Refroidissement thermoélectrique

Le refroidissement thermoélectrique est une technique de refroidissement utilisant la thermoélectricité. On utilise pour cela des composants nommés « modules Peltier » qui exploitent l'effet Peltier, par lequel un courant électrique est converti en une différence de température. Généralités Les modules Peltier sont nommés ainsi car ils mettent en œuvre la thermoélectricité et plus précisément l’effet Peltier. Un tel module est alimenté par un courant et présente deux faces, l’une dite froide et l’autre chaude. L’objet à refroidir est mis au contact de la face froide, tandis que l'autre face est accouplée à un mécanisme d’évacuation de la chaleur (ventilateur...). Ce type de module peut également être utilisé pour l'application inverse, c'est-à-dire la génération d'électricité à partir d'une différence de températures, appelé effet Seebeck. Fonctionnement thumb | Schéma d'une cellule à effet Peltier. Thermoélectricité Un module Peltier est constitué d’une sér

Design Of Passive Two-Phase Thermosyphons For Server Cooling

Raffaele Luca Amalfi, Filippo Cataldo, Jackson Braz Marcinichen, John Richard Thome

The main objective of this paper is to utilize an improved version of the simulator presented at InterPACK 2017 to design a thermosyphon system for energy-efficient heat removal from 2-U servers used in high-power datacenters. Currently, between 25% and 45% of the total energy consumption of a datacenter (this number does not include the energy required to drive the fans at the server-level) is dedicated to cooling, and with a predicted annual growth rate of about 15% (or higher) coupled with the plan of building numerous new datacenters to handle the "big data" storage and processing demands of emerging 5G networks, artificial intelligence, electrical vehicles, etc., the development of novel, high efficiency cooling technologies becomes extremely important for curbing the use of energy in datacenters. Notably, going from air cooling to two-phase cooling, not only enables the possibility to handle the ever higher heat fluxes and heat loads of new servers, but it also provides an energyefficient solution to be implemented for all servers of a datacenter to reduce the total energy consumption of the entire cooling system. In that light, a pseudo -chip with a footprint area of 4 x 4 cm2 and a maximum power dissipation of 300 W (corresponding heat flux of about 19 W/cm2), will be assumed as a target design for our novel thermosyphon-based cooling system. The simulator will be first validated against an independent database and then used to find the optimal design of the chip's thermosyphon. The results demonstrate the capability of this simulator to model all of the thermosyphon's components (evaporator, condenser, riser and downcomer) together with overall thermal performance and creation of operational maps. Additionally, the simulator is used here to design two types of passive two-phase systems, an air- and a liquid-cooled thermosyphon, which will be compared in terms of thermal -hydraulic performance. Finally, the simulator will be used to perform a sensitivity analysis on the secondary coolant side conditions (inlet temperature and mass flow rate) to evaluate their effect on the system performance.

AMER SOC MECHANICAL ENGINEERS2020

Macro-to-Microchannel Transition in Two-Phase Flow and Evaporation

Chin Lee Ong

Continuous development of highly efficient and compact cooling elements are driven by extensive developments of Micro-Electro-Mechanical Systems (MEMS) devices such as microprocessors or micro high-powered laser systems. As microprocessors continue to head in the direction of miniaturization, it was quickly realized that the major obstacle to overcome was "heat". This justified the need for the development of a new generation of liquid cooling technologies that involves phase-change processes. However, significant differences in two-phase transport phenomena have been reported in the microscale sized channels as compared to conventional macroscale channels. The classification of macroscale, mesoscale and microscale channels with respect to two-phase processes is still an open question. This research project focuses on investigating the macro-to-microscale transition during flow boiling in small scale channels of various size and refrigerants to investigate the effects of channel confinement on flow boiling heat transfer, two-phase flow patterns, pressure drop, critical heat flux and liquid film stratification in a single circular horizontal channel. In this project, we systematically investigated the trends observed in the heat transfer data, pressure drop, critical heat flux and film stratifications for wide range of conditions as a function of flow pattern, creating a uniquely comprehensive experimental database for R134a (high pressure), R236fa (medium pressure) and R245fa (low pressure) in the 1.03, 2.20 and 3.04 mm channels. From a heat transfer viewpoint, the prediction of the heat transfer requires first the prediction of the two-phase flow regimes in these small scale channels. So, in that respect an improved flow pattern map has been proposed and by determining the flow patterns transitions existing under different conditions, the effects of the flow regimes and channel dimensions on flow boiling heat transfer is thus explained. A flow pattern based heat transfer prediction model, i.e. the three-zone model showed good agreement in the prediction of heat transfer coefficients corresponding to the isolated bubble (IB) and coalescing bubble (CB) flows. As for the two-phase pressure drops, various statistical comparisons have been made by comparing the pressure drop database with various macroscale and microscale prediction methods, finding that three macroscale and two microscale methods predicted the pressure drop database with good accuracy. From this research, a distinctive peak in the CHF has been identified when comparing the experimental CHF database for 0.50, 0.80, 1.03, 2.20 and 3.04 mm channels (the first two from previous study). A new CHF prediction method was developed that is applicable for the CHF prediction of single, square multi-microchannels and split flow multi-channels. Finally, the processing of the high speed flow visualization images provided the interpretation of the lower threshold of the macro-microscale transition. As an approximate rule, the lower threshold of macro-scale flow is Co= 0.3-0.4 while the upper threshold of the symmetric microscale flow is Co≈1.

EPFL2010

Hybrid Two-Phase Cooling Technology For Next-Generation Servers: Thermal Performance Analysis

Raffaele Luca Amalfi, Filippo Cataldo, Jackson Braz Marcinichen, John Richard Thome

This paper advances the work presented at ITHERM 2020 where a novel passive two-phase technology was introduced for more efficient cooling of datacenters compared to air-based cooling solutions (e.g. In-Room, In-Row, etc.). The proposed hybrid two-phase cooling technology uses passive low-height thermosyphons to dissipate the heat generated by high power components inside the servers. The heat is then transferred to multiple rack-level thermosyphons, equipped with one or more overhead compact condensers, which in turn dissipate the total heat from the rack into a room-level water-based or air-based cooling loop. Air-cooling is still used for the low heat-generating components (e.g. memory units, secondary chips, etc.) to make the cooling technology cost effective. This study is focused on a thermal performance analysis of the hybrid two-phase cooling technology applied to a single server (2U HP ProLiant DL180 G6), where low-height thermosyphons are installed to cool the two CPUs, and the remaining server components are cooled via air in forced convection using server-level fans. The thermal performance of the low-height thermosyphons is extracted from previous experimental measurements carried out at Nokia Bell Labs and presented at ITHERM 2020. Additional measurements considering the effect of the refrigerant charge on the thermal resistance and associated chip case temperature are conducted. The air-cooling performance and flow distribution are investigated via CFD simulations performed in COMSOL that characterize the conjugate heat transfer between server components and cooling air. The experimental and numerical results presented here show that, at the maximum server IT load of 587 W, the hybrid two-phase technology ensures sufficient cooling for all the hardware components while significantly reducing the energy consumption of the fans. Specifically, the fan contribution is reduced from 24% (traditional air-cooling) to about 2% of the server effective IT load (hybrid two-phase cooling), demonstrating the potential of the proposed technology to scale existing hardware and build next-generation datacenters, while keeping low costs and being environmentally-friendly.

IEEE2021

Design Of Passive Two-Phase Thermosyphons For Server Cooling

Raffaele Luca Amalfi, Filippo Cataldo, Jackson Braz Marcinichen, John Richard Thome

AMER SOC MECHANICAL ENGINEERS2020

Macro-to-Microchannel Transition in Two-Phase Flow and Evaporation

Chin Lee Ong

EPFL2010

Hybrid Two-Phase Cooling Technology For Next-Generation Servers: Thermal Performance Analysis

Raffaele Luca Amalfi, Filippo Cataldo, Jackson Braz Marcinichen, John Richard Thome

IEEE2021