What device is often used to prevent bubbles in the fuel when atmospheric pressure is lower than fuel vapor pressure?

The correct answer is fuel flow meters. While fuel flow meters play an important role in measuring the amount of fuel flowing through the system, their primary purpose is not to prevent bubbles in the fuel caused by atmospheric pressure being lower than fuel vapor pressure.

In aircraft fuel systems, the prevention of fuel vaporization and associated bubbling is typically managed by other devices—namely, boost pumps. Boost pumps are used to ensure that fuel is delivered to the engine at an adequate pressure, especially when conditions could lead to vapor formation, such as low atmospheric pressure situations. They maintain positive pressure in the fuel lines, which helps prevent the fuel from boiling and turning into vapor. This action minimizes the risk of vapor lock, ensuring consistent fuel delivery to the engine.

In summary, while fuel flow meters measure fuel flow, it is the boost pumps that are specifically designed to prevent bubbles and keep the fuel system operating normally under varying atmospheric conditions.