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Unformatted text preview: Heat Exchanger Functions Examples from HDA of Toluene Simulation of counter current heat transfer in exchanges is very straightforward, but a number of special cases may require special functions to handle them. The following Matlab functions have been used for several years in CENG 403: Program Simulates Assumptions htxcc1 Counter (or co-) current heat exchanger. Constant flow*specific heat for each fluid, constant U and A. htxcc2 Constant temperature on one side of exchanger. Constant flow*specific heat for one fluid, constant U and A. htxcc3 Similar to htxcc1 , but the arguments are different. Constant flow*specific heat for each fluid, constant U and A. htx2tub Two pass counter current heat exchanger. Constant flow*specific heat for each fluid, constant U and A. The restriction to fluids with constant flow*heat capacity could be interpreted to mean that those programs cannot be used if there is a change of state of the fluid. In a strict sense that is true, but we can get reasonable approximations by ignoring that restriction in some cases. None of the programs listed in the table require compound data to be used, but we will see that in most our examples, it is convenient to load a data file so we can get reasonable heat capacity data. htxcc1 Counter (or co-) current heat exchanger. Constant flow*specific heat for each fluid, constant U and A Example 1: Heating the HDA Reactor Streams Using HTXCC1 The effluent from the reactor in HDA process needed to be cooled before it could be sent to a flash unit. It appeared as stream 1 in the section on flash units. Inlet | Outlet Stream 1 | 2 3 Total Tmp K 929.00 | 300.00 300.00 State vapor | vapor liquid Enthalpy -50020930.3 | -176426148.5 7900057.8 -168526090.7 Compound Stream Flows toluene 28631.5 | 1039.2 27592.3 28631.5 hydrogen 795956.6 | 795431.9 524.7 795956.6 benzene 150568.2 | 16569.3 133998.8 150568.2 methane 2387533.0 | 2378826.1 8706.9 2387533.0 biphenyl 5726.3 | 0.2 5726.1 5726.3 Total 3368415.7 | 3191866.8 176548.9 3368415.7 The two heat exchanger functions htxcc1 and htxcc3 simulate the same system. It is shown below: We will reproduce the process stream shown in the table, but make a data file that includes water since that is probably what will be used to do at least part of the cooling. The "help" comments for the first heat exchanger function shows: >> help htxcc1 Htxcc1 - simple counter current heat exchanger function [Q,To0,A]=htxcc1(Ti0,TiL,ToL,Fcpi,Fcpo,U,... dTmin,nplt) Counter Current Heat Exchanger Argument List Ti0 Inlet temperature of inner fluid TiL Exit temperature of inner fluid ToL Inlet Temperature of outer fluid Fcpi Flow*heat capacity of inner fluid Fcpo Flow*heat capacity of outer fluid U Overall Heat Transfer coefficient dTmin Minimum approach temperature Return List Q Heat Transfer Rate from outer to inner fluid To0 Exit Temperature of outer fluid A Required Heat Transfer Area nplt If given is the number of points to plot Example: >> [Qx,TAout,Area]=htxcc1(60,150,160,25,35,50,10,20)...
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This note was uploaded on 09/02/2011 for the course CHEM 102 taught by Professor Kmn during the Spring '11 term at Babson College.
- Spring '11