Supported by National Nature Science Foundation of China (NSFC)
Dec., 2009 ~ Sep., 2010
Utilizing zeotropic mixture as working fluid can improve the COP of heat pump system, when the perfect temperature match occurring in counter-flow heat exchanger. However, zeotropic working fluid has non-linear variation of two-phase enthalpy with temperature. This characteristic will result temperature difference between working fluid and heat transfer fluid can not be equivalent at everywhere in heat exchanger. Then the pinch point or maximum temperature difference between working fluid and heat transfer fluid will occur. This research’s object is to reveal the component migration’s effect on position of pinch point or maximum temperature.
The experimental system, Figure 1, mainly contains two subsystems: (1) The temperature detecting system for detecting position of pinch point or maximum temperature difference; and (2) the component detection system for detecting component migration of zeotropic mixture in heat exchanger.
 |
| Figure 1- Schematic diagram of experimental system |
(1) Detecting position of pinch point
The temperature detection system is shown in Figure 2. The temperatures of working fluid are measured by thermocouples along the evaporator. Through correlations, the temperature of working fluid along the evaporator can be calculated. Then the temperature difference along the evaporator can be calculated, and the position of pinch point or maximum temperature difference can be detected. Figure 3 is the conclusion about influence of heat transfer fluid on position of pinch point.
 |
| Figure 2- Photo of the temperature detecting system |
 |
| Figure 3- 3D pattern about influence of heat transfer fluid on position of pinch point |
(2) Detection component migration
The components of zeotropic mixture has different component ratio at different position of evaporator. To detect the component migration of zertropic, six collectors are distributed along evaporator. Through controlling the valves of collector, the zeotropic working fluid can be collected online. The collected working fluid is transported to and analyzed by chromatogram, Figure 4. Then the component migration can be detected along evaporator. Some results of chromatographic analysis are shown in Figure 5.
 |
| Figure 4 - Photo of chromatogram |
 |
| Figure 5- Results of chromatographic analysis |
Publications
[1] W. Wu, L. Zhao. Experimental investigation on the pinch point and maximum temperature difference of zeotropic working fluid in horizontal tube-in-tube evaporator. Energy Conversion and Management. (Revised)
[2] W. Wu, L. Zhao. Pinch points of R245fa/R152a zeotropic refrigerant mixture in horizontal tube-to-tube evaporator. The 3rd International Workshop of Energy Conversion, November 25-27, 2009, Kyoto, Japan.
[3] W. Wu, L. Zhao. Experimental investigation on pinch point of zeotropic working fluid in horizontal tube-in-tube evaporator. Engineering thermophysics conference, November 11-13, 2010, Nanjing, China.
[4] W. Wu, L. Zhao. The heat transfer characteristics of zeotropic refrigerant working fluid in tube-in-tube evaporator. The 16th University engineering thermophysics conference, May 21-23, 2010, Changsha, China.