Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Mass Transfer

Modeling the Behavior of Frost Growth on Finned Tube Heat Exchanger

Zainab Hasoun H.Naji

Engineering and Technology Journal, 2014, Volume 32, Issue 1, Pages 215-229

A quasi-steady finite-volume model was developed for modeling a plain-finround-tube heat exchanger under frosted conditions. In this study, the heat and mass transfer characteristics of heat exchangers during frost formation process are analyzed numerically. Unsteady heat and mass transfer coefficients of the air side, heat transfer coefficient of the refrigerant side, frost layer thickness, the surface efficiency of the
heat exchanger and the mass flow rate of the frost accumulated on the heat exchanger surface are calculated. The total conductivity (UA) and pressure drop of the heat exchanger are reported for different air inlet and refrigerant temperature. Results have shown that frost layer growth is faster with lower inlet air temperature. Using the developed mathematical model, the algorithm and the computer code, which have
been experimentally validated, it is possible to predict a decrease of exchanged heat flux in the heat exchanger under frost growth conditions. The model could be further extended to simulate direct expansion evaporators with varying operating conditions and variable heat exchanger geometry.

Experimental and Theoretical Study of Vacuum Cooling System

Ahmed A. M. Saleh; Qussai J. Abdul Ghafour; Luay T. Al-Rawi

Engineering and Technology Journal, 2013, Volume 31, Issue 14, Pages 2619-2631

A vacuum cooling system and the parameters which affect on its performance
were studied experimentally and theoretically. For the experimental study the rig was
built up to studying the performance of cooling system in three cases. These cases
are: Cooling water by vacuum only, cooling water in conventional method, and
cooling water by vacuum with condensation.
The experimental results show that the addition of a condenser to the vacuum
cooling system leads to sweep of largest amount of generated vapor, also the time
consumed for the process was decreased. The times required for cooling 45 g from
water from temperature 29oC to 10oC for the three test cases were 4375 second, 3535
second and 263 second, respectively. Vacuum cooling with condenser is a fast
cooling of three systems test, which is about (13.7 times) faster than the system of
natural convection cooling. To work properly, the existence of condenser is very
important in vacuum cooling. It normally removes the large amount of water vapor
generation (about 94%).
For the theoretical study, a computer program was built up by employing the
governing equation to simulate the performance of the vacuum cooling system. The
theoretical results indicate an acceptable agreement with the experimental results.
Also, the results show that the decreasing of condenser temperature causes decreasing
of cooling time according to the equation (t = 0.2031Tcd4 - 2.8958 Tcd3 + 16.406
Tcd2 - 21.104 Tcd + 313.39), and increasing the evaporation surface area leads to
decreasing of cooling time according to the equation (t=1/ (0.0006*Area+0.0005)),
and the increasing of water mass causes in increasing of cooling time according to the
equation (t=7.2667*mass+14).

Modeling of Single Channel Monolithic Reactor with The Single pass Flow Operation System

Lange; Zaidoon; A Al-Najar; Jenan; Adel; A. Shuhaib

Engineering and Technology Journal, 2010, Volume 28, Issue 11, Pages 2221-2236

In the following sections, the recent published studies on modeling and
simulation of monolith reactors were reviewed. Mass transfer, and reaction kinetics
were achieved by establishing mass, energy and momentum balance equations. The
model equations were solved simultaneously. Such a model can be useful for studying
the impact of changes of superficial gas and liquid velocities on reaction rate within
the slug flow regime. The reaction system used is the hydrogenation α–methyl styrene
(AMS) to cumene over a palladium on γ–alumina catalyst, It is a well known
system used to understand three-phase reactor performance under mass transfer
limited condition by the gas mass transfer through the liquid film at the catalyst
surface to the active sites. The effects of superficial gas and liquid velocities on
reaction rate were studied with the range of 10 cm/s ≤ UL ≤ 30 cm/s, and 10 cm/s
≤ UG ≤ 30 cm/s. The flow pattern for all these range of velocities was in the Taylor
flow pattern.