Dynamic And Distributed Model Of Double-Tube Heat Exchanger And Fin-and-Tube Heat Exchanger

The conditions of heat exchangers are variable and unstable while the air-conditioner is in practical operation. In order to make the heat exchanger work under high efficiency, the dynamic characteristics of heat exchangers need to be discussed. The distributed dynamic models of two types of heat exchangers, double-tube heat exchanger and fin-and-tube heat exchanger, were established. The corresponding algorithms were also developed. Based on this purpose, the dissertation realized the following work.(1) A problem in the reported original algorithm of double-tube heat exchanger is firstly analyzed. The stability of the original algorithm relies on the first iterative value of pressure to much extent. Based on the analysis of the phenomenon that the original algorithm conduces to the instability of calculation, an improved dynamic distributed algorithm is developed. Before solving the flow rate field, the relation between the pressure and mass of phase-change fluid is adopted to determine an appropriate iterative value of pressure, which will improve the algorithm stability and broaden the algorithm applicability. The computing speeds of two algorithms are compared, which shows they have equivalent speed.(2) Generalize the improved algorithm of double-tube heat exchanger to fin-and-tube heat exchanger. The gravity effect, heat conduction, path branches and confluences were taken into consideration. Especially, a general stable model and corresponding algorithm for fin-and-tube heat exchanger were developed, and the different dry and wet conditions were discussed.(3) A direct mathematical representation, so-called Flow Path Array (FPA) method, was proposed. The new representation method is compared with the existing methods and shows its advantages in three aspects: a) description capability for the arbitrary tube circuitry; b) visual capability of the representation format; c) Compared with the existing methods, FPA can save more than 37%~80% memory space.(4) The dynamic simulation program of double-tube heat exchanger was validated with the experimental data in published documents. The relative error between simulated data and experimental data was less than 5%.(5) The validation experiment rig of fin-and-tube heat exchanger was built. Experiments were carried out for validating the dynamic simulation program of fin-and-tube heat exchanger. The results show that: a) the dynamic simulation program of fin-and-tube heat exchanger reflects the parameters along the flow direction well. b) The simulated transient process fits in the experimental one basically. But the errors still exists. The reason of errors and corresponding solutions were discussed.At the end of this dissertation, the author explains the main research shortcomings and the further research ideas in the field.