Conjugate Heat Transfer Modeling of a Cold Plate Design for Hybrid-Cooled Data Centers

Overview

Liquid-cooled servers can reduce the energy consumption and environmental footprint of hybrid-cooled data centres, and a CFD model can give very useful insights for thermal simulation of air- and liquid-cooled servers in a single environment. The study develops a conjugate heat transfer (CHT) numerical model, validated with experimental data, that simulates heat transfer from the CPU to the air and cold plate considering the effect of thermal paste. The model explicitly represents the thermal paste between CPU and cold plate, coupling regions with T_f = T_s and Q_f = -Q_s boundary conditions and a contact-resistance relation.

Validation cases held surrounding air at 300 K with water at 315-330 K (velocity 5 m/s) for natural and forced convection. A dataset of one hundred samples covering flow, thermal and workload conditions was generated with Latin hypercube sampling from an operating hybrid-cooled data centre's thermal and IPMI data. The serpentine micro-channel cold plate transferred approximately 97% of the heat generated by the CPUs to the water.

From this dataset an empirical equation was fitted for the residual CPU heat that escapes to air, and its accuracy was confirmed on a test dataset. With this compact model, a rack of mixed air- and liquid-cooled servers can be simulated quickly in room-level CFD. A cited micro data centre with 1.2 kW IT capacity reached a maximum outlet water temperature of approximately 50 °C.

Limits: a single cold plate design and an equation fitted for an OCP server CPU, which do not transfer directly to other plate or server geometries. The OpenFOAM case files are publicly shared (GitHub DSTECHNO/NusseltNumber).

Key points

1. The serpentine micro-channel cold plate transferred approximately 97% of the heat generated by the CPUs to the water.
2. The CHT model explicitly represents the thermal paste between CPU and cold plate, coupling regions with T_f = T_s and Q_f = -Q_s boundary conditions and a contact-resistance relation.
3. Validation cases held surrounding air at 300 K with water at 315-330 K (velocity 5 m/s) for natural and forced convection.
4. A dataset of one hundred samples covering flow, thermal and workload conditions was generated with Latin hypercube sampling from an operating hybrid-cooled data centre's thermal and IPMI data.
5. A cited micro data centre with 1.2 kW IT capacity reached a maximum outlet water temperature of approximately 50 °C.
6. The OpenFOAM case files are publicly shared (GitHub DSTECHNO/NusseltNumber).

Using it in design

• In hybrid-cooled racks, represent a cold-plate server as a compact model in room-scale CFD: model the share of CPU heat going to the cold plate (~97%) and the residual escaping to air separately.
• Make the thermal-paste (contact-resistance) layer an explicit input in the cold-plate model; the CPU-plate interface contributes significantly to thermal resistance.
• Use the fitted residual-heat equation only for the server and plate design it was trained on, and re-derive it for other designs.

Who should read it

Thermal engineers and researchers modelling hybrid air- and liquid-cooled servers in room-scale CFD.

Document contents

1. 1. Introduction
2. 2. Methods (2.1 Governing Equations, 2.2 Numerical Model, 2.3 Modeling Thermal Paste)
3. 3. Results (three-dimensional model, mesh-independence study, 3.2 Thermal analysis, temperature and velocity fields, implementation)
4. 4. Conclusions

Related standards

• OCP server specifications

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Publication details

Authors

Aras Dogan; Sibel Yilmaz; Mustafa Kuzay; Dirk-Jan Korpershoek; Jeroen Burks; Ender Demirel

Publisher

Energies (MDPI AG)

Year

2023

Volume

16

Issue

7

Pages

3088

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/en16073088

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation