Analysis of self-pressurization phenomenon of cryogenic fluid storage tank with thermal diffusion model

Self-pressurization phenomenon is one of the most important problems in the storage of cryogenic liquid. Until now, it has been difficult to predict exact pressurization process due to its complex non-equilibrium thermal behavior. This paper analyzes the self-pressurization with the trend of pressurization curves from experiment using liquid nitrogen with various heat leaks and liquid fractions. The trend of pressurization curves are classified on the basis of shape of pressurization curve. The qualitative relation between transient period, heat leak and liquid fractions is suggested. Thermal diffusion model (TDM) considering thermal stratification and thermal equilibrium model (TEM) can properly predict the respective pressurization curves with suitable condition for each model.     

Thermoacoustic power effect on the refrigeration performance of thermal separators

An experimental investigation on the refrigeration processes occurring in a receiving tube of a thermal separator was conducted in order to determine the primary factors affecting the refrigeration performance of this new type of refrigerator. In the current investigation, the gas in the system is divided into the oscillating gas and driving gas. While the compression/expansion of the oscillating gas caused by the driving gas determines the refrigeration process occurring in the receiving tube of the thermal separator, the temperature gradient on the receiving tube significantly affects the acoustic power generation and refrigeration performance. Experimental results demonstrate that when the tube-wall temperature difference near the open end of the receiving tube increases, the refrigeration coefficient increases. Using the information presented in the paper, a new cryogenic refrigeration system was developed, and the experimental data shows that the temperature of the cryogenic air flow in the system could reach −130 °C within 50 min. It suggests that the thermal separator investigated in the paper can be employed in the field of cryogenic engineering.     

Low Temperature Thermal Conductivity of Ti6Al4V Alloy

The CUORE detector, to be installed in 2010 at LNGS, is made of 988 TeO₂ crystals to be cooled to 10 mK. It consists of a large cryogen-free cryostat cooled by five pulse tubes and one high-power specially designed dilution refrigerator (R. Ardito et al. in , [2005]). The cryostat is ∼ 3 m high and has a diameter of ∼ 1.6 m. About 5 tons of lead shielding are to be cooled to below 1 K and a mass of 1.5 ton must be cooled to 10 mK. Some tie-rods sustain the different parts of the experiment. One end of each rod is at low temperature (10 mK for the detector frame, 50 mK for the coldest radiation shield, 700 mK for the shield linked to the still) with the other end usually at room temperature. A thermalization of the rods at the temperature of the first stage of the pulse tubes will be realized. Hence the value of the thermal conductivity of the material up to room temperature is important. At the lowest temperatures, the thermal conductivity has great influence in establishing the thermal load on the dilution refrigerator. The thermal conductivity of the structural material candidates for such tie-rods is usually known down to 4.2 K. Here we present data of thermal conductivity for the Ti6Al4V alloy below its superconductive transition temperature (4.38 K). A comparison over the full temperature range of operation is also done with other materials, such as 316 stainless steel and Torlon, candidates for the realization of the tie-rods.      

Numerical simulation of unsteady cavitating flows using a homogenous equilibrium model

 Numerical simulations of two-dimensional cavity flows around a flat plate normal to flow and flows through a 90^∘ bent duct are performed to clarify unsteady behavior under various cavitation conditions. A numerical method applying a TVD-MacCormack scheme with a cavitation model based on a homogenous equilibrium model of compressible gas-liquid two-phase media proposed by the present authors, is applied to solve the cavitating flow. This method permits the simple treatment of the whole gas-liquid two-phase flow field including wave propagation and large interface deformation. Numerical results including detailed observations of unsteady cavity flows and comparisons of predicted results with experimental data are provided. Received: 5 August 2002 / Accepted: 6 January 2003     

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 15 K 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.     

低温用膨胀珍珠岩绝热性能的实验研究

本文以常用低温保温材料膨胀珍珠岩 (珠光砂 )为研究对象 ,实验测量了在稳态和非稳态传热条件下的导热性能、热扩散性能及其随温度的变化规律 ,并对两种传热条件下的绝热特性进行了分析和研究 ,为工程应用提供可靠的理论依据 ,也为低温绝热方案的选择及优化提供参考资料     

Negative thermal expansion and electrical properties of Mn3(Cu0.6NbxGe0.4 − x)N (x = 0.05-0.25) compounds

Bulk materials with the general formula of Mn₃(Cu_0.6Nb_xGe_0.4 − x)N (x = 0.05, 0.1, 0.15, 0.2, 0.25), Mn₃(Cu_0.6Ge_0.4)N and Mn₃(Cu_0.7Ge_0.3)N were fabricated by mechanical ball milling and solid state sintering. Their thermal expansion coefficients and electrical conductivities were investigated in the temperature range of 80-300 K. It is found that the temperature interval of negative temperature expansion behavior is about 95 K in the samples of Mn₃(Cu_0.6Nb_0.15Ge_0.25)N and Mn₃(Cu_0.6 Nb_0.2Ge_0.2)N, which is twice as large as that of Mn₃(Cu_0.7Ge_0.3)N. The negative thermal expansion of Mn₃(Cu_0.6Nb_0.15Ge_0.25)N can reach to − 19.5 × 10⁻⁶ K^− 1 in the temperature range of 165 to 210 K. The electrical conductivity of this series materials is in a level of about 2.5 × 10⁶ (Ω m)^− 1.     

The thermal conductivity of cryogenic insulation materials and its temperature dependence

For the presentation of the thermal conductivity of cryogenic insulation materials and their integral mean values an empirical function is suggested, with which experimentally found values can be extrapolated to other temperature levels.The selection of materials includes granulated and fibrous insulations under atmospheric pressure as well as under vacuum and a multilayer insulation for most high performances.It is shown theoretically, how the constants in the empirical function can be determined. Their calculation is demonstrated practically by using real measurements.For a multilayer insulation a theory is developed, with which a measured value can be extrapolated to other temperatures, gas pressures and numbers of layers. Its application to a real insulation system is demonstrated too.The results are listed in a tabular summary.     

Influence of cryogenic thermal cycling treatment on the thermophysical properties of carbon/carbon composites between room temperature and 1900 °C

Influence of cryogenic thermal cycling treatment (from ?120 °C to 120 °C at 1.3 × 10^?3 Pa) on the thermophysical properties including thermal conductivity (TC), thermal diffusivity (TD), specific heat (SH) and coefficient of thermal expansion (CTE) ranging from room temperature to 1900 °C of carbon/carbon (C/C) composites in x-y and z directions were studied. Test results showed that fiber/matrix interfacial debonding, fiber pull-out and microcracks occurred after the cryogenic thermal treatment and they increased significantly with the cycle number increasing, while cycled more than 30 times, the space of microdefects reduced obviously due to the accumulation of cyclic thermal stress. TC, TD, SH and CTE of the cryogenic thermal cycling treated C/C composites were first decreased and then increased in both directions (x-y and z directions) with the increase of thermal cycles. A model regarding the heat conduction in cryogenic thermal cycling treated C/C composites was proposed.     

Spherical dendritic particles formed in cavitation erosion

Micro spherical particles were found in a vibrating cavitation erosion experiment. Examination of the spherical particles reveals the dendritic pattern on the surface and the hollow structure of the interior. The surface and interior structures of the particle are also related to the particle’s size. For smaller particle, the dendritic structure is replaced by the fine cell and the interior becomes solid. Such special structures are considered to be the result of particle’s solidification from molten state at a rapid cooling rate, which happens in a special transient environment with transient high temperature and high pressure provided by cavity collapsing. The specific area and surface tension force are the main reasons for the different structures of the particles in different size.     

Smart cure cycles for the adhesive joint of composite structures at cryogenic temperatures

Adhesive joints are employed for composite structures used at the cryogenic temperatures such as LNG (liquefied natural gas) insulating tanks and satellite structures. The strength of the adhesive joints at the cryogenic temperatures is influenced by the property variation of adhesive and the thermal residual stress generated due to the large temperature difference (ΔT) from the adhesive bonding process to the operating temperature. Therefore, in this work, the strength and thermal residual stress of the epoxy adhesive at cryogenic temperatures were measured with respect to cure cycle. Also, the cure cycles composed of gradual heating, rapid cooling and reheating steps were applied to the adhesive joints to reduce the thermal residual stress in the adhesive joints with short curing time. Finally, a smart cure method was developed to improve the adhesive joint strength and to reduce the cure time for the composite sandwich structures at cryogenic temperatures.     

Cavitation inception

In this paper, some general aspects of cavitation inception in flowing situations are considered. Special attention is paid to the problem of the scale effects commonly encountered by design engineers in extrapolating results from model tests to prototype situations. Past experimental and theoretical investigations relevant to the problem are reviewed. Recent advances in the field, particularly the influence of viscous effects in cavitation inception on smooth bodies, are discussed. Several useful scaling laws which are primarily based on empirical correlations or physical observations are suggested. A specific criterion which could be used to assess the importance of thermodynamic effects in cavitation inception is indicated.     

Numerical analysis of unsteady behavior of cloud cavitation around a NACA0015 foil

Three-dimensional unsteady cavitating flow around a NACA0015 hydrofoil fixed between the sidewalls was simulated and the mechanism of U-shaped cloud cavity formation was clarified. A local homogeneous model was used for the modeling of the vapor–liquid two-phase medium. The compressible two-phase Navier–Stokes equations as the governing equations were solved. To describe the phase change between water and vapor, the mass transfer model based on the theory of evaporation/condensation on a plane interface was introduced. The cell-centered finite volume method was employed to discretize the governing equations. Assuming turbulent flow, the turbulent eddy viscosity coefficient was computed by using the Baldwin–Lomax model with the Degani–Schiff modification. As a result, even in the case of cavitating flow without sidewalls, the shed cloud cavities has slightly 3D structure, which was not so much large as extending across the whole spanwise direction. On the other hand, in the case of cavitating flow with sidewalls, the end of sheet cavities bows in the spanwise direction because of the development of boundary layer near both sidewalls. After that, due to the occurring of the reentrant jet towards the mid-span region, the sheet cavities breaks off from mid-span region near the leading edge of the hydrofoil, and became the vortical cloud cavities, which have the large-scale U-shaped structure.     

Optimal control of thermal fluid flow using automatic differentiation

The aim of this study is to present a method for numerical optimal control of thermal fluid flow using automatic differentiation (AD). For the optimal control, governing equations are required. The optimal controls that have been previously presented by the present authors’ research group are based on the Boussinesq equations. However, because the numerical results of these equations are not satisfactory, the compressible Navier–Stokes equations are employed in this study. The objective is to determine whether or not the temperature at the objective points can be kept constant by imposing boundary conditions and by controlling the temperature at the control points. To measure the difference between the computed and target temperatures, the square sum of these values is used. The objective points are located at the center of the computational domain while the control points are at the bottom of the computational domain. The weighted gradient method that employs AD for efficiently calculating the gradient is used for the minimization. By using numerical computations, we show the validity of the present method.