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  "title": "Cold plates, manifolds and separated coolant loops",
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  "description": "Transports heat through controlled fluid circuits without treating circulation as consumption.",
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  "revisionDate": "2026-10-07",
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  "topic": "Data-center physical systems",
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      "title": "Cold plates, manifolds and separated coolant loops",
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      "title": "What happens when heat load rises at fixed flow and fluid properties?",
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      "title": "Explore in Atlas",
      "url": "https://semiaifoundry.com/ai-atlas/#coolant-loop-separation"
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      "title": "NVIDIA DGX GB Rack Scale Systems: Hardware",
      "url": "https://docs.nvidia.com/dgx/dgxgb200-user-guide/hardware.html"
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    {
      "title": "Cooling Water Efficiency Opportunities for Federal Data Centers",
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      "title": "Liquid-cooling coldplate",
      "url": "https://semiaifoundry.com/learn/atlas/coldplate/"
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    {
      "title": "Coolant distribution unit and separated loops",
      "url": "https://semiaifoundry.com/learn/atlas/cdu/"
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  "content": "Data-center physical systems · Atlas v1.3.0\n\n# Cold plates, manifolds and separated coolant loops\n\nTransports heat through controlled fluid circuits without treating circulation as consumption.\n\n[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#coolant-loop-separation)Chip voltage rails to facility heat rejection\n\nLearning objectiveSeparate thermal transport, loop ownership and water consumption.\n\n## The mechanism\n\nA cold plate conducts chip heat into a fluid. A rack manifold distributes that fluid among components, and a coolant distribution unit can exchange heat with a separate facility loop. Separating loops allows different pressure, chemistry and service requirements on each side. Heat captured by liquid may be only part of rack heat; fans and room air still handle other components in many systems. The NVIDIA rack guide explicitly describes mixed cooling. Fluid flow, temperature rise and pressure drop determine transport capability, while the facility’s final heat-rejection method determines how much energy or water is consumed beyond the rack.\n\n1.  Identify which components transfer heat to liquid and which remain on an air path.\n2.  Follow thermal interfaces into the cold plate and measure inlet and outlet temperatures.\n3.  Distribute fluid through manifolds while respecting pressure and chemistry requirements.\n4.  Exchange heat with the facility circuit through the specified CDU arrangement.\n5.  Balance captured heat, residual air heat and pump demand before declaring cooling readiness.\n\n## Science and assumptions\n\n### Single-phase heat transport\n\n$$\n\\dot Q=\\dot m c_p\\Delta T\n$$\n\nSingle-phase transported heat is mass flow times specific heat times stream temperature rise.\n\nSymbols and units\n\nQ̇\n\nHeat transported by the selected single-phase stream\n\nW\n\nṁ\n\nStream mass-flow rate\n\nkg/s\n\nc\\_p\n\nSpecific heat capacity\n\nJ/(kg·K)\n\nΔT\n\nStream outlet-to-inlet temperature rise\n\nK\n\nQ̇ is watts, ṁ kg/s, cp J/(kg·K) and ΔT kelvin.\n\nAssumptions Single-phase fluid with approximately constant properties; pressure limits and local thermal resistances are separate constraints.\n\n## Engineering example\n\nSynthetic water loop carrying 100 kW with a 10 K rise and cp ≈ 4,180 J/(kg·K) needs about 2.39 kg/s. This is circulating mass flow, not a consumption estimate.\n\n## Distinctions and tradeoffs\n\nLiters per minute circulating through a closed loop are not liters of water consumed by the facility.\n\nGreater flow can reduce temperature rise but increases pumping requirements; hotter coolant can aid heat rejection while narrowing component thermal margin.\n\nDense accelerator racks require sufficient heat transport before their installed arithmetic can operate continuously.\n\n## Specifications and interfaces\n\nTransport rate\n\nMass flow × specific heat × temperature rise\n\nHeat rate in watts; flow is not consumed water.\n\nLoop boundary\n\nIT-side fluid versus facility-side fluid\n\nA heat exchanger transfers heat without requiring fluid mixing.\n\n### Interfaces\n\nChip and component heat Input\n\nConducted heat entering cold plates or air paths\n\nFacility heat exchanger Output\n\nHeat carried in a controlled secondary loop\n\n## Check your understanding\n\n### What happens when heat load rises at fixed flow and fluid properties?\n\n1.  The heat exchanger stops needing a sink\n2.  The required fluid temperature rise increases\n3.  The circulating water disappears\n\nAnswer and reasoning\n\nThe required fluid temperature rise increases\n\nThe energy balance requires greater temperature gain unless another variable or heat path changes.\n\n## Evidence and scope\n\nThis is a heat-balance example, not a qualified coolant recipe. Product-specific pressure, chemistry and temperature limits remain required.\n\nNo current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.\n\n## Sources\n\n-   [NVIDIA DGX GB Rack Scale Systems: Hardware](https://docs.nvidia.com/dgx/dgxgb200-user-guide/hardware.html)\n-   [Cooling Water Efficiency Opportunities for Federal Data Centers](https://www.energy.gov/cmei/femp/cooling-water-efficiency-opportunities-federal-data-centers)\n\n[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/coolant-loop-separation-cc65e3a89d10352f.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)\n\n## Continue exploring\n\n### Foundations\n\n-   [Liquid-cooling coldplate](https://semiaifoundry.com/learn/atlas/coldplate/)\n-   [Coolant distribution unit and separated loops](https://semiaifoundry.com/learn/atlas/cdu/)\n\n### Related lessons\n\n-   [Facility heat rejection and cooling tradeoffs](https://semiaifoundry.com/learn/atlas/facility-heat-rejection/)"
}