Features
The heat and moisture exchange of the condenser is between the temperature difference and humidity difference between the main air and the boundary layer air adhering to the exterior surface of the heat exchanger.Vapor PressureIt operates under adverse conditions. It can achieve two air treatment processes: a dehumidification cooling process, also known as a wet cooling process (wet condition), occurs when the air temperature in the boundary layer is below the dew point temperature of the main air; an isothermal cooling process (dry condition) occurs when the air temperature in the boundary layer is lower than that of the main air but still above its dew point temperature.
During the dehumidification cooling process, not only is there a temperature difference between the boundary layer air and the bulk air, but also a difference in vapor pressure. Therefore, heat exchange occurs not only in the form of sensible heat exchange but also latent heat exchange associated with moisture exchange across the heat exchanger surface. Consequently, under wet conditions, the surface cooler has a greater heat exchange capacity compared to dry conditions. Alternatively, for the same surface cooler, when the dry bulb temperature of the air and the water temperature are kept constant, the higher the wet bulb temperature of the air, the greater the cooling and dehumidification capacity of the cooler.
Thermal Calculation
The air cooler is primarily used for air cooling and dehumidification, resulting in changes in both air temperature and humidity.
1. Heat Exchanger Efficiency of the Condenser
Full Heat Exchange EfficiencyIn the formula:—Dry bulb temperature of air before and after treatment, ℃;Cold water temperature, ℃.
(2) General Heat Exchange Efficiencyt3—Ideal air temperature after treatment, °C.
2. Heat Exchanger Thermodynamic Calculation Type
There are two types: one is design-oriented, commonly used for selecting fixed-type air coolers to meet known initial and final air parameters.
Processing requirements; The other is a verification type, commonly used to check how a certain model of air cooler can process air with certain air parameters to achieve what final parameters.
3. Heat Exchanger Thermal Calculation Method
Dry Bulb Temperature Efficiency Method — For a specific model of air cooler, the principles of thermal calculation should meet the following conditions:
(1) Air Treatment Process Required EgShould equal the E that the evaporator can achieveg；
(2) The required E for the air treatment process should equal the E that the evaporative cooler can achieve.
(3) The heat released by the air should equal the heat absorbed by the cold water.
4. Consideration of safety factor in the thermal calculation of the condenser
After prolonged use, the heat exchanger's heat transfer coefficient may decrease due to reasons such as accumulated dust on the outer surface and scaling on the inner surface. To ensure the continued safety and reliability of the heat exchanger under these conditions, a certain safety factor should be considered in the selection calculation. The safety factor can be taken into account by increasing the heat transfer area, such as by adding rows or increasing the windward area. However, due to limited product specifications, this method often does not achieve an exactly suitable safety factor or can complicate the selection calculation. Therefore, in engineering, one may consider:
At the onset of calculation selection, the obtained EgMultiply by safety factor 'a'. For condensers used only for cooling, take 'a' as 0.94; for those used for both cooling and heating, take 'a' as 0.9.
(2) The safety factor is not considered during the calculation process. After selecting the evaporator specifications, the calculated initial water temperature is further reduced. The reduction in initial water temperature can be considered as 10% to 20% of the water temperature rise.
Cautionary Notes
(1) When not using air conditioning during winter, it's crucial to drain all remaining water from the pipes to prevent freezing due to low winter temperatures, which could crack the steel pipes.
(2) The water in the condenser should not contain impurities, such as sand.
(3) Ensure adequate insulation during winter to minimize heat loss or prevent pipe icing.
