
  • The heat source capacity is then given by the Cooler conditions, and the other unit will attempt to absorb all heat removed in the Cooler.
  • The heat sink capacity will be capped by the computed outlet temperature of the other unit. The outlet temperature from the unit recieving heat can never be higher than the inlet temperature of the cooler.

• If the Heat to Sink option is selected on the Cooler

  • A unit connected to the Cooler via a heat flow can act as a heat sink for the Cooler.
  • The Cooler will attempt to supply all heat consumed by the connected unit.
  • The heat source capacity will then be capped by the computed outlet-temperature of the Cooler. The outlet temperature of the Cooler can never be lower than the temperature of the heat sink.

Work calculation

Any real cooling process will eventually need to dump the heat removed from from the process stream to the environment. This can occur in many ways, but the fact remains that energy removed from the process somehow must make its way to the surroundings. A complicated cooling process can be modeled explicitly, but the Cooler unit can also be used as a proxy for an arbitrarily complicated cooling process.

The options for how this cooling process should be modeled can be selected through the Work Calculation setting on the cooler. The options are

• None (default): Do not model a complete cooling process.
  • When this option is selected, added work is set to zero, and the heat from the cooler is simply treated as "removed from the system". This option will strictly speaking be non-physical if the cooler is operating at a temperature lower than the ambient, since in this case the Second Law requires a positive work input. If you want to do exergy analysis, consider choosing one of the other options.
• No work output (consistent): Do not allow the model to produce work output.
  • This option is useful if an ideal/non-ideal cycle would otherwise predict work recovery (negative work) when removing heat at conditions where work could, in principle, be extracted.
  • The computed work is clamped to be non-negative (never a work output). When work input is required, it is computed using a specified COP or exergy efficiency (as for Non-ideal cycles).
• Ideal cycle: Model the Cooler as an ideal heat pump working against the ambient. The work will then have the same magnitude as the exergy of the heat flow.
  • See below for details
• Non-ideal cycle: Model the cooler as a real cooling cycle with a specified COP (coefficient of performance).
  • See below for details

A schematic of an arbitrary cooling process represented by the cooler is illustrated in the figure below.

The output computed for a Cooler when a process is solved is

• Total heat removed: The heat removed from the process stream. This equals the difference in enthalpy flow between output and input stream.
• Heat to Sink (optional): If a heat sink is connected to the cooler, this value is the amount of heat the sink is capable of absorbing without violating the second law.
• Cooling utility: The amount of heat that is not dumped to another process unit via a heat flow, and therefore must be moved to the ambient.
• Total work input: The required input to the hypothetical process that moves the heat to the ambient.
  • For Non-ideal cycles, this is given by COP $= Q / W$, where $Q$ is the Cooling utility (> 0).
  • For Ideal cycles, the work requirement is computed from the entropy balance.
• Total heat input: The heat added to the hypothetical cooling cycle (< 0) from the surroundings.

When the "None" option is selected for "Work calculation", the work input is set to zero, and Total heat input = - (Cooling utility).