Uniform Heat Distribution Research Articles

Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces non-uniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

Cooling Enhancement and Stress Reduction Optimization of Disk-Shaped Electronic Components Using Nanofluids

Mechanical strength and thermal properties may limit the usage of an electronic component in the high-tech industry. This paper investigated the influence of using CuO nanoparticles in a radial configuration microchannel of a disk from the mechanical and thermal points of view. In this regard, a disk under thermal and mechanical loading had been considered. The cooling setup consisted of a radial configuration microchannel with a constant fluid volume. Water was used as the base fluid and CuO particles were used as the coolant fluid. The results showed that the use of CuO nanoparticles would reduce the maximum disk temperature, the maximum thermal stress, and the maximum stress, as well as the maximum deformation on the body. The increasing number of channels would increase the maximum stress in the object as well. Another remarkable point was that increasing the nanoparticles did not necessarily lead to a more uniform heat distribution in the disk.

Investigation of the Effect of Different Materials on Uniform Heat Distribution Over a Solar Collector Pipe

Collector pipe used in solar power plant is a device for converting water from ambient temperature to the raised temperature which in turn used to rotate turbine blades. The raise in temperature is not that much when compared to thermal or nuclear power plant, so researches are going on for improving the heat carrying capacity of collector pipes. The productivity in pipe directly depends on the factors such as solar radiation incident on it, temperature distribution over the pipe, surrounding temperature, material of the pipeline used, and thickness of the pipe. When comparing to all of such parameters, the temperature distribution over the pipe is the main parameter which determines the performance of the collector pipe. For a particular type of solar collector pipe, the temperature distribution is function of length with day variation of solar incidence over it. In this work a collector pipe of length 2.2 m and 7 cm diameter is fabricated and tested under standard laboratory conditions for the uniform heat dissemination over the pipe. For keeping up the uniform temperature over the collector pipe, it is necessary to wound the pipe with metals like copper, aluminum. The results show that the heat distribution over the pipe is increased in case of copper when compared with aluminium.

Electrothermally Driven Hydrogel-on-Flex-Circuit Actuator for Smart Steerable Catheters.

This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of poly(N-isopropylacrylamide) hydrogel (PNIPAM), on top of a 20 × 3.5 mm2 flexible polyimide film that embeds a micropatterned heater fabricated using a low-cost flex-circuit manufacturing process. The heater activation stimulates the PNIPAM layer to shrink and bend the tip structure. The bending angle is shown to be adjustable with the amount of power fed to the device, proving the device’s feasibility to provide the integrated catheter with a controlled steering ability for a wide range of navigation angles. The powered device exhibits uniform heat distribution across the entire PNIPAM layer, with a temperature variation of <2 °C. The operation of fabricated prototypes assembled on commercial catheter tubes demonstrates their bending angles of up to 200°, significantly larger than those reported with other smart-material-based steerable catheters. The temporal responses and bending forces of their actuations are also characterized to reveal consistent and reproducible behaviors. This proof-of-concept study verifies the promising features of the prototyped approach to the targeted application area.

A 3D-printed metal column for micro gas chromatography.

In this work, a 3D-printed metal column was developed for micro gas chromatography (GC) applications and its properties and gas separation performances were characterized. By using a Ti6Al4V grade 23 powder, a square spiral one meter-long column (3D-column) was 3D-printed on a planar substrate of 3.4 × 3.3 × 0.2 cm and then perhydropolysilazane (PHPS) was deposited as a pre-treatment agent, followed by a coating of stationary phase (OV-1) onto the inner wall of the micro-channel. The 500 μm-diameter circular channel and two 800 μm-wide ports of the 3D-column were confirmed to be uniform by 3D X-ray microscopy without any distortion. The physical and thermal properties of the 3D-column were found to be very similar to that of the standard Ti6Al4V grade 23 alloy with near zero porosity (∼0.07%). The 3D-column with pre-treatment and stationary coating demonstrated efficient separation performance of gas mixtures containing alkanes, aromatics, alcohols, and ketones compared to a bare or only pretreated 3D-column in terms of the peak shape, broadening, and resolution (R > 1) within 2-3 min. The well-matched thermal responses to the target temperatures were demonstrated at the ramping rates of 10-20 °C min-1 upto 200 °C with uniform heat distribution over the 3D-column. In addition, the column bleed profiles showed that the 3D-column with PHPS had a 71% lower baseline intensity at 350 °C than that without PHPS. The 3D-column was then employed to separate a gas mixture of twelve alkanes (C9-C18, C22, C24) without any significant column bleeding and peak tailing. Therefore, the thermal responses and stability of the 3D-column promise its applicability in high temperature GC applications.

Design and Simulation of Platinum Micro Heater for VOC sensing Applications

Micro electro-mechanical system (MEMS) technology is flourishing the development of various sensors. Conventionally MEMS devices have been extensively used for upward performance of gas sensors over a period of time. This paper presents the designing of meander shaped microheater with the commercial FEM tool is used for simulation. Microheater is designed for application of VOC sensing applications. As the volatile organic compounds are to be vaporized a microheater is used. The geometric aspects of the microheater state the temperature effects on the VOC’s.Thus the dimensions were optimized for uniform distribution of heat across the surface. It was observed from the analytical analysis and FEM simulation that at 2um thickness, Microheater was able to distribute the heat uniformity across the surface

Dramatic improvement enabled by incorporating thermal conductive TiN into Si-based anodes for lithium ion batteries

Building stable SEI film is highly desirable for high-performance Si-based anode materials used in high energy-density lithium ion batteries (LIBs), which is strongly related with the generated-heat distribution in the electrode. Herein, Si/graphene@carbon embedding with TiN nanoparticles (Si/G@C/TiN) are prepared via a facile ultrasonic spraying method. The Si/G@C/TiN delivers a reversible discharge capacity of 660 ​mAh▪g−1 ​at 10 A▪g−1 and 776.5 ​mAh▪g−1 ​at 5 A▪g−1 after 400 cycles. High electronical conductivity of TiN embedding in the porous carbon framework can not only facilitate electrons transfer in the electrode, but also improve Li-ion kenetic diffusion. High thermal conductivity of TiN would be helpful to faster heat-dissipation and uniform heat-distribution in the electrode during the charging/discharging process, resulting in balanced growth of stable SEI film and excellent cycling stability especially at elevated temperature. Moreover, Si/G@C/TiN pouch cells using LiNi0.5Co0.2Mn0.3O2 as cathode, deliver impressive energy density of ~476 ​Wh▪kg-1 based on the total weight of active materials, suggesting its promising application in the high energy-density LIBs.

Assessment and comparison of different arrangements of horizontal ground heat exchangers for high energy required applications

Horizontal ground heat exchangers (GHEs) have a lower initial installation cost in comparison to vertical ones; however, they require more land area. In order to reduce the required land area of horizontal GHEs, their heat exchange rate per unit land area needs to be enhanced. A remedy to this problem is installing horizontal GHEs in an arrangement with maximum heat exchange rate per unit land area. However, such arrangements have not been introduced for different types of horizontal GHEs thus far. To this end, in this study, the thermal performance of various GHE pipe arrangements for three different types (linear, spiral, and slinky) of horizontal GHEs is evaluated. Comparing the obtained results, the arrangement that provides the maximum heat exchange rate per unit land area for each type is introduced. A 3D numerical model based on the finite-element method is developed to simulate the GHEs performance. In order to have a fair comparison, all studied arrangements are designed to have the same installation cost. The obtained results indicated that the linear GHE with quadruple-layer arrangement provides the most uniform heat distribution in the ground and, therefore, has the highest heat exchange rate per unit land area among all cases studied. This arrangement has about a 34% higher heat exchange rate per unit land area than the conventional single-layer arrangement. The staggered double-layer arrangement is the best arrangement for the slinky and spiral GHE types, which has about 22 and 7% higher heat exchange rate per unit land area than conventional single-layer arrangement, respectively. Furthermore, the thermal performance of the best arrangement for each type is evaluated for three different values of soil thermal conductivities.

Evaluation and Safety Validation of Dehydrating Methods for Goat Meat in Rural Malawi

ObjectivesThis study was conducted to evaluate the dehydration methods of goat meat based in Malawi and the effects on food safety.Materials and MethodsGoat meat was prepared as ground, minced, and whole muscle strips. Samples were treated with 6% lemon juice marinade, 6% vinegar marinade, or salt rub. During phase 1, dehydration of the meat was performed with a solar dehydrator (n = 108), electric oven (n = 108) or drum oven (n = 108). Qualitative data on the three drying methods was collected from a panel of students from Mzuzu University, Malawi, on the practicality of each method in a local rural setting. Additionally, visual observations were conducted 30 d prior to drying for the presence of mold and insects to give an indication of shelf life. Phase 2 was performed at Texas Tech University in Lubbock, Texas where whole muscle strips of lamb were submerged in a five-strain Escherichia coli surrogate cocktail of Escherichia coli for 5 min, allowed 30 min for cell attachment, then dried using an electric and drum oven, replicating the dehydration procedure in Malawi. For each replicate (n = 2), attachment samples (n = 10), samples dried in the electric oven (n = 10) and samples dried in drum oven samples (n = 10) were aseptically plated on MacConkey agar with a TSA overlay and enumerated for E. coli.ResultsIn phase 1, mold growth was observed on 15.7% (34/216) of samples dried in the solar dehydrator and drum oven. Of those positive for mold, 32.4% (n = 11) were minced, and 67.6% (n = 23) were whole muscle strips. No samples dried using the electric oven displayed mold (0/108). No samples displayed insects. Based on qualitative data that was gathered, top reasons to dry goat meat using the drum oven include “not requiring electricity” and “drum ovens are a common piece of equipment in villages”. Top reasons against using a drum oven include “unequal distribution of heat” and “high level of oversight required during drying”. Top reasons to dry goat meat using electric oven include “fast drying time”, “uniform distribution of heat”, and “limited oversight required”. Top reasons against using electric oven to dry goat meat include “requiring electricity” and “low knowledge of electric oven operation in a community setting”. Top reasons to use the solar dehydrator to dry goat meat include “not requiring electricity or firewood” and “limited oversight required”. Top reasons against using the solar dehydrator to dry goat meat include “slow drying time” and “uneven heat distribution due to time of day and shadows”. In phase 2, a 5-log reduction was observed for all electric oven treatment replicates (100%, 2/2) and half drum oven (50%, 1/2) replicates. However, variation in the reduction of E.coli is a direct result of weather and fuel provided to the drum oven.ConclusionElectric drying oven displayed the most consistent results for shelf life and safety. However, in rural Malawi, dehydrating methods should be chosen on a case by case basis.

Influence of carbon-containing additives on sintering of limestone-nepheline furnace charge in alumina production

The article is devoted to the influence of brown coal additives on the sintering of the lime-nepheline charge in the technology of alumina production from nepheline. It is shown that carbon-containing materials added to the limestone-nepheline charge intensify sintering, and thus, contribute to a more uniform heat distribution along the furnace, improve the passage of the sintered material in the chain curtains, accelerate interaction of the charge components and increase recovery of alumina from the sintered mass. The mechanism of influence of coal during its combustion on the passage of solid-phase reactions in the charge is studied. Fossil brown coals with a high content of volatile substances and carbon graphite materials were used as coal additives.

A Review of the Performance and Characterization of Conventional and Promising Thermal Interface Materials for Electronic Package Applications

Thermal interface materials (TIMs) play a key role in reducing thermal resistance between jointed solid surfaces in order to increase thermal transfer efficiency. A TIM is a thermally conductive material which is applied between the interfaces of two components (such as circuit board and heat sinks) to enhance the thermal conductance between them. The present paper provides a detailed review in order to characterize conventional and advanced TIMs in terms of thermal performance. The paper also discusses the measurement of TIM performance using different techniques. It was found that greases are the most widely used TIMs and offer thermal resistance in the range of 0.1–1 cm2°C/W. However, greases are messy and difficult to apply and remove due to their high viscosity. Moreover, they have reliability issues such as pump-out, phase separation and dry-out, which limits their use as an efficient TIM. The thermal resistance of TIMs which contain carbon nanotubes (CNT) fall in the range of 0.01–0.19 cm2°C/W. However, the use of CNT as a TIM at high temperatures does not allow for uniform distribution of heat on cooling of electronic packaging systems. Although TIMs with the addition of nano--metal particles are considered promising, it is necessary to carry out extensive research on CNT as a TIM.

Numerical Analysis of Heat and Mass Transfer Coupled With Gaseous Fuel Injection in Reactive Porous Media

Abstract Iron ore sintering is a typical application of reactive porous media combustion (RPMC) which has been widely reported. In this work, a computational model of RPMC is developed, in which heat and mass transfer, as well as main chemical subprocesses in reactive porous media are incorporated. A gaseous-fuel injection method is examined to enable better heat pattern. However, the imbalance of heat distribution in the flow direction caused by internally recirculating heat released via a solid matrix is still problematic on energy efficiency. Through computations, it is observed that the heat pattern and melting quantity index (MQI) are sensitive on gaseous-fuel concentration, providing a possibility of improving the heat distribution imbalance. Numerical results are presented to demonstrate the benefits of fuel segregation. Finally, more reasonable heat pattern is observed by combinations of gaseous-fuel segregation with hot air and oxygen enrichment. The dynamics of gaseous/solid-fuel combustion zones caused by the hot air and oxygen enrichment would contribute to an expansion of melting zone near the inlet, producing a more reasonable and uniform heat distribution in a sintering bed.

An experimental and numerical investigation on thermal performance of a new modified baseboard radiator

In this investigation the performance of a new modified skirting board heating system is analyzed. Two important aims have been pursued in this work. At the first in order to enhance thermal efficiency a new modified geometry of the baseboard radiator is designed and presented. Using of waving fins and change the cross-section of the fluid transfer are among the innovations of the new design. Experimental method based on the EN-442 is employed to measure the thermal efficiency of the new system. Also based on the obtained experimental data an equation for output heat rate is created by curve fitting. The proposed function can be used in heating calculations. In the next step thermal comfort conditions is studied. Fanger comfort model in the Design Builder software is used to predict the level of thermal comfort and also temperature distribution inside the building. Experimental results showed that thermal efficiency of the new modified baseboard radiator increased about 32% compared with the conventional model. Baseboard radiators due to the uniform distribution of heat in the space compared to the panel radiator, in addition to energy saving, also provides more thermal comfort conditions.

Studies on spin arc welding process on the behavior of C1018 plates-an insight into mechanical and metallurgical transformation

AISI 1018 low carbon steels are materials of highest priority in marine structures for its superior weldability and case hardening properties. The effects of spin arc weld with filler wire made of ER 70S6 on mechanical properties and metallurgical behaviors of 10 mm thick C1018 plates are investigated and presented. Destructive tests are performed to access the strength of weldment while recording their elastic limit to enable their choice for various application ranges. The ductility yielded by the sample during bend test clearly indicated a high value which is a prominent beneficiary feature. Phase changes are monitored to understand the nature of the process on material behavior and identify the compositional variation if any and its implications on the grains and associated phenomenon. Portion of any structure for an application is designed to withstand a load of specific value, above which it is prone to attain fracture or deformation. Accordingly, scanning electron microscopic images are captured for such fractographic analysis. Experiments emphasize that spin arc augments better bead formation with uniform heat distribution, wherein spin frequency influences the melting rate and provides an impetus to the adoption of spin arc welding on larger scale.

Bubble dynamic parameters during subcooled flow boiling under uniform and non-uniform transverse heat distribution

Bubble behaviors and their interactions with each other affect the two-phase flow characteristics. In this study, experiments are conducted to investigate the bubble characteristics during subcooled flow boiling under uniform and non-uniform transverse heat flux distribution. The non-uniform heat flux distribution creates non-uniform bubble characteristics on the heated surface as opposed to under uniform heating. The working fluid is demineralized water that flows through a narrow rectangular channel heated from one side. The experimental loop used in the study operates at low pressure. A wide range of experimental operating conditions, such as inlet temperature (35–65 °C), thermal power (500–6250 W), and mass flow rates (0.03–0.13 kg/s), are applied to the upward flow channel. The bubble behaviors are visualized using a high-speed camera (2200 fps) at a resolution of 512 × 512 pixels. The results indicate that the bubbles exhibit different departure diameters, nucleation site density distributions, and bubble departure frequencies. In the uniform case, bubbles are generated uniformly across the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated where the heat flux is concentrated, which disturbs the flow velocity profile in the transverse direction. The differences in bubble generation in the transverse direction result in differences in the two-phase flow instability through the heated channel. As a result, new empirical correlations are proposed based on the experimental results to estimate the bubble departure diameter, nucleation site density, and bubble departure frequency. The correlations are applicable for both heated surface conditions, uniform and non-uniform, under low-pressure conditions. CFD analysis using ANSYS FLUENT incorporates the RPI wall boiling model is conducted to validate the empirical correlations. Comparison of the CFD calculations with the experimental data for void fraction, wall temperature, and bulk temperature show good agreement. The simulation results show an accurate prediction of the ONB (Onset of Nucleate Boiling) and OFI (Onset of Flow Instability).

Neutronic and Thermo-Hydraulic Analyses of Water-Cooled Blanket Based on Pressurized/Supercritical Water Conditions for CFETR

China Fusion Engineering Test Reactor (CFETR) is a test tokamak reactor being designed in China to bridge the gap between International Thermonuclear Experimental Reactor (ITER) and future fusion power plant. As one of the candidates, a water-cooled solid breeder blanket based on pressurized water and supercritical water conditions were proposed. In the concept, multiplying layers separated by three breeding layers were designed and optimized for higher tritium breeding ratio (TBR) and uniform heat distribution. This blanket adopts the Li2TiO3 lithium ceramic pebbles as the breeder, while beryllium pebbles as the neutron multiplier. In this paper, the thermal and fluid dynamic analyses of the optimized blanket on both water conditions were performed by numerical simulation, to discuss thermo-hydraulic performance of the blanket using pressurized water/supercritical water as its coolant. At first, the neutronic analysis was performed and based on the typical outboard equatorial blanket. Then, thermal and fluid dynamic analysis of the 3D model was carried out by CFX with fluid–solid coupling approach. It was found that the blanket can be effectively cooled on both water conditions, certified the feasibility of the blanket design with pressurized/supercritical water conditions. It indicated that supercritical water blanket had smaller safety margin than pressurized water blanket, but supercritical water blanket would lead to higher outlet temperature, thermal conductivity, and heat exchange efficiency also. In addition, the beryllium fraction was considered as one of the dominant factor, which leading a higher TBR in our simulations.

Optoelectronic and Electrothermal Properties of Transparent Conductive Silver Nanowires Films.

Silver nanowires (AgNWs) show promise for fabricating flexible transparent conductors owing to their excellent conductivity, high transparency, and good mechanical properties. Here, we present the fabrication of transparent films composed of AgNWs with diameters of 20–30 nm and lengths of 25–30 μm on polyethylene terephthalate substrates and glass slides substrates using the Meyer rod method. We systematically investigated the films’ optoelectronic and electrothermal properties. The morphology remained intact when heated at 25–150 °C and the AgNWs film showed high conductivity (17.6–14.3 Ω∙sq−1), excellent transmittance (93.9–91.8%) and low surface roughness values (11.2–14.7 nm). When used as a heater, the transparent AgNW conductive film showed rapid heating at low input voltages owing to a uniform heat distribution across the whole substrate surface. Additionally, the conductivity of the film decreased with increasing bending cycle numbers; however, the film still exhibited a good conductivity and heating performances after repeated bending.

The Effect of Iron‐ and Manganese‐Based Oxygen Carriers as Bed Materials in Oxygen Carrier Aided Combustion

Combustion of organic materials in fluidized bed combustion is generally performed using an over‐stoichiometric air‐to‐fuel ratio. Despite excess air in the system, sub‐stoichiometric combustion regions are present in the fluidized bed because of nonperfect mixing of reactants in the system. These regions with oxygen‐deficient combustion contribute to increased levels of nonoxidized or partially oxidized carbon species. To enhance heat transfer and uniform heat distribution in the incineration chamber, an inert fluidized bed material such as silica sand is generally used. Substitution of silica sand in favor of an oxygen carrier could potentially be used to promote oxygen distribution in the incineration chamber. This is referred to as oxygen carrier‐aided combustion. In this work, three alternative bed materials, previously investigated in chemical looping combustion, are investigated and compared with silica sand in over‐ and sub‐stoichiometric combustion. The materials investigated as bed materials are a manganese ore, the mineral ilmenite, and a synthetic material mixture of Fe2O3 on a ZrO2 support. Results show that during combustion using sub‐stoichiometric air‐to‐fuel ratios, the amount of CO in the effluent gases can be reduced using an active bed material compared to inert silica sand.

Design optimization and control approach for a solar-augmented industrial heating

Process level integration of solar energy could give an economically feasible solution if the industrial process allows its practical integration. The solar-augmented industrial process behaves as a complex system influenced by uncertainty of solar radiation, variability of demand temperature and process time schedule as well as possibility of thermal stratification in the storage. Addressing these issues to reach the most economical solution has two dimensions to it. First, the solar thermal system needs to be optimally designed. This requires the development of a performance criterion that will deliver maximum solar energy to the industrial process, avoid large variations of energy in the storage, and meet investment constraints. Second, the identified optimal system should be dynamically controlled to enable uniform heat distribution and efficient auxiliary heat utilization. This paper presents a holistic design optimization and control approach for a solar-augmented industrial process to facilitate decision support. The proposed solution is designed and optimized for a dyeing industrial process case study that resulted in a 5.7 year payback period, 56.3% solar fraction, and 252.2 tons equivalent carbon emission reduction. Furthermore by implementing dynamic control, about 12.4% increase in solar gain that led to a 5.6% reduction in payback period is identified.

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