We describe the use of computer-aided molecular design (CAMD) and figure of merit (FOM) analysis to identify new heat transfer fluids for direct immersion cooling of electronic systems. Thirty-five new fluids, with thermophysical properties in the range 320 K < T-b < 370 K, k > 0.09 W m(-1) K-1 and H-vap > 35 kJ mol(-1), were identified via a CAMD approach. Further analysis of these 35 fluids led to the selection of 1,1,1-trifluoro-3-methylpentane (C6H11F3) for experimental evaluation. C6H11F3 was synthesized from commercially available precursors, and its thermophysical properties were measured to verify its FOM. Next, the pool boiling performance of a mixture of 7 wt.% C6H11F3 + 93 wt.% HFE 7200 was determined using a 10 mm x 10 mm grooved Si thermal test chip coated with copper. An improvement of 7% in the critical heat flux (CHF) was obtained, suggesting that C6H11F3 is worth further examination as a candidate for direct immersion phase change cooling applications. (C) 2012 Elsevier Ltd. All rights reserved.

We have identified new organosilicon coolants for direct immersion phase change cooling of electronic systems using a computer-aided molecular design (CAMD) approach combined with a figure of merit (FOM) analysis (hereafter termed the CAMD-FOM approach). Seven candidates with predicted thermophysical properties in the range suitable for direct immersion cooling of electronics were identified, and the thermophysical properties of two candidates, dimethoxydimethylsilane and ethyldimethylsilane, were measured in order to validate the CAM.D-FOM procedure. In addition, the pool boiling characteristics of a mixture of dimethoxydimethylsilane and HFE 7200 (10:90 w/w) on a grooved silicon surface were investigated and compared with those of pure HFE 7200. The addition of dimethoxydimethylsilane was shown to lead to an approximately 20% enhancement in the critical heat flux, confirming that the CAMD-FOM approach can be employed for designing new heat transfer fluids.

Steadily increasing heat dissipation in electronic devices has generated renewed interest in direct immersion cooling. The ideal heat transfer fluid for direct immersion cooling applications should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by poor thermal properties like low thermal conductivity (about twice that of air) and low specific heat (same as that of air). These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. C4H4F6O is a new heat transfer fluid which has been identified using computer-aided molecular design (CAMD) and knowledge-based approaches. A mixture of Novec fluid (HFE 7200) with C4H4F6O is evaluated in this study. Pool boiling experiments are performed at saturated condition on a 10 mm × 10 mm silicon test chip with CuO nanostructures on a microgrooved surface, to investigate the thermal performance of this new fluid mixture. The mixture increased the critical heat flux moderately by 8.4% over pure HFE 7200. Additional investigation is necessary before C4H4F6O can be considered for immersion cooling applications.

Computer-aided molecular design and figure of merit analysis were used to screen mixture formulations that enhance the pool boiling heat transfer performance of Novec fluid HFE 7200. Mixtures of HFE 7200 with methanol and ethoxybutane were identified as promising candidates for further study, and their thermophysical and dielectric properties were measured. The pool boiling performance of the two mixtures was investigated on a 1 cm × 1 cm silicon substrate with copper nanowire arrays. The addition of both methanol and ethoxybutane to HFE 7200 resulted in a substantial increase in the critical heat flux. However, the addition of methanol had a detrimental effect on incipience superheat and heat transfer coefficient, whereas these properties only changed marginally upon the addition of ethoxybutane to HFE 7200. This suggests that HFE 7200 + ethoxybutane mixtures show promise as candidates for direct immersion cooling of electronics.

Electrical and chemical compatibility requirements of electronic components pose significant constraints on the choice of liquid coolants. Dielectric coolants such as Novec fluids and fluoroinerts are plagued by poor thermal properties. This necessitates the development of new heat transfer fluids. In this study we examine mixture formulations that provide an avenue for enhancing the properties of existing heat transfer fluids. Mixture formulations of Novec fluid (HFE 7200) with Methanol and Ethoxybutane are considered. Pool boiling experiments are performed on a copper nanowire surface. The results show an improvement of 24% and 11% in the CHF of HFE 7200 - Methanol and HFE 7200 - Ethoxybutane mixtures respectively, when compared to pure HFE 7200 at saturation condition. The mixtures also showed an enhancement in the CHF at subcooled conditions.

Electrical and chemical compatibility requirements of electronic components pose significant constraints on the choice of liquid coolants. These constraints have led to the use of fluoroinerts and Novec liquids as coolants, which are plagued by significantly lower thermal conductivity, specific heat, and latent heat of vaporization compared to water, and also a number of these chemicals have significant environmental impact. These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. Mixture formulations provide an avenue for enhancing the properties of existing heat transfer fluids. These can be tuned for specific applications. Mixture formulations of Novec fluid (HFE 7200) with alcohols and ethers (HFE 7200 and methanol; HFE 7200 and ethoxybutane) are considered in this study. A 1 cm × 1 cm Silicon (Si) sample having copper nanowire arrays is used as the test surface for pool boiling. Experiments are done under saturated conditions and also at different sub-cooled conditions to investigate the thermal performance of these new fluid mixtures. Pool boiling heat transfer performance and the critical heat flux are measured for fluid mixtures and compared with the corresponding base fluid. From the pool boiling experiments, it was observed that adding methanol to pure HFE 7200 enhances the CHF of the resulting mixture and adding ethoxybutane to pure HFE 7200 reduces the incipience temperature for boiling.

Forced convection of liquids along with phase change heat transfer will be necessary for cooling electronic devices of the future with heat fluxes in excess of 1 kW/cm2. However, electrical and chemical compatibility of the liquid and electronic components pose significant constraints on the implementation of most liquid coolants. These constraints have led to the use of fluoroinerts and Novec fluids as coolants which are plagued by low thermal conductivity and specific heat. These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. Mixture formulations provide an added dimension in the development of new heat transfer fluids. Heat transfer properties can be enhanced by adding certain liquids having better thermal properties, to the existing heat transfer fluids. Mixture formulations of Novec fluid (pure HFE 7200) with alcohols and ethers (HFE 7200 and methanol; HFE 7200 and ethoxybutane) are considered for this study. A 1 cm × 1 cm silicon (Si) substrate having copper nanowire arrays is used as the test surface for pool boiling and experiments are done at saturation conditions to investigate the thermal performance of these new fluid mixtures.