scholarly journals Heat and Mass Transfer of Droplet Vacuum Freezing Process Based on Dynamic Mesh

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Lili Zhao ◽  
Yuekai Zhang ◽  
Zhijun Zhang ◽  
Xun Li ◽  
Wenhui Zhang
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Droplet Diameter ◽  
Dynamic Mesh ◽  
Freezing Process ◽  
Freezing Time ◽  
Droplet Temperature ◽  
Obvious Effect ◽  
Initial Droplet ◽  
Vacuum Freezing

A numerical simulation using dynamic mesh method by COMSOL has been developed to model heat and mass transfer during vacuum freezing by evaporation of a single droplet. The initial droplet diameter, initial droplet temperature, and vacuum chamber pressure effect are studied. The surface and center temperature curve was predicted to show the effect. The mass transfer rate and radius displacement were also calculated. The results show the dynamic mesh shows well the freezing process with the radius reduction of droplet. The initial droplet diameter, initial droplet temperature, and vacuum pressure have obvious effect on freezing process. The total freezing time is about 200 s, 300 s, and 400 s for droplet diameter 7.5 mm, 10.5 mm, and 12.5 mm, respectively. The vacuum pressure less than 200 Pa is enough for the less time to freezing the droplet, that is, the key point in freezing time. The initial droplet temperature has obvious effect on freezing but little effect on freezing temperature.

Numerical Study on Microwave Dehydro-Freezing of Fish Tissues

2011 ◽  
Author(s):  
Yuichiro Oku ◽  
Hirofumi Tanigawa ◽  
Takaharu Tsuruta
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Numerical Study ◽  
Fish Tissue ◽  
Cell System ◽  
Moisture Distribution ◽  
Freezing Process ◽  
Tissue Cell ◽  
Frozen Fish ◽  
Fundamental Equations

In this study, a numerical simulation on the freezing process is carried out to evaluate the effects of pre-dehydration on the quality of frozen fish tissue. We use a simulation model which contains a muscle fiber to express the microscale heat and mass transfer phenomena inside the tissue cell system. Fundamental equations on heat and mass transfer are formulated in a two-dimensional coordinate system. The governing equations include phase-change terms. In order to take account of the characteristic moisture distribution produced by the microwave room-temperature drying, initial moisture distributions are given in this calculation. The numerical results indicate that the control of the water content by the pre-dehydration can shorten the freezing time. It is found that the cell shrinkage ratio is larger than that of the result using uniform distribution. As an increase of pre-dehydration, the central cell significantly shrinks but the surface-layer cell doesn’t shrink so much due to the large cooling rate.

Modeling heat and mass transfer during vacuum freezing of puree droplet

2013 ◽  
Vol 36 (4) ◽  
pp. 1319-1326 ◽  
Author(s):  
C. Cogné ◽  
P.U. Nguyen ◽  
J.L. Lanoisellé ◽  
E. Van Hecke ◽  
D. Clausse
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Vacuum Freezing

scholarly journals Parameter Sensitivity of the Microdroplet Vacuum Freezing Process

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Zhijun Zhang ◽  
Yuekai Zhang ◽  
Lili Zhao ◽  
Wenhui Zhang ◽  
Shuangshuang Zhao
Keyword(s):  
Thermal Conductivity ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Initial Temperature ◽  
Parameter Sensitivity ◽  
Chamber Pressure ◽  
Freezing Process ◽  
Cooling Stage ◽  
Vacuum Freezing

The vacuum freezing process of microdroplets (<100 μm in diameter) is studied by dynamic mesh method. The mass transfer coefficient was studied using the results of related papers that considered droplet diameters exceeding 1 mm. The diameter, initial temperature, and vacuum chamber pressure effects are also discussed. To estimate parameter sensitivity, the effects of material density, specific heat, and thermal conductivity in 20% scope, as well as latent evaporation/sublimation in 5%, were simulated. The results show that the mass transfer coefficientKis essentially different between microdroplets (<100 μm) and macrodroplet (>1 mm). Pressure and droplet diameter have an effect on cooling and freezing stages, but initial temperature only affects the cooling stage. The thermal conductivity coefficientklaffected the cooling stage, whereaskiaffected the freezing stage. Heat capacityClaffected the cooling stage, butCihas virtually no effect on all stages. The actual latent heat of freezingΔHwas also affected. Higher density corresponds to lower cooling rate in the cooling stage.

An Investigation of Liquid Droplet Evaporation Model Used in Multiphase Flow Simulation

2012 ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Mass Transfer ◽  
Thin Layer ◽  
Heat And Mass Transfer ◽  
Source Term ◽  
Liquid Droplet ◽  
Droplet Evaporation ◽  
Droplet Temperature ◽  
Evaporation Model ◽  
Commercial Code ◽  
Evaporation Energy

Modeling liquid droplet evaporation in a flow stream is very important in many engineering applications. It was discovered that the result of predicted droplet and main flow temperatures from using commercial codes sometimes presents unexplainable phenomena; for example, the droplet temperature drops too low. The objective of this study is to investigate the issues involved in the built-in droplet evaporation model by using three different approaches: (a) use the existing built-in correlations model in a commercial code, (b) use the lumped analytical analysis, and (c) actually solve the heat and mass transfer by directly using CFD without employing the built-in correlation model. In the third approach, the evaporation process is simulated by imposing water evaporation in a very thin layer at the surface of a stagnant water droplet; in the meantime, the evaporation energy is subtracted from the same place. This is performed by imposing a positive mass source term and a negative energy source term in a thin layer of cells wrapping around the droplet surface. The transport equations are then solved using the commercial CFD solver Ansys/Fluent to track the mass and energy transfer across the shell sides into the liquid droplet and out to the ambient. Unlike the built-in evaporation model in commercial codes, which assumes that all the evaporation energy (latent heat) is supplied by the droplet, in the direct CFD calculation, the evaporation energy is absorbed partly from the droplet and partly from the surrounding air according to the natural process based on the property values and the heat and mass transfer resistance inside and outside the droplet. The direct CFD result (without using evaporation correlation) is consistent with that of the lumped analytical analysis (2nd approach). During the development of the direct CFD calculation, several technical difficulties are overcome and discussed in detail in this paper. A revised equation is proposed to improve the existing built-in model in the current commercial code. Both the direct CFD method and the zero-dimensional lumped method show the droplet temperature always increases.

scholarly journals Modelling Droplet Heat and Mass Transfer in Aero-Engine Bearing Chambers

2019 ◽  
Author(s):  
Dafne Gaviria Arcila ◽  
Hervé Morvan ◽  
Kathy Simmons ◽  
Stephen Ambrose ◽  
Michael Walsh ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Evaporation Rate ◽  
Numerical Study ◽  
Droplet Diameter ◽  
Air Flow ◽  
Core Region ◽  
Evaporation Process ◽  
Data Set ◽  
The Core

Abstract The oil inside aeroengine bearing chambers can be found in many forms, including droplets which interact with the core airflow. The ability to model such bearing chambers computationally is desirable and thus a better understanding of the evaporation process of oil droplets is of great interest. Previous studies have analyzed the flow of isothermal droplets in bearing chambers. However, further investigation is needed into the heating of droplets in the highly rotating core region. This will enable designers to evaluate the behavior of droplets in a chamber and the likelihood that they will evaporate. The aim of this research is to analyze the oil droplet evaporation process under aeroengine bearing chamber representative conditions. An ultimate goal is the ability to predict the oil-air heat and mass transfer in the core flow region, as well as to develop an understanding of the flow inside a droplet, and how this affects evaporation. This latter is important as it has not been studied before. This paper presents the results of a numerical study of the evaporation process of a single droplet under bearing chamber temperature and air flow conditions. The two-phase flow is simulated using ANSYS Fluent with the volume of fluid approach and the evaporation process with the “D−square law”. First, the modelling approach is validated against previous experimental and numerical analysis of fuel droplets in an air flow with heat transfer. The simulation results were in excellent agreement with a benchmarking data set. The validated approach is then applied for investigation to smaller, bearing chamber representative droplets of an oil base stock used in jet engines. The oil evaporation rate was quantified as well as the evolution of droplet diameter, which revealed the effect of different air velocities and temperatures on the droplet. The extent to which evaporation rate increased with air velocity and temperature is quantified. It is concluded that droplets of initial diameters less than 200μm that remain in the chamber core region for more than 0.3s are likely to evaporate completely. This study allows us to estimate droplet heat and mass transfer and the associated phase change in a bearing chamber. It also provides best practice to predict the performance of small droplets under the effects of high temperature and velocity convective air flows. In future work this methodology will be applied in simulations in a representative bearing chamber to predict how the cooling process is affected by oil evaporation.

scholarly journals Modeling of the Drying Kinetics of Slurry Droplet in Spray Drying

2012 ◽  
Vol 11 (2) ◽  
pp. 1 ◽  
Author(s):  
Boris Golman
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Spray Drying ◽  
Parametric Study ◽  
Suspended Solids ◽  
Droplet Diameter ◽  
Gas Temperature ◽  
Drying Time ◽  
Droplet Drying ◽  
Kinetics Of

The detail analysis of the heat and mass transfer between the droplet containing suspended solids and the drying gas was carried out numerically. The temperature and moisture distributions within the slurry droplet were calculated during the first and second drying phases. The parametric study revealed that the droplet drying time decreases with increasing the drying gas temperature and decreasing the droplet diameter.

scholarly journals Modeling the kinetics of heat and mass transfer in the process of vacuum freezing of minced fish

2020 ◽  
Vol 10 (2) ◽  
pp. 11-21
Author(s):  
I.Yu. Aleksanian ◽  
◽  
A.H.-H. Nugmanov ◽  
N.V. Yartseva ◽  
Yu.M. Hudaliev ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Minced Fish ◽  
Vacuum Freezing ◽  
Kinetics Of
Sign in / Sign up

Export Citation Format

Share Document