Microchannels are effective heat sinks for integrated electronic circuits. However, it remains unclear what form of channels will be most effective in improving the overall performance of ...microchannel heat sinks. The effect of channel geometry on overall performance was studied to understand the fluid flow and heat transfer characteristics of microchannel heat sinks having groove sidewalls. Five types of silicon-based microchannel heat sinks were designed, and the periodic grooves arranged on channel sidewalls were rectangular, triangular, trapezoidal, water-droplet, and semicircular in shape. A three-dimensional computational fluid dynamics model was developed, validated, and used to optimize the geometric structure. Comparisons were made between different groove shapes in order to determine the optimum structure. The results indicated that the overall performance can be greatly improved by arranging grooves on channel sidewalls. The significant improvement of overall performance can be achieved with all the groove shapes except rectangles. When the Reynolds number falls within the range from 194 to 610, triangles are the optimum groove structure in terms of the level of the maximum heat transfer performance improvement, but with a significant increase in pressure drop. Water-droplet shaped grooves offer many advantages and improvements that make them the preferred choice for the development of microchannel heat sinks. They offer significant advantages as an effective heat transfer enhancement structure at higher Reynolds numbers, and allow for the lowest pressure drop at lower Reynolds numbers due to the vortexes formed inside the grooves.
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•Overall performance can be greatly improved by arranging grooves on sidewalls.•The shape of grooves can strongly affect hydraulic-thermal performance.•Water-droplet shaped grooves are the optimal choice based on overall performance.•Triangles are the optimum structure if only thermal performance is considered.•Rectangles must be avoided in design due to poor overall performance.
Nuclear magnetic resonance (NMR) has been applied widely and successfully in conventional and unconventional reservoirs, and can be used to investigate petrophysical properties and fluid flow ...characteristics. This non-destructive, sensitive, and quick technique has been utilized in determination of pore type, porosity, pore size distribution, permeability prediction, wettability estimation, and fluid type, state and flow behavior.
In this paper, the application of NMR to investigate coalbed methane and shale reservoirs is reviewed. Most of the reviewed studies are related to porosity and pore characteristics, which can be determined by analyzing the characteristics of the T2 distribution, allowing for examination of pore type and pore connectivity as well as calculation of total porosity and pore size distribution. Permeability models developed for reservoir rocks and based on porosity determined using NMR are well established and have been extended or modified to evaluate the permeability of coal or shale. Reviewed studies also include wettability investigation by comparing the subtraction of T2 distribution before and after fluid injection. Reviewed recent advances have further discussed the method of distinguishing fluid type, fluid state, and simulating fluid behavior using one-dimensional and two-dimensional NMR methods combined with changes of T2 distribution. The aim of this review is to provide readers with an overview of the capabilities of NMR and its extension to scientific research by improving the parameter optimization of the instrument and establishing the calculation method for effective surface relaxivity for coals or shales.
•Conclusion of nuclear magnetic resonance (NMR) measurement and theory•Pore type, porosity, pore size distribution of coal and shale by NMR T2 distributions•Permeability prediction models and wettability estimation based on NMR•Distinguishing fluid type, state by using one-dimensional and two-dimensional NMR methods•Simulating fluid behavior according to the changes of T2 distributions
The thermal-hydraulic performance of the circular pipe heat exchanger is determined by numerical simulations of the flow field and pressure drop inside the pipe. Initially, a three-dimensional ...numerical model is validated using experimental results. Turbulent flows are solved using the governing, momentum and energy equations. With constant heat flux as the boundary condition, the (RNG) k-ω turbulent model predicts flow structures. Different twisted tape inserts (NTTI) (1, 3 and 5) are considered when analysing the influence of different twisted tape geometric parameters. A variety of important parameters are compared quantitatively and qualitatively using six different twisted turns (NTT): static pressure, velocity magnitude, vorticity and static temperature. Twisted tape inserts in pipes can increase flow resistance, which leads to an increase in pressure difference. Furthermore, thetwisted tapes inside the pipe caused more vortex motion (swirl flows), which resulted in different radial velocities. As compared to the temperature difference in a smooth pipe, the numerical results show that the temperature difference increases up to 38.1%, 46.11% and 50.52% when the NTTI is increased from 1 to 5.
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•The shape and configuration of ribs are important factors affecting performance.•The shape and position must be optimized to maximize the comprehensive performance.•Larger rib ...dimensions enhance heat transfer while causing performance degradation.•The use of ribs combined with cavities can improve performance and efficiency.•The effect of trailing edge vortexes on heat transfer performance is significant.
Cavities and ribs are usually utilized in the design of microchannel heat sink systems, and their combination may lead to the optimum overall performance. However, it remains unclear how different combination methods contribute to the performance and efficiency of the systems. Computational fluid dynamics simulations were conducted to identify the optimum rib shape and configuration for the systems with fan-shaped cavities. The ribs are rectangular, diamond, hexagonal, or elliptic in cross-section. The effects of rib shape, dimensions, and configuration are investigated, and the optimum comprehensive performance was determined. The results indicated that the shape, dimensions, and configuration of ribs are important factors that affect performance and heat transfer efficiency. The shape and position of ribs must be optimized to minimize pressure drop while maximizing heat removal efficiency. The shape of ribs can be an important factor in obtaining high efficiency of heat removal while limiting the pressure drop across the channels. When the ribs are rectangular in shape, the maximum pressure drop occurs but the maximum relative Nusselt number is achieved. The maximum comprehensive performance factor is achieved when the ribs are elliptic in shape and the Reynolds number is highest. Further improvement in performance can be achieved by choosing particular rib dimensions and configuration. In order to provide appropriate benefit to such a microchannel heat sink system without inducing additional pressure drop that reduces the performance of the system, it is desirable to properly shape and position the ribs relative to the cooling flow and the cavities in a way that takes best advantage of the benefits provided by the combination of cavities and ribs. The effect of trailing edge vortexes on heat transfer performance is significant. A maximum comprehensive performance factor of 1.96 is achieved when the Reynolds number of the laminar flow is 460.
In order to understand the transmission mode of laser in water jet–guided laser (WJGL) after entering blind holes, the flow characteristics of water jet in blind holes and the formation process of ...WJGL processing blind holes were studied. Firstly, the flow characteristics of water jets in blind holes under different water jet and blind hole conditions were studied through numerical simulation, including water jet diameter
d
(0–300 μm), hole diameter
D
(0–300 μm), and water jet velocity
v
(0–200 m/s). Secondly, single-point drilling experiments with different processing times (2–40 s) were conducted using WJGL technology to characterize the formation process of blind holes. Finally, the transmission mode of laser in blind holes and formation process mechanism of blind hole processed by WJGL were analyzed. The simulation results indicate that the process of water jet entering the blind hole can be divided into incident stage, rebound stage, and stable stage. The transmission of water jet in blind holes is influenced by
D
/
d
and
v
. When
D
/
d
is greater than 2.3, the water jet can stably transmit to the bottom of the blind hole. Taking 75 m/s and 150 m/s as the change points, as
v
increases, the stable transmission length of the water jet first decreases, then remains unchanged, and then increases. The experimental results indicate that with the increase of processing time, the formation process of blind holes undergoes rapid drilling stage, uniform reaming stage, bottom reaming stage, and stable stage. Under experimental conditions, the depth of blind holes first increases and then stabilizes with increasing processing time. The maximum depth of blind holes processed by WJGL is 720 μm. This article reveals the flow pattern of micro water jets in blind holes and the factors that affect their stable transmission for the first time. From the perspective of the guiding effect of water jets on laser, it is revealed that laser propagates along a straight line in a blind hole. The simulation and experimental results have guiding significance for improving the application of WJGL technology in blind hole processing.
Numerical simulation was performed to analyze the behavior of a flow field, characteristic of pressure drop, and hydraulic thermal performance. Moreover, influences of different twisted tape ...geometric parameters, including three twisted tape inserts (NTTI) 1, 3 and 5. Also, six different twisted turns (NTT) were comparably quantitative and qualitative studied using various important parameters, including static pressure, dynamic pressure, and velocity magnitude, respectively. The results revealed that the value of pressure drop between each cross section in the pipe decreases as pipe length increases. When the NTTIs increases that leads to a pressure difference also increasing as compared to the smooth pipe. It is found that inserting twisted tape in the pipe leads causes considerably high resistance in the flow, then leads to increase the pressure difference. In addition, the results show that existence of the twisted tapes inside the pipe can create more vortex motion (swirl flows) that leads to formation of different radial velocities. Also, the PEF factor decreases as the Re increases. The comparison results for the numerical and experimental indicate that a good agreement of the average deviation for f (friction factor) and Nu is around 6.5% and 7%. The minimum Nu number value was 10 for NTT1 at Re number of 900 and the higher value was 50 at Re of 14,000. The PEF is more than 1.6 for NTT6 configuration. The results indicate that the temperature difference increases up to 38.1%, 46.11% and 50.52% with increasing the NTTI from 1 to 5, respectively, as compared to the temperature difference in a smooth pipe.
A full-scale, three-dimensional, transient CFD modelling approach capable of predicting the three-phase fluid-flow characteristics and desulphurisation behaviour in an argon-stirred ladle was ...developed. The model can accurately predict the molten steel flow and slag eye behaviour. The predicted sulphur content in ladle as a function of time agrees well with the experimental data. The effects of the initial sulphur content, the gas flow rate and the slag layer thickness on the desulphurisation efficiency were also investigated. The predicted results show that the desulphurisation efficiency improves with the increase of the initial sulphur content, the gas flow rate and the slag layer thickness. Higher gas flow rate can improve the slag-steel interaction, which, in turn, helps improving the desulphurisation rate. The thinner the slag layer, the larger the slag eyes and the smaller the interfacial area between the slag and steel phases. The consequence is the decrease in the desulphurisation rate.
Experimental study on 75 kWth, downdraft (biomass) gasifier system has been carried out to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous ...gasifier bed, cooling-cleaning train and across the system as a whole in both firing as well as non-firing mode. Some issues related to re-fabrication of damaged components/parts have been discussed in order to avoid any kind of leakage. In firing mode, the pressure drop across the porous bed, cooling-cleaning train, bed temperature profile, gas composition and gas calorific value are found to be sensitive to the gas flow rate. The rise in the bed temperature due to chemical reactions strongly influences the pressure drop through the porous gasifier bed. In non-firing mode, the extinguished gasifier bed arrangement (progressively decreasing particle size distribution) gives much higher resistance to flow as compared to a freshly charged gasifier bed (uniformly distributed particle size). The influence of ash deposition in fired-gasifier bed and tar deposition in sand filters is also examined on the pressure drop through them. The experimental data generated in this article may be useful for validation of any simulation codes for gasifiers and the pressure drop characteristics may be useful towards the coupling of a gasifier to the gas engine for motive power generation or decentralized electrification applications.
Magmatic intrusions can deteriorate coalbed methane reservoir quality by precipitating minerals in natural fracture and cleat system. To date, the effect of magmatic intrusions on coal rank and ...maturity has been studied extensively. However, their impact on fluid flow capacity and gas content is poorly investigated. This study evaluates the impact of magmatic intrusions on reservoir characteristics of the Hoskissons coal interval in the Gunnedah Basin (eastern Australia) where numerous coal-intrusion associations exist. Drill stem test (DST), borehole image logs and core data are used to determine fluid flow characteristics, gas content and quality in 14 wells across the Gunnedah Basin. The integration of borehole image logs and DST data analysis enables us to determine the existence, openness, and hydraulic conductivity of natural fracture and cleat systems in the Hoskissons coal interval. In addition, available desorption canister data, gas composition data, and conventional well logs are interpreted to investigate probable thermal effect on gas content.
Our analyses of different datasets reveal that the thickness of intrusions and their positions with respect to the Hoskissons coal interval are variable in the studied wells. Permeability varies from 1091mD down to zero owing to heterogeneous fracture and cleat systems. Interpreted natural fracture/cleat systems are well correlated with measured permeability from DST data analysis. This highlights the role of open natural fractures/cleats in fluid flow characteristics of the Hoskissons coal interval. Results indicate that the mineralizing effect of hydrothermal fluids derived either from magmatic intrusions or coal itself is not a controlling factor in fluid flow capacity of the Hoskissons coal interval in the studied wells. This is described by either the distance between coal section and major intrusions in some wells or perhaps emplacement of intrusive bodies prior to development of cleat and natural fracture networks. The destructive impact of intrusions on permeability is observed in one of the studied wells in which in-situ stress perturbation is large (due to presence of magmatic intrusions in sedimentary rocks). Variable in-situ stress orientation can decrease fracture connectivity and consequently fluid flow properties are affected. Gas content largely varies in heat affected coal intervals. This signature is the result of thermal effect fading with distance and is more pronounced when intrusions are in close proximity to coal intervals. Gas composition is variable in the studied wells. Gas composition data indicate that high quality desorbed gas with methane concentration higher than 90% could be found even in coal intervals which are heavily intruded.
•The effect of magmatic intrusions on reservoir characteristics of the Hoskissons coalbed in the Gunnedah Basin is studied.•The position of magmatic intrusions with respect to the coal interval is investigated by wellbore data.•Borehole image logs and drill stem tests are used to study the quality of natural fracture/cleat system.•Gas content and its quality are studied by available desorption canister and gas composition data.•The effect of hydrothermal circulations derived either from intrusions or coal itself on coal permeability is studied.
