Error estimation of single phase effectiveness and LMTD methodologies when applied to heat exchangers with phase change

7th European Thermal-Sciences Conference

Corberán, José-M.^1 ; Martinez-Ballester, Santiago^1 ; Gonzálvez-Maciá, José^1 ; La-Barbera, Claudio^1

Instituto de Ingenieria Energética, Universitat Politecnica de Valencia, Camino de Vera s/n, Valencia

46022, Spain^1

关键词: Concentration change;    Counter flow arrangement;    Evaporator and condensers;    Linear temperature;    Logarithmic-mean temperature differences;    Nonazeotropic refrigerant mixture;    Pressure variations;    Temperature variation;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/745/3/032125/pdf
DOI  :  10.1088/1742-6596/745/3/032125

来源: IOP

【 摘 要 】

Single phase formulas based on logarithmic mean temperature difference (LMTD) or Effectiveness (-NTU) are widely and wrongly used for the thermal analysis of evaporators and condensers. Those formulas do not take into account that temperature variation during phase change is due to pressure variation and/or concentration changes when using nonazeotropic refrigerant mixtures. This paper first presents the correct evaluation of the mean temperature difference and effectiveness, for parallel and counter flow arrangements, under the hypothesis of linear temperature variation, for both evaporator and condenser cases. Then, the analytical solution is employed to evaluate the error of applying the single phase formulas of LMTD and Effectiveness to the phase change part of evaporators and condensers.