Engineering CalculatorsCold Plate Designer
Hydraulic and thermal performance of a liquid cold plate whose coolant channel you build up from straight sections and 45°/90°/180° bends — heat-transfer coefficient, pressure drop, thermal resistance and base temperature for a given heat load. Pairs with the Heatsink, Heat Exchanger and Flow-in-Pipes calculators.
New to Liquid Cold Plate Design? Read the guide: Cold Plate Design: Rectangular-Channel Heat Transfer and Pressure Drop — a plain-language explainer of the standard behind this calculator.
Rectangular-channel liquid cold plate, steady single-phase Newtonian flow. Each straight section is solved on its own hydraulic diameter Dh = 2·w·h/(w+h) and per-channel velocity. The Darcy friction factor uses the rectangular-duct Poiseuille number f·Re = 96·(1 − 1.3553α + 1.9467α² − …) for laminar flow (Shah & London, α = short/long side — 56.9 at a square, 96 at parallel plates, so a channel is not the 64/Re of a round pipe) and Swamee-Jain when turbulent, interpolated across the 2300–4000 transitional band. The heat-transfer coefficient h = Nu·k/Dh uses the constant-heat-flux (H1) rectangular-duct laminar Nusselt 8.235·(1 − 2.0421α + …) (3.61 at a square) and Dittus-Boelter when turbulent. Bend losses use ΣK·(ρv²/2) with representative sharp-milled-bend K (45°≈0.3, 90°≈1.1, 180°≈2.0), which vary with bend radius. Thermal resistance from the channel wall to the inlet fluid is R_conv = 1/UA (UA = Σ h·wetted-area over every section and channel) plus R_caloric = 1/(2·ṁ·cp); optional 1-D base conduction t/(k·A) adds the module path. The channel side and top walls are counted as fully-effective heat-transfer area (no fin-efficiency derating), which over-estimates UA for tall/thin channels — treat the thermal result as a first-order estimate. Fluid density and cp reuse this site's coolant presets; ν/k/Pr reuse the Heat Exchanger transport table. Verify against CFD or a bench test before committing a design.
Validated: the rectangular-duct correlations reproduce their Shah & London anchor values exactly — laminar f·Re = 56.92 and Nusselt = 3.61 for a square channel, and 96 / 8.235 for the parallel-plate limit. A hand-worked single 5×3 mm × 100 mm water channel at 1 L/min (Dh = 3.75 mm, v = 1.11 m/s, Re ≈ 4150 turbulent) reproduces h ≈ 6270 W/m²K, a 0.66 kPa section pressure drop, a 1.44 °C coolant temperature rise and a 180° bend loss of 1.23 kPa — all matching hand calculation.