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Several tests were done to examine consistency and stability of the system. The dependence of thermo-physical properties on temperature and pressure at a certain point or state was calculated using NIST REFPROP software. A temperature-entropy (T-S) diagram was used to present the output of the system. To see the output of the CO2 system when run under sub critical conditions, the charge was reduced to quarter of the full amount and the test rig operated. Several experiments were conducted in these conditions and the average taken. The standard deviation of the output was less than 5%. 3 Results and Discussion Table 2: Preliminary tests output. GAS COOLER Outlet EVAPORATOR Run Inlet Inlet P3 (MPa) 3.76 3.77 3.80 3.80 3.71 3.71 3.70 3.70 3.70 3.69 3.67 3.57 3.57 1.15 Outlet T1 (°C) 1 75.37 2 75.37 3 75.57 4 75.57 5 79.60 6 79.80 7 79.80 8 79.80 9 80.00 10 80.00 11 79.80 12 81.71 13 81.91 14 64.2 P1 (MPa) 7.61 7.61 7.59 7.59 7.72 7.72 7.01 7.01 7.70 7.70 7.69 7.77 7.77 1.8 T2 (°C) 31.00 31.00 31.00 31.00 29.79 29.79 29.99 29.99 29.99 29.99 29.99 29.09 29.09 20.3 P2 (MPa) 7.30 7.30 7.27 7.27 7.45 7.45 7.44 7.44 7.44 7.44 7.42 7.54 7.54 1.6 T3 (°C) 4.94 4.94 5.15 5.15 4.14 4.14 4.14 4.14 4.14 4.14 3.94 2.93 2.93 17.2 T4 (°C) 5.95 6.65 8.57 8.57 10.08 10.08 8.87 8.87 8.37 8.37 6.65 5.44 5.44 18.9 P4 (MPa) 3.48 3.49 3.52 3.52 3.45 3.45 3.44 3.44 3.43 3.43 3.41 3.32 3.32 1 After the initial experiments, the output was put in tabular form as shown in table 2. Run 1 to 13 represent the initial output when the system is fully charged while run 14 is the output when the system is charged by less amount of the refrigerant. NIST REFROP was used to calculate the relevant thermo-physical properties using the values gotten. Figure 3 shows the practical cycle of the system when run 1 was considered. As it is seen, the cycle has some inefficiency thus the use of dotted line. Other researchers in the same field got approximately the same values of COP in their initial experiments [12]. The same researchers improved their system’s efficiency by optimizing the working conditions and improving the system apparatus. In the same way, the system in this study is under investigation to improve its performance. Variation of operation parameters like the evaporation temperature, the gas cooler temperature and pressure, the cooling water temperature and flow rates and amount of refrigerant is being undertaken. These parameters were found to affect the operation of similar systems by a wide margin, thus deemed very important [13]. Optimizing these parameters will reduce irreversibility causes especially friction and pressure drop because these causes depend on operating conditions and their interactivity. The effect of refrigerant amount of them is discussed briefly in this study. Table 3: Heat output and efficiency of the cycle. 322PDF Image | TYPICAL INITIAL OUTPUT OF A CO2 HEAT PUMP
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CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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