Heating/Cooling Curve for Heat Exchanger
For the heat exchanger, you can generate heating/cooling curves for both hot side and cold side streams. For both of these streams you can perform isothermal and fixed-enthalpy calculations. The temperature, pressure and enthalpy ranges are between the inlet and outlet stream conditions, which are retrieved by PRO/II automatically.
Note: For each heat exchanger entry in the Heating/Cooling Curve Main Window, PRO/II will perform only one type of calculation. If more than one type of curve is desired for the same unit, you will have to duplicate the exchanger entry in the main window and select one curve for each entry.
Usage
From the Heating/Cooling Curve Main Window, select the desired heat exchanger in the unit operations table. Push the corresponding Enter Data button to display this window.
Evaluation Condition
Isothermal Calculation
Select the first or third option to perform isothermal calculation for the hot and cold side streams, respectively. For both sides, the temperature and pressure ranges lie between the inlet and outlet stream conditions. In the case of multiple feed streams, the inlet temperature is taken to be the average inlet temperature and the pressure is taken to be the lowest feed stream pressure.
Fixed-Enthalpy Calculation
Select the second or fourth option to perform fixed-enthalpy calculations for the hot and cold side streams, respectively. For both streams, the enthalpy range is between the total inlet and outlet enthalpies. The pressure range is between the lowest feed stream pressure and outlet stream pressure.
If you want to override the default pressure range, enter the Starting and Ending Pressures for both calculation types. If you do not enter the starting pressure, by default, it is set to the unit inlet pressure and if you do not enter the ending pressure, by default, it is set to the unit outlet pressure. These pressure attributes can be defined too.
Select the number of isobars from the range of 0 to 12 to generate the heating/cooling curves at different fixed pressures.
The first evaluation point is at the inlet conditions. The total number of increments over the temperature and enthalpy ranges is equal to the value specified in the Number of Evaluation Points field minus one. The pressure increments are decided based on the number of isobars. If the number of isobars is
0, a linear pressure profile from starting pressure to ending pressure is considered for generating a single heating/cooling curve for each side of the heat exchanger.
1, heating/cooling curve is generated at a constant midpoint pressure, which is an average of starting and ending pressures.
2, heating/cooling curves are generated at the inlet pressure and outlet pressure.
3, heating/cooling curves are generated at the inlet pressure, outlet pressure, and midpoint pressure.
A value between 4 and 12, heating/cooling curves are generated at multiple pressure values. These pressure values are calculated by adding the following increment to the starting pressure: Increment = (Ending Pressure – Starting Pressure)/(Number of isobars - 1).
In all the above cases, if starting and ending pressures are not provided by the user, heat exchanger inlet (Merged feed) pressure and outlet (Merged product) pressure are considered.
Report Options
You can request the results printout to contain additional data such as Liquid Activity Coefficients, K-Values, etc., by selecting the appropriate options. These selections will apply only to the curve for which you are entering the evaluation data. The first of these options (liquid activity coefficients, etc.) will produce meaningful results only if a liquid-activity K-value method is chosen in the thermodynamic data section of input.
Number of Evaluation Points
The temperature, pressure and enthalpy ranges are divided equally into the number of evaluation points where the flash calculations are performed. The default value is eleven. Note that the first evaluation point is at the unit inlet conditions.
Related Topics