Improvement of Dynamic Modelling for Single-phase Heated Tubes

Wuhan Second Ship Design and Research Institute, 430205 Wuhan, China

^* Corresponding author: shunli878@163.com

Abstract

To improve the currently available multi-segment lumped parameter models, a new dynamic mathematic model for single-phase heated tubes is established by employing dynamic equations instead of the traditional static equations for calculating the heat transfer across the control volume’s tube wall. Through separating the temporal and spatial terms of the partial differential equations, and combining both lumped and analytical methods, an analytical solution for the temperature distribution of the steam and water in the tubes is derived. Then, by integrating the elemental volume equations, dynamic equations for the heat release of the tube wall are achieved. The improved model, which can be explicitly solved, is more stable and has much wider applicability. After applying the improved model to an ultra-supercritical boiler superheater, the results show that the response characteristics for inlet temperature step change are significantly improved, and the results during the puredelay periods are in accordance with those of the distributed parameter models. Compared with traditional multi-segment models, the improved model can achieve higher precision even with less segments. Besides, the transport delay characteristics of water or steam within tubes can be analyzedmore accurately with the improved model.