Modified efficiency-NTU method (m-ε-NTU) for calculating air coolers in dehumidifying or frost conditions. Part IV

Abstract

In the fourth part of the article, the algorithm for applying the newly developed the m-ε-NTU method for calculating air coolers in dehumidifying or frost conditions is described step by step, and its comparison with the method of segmented division of the heat exchanger is also given. This comparison showed good convergence of the calculation results with a multiple reduction in their execution time. The value of the deviation of the calculated value of thermal power calculated using the newly developed method from the same value calculated using the method of segmented division averaged 3.23% modulo and does not exceed 4.5% modulo. When the heat exchanger is divided into 40 segments, the execution time of the calculation programs increases approximately 18 times compared to using the newly developed method, which can be called a significant advantage of the latter. Considering the above, the newly developed method can be widely used for the selection of air coolers, their verification and design calculations.
 BACKGROUND: A universal method for calculating air coolers that is applicable to design and verification calculations is necessary. The method should consider the effect of dehumidification and frosting on the heat exchange process and allow the quick performance of many calculations to simulate the operation of refrigeration and air conditioning systems without significant loss of accuracy. However, this example of calculation method that addresses all the above-mentioned criteria is unavailable in the domestic and foreign literature.
 AIM: This study develops a universal method for calculating air coolers that is applicable to design and verification calculations. This method considers the influence of dehumidification and frosting on the heat exchange process and allows the quick performance of many calculations to simulate the operation of refrigeration and air conditioning systems without significant loss of accuracy.
 MATERIALS: The developed method for calculating air coolers is based on the classical approach of ε-NTU (efficiency– the number of heat transfer units) and is its adaptation, allowing consideration of the influence of dehumidification and frosting on the heat exchange process and performing the calculation (including the combined operating mode of the air cooler) without dividing the heat exchanger into separate segments. The estimation of the error of calculations performed using the developed method was conducted by comparing the calculated values of the thermal power of the device with those using the segmented division method for various operating modes (including combined).
 RESULTS: Comparison with the segmented division method of the heat exchanger showed good convergence of the calculation results with multiple reductions in execution time. The deviation value of the calculated value of the thermal power computed using the developed method from that using the segmented division method averaged 3.23% modulo and did not exceed 4.5% modulo. When the heat exchanger was divided into 40 segments, the execution time of the calculation programs increased approximately 18 times compared to using the developed method, which can be called a significant advantage of the latter.
 CONCLUSION: The division of the heat exchanger into segments for calculation does not result in a significant increase in accuracy compared with the new method. Thus, the developed m-ε-NTU method can be widely used for the selection of air coolers, their verification, and design calculations.