Internal Heater Research Articles

Resonances and nonlinear vibrations of circular cylindrical shells, effects of thermal gradients

In this paper, the results of an experimental campaign focused on the vibrations of shells are presented. More specifically, the goal is to investigate the effect of thermal gradients across the shell thickness on the nonlinear dynamics. The shell is made of polymeric material and an aluminum mass is clamped on one end of the shell; the other shell end is clamped to an electrodynamic shaker, which provides a base harmonic excitation. Tests are performed in a controlled environment where a thermal gradient on the shell thickness is generated by means of a climatic chamber and an internal cartridge heater. Different temperature gradients and base excitation levels have been considered. The nonlinear dynamic scenario is analyzed through amplitude–frequency diagrams, bifurcation diagrams, waterfall diagrams, time histories, Fourier spectra, phase portraits, and Poincaré maps. Results show a strong effect of the temperature on the dynamic response of the shell: subharmonic, quasi-periodic, and chaotic vibrations take place as well as large amplitude vibrations, high sound levels are detected.

A Study on Sodium–Concrete Reaction in Presence of Internal Heating

Abstract The sodium–concrete reaction (SCR) is an important phenomenon during severe accidents in sodium-cooled fast reactors (SFRs), as it generates large volumes of hydrogen and aerosols in the containment vessel along with structural concrete ablation. In this study, the chemical reaction beneath the internal heater (800 °C) was investigated in SCR experiments with internal heating. The experiments simulate the effects of obstacles and heating on the SCR. Especially, we focused on the concrete ablation phenomenon because the hydrogen generation is sourced from the moisture in the concrete. The effects of internal heating on the self-termination mechanism are also discussed. The internal heater on the concrete hindered the transport of sodium (Na) into the concrete. Therefore, the reaction between Na and the concrete began at the periphery of the internal heater, where the concrete ablation depth was larger than under the internal heater. The high Na pool temperature (800 °C) largely increased the Na aerosol-release rate, which was explained by Na evaporation and formed a porous reaction-product layer. The Si mass balance and image mapping by an electron-probe micro-analyzer yielded consistent porosities in the reaction-product layer (0.54–0.59). The porous reaction products suppressed the amount of Na transported into the reaction front. Regardless of the internal heater placement, the Na concentration around the reaction front was limited to around 30 wt %. The Na concentration condition was dominantly responsible for the self-termination of the internally heated SCR.

Исследование теплообмена при кипении фреономасляной смеси в трубах испарителей судовых холодильных установок

The paper describes small-capacity irrigation evaporators that improve the performance of a refrigeration unit, as they exclude the release of liquid freon into the compressor suction pipe under sharp increasing of heat load or during ship rolling. The relevance of studying heat transfer at freons boiling in a moving film has been proved. The results and analysis of experimental data on average heat transfer coefficients are presented. The graph shows the dependence of the average heat transfer coefficients on the heat flux density at various irrigation densities. There are presented the results of special experiments determining the effect of irrigation density on heat transfer. It has been stated that the effect of pressure or saturation temperature in the modes of evaporation and developed boiling manifests itself in different ways. With developed boiling, the beam pitch does not have a significant effect on heat transfer. The experiments were carried out on two stands: small-row and multi-row. The pipes were heated with an internal electric heater. It has been inferred that heat transfer in the film is more intense than in volume, therefore, smooth steel pipes can be used in irrigation evaporators instead of finned copper tubes, which are used in flooded devices. The boiling process in a film can be described by equations valid for a large volume, taking into account quantitative differences. The values of a constant coefficient and the criteria exponents are given; the similarity equation for the regime of developed bubble boiling of freons is derived. The calculated dependencies can be applied in evaluating the operation of irrigation evaporators of ship refrigeration units.

Capacitive Humidity Sensing Characeristics of Porous Silicon Oxide Via Electrodeposition Assisted Stripping and Metal Assisted Chemical Etching Process

Sensor devices are widely used for increasing human convenience to detect various environmental parameters such as humidity, temperature, pressure and lots of hazardous chemicals. Also, specific sensor devices are utilized for private security using iris or finger print. Among them, humidity sensors are widely utilized in the fields of food science, meteorology, preservation of relics, so on [1-2]. Therefore, measuring the humidity is substantial interest in research fields. For detecting the humidity, many materials including silicon, silicon oxide, metal oxide, conducting polymers, and carbon group materials have been used. Among them, silicon oxide is considered because of its low process cost and simple fabrication process. Moreover, silicon oxide is hydrophilic materials that water molecules were easily adsorbed on its surface. In order to increasing sensing characteristics, lots of researchers put an enormous efforts such as increasing surface to volume ratio, improving the structure of sensor device, and doping the impurities to electrode materials and so on. Among them, increasing the effective surface area is the most common and simple way to enhancing the sensing characteristics. Electrodeposition assisted stripping (EAS) process is the one of the most effective kerf-free method for obtaining the thin silicon film [3]. The EAS process is using a spalling which is the unique mode of brittle fracture, caused by high tensile stress. High tensile stressed layer can induce fracture at a certain depth, parallel to substrate interface, which was deposited by electrochemical deposition of nickel layer on the silicon surface. In order to control the thickness of spalled silicon layer, current density is the critical parameter of electrodeposition process. Metal assisted chemical etching (MACE) process is utilized to fabricate the porous structure. The MACE process is using the anisotropic etching phenomenon through metal catalysts in wet etching solution, which is consisted of hydrogen peroxide and hydrofluoric acid. Compared to dry etching process, MACE can fabricate the high aspect ratio of porous structure much easier and cheaper than vacuum based process. In this study, we fabricated the porous silicon oxide film using EAS, MACE and oxidation process and it was characterized as humidity sensor device. Before the EAS process, the thickness of 20 and 200 nm of titanium and nickel layer was deposited by E-beam evaporator. The current density of 10 mA/cm2 was conducted to deposit the high tensile stressed nickel layer in watt bath which was consisted of nickel sulfate, nickel chloride and sodium citrate. The thickness of spalled silicon layer was around 90 ~ 100 um. After the spalling the silicon, MACE and oxidation process was conducted in consecutive order. Tin and silver electro-less deposition was conducted to make the metal catalyst and hydrogen peroxide and hydrofluoric acid were used for etching electrolyte. The oxidation process was conducted in ambient air condition at 1000 ℃ in 3-zone quartz tube furnace. Surface morphology and thickness of spalled silicon were observed with field-emission scanning electron microscope (FE-SEM). Electrical characteristics of porous Si humidity sensor were characterized by 2-point probe station. The humidity was controlled by changing the ratio of dry gas to wet gas. Variation of capacitance of humidity sensor was measured and recorded using an LCR meter. The sensitivity is represented by (CDry - CRH) / CRH, where CRH is the capacitance with the varied humidity and CDry is the capacitance with the lowest humidity. Moreover, response and the recovery time are defined as the time to reach 90% of the total variation. In order to verifying the humidity sensing mechanism, electrochemical impedance spectroscopy (EIS) analysis was conducted. From the EIS results, proper equivalent circuit of humidity sensor and sensing mechanism were suggested. REFERENCES [1] P. Hurjes, A. Kovacs, Cs. Ducso, M. Adam, B. Muller, U. Mescheder, “Porous silicon-based humidity sensor with interdigital electrodes and internal heaters”, Sensors and Actuators B: Chemical 2003, 95, 140-144. [2] Z.M. Rittersma, A. Splinter, A. Bodecker, W. Benecke, “A novel surface-micromachined capacitive porous silicon humidity sensor” Sensors and Actuators B: Chemical 2000, 68, 210-217. [3] Youngim Kwon, Changyeol Yang, Sang-Hwa Yoon, Han-Don Um, Jung-Ho Lee and Bongyoung Yoo, “Spalling of a Thin Si Layer by Electrodeposit-Assisted Stripping”, Applied Physics Express, 2013, 6 (11), 116502.

Development of Commissioning and operation of CSNS Cryogenic System

China Spallation Neutron Source (CSNS) cryogenic system provides supercritical cryogenic hydrogen for two moderators of the target station. The commissioning work of the cryogenic system is mainly divided into four steps:(1) the acceptance test of the helium refrigerator, using the refrigerator internal heater as thermal load, and verify whether the helium refrigerator refrigerating capacity meet the requirements of the contract or not; (2) Helium commissioning, using dummy load to simulate the dynamic heat load of the moderator, and system cool down to 20K with He instead of H2. (3) Hydrogen commissioning based on the step 2, while system is cooled down to 20K with hydrogen as working medium. (4) Joint Commissioning with two moderators. So far, the CSNS cryogenic system has completed all commissioning work and finished four rounds of stable operation for the commissioning of the target station and spectrometer.

Vibrational effect on internal heated porous medium in the presence of chaos

The present article investigates a chaotic convection under modulation in the presence of internal heat generation. The viscoelastic fluid saturating porous medium, heated from below is considered; a modified Darcy’s momentum equation and heat generation term used in energy equation. An autonomous system of fourth order differential equations have been deduced by using truncated Galerkin expansions. The asymptotic behavior can be stationary, periodic, or chaotic, depending upon the values of system parameters. It is found that a better combination of values of modulation parameters and scaled Rayleigh, internal Rayleigh numbers provides a way for chaos. Both a temperature and gravity modulation of the medium is to enhance or diminish the behavior of chaotic nature of the system. Due to high internal heat generation there is a chance to devolve a new kind of stable or unstable points in the system. Finally, heat transfer results are presented in terms of Nusselt number.

Development of a high temperature diamond anvil cell for x ray absorption experiments under extreme conditions

X-ray absorption spectroscopy (XAS) is presently a powerful and established tool to investigate solid and liquid matter at high pressure and high temperature (HP-HT). HP-HT XAS experiments rely on high pressure technology whose continuous development has extended the achievable range up to 100 GPa and more. In high pressure devices, high temperature conditions are typically obtained by using internal and external resistive heaters or by laser heating. We have recently developed a novel design for an internally heated diamond anvil cell (DAC) allowing XAS measurements under controlled high temperature conditions (tested up to about 1300 K). The sample in the new device can be rapidly heated or cooled (seconds or less) so the cell is suitable for studying melting/crystallization dynamics when coupled with a time-resolved XAS setup (second and sub-second ranges). Here we describe the internally heated DAC device which has been realized and tested in experiments on pure selenium at the energy dispersive ODE beamline of Synchrotron SOLEIL. We also present results obtained in XAS experiments of elemental Se using a large volume Paris-Edinburgh press, as an example of the relevance of structural studies of matter under extreme conditions.

Multi-layered Porous Foam Effects on Heat Transfer and Entropy Generation of Nanofluid Mixed Convection Inside a Two-Sided Lid-Driven Enclosure with Internal Heating

Mixed convection of Cu-water nanofluid inside a two-sided lid-driven enclosure with an internal heater, filled with multi-layered porous foams is studied numerically and its heat transfer and entropy generation number are evaluated. Use of multi-layered porous media instead of homogeneous ones is capable of heat transfer enhancement, by weakening flow where does not impose a pivotal role on heat transfer and amplifying the flow in regions where have more effects on the heat transfer. Eight different arrangements of porous layers are considered and the two-phase mixture model is implemented to simulate nanofluid mixed convection inside the cavity. Results are presented in terms of stream functions, isotherms, Nusselt and entropy generation number for the eight cases considering various Richardson numbers (Ri = 10−4 to 103) and nanofluid concentrations (φ = 0 to 0.04). Results indicate that using the multi-layered porous material can confine flow vortices in the vicinity of the moving walls and could enhance the heat transfer up to 17 percent (with respect to the case using homogeneous porous material with the highest permeability), such that this enhancement is more in lower Ri values (stronger convective effects). Entropy generation number also increases by nanofluid volume fraction increment and Ri decrement. Cases with a higher heat transfer rate also have the higher entropy generation number. In addition, an increase of volume fraction decreases the relative entropy generation number (S*) for low Ri number, while contrary fact observed for high Ri values.

Microfluidic Control Board for High-Pressure Flow, Composition, and Relative Permittivity.

Flow control is central to microfluidics and chromatography. With decreasing dimensions and high pressures, precise fluid flows are often needed. In this paper, a high-pressure flow control system is presented, allowing for the miniaturization of chromatographic systems and the increased performance of microfluidic setups by controlling flow, composition, and relative permittivity of two-component flows with CO2. The system consists of four chips: two flow actuator chips, one mixing chip, and one relative permittivity sensor. The actuator chips, throttling the flow, required no moving parts as they instead relied on internal heaters to change the fluid resistance. This allows for flow control using miniaturized fluid delivery systems containing only a single pump or pressure source. Mobile phase gradients between 49% and 74% methanol in CO2 were demonstrated. Depending on how the actuator chips were dimensioned, the position of this range could be set for different method-specific needs. With the microfluidic control board, both flow and composition could be controlled from constant pressure sources, drift could be removed, and variations in composition could be lowered by 84%, resulting in microflows of CO2 and methanol with a variation in the composition of ±0.30%.

Improving degree of cure in pultrusion process by optimizing die-temperature

Pultrusion is a continuous process for manufacturing polymer composite with uniform cross-sectional profiles. In this process the die temperature process variable can be used to improve the chemical and mechanical properties of the polymer composite. Several works have been done regarding simulation tools for pultrusion analysis. Usually, the development of manufacturing processes is mostly a trial-and-error exercise. However, few studies focus on optimizing this manufacturing process. In this paper, the pultrusion process of a glass fibre-epoxy set with different geometries are simulated by using a three-dimensional finite element-nodal control volume (FE/NCV) approach, a quadratic programming algorithm and a particle swarm heuristic was used to optimize the manufacturing process. The aim is to show that to optimize pultrusion process, quadratic programming algorithm can also be very efficient in finding the optimal distribution of the temperature in the pultruded material. The second proposal of this paper is to present a simulation for pultrusion process based on a total number of 16 heaters embedded into die block, instead of external planar heaters. The results show that the mean of the cure degree is satisfactory when used with many internal heaters.

Fabrication of Thin Film of Porous Silicon Using Electrodeposition Assisted Stripping (EAS) Process and Its Humidity Sensing Properties

Humidity is one of the most important factors in human life to live comfortably. Especially, detecting and measuring humidity has been attracted in various fields such as food science, meteorology, agriculture, and so on. At present, most of the humidity sensors, fabricated to detect humidity through variation of the electrical signals using metal oxide which was zinc oxide1, copper oxide2, titanium oxide3, conducting polymer4, and silicon based materials5-6. Especially, among the silicon based materials, porous silicon was currently one of the promising materials because of its easy fabrication process and low cost. Silicon is used as a key material for the electrical devices. The silicon occupies about 40 percent of the device production cost. Therefore, there were lots of study using spalling process for reducing the thickness of the silicon wafer. One of the most effective and inexpensive techniques is the Electrodeposition Assisted Stripping (EAS) process7. Electrodeposition assisted stripping (EAS) process was used to obtain a thin Si substrate by electroplating high tensile stress layer, which induced the lift-off behavior of thin Si layer. Ni buffer layer was deposited using electrodeposition process with the Watts bath. The buffer layer protects the Si substrate from the high stress layer which can cause damage to the substrate. Also, buffer layer thickness can control the spalled Si thickness. In this study, we fabricated thin porous Si using EAS process and thin porous Si was characterized as humidity sensor. The porous silicon was fabricated by dry etching process. Before the EAS process, titanium and nickel layer was deposited by E-beam evaporator. The thickness of titanium and nickel layer was 20 nm and 200 nm, respectively. The thickness of thin porous Si layer was controlled by controlling current density of Ni electrodeposition process. The current density was controlled 10 mA/cm2 to 50 mA/cm2. The thickness of spalled porous silicon layer was controlled 100 um to 60 um. Surface morphology, and thickness of porous Si layer were observed with a field emission scanning electron microscope (FE-SEM). Electrical characteristics of porous Si humidity sensor were measured by 2-point probe station. The humidity was controlled by changing the ratio of dry gas to wet gas. The resistance of humidity sensor was recorded using an electrical source meter. The sensitivity is represented by RDry/RRH, where RRH is the resistance with the varied humidity and RDry is the resistance with the lowest humidity. Moreover, response and the recovery time are defined as the time to reach 90% of the total variation. REFERENCES [1] Hsu, N.-F.; Chung, T.-K., “A rapid synthesis/growth process producing massive ZnO nanowires for humidity and gas sensing”. Applied Physics A 2014, 116 (3), 1261-1269. [2] Hsueh, H. T.; Hsueh, T. J.; Chang, S. J.; Hung, F. Y.; Tsai, T. Y.; Weng, W. Y.; Hsu, C. L.; Dai, B. T., “CuO nanowire-based humidity sensors prepared on glass substrate”. Sensors and Actuators B: Chemical 2011, 156 (2), 906-911. [3] Li, Z.; Zhang, H.; Zheng, W.; Wang, W.; Huang, H.; Wang, C.; MacDiarmid, A. G.; Wei, Y., “Highly Sensitive and Stable Humidity Nanosensors Based on LiCl Doped TiO2 Electrospun Nanofibers”. Journal of the American Chemical Society 2008, 130 (15), 5036-5037. [4] Hwang, L. S.; Ko, J. M.; Rhee, H. W.; Kim, C. Y., “A polymer humidity sensor”. Synthetic Metals 1993, 57 (1), 3671-3676. [5] P. Hurjes, A. Kovacs, Cs. Ducso, M. Adam, B. Muller, U. Mescheder, “Porous silicon-based humidity sensor with interdigital electrodes and internal heaters”, Sensors and Actuators B: Chemical 2003, 95, 140-144. [6] Z.M. Rittersma, A. Splinter, A. Bodecker, W. Benecke, “A novel surface-micromachined capacitive porous silicon humidity sensor” Sensors and Actuators B: Chemical 2000, 68, 210-217. [7] Youngim Kwno, Changwol Yang, Sang-Hwa Yoon, Han-Don Um, Jung-Ho Lee and Bongyoung Yoo, “Spalling of a Thin Si Layer by Electrodeposit-Assisted Stripping”, Applied Physics Express, 2013, 6 (11), 116502.

Automotive Fuel Cell Subzero Cold-Starts in a Single Cell Quasi-Adiabatic Fixture

Proton exchange membrane fuel cells (PEMFC) mirror current amenities available from the internal combustion engine such as: rapid start-up time, refueling time, and travel range. For an automotive PEMFC stack to attain 80 kW of power, typically greater than 300 repeat cells are required. A single cell is comprised of 7 layers between the anode and cathode flow fields/current collectors and include layers of macro/microporous diffusion media, ionomer bound carbon supported platinum catalyst layers, and a central proton exchange membrane (PEM). In the presence of partially humidified fuel and oxidant feeds (H2 and 21%O2/79%N2 on the anode and cathode, respectively) energy is produced under applied load as electrons and protons are formed from H2 oxidation on the anode and water is formed by the exothermic reduction of the protons and electrons with O2 on the cathode. The hygroscopic PEM inherently retains humidified reactant gas and oxygen reduction reaction product water which facilitates proton conduction. Four main issues limit commercial viability of automotive fuel cells – (i) cathode catalyst durability, (ii) fuel cell cost, (iii) subzero cold-starts, and (iv) refueling infrastructure. Automotive subzero cold-starts are challenging due to residual water inventory of the PEMFC and product water formation and retention. Water retained within the ionomer of the membrane and catalyst layers partially remains in a liquid phase above -40°C due to pore size and acidity induced freezing point depression.1 For successful cold-start, the temperature of the PEMFC must increase above 0°C before the accumulation of product water in the cathode catalyst layer significantly restricts O2 mass transport. Catalyst layer fabrication affects the water storage capacity of the PEMFC at subzero temperatures. Directly spraying the cathode catalyst layer on the membrane vs. decal transfer of a screen printing results in a nearly 60 mV increase in the initial on load voltage that would translate to a high initial power output, but a 2-2.5x decrease in the water storage capacity at -20°C.2 Partially dehydrating the PEMFC to lower initial water contents (λinitial) increases that water storage capacity at the expense of the initial on load voltage.3 A prototype quasi-adiabatic cold-start single cell PEMFC fixture was designed in-house to address several of the initial issues found in UTRC’s4 original design. The insulating materials selected for permeability and mechanical stability were polycarbonate and balsa wood, respectively. Internal Kapton heaters were used to emulate adjacent cell heading. Figure 1 show the impact of λinitial of 3.2 and 6.2, heater output levels equivalent to 1x and 2x adjacent cell heating (to compensate for non-adiabatic losses), and constant current (600 mV cm-2) vs. constant potential (0.1V) starts. The initial temperature rise increased with higher λinitial and under constant potential control. Isothermal water fill tests were performed on the same membrane electrode assembly after cold starts. Performance degradation due to subzero testing was higher for isothermal water fill tests compared to cold starts. Balliet, R.J. and J. Newman, 'Cold Start of a Polymer-Electrolyte Fuel Cell I. Development of a Two-Dimensional Model', J. Electrochem. Soc., 2011, 158, B927.Pistono, A. and C.A. Rice, 'The Effect of Material Properties on the Subzero Water Storage Capacity of Cathode Catalyst Layers for Proton Exchange Membrane Fuel Cells', J. Electrochem. Soc., 2017, 164, F582.Pistono, A. and C.A. Rice, 'Subzero Water Storage Capacity in Proton Exchange Membrane Fuel Cells: Effects of Preconditioning Method', The Journal of Power Souces, 2018 Under Review.Rice-York, C., J. Needham, N. Gupta, and P.L. Hagans, 'Platform for Rapid Prototyping of PEM Fuel Cell Designs with Enhanced Cold-Start Performance and Durability', ECS Transactions, 2006, 1, 383. Figure 1

Tunable enhanced infrared absorption spectroscopy surfaces based on thin VO2 films

Infrared absorption spectroscopy takes advantage of the electric field enhancement to detect low amounts of materials such as monolayer biomolecules. While the plasmonic field enhancement is the popular approach, it has been demonstrated that the interference-based uniform field enhancement using a simple dielectric/metal structure exhibits higher sensitivity and larger spectral bandwidth for ultrathin materials. Here, we numerically demonstrate that the enhancement bandwidth of such interference coatings can be further increased by inserting a VO2 thin film between the dielectric and metal layers. The field enhancement spectrum blueshifts upon thermally-induced insulator-to-metal transition in the VO2 layer. The structure that maximizes the enhancement bandwidth is determined as 880-nm-thick CaF2 on 350-nm-thick VO2 on optically thick Al. The study is completed with the investigation of using a bottom metal layer as an internal heater to electrothermally induce the phase change.

Commissioning of cryogenic system for China Spallation Neutron Source

China Spallation Neutron Source(CSNS) cryogenic system provides supercritical cryogenic hydrogen to neutron moderators, including a helium refrigerator, hydrogen loop and hydrogen safety equipment. The helium refrigerator is provided by Linde with cooling capacity of 2200 W at 20 K. Hydrogen loop system mainly includes cryogenic hydrogen pipes, hydrogen circulator cold-box and accumulator cold-box. Cryogenic hydrogen pump, ortho-para convertor, helium-hydrogen heat-exchanger, hydrogen heater and accumulator are integrated in hydrogen circulation cold-box, and accumulator cold-box. Hydrogen safety equipment includes safety valves, rupture disk, hydrogen sensor, flame detector and other equipment to ensure that cryogenic system in dangerous situations will go down, vents, or takes other measures. The cryogenic system commissioning work includes four steps. First, in order to test the refrigerating capacity of refrigerator, when acceptance testing, refrigerator internal heater was used as thermal load. Second, using simulation load as heat load of moderator, hydrogen loop use helium instead of hydrogen, and cooled down to 20 K, then re-warming and test the leak detection of hydrogen loop system. Third, base on the step 2, using hydrogen as working medium, and optimized the control logic. Forth, cryogenic system with the moderators joint commissioning. Now, cryogenic system is connected with the moderators, and the forth step will be carried out in the near future.

Reforming results of a novel radial reactor for a solid oxide fuel cell system with anode off-gas recirculation

A novel reactor of a natural gas (NG) fueled, 1 kW net power solid oxide fuel cell (SOFC) system with anode off-gas recirculation (AOGR) is experimentally investigated. The reactor operates as pre-reformer, is of the type radial reactor with centrifugal z-flow, has the shape of a hollow cylinder with a volume of approximately 1 L and is equipped with two different precious metal wire-mesh catalyst packages as well as with an internal electric heater. Reforming investigations of the reactor are done stand-alone but as if the reactor would operate within the total SOFC system with AOGR. For the tests presented here it is assumed that the SOFC system runs on pure CH4 instead of NG. The manuscript focuses on the various phases of reactor operation during the startup process of the SOFC system. Startup process reforming experiments cover reactor operation points at which it runs on an oxygen to carbon ratio at the reactor inlet (ϕRI) of 1.2 with air supplied, up to a ϕRI of 2.4 without air supplied. As confirmed by a Monte Carlo simulation, most of the measured outlet gas concentrations are in or close to equilibrium.

An experimental analysis of quenching of continuously heated vertical rod with aqueous Al 2 O 3 nanofluid

Quenching characteristics of metallic vertical rod with an internal heater has been investigated in pure water and water-based nanofluid with alumina nanoparticles of 0.001% by volume. Initial temperature of the testing rod (12 mm diameter and 10 0 0 mm length) ranges from 200 °C to 250 °C. The internal heater may be used to simulate the decay heat generated by the nuclear fuel rod after the power plant shut- down. Tests have been performed with varied range of experimental conditions of decay heat, constant water and nanofluid flow rates. The cooling curves follow a general trend of a rapid temperature drop up to almost 100 °C of the rod surface temperature irrespective of the operating parameters and the location of the thermocouple. The obtained results during quenching process indicated that HTC (heat transfer coefficient) for nanofluids are more than de-ionized water. It was also observed that in identical circum- stances, the quenching time of the specimen in Al 2 O 3 nanofluid considerably decreased as compared to water. The results exhibit that nanofluids can enhance the reflood heat transfer performance in terms of quenching rate for a long vertical rod causing liquid-droplets-induced depositions of nanoparticles result- ing in making a pre-coating effect characterized by higher wettability.

Novel highly-integrated mems based solid state detectors for analytical gas chromatography

In this work, a novel detector of gaseous analytes for monitoring of low levels of BTEX (benzene, toluene, ethylbenzene and o-xylene) is discussed. The detector is based on SnO2 thin (30nm) films functionalized with gold-palladium (9:1 molar ratio) bimetal nanoparticles. The detector consists of four independent sensing elements thermally activated by an internal heater. The performance of Au/Pd@SnO2 sensing elements was evaluated in comparison with some other gas sensitive materials, such as: pure SnO2, SnO2 decorated with gold (Au), and SnO2 decorated with palladium (Pd) nanoparticles. The superiority of the gas sensing performance of the Au/Pd@SnO2 nanocomposite structure was demonstrated based on its response to low concentrations (12.5-500 ppb) of benzene or toluene. A more complex analysis of gaseous mixtures with different concentrations (0.3–20ppb) of BTEX mixture was accomplished by incorporating the novel detector into the portable gas chromatograph (GC) PAC R1120. High sensitivity of the detector in combination with fast response and recovery time allowed us to obtain fine gas chromatograms and to perform a complete analysis of a gas sample in less than 11min. Ultra-low concentrations of BTEX components at sub-ppb level (0.3 ppb) were identified and detected by the GC analysis. Besides the experimental data, the theoretical validation of the detector’s high performance was provided based on high catalytic activity of Au/Pd nanoparticles and electronic interaction of bimetal nanoclusters with SnO2 support.

Natural convection analysis by entropy generation and heatline visualization using lattice Boltzmann method in nanofluid filled cavity included with internal heaters- Empirical thermo-physical properties

The natural convection heat transfer analysis is performed by different approaches such as heatline visualization, total and local entropy generation, average ad local Nusselt number using lattice Boltzmann numerical method in nanofluid-filled cavity with partially heated and cooled walls included by internal heaters. The cavity is filled with DWCNTs-water nanofluid which its thermal conductivity and dynamic viscosity are measured experimentally at different solid volume fractions of 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, and 0.5% and a temperature range of 300–340 (K). Two sets of correlations for theses parameters based on temperature are developed and used in the numerical simulations. The side walls of cavity are cooled uniformly, two partially hot and cold surfaces at the bottom and top walls are located, respectively. The internal heaters are heated uniformly as well. The influences of different governing parameters such different arrangements of internal heaters, different concentrations of nanofluid and Rayleigh numbers on the fluid flow, temperature filed, average and local Nusselt number, total and local entropy generation and heatlines are presented. The results show that the arrangements of the internal heaters have pronounced effects on the fluid flow, heat transfer performance and entropy generation. Furthermore, the Nusselt number has direct relationship with Rayleigh number and solid volume fraction. On the other hand, the total entropy generation has direct and reverse relationship with Rayleigh number and solid volume fraction, respectively.

Numerical analysis of performance enhancement and non-isothermal reactant transport of a cylindrical methanol reformer wrapped with a porous sheath under steam reforming

This paper accomplished a three-dimensional computational analysis of the methanol reformer with steam reforming by the Arrhenius form of reaction model and SIMPLE-C algorithm. The performance enhancement and non-isothermal reactant transport of the cylindrical reformer wrapped with a porous sheath were investigated. The parameters, including temperature of internal heater (TH), porosity (ε), and thickness of porous sheath (RP), on methanol conversion, hydrogen, carbon monoxide, carbon dioxide productions, temperature and velocity fields with the same inlet conditions have been investigated. The results present that higher methanol conversion and richer hydrogen production occur as temperature of heater, porosity, and porous sheath thickness increase. As temperature of internal heater is equal to 250 °C, employing a porous sheath with ε = 0.9 and RP = 10 mm to wrap a reformer results in the maximum enhancements of 35.71% in methanol conversion and 21.18% in hydrogen production. Besides, a porous sheath with ε = 0.5 and RP = 10 mm leads to the maximum reduction of 2.23% in carbon monoxide produced from the reformer at TH = 300 °C.

Thermodynamic analysis of low-grade solar heat source-powered modified organic Rankine cycle using zeotropic mixture (Butane/R1234yf)

ABSTRACTThis paper communicates detailed energy and exergy analysis of low-grade energy resource of solar-powered organic Rankine cycle (ORC) integrated with both the internal heat exchanger and open feed water heater, ORC incorporated with the internal heat exchanger, with open feed water heater and basic ORC, respectively. Results indicate that highest first law efficiency (11.9%), exergetic efficiency (51.88%) and lowest exergy destruction (1749 kW) are obtained for ORC integrated with both internal heat exchanger and open feed water heater among other considered ORCs. Moreover, zeotropic mixture (butane/R1234yf) shows better first law and exergetic efficiency and lower exergy destruction than pure fluid.