Heat Transfer Through Jacket

Heat Transfer Through Jacket

Objective

The objective of this example is to analyze heat transfer in a pilot plant using simulation models. The first step is to use pilot plant data to calculate heat transfer parameters. The second part involves using simulation models to examine the trade-off between jacket parameters and heating times.

Process Description

Assumptions: The stirred tank is assumed to be perfectly mixed. The contributions of agitator work, heat loss to environment, and evaporation to the energy and mass balances are assumed to be negligible.

Variables and Parameters: , Mass of bulk liquid; , heat capacity; , Temperature of bulk liquid; , flow rate of heat transfer fluid in jacket; , heat capacity of heat transfer fluid in jacket; , jacket inlet temperature; , jacket outlet temperature, , overall heat transfer coefficient times area.

Balance Equations:

where,

Pilot Plant Data: The following data relating bulk liquid temperatures to the jacket temperature is available from pilot plant tests.

We want to use this information to determine the UA values for the stirred tank and to study the impact of jacket parameters on heating times.

Process Parameters

The process parameters and initial conditions for Example 1 are given in the table below.

(initial bulk liquid temperature)
27.2
C (heat capacity)
2.516
kJ/kg K (mass of bulk liquid in vessel)
329
kg (heat capacity)
1.65
kJ/kg K (initial guess)
257
W/K
Jacket flow rate
5
kg/s

Model Summary

DynoChem provides several utilities for characterizing vessels. These include a template for fitting heat transfer coefficients to test data. A customized template for this example is provided in the file TemplateFitUA.xls. The following information is entered under the Components tab, Process tab and Scenarios tab.

Components. Two components are defined for this example, the solvent in the vessel and the heat transfer fluid in the jacket.

Process Definition (Statements). The process statements define the bulk liquid phase and heat transfer with a jacket.

Scenarios (Initial Values and Parameters). The values from the table above are entered under the scenarios tab for the model. The pilot plant data is specified on the data sheet.

Fitting the UA Value to the Plant Data

The simulation runs below show the calculated temperature profile of the bulk liquid using various guessed values for the UA parameter. These trial runs show a mismatch with the experimental data.

DynoChem provides a fitting tool which uses least squares regression to fit simulation parameters to experimental data. The output from the fitting exercise is shown below. The UA value from the fitting tool can then be incorporated into the simulation tool and used for design exercises.

Scenarios

Once the heat transfer parameters have been determined the simulation model can be used to estimate the heating times for different values of the jacket temperature as shown by the plots below. Variations in other parameters such as the jacket flow rate can be studied in a similar manner.