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⎢⎝⎠⎥ ⎣⎦ 6 – Modelling Since the gas coolers were modelled as a tube coils, the change-over from laminar to turbulent flow will occur at higher Reynolds number than that of straight tubes. According to Schmidt (VDI, 1993), the critical Reynolds number Recrit for single-phase flow in a tube coil can be expressed as: ⎡ ⎛ d ⎞0.45 ⎤ Recrit = 2300⋅⎢1+8.6⋅⎜D⎟ ⎥ (6.20) where D is the average diameter of the tube coil, and d is the diameter of the tube. Figure 6.4 shows an example of how the critical Reynolds number varies at different tube and coil dimensions. 7000 6500 6000 5500 5000 4500 4000 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 6 mm 8 mm 10 mm Average Coil Diameter [m] Figure 6.4 The Critical Reynolds number for different coil geometries. The centrifugal forces caused by fluid flow through a tube coil give rise to a secondary current, which improves the heat transfer and increase the pressure drop compared to a straight tube (VDI, 1993). Since the heat transfer process in the water-cooled CO2 gas cooler only involved single-phase fluids, the commonly used Gnielinski correlation (VDI, 1993) was applied to estimate the convective heat transfer coeffi- cients. Although the Gnielinski correlation is originally developed for flow in circular tubes, it can also be applied with good accuracy for annulus flow, when the geometric diameter is replaced with the hydraulic diameter of the annulus (Adriansyah, 2001). 177 Critical Reynolds Number [-]PDF Image | Residential CO2 Heat Pump System for Combined
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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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