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The passage around this formula

The following is my own worked calculation, using standard property values rather than any cited source. At around 27 °C and atmospheric pressure, air has $\rho$ $c_p$ $\approx$ 1.17\ $\mathrm{kJ/(m^3{\cdot}K)}$ ; liquid water has $\rho$ $c_p$ $\approx$ 4180\ $\mathrm{kJ/(m^3{\cdot}K)}$ . The ratio is roughly 3,600 to one. Rejecting 100 kW at a 15 K rise therefore requires about 5.7\ $\mathrm{m^3/s}$ of air — near 12,000 cubic feet per minute, through a single rack aperture — or about 1.6\ $\mathrm{L/s}$ of water, which is a garden hose. There is no engineering cleverness that closes a factor of 3,600; the only levers are a larger $\Delta$ T or a larger duct, and both run out.

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