What is required to lower the boiling point of the refrigerant in a lithium bromide refrigeration system?

To lower the boiling point of the refrigerant in a lithium bromide refrigeration system, creating an extremely high vacuum is essential. In refrigeration systems, the boiling point of a fluid is influenced by the surrounding pressure; lower pressure conditions lead to a decrease in the boiling point. By establishing a high vacuum, the pressure above the refrigerant is significantly reduced, enabling it to boil at a lower temperature. This principle is crucial for effective operation in absorption refrigeration systems like those utilizing lithium bromide, as it helps achieve efficient heat transfer and cooling performance.

The other options involve factors that don't directly lower the boiling point of the refrigerant. For instance, low ambient temperature may assist in improving the overall efficiency of the system, but it does not impact the boiling point directly through pressure adjustments. Increased pressure, on the other hand, would raise the boiling point of the refrigerant, which is contrary to what is needed for effective operation in such systems. Finally, introducing a mixture of two refrigerants does not inherently lower the boiling point of lithium bromide itself; it may alter the system's performance, but it doesn't fundamentally change the boiling point of the refrigerant involved.