Enhanced cooling in a sealed cabinet using an evaporating-condensing dielectric mist

Abstract

Many factors, such as acoustic noise limits and fan reliability considerations, limit the heat dissipation capacity of air-cooled cabinets housing telecommunications or computing hardware. The present work examines the potential of enhanced cooling in a sealed telecommunications cabinet using an evaporatingcondensing dielectric mist introduced upstream of heat sinks attached to high-power components in a circuit pack, or at the inlet to the circuit packs. The conceptualized system is of a two-component (air and dielectric fluid) and two-phase nature, wherein droplets of mist are dispersed within the air circulating through a sealed cabinet. The evaporated mist is condensed at the outlet of the circuit packs in a cabinet and recycled back to their inlets. First-order models of the mist flow through a heat sink are developed to estimate its influence on flow and heat transfer. The optimum droplet diameter and the optimum mist concentration are obtained from these models for representative conditions. Moreover, the models are used to obtain a first-order estimate of the heat dissipation capacity and the pressure drop required for sustaining the mist flow. The results show that the proposed mist cooling approach offers significant promise for providing high-flux heat removal solutions for sealed cabinets in telecommunications central offices and data centers. A cross-sectional area of the heat sink, m 2 D droplet diameter, m h m mass transfer coefficient, m/s m mass of a single droplet, kg . m mass flow rate through the heat sink, kg/s n number of moles p pressure, Pa t time, s v velocity, m/s x axial distance along heat sink, m D AB mass diffusion coefficient, m 2 /s Ja Jacob number Re Reynolds number RH relative humidity Sc Schmidt number Sh Sherwood number .

Analysis of evaporating mist flow for enhanced convective heat transfer

“…2 and has a footprint of 32 mm by 32 mm. The single-droplet Lagrangian model as developed in [15] analyzes the evaporation of droplets as they flow through the heat sink. It assumes that the Sherwood number characterizing mass transfer between the droplet and continuous phase is constant and equal to 2, its value for steady-state, diffusive mass transfer in an infinite medium.…”

“…The mass, momentum and energy source/sink terms are then updated using Eqs. (13)- (15) and employed in the next iteration. These iterations are repeated until a steady-state solution is reached.…”

“…Bahadur et al [15] introduced a novel concept of a recirculating, two-phase, evaporating-condensing mist flow for high-heat-flux thermal management. The cooling scheme introduces finely dispersed liquid droplets into the airstream (subsequently referred to as mist) entering a channel populated with electronic components as shown in Fig.…”

“…Bahadur et al [15] developed first-principles-based analytical models to arrive at estimates of key operational and performance parameters for mist cooling systems. A major focus of that work was to develop first-order models to simulate the physics governing droplet evaporation in such systems.…”

Thermal management: Enabling enhanced functionality and reduced carbon footprint

“…Our solution is to introduce dielectric liquid droplets into the airflow within our cabinets (shown schematically in Figure 10 and detailed in [2]). Using this approach, we have calculated an enhancement of 7X more heat dissipation with a possible reduction in energy consumption.…”