Performance Analysis and Optimal Design of Heat Exchangers and Heat Exchanger Networks
Abstract: This thesis presents a study on performance analysis and optimal design of heat exchangers and heat exchanger networks. The study includes an experimental investigation of steam condensation in plate heat exchangers, optimal design of plate heat exchangers and plate-fin heat exchangers, and optimization of heat exchanger networks. In the experimental investigation of steam condensation in plate heat exchangers, seven different plate heat exchangers were tested. Based on the experimental data, correlations for predicting heat transfer coefficients and pressure drops have been obtained with satisfactory accuracy. In addition, a calculation procedure in a stepwise fashion for two-phase applications has been developed. A thermal-hydraulic model for plate heat exchangers has been derived. It represents the relationship between heat transfer, pressure drop and exchanger area, and gives the possibility to predict heat transfer coefficients from pressure drops. It is used in the optimal design of plate heat exchangers as well as the optimization of heat exchanger networks using the pinch technology. In all these designs, the plate pattern is optimized for the most common chevron-type plate heat exchangers. Both multi-stream plate heat exchangers and multi-stream plate-fin heat exchangers have been considered. They are important in the optimization of heat exchanger networks because they can reduce both cost and complexity of the network. A design methodology for multi-stream plate-fin heat exchangers has been developed, and the thermal performance of different multi-stream plate heat exchangers has been analyzed and compared. In the investigation of flexibility analysis for heat exchanger networks, the detailed simulation is employed to obtain the steady responses to the disturbances of supply temperatures, flow rates, fouling, etc. The possible candidates for canceling out the disturbance influences are provided through “downstream paths” analysis. Less surface margin, corresponding to less conservative fouling factors, is also studied. This is achieved through trade-off optimization. A case study was conducted at a Swedish pulp and paper mill, Stora Enso Fine Paper at Nymölla. The studied design methods were applied to a heat recovery system at the mill. It was found that the current situation is not energy-efficient, and significant improvement can be achieved through some retrofit measures with a short payback period. In addition, the flexibility analysis shows that up to 12.6% of the total heat transfer surface can be saved due to less conservative fouling factors.
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