Cooling capacity | EPFL Graph Search

Cooling capacity is the measure of a cooling system's ability to remove heat. It is equivalent to the heat supplied to the evaporator/boiler part of the refrigeration cycle and may be called the "rate of refrigeration" or "refrigeration capacity". As the target temperature of the refrigerator approaches ambient temperature, without exceeding it, the refrigeration capacity increases thus increasing the refrigerator's COP. The SI unit is watt (W). Another unit common in non-metric regions or sectors is the ton of refrigeration, which describes the amount of water at freezing temperature that can be frozen in 24 hours, equivalent to or . The basic SI units equation for deriving cooling capacity is of the form: :\dot{Q}=\dot{m}C_p\Delta T Where :\dot{Q} is the cooling capacity [kW] :\dot{m} is the mass rate [kg/s] :C_p is the specific heat capacity [kJ/kg K] :\Delta T is the temperature change [K]

Dynamic Modeling and Experimental Evaluation of a Controlled Two-Phase On-Chip Cooling System Designed for High Efficiency Datacenters

Nicolas Lamaison

An important challenge for the next generation of high performance datacenters is to guarantee sufficient, reliable, green and cheap cooling of the server blades. Since this seems unrealistic with air cooling technologies due to the expected ever higher chip heat fluxes (in excess of 100 W/cm2), a novel more effective cooling system is required. Switching to two-phase on-chip cooling systems would decrease the energy consumption, enhance the thermal performance and allow the reuse of the extracted heat. However, the design of such systems seems nontrivial because of the lack of simulation tools able to reproduce their behavior. In this context, the present thesis describes the one-dimensional dynamic modeling of an on-chip two-phase liquid pump cooling system for multiple micro-processors. The simulation code includes state-of-the art two-phase flow methods, two-dimensional conduction in the heat sink, heat flux dependent mass flow rate distribution between parallel micro-evaporators, and micro-condenser and in-line liquid accumulator models. Three different scales of simulations, namely the heat sink, multiple parallel heat sinks and entire system scales, are presented. An experimental test bench with a cooling capacity of about 300W is used to validate the code. Mass flow rate distribution, energy oriented performance maps, chip temperature profile, heat flux disturbances under controlled conditions and charge influence are studied experimentally. The experimental data are satisfactorily reproduced by the simulations with, for example, 266 steady-state mean chip temperatures, obtained for balanced and unbalanced heat fluxes conditions, predicted within ± 2K. The most significant discrepancy between simulations and experiments is found to be the pressure transient prediction. The validated code is then used to simulate a compact two-phase on-chip cooling system designed for a real datacenter blade server. At the heat sink level, start-up and hot-spots are studied using 2D temperature maps and time-strip analysis. Furthermore, the flow distribution between the parallel micro-evaporators of the studied layout is shown to be unique and thermal-hydraulic maps are generated. The system start-up and operation under random and periodic heat load disturbances with different control strategies are then analyzed. Finally, the thermo-economic integration of a datacenter with a district heating network is investigated.

EPFL2014

Role Of A Liquid Accumulator In A Passive Two-Phase Liquid Cooling System For Electronics: Experimental Analysis

Raffaele Luca Amalfi, Nicolas Lamaison, Jackson Braz Marcinichen, John Richard Thome

Gravity-driven two-phase liquid cooling systems using flow boiling within micro-scale evaporators are becoming a game changing solution for electronics cooling. The optimization of the system's filling ratio can however become a challenging problem for a system operating over a wide range of cooling capacities and temperature ranges. The benefits of a liquid accumulator to overcome this difficulty are evaluated in the present paper. An experimental thermosyphon cooling system was built to cool multiple electronic components up to a power dissipation of 1800 W. A double-ended cylinder with a volume of 150 cm(3) is evaluated as the liquid accumulator for two different system volumes (associated to two different condensers). Results demonstrated that the liquid accumulator provided robust thermal performance as a function of filling ratio for the entire range of heat loads tested. In addition, the present liquid accumulator was more effective for a small volume system, 599 cm(3), than for a large volume system, 1169 cm(3), in which the relative size of the liquid accumulator increased from 12.8 % to 25% of the total system's volume.

Amer Soc Mechanical Engineers2017