Experimental Study on the Effect of Air Intake on Temperature Distribution in the Combustion Chamber of a Fire-Tube Boiler with a Capacity of 100 kg/hour

Abstract

Mini fire-tube boilers with a capacity of 100 kg/h are widely used in small industries and MSMEs, yet their performance is often limited due to suboptimal furnace design and improper air supply settings. This study aims to analyze the effect of air inlet variations on temperature distribution and thermal efficiency in the furnace of a fire-tube boiler. The research was conducted experimentally using a modified energy losses in pipe apparatus as the controlled air supply system. Airflow velocities were varied from 3 to 17 m/s. Furnace temperatures were measured using Type-K thermocouples placed at five locations, and the data were analyzed through graphical comparison and temperature stability evaluation based on standard deviation. The results indicate that an airflow velocity of 11 m/s provides the best performance, achieving a thermal efficiency of 86% at 1 bar and producing a furnace temperature distribution of 720–760 °C with a ±12 °C deviation, demonstrating a more uniform heat distribution. Low airflow velocity (3 m/s) produced unstable temperatures (520–640 °C) due to incomplete combustion, while excessively high velocity (17 m/s) caused significant temperature reduction (580–610 °C) due to excessive cooling. The novelty of this study lies in determining the optimum air velocity based on furnace temperature stability rather than overall efficiency alone. This research contributes to the operational optimization of small-scale boilers to enhance performance and energy conservation. The limitation of this study is that burner configuration and furnace geometry were not varied.