Cooling Principle of Mobile Air Conditioner in Toilets

The cooling principle of mobile air conditioners is based on the vapor compression cycle, achieving indoor cooling through heat transfer. Its core processes include heat absorption, compression, heat rejection, and throttling in four steps.

1. Heat Absorption Process
   When the low-temperature, low-pressure liquid refrigerant flows through the evaporator, the evaporator fins draw in indoor air via a fan and blow it over their surface. The heat in the air is absorbed by the refrigerant, causing it to evaporate into a low-temperature, low-pressure gas. Simultaneously, the cooled air is blown back into the room. This process transfers heat from the indoor air to the refrigerant and marks the starting point of the cooling cycle.

2. Compression Process
   The low-temperature, low-pressure gaseous refrigerant is drawn into and compressed by the compressor, causing its pressure and temperature to rise sharply and transforming it into a high-temperature, high-pressure gas. The compression process provides the refrigerant with the energy needed for subsequent heat rejection and ensures efficient heat release.

3. Heat Rejection Process
   After the high-temperature, high-pressure gaseous refrigerant enters the condenser, the condenser fan forces air in through the heat rejection tubes (single-tube designs draw in indoor air, while dual-tube designs draw in outdoor air) to dissipate heat from the condenser. The refrigerant releases heat and liquefies into a high-pressure liquid. The heated air is then expelled outdoors through the heat rejection tubes. If heat cannot be effectively rejected (e.g., due to blocked heat rejection tubes or design flaws), it can lead to 'heat internal circulation,' causing the indoor temperature to rise instead of fall.

4. Throttling Process
   When the high-pressure liquid refrigerant flows through the throttling device (e.g., a capillary tube), its pressure and temperature drop sharply, reverting it to a low-temperature, low-pressure liquid. It then flows into the evaporator to begin the next cycle. The throttling process controls the refrigerant flow rate, maintaining the low-temperature, low-pressure state inside the evaporator and ensuring efficient heat absorption.

The cooling effectiveness of mobile air conditioners is limited by the design of the exhaust duct. Single-duct exhaust models expel hot air, creating negative pressure indoors and causing outdoor hot air to infiltrate through gaps in doors and windows, reducing cooling efficiency. Dual-duct models can mitigate negative pressure effects but are more complex to install. Additionally, the length and degree of bending of the exhaust duct directly affect heat dissipation efficiency—longer ducts or excessive bends increase exhaust resistance, preventing timely heat rejection. Therefore, selecting an appropriate exhaust duct length, minimizing bends, and ensuring the heat rejection tube leads outdoors are key to improving the cooling performance of mobile air conditioners.