Well-stirred Furnace Model — Lesson 11

This lesson covers the analysis of furnace efficiency using different models. It starts with a review of the well stirred furnace model, which treats the entire furnace at a single temperature. The lesson then discusses the limitations of this model, such as the assumption of a gray gas and the neglect of convection. It also explains how the model can be extended to more complex situations using high-speed computers. The lesson then delves into the impact of ash deposits on furnace efficiency and how to account for this in the model. It concludes with a discussion on the need for more accurate input data for more precise furnace efficiency calculations. For instance, a real-world example of a coal-fired boiler is used to illustrate the application of these models.

Video Highlights

00:14 - Introduction to the well stirred furnace model and its assumptions.
13:38 - Explanation of the relationship between efficiency and firing rate for a large class of furnaces.
21:19 - Explanation of the impact of ash deposit on furnace performance and how to account for it in the model.
30:14 - Discussion on the need for a full 3D model for accurate information about the performance of the furnace.
52:43 - Explanation of the concept of mean beam length used to estimate the typical distance in a three-dimensional furnace for the calculation of emissivity.

Key Takeaways

- The well stirred furnace model is a simple analysis tool that provides insight into the major parameters affecting furnace efficiency.
- The model has limitations, such as the assumption of a gray gas and the neglect of convection.
- High-speed computers allow for more complex analysis, extending the model to more complicated situations.
- Ash deposits can significantly impact furnace efficiency, and this can be accounted for in the model.
- More accurate input data is needed for more precise furnace efficiency calculations.