Local Single- and Two-Phase Heat Transfer from an Impinging Cross-Shaped Jet

Local single- and two-phase heat transfer distributions are measured under a confined impinging jet issuing from a cross-shaped orifice. Spatially resolved temperature maps and convection coefficients resulting from the impinging flow are obtained via infrared imaging of a thin-foil heat source. The cooling patterns in single- and two-phase operation are explained by an accompanying numerical investigation of the fluid flow issuing from the orifice; computed velocity magnitudes and turbulence intensities are presented. In single-phase operation, the coolest surface temperatures correspond to areas with high liquid velocities. High velocities and developing turbulence are also shown to increase convective heat transfer along the diagonal outflow directions from the impinging jet. During two-phase transport, boiling preferentially begins in regions of low velocity, providing enhanced heat transfer in the areas least affected by the impingement. The cross-shaped orifice achieves local heat transfer coefficients that exceed the stagnation-point value of a circular jet of equivalent open orifice area by up to 1.5 times, while resulting in an increased pressure drop only 1.1 times higher than that of the circular jet

Boiling Heat Transfer from an Array of Round Jets with Hybrid Surface Enhancements

The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5x5 array of jets, each 0.75mm in diameter, is compared to that of a single 3.75mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates

Transformasi Novel Perempuan Berkalung Sorban Ke Dalam Film Perempuan Berkalung Sorban: Kajian Ekranisasi

The purposes of this research are (1) describe the reduction of the story of the novel Perempuan Berkalung Sorban which was adapted into a movie entitled Perempuan Berkalung Sorban, (2) describe the addition of the story of the movie Perempuan Berkalung Sorban which was adapted from the novel Perempuan Berkalung Sorban, (3) describe various form of changing or alterations of the novel Perempuan Berkalung Sorban which was adapted into the movie Perempuan Berkalung Sorban, (4) describe the function of alterations of the novel Perempuan Berkalung Sorban which has been adapted into the movie Perempuan Berkalung Sorban. Data of this research are parts of the story in the novel and movie Perempuan Berkalung Sorban which shows the reduction, addition, and various alterations that is measured from the novel Perempuan Berkalung Sorban. Sources of the data are the novel and movie Perempuan Berkalung Sorban. The data were taken through notetaking method. Research findings shows that there are 24 events, 9 characters, and 5 settings

Daya Simpan Benih Jabon Putih [Neolamarckia Cadamba (Roxb.) Bosser] Berdasarkan Populasi Dan Karakteristik Benih (Seed Storability of Jabon Putih [Neolamarckia Cadamba (Roxb.) Bosser] Base on Populations and Seed Characteristics)

Jabon putih [Neolamarckia cadamba (Roxb.) Bosser] has been cultivated in large scale. However it is constrained by the availability of high quality seeds and seed storability information. This study aimed to identify seed storability of jabon putih based on populations and seed morpho-physiological characteristics. Seeds were collected from eight populations, located in eight provinces. Population was a single factor in a completely randomized design for testing the germination characteristics (germination capacity, germination uniformity, germination speed, mean germination time and germination value) before and after storage. Geo-climate and soil macro elements were used as parameters to examine the correlation between environmental factors and seed characteristics before and after storage. Population was significantly correlated with germination characteristics, before and after storage for 54 months. The results indicated that seeds from Pomalaa population had the best germination characteristics, while those from Ogan Kemiring Ilir had the worst germination characteristics. Based on moisture content and storability, jabon putih seed could be categorized as orthodox that can be stored in long time at low temperatures with low moisture content. Geo-climate and soil macro element were not significantly correlated with germination. This result indicated that genetic factor had high contribution to seed storability of jabon putih

Area-scalable high-heat-flux dissipation at low thermal resistance using a capillary-fed two-layer evaporator wick

A two-layer sintered porous evaporator wick for use in vapor chambers is shown to offer very high performance in passive high-heat-flux dissipation over large areas at a low thermal resistance. The two-layer wick has an upper cap layer dedicated to capillary liquid feeding of a thin base layer below that supports boiling. An array of vertical posts bridges these two layers for liquid feeding, while vents in the cap layer provide an unimpeded pathway for vapor removal from the base wick. The two-layer wick is fabricated using a combination of sintering and laser machining processes. The thermal resistance of the wicks during boiling is characterized in a saturated environment that replicates the capillary-fed working conditions of a vapor chamber evaporator. Thermal characterization tests are first performed using conventional single-layer evaporator wicks to analyze the effect of sintered particle size on capillaryfed boiling of water. Of the particle size ranges tested, wicks sintered from 180 to 212 micrometer-diameter particles provided the best combination of high dryout heat flux and a low boiling resistance. A two-layer evaporator wick comprising particles of this optimal size and a 15 x 15 array of liquid feeding posts yielded a maximum heat flux dissipation of 485 W/cm2 over a 1 cm2 heat input area while also maintaining a low thermal resistance of only ~0.052 K/W. The thermal performance of the two-layer wick is compared against various hybrid and biporous evaporator wicks previously investigated in the literature. While previous wick designs are typically restricted to small areas and low power levels or high surface superheats when dissipating such heat fluxes, the unique area-scalability of the two-layer wick design allows it to achieve an unprecedented combination of high total power and low-thermal-resistance heat dissipation over larger areas than were previously possible

The Role of Vapor Venting and Liquid Feeding on the Dryout Limit of Two-Layer Evaporator Wicks

Vapor chambers developed for high-heat-flux operation require advanced evaporator wick designs that can sustain capillary flow when boiling occurs over the heater region. A two-layer evaporator wick inte- grates a thin base wick layer that is supplied with liquid from a thick cap layer through an array of ver- tical feeding posts distributed over the heated area. This design allows boiling to occur within the thin base layer, while separating the incoming liquid feeding and outgoing vapor venting pathways. In our prior work, boiling in two-layer wicks was experimentally demonstrated to provide high-heat-flux dissi- pation over larger heater areas and at low thermal resistance. The current study experimentally explores the effect of two-layer wick design parameters, specifically the dimensions that alter the area available for liquid feeding and vapor venting, on the thermal performance and dryout limit of the wick, using water as the working fluid. Four different two-layer wick designs are fabricated over a 1 cm 2 evaporator area by sintering 180–212 μm copper particles. Increasing the vapor-venting area from 7% to 16% of the total evaporator area yielded a significant increase in the dryout limit, from 315 W/cm 2 to 405 W/cm 2 . Increasing the liquid-feeding area using wider posts increased the dryout limit further. Finally, a paramet- rically optimized design with fewer but larger posts and vents resulted in better performance compared to a design with denser features. With this two-layer wick design, we demonstrate an extremely high dryout limit of 512 W/cm 2 over the large 1 cm 2 heated area at a thermal resistance of 0.08 K/W