Constant Total Length Research Articles

Regulation of the interaction of heat exchange and throttling effect for a Joule-Thomson cooler with rectangular microchannels

Applying microchannels in Joule-Thomson (J-T) coolers can enhance precooling. The regulation of heat transfer and throttling is crucial to lower the cold terminal temperature Tcold.The present cooler with rectangular microchannels served as the prototype. The experiments were carried out under 4, 5 and 6 MPa, with Ar and N2 as the refrigerants. The cooler can achieve the lowest cold terminal temperature (Tcold, 194.9 K) at 6 MPa. Then, the mathematical model was verified. The analysis showed that under the premise of constant total length and working condition, the precooled temperature before throttling could be reduced, and finally, the Tcold could be reduced. There are two ways to regulate. On the one hand, extending the recuperative structure (CFHX)’s length and reducing the length and cross-sectional flow area of the throttling structure (THR). This regulation increased the heat exchange per unit mass qm and the integral throttling effect ΔTjt in each section and finally reduced the Tcold. When the length of THR was decreased to 15 mm, and the end of THR reached the chocked flow, the Tcold reached the lowest value of 166.3 K. On the other hand, when fins were added in CFHX, THR became shorter. This method enhanced the precooling at the expense of pressure drop in CFHX. When the fins’ number raised from 0 to 6, Tcold declined. When the number is 6, the Tcold decreased by 7.7 K. As the number went on rising, the performance eventually deteriorated.

Experimental analysis of overpressure characteristics of gasoline–air mixture explosion in multi-branch tubes

Taking the multi-branch structure pipelines common in the field of energy and chemical industry as the research object, the combined experimental pipeline was used to control the constant total length of the pipeline, and the experimental analysis was carried out on the characteristics of oil and gas explosion overpressure under different distribution forms, distribution locations, length and number of branch tubes. The results showed that: Compared with straight pipelines, multi-branch pipelines have great influence on the peak value and rise rate of overpressure. Under the relative arrangement, the maximum overpressure and the maximum overpressure rise rate are less than those of the one-line arrangement and staggered arrangement, and the time to reach the maximum overpressure and the maximum overpressure rise rate is also delayed. The relationship of the maximum explosion overpressure rising rate at different branches of the tube is as follows: far from the ignition end > near the ignition end > evenly distributed along the main tube. With the increase of branch pipe length, both the peak value of overpressure and the rise rate of the maximum overpressure show a trend of decreasing first and then increasing. When the branch length is 1.5 m, the peak value of overpressure and the rise rate are smaller than the straight pipe condition. The increase in the number of branches does not lead to a continuous increase in the peak and maximum rate of overpressure rise. When the number of branches is less than 3, the peak value and the rate of rise of the maximum overpressure increase with the increase of the number of branches, while when the number of branches is more than 3, both the peak value and the rate of rise of the maximum overpressure decrease.

Design of thermal imaging continuous-zoom optical system

The report tells about the design of a middle wave infrared continuous-zoom imaging optical system. To capture the image in an «eye-type» infrared optical system a multi-element sensor is used. To increase the contrast of the thermal image the sensor is equipped with a cold aperture. The use of an optical system based on the continuous-zoom lens makes it possible to solve the problems of object detection and identification more effectively but requires taking into account some features of varifocal lenses. The optical system being analyzed in the report includes front zoom objective system and secondary imaging system. The front zoom optical system is composed of four groups and provides the focal length that is continuously changed with a large zoom ratio (15–20X) under the condition of a constant total length of the system. The secondary imaging system is designed for zoom system exit stop and sensor cold stop conjugation. The design technique represents analytical expressions and equations to obtain optical parameters of the front and secondary system components and the motion curves for movable groups.

Acoustic wave frequency filtering in constant total length phononic crystals of Al/Pb multilayer

In this study, we have scrutinized the frequency gap generation by changing the geometrical parameters of a one-dimensional phononic crystal. For this purpose, we have calculated the transmission coefficient of an incident acoustic wave by using the transfer matrix method. We have retained and fixed the total length of the system and changed the system internal geometry not to increase the system length too much. Another reason was to adjust the phononic band gaps and get the desired transmission properties by finding the optimum internal geometry without increasing or decreasing the total length of phononic crystals. In addition, we also propose few structures with the opportunity of applications in acoustical devices such as sonic reflectors. Our results can also be of high interest to design acoustic filters in the case that transmission of certain frequencies is necessary.

Shannon entropies of asymmetric multiple quantum well systems with a constant total length

Shannon entropies of asymmetric multiple quantum well systems with a constant total length

Spin filtering in GaAs/Al0.3Ga0.7As multiple quantum wells

In this study, spin polarization efficiency and spin-dependent transmission of electrons passing through a multiple quantum well structure with constant total effective length (60 nm) made of GaAs/Al0.3Ga0.7As, which was grown along [001] direction, were investigated. The calculations were done with the quantum transmitting boundary method. We presented the number of wells in a constant total length as a tuning tool for spin filtering purposes. In some energy intervals, 100% spin polarization and spin-dependent transmission were observed.

Inverted structurally inhomogeneous stepped agitators in a channel flow

Homogeneous thin-film agitators used in a channel flow have shown enhanced thermal-hydraulic performances compared to a clean channel benchmark. In this study, an experimental study was carried out to explore the performances of three inverted structurally inhomogeneous stepped agitator designs in the same channel flow in order to further improve the overall thermal-hydraulic performance of a heatsink. The three agitator designs were constructed by connecting two sections of material with different lengths while maintaining the constant total length of 6 mm as in our previous study: a relatively thicker 125-μm material mounted on the channel wall as the trailing edge and a thinner 25-μm material as the free leading edge. The new designs were expected to maximize fluid mixing enhancement but minimize pressure loss due to the unique structure of the inhomogeneous materials. Experiments in this study covered a wide Reynolds number range from 300 to 9000. High-speed footage was used to capture the dynamic motion of the agitators. At the same time, a time-resolved particle image velocimetry (TR-PIV) system was used to characterize the vortex dynamics due to the motion of agitators in various flow conditions. A synthetic thermal-hydraulic performance factor, η, taking into consideration both the Nu number enhancement and friction factor increment, was used to evaluate the overall effects of the added agitator features in the channel flow compared to a clean channel benchmark. Results show that a maximum factor of about 1.5 has been achieved, and it stays above 1 under most of the test conditions in this study, indicating great benefits for enhanced thermal transport.

Band gap engineering in constant total length nonmagnetized plasma-dielectric multilayers

In this paper, we have employed the transfer matrix method to theoretically study the light waves propagation in constant total length plasma one-dimensional photonic crystal, which is composed of alternative non-magnetized cold plasma and dielectric. The effects of the polarization, angle of incidence and the thickness of the layers, and electron density and dielectric permittivity on the position, width and number of band gaps are investigated. The numerical results show that incident angle of both TE and TM polarization waves have an effect on the width and the position of the band gaps and gaps are blue-shifted by increasing the angle of incidence. Moreover, in studying of the intrinsic parameters of the materials, the behavior of the band gaps is found to be quite interesting. We show that by increasing the permittivity of the dielectric material, band gaps tune to the lower frequency while increasing the electron density of plasma layer shows a different trend. The proposed structure and findings can provide useful information to design new types of tunable multichannel filters for different plasma applications.

Numerical study of flat plate solar collector performance with square shape wicked evaporator

In this work, a system of a heat pipe is implemented to improve the performance of flat plate solar collector. The model is represented by square shape portion of the evaporator section of wicked heat pipe with a constant total length of 510 mm, and the evaporator section inclined by an angle of 30o. In this models the evaporator, adiabatic and condenser lengths are 140mm, 140mm, and 230mm respectively. The omitted energies from sunlight simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 240%. The efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20o C). The numerical result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRAE standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of wicked heat pipe is decreases, where the heat transfer from the evaporator to condenser increases. The numerical results showed the performance of solar collector with square shape evaporator greater than other types of evaporator as a ratio 15 %.

Experimental study of flat plate solar collector performance with twisted heat pipe

In this work, a system of heat pipe is implemented to improve the performance of flat plate solar collector. The experiment rig consists of sun light simulator, flat plate, heat pipe (wickless), heat exchanger, and measurement instruments. The model is represented by twisting portion of the evaporator section and also inclined by an angle of 30° with a constant total length of 1140 mm. In this model the evaporator, adiabatic and condenser lengths are 780mm, 140mm and 230mm respectively. The omitted energies from sun light simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 30% and the efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20° C). The experimental result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRA standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of thermosyphon is decreases, where the heat transfer from the evaporator to condenser increases. The experimental results showed the performance of solar collector with twisted evaporator greater than other types of evaporator as a ratio 13.5 %.

Nanoaerosol Filtration with Fine-Fiber Polydisperse Filters

The self-consistent theory of nanoaerosol filtration has been considered at small Peclet numbers. It has been shown that, at Pe < 1, it is necessary to consider the deposition of particles simultaneously on thePe < entire ensemble of fibers. Only at can the filtration efficiency be found from the collection efficiencies calculated separately for each fiber. The self-consistent theory has been used to estimate the efficiencies of filtration with polydisperse fibrous filters. The penetrations of particles through filters with different variances of the functions of fiber length distribution over fiber radii have been compared at a constant packing density or a constant total length of all fibers. It has been shown that, at a constant packing density, a rise in the variance leads to a decrease in the filtration efficiency, while, at a constant total fiber length, the efficiency is almost independent of the width of the distribution function.

Shannon information entropies for rectangular multiple quantum well systems with constant total lengths* *Project supported by the Iranian Nanotechnology Initiative Council (INIC), the 20180677-SIP-IPN, Mexico, and the CONACYT 288856-CB-2016, Mexico.

We first study the Shannon information entropies of constant total length multiple quantum well systems and then explore the effects of the number of wells and confining potential depth on position and momentum information entropy density as well as the corresponding Shannon entropy. We find that for small full width at half maximum (FWHM) of the position entropy density, the FWHM of the momentum entropy density is large and vice versa. By increasing the confined potential depth, the FWHM of the position entropy density decreases while the FWHM of the momentum entropy density increases. By increasing the potential depth, the frequency of the position entropy density oscillation within the quantum barrier decreases while that of the position entropy density oscillation within the quantum well increases. By increasing the number of wells, the frequency of the position entropy density oscillation decreases inside the barriers while it increases inside the quantum well. As an example, we might localize the ground state as well as the position entropy densities of the 1st, 2nd, and 6th excited states for a four-well quantum system. Also, we verify the Bialynicki–Birula–Mycieslki (BBM) inequality.

Retention and Scalability Perspective of Sub-100-nm Double Gate Tunnel FET DRAM

This paper reports on the design optimization of double gate (DG) tunnel FET (TFET) for dynamic memory applications in sub-100-nm regime. It is shown that incorporation of lateral spacing ( ${L}_ {\text {gap}})$ between the gates, and an underlap region ( ${L}_{\text {un}})$ between drain and back gate reduces state “0” degradation, which along with optimal biases, results in an improved Retention Time (RT) at 85 °C. The systematic design optimization increases RT from ~80 to ~300 ms with the use of ${L}_{\text {gap}}$ at 85 °C, which can be further improved to ~600 ms with the introduction of ${L}_{\text {un}}$ . The careful investigation shows the back gate scaled down to 25 nm with a front gate region of 100 nm, and operation even at elevated temperatures (125 °C). The insights into DG TFET DRAM operation in terms of individual as well as total lengths highlights the RT enhancement by a factor of 3 with constant total length (200 nm) and an improved scalability with total length scaled down to 160 nm. This paper provides new opportunities to realize TFET-based DRAM with improved RT, scalability, and high temperature operation.

Effect of electric field on optical properties of GaN/AlN constant total effective length multiple quantum well systems

In this work we have investigated the effect of external electric field and number of wells on the absorption coefficient of GaN/AlN constant total effective length multiple quantum well system. We found that there is a blue shift in the absorption peak positions when number of wells increases while we have retained the total length of the structure constant. Systems with two and four numbers of wells have minimum and maximum absorptions among the studied systems. Thus, at constant total length, excess increasing of the number of wells do not help too much to increase the absorption coefficient amplitude. This fact is important from experimental point of view, since we can grow less number of thin films in a multiple quantum well system while we have larger absorption coefficients.

The effect of the size of polymer chain on the energy transfer between chromophores bound to the ends of the chain

The dependence of the luminescence quantum yield of linear polymer molecules that contain chromophores at the ends on the number of units of polymer chain is studied. Numerical calculations for the dipole-dipole energy transfer between chromophores show that an increase in the chain length by a factor of 2 leads to a several-fold increase in the luminescence quantum yield depending on the ratio of the Forster radius to the radius of polymer coil. An approximate formula is derived for the adequate analysis of the dependence at the Forster radius that is significantly less than the radius of polymer coil. The dependence of the luminescence quantum yield of linear polymer molecules on the length of the statistical segment (unit) at a constant total length of the chain is also studied.

Numerical Prediction of Turbulent Flow and Heat Transfer Enhancement in a Square Passage With Various Truncated Ribs on One Wall

Repeated ribs are often employed in the midsection of internal cooling passages of turbine blades to augment the heat transfer by air flowing through the internal ribbed passages. Though the research of flow structure and augmented heat transfer inside various ribbed passages has been well conducted, previous works mostly paid much attention to the influence of rib topology (height-to-pitch, blockage ratio, skew angle, rib shape). The possible problem involved in the usage of ribs (especially with larger blockage ratios) is pressure loss penalty. Thus, in this case, the design of truncated ribs whose length is less than the passage width might fit the specific cooling requirements when pressure loss is critically considered. A numerical study of truncated ribs on turbulent flow and heat transfer inside a passage of a gas turbine blade is performed when the inlet Reynolds number ranges from 8000 to 24,000. Different truncation ratio (truncated-length to passage-width) rib geometries are designed and then the effect of truncation ratio on the pressure drop and heat transfer enhancement is observed under the condition of constant total length. The overall performance characteristics of various truncated rib passages are also compared. It is found that the heated face with a rib that is truncated 12% in length in the center (case A) has the highest heat transfer coefficient, while the heated face with a rib that is truncated 4% at three locations over its length, in the center and two sides (case D), has a reduced pressure loss compared with passages of other designs and provides the lowest friction factors. Although case A shows larger heat transfer augmentation, case D can be promisingly used to augment side-wall heat transfer when the pressure loss is considered and the Reynolds number is relatively large.

天然フラクチャー型貯留層の有効浸透率予測

Appropriate modeling of naturally fractured reservoirs is one of the most important and challenging issues in reservoir characterization. In simulation, a dual porosity or dual permeability model is applied when fractures are well developed to form a fracture network. On the other hand, the single-continuum approach, where the fracture system is represented by effective permeability, is commonly used if fractures are discrete or disconnected. Focusing on the latter case, this paper proposes a semi-analytical technique to evaluate effective permeability for periodically or randomly fractured media including infinitely thin, infinite-conductivity fractures.The complex variable boundary element method is used to compute potential fields and streamlines in the two-dimensional space for discretely distributed fracture systems under the periodic boundary conditions. Effective permeability is evaluated first for discrete fracture systems of regular patterns to demonstrate the validity of the method and to examine the sensitivity of the effective permeability to the variations in the basic fracture parameters. With a constant total length of fractures, systems of varied fracture lengths show higher effective permeability than systems of uniform fracture length. 500 distributions of stochastic fractures are next generated to establish correlation between effective permeability and the fracture parameters, total length L, mean length m, and standard deviation of fracture length ?D. Sensitivity to the parameters shows that non-zero a increases effective permeability, that the incremental gain of effective permeability is proportional to L, and that the larger m, the larger effective permeability. The effective permeability tensors are also determined for oriented fractures. Analyses by non-parametric regression show that the diagonal elements, kxx and kyy, are highly affected by the angle between the oriented fractures and the pressure gradient, while the off-diagonal elements, kxy and kyx, are strongly affected by both the total length and the angle.

Are diameter, length and branching ratios meaningful in the lung?

The morphology of branching trees in general, and of the bronchial tree in particular, can be described in terms of three parameters, the diameter, length and branching ratios. These are the factors by which mean diameter and mean length increase in successive orders towards the trachea, and by which the number of branches increases in successive orders away from the trachea. Orders of branching are counted from the periphery towards the trachea, according to the method of Strahler. A model of from two to nine orders, and of constant total length and volume, was used to investigate the effect of varying the above parameters on the calculated pressure difference across the model during flow. In particular, the branching ratio was set at known values for dog and human lungs, and diameter and length ratios were independently varied. Known data from dog and human lungs were found to be close to the points predicted by the model where the lines of minimal resistance and minimal entropy production crossed. Other factors which may affect the values of these parameters are discussed.

Limiting deformations in bulge forming of thin cylinders of fixed length

An analysis has been made of the bulge height and pressure at instability of short thin cylinders subjected to internal pressure and clamped so as to maintain constant total length, such that the axial pressure forces are carried by the clamps. The stresses in the cylinder wall then arise only from the curvature of the cylinder wall. The material is assumed incompressible, and to obey the Mises yield criterion, its associated flow rule and a power law of strain hardening. Experiments on impact-extruded and annealed aluminium tubes indicate good agreement with theory except for very short tubes.