Factors influencing the precision of optimizing the values of definite scalar quantities according to the accepted criteria used in designing heat exchangers

The paper outlines the essential factors influencing the precision of optimizing the values of definite scalar quantities according to the criteria that are used in designing heat exchangers. The paper refers to the method of designing heat exchangers of technical power systems in view of the required reliability of these systems described in the work [1]. Optimization is used for the velocity values of the flow of definite fluids through the heat exchanger and for the cooling fluid temperature T2’’ at the output of the definite heat exchanger, as they occur in significant relationships with definite scalar quantities in designing heat exchangers. The paper emphasizes divergences in the results of calculations of the above mentioned optimized values of definite scalar quantities on the example of designing a shell and tube condenser of marine steam turbine. The criterion of optimizing the values of definite scalar quantities is the minimum of total costs min Σ n i=1 Ki τ in the time τ. The time is the set value τ z and constitutes the period, in which the optimization is considered. The paper presents the following factors: time assumption τ z of the period, in which optimization is considered, price assumption of electrical energy KCe consumed in order to pump the cooling water in time τ z, assumption of the values of efficiency τ p of the pump of the cooling water in time τ z, assumption of the values of the friction factor λ str2 of the inside surfaces of the condenser tube in time τ z, at the cooling water flow, the selection of a model of the function determining the Nusselt number Nu2 from the set of models that can be used in a given designing case, price assumption (the selection of a manufacturer) of heat exchanger area KCA of a shell and tube condenser, assumption of the forecasted thickness δos2 of fouling on the heat exchanger area from the side of the flow of the condenser cooling water in time τ z. Finally, the conclusions resulting from the paper’s contents are presented.