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Thermal Energy Mixer

The thermal energy mixer mixes several thermal energy inlet streams to produce one thermal energy outlet stream.

A variable number of inlets can be specified. The outlet stream will contain a heat duty that matches the sum of the heat duties of the inlet streams.

Apart from a heat duty, thermal energy streams contain the limits between which the heat is produced (positive sign) or consumed (negative sign). As only the upper and lower temperature limits are available, the heat consumption vs temperature is assumed to be linear. Heat produced or consumed at a single temperature will have equal upper and lower limits.

If any of the temperature limits on the inlets is missing, the outlets will simply contain the minimum and maximum values of the temperature limits on the inlet streams (if all are missing, so are the limits on the outlet stream).

Heat curve

If all of the temperature limits on the inlets are available the heat curve will be constructed. The heat curve represents the heat available or produced versus the temperature. If the sum of the heats on the inlets is positive, the heat curve will start at 0 W at the lower temperature limit and will run up to the total heat produced at the higher temperature limit. If the sum of the heats on the inlet is negative, the heat curve will start at 0 W at the upper temperature limit and will run up to the total heat consumed at the lower temperature limit.

Example:

Feed stream 1 contains 100 kW of heat between 200 and 800 K. Feed stream 2 contains -140 kW of heat between 200 and 600 K. Feed stream 3 contains -40 kW of heat between 200 and 300 K. The total heat is negative; a total of -70 kW is consumed. The heat curve:

Cancellation of heat consumption and heat production

If at least one inlet contains a positive amount of heat, and at least one inlet contains a negative amount of heat, the heats of opposite sign are canceled out. That is: heat can transfer only from high to low temperature, so the heat that is consumed is subtracted from the produced heat at equal or higher temperature. If such heat is not available, the operation of the heat mixer is infeasible, and a warning is issued.

Example:

in the previous example 100 kW is produced between 200 and 800 K. At a temperature of 531.034 K the hot and cold heats cancel each other out. The corrected heat curve:

Here, the net heat consumption is still 70 kW, but the upper temperature limit has been adjusted reflected cancelling out the heat production.

Relinearization

If the operation of the heat mixer is feasible, the resulting curve may not be linear. However, the unit will produce upper and lower limits of the (corrected) heat curve. Optionally, an option can be selected in which the temperature limits are adjusted once more such that the resulting temperature limits can be assumed linear. That is, all heat produced or consumed will fall under a curve described by the linearized results. This of course requires lowering the temperature limits for heat production, or increasing the temperature limits for heat consumption (effectively making for 'less useful' heat). This operation is possible in a number of ways. The thermal energy mixer relinearizes the result by adjusting only the upper temperature limit for produced heat, or only the lower temperature limit for consumed heat.

Example:

The linearized curve shows encapsulates the corrected curve of the previous example:

To obtain this, the lower limit was increased, keeping the upper limit and the total consumed heat equal.

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