Heat and mass transfer of ambient air flowing over cold fins

2016 ◽  
Author(s):  
Run Yan
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Ambient Air

Heat and Mass Transfer Analysis of a Pot-in-Pot Refrigerator Using Reynolds Flow Model

2016 ◽  
Vol 8 (3) ◽  
Author(s):  
Ramendra Pandey ◽  
Bala Pesala
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Ambient Temperature ◽  
Heat And Mass Transfer ◽  
Heat Load ◽  
Radiation Heat Transfer ◽  
Ambient Air ◽  
Total Heat ◽  
Maximum Efficiency ◽  
Radiation Heat

Heat and mass transfer analysis of evaporative cooling process in a pot-in-pot cooling system is done based on Reynolds flow hypotheses. The model proposed herein assumes that the heat transfer due to natural convection is coupled with an imaginary ambient air mass flow rate (gAo) which is an essential assumption in order to arrive at the solution for the rate of water evaporation. Effect of several parameters on the pot-in-pot system performance has been studied. The equations are iteratively solved and detailed results are presented to evaluate the cooling performance with respect to various parameters: ambient temperature, relative humidity (RH), pot height, pot radius, total heat load, thermal and hydraulic conductivity, and radiation heat transfer. It was found that pot height, pot radius, total heat load, and radiation heat transfer play a critical role in the performance of the system. The model predicts that at an ambient temperature of 50 °C and RH of 40%, the system achieves a maximum efficiency of 73.44% resulting in a temperature difference of nearly 20 °C. Similarly, for a temperature of 30 °C and RH of 80%, the system efficiency was minimum at 14.79%, thereby verifying the usual concept that the pot-in-pot system is best suited for hot and dry ambient conditions.

Geometrical Effects of Cabinet Size and Aspect Ratio on Heat and Mass Transfer During Open Door Conditions

2005 ◽  
Author(s):  
W. Terrell
Keyword(s):  
Mass Transfer ◽  
Aspect Ratio ◽  
Heat And Mass Transfer ◽  
Ambient Air ◽  
Open Door ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Mass Fluxes ◽  
Geometrical Effects ◽  
Aluminum Plates

The goal of this paper is to examine the effects of size and aspect ratio (H/L) of open cavities on heat and mass transfer during open door conditions of refrigerator cabinets. An experimental investigation was conducted using test cavities constructed from foam board insulation and interior covered with aluminum plates acting as calorimeters. Various size cavities with heights of 15.24 cm, 30.48 cm, and 45.72 cm along with aspect ratios of 0.5, 1.0, and 2.0 were tested. Cavities were heated to an initial temperature of 50°C, 60°C, 70°C, and 80°C before being exposed to the ambient air. In addition, tests were conducted in which the cavities were cooled before being exposed to the ambient. The relative humidity was varied from 60% to 75% and initial temperatures varied from 5°C, 1°C, and −5°C. The cavity mass fluxes were measured to validate the heat/mass transfer analogy for the tests. Experimental results were also presented for Rayleigh numbers from 5.88 × 106 to 2.21 × 108 with Nusselt numbers ranging from 15.48 to 53.51. The Nusselt numbers for cavities with an aspect ratio of one and two were in good agreement with each other. The Nusselt numbers for the cavity with an aspect ratio of 0.5 were slightly lower than the other cavities at given Rayleigh values.

Mathematical Modeling of a Thin Layer Solar Kiln

1990 ◽  
Vol 112 (3) ◽  
pp. 196-203 ◽  
Author(s):  
Moustafa M. Elsayed
Keyword(s):  
Mathematical Modeling ◽  
Mass Transfer ◽  
Thin Layer ◽  
Heat And Mass Transfer ◽  
Initial Conditions ◽  
Ambient Air ◽  
Glass Temperature ◽  
Humidity Ratio ◽  
Solar Kiln ◽  
Empirical Relations

Mathematical modeling of a thin layer solar kiln for drying of agricultural products is presented. Governing equations of the air temperature and air humidity ratio, material temperature and its moisture content, and the glass temperature are derived together with their initial conditions. Heat and mass transfer between the material and the air and the air and the glass cover are estimated using empirical relations for the coefficients of heat and mass transfer. The results of the calculations are analyzed to predict the effect of the following parameters on the transient performance of the kiln: (a) rate of absorbed solar energy in the kiln, (b) rate of air flow through the kiln, (c) volume of the dried material, (d) ambient temperature, and (e) humidity ratio of the ambient air.

Evaluation of Convective Heat and Mass Transfer in Open Sun and Green House Drying

2008 ◽  
Author(s):  
S. K. Shukla
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Ambient Air ◽  
Natural Mode ◽  
Transfer Coefficients ◽  
Drying Time ◽  
Sun Drying ◽  
Green House ◽  
Hourly Data

In this communication, a study on open sun and green house drying has been performed to evaluate the convective heat and mass transfer coefficients as a function of climatic parameters. The hourly data for the rate of moisture removal, crop temperature, relative humidity inside greenhouse and outside greenhouse and ambient air temperature for complete drying have been recorded. The experiments were done in the premises of Allahabad Agricultural Institute-Deemed University, after the crop-harvesting season from February 2006 to April 2006. Using these data, the value of convective heat and mass transfer in open sun drying (OSD) and green house sun drying (GHD) under natural and forced convection mode, have been calculated. Also the empirical relations of convective heat and mass transfer with drying time under natural and forced modes have been developed. On the basis of the present study, it is inferred that the value of convective heat and mass transfer is more in open sun drying than in the green house drying under natural convection mode. However its value increases in forced mode of greenhouse drying as compared to natural mode in the initial stage of drying.

Simultaneous Heat and Mass Transfer From a Two-Dimensional, Partially Liquid-Covered Surface

1991 ◽  
Vol 113 (4) ◽  
pp. 874-882 ◽  
Author(s):  
Y.-X. Tao ◽  
M. Kaviany
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Surface Temperature ◽  
Heat And Mass Transfer ◽  
Solid Surface ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Ambient Air ◽  
Simultaneous Heat

Simultaneous heat and mass transfer from partially liquid-covered surfaces is examined experimentally using a surface made of cylinders with the voids filled with liquid. The steady-state evaporation rate, surface temperature of the liquid and exposed solid, and location of meniscus are measured for various ambient air velocities and temperatures. Using these, we examine the effect of the extent to which the liquid covers the surface on the evaporation mass transfer rate resulting from the convective heat transfer from the ambient gas to this surface. The results show strong Bond and Reynolds number effects. For small Bond and Reynolds numbers, the presence of dry (exposed solid) surface does not influence the mass transfer rate. As the Bond or Reynolds number increases, a critical liquid coverage is found below which the mass transfer begins to decrease. Heat transfer from the exposed solid to the liquid is also examined using the measured surface temperature, a conduction model, and an estimate of the liquid and solid surface areas (using a static formation for the liquid meniscus). The results show that at the liquid surface an analogy between heat and mass transfer does not exist.

Variation of Heat and Mass Transfer Coefficients During Drying of Granular Beds

1990 ◽  
Vol 112 (3) ◽  
pp. 668-674 ◽  
Author(s):  
J. A. Rogers ◽  
M. Kaviany
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Evaporation Rate ◽  
Ambient Air ◽  
Spherical Particles ◽  
Convective Drying ◽  
Transfer Processes ◽  
Surface Areas ◽  
Mass Transfer Processes

During convective drying of initially fully saturated granular beds, the solid matrix is gradually exposed to the ambient air, resulting in heat transfer to both the liquid and solid. In an attempt to examine the heat and mass transfer processes occurring on the surface and to examine the influence of particle size and Bond number on the drying rate, experiments are performed in which granular beds constructed of spherical particles (which range from d = 0.2 mm to d = 25.4 mm) are convectively dried. For beds constructed of very small particles (d = 0.2 mm, Bo = 0.0035) the surface areas of the liquid and solid are difficult to estimate due to the random arrangement of the particles. The experimental results confirm existing knowledge that the evaporation rate is nearly constant during the funicular state of drying. For beds constructed of large particles (d = 25.4 mm, Bo = 21.7) an estimate of the surface areas of the liquid and solid reveals that the surface areas and the evaporation rate are highly dependent on surface saturation, contact angle, and surface tension. The results indicate that heat transfer from the solid to the liquid is significant and that the heat and mass transfer processes are not analogous.

Simultaneous Heat and Mass Transfer in Inclined Channel With Asymmetrical Conditions

2010 ◽  
Author(s):  
Othmane Oulaid ◽  
Brahim Benhamou ◽  
Nicolas Galanis
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Mass Fraction ◽  
Numerical Study ◽  
Water Film ◽  
Ambient Air ◽  
The Body ◽  
Parallel Plates ◽  
Inclined Channel ◽  
Simultaneous Heat

This work deals with a numerical study of simultaneous heat and mass transfer with phase change in an inclined channel formed by two parallel plates. The lower one is covered by a thin liquid water film and the upper one is considered impermeable. The plates are maintained at a constant temperature TW. Ambient air with uniform dry bulb temperature Tin and relative humidity φin enters the channel with a uniform upward velocity Uin. The liquid film is assumed to be extremely thin and its temperature is equal to the wall temperature. Steady state conditions are considered and the flow is assumed to be laminar. Viscous dissipation, radiation heat transfer and other secondary effects (pressure work, energy transport by the inter-diffusion of species, Dufour and Soret effects) are neglected. The physical properties are taken constant except for the density in the body forces, which is considered to be a linear function of temperature and mass fraction. Results show that buoyancy forces have an important effect on the hydrodynamic, thermal and mass fraction fields and this effect depends on the channel inclination. A flow reversal chart and analytical correlations for the corresponding critical values of the thermal and solutal Grashof numbers are presented for different channel inclinations.

Naturally Driven Flow, Heat and Mass Transfer in Soil Saturated With Light Fuel Vapor and Heated Asymmetrically

2001 ◽  
Author(s):  
A. A. Mohamad ◽  
G. A. Karim
Keyword(s):  
Mass Transfer ◽  
Porous Medium ◽  
Heat And Mass Transfer ◽  
Ambient Air ◽  
Fuel Vapor ◽  
Complex Flow ◽  
Flow Temperature ◽  
Fire Hazards ◽  
Thermally Driven ◽  
Flow Heat

Abstract Natural convection heat and mass transfer in a soil saturated with light fuel vapor and heated from one side is modeled and solved numerically. The system is simulated as a porous medium in a large horizontal enclosure exposed to ambient air from the top and saturated with a fuel vapor from the bottom. It is assumed that one of the vertical boundaries is heated to a constant temperature while the other vertical boundary kept cold at the ambient temperature. The problem is approximated as a two-dimensional, steady state, laminar flow with constant properties. The rate of outflow of species is calculated together with the rates of heat and mass transfer. Also, flow, temperature and species distributions are shown. For a thermally driven flow, i.e., N<1.0, the flow is driven into the cavity from a distance if the strength of the heat source and/or the permeability of the porous medium is high. For N>1.0, solutal plumes and complex flow pattern are formed as N increases. Such results will aid in providing guidelines for reducing the fire hazards from fuel wetted soils.

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