CFD MODELING OF MICROCHANNELS COOLING FOR ELECTRONIC MICRODEVICES

A simulation of the cooling of electronic devices was carried out by means of microchannels, using water as a coolant to dissipate the heat generated from a computer processor, and thus stabilize its optimum operating temperature. For the development of this study, computational fluid mechanics modeling was established in order to determine the temperature profiles, pressure profiles, and velocity behavior of the working fluid in the microchannel. In the results of the study, the operating temperatures of the computer processor were obtained, in the ranges of 303 K to 307 K, with fluid velocities in the microchannels of 5 m/s, a pressure drop of 633.7 kPa, and a factor of safety of the design of the microchannel of 15. From the results, the improvement of the heat transfer in a cooling system of electronic devices was evidenced when using a coolant as a working fluid compared to the cooling by forced air flow traditional. ABSTRAK: Simulasi penyejukan alatan elektronik telah dibina menggunakan saluran mikro, di samping air sebagai agen penyejuk bagi menghilangkan haba yang terhasil dari pemproses komputer, dan penstabil pada suhu operasi optimum. Kajian ini mengenai model komputasi mekanik bendalir bagi menentukan profil suhu, profil tekanan, dan halaju perubahan bendalir dalam saluran mikro. Dapatan kajian menunjukkan suhu operasi pemproses komputer adalah pada julat suhu 303 K sehingga 307 K, dengan halaju bendalir dalam saluran mikro adalah pada kelajuan 5 m/s, penurunan tekanan sebanyak 633.7 kPa, dan faktor keselamatan 15 bagi reka bentuk saluran mikro. Ini menunjukkan terdapat kenaikan pemindahan haba bagi sistem penyejukan alatan elektronik ini, terutama apabila cecair digunakan sebagai penyejuk haba berbanding kaedah tradisi iaitu dengan mengguna pakai aliran udara sebagai agen penyejuk.

New Comparative Study of High-Sensitivity H2Gas Sensors at Room Temperature Based on ZnO NWs Grown on Si and PS/Si Substrates without Catalyst by Wet Thermal Evaporation Method

A novel approach for growing high-quality ZnOnano-structures with no catalyst using an inexpensive technique that is called wet thermal evaporation has been investigated for gas sensor applications. For a novel comparative investigation of H2 gas sensors, large regions regarding the well-aligned coral reef-like ZnOnano-structures on the porous Si (PS) and flower-like nano-rods on Silicon were successfully utilized. In the presented study, a Pd/ZnO/Pd metal-semiconductor-metal was efficiently created for H2 gas sensor device employing high-quality ZnOnano-structures that are grown on a variety of the substrates. At room temperature, the sensitivity related to ZnO/PS and ZnO/Si is evaluated at various flow rate values (25sccm, 50sccm, 100sccm, and 150sccm) of 2% H2 gas. The I-V characteristics revealed that ZnO/Si has a larger hydrogen gas barrier height than ZnO/PS. At room temperature, the ZnO/Si sensitivity was about 105% and 190% for ZnO/PS at 150sccm flow rate. The sensors’ sensitivity and optimum operating temperature for ZnO/PS at 150sccm of H2 gas are 350% (at 100 Celsius), which is higher compared to double the maximal sensitivity with regard to ZnO/Si device at a temperature of 150 Celsius. This research concluded that because ZnO/PS has a large specific area, it has a greater possibility of reacting with gases and increasing sensitivity at the temperature of theroom.

Significant effect of SDS on the optimum operating temperature of ZnO nanosheets gas-sensitive materials

Many methods have been used to reduce the operational energy consumption of ZnO gas-sensitive material effectively. In this paper, different morphologies of ZnO nanomaterials are respectively prepared in the anionic hydrophilic surfactant sodium lauryl sulfate (SDS) with different concentrations as soft templates by hydrothermal method. The influence of SDS concentrations is investigated on the morphology of materials under the conditions of a weak alkali environment with the same pH, and their gas sensitivity after annealing with the same temperature and time. The morphologies and phase structures of all samples are characterized by FESEM and XRD, and their gas-sensitive properties are analyzed by CGS-1TP. Interestingly, the experimental results show that the optimal working temperature of ZnO gas-sensitive materials containing low concentration SDS is reduced by nearly 55% than that of containing 10 times this concentration, and its sensitivity is also slightly improved. The possible mechanism by which the SDS concentration affects the gas sensitivity of the material is also proposed.

Ppb-Level Butanone Sensor Based on ZnO-TiO2-rGO Nanocomposites

In this paper, ZnO-TiO2-rGO nanocomposites were successfully synthesized by the hydrothermal method. The morphology and structure of the synthesized nanomaterials were characterized by SEM, XRD, HRTEM, and XPS. Butanone is a typical ketone product. The vapors are extremely harmful once exposed, triggering skin irritation in mild cases and affecting our breathing in severe cases. In this paper, the gas-sensing properties of TiO2, ZnO, ZnO-TiO2, and ZnO-TiO2-rGO nanomaterials to butanone vapor were studied. The optimum operating temperature of the ZnO-TiO2-rGO sensor is 145 °C, which is substantially lower than the other three sensors. The selectivity for butanone vapor is greatly improved, and the response is 5.6 times higher than that of other organic gases. The lower detection limit to butanone can reach 63 ppb. Therefore, the ZnO-TiO2-rGO sensor demonstrates excellent gas-sensing performance to butanone. Meanwhile, the gas-sensing mechanism of the ZnO-TiO2-rGO sensor to butanone vapor was also analyzed.

Investigation of the optimum conditions for adsorptive hydrogen storage

Cryogenic adsorption using microporous materials is one of the emerging technologies for hydrogen storage in fuel cell vehicles. Metal–organic frameworks have been identified as suitable adsorbents exhibiting large hydrogen sorption at 77 K. With respect to technical realization, in this work, the deliverable capacity at the optimal storage temperature was determined for a series of MOFs in comparison to zeolite Ca-A. The deliverable capacity is defined as the amount of hydrogen released between a maximum tank pressure and a minimum back pressure and shows a maximum which defines the optimum operating temperature. This optimum operating temperature depends on the pore size of the adsorbent and the chemical properties of the surface. A number of materials are identified that exhibit optimal operating temperatures well above 100 K. A higher optimal storage temperature, however, typically results in a lower deliverable capacity.

Study on the Ozone Gas Sensing Properties of Rf-Sputtered Al-Doped NiO Films

Al-doped NiO (NiO:Al) has attracted the interest of researchers due to its excellent optical and electrical properties. In this work, NiO:Al films were deposited on glass substrates by the radio frequencies (rf) sputtering technique at room temperature and they were tested against ozone gas. The Oxygen content in (Ar-O2) plasma was varied from 2% to 4% in order to examine its effect on the gas sensing performance of the films. The thickness of the films was between 160.3 nm and 167.5 nm, while the Al content was found to be between 5.3at% and 6.7at%, depending on the oxygen content in plasma. It was found that NiO:Al films grown with 4% O2 in plasma were able to detect 60 ppb of ozone with a sensitivity of 3.18% at room temperature, while the detection limit was further decreased to 10 ppb, with a sensitivity of 2.54%, at 80 °C, which was the optimum operating temperature for these films. In addition, the films prepared in 4% O2 in plasma had lower response and recovery time compared to those grown with lower O2 content in plasma. Finally, the role of the operating temperature on the gas sensing properties of the NiO:Al films was investigated.

Highly Fast Response of Pd/Ta2O5/SiC and Pd/Ta2O5/Si Schottky Diode-Based Hydrogen Sensors

Herein, the fabrication of a novel highly sensitive and fast hydrogen (H2) gas sensor, based on the Ta2O5 Schottky diode, is described. First, Ta2O5 thin films are deposited on silicon carbide (SiC) and silicon (Si) substrates via a radio frequency (RF) sputtering method. Then, Pd and Ni are respectively deposited on the front and back of the device. The deposited Pd serves as a H2 catalyst, while the Ni functions as an Ohmic contact. The devices are then tested under various concentrations of H2 gas at operating temperatures of 300, 500, and 700 °C. The results indicate that the Pd/Ta2O5 Schottky diode on the SiC substrate exhibits larger concentration and temperature sensitivities than those of the device based on the Si substrate. In addition, the optimum operating temperature of the Pd/Ta2O5 Schottky diode for use in H2 sensing is shown to be about 300 °C. At this optimum temperature, the dynamic responses of the sensors towards various concentrations of H2 gas are then examined under a constant bias current of 1 mA. The results indicate a fast rise time of 7.1 s, and a decay of 18 s, for the sensor based on the SiC substrate.

A Novel Ceramic Sensing Material for Acetone Detection from Asphalt

A novel ceramic sensing material, orthorhombic molybdenum trioxide (a-MoO3) nanobelts, was successfully prepared through a simple hydrothermal strategy. And its crystalline phase and microstructures were characterized via X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The results indicate that the size of the a-MoO3 nanobeltsis 180-250 nm in width and several microns in length. Gas sensing performances of the as-synthesized a-MoO3 nanobelts towards acetone vapor which was a representative VOCs in asphalt were investigated. The a-MoO3 nanobelts based gas sensor exhibits superior response at the optimum operating temperature of 300 °C for 200 ppm acetone vapor and excellent stability. The gas sensing mechanism for the a-MoO3 nanobelts to acetone vapor was also discussed.

Sunflower-Like Zinc Oxide Architectures: The Application of Acetone Gas Sensor for Asphalt Pavement Construction

In this work, hierarchical nanorod-assembled ZnO sunflower-like structures were successfully synthesized through a water bath route. Crystalline phase and surface morphology of as-prepared ZnO were investigated via XRD and SEM techniques, respectively. Gas sensor fabricated from nanorod-assembled ZnO sunflowers was made, which exhibits excellent gas sensing properties at various concentrations of acetone and different operating temperatures. The gas response values at the optimum operating temperature (300 °C) are 49 towards 200 ppm acetone. The sensing measurement results indicates that the as-synthesized ZnO material may depict potential application as an acetone detector in asphalt pavement construction.

On the optimum operating temperature for steam floods

The technical, environmental and economic performances of a steam flood are partly influenced by the operating temperature (pressure). However, the definition and procedure for determining the optimum operating temperature are still debatable. Employing a combination of analytic modelling and numerical simulations, this paper investigates the existence (or otherwise) of an optimum injection temperature Topt for saturated-steam floods. Considering the maximization of productivity and thermal efficiency as objective, an analytic procedure, which explores the effects of temperature on injectivity, total steam enthalpy, oil viscosity and relative permeabilities, shows that the operating temperature (pressure) of a steam flood should not exceed 515 K (3.5 MPa). A simple closed-form expression is proposed for Topt as a function of basic rock and fluid properties. For an example three-dimensional reservoir model comprising an 8-m oil shale unit sandwiched between two sandy units each 15 m thick, numerical simulations show sensitivity to temperature (and viscosity effect) in the range 350–450 K, but becomes increasingly insensitive in the band 500–650 K. It is established that ~500–550 K is the optimum band when the optimization objective is to maximize both discounted oil recovery and cumulative oil-steam ratio. These results agree with an optimum injection temperature of ~501 K estimated from the proposed analytical model in this case. Therefore, based on the results of the analytical model, thermal simulations and other considerations, it is concluded that the optimum steam-injection temperature is project and system specific. The insights gained should find relevance in the design and management of steam floods, as well as other steam-based recovery processes.