scholarly journals Influence of Frost Growth and Migration in Cryogenic Heat Exchanger on Air Refrigerator

2019 ◽  
Vol 9 (4) ◽  
pp. 753 ◽  
Author(s):  
Shanju Yang ◽  
Zhan Liu ◽  
Bao Fu ◽  
Yu Chen
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Numerical Model ◽  
Heat And Mass Transfer ◽  
Frost Formation ◽  
Transient Model ◽  
Transfer Rates ◽  
Low Humidity ◽  
And Migration ◽  
Frost Layer

Frost formation degrades the performance of heat exchangers greatly, thus influencing the cryogenic refrigerator. Different from frost formation on the evaporator surface, the growth and migration of frost layer inside the heat exchanger is of low temperature and humidity. In addition to the constantly changing boundary conditions, the effective prediction is difficult. In the present study, a numerical model was proposed to analyze the frost formation in the cryogenic heat exchanger of a reverse Brayton air refrigerator. Under small amounts of moisture, the growing of frost layer was simulated through the numerical heat and mass transfer by adopting semiempirical correlations. The frost formation model was inserted into the transient model of refrigerator, and numerical calculations were performed on heat and mass transfer rates, and growth and migration of frost layers in forced convection conditions. Experiments were conducted under different air humidity to investigate the frost formation and verify the numerical model. Through the model, the influences of frosting on the refrigerator were evaluated under different moisture contents and running time. It can be used to predict the performance of air refrigerators with low humidity and provide a basis for improving the system operation and efficiency.

A New Approach to Delay or Prevent Frost Formation in Membranes

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Pooya Navid ◽  
Shirin Niroomand ◽  
Carey J. Simonson
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Water Vapor ◽  
Numerical Model ◽  
Heat And Mass Transfer ◽  
Moisture Transfer ◽  
Frost Formation ◽  
Permeable Membrane ◽  
New Approach ◽  
Temperature And Humidity

Saturation of the water vapor is essential to form frost inside a permeable membrane. The main goal of this paper is to develop a numerical model that can predict temperature and humidity inside a membrane in order to show the location and time of saturation. This numerical model for heat and mass transfer is developed to show that frost formation may be prevented or delayed by controlling the moisture transfer through the membrane, which is the new approach in this paper. The idea is to simultaneously dry and cool air to avoid saturation conditions and thereby eliminate condensation and frosting in the membrane. Results show that saturation usually occurs on side of the membrane with the highest temperature and humidity. The numerical model is verified with experimental data and used to show that moisture transfer through the membrane can delay or prevent frost formation.

scholarly journals Effects of Variable Transport Properties on Heat and Mass Transfer in MHD Bioconvective Nanofluid Rheology with Gyrotactic Microorganisms: Numerical Approach

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 231
Author(s):  
Muhammad Awais ◽  
Saeed Ehsan Awan ◽  
Muhammad Asif Zahoor Raja ◽  
Nabeela Parveen ◽  
Wasim Ullah Khan ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Transport Properties ◽  
Heat And Mass Transfer ◽  
Group Analysis ◽  
Numerical Approach ◽  
Validity Of Results ◽  
Gyrotactic Microorganisms ◽  
Transfer Rates ◽  
Buongiorno’S Model ◽  
Density Distributions

Rheology of MHD bioconvective nanofluid containing motile microorganisms is inspected numerically in order to analyze heat and mass transfer characteristics. Bioconvection is implemented by combined effects of magnetic field and buoyancy force. Gyrotactic microorganisms enhance the heat and transfer as well as perk up the nanomaterials’ stability. Variable transport properties along with assisting and opposing flow situations are taken into account. The significant influences of thermophoresis and Brownian motion have also been taken by employing Buongiorno’s model of nanofluid. Lie group analysis approach is utilized in order to compute the absolute invariants for the system of differential equations, which are solved numerically using Adams-Bashforth technique. Validity of results is confirmed by performing error analysis. Graphical and numerical illustrations are prepared in order to get the physical insight of the considered analysis. It is observed that for controlling parameters corresponding to variable transport properties c2, c4, c6, and c8, the velocity, temperature, concentration, and bioconvection density distributions accelerates, respectively. While heat and mass transfer rates increases for convection parameter and bioconvection Rayleigh number, respectively.

CFD-based structure optimization of plate bundle in plate-fin heat exchanger considering flow and heat transfer performance

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yao Li ◽  
Haiqing Si ◽  
Jingxuan Qiu ◽  
Yingying Shen ◽  
Peihong Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Field Performance ◽  
High Specific Surface Area ◽  
Calculation Model ◽  
Air Separation ◽  
Transfer Efficiency ◽  
Heat Transfer Efficiency

Abstract The plate-fin heat exchanger has been widely applied in the field of air separation and aerospace due to its high specific surface area of heat transfer. However, the low heat transfer efficiency of its plate bundles has also attracted more attention. It is of great significance to optimize the structure of plate-fin heat exchanger to improve its heat transfer efficiency. The plate bundle was studied by combining numerical simulation with experiment. Firstly, according to the heat and mass transfer theory, the plate bundle calculation model of plate-fin heat exchanger was established, and the accuracy of the UDF (User-Defined Functions) for describing the mass and heat transfer was verified. Then, the influences of fin structure parameters on the heat and mass transfer characteristics of channel were discussed, including the height, spacing, thickness and length of fins. Finally the influence of various factors on the flow field performance under different flow states was integrated to complete the optimal design of the plate bundle.

Prediction of Growth Parameters of Frost Deposits in Forced Convection

1981 ◽  
Vol 103 (1) ◽  
pp. 3-6 ◽  
Author(s):  
J. E. White ◽  
C. J. Cremers
Keyword(s):  
Mass Transfer ◽  
Forced Convection ◽  
Growth Parameters ◽  
Experimental Investigations ◽  
Experimental Conditions ◽  
Transfer Rates ◽  
Air Stream ◽  
Transient Period ◽  
Approximate Expressions ◽  
Frost Layer

Experimental investigations of frost deposition under forced convection conditions have shown that in most cases heat and mass transfer rates become constant after an initial transient period. It is shown that, in such cases, approximately half of the mass transfer from a humid air stream to a frost layer diffuses inward, condenses and increases the density of the frost. The other half is deposited at the surface and increases the thickness of the layer. Approximate expressions for density and thickness of the frost layer are derived and compared with data from the literature and also with experimental work reported in this paper. The correlations are shown to work well for a broad range of experimental conditions.

Physical statement of the problem for a numerical model of soil freezing and heaving taking into account heat and mass transfer

2021 ◽  
pp. 244-256
Author(s):  
Виктор Григорьевич Чеверев ◽  
Евгений Викторович Сафронов ◽  
Алексей Александрович Коротков ◽  
Александр Сергеевич Чернятин
Keyword(s):  
Finite Element Method ◽  
Mass Transfer ◽  
Finite Element ◽  
Numerical Model ◽  
Boundary Conditions ◽  
Heat And Mass Transfer ◽  
Soil Freezing ◽  
The Finite Element Method ◽  
Freezing Front ◽  
Element Method

Существуют два основных подхода решения задачи тепломассопереноса при численном моделировании промерзания грунтов: 1) решение методом конечных разностей с учетом граничных условий (границей, например, является фронт промерзания); 2) решение методом конечных элементов без учета границ модели. Оба подхода имеют существенные недостатки, что оставляет проблему решения задачи для численной модели промерзания грунтов острой и актуальной. В данной работе представлена физическая постановка промерзания, которая позволяет создать численную модель, базирующуюся на решении методом конечных элементов, но при этом отражающую ход фронта промерзания - то есть модель, в которой объединены оба подхода к решению задачи промерзания грунтов. Для подтверждения корректности модели был проделан ряд экспериментов по физическому моделированию промерзания модельного грунта и выполнен сравнительный анализ полученных экспериментальных данных и результатов расчетов на базе представленной численной модели с такими же граничными условиями, как в экспериментах. There are two basic approaches to solving the problem of heat and mass transfer in the numerical modeling of soil freezing: 1) using the finite difference method taking into account boundary conditions (the boundary, for example, is the freezing front); 2) using the finite element method without consideration of model boundaries. Both approaches have significant drawbacks, which leaves the issue of solving the problem for the numerical model of soil freezing acute and up-to-date. This article provides the physical setting of freezing that allows us to create a numerical model based on the solution by the finite element method, but at the same time reflecting the route of the freezing front, i.e. the model that combines both approaches to solving the problem of soil freezing. In order to confirm the correctness of the model, a number of experiments on physical modeling of model soil freezing have been performed, and a comparative analysis of the experimental data obtained and the calculation results based on the provided numerical model with the same boundary conditions as in the experiments was performed.

Computational analysis of heat and mass transfer in a micropolar fluid flow through a porous medium between permeable channel walls

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sohail Ahmad ◽  
Muhammad Ashraf ◽  
Kashif Ali ◽  
Kottakkaran Sooppy Nisar
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Micropolar Fluid ◽  
Numerical Data ◽  
Substantial Effect ◽  
Linearization Method ◽  
Transfer Rates ◽  
Micropolar Fluid Flow ◽  
Permeable Walls ◽  
Model Equations

Abstract The present work numerically investigates the mass and heat transport flow of micropolar fluid in a channel having permeable walls. The appropriate boundary layer approximations are used to convert the system of flow model equations in ODEs, which are then numerically treated with the quasi-linearization method along with finite difference discretization. This technique creates an efficient way to solve the complex dynamical system of equations. A numerical data comparison is presented which assures the accuracy of our code. The outcomes of various problem parameters are portrayed via the graphs and tables. The concentration and temperature accelerate with the impacts of the Peclet numbers for the diffusion of mass and heat, respectively. It is also found that the porosity of the medium has a substantial effect on the skin friction but low effect on the heat and mass transfer rates. Our results may be beneficial in lubrication, foams and aerogels, micro emulsions, micro machines, polymer blends, alloys, etc.

scholarly journals Analysis of Heat and Mass Transfer for Second-Order Slip Flow on a Thin Needle Using a Two-Phase Nanofluid Model

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1176
Author(s):  
Siti Nur Alwani Salleh ◽  
Norfifah Bachok ◽  
Fadzilah Md Ali ◽  
Norihan Md Arifin
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Slip Flow ◽  
Second Order ◽  
Two Phase ◽  
Specific Domain ◽  
Transfer Rates ◽  
Similarity Transformations ◽  
The Stability ◽  
Good Agreement

The present paper concentrates on the second-order slip flow over a moving thin needle in a nanofluid. The combined effects of thermophoresis and Brownian motion are considered to describe the heat and mass transfer performance of nanofluid. The resulting system of equations are obtained using similarity transformations and being executed in MATLAB software via bvp4c solver. The physical characteristics of embedded parameters on velocity, temperature, concentration, coefficient of skin friction, heat and mass transfer rates are demonstrated through a graphical approach and are discussed in detail. The obtained outcomes are validated with the existing works and are found to be in good agreement. It is shown that, for a specific domain of moving parameter, dual solutions are likely to exist. The stability analysis is performed to identify the stability of the solutions gained, and it is revealed that only one of them is numerically stable. The analysis indicated that the percentage of increment in the heat and mass transfer rates from no-slip to slip condition for both thin and thick surfaces of the needle ( a = 0.1 and a = 0.2 ) are 10.77 % and 12.56 % , respectively. Moreover, the symmetric behavior is noted for the graphs of reduced heat and mass transfer when the parameters N b and N t are the same.

A Fully Wet and Fully Dry Tiny Circular Fin Method for Heat and Mass Transfer Characteristics for Plain Fin-and-Tube Heat Exchangers Under Dehumidifying Conditions

2006 ◽  
Vol 129 (9) ◽  
pp. 1256-1267 ◽  
Author(s):  
Worachest Pirompugd ◽  
Chi-Chuan Wang ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Heat Transfer Characteristic ◽  
Transfer Characteristic ◽  
Tube Heat Exchanger ◽  
Mass Transfer Characteristic ◽  
Transfer Characteristics

This study proposes a new method, namely the “fully wet and fully dry tiny circular fin method,” for analyzing the heat and mass transfer characteristics of plain fin-and-tube heat exchangers under dehumidifying conditions. The present method is developed from the tube-by-tube method proposed in the previous study by the same authors. The analysis of the fin-and-tube heat exchangers is carried out by dividing the heat exchanger into many tiny segments. A tiny segment will be assumed with fully wet or fully dry conditions. This method is capable of handling the plain fin-and-tube heat exchanger under fully wet and partially wet conditions. The heat and mass transfer characteristics are presented in dimensionless terms. The ratio of the heat transfer characteristic to mass transfer characteristic is also studied. Based on the reduced results, it is found that the heat transfer and mass transfer characteristics are insensitive to changes in fin spacing. The influence of the inlet relative humidity on the heat transfer characteristic is rather small. For one and two row configurations, a considerable increase of the mass transfer characteristic is encountered when partially wet conditions take place. The heat transfer characteristic is about the same in fully wet and partially wet conditions provided that the number of tube rows is equal to or greater than four. Correlations are proposed to describe the heat and mass characteristics for the present plain fin configuration.

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