Abstract: Applying corona wind as a novel technique can lead
to a great level of heat and mass transfer augmentation by using very
small amount of energy. Enhancement of forced flow evaporation
rate by applying electric field (corona wind) has been experimentally
evaluated in this study. Corona wind produced by a fine wire
electrode which is charged with positive high DC voltage impinges
to water surface and leads to evaporation enhancement by disturbing
the saturated air layer over water surface. The study was focused on
the effect of corona wind velocity, electrode spacing and air flow
velocity on the level of evaporation enhancement. Two sets of
experiments, i.e. with and without electric field, have been
conducted. Data obtained from the first experiment were used as
reference for evaluation of evaporation enhancement at the presence
of electric field. Applied voltages ranged from corona threshold
voltage to spark over voltage at 1 kV increments. The results showed
that corona wind has great enhancement effect on water evaporation
rate, but its effectiveness gradually diminishes by increasing air flow
velocity. Maximum enhancements were 7.3 and 3.6 for air velocities
of 0.125 and 1.75 m/s, respectively.
Abstract: The quality of Ribbed Smoked Sheets
(RSS) primarily based on color, dryness, and the presence or
absence of fungus and bubbles. This quality is strongly
influenced by the drying and fumigation process namely
smoking process. Smoking that is held in high temperature
long time will result scorched dark brown sheets, whereas if
the temperature is too low or slow drying rate would resulted
in less mature sheets and growth of fungus. Therefore need to
find the time and temperature for optimum quality of sheets.
Enhance, unmonitored heat and mass transfer during smoking
process lead to high losses of energy balance. This research
aims to generate simple empirical mathematical model
describing the effect of smoking time and temperature to RSS
quality of color, water content, fungus and bubbles. The
second goal of study was to analyze energy balance during
smoking process. Experimental study was conducted by
measuring temperature, residence time and quality parameters
of 16 sheets sample in smoking rooms. Data for energy
consumption balance such as mass of fuel wood, mass of
sheets being smoked, construction temperature, ambient
temperature and relative humidity were taken directly along
the smoking process. It was found that mathematical model
correlating smoking temperature and time with color is Color
= -169 - 0.184 T4 - 0.193 T3 - 0.160 0.405 T1 + T2 + 0.388 t1
+3.11 t2 + 3.92t3 + 0.215 t4 with R square 50.8% and with
moisture is Moisture = -1.40-0.00123 T4 + 0.00032 T3 +
0.00260 T2 - 0.00292 T1 - 0.0105 t1 + 0.0290 t2 + 0.0452 t3
+ 0.00061 t4 with R square of 49.9%. Smoking room energy
analysis found useful energy was 27.8%. The energy stored in
the material construction 7.3%. Lost of energy in conversion
of wood combustion, ventilation and others were 16.6%. The
energy flowed out through the contact of material construction
with the ambient air was found to be the highest contribution
to energy losses, it reached 48.3%.
Abstract: Vacuum membrane distillation (VMD) process can be
used for water purification or the desalination of salt water. The
process simply consists of a flat sheet hydrophobic micro porous
PTFE membrane and diaphragm vacuum pump without a condenser
for the water recovery or trap. The feed was used aqueous NaCl
solution. The VMD experiments were performed to evaluate the heat
and mass transfer coefficient of the boundary layer in a membrane
module. The only operating parameters are feed inlet temperature,
and feed flow rate were investigated. The permeate flux was strongly
affected by the feed inlet temperature, feed flow rate, and boundary
layer heat transfer coefficient. Since lowering the temperature
polarization coefficient is essential enhance the process performance
considerable and maximizing the heat transfer coefficient for
maximizes the mass flux of distillate water. In this paper, the results
of VMD experiments are used to measure the boundary layer heat
transfer coefficient, and the experimental results are used to reevaluate
the empirical constants in the Dittus- Boelter equation.
Abstract: There have been widespread applications of fluidized beds in industries which are related to the combination of gas-solid particles during the last decade. For instance, in order to crack the catalyses in petrochemical industries or as a drier in food industries. High capacity of fluidized bed in heat and mass transfer has made this device very popular. In order to achieve a higher efficiency of fluidized beds, a particular attention has been paid to beds with pulsating air flow. In this paper, a fluidized bed device with pulsating flow has been designed and constructed. Size of particles have been used during the test are in the range of 40 to 100μm. The purpose of this experimental test is to investigate the air flow regime, observe the particles- movement and measure the pressure loss along the bed. The effects of pulsation can be evaluated by comparing the results for both continuous and pulsating flow. Results of both situations are compared for various gas speeds. Moreover the above experiment is numerically simulated by using Fluent software and its numerical results are compared with the experimental results.
Abstract: A steady two-phase flow model has been developed to simulate the drying process of porous particle in a pneumatic conveying dryer. The model takes into account the momentum, heat and mass transfer between the continuous phase and the dispersed phase. A single particle model was employed to calculate the evaporation rate. In this model the pore structure is simplified to allow the dominant evaporation mechanism to be readily identified at all points within the duct. The predominant mechanism at any time depends upon the pressure, temperature and the diameter of pore from which evaporating is occurring. The model was validated against experimental studies of pneumatic transport at low and high speeds as well as pneumatic drying. The effects of operating conditions on the dryer parameters are studied numerically. The present results show that the drying rate is enhanced as the inlet gas temperature and the gas flow rate increase and as the solid mass flow rate deceases. The present results also demonstrate the necessity of measuring the inlet gas velocity or the solid concentration in any experimental analysis.
Abstract: Although water only takes a little percentage in the total mass of soil, it indeed plays an important role to the strength of structure. Moisture transfer can be carried out by many different mechanisms which may involve heat and mass transfer, thermodynamic phase change, and the interplay of various forces such as viscous, buoyancy, and capillary forces. The continuum models are not well suited for describing those phenomena in which the connectivity of the pore space or the fracture network, or that of a fluid phase, plays a major role. However, Lattice Boltzmann methods (LBMs) are especially well suited to simulate flows around complex geometries. Lattice Boltzmann methods were initially invented for solving fluid flows. Recently, fluid with multicomponent and phase change is also included in the equations. By comparing the numerical result with experimental result, the Lattice Boltzmann methods with phase change will be optimized.
Abstract: In this study, an analysis has been performed for
heat and mass transfer of a steady laminar boundary-layer flow
of a viscous flow past a nonlinearly stretching sheet.
Parameters n, Ec, k0, Sc represent the dominance of the
nonlinearly effect, viscous effect, radiation effect and mass
transfer effect which have presented in governing equations,
respectively. The similarity transformation and the
finite-difference method have been used to analyze the present
problem.
Abstract: Double-diffusive natural convection in an open top
square cavity and heated from the side is studied numerically.
Constant temperatures and concentration are imposed along the right
and left walls while the heat balance at the surface is assumed to obey
Newton-s law of cooling. The finite difference method is used to
solve the dimensionless governing equations. The numerical results
are reported for the effect of Marangoni number, Biot number and
Prandtl number on the contours of streamlines, temperature and
concentration. The predicted results for the average Nusselt number
and Sherwood number are presented for various parametric
conditions. The parameters involved are as follows; the thermal
Marangoni number, 0 ≤ MaT ≤1000 , the solutal Marangoni number,
0 1000 c ≤ Ma ≤ , the Biot number, 0 ≤ Bi ≤ 6 , Grashof number,
5 Gr = 10 and aspect ratio 1. The study focused on both flows; thermal
dominated, N = 0.8 , and compositional dominated, N = 1.3 .
Abstract: Double-diffusive steady convection in a partially
porous cavity with partially permeable walls and under the combined
buoyancy effects of thermal and mass diffusion was analysed
numerically using finite volume method.
The top wall is well insulated and impermeable while the bottom
surface is partially well insulated and impermeable and partially
submitted to constant temperature T1 and concentration C1. Constant
equal temperature T2 and concentration C2 are imposed along the
vertical surfaces of the enclosure. Mass suction/injection and
injection/suction are respectively considered at the bottom of the
porous centred partition and at one of the vertical walls.
Heat and mass transfer characteristics as streamlines and average
Nusselt numbers and Sherwood numbers were discussed for different
values of buoyancy ratio, Rayleigh number, and injection/suction
coefficient.
It is especially noted that increasing the injection factor
disadvantages the exchanges in the case of the injection while the
transfer is augmented in case of suction. On the other hand, a critical
value of the buoyancy ratio was highlighted for which heat and mass
transfers are minimized.
Abstract: A rigorous two-dimensional model is developed for simulating the operation of a less-investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non-availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. Due to severe operating conditions, in all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer.
Abstract: The hydromagnetic flow of a Maxwell fluid past a vertical stretching sheet with thermophoresis is considered. The impact of chemical reaction species to the flow is analyzed for the first time by using the homotopy analysis method (HAM). The h-curves for the flow boundary layer equations are presented graphically. Several values of wall skin friction, heat and mass transfer are obtained and discussed.
Abstract: In the present work an investigation of the effects of
the air frontal velocity, relative humidity and dry air temperature on
the heat transfer characteristics of plain finned tube evaporator has
been conducted. Using an appropriate correlation for the air side heat
transfer coefficient the temperature distribution along the fin surface
was calculated using a dimensionless temperature distribution. For a
constant relative humidity and bulb temperature, it is found that the
temperature distribution decreases with increasing air frontal
velocity. Apparently, it is attributed to the condensate water film
flowing over the fin surface. When dry air temperature and face
velocity are being kept constant, the temperature distribution
decreases with the increase of inlet relative humidity. An increase in
the inlet relative humidity is accompanied by a higher amount of
moisture on the fin surface. This results in a higher amount of latent
heat transfer which involves higher fin surface temperature. For the
influence of dry air temperature, the results here show an increase in
the dimensionless temperature parameter with a decrease in bulb
temperature. Increasing bulb temperature leads to higher amount of
sensible and latent heat transfer when other conditions remain
constant.
Abstract: Majority of pepper farmers in Malaysia are using the
open-sun method for drying the pepper berries. This method is time
consuming and exposed the berries to rain and contamination. A
maintenance-friendly and properly enclosed dryer is therefore
desired. A dryer design with a solar collector and a chimney was
studied and adapted to suit the needs of small-scale pepper farmers in
Malaysia. The dryer will provide an environment with an optimum
operating temperature meant for drying pepper berries. The dryer
model was evaluated by using commercially available computational
fluid dynamic (CFD) software in order to understand the heat and
mass transfer inside the dryer. Natural convection was the only mode
of heat transportation considered in this study as in accordance to the
idea of having a simple and maintenance-friendly design. To
accommodate the effect of low buoyancy found in natural convection
driers, a biomass burner was integrated into the solar dryer design.