In an absorption chiller where steam or hot water is the energy source, the pressure difference is produced using what type of solution?

In an absorption chiller that utilizes steam or hot water as its energy source, the pressure difference needed for the refrigeration cycle is primarily produced using a lithium bromide solution. Lithium bromide serves as the absorbent in this type of system, effectively absorbing the refrigerant vapor (typically water vapor). The concentration of the lithium bromide solution influences the pressure and, consequently, the performance of the absorption cycle.

When heat is applied, the lithium bromide solution absorbs water vapor which generates a low-pressure environment in the evaporator. This low pressure allows the refrigerant (water) to evaporate from a liquid to a vapor at a low temperature, which is essential for the cooling process. The cycle then completes as the vapor is absorbed back into the lithium bromide solution, releasing heat in the process and allowing for continuous operation of the chiller.

In contrast, aqueous ammonia is primarily used in ammonia absorption chillers, propylene glycol is typically used as an antifreeze solution in various heating and cooling applications, and calcium chloride is not commonly used in absorption chillers for generating pressure differences. Hence, lithium bromide is the correct answer here, as it specifically plays the key role in the absorption process within the absorption chiller.