Numerical investigation of cross-flow indirect evaporative cooling with in-channel condensation: Parametric analysis and performance characterization

Indirect evaporative cooling (IEC) provides a zero-refrigerant route to space cooling, achieving coefficients of performance (COP) far above those of conventional vapor-compression systems. Yet the combined influence of water-side operating conditions on cross-flow IEC performance under condensing conditions has not been adequately characterized. This study extends existing cross-flow IEC models in two respects: (i) the condensation criterion is evaluated cell-by-cell across a two-dimensional grid, removing the need for any prior assumption on condensation zone extent, and (ii) a fourth-order Runge–Kutta spatial-marching scheme captures the diagonal condensation boundary with a precision beyond that of first-order finite-difference approaches. These capabilities are applied for the first time to a systematic parametric study of water-side operating conditions, covering 31 cases across secondary inlet temperature (21–31°C), spray density (0.002–0.010 kg s⁻¹ m⁻¹), and water inlet temperature (20–30°C). The model was validated against published wet-bulb effectiveness data at three flow-rate ratios, giving RMSE of 0.005–0.008 kg kg⁻¹ and R² of 0.52–0.95. Results indicate the condensation zone spans 42% of the plate area but contributes 38% of total heat removal, with a peak driving force of +5.1°C; primary-air temperature drop falls by 34.1% as secondary inlet temperature increases from 21 to 31°C; and spray-density benefits plateau beyond 0.006 kg s⁻¹ m⁻¹. A Pareto-optimal operating frontier (Ts,i = 22–24°C, Γ = 0.004–0.006 kg s⁻¹ m⁻¹, Tw,i = 20–22°C) yields εWB = 70–76% and COP = 85–130, while the spray-density saturation threshold identifies the economic limit of water consumption beyond which additional spray provides negligible performance benefit.