Experimental Study of Maisotsenko Cross-Flow Cooler and Numerical Solution of Air in Mass and Heat Exchanger

Introduction: In hot seasons, various types of cooling equipment are used to create comfortable condition. Generally, in arid climates, evaporative cooling can reduce energy consumption and can replace compressor-based cooling. In Iran, swamp water coolers are widely used due to the simplicity of the mechanism and its reasonable price. Improper cooling, excessive water use, musty odor from swamp cooler, and improper airflow are common issues with these evaporative units. A better energy management, the water shortage crisis, as well as an increase in the humidity of cold air produced by these types of air conditioners requires other cooling systems of the same price and better efficiency. The shortage of the indirect evaporative cooling products in the cooling market compared with the cooling markets of some other leading countries calls for research and development of these types of air conditioners. In this paper, a type of indirect evaporative cooling system based on a cross-flow heat exchanger is made and its cooling performance is investigated.
 
Materials and methods: The main part of this type of cooler is a heat exchanger which is of the type of cross flow. This cross-flow heat exchanger consists of a few wet and dry channels. In part of the product dry channels, a few holes are located along the direction of product air flow. While the inlet air flows into the product channel, part of the air can be steadily branched into the wet channels by passing through these holes. The product air which has been cooled acts as working air and moves in a perpendicular direction towards the initial product air flow. A variable speed blower, which is used to control the inlet air flow rate, is equipped at the inlet of the cross-flow heat exchanger. The measured parameters includes air temperature, humidity, and velocity.
In order to study the thermal performance, the data should be measured for a period of time. Relative humidity, air temperature, and flow rates of inlet air, relative humidity, air temperature of product flow, relative humidity, and air temperature of working flow should all be measured.
 
Result: All of the measuring devices were calibrated simultaneously against a laboratory standard prior to the tests. Air velocity was measured using ananemometer. The type of anemometer is PROVAAVM 301 which measures the velocity in the range of 0 to 45 m/s. Temperature is measured by a digital thermometer with the measuring range of -50℃ to 300℃. The humidity is measured by a hygrometer with the measuring range of 0 to 99%. Wet bubble effectiveness and dew point effectiveness were calculated in different climatic conditions. Numerical solution was also compared with the experimental values. For three humidity ratios, the experiment was conducted and a good agreement between experimental and numerical results was achieved. The most important factor of the inlet air that affects the cooling performance is the humidity of the incoming air. Increasing the humidity ratio of the inlet air under similar operating conditions leads to an increase in the temperature of the outlet product and a decrease in the cooling performance of the heat exchanger. The behavior of the outlet air temperature changes is almost linear with respect to the inlet air temperature changes in the constant humidity ratio.The larger temperature difference between the inlet and the outlet at higher temperatures of the inlet air flow caused a more intense evaporation process in the wet duct, which in turn increased the cooling capacity. The experimental results while testing the heat exchanger during the experiment showed that, it takes the inlet flow with the temperature of 23℃ and delivers it to 19.2 and takes it in 42.3℃ and decreases the temperature to 24.4℃. This means that as the inlet air temperature increases, the heat exchanger cooling capacity increases. Also, the highest cooling was obtained for the inlet air temperatureof 42℃ and humidity ratio of 10.8 gr/kg. With increasing flow, the outlet air temperature rises from 20.1℃ to 21.7℃, it means an increase of about 1.6% in temperature; that is, lower outlet temperature can be achieved by reducing the inlet air flow rate.
 
Discussion and Conclusion: In summary, the results show that increasing temperature and decreasing the relative humidity of the inlet air improves the performance of this type of cooler. Higher efficiency for lower humidity means that in climates not considered arid, indirect evaporative cooling can still take an advantage of the evaporative cooling process without increasing humidity. Although, an increase in the inlet air flow rate increases the outlet air temperature, the cooling capacity improves.