In the presented study, a novel micro cooling system for electronic devices using a micro capillary groove evaporator was proposed. Based on experimental data in open(atmospheric) condition, we found that liquid level has an obvious influence on evaporating heat flux. For a given liquid level, there exists an optimum groove size, which maximizes evaporation heat transfer capacity. By using the optimum groove sizes in the open condition, two types of closed cooling sytems for CPU chips for personal computers were designed: one was for desktop models and the other for notebook models. Their cooling performance to keep CUP chip temperature belos 90℃ reached 3.35×105W/m2 and 2.51×105W/m2,respectively, for the desktop model by using ethanol and the notebook model by using methanol. Experimental results show that the maximum cooling capacities strongly depend on the condensation capacities of condensers in the closed cooling systems and volume fractions of working liquid in the evaporators.

A numerical analysis of flow and concentration fields of macromolecules in a slightly curved blood vessel was carried out. Based on these results, the effect of the bifurcation of a flow on the mass transport in a curved blood vessel was discussed. The macromolecules turned out to be easier to deposit in the inner part of the curved blood vessel near the critical Dean number. Once the Dean number is higher than the critical number, the bifurcation of the flow appears. This bifurcation can prevent macromolecules from concentrating in the inner part of the curved blood vessel. This result is helpful for understanding the possible correlations between the blood dynamics and atherosclerosis.

Analytical research was conducted to study the heat transfer from horizontal surfaces to normally impinging circular free-surface jets under arbitrary-heat-flux conditions. General expressions of heat transfer coefficients and recovery factor were obtained in the stagnation region and boundary layer region as well as viscous similarity region by the integral method. Then by using the analytical results, the conjugated heat transfer between a water jet and the impinged wall was numerically solved. Finally, an experimental study was also performed to characterize conjugated heat transfer coefficient on a thick copper target base impinged normally by circular free-surface jet. The present predictions of the mean conjugated heat transfer coefficient were good agreement with the experimental data.

The critical heat flux(CHF) is studied in a confined space both experimentally and analytically. The confined space is consisted of two horizontal surfaces with the lower surface heated and the upper mesh screen. The observation shows that the behaviors of the vapor mushroom over the mesh screen have not significant differences with that in the conventional pool boiling. However, the CHF reduces with the decrease of the space gap when it is narrower than someone critical value. The theoretical analyses show that the reduced CHF is related to the earlier dryout of macrolayer during the period of vapor mushroom because the initial thickness of the macrolayer reduces with the decrease of the space gap. However, for larger enough space, the CHF is reached due to the crisis of the local heat transfer by the microlayer model but not the macrolayer dryout. Analyses show that the heat transfer crisis(CHF) causedby the macrolayer dryout occurs only in advance of that by the microlyer model and the conventional macrolayer dryout model is a special case of the microlayer model. Theoretic prediction of CHF agrees reasonable well with experimental data.

The critical heat flux (CHF) of subcooled boiling is theoretically predicted by means of the microlayer model. The enhancement of heat transfer for subcooled boiling is mainly due to the augmented heat convection caused by the forming and collapsing of individual bubbles. For a uniform heat flux surface, CHF approaches a constant in the high subcooling region. For a uniform temperature surface, CHF increases with the subcooling. The evaporative heat transfer becomes small and the total heat flux is mainly due to the heat conduction outside the evaporating area as the subcooling is increased. The boiling crisis(CHF) is caused by the local dryout of microlayer at low subcooling and by the rapid increase of the duration of bubble condensation with the increase of wall superheat at high subcooling.

The fractional calculus approach in the constitutive relationship model of viscoelastic fluid was introduced. The velocity and temperature fields of the vortex flow of a generalized second fluid with fractional derivative model were described by fractional partial differential equations. Exact analytical solutions of these differetial equations were obtained by using the discrete Laplace transform of the sequential fractional derivatives and generalized Mittag-Leffler function. The influence of fractional coefficient on the decay of vortex velocity and diffusion of temperature was also analyzed.

Saturated nucleate boiling heat transfer and critical heat flux (CHF) were experimentally studied in a confined space which consisted of two horizontal surfaces with a lower heated surface and an upper mesh screen. The nucleate boiling heat transfer was much enhanced in such a confined space, because the mesh screen kept primary vapor bubbles forming coalescence bubble within the confined space in lower heat flux region and allowed the vapor bubble to easily escape from the confined space in higher heat flux region. Observation by a high-speed camera showed that the behaviors of vapor mushroom over the mesh screen were not significantly different from that in the unconfined pool boiling at higher heat flux. The peripheral conditions of the confined space had no obvious effects on the heat transfer characteristics. The experimental CHF data showed a good agreement with the theoretical predictions based on the microlayer model proposed by some of the present authors.

Distilled water and nitrogen gas used as the working fluids flow through the stainless steel microtube with inner diameter 168 μm outer diameter 406 μm. Using the Joule heating, the wall temperature field photos of the microtube is acquired by employing an IR camera and the temperature and the volume flow rate of the inlet and the outlet of microtube are measured. A correlation between the axial wall heat conduction and the convective heat transfer is obtained by theoretical analysis based on the experimental results. The investigative results clearly show that the axial heat conduction can reduce the convective heat transfer in the stainless steel microtube and the decrement may reach 2% compared to the convective heat transfer when the working fluid is nitrogen gas, however, the decrement can be neglected for distilled water as the working fluid.

An experimental study was conducted to visualize the flow field and confirm the transitional Reynolds number from laminar to turbulent flow, as distilled water flows through quartz glass microtubes with inner diameter 315 and 520 um. With gentian violet as colorant, the flow field pictures in the microtube, and therefore, is shot by a CCD camera with a microscope at different Reynolds numbers. Pressure drop data were also used to characterize the triction factor for those microtubes in the Reynolds number range of 200-2300. The experimental results clearly showed that the flow in the microtube was the laminar state and the friction factors agreed well with the Poiseuille equations when the Reynolds number was low. As the Reynolds number was larger than 1200 and 1500 for the microtube with inner diameter 315 and 520um, respectively, the friction factor departed from the classical laminar solution due to the earlier transition from laminar to turbulent flow. The flow turned into full turbulent when the Reynolds number reached 1500-1800.

Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditons at 0.9Mpa.Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients. This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Theme. For ternary mixture, the boiling range of binary mixture comportant effects on boiling heat transfer coefficieats.