What describes the circulation of water within a sterling boiler?

In a Stirling boiler, the circulation of water is an essential function for effective thermal transfer and efficient operation. The correct description highlights that water enters the top rear drum and then passes down to the mud drum. This movement allows for the efficient collection of sediments and ensures that the water can absorb heat effectively while being heated to form steam.

The design of the Stirling boiler facilitates this specific flow pattern, enabling the water to circulate and maintain optimal conditions for steam generation. By entering from the top rear drum, the water benefits from the heat generated, and as it flows downward towards the mud drum, it maximizes the exposure to hot gases. This process is crucial for maintaining the continuous operation of the boiler, ensuring that the water is adequately heated and that the steam generation process remains effective.

In this context, the other options misrepresent the typical operational dynamics within a Stirling boiler. For example, the description of water circulating in a closed loop may suggest a system where no movement from one chamber to another occurs, which is not accurate for this boiler type. Additionally, the ideas of steam circulation or only steam movement do not capture the essential role that water plays in heat absorption and circulation in the system.