Estimate energy for heating a solution

An energy estimate gives an order of magnitude. Actual power also depends on losses and transfer conditions.

Estimate the requirement

For heating without phase change, use Q = m·cₚ·ΔT if heat capacity is approximately constant. The vessel and losses add requirements.

Assess the time

The ideal time is Q/P. Not all rated electrical power reaches the liquid. Viscosity, mixing and geometry affect heat transfer.

Practical example

Exercise: 1 kg water, assumed cₚ = 4.18 kJ/(kg·K), ΔT = 30 K: Q ≈ 125.4 kJ. At constant useful 300 W, ideal time is 418 s, about 7 min, excluding losses.

References

DOE — Heat Transfer, Volume 2

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