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Deionized water is replacing fluorinated liquids as the preferred choice for two-phase immersion cooling in data centers. Yet, insufficient bubble removal capability at low saturated pressure is a key challenge hindering the widespread application. To solve this issue, this study employs non-ionic surfactant (Tween 20) and asymmetric structures (expanding microchannel) to enhance the boiling performances of deionized water under sub-atmospheric pressure. The research examines the effects of pressure (8.8~38.5 kPa), surfactant concentration (0.1~0.5 mL/L), and heat flux density (10~180 W/cm2) on the boiling heat transfer characteristics and analyzes the mechanism of unusual temperature oscillations induced by surfactants. It was found that the trade-off between the sub-atmospheric pressure, surface tension coefficient, and reduced static contact angle results in pronounced intermittent boiling on the heated surface. Even with the addition of surfactants, the improvement in heat transfer requires demanding conditions. Boiling enhancement throughout all heat flux conditions was achieved when the surfactant concentration was higher than 0.2 mL/L for the expanding microchanneled surface. The heat transfer coefficient reached 6.89 W·cm−2·K−1 under 8.8 kPa, which was 45% higher than without the surfactant. Under the same heat flux and sub-atmospheric pressure, as the concentration increased from 0.1 to 0.5 mL/L, the amplitudes of temperature fluctuation of the plane surface and expanding microchanneled surface decreased from 10 K to 2 K and 18 K to 1 K, respectively. The onset of nucleate boiling and wall superheat of the expanding microchanneled surface gradually decreased with the increase in surfactant concentration, where the onset of nucleate boiling decreased by 10.54 K. When the heat flux is 160 W/cm2, the wall superheat is reduced by 12.8 K. [ABSTRACT FROM AUTHOR]

An efficient angle-rotation architecture, suitable for use in a digital mixer, is presented. The architecture employs a decomposition of the high-precision rotation-angle into a coarse angle and a fine angle, and employs two processing stages, coarse and fine. Only the coarse stage employs a ROM, and that ROM is extremely small. Small multipliers are shown to suffice while providing full accuracy at the system output. A systematic development of the architecture and its supporting theory and assumptions is given, along with the rationale for determining its structure. A rigorous analysis of its error sources is presented, as well as the computation of bounds for the various errors they induce at the system output. This error analysis is shown to lead to a straightforward means of designing an efficient two-stage angle-rotation unit for a digital mixer, given input/output bitwidths and performance specifications. Index Terms--Angle rotation, CORDIC, direct digital synthesizer (DDS), digital mixer, low-latency, synchronization, trigonometric function generation.

In an all-digital timing-adjustment system for digital modems, interpolation can be employed to recover samples that are synchronous with the data symbols. In this paper, a novel interpolation method is described for such systems. Instead of approximating a continuous-time signal with a conventional (algebraic) polynomial and computing the synchronized samples using a Farrow structure, a trigonometric polynomial is employed. It is demonstrated that this approach produces a particularly simple implementation structure, reduces computational delay and, for practical signals, can improve the interpolation performance. Moreover, to recover a synchronized sample from existing samples, given a timing offset, it is shown that the method can be optimized such that a recovered sample's interpolation error is minimized for that specific timing offset value. The input signal's spectrum is also taken into account. Simulation results indicate that the method can achieve the best performance among all state-of-the-art methods tested. In addition, the optimal interpolator can be implemented without increased hardware requirements. Index Terms--Fractional delay filter, interpolation, sample-rate conversion, synchronization, timing recovery, trigonometric polynomial.