Automotive refrigeration; Modified Otaki method; Experiment; Refrigerant inventory.
The knowledge about the refrigerant charge distribution in each component of an automotive air-conditioning system (AACS) is essential to predict any leakage into the system, health monitoring and estimation of overall system performances. However, estimating charge distribution in each component is not as easy as finding the total refrigerant mass into the system. There are some additional factors which also govern the distribution of refrigerant such as ambient temperature, compressor speed, blower speed, etc. Due to this, the refrigerant distribution in each component of an AACS is not uniform in a particular driving condition. Further, the condenser and the evaporator are the two major components which consume maximum volume of refrigerant. Previous investigation shows that the condenser and the discharge line would almost consume 88% of the total refrigerant mass while the remaining refrigerant is distributed in all other components . In view of the above discussion, in this present work the refrigerant inventory in each component of an AACS are estimated by using an analytical technique which is a modified version of Otaki method [1,2]. The modified Otaki method descries to solve the energy equation of the heat exchangers to obtain the lengths of different phase regions. It gives an advantage over actual Otaki method by ignoring the outside heat transfer coefficient to accommodate the design complexity of an automotive heat exchanger. Though the heat exchangers are the major stake holders of refrigerant, the residual refrigerant in compressor, liquid line, vapor line and expansion device is estimated according to their volume and density by this modified Otaki method. A comparative study between the Otaki and modified Otaki method justifies the acceptability of the later for a wide range of experimental data with the variation of compressor speed, blower speed and refrigerant charge from undercharging to overcharging . The obtained results for both the heat exchangers from modified Otaki method are compared with the output of a commercial software CoilDesiger . A good agreement is observed between them. The other system performances like cooling capacity, compression work and coefficient of performance of the system are also reported for all different operating conditions. References:  M.P. Porto, R.N.N. Koury, L. Machado, An alternative method to estimate refrigeration system inventory, Appl. Therm. Eng. 52 (2013) 313–320. doi:10.1016/j.applthermaleng.2012.12.023.  T. Otaki, Holding refrigerant in refrigeration unit. Prog. Refrigeration Sci. Technol., in: Proc. XIII Int. Congr. Refrig., AVI Publishing Company, Inc., Washington, DC, 1971: pp. 535–544.  S.P. Datta, P.K. Das, S. Mukhopadhyay, Effect of refrigerant charge, compressor speed and air flow through the evaporator on the performance of an automotive air conditioning system, in: 15th Int. Refrig. Air Cond. Conf. Purdue, West Lafayette, USA, 2014.  CoilDesigner, A sophisticated tool for design and optimization of air-cooled heat exchangers, Center for Environmental Energy Engineering, 4164, Glenn L. Martin Hall, Mechanical Engineering Department, University of Maryland, College Park, MD 20742, USA, 2007.