Cold Cylinder Research Articles

Experimental investigation and optimization of small-scale helium liquefaction with multi-cryocoolers

Small-scale helium liquefiers using regenerative cryocoolers with cooling power up to 1.5W at 4.2K could be used to re-liquefy evaporated helium gas of small- and medium-sized cryogenic devices such as MEG and PPMS. A serial–parallel-path helium liquefier with a liquefaction rate of 83Litres per day (L/d) using five 4K G-M cryocoolers is developed, and has been applied to the Wuhan National High Magnetic Field Center (WHMFC) in China. Different from parallel-path helium liquefier, the helium gas is effectively, stepwise precooled by heat exchangers on multi-cold flanges, and thus the additional purifier and precooling coil heat exchangers on the thinner part of the cold head cylinder containing the 2nd stage displacer could be removed to simplify the construction. Through theoretical calculation and conclusive analysis, an optimum configuration is proposed and makes a reference to the design of serial–parallel-path helium liquefier with multi-cryocoolers.

Characteristics of thermal convection in a rectangular channel with an inner cold circular cylinder

Based on three-dimensional numerical simulations, results are presented for natural convection in a rectangular channel with an inner cold circular cylinder. The Prandtl number is 0.7 and the Rayleigh number is changed in the range of 1×103 to 1×106. The rectangular channel is heated from the bottom wall of the channel and cooled from the top wall. The adiabatic thermal boundary condition is implemented at the vertical side walls of the rectangular channel. A low-temperature isothermal boundary condition is applied at the surface of the cylinder. The radius of the inner circular cylinder is changed in the range of 0.1–0.4L, where L is the height of the rectangular channel. By changing the radius of the cylinder, we investigate the effect of the inner cold circular cylinder on thermal convection and heat transfer in the space between the cylinder and the rectangular channel. With respect to the radius and Rayleigh number of the cylinder, the thermal and flow field is categorized into six regimes: steady symmetric two-dimensional convection, steady asymmetric two-dimensional convection, steady symmetric three-dimensional convection, steady asymmetric three-dimensional convection, time periodic convection, and aperiodic convection. The map of thermal and flow regimes is presented as a function of the radius and Rayleigh number of the cylinder. This paper presents detailed analysis results for the isotherms, vortical structure, boundary layer thicknesses, and Nusselt numbers and includes a comparison of the results for a rectangular channel without an inner cylinder.

An Investigation of a Self-Pressurized Alpha V-Type Stirling Engine Converted Diesel Engine

This study reports the investigation results of 194cc. alpha V-type Stirling engine converted from a four-stroke diesel engine that operated in self-pressurized mode. Tests were conducted with air as the working gas and liquefied petroleum gas (LPG) as the heat source. The engine started operating at 600 °C for hot cylinder temperature and 60 °C for cold cylinder temperature, respectively. At heat input of 1100 J/s, the engine performance was successfully tested at both no load and load conditions. For mechanical shaft power assessment, the engine approximately produced a maximum brake power of 7 W, brake thermal efficiency of 0.6% at 717 rpm speed, 811 °C hot cylinder temperature and 96 °C cold cylinder temperature. For electrical power assessment, the engine was capable of generating a maximum electrical output power of 1.7 We at 657 rpm speed, 855 °C hot cylinder temperature and 98 °C cold cylinder temperature. Despite its low engine performance, the study of alpha V-type Stirling engine is a worthwhile step towards clean and sustainable energy in mass production.

Analysis of natural convection heat transfer from a cylinder enclosed in a corner of two adiabatic walls

A steady two-dimensional laminar natural convection heat transfer from a cold single horizontal isothermal cylinder enclosed between two adiabatic walls is studied both experimentally and numerically. Experiments are performed to study the effects of cylinder distance from horizontal and vertical walls for Rayleigh numbers of 3×105 and 6×105. Numerical computations are carried out by solving the governing equations of laminar natural convection using the finite volume technique. OpenFOAM which is an open source code software is used. Computations are made for a wide range of Rayleigh numbers from 104 to 106 and different ratios of vertical cylinder spacing (L/D) and that of horizontal cylinder spacing (S/D). Comparisons are made with the corresponding experimental measurements. Flow streamlines and isothermal lines around the cylinder so that by changing the value of L/D and S/D, due to damping effects of the adiabatic walls, the cold plume moves away from the cylinder at different angles. Results also indicate that local and average heat transfer coefficient is highly affected by L/D and Rayleigh number while S/D has a limited influence on heat transfer from the tube.

Standing sausage modes in coronal loops with plasma flow

Magnetohydrodynamic waves are important for diagnosing the physical parameters of coronal plasmas. Field-aligned flows appear frequently in coronal loops.We examine the effects of transverse density and plasma flow structuring on standing sausage modes trapped in coronal loops, and examine their observational implications. We model coronal loops as straight cold cylinders with plasma flow embedded in a static corona. An eigen-value problem governing propagating sausage waves is formulated, its solutions used to construct standing modes. Two transverse profiles are distinguished, one being the generalized Epstein distribution (profile E) and the other (N) proposed recently in Nakariakov et al.(2012). A parameter study is performed on the dependence of the maximum period $P_\mathrm{max}$ and cutoff length-to-radius ratio $(L/a)_{\mathrm{cutoff}}$ in the trapped regime on the density parameters ($\rho_0/\rho_\infty$ and profile steepness $p$) and flow parameters (magnitude $U_0$ and profile steepness $u$). For either profile, introducing a flow reduces $P_\mathrm{max}$ relative to the static case. $P_\mathrm{max}$ depends sensitively on $p$ for profile N but is insensitive to $p$ for profile E. By far the most important effect a flow introduces is to reduce the capability for loops to trap standing sausage modes: $(L/a)_{\mathrm{cutoff}}$ may be substantially reduced in the case with flow relative to the static one. If the density distribution can be described by profile N, then measuring the sausage mode period can help deduce the density profile steepness. However, this practice is not feasible if profile E better describes the density distribution. Furthermore, even field-aligned flows with magnitudes substantially smaller than the ambient Alfv\'en speed can make coronal loops considerably less likely to support trapped standing sausage modes.

PET motion correction using PRESTO with ITK motion estimation.

The Siemens BrainPET scanner is a hybrid MRI/PET system. PET images are prone to motion artefacts which degrade the image quality. Therefore, motion correction is essential. The library PRESTO converts motion-corrected LORs into highly accurate generic projection data [1], providing high-resolution PET images. ITK is an open-source software used for registering multidimensional data [2]. ITK provides motion estimation necessary to PRESTO. For this study the Utah phantom, a brain phantom and clinical images were used. The data was simulated with different statistics and included scatter and random events. The data was reconstructed using OP-OSEM [3] with 41 iterations. The patient was administrated with [18]F-FDG. The acquisition took about 35min (96min p.i.). Different motions considering translations and rotations with dimensions of 1, 5, 10 and 30mm and degrees in three axes were simulated with PRESTO. In addition to PET images, EPI sequence [3] images were also used. The metric used in ITK registration algorithm was the Mutual Information. Given a fixed image and a moved image, the outputs are six parameters, which represent motion: three translations and three rotations. Then, the images were corrected in PRESTO using these parameters. For low statistics (1E6) and larger motion (30mm/degrees) ITK showed considerable errors (Figure ​(Figure1).1). PRESTO using ITK estimated parameters can correct well the moved images. Regarding the PET images, clinical data has bigger errors than phantom data as expected. For MR images ITK errors are smaller than for PET images (Figure ​(Figure11). Figure 1 Simulated images in the study with Utah phantom (with a hot and a cold cylinder). On left side of the figure, in the first row, are the acquired PET images of the phantom: first transversal view and then coronal view. The next row shows the simulated ... ITK has some limitations, such as, images with low statistics hamper the correction because of the blurring and if the motion is severe the object of study goes out the FOV and then correction is not possible. ITK is a viable image-based correction, which used with PRESTO makes it possible to easily use PET or MR images for motion correction.

Non-Newtonian Mixed Convection Flow along an Isothermal Horizontal Circular Cylinder

The mixed convective laminar two-dimensional boundary-layer flow of non-Newtonian pseudo-plastic fluids is studied along an isothermal horizontal circular cylinder using a modified power-law viscosity model. In this model, there are no unrealistic limits of zero or infinite viscosity; consequently, no irremovable singularities are introduced into boundary-layer formulations for such fluids. Therefore, the boundary-layer equations can be solved numerically by using marching order implicit finite difference method with double sweep technique. Numerical results are presented for the case of shear-thinning fluids in terms of the fluid velocity and temperature distributions, shear stresses and rate of heat transfer in terms of the local skin-friction and local Nusselt number respectively. Here, it is found that heating the cylinder delays separation and if the cylinder is warm enough, suppress it completely. Cooling the cylinder brings the separation point nearer to the lower stagnation point and for a very cold cylinder there will not be boundary-layer on the cylinder.

Mixed convection flow from a horizontal circular cylinder embedded in a porous medium filled by a nanofluid: Buongiorno–Darcy model

Steady mixed convection boundary layer flow from an isothermal horizontal circular cylinder embedded in a porous medium filled with a nanofluid has been studied for both cases of a heated and cooled cylinder using the Buongiorno–Darcy mathematical nanofluid model. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme. The solutions for the flow and heat transfer characteristics are evaluated numerically for various values of the governing parameters, namely the constant mixed convection parameter λ, the traditional Lewis number Le, the buoyancy ratio parameter Nr, the Brownian motion parameter Nb and the thermophoresis parameter Nt. It is found that in the present case of the porous medium flow, the separation is always suppressed at negative values of λ. When λ changes from −2.1 to 0, one has a “heating” of the cylinder, but a heating in the negative range of λ (λ < 0). However, for a clear (Newtonian) fluid, Merkin (1977) found that heating the cylinder (λ > 0) delays the separation of the boundary layer and if the cylinder is hot enough (large values of λ > 0), then it is suppressed completely at a positive value of λ, somewhere between 0.88 and 0.89. On the other hand, cooling the cylinder (λ < 0) brings the boundary layer separation point nearer to the lower stagnation point and for a sufficiently cold cylinder (large values of λ < 0) there will not be a boundary layer on the cylinder.

Estimation of a Nusselt Correlations for Numerical Prediction of Frost Thickness Growth over a Cold Cylinder

This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.

Surface temperature control using thermal image processing

Abstract In the paper the computerized system for the surface temperature control of the rotating cylinder has been presented. In the presented solution, an IR camera works as a source of information about the thermal state of cylinder surface for the rest of the system. The necessary image processing algorithm as a basis for a control algorithm has been developed. An algorithm for the automatic localization of the cold cylinder by an IR camera using a set of thermal markers and a fuzzy recognition algorithm was developed. It enables one to calibrate the system properly in various operating conditions.

Natural Convection in a Square Enclosure with Differentially Heated Two Horizontal Cylinders

The present study numerically investigates two-dimensional natural convection in a cooled square enclosure with two inner circular cylinders, which have different isothermal conditions for different Rayleigh numbers in the range of 103 ≤ Ra ≤ 105. The cooled and heated isothermal conditions are imposed on the upper and lower cylinders, respectively. The centers of two equidiameter cylinders are placed at those of the lower and upper half of the enclosure, respectively, and the radius of inner cylinders varies. For all Rayleigh numbers, as the radius increases, the cold upper cylinder occupies a much wider area in the upper half of the cold enclosure, resulting in the formation of a wider dead zone of the heat transfer and fluid flow in the upper half of the enclosure. Regardless of the radius variation, the circulation of the flow shows two overall rotating symmetric eddies with the secondary vortices over the upper surface of the upper cylinder. The trajectories of the primary eddy and secondary vortices considerably depend on the radius, especially at a higher Rayleigh number. The dependence of the Nusselt number on the radius and the Rayleigh number is presented.

Performance evaluation of Maxwell and Cercignani-Lampis gas-wall interaction models in the modeling of thermally driven rarefied gas transport

A systematic study on the performance of two empirical gas-wall interaction models, the Maxwell model and the Cercignani-Lampis (CL) model, in the entire Knudsen range is conducted. The models are evaluated by examining the accuracy of key macroscopic quantities such as temperature, density, and pressure, in three benchmark thermal problems, namely the Fourier thermal problem, the Knudsen force problem, and the thermal transpiration problem. The reference solutions are obtained from a validated hybrid DSMC-MD algorithm developed in-house. It has been found that while both models predict temperature and density reasonably well in the Fourier thermal problem, the pressure profile obtained from Maxwell model exhibits a trend that opposes that from the reference solution. As a consequence, the Maxwell model is unable to predict the orientation change of the Knudsen force acting on a cold cylinder embedded in a hot cylindrical enclosure at a certain Knudsen number. In the simulation of the thermal transpiration coefficient, although all three models overestimate the coefficient, the coefficient obtained from CL model is the closest to the reference solution. The Maxwell model performs the worst. The cause of the overestimated coefficient is investigated and its link to the overly constrained correlation between the tangential momentum accommodation coefficient and the tangential energy accommodation coefficient inherent in the models is pointed out. Directions for further improvement of models are suggested.

A calorimeter for multilayer insulation (MLI) performance measurements at variable temperature

Here we describe a concentric cylindrical calorimeter with radiation guards developed to measure the thermal performance of multilayer insulation (MLI) for low temperature applications. One unique feature of this calorimeter is its ability to independently control the boundary temperatures between room temperature and about 15K using two single-stage Gifford–McMahon cryocoolers. Also, unlike the existing calorimeters that use the evaporation rate of a liquid cryogen to measure the heat load, in the present system the total heat transfer through the MLI is measured by recording the temperature difference across a calibrated heat load support rod that connects the cold inner cylinder to the lower temperature cryocooler. This design allows the continuous mapping of MLI performance over a much wider temperature range with independently controlled boundary conditions. The calorimeter is also suitable for performing a variety of radiation heat transfer experiments including the determination of the temperature dependence of the total emissivity.

EVALUATION OF EMPIRICAL NUSSELT CORRELATIONS FOR NUMERICAL PREDICTION OF FROST THICKNESS GROWTH OVER A COLD CYLINDER

This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. The model employs one-dimensional transient formulation based upon the local volume averaging technique. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.

Lattice Boltzmann simulation of melting phenomenon with natural convection from an eccentric annulus

In the present study, a double-population thermal lattice Boltzmann was applied to solve phase change problem with natural convection in an eccentric annulus. The simulation of melting process from a concentrically and eccentrically placed inner hot cylinder inside an outer cold cylinder with Prandtl number of 6.2, Stefan number of 1 and Rayleigh number of 105 was carried out quantitatively. It was found that the position of the inner cylinder inside the outer cylinder significantly influence the flow patterns including the size and shape of two formed vortexes. It is also observed that the maximum of liquid fractions occurs where the inner cylinder is mounted at the bottom of outer cylinder.

Constant-flux discrete heating in a unit aspect-ratio annulus

Natural convection in an annulus with a discrete heat source on the inner cylinder is studied numerically. The outer cylinder is isothermally cooled at a fixed low temperature, and the top wall, the bottom wall and unheated portions of the inner cylinder are thermally insulated. For low applied heat flux through the heater, as measured non-dimensionally by a Grashof number, Gr, the flow in the annular gap consists of a single-cell overturning meridional flow driven by the radial temperature gradient between the heater on the inner cylinder and the cold outer cylinder. In this regime, the flow is very weak and heat is transported primarily via conduction. The flow structure does not change until Gr ∼ 104, although the flow strength steadily increases with Gr. As the nonlinear convection terms become more important, the meridional circulation sweeps the isotherms from being almost vertical near the outer cylinder to almost horizontal near the bottom wall. By the end of the transition from the conduction-dominated regime (Gr < 104) to the convection-dominated regime (Gr ∼ 106), the flow becomes segregated into three distinct regions: (i) for vertical levels below that of the bottom of the heater, an essentially cold stagnant pool develops, with the heat flux through the outer cylinder dropping to zero. (ii) At vertical levels between the bottom and the top of the heater, most of the region in between the two cylinders is stably stratified with a relatively weak radial flow from the cold to the heated cylinder. The horizontal isotherms adjust to the temperatures on the cylinders in thin buoyancy boundary layers which drive fluid down the cold cylinder and up the heated cylinder segment. The boundary layer on the heater is about half as thick as that on the cold cylinder, but about twice as intense. (iii) The third region is above the heater top. The boundary layer flow from the heater continues upward where it meets the top endwall and bounces off of it. A wavy jet bounces on its way radially outward between the top insulated wall and the stably stratified region below. Flow separation on the top wall leads to the formation of a recirculation zone there. The vast majority of the heat flux through the outer cylinder occurs at this upper level, and is heavily concentrated near the very top. Geometric factors, such as the radius ratio of the cylinders and the heater placement, have quantitative effects, which are described, but the overall qualitative picture remains unchanged.

Natural convection in square enclosure with hot and cold cylinders at different vertical locations

This study investigates the natural convection in a square enclosure with hot and cold cylinders, induced by the temperature difference between a cold enclosure and the hot and cold circular cylinders contained within it. The immersed boundary method is used to model the two enclosed cylinders, based on the finite volume method, and two-dimensional natural convection was studied for different Rayleigh numbers in the range 103⩽Ra⩽106. Additionally, the study investigates the effect the presence of the hot and cold cylinders at different locations within the enclosure have on the heat transfer and fluid flow. The locations of the hot and cold circular cylinders are varied vertically along the centerline at the left and right parts of the enclosure, respectively. The existence of local peaks for the Nusselt numbers along the surfaces of the cylinders and enclosure is determined by the gap between the cylinders and the enclosure and thermal plume governed by the convection, respectively. Detailed analysis results for the distributions of the streamlines, isotherms, and Nusselt numbers are presented in this paper.

Measure dimension of rotating large hot steel shell using pulse laser on PRRR robot

During the industrial forging or rolling of hot steel shells, the raw material utilization ratio is very low because of the absence of precise on-line measurement instrument for the forging dimensions. In order to reduce the waste and increase the productivity, the pulse laser measuring instrument with dual PRRR mechanism has been developed in this study. The adjusting algorithm of rotary table based on the dual PRRR mechanism has been presented, which ensures that the scanning plane is perpendicular to the axis of cylinder shell. So the circle fitting can be adopted and the robust and accurate dimensions can be obtained rapidly by the present data-processing method. The measurement error of cold cylinder shell’s diameter is less than 3mm. The measuring results of hot steel shells are also very accurate. The present system has been used in the rolling production of large hot steel shells, which enhances the raw material utilization ratio during the rolling.

Correlation for frost properties on a cold cylinder surface in cross flow

An experimental study was reported earlier on the development of frost formation by humid flow passing over the cylinder. In this study, dimensionless correlations based on previous experimental data and reported empirical correlations of others for frost properties are proposed. The frost conduction coefficient is determined by using an analytical equation. Subsequently, correlations are sought for the heat conduction coefficient, dimensionless temperature, dimensionless thickness and density. The advantages of these correlations to any other proposed correlations are their explicit and dependency on time. Furthermore, an estimation of characteristics of the frost is followed by using the same approach and the established correlations.

두 개의 뜨거운 원형 실린더가 존재하는 사각형 실린더 내부의 자연대류에 관한 수치적 연구

Numerical calculations are carried out for the natural convection in a square enclosure with two hot cylinders induced by temperature difference between a cold outer rectangular cylinder and two hot circular cylinders. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model two inner circular cylinders based on finite volume method, for different Rayleigh numbers varying over the range of <TEX>$10^3$</TEX> to <TEX>$10^5$</TEX>. The study goes further to investigate the effect of the location of two cylinders on the heat transfer and fluid flow. The location of inner circular cylinders is changed vertically along the center-line of square enclosure. The changes of heat transfer quantities have been presented.