Carlos T. Salinas

Frost growth around a cylinder in a wet air stream

Abstract This paper describes a two-dimensional model which permits the evaluation of the local properties during the frost formation. To achieve this objective it is necessary to know the local coefficients of heat and mass transfer which were determined by solving the flow, temperature and humidity fields. To solve the flow field, the governing equations were developed in terms of the stream and vorticity functions. A numerical solution is obtained for low Reynolds number up to 400. With the flow field solved, the temperature and humidity fields are determined and hence the local heat and mass coefficients. These coefficients were then used in the solution of a two stage model for frost formation permitting the prediction of the local frost properties around the cylinder such as density, thickness and temperature.

APPLICATION OF A LOCAL-SPECTRUM CORRELATED MODEL TO MODELING RADIATIVE TRANSFER IN A MIXTURE OF REAL GAS MEDIA IN BIDIMENSIONAL ENCLOSURES

ABSTRACT Calculating radiative transport through nongray gases as combustion gases, atmospheric gases, and others is extremely difficult because of the strong spectral variation of the absorption coefficients of molecular gases. In the local-spectrum correlated model the spectral integration of the radiative transfer equation (RTE) is performed using one new gas absorption spectrum distribution function termed the cumulative wavenumber (CW). The CW model was first coupled with the discrete ordinates method to solve the transformed RTE. The accuracy of the model and algorithm first was examined for the one-dimensional homogeneous media, and results are compared with line-by-line calculations. It is found that the CW model is exact for homogeneous media, and inhomogeneous cases are examined. Then the CW model is implemented in a bidimensional enclosure with diffuse reflecting boundaries containing a mixture of real gases in isothermal and in strong nonisothermal cases. The spectral databases HITRAN and HITEMP are used to obtain the molecular absorption spectrum of the gases at different temperatures. Different cases are analyzed and results are compared.

APPLICATION OF THE CW MODEL FOR THE SOLUTION OF NON-GRAY COUPLED RADIATIVE CONDUCTIVE HEAT TRANSFER IN DOUBLE GLASS WINDOW WITH A CAVITY FILLED WITH MIXTURES OF ABSORBING GASES

Coupled radiation conduction heat transfer in non-gray participant media is present in many practical applications, such as thermal insulation at high and ambient temperatures. In glass window thermal insulation applications in hot climates, infrared absorbing gases appear as an alternative to improve their thermal performance. The thermal modeling of glass windows filled with absorbing gases is somewhat difficult due the spectral variations of the absorption coefficients of the gases. In this work, the CW model is used to treat the spectral properties of mixtures of absorbing gases and the radiative transport equation is solved using CW model and the discrete ordinates method. Due to the range of temperature variation, the mixture of gases is considered as homogeneous. The absorption coefficients were obtained from the database HITRAN. The energy equation in its two-dimensional form is solved by the finite volume technique. Three types of gas mixtures highly absorbing, medium and transparent are investigated, to determinate their effectiveness in reducing heat gain by internal ambient. Reflective glasses are also treated. The numerical method to solve radiative heat transport equation in gray and non-gray participant media was validated previously. The temperatures distributions in the gas and the glass domain are computed and the thermal performance of the gas mixtures is evaluated and discussed.

Estimation of a Nusselt Correlation for the Numerical Prediction of Frost Thickness on a Tube Banks of Triangular Arrangement

This paper presents a frost numerical model for predicting the frosting behavior in terms of the correlation of the heat transfer coefficient, Nusselt number. In this work the correlations of the Nusselt number from various references is examined and compared with experimental data. In this study, a mathematical model that can predict the behavior of the frost growth on a bank of triangularly arranged tubes is developed. Because of the complex heat transfer during frost formation on a tube bank, this subject is receiving much attention. Heat transfer in flow across a bank of tubes has particular importance in the design of heat exchangers. For this study various empirical relations are analyzed to determine the Nusselt number and compared with experimental data.

Estimation of a Nusselt Correlations for Numerical Prediction of Frost Thickness Growth over a Cold Cylinder

This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.