Особенности динамики струйного потока, генерируемого при поверхностном кипении жидкости на лазерном нагревателе

It was experimentally found that hot submerged jets appeared at laser induced nucleation boiling near the tip optical fiber placed in water exponentially decrease the velocity with the increasing of laser power (heat flux). This result was obtained for closed cylindrical cuvette where hot jets collided with walls slipped the cuvette boundary and transfer the heat. Obtained result is necessary to take into account at precise laser induced surface cleaning inside the closed volumes, for development of medical technologies of laser therapy of pathologically changed vessels, cysts, and for other applications.

Enhanced Flow Boiling in Microchannels Using Auxiliary Channels and Multiple Micronozzles

Flow boiling in an array of five parallel microchannels (W=200 μm, H=250 μm, L=10 mm) can be dramatically enhanced using self-excited and self-sustained high frequency two-phase oscillations induced by two-nozzle configuration. However, the effect of the two-phase oscillations is confined to the downstream of the microchannels. In this study, four-nozzle microchannel configuration is developed with an aim to extend mixing to the entire channel. Flow boiling in the four-nozzle microchannel is experimentally studied with deionized water over a mass flux range of 120 to 600 kg/m2 s. Overall average heat transfer coefficient (HTC) is significantly enhanced approximately 54.5% by extending the enhanced multi-channel mixing to the whole channel. It is equally important that the pressure drop can be further reduced by approximately 50%. Compared with previous two-nozzle design, four-nozzle configuration not only extends the mixing to the whole channel but also increase nucleation sites, which has been confirmed by visualization study to promote nucleation boiling.

Silicon-Based Micro Pulsating Heat Pipe for Cooling Electronics

This paper reports a micro-pulsating heat pipe (micro-PHP) fabricated in a silicon wafer that consists of trapezoidal microchannels with a hydraulic diameter of 394μm for electronic cooling applications. Electronic liquid FC-72 was used as the working fluid. To evaluate the maximum temperature reduction of the evaporator wall, experimental results of the vertical and horizontal-located micro-PHP at filling ratios ranging from 47% to 62% were compared with those measured from the empty micro-PHP (0% filling ratio). Results show that incorporating a micro-PHP as an integral part of silicon wafer could significantly decrease the maximum wafer temperatures and reduce the intensity of localized hot spots. At a power input of 6.0W, reductions in the evaporator wall temperature of about 32.3°C and 24.4°Cwere obtained for the micro-PHP at vertical and horizontal orientations, respectively. In addition, a CCD camera was employed to record the fluid movement inside microchannels and affirmed the existence of nucleation boiling and bulk circulation flow in the micro-PHP.

Lower Limit of Homogeneous Nucleation Boiling Explosion in Water During Linear Boundary Heating and Contact With High Temperature Surface

The lower limit for the occurrence of homogeneous nucleation boiling explosion during water heating at atmospheric pressure has been determined by applying a new theoretical model proposed by the authors. Two different cases of liquid heating have been considered for the study of homogeneous nucleation boiling explosion. In one case, the liquid on the surface is linearly heated at a rate of 10 K/s to 109 K/s. In another case, the liquid suddenly contacts with a high temperature surface such as in case of quenching with jet impingement or droplet. For the linear boundary heating case, the liquid temperature limit at which homogeneous boiling explosion occurs without any cavity or surface effect, essentially corresponds to a value of 302 °C even though the surface is heated very slowly. On the other hand, during water contact with hot surfaces, the occurrence of the homogeneous boiling explosion within a characteristic time period of 1 millisecond is obtained at a maximum liquid temperature of 303 °C for a limiting steady state boundary temperature of about 304 °C. From the definition of the steady-state interface boundary temperature of two 1-D semi-infinite body contact, the lower limiting surface temperatures for the occurrence of the homogeneous nucleation boiling explosion have been determined for water contact with various solid surfaces with different liquid initial temperatures ranging from 0 °C to 100 °C. The effects of the parametric variation in the boundary heating conditions on various characteristics of the homogeneous boiling explosion such as liquid temperature and time of boiling explosion, heat-flux across the liquid-vapor interface at the boiling explosion etc. are also determined and discussed in context with other results available in the literature.