The mechanism
A coolant distribution unit sits between the cooling needs of IT equipment and the available facility heat-removal system. In a liquid-to-liquid design, a controlled secondary loop circulates through the equipment while a heat exchanger transfers energy to the primary facility loop. The fluids do not need to mix. Pumps, filters, sensors, and control valves help maintain the required flow, pressure, fluid quality, and temperature. The atlas renders the two loops in separate colors so viewers can trace heat crossing the exchanger while following the actual fluid paths independently. CDU designs vary, including liquid-to-air arrangements. A CDU manages and transfers heat; the final destination still lies elsewhere in the facility cooling chain.
- Circulate secondary coolant through the IT equipment.
- Transfer its heat across an exchanger to the primary cooling side.
- Control the secondary conditions while the facility carries heat onward.
Science and assumptions
Sensible heat transport
Heat transport equals mass flow times specific heat times the return-to-supply temperature rise.
Symbols and units
- Q̇
- Heat transported at the selected coolant-loop boundary
W
- ṁ
- Coolant mass flow
kg/s
- c_p
- Coolant specific heat capacity
J/(kg·K)
- T_return
- Return-fluid temperature
°C
- T_supply
- Supply-fluid temperature
°C
Heat transport increases with mass flow, fluid heat capacity, and the temperature rise across the equipment. This relates device heat load to the thermal circuit that carries it away.
Assumptions Single-phase sensible heat with approximately constant and steady flow; real equipment must also satisfy pressure, approach-temperature, and control limits.
Engineering example
For a known mass flow and temperature rise, Q̇=ṁΔT; the CDU does not make heat disappear, it moves it to a plant boundary.
Distinctions and tradeoffs
A liquid-to-liquid CDU is not the final heat sink and does not require the two fluid circuits to mix.
Liquid transport supports dense heat loads. Pumps, controls, fluid quality, and facility integration add system requirements.
Accelerators can sustain useful work only while heat is removed. CDU control connects chip cooling to building infrastructure.
Specifications and interfaces
- Illustrated design
- Liquid-to-liquid CDU
Other architectures exist.
- Separated circuits
- Primary and secondary loops
Heat crosses the exchanger without intentional fluid mixing.
- Controlled variables
- Flow, pressure, temperature
Equipment- and facility-dependent specifications.
Interfaces
- Warm IT coolant Input
- Heat collected from equipment
- Facility loop Output
- Transferred thermal energy for rejection
Check your understanding
What crosses between the two separated loops?
- Model parameters
- Heat
- The entire secondary fluid inventory by design
Answer and reasoning
Heat
The heat exchanger transfers thermal energy while maintaining separate fluid paths.
Evidence and scope
The model excludes pump power, exchanger approach temperature and redundancy.
No current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.