Research on segregation evaluation methods of asphalt pavement based on air voids distribution

Eye observation was used to evaluate the segregation degree of asphalt pavement, which was not much creditable. To the asphalt pavement, road surface texture measuring method which has appeared recently can identify gradational segregation; but it can’t reflect the influence of the temperature segregation. However, using infrared temperature detector to evaluate the segregation must be taken during paving, which brings much inconvenience. In this paper, measuring the air voids distribution using non-nuclear density gauge to evaluate asphalt pavement segregation was introduced. Result shows that this method can directly reflect the comprehensive results of the two types of segregation in a high efficient and accurate way. Moreover, using the sketch map of segregation area can help to analyze the segregation reason visually.

Voids size distribution in gelled waxy crude oil under dynamic and static cooling

Waxy crude oil is known for its high wax contents that can potentially result in gelling following sufficient cooling of the transportation line in the subsea bed at offshore fields.The gelling over the entire lines requires an accurately predicted restart pressure to restart the clogged and idle system.However,the common way of predicting the restart pressure has been reported to result in over-designed and predicted piping parameters.Recent research findings evidenced the formation of voids which would reduce the restart pressure significantly.The study conducted in this paper is aimed at investigating the voids size distribution in gelled crude oil across and along transportation pipelines.Sets of experiments simulating crude oil transportation during both static and dynamic cooling were conducted.The gelled crude oil below the pour point temperature was then scanned using a Magnetic Resonance Imaging(MRI)system to detect the voids formed.The resulting voids at each scanning cross-section were quantified,and their distributions were investigated.It was observed that dynamic cooling had minimal impacts on the voids size difference along the pipeline with the difference in voids areas within 10 mm^(2) to be twice and uniform for the entire flow rates tested.However,voids size in statically cooled waxy crude oil was found to be highly distributed with a maximum of 6 voids size distribution in 10 mm2 ranges.The low-end temperature had the highest size difference while the difference was decreasing with higher end temperatures.This study shows that the voids amount in dynamically cooled waxy crude oil could also be estimated with lower numbers of cross-sectional voids areas.However,the higher cross-sectional voids detection is recommended while estimating voids in statically cooled waxy crude oil.

Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow

A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction dis- tribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is deter- mined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.

Heat Absorbing and Releasing Experiments with Improved Phase-change Thermal Storage Canisters

This article,based on authors＇ long-term study,proposes an improved foamed-Ni-packed phase-change thermal storage canister,which takes advantage of the foamed-Ni characteristic of instinctive porous structure and excellent properties to ameliorate its void distribution and thermal conductivity. The improved canister and the unimproved one without foamed-Ni package,are put to heat absorbing and releasing tests to investigate the effects of heat absorbing temperature upon the phase-change materials （PCM） melting time under three temperature schemes by using platinum resistance thermometers （PT100） and data acquisition modules （ADAM-4000） to gather the data of varying temperature. Afterwards,the computerized tomography （CT） is employed to scan the void distribution in both canisters. Compared to the unimproved canister,the experimental results evidence the superiority of the improved one in higher uniformity in void and temperature distribution as well as faster thermal responses.

Thermal Analysis of Void Cavity for Heat Pipe Receiver under Microgravity

Based on theoretical analysis of PCM(Phase Change Material) solidification process, the model of improved void cavity distribution tending to high temperature region is established. Numerical results are compared with NASA(National Aeronautics and Space Administration) results. Analysis results show that the outer wall temperature, the melting ratio of PCM and the temperature gradient of PCM canister, have great difference in different void cavity distribution. The form of void distribution has a great effect on the process of phase change. Based on simulation results under the model of improved void cavity distribution, phase change heat transfer process in thermal storage container is analyzed. The main goal of the improved designing for PCM canister is to take measures in reducing the concentration distribution of void cavity by adding some foam metal into phase change material.