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temperature. First, the air is cooled down in the evaporator to enforce condensation and remove moisture. Afterwards, it is reheated again by the gas cooler to provide relatively dry hot air to the drying chamber. In the CO2-cycle a second gas cooler is required. On one hand to ensure an efficient CO2-cycle with crossing the critical point before the following expansion in the valve, on the other hand to dispose excess heat: surplus heat is introduced into the heat pump system via the compressor load, and since drying is an isenthalpic process and since the moist air cycle is a closed-loop system, an additional heat sink is needed. Figure 4 shows a CO2 heat pump cycle in a temperature-entropy diagram, with the corresponding cooling and re-heating of the moist air for humidity removal in the evaporator. Figure 4: Heat pump assisted drier with R744 for a drying temperature of 50 °C Furthermore, an assessment of the control variables for the system in figure 3 (right) shows that a second evaporator might be beneficial: The load of the second gas cooler is controlled by the speed of the fan to control the inlet temperature to the valve. The valve position is controlling the high pressure and the compressor speed is used to control the inlet temperature to the drying chamber. The moist air fan is providing a constant volume flow. Therefore, there is a lack of a control variable to control the low pressure of the CO2-cycle and thus the evaporator load. This leads to the introduction of a second evaporator arranged in a parallel setup, as shown in figure 5 (left). Figure 5: Enhanced components of the simulated heat pump drying process (left) and exemplary scheme for a heat pump drying process with a bypass on air side, with cut-off heat pump (right)PDF Image | Design of a CO2 heat pump drier with dynamic modelling tools
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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
Heat Pumps CO2 ORC Heat Pump System Platform More Info
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