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Calculate Pressure Drop in Liquid Coolers
Pressure drop is one of the most important parameters when designing liquid cooling systems. Excessive pressure drop increases pump requirements, raises energy consumption and can impair the efficiency of the entire cooling system.
Pressure Drop Calculator
Why Is Pressure Drop Critical?
In liquid coolers, heat is transported via a coolant through channels in the cooler. This creates flow resistance that the pump must overcome. The higher the pressure drop, the larger the pump must be dimensioned, the higher the energy consumption and the greater the mechanical stresses in the system. An optimally designed liquid cooler therefore achieves not only good thermal performance but also the lowest possible pressure drop.
How Does Pressure Drop Arise?
Pressure drop is caused by friction and flow deflections within the cooling system. High-performance cold plates in particular often use complex channel structures to maximise heat transfer. This improves cooling performance but can simultaneously increase pressure drop.
- Narrow cooling channels and high flow velocities
- Many flow deflections along the flow path
- Rough surfaces and long flow paths
- Filters, valves and quick couplings
- Hoses and pipe fittings
Why Does Pressure Drop Rise So Steeply?
A common misconception is that pressure drop changes linearly with flow rate. In reality, pressure drop increases approximately quadratically with flow rate.
If the flow rate doubles, the pressure drop approximately quadruples.
Simplified Formula
The following relationship is commonly used for initial technical estimates. It is particularly suited for rough calculations with identical geometry and the same coolant.
The new pressure drop equals the known pressure drop multiplied by the square of the flow rate ratio.
Known and new pressure drop, each in bar.
Known and new flow rate, each in litres per minute.
Worked Example
A liquid cooler produces a pressure drop of 0.5 bar at a flow rate of 5 l/min. The flow rate is to be increased to 8 l/min.
-
Δp₂ = 0.5 × (8² / 5²) -
Δp₂ = 0.5 × (64 / 25) -
Δp₂ = 0.5 × 2.56 = 1.28 bar
Although the flow rate only increases by 60%, the pressure drop more than doubles.
Which Factors Affect Pressure Drop?
Channel geometry
The smaller and more complex the channels, the higher the flow velocity and the greater the pressure drop.
Flow rate
The most important factor. Even small increases can significantly raise pressure drop.
Coolant
Water-glycol mixtures or special coolants have higher viscosities and thus increase hydraulic resistance.
Temperature
The viscosity of the coolant changes with temperature and thereby affects flow behaviour.
System components
Not just the cooler itself: hoses, couplings, valves, heat exchangers and filters all contribute to the total pressure drop.
Pressure Drop vs. Cooling Performance
More flow rate does not automatically mean better cooling. Beyond a certain point, cooling performance improves only marginally while pressure drop rises sharply. In practice, the optimal operating point is therefore sought.
- Highest possible heat dissipation
- Lowest possible energy consumption
- Lowest possible pressure drop
When Does Simulation Make Sense?
Simplified formulas provide valuable initial estimates. For complex cooling systems, however, they are often insufficient.
Particularly useful for:
- High power densities and critical temperature limits
- Complex channel structures or multiple coolers in the circuit
- Custom cold plates under development
- Optimisation of channel geometries
Simulation enables:
- Determine pressure drops more precisely
- Identify hotspots
- Optimise channel geometries
- Reduce development time
Frequently Asked Questions
This depends strongly on application, pump and cooling capacity. Many industrial systems operate in the range of a few tenths of a bar to several bar. COOLTEC provides specific pressure drop characteristic curves for each cooler as a function of flow rate.
As flow velocity increases, friction and turbulence increase disproportionately. The dynamic pressure component is proportional to the square of velocity – and velocity increases linearly with flow rate. Hence pressure drop rises quadratically.
Not indefinitely. At some point, pump power and pressure drop increase more than the thermal benefit. The optimal operating point is where cooling performance and hydraulic resistance are in the best balance.
Not necessarily. Very low pressure drop can indicate low flow velocity and therefore also lower heat transfer. The goal is always an optimal ratio of cooling performance to hydraulic resistance.
Pressure Drop Calculated – But Does the Solution Really Fit Your Application?
The actual pressure drop depends on geometry, coolant, temperature, flow rate and many other factors. Our thermal management experts support you with thermal design, CFD simulation, pressure drop optimisation and the development of custom liquid coolers.
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