Abstract
A non-linear multi-cell network model is developed and methods of digital simulation are outlined. Experimental steady state and transient response data for open and closed loop operation of an industrial typo, of finned tube steam heat exchanger have been analyzed. Specification of the network resistance parameters has been made on the basis of matching steady state conditions. The use of steam flow rate as an input forcing function for the model was made possible by including vapor flow from cell to cell in proportion to pressure difference between cells. The open loop dynamic response characteristics of the heat exchanger with step changes in coolant flow and steam flow were compared with the model responses. This allowed the specification of an effective capacitance term for the variation of condensate holdup with steam flow. The model is of general utility because steam flow can be used as the manipulated variable for closed loop control studies. Most previous studies considered the forcing function to be a change in uniform steam temperature. The control of the outlet coolant temperature by manipulation of the steam flow rate was investigated for changes in set point and coolant flow rate. The calculated responses of the model were experimentally verified. Two modes of regulating the mid-point steam temperature were studied. In one case, in a effort to produce a fairly constant mid-point steam temperature with respect to time for changes in coolant flow rate, the control loop was closed upon the steam flow control valve. The other case involved the operational mode of a condenser with the coolant flow rate as the manipulated variable. Dynamic responses were compared for step changes in set point of the midpoint steam temperature and, also, for a load change in the steam flow rate. For the closed loop responses, the inclusion of the condensate holdup as a function of the steam flow rate in the model gave superior agreement with experimental data. In general, the complete model with the specified parameters does a good job of predicting the experimental responses under the variety of conditions that are noted above.
Ruedrich, Randolph Albert (1970). Dynamics of a steam heated finned tube heat exchanger with temperature and flow variations. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -179584.