scholarly journals A Novel 2D Model for Freezing Phase Change Simulation during Cryogenic Fracturing Considering Nucleation Characteristics

2020 ◽  
Vol 10 (9) ◽  
pp. 3308
Author(s):  
Chengyu Huang ◽  
Wenhua Wang ◽  
Weizhong Li
Keyword(s):  
Multiphase Flow ◽  
Phase Change ◽  
Heterogeneous Nucleation ◽  
Initial Distribution ◽  
Freezing Process ◽  
Computational Domain ◽  
Comparison Results ◽  
Fracturing Process ◽  
Cryogenic Fracturing ◽  
Ice Phase

A 2D computational fluid dynamics (CFD) model in consideration of nucleation characteristics (homogeneous/heterogeneous nucleation) using the volume of fluid (VOF) method and Lee model was proposed. The model was used to predict the process of a multiphase flow accompanied by freezing phase change during cryogenic fracturing. In this model, nucleation characteristic (homogeneous and heterogeneous nucleation) during the freezing process and the influence of the formed ice phase on the flowing behavior was considered. Validation of the model was done by comparing its simulation results to Neumann solutions for classical Stefan problem. The comparison results show that the numerical results are well consistent with the theoretical solution. The maximum relative differences are less than 7%. The process of multiphase flow accompanied by the freezing of water was then simulated with the proposed model. Furthermore, the transient formation and growth of ice as well as the evolution of temperature distribution in the computational domain was studied. Results show that the proposed method can better consider the difference between homogeneous nucleation in the fluid domain and heterogeneous nucleation on the wall boundary. Finally, the main influence factors such as the flow velocity and initial distribution of ice phase on the fracturing process were discussed. It indicates that the method enable to simulate the growth of ice on the wall and its effect on the flow of multiphase fluid.

Phase Change Process Inside a Small-radii Cylinder Subjected to Cyclic Convective Boundary Conditions: a Numerical Study

2021 ◽  
Author(s):  
Yousef Kanani ◽  
Avijit Karmakar ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Freezing Process ◽  
Fourier Number ◽  
Two Phase ◽  
Convective Boundary

Abstract We numerically investigate the melting and solidi?cation behavior of phase change materials encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square wave). Initially, we explore the effect of the Stefan and Biot numbers on the non-dimensionalized time required (i.e. reference Fourier number Tref ) for a PCM initially held at Tcold to melt and reach the cross?ow temperature Thot. The increase in either Stefan or Biot number decreases Tref and can be predicted accurately using a correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed for the above process. We further study the effect of the cyclic Fourier number on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates towards the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and higher overall heat transfer is achieved as the surface temperature oscillates in the vicinity of the melting temperature, which increases the effective temperature difference driving the convective heat transfer.

Solidification of Phase Change Materials Infiltrated in Porous Media in Presence of Voids

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Mahmoud Moeini Sedeh ◽  
J. M. Khodadadi
Keyword(s):  
Phase Change ◽  
Porous Structure ◽  
Phase Change Materials ◽  
Solidification Process ◽  
Volume Shrinkage ◽  
Freezing Process ◽  
Infiltration Process ◽  
Noticeable Increase ◽  
Melting Characteristics ◽  
Micron Size

Infiltration of phase change materials (PCM) into highly conductive porous structures effectively enhances the thermal conductivity and phase change (solidification and melting) characteristics of the resulting thermal energy storage (TES) composites. However, the infiltration process contributes to formation of voids as micron-size air bubbles within the pores of the porous structure. The presence of voids negatively affects the thermal and phase change performance of TES composites due to the thermophysical properties of air in comparison with PCM and porous structure. This paper investigates the effect of voids on solidification of PCM, infiltrated into the pores of graphite foam as a highly conductive porous medium with interconnected pores. A combination of the volume-of-fluid (VOF) and enthalpy-porosity methods was employed for numerical investigation of solidification. The proposed method takes into account the variation of density with temperature during phase change and is able to predict the volume shrinkage (volume contraction) during the solidification of liquids. Furthermore, the presence of void and the temperature gradient along the liquid–gas interface (the interface between void and PCM) can trigger thermocapillary effects. Thus, Marangoni convection was included during the solidification process and its importance was elucidated by comparing the results among cases with and without thermocapillary effects. The results indicated that the presence of voids within the pores causes a noticeable increase in solidification time, with a sharper increase for cases without thermocapillary convection. For verification purposes, the amount of volume shrinkage during the solidification obtained from numerical simulations was compared against the theoretical volume change due to the variation of density for several liquids with contraction and expansion during the freezing process. The two sets of results exhibited good agreement.

Three-Dimensional Numerical Study on Freezing Phase Change Heat Transfer in Biological Tissue Embedded With Two Cryoprobes

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Fang Zhao ◽  
Zhenqian Chen
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Biological Tissue ◽  
Clinical Medicine ◽  
Numerical Study ◽  
Biological Tissues ◽  
Freezing Process ◽  
Ice Crystal ◽  
Obvious Effect ◽  
Phase Change Heat Transfer

Biological tissues undergo complex phase change heat transfer processes during cryosurgery, and a theoretical model is preferable to forecast this heat experience. A mathematical model for phase change heat transfer in cryosurgery was established. In this model, a fractal treelike branched network was used to describe the complicated geometrical frame of blood vessels. The temperature distribution and ice crystal growth process in biological tissue including normal tissue and tumor embedded with two cryoprobes were numerically simulated. The effects of cooling rate, initial temperature, and distance of two cryoprobes on freezing process of tissue were also studied. The results show that the ice crystal grows more rapidly in the initial freezing stage (<600 s) and then slows down in the following process, and the precooling of cryoprobes has no obvious effect on freezing rate of tissue. It also can be seen that the distance of 10 mm between two cryoprobes produces an optimal freezing effect for the tumor size (20 mm × 10 mm) in the present study compared with the distances of 6 mm and 14 mm. The numerical results are significant in providing technical reference for application of cryosurgery in clinical medicine.

A New Type Phase Change Energy-Saving Device for Building Field

2012 ◽  
Vol 608-609 ◽  
pp. 1147-1150
Author(s):  
Yong Qi Xie ◽  
Peng Tao Chi ◽  
Jian Zu Yu ◽  
Jun Song
Keyword(s):  
Phase Change ◽  
Maximum Temperature ◽  
Storage Device ◽  
Melting Time ◽  
Freezing Process ◽  
Maximum Temperature Difference ◽  
Copper Foam ◽  
Prototype Test ◽  
New Type ◽  
Change Material

The heat transfer enhancement in a latent heat energy storage device through embedment of copper foam (CF) is reported. The CF had a 96% porosity and the phase change material (PCM) was 25# paraffin. The CF and PCM were contained in a cuboid sample. A prototype test room was designed to numerically investigate the performance of the device. The melting and freezing process of the PCM and the day-night temperature of the room were observed. The results show that the tested totally melting time of the PCM is 8.72 hours during the daytime while the freezing time is 8.19 hours at night, and the phase change process could accomplish within 8-9 hours. The maximum temperature difference of the room is reduced 8.3°C. The room comfort could be significantly enhanced under the premise of less air conditioning energy consumption by applying the device.

scholarly journals Multiphase Flow and Phase Change in Microgravity: Fundamental Research and Strategic Research for Exploration of Space

2003 ◽  
Author(s):  
Bhim S. Singh
Keyword(s):  
Multiphase Flow ◽  
Phase Change ◽  
Space Flight ◽  
Closed Loop ◽  
Life Support ◽  
Support Systems ◽  
Pool Boiling ◽  
Microgravity Environment ◽  
Strategic Research ◽  
Fundamental Research

NASA is preparing to undertake science-driven exploration missions. The NASA Exploration Team’s vision is a cascade of stepping stones. The stepping-stone will build the technical capabilities needed for each step with multi-use technologies and capabilities. An Agency-wide technology investment and development program is necessary to implement the vision. The NASA Exploration Team has identified a number of areas where significant advances are needed to overcome all engineering and medical barriers to the expansion of human space exploration beyond low-Earth orbit. Closed-loop life support systems and advanced propulsion and power technologies are among the areas requiring significant advances from the current state-of-the-art. Studies conducted by the National Academy of Science’s National Research Council and Workshops organized by NASA have shown that multiphase flow and phase change play a crucial role in many of these advanced technology concepts. Lack of understanding of multiphase flow, phase change, and interfacial phenomena in the microgravity environment has been a major hurdle. An understanding of multiphase flow and phase change in microgravity is, therefore, critical to advancing many technologies needed. Recognizing this, the Office of Biological and Physical Research (OBPR) has initiated a strategic research thrust to augment the ongoing fundamental research in fluid physics and transport phenomena discipline with research especially aimed at understanding key multiphase flow related issues in propulsion, power, thermal control, and closed-loop advanced life support systems. A plan for integrated theoretical and experimental research that has the highest probability of providing data, predictive tools, and models needed by the systems developers to incorporate highly promising multiphase-based technologies is currently in preparation. This plan is being developed with inputs from scientific community, NASA mission planners and industry personnel. The fundamental research in multiphase flow and phase change in microgravity is aimed at developing better mechanistic understanding of pool boiling and ascertaining the effects of gravity on heat transfer and the critical heat flux. Space flight experiments conducted in space have shown that nucleate pool boiling can be sustained under certain conditions in the microgravity environment. New space flight experiments are being developed to provide more quantitative information on pool boiling in microgravity. Ground-based investigations are also being conducted to develop mechanistic models for flow and pool boiling. An overview of the research plan and roadmap for the strategic research in multiphase flow and phase change as well as research findings from the ongoing program will be presented.

scholarly journals Thermal Analysis of Solid/Liquid Phase Change in a Cavity with One Wall at Periodic Temperature

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5957
Author(s):  
Shogo Tomita ◽  
Hasan Celik ◽  
Moghtada Mobedi
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Storage ◽  
Heat Transfer Process ◽  
Freezing Process ◽  
Dimensionless Frequency ◽  
Governing Equations ◽  
Stefan Number ◽  
Wide Range ◽  
Almost All

In this study, heat transfer in a square cavity filled with a Phase Change Material (PCM) under a sinusoidal wall temperature during solidification and melting is analyzed. All surfaces of the cavity are insulated except one surface, which is under the sinusoidal temperature change. The governing equations and boundary conditions are made dimensionless to reduce the number of governing parameters into two as dimensionless frequency and Stefan number. The governing equations were solved numerically by using Finite Volume Method for a wide range of Stefan number (0.1 < Ste < 1.0) and dimensionless frequency (0.23 < < 2.04). Based on the obtained results, a chart in terms of Stefan number and dimensionless frequency is obtained to divide the heat transfer process in the cavity into three regions as uncompleted, completed, and overheated phase-change processes. For the uncompleted process, some parts of the cavity are inactive, and no phase change occurs in those parts of the cavity during the melting and freezing process. For the overheated phase change, the temperature of the cavity highly increases (or decreases), causing the sensible heat storage to compete with latent thermal storage. In the completed process, almost all thermal storage is done by the utilization of latent heat. The suggested graph helps thermal designers to avoid wrong designs and predict the type of thermal storage (sensible or latent) in the cavity without doing any computations.

Sign in / Sign up

Export Citation Format

Share Document