The identification of the imperfection originating from finite-temperature-difference heat transfer is an indispensable step for both the performance analysis and the better design of a heat exchanger network （HEN） ...The identification of the imperfection originating from finite-temperature-difference heat transfer is an indispensable step for both the performance analysis and the better design of a heat exchanger network （HEN） with the aim of energy saving. This study develops a convenient area method for visualizing the heat-transfer imperfection of a HEN in terms of temperature-heat flow diagrams （ T-Q diagrams） by combining the composite curves that have already been used in pinch analysis and the re- cently developed entransy analysis. It is shown that the area between the hot and cold composite curves and the hot and cold utility lines on a T-Q diagram is just equal to the total entransy dissipation rate during the multi-stream heat transfer process occurred in a HEN, and this area can be used to graphically represent the total heat-transfer imperfection of the HEN. The increase in heat recovery or decrease in energy requirements with decreasing the minimum temperature difference, ATmin, of a HEN can then be attributed to a lower entransy dissipation rate, quantitatively represented by the decrease of the area between the composite curves and the utility lines. In addition, the differences between the T-Q diagram and the pre-existing energy level-enthalpy flow diagram （12-H diagram） in the roles of visualizing process imperfection and designing HENs are dis- cussed.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51206079,51356001)
文摘The identification of the imperfection originating from finite-temperature-difference heat transfer is an indispensable step for both the performance analysis and the better design of a heat exchanger network （HEN） with the aim of energy saving. This study develops a convenient area method for visualizing the heat-transfer imperfection of a HEN in terms of temperature-heat flow diagrams （ T-Q diagrams） by combining the composite curves that have already been used in pinch analysis and the re- cently developed entransy analysis. It is shown that the area between the hot and cold composite curves and the hot and cold utility lines on a T-Q diagram is just equal to the total entransy dissipation rate during the multi-stream heat transfer process occurred in a HEN, and this area can be used to graphically represent the total heat-transfer imperfection of the HEN. The increase in heat recovery or decrease in energy requirements with decreasing the minimum temperature difference, ATmin, of a HEN can then be attributed to a lower entransy dissipation rate, quantitatively represented by the decrease of the area between the composite curves and the utility lines. In addition, the differences between the T-Q diagram and the pre-existing energy level-enthalpy flow diagram （12-H diagram） in the roles of visualizing process imperfection and designing HENs are dis- cussed.
