A Decision-Analytic Model for the Bi-Objective Sizing of Heat Exchangers Under Uncertainty

The aim of this work is to show that the preliminary sizing of process equipment, which is done relying on ranges of typical values of several key parameters, can be conveniently approached as a bi-objective “basic risky decision under uncertainty” problem from Decision Analysis.

In the early stages of chemical process design, equipment sizing is done without knowing the exact value of several key process parameters. This is the case of heat exchangers, as convective heat transfer coefficients are highly sensitive to temperature, pressure, and flow conditions, which will be known with certainty only after the equipment enters operation.

This work shows how heat exchanger sizing with uncertain information can be modelled as a decision-making problem under uncertainty, from a decision-analytic point of view.

The decision model consists of a factual model that produces the probability distribution of the consequences (quality of outlet temperature control and equipment cost) for the alternatives, and a value model, which provides a quantitative metric for the consequences' desirability.

The results are presented as a chart showing the recommended design given the decision-maker´s relative strength of preference between equipment performance and cost.

Chemical process equipment design depends on physical parameters, some of which are not precisely known at the initial project stages. In said situations, equipment sizing can be stated as a decision-making problem under uncertainty and approached using Decision Analysis, as shown in this paper for the design of heat exchangers.