Investigation of Heat Transfer Characteristics During Flow Condensation
of Next Generation Refrigerants With Al2O3 Nanoparticle Inside
Horizontal Tube With Micro-Fin
A thesis report submitted for the partial fulfilment of the requirement for the course
ME 4000 of Bachelor of Science Degree on Mechanical Engineering.
Supervised By Submitted By
Dr. Dipayan Mondal Zahidul Islam
Professor Roll: 1905114
Department of Mechanical Engineering, Department of Mechanical Engineering,
KUET KUET
Department of Mechanical Engineering
Khulna University of Engineering & Technology
Khulna 9203, Bangladesh
TABLE OF CONTENTS
CHAPTER I 1.1 Introduction 1
1.2 Objectives 2
CHAPTER II 2.1 Literature Review 3
2.2 Research Gap 6
CHAPTER III 3.0 Methodology 7
3.1 Geometry & Modeling 7
3.2 Governing Equations 8
3.3 Boundary Conditions 9
3.4 Work Plan 10
CHAPTER IV 4.1 References 11
CHAPTER I
1.1 INTRODUCTION
The condensers have a very important role to play in different industries such as
refrigeration, air-conditioning, power plants etc. Optimization of the condensers is very
important to increase the overall efficiency of the system [2]. Micro-fin tubes are being
widely studied for their vast industrial applications including refrigeration and air-
conditioning systems, condensers etc. Micro-fin tubes can enhance heat transfer
characteristics due to their large heat transfer surface area, turbulence induced in the flow
and the liquid drainage due to surface tension in two-phase applications. Compared to the
heat transfer enhancement, the pressure drop is relatively low and for this reason micro-
fins are being used nowadays in lot of applications [3].
Besides, the new environmental laws are calling for the use of refrigerants with lower value
of Global Warming Potential (GWP). Hydrofluorocarbons (HFC) have high values of GWP
although they are being widely used in various HVAC and refrigeration systems. For the
new systems being developed, they cannot be used as they have high environmental impact.
For this reason, new pure refrigerants or refrigerant mixtures with lower values of GWP
are in great demand to accomplish the newly developed rules [6]. The newly developed
refrigerants should have similar properties to those of the actual implemented refrigerants
while being safe for the environment. For example, R134A is one of the most common
refrigerants implemented in a wide range of refrigeration and air conditioning systems,
such as domestic and industrial air conditioning, automobile air conditioning etc. In these
regard, R513A can be a direct substitute of the R134A which is an azeotropic mixture of
R1234yf and R134a (56% and 44%, in mass, respectively) [6]. It has a lower value of GWP
about 630. Some more examples of next generation refrigerants are R450A which is a
mixture of R134a, R1234yf and R123ze (42%, 18% and 40% by mass respectively).
R1234yf, L40, Dr-5 and R444B refrigerants can be good alternatives to R134A, R404A,
R401A and R22 respectively [8].
Monetary savings form energy efficient systems and as a contribution to save environment
are motivational factors for new researchers to use different technologies & advancements
in science to make their systems and equipment more energy efficient. Nano particles are
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one of the ways to enhance heat transfer characteristics of a refrigeration system although
studies are still going on to make the Nano-particle usable for practical applications.
Nanofluid is a colloidal suspension of nanoparticle in base fluids, showing enhanced
thermal properties. Nanofluids are prepared by dispersing nanoparticles in base fluid.
Dispersion stability affects thermo-physical properties of nanofluids. Dispersions can
remain stable for some amount of time without coagulation, clustering & deposition. Many
researchers have done the experiments within this stability time & produced the results. In
real life, the refrigeration system can be continuously operated or intermittently operated,
the pressure & temperatures of refrigerant change as it passes through different components
in system. Therefore, if Nano-refrigerant is to be used in actual refrigeration system then it
needs to be stable continuously & in all practical pressure temperature conditions. Usage
of nanofluid in some applications show high improvement of heat transfer rate and other
having minimal or negative effects [7].
1.2 OBJECTIVES:
The main purpose of this thesis is to investigate the heat transfer characteristics during the
flow condensation of next generation refrigerant with Nano-particle inside a horizontal tube
having micro fins. The specific objectives are:
1. To investigate the heat transfer rate at different location of the condenser tube and find
the relation between heat transfer rate and mas flux, vapor quality.
2. To analyze the frictional pressure drop in the condenser tube.
3. To optimize the shape and dimensions of the micro-fins in order to improve heat
transfer rate.
4. To identify the factors that affect the flow and heat transfer rate of new generation
refrigerant with nano-particle.
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CHAPTER II
2.1 LITERATURE REVIEW
Man-Hoe Kim and Joeng-Seob Shin in their paper titled “Condensation heat transfer of
R22 and R410A in horizontal smooth and microfin tubes “ did an experimental investigation
of condensation heat transfer rate in 9.52 mm O.D. horizontal copper tubes with R22 and
R401A refrigerants. The test section length was 0.92m and was cooled using the heat transfer
fluid (cold water) circulated in surrounding annulus. During the experiment, a constant heat
flux of 11.0 KW/m2 was maintained and the quality of the refrigerant was varied from 0.9 to
0.1. The local and average condensation coefficients for seven microfin tubes were compared
to a smooth tube. It was found that the average condensation coefficients of R22A and R410A
for the microfin tubes were 1.7-3.19 and 1.7-2.94 times larger than those in smooth tube [1].
M.A. Akhavan-Behabadi, Ravi Kumar and S.G. Mohseni in their paper titled “Condensation
heat transfer of R-134a inside a microfin tube with different tube inclinations” carried out
condensation heat transfer analysis at different angles of a microfin tube with respect to the
horizontal x axis. The data was recorded for seven different tube inclinations α in a range of -
90 to +90 degree angle. The mass velocities were 54, 81 and 107 kg/m2 s for each inclination
angle during condensation of R-134a vapor. It was found from the experiment that the
inclination angle α affects the condensation heat transfer coefficient greatly. The maximum
heat transfer coefficient was found at an inclination angle of α = +30o. At low vapor quality
and mass velocity the effect of inclination is more significant. [2]
Jingzhi Zhanga, Wei Li, and W. J. Minkowycz have done numerical simulation of R410A
condensation in horizontal microfin tubes with microfin tubes having 00 and 180 helical angles.
It was found from their simulation that the numerical and experimental data fit well with the
empirical correlations. In their simulation they have considered a computational domain of
length 43.9 mm for the two microfin tubes. One having 00 and another 180 helical angle. The
rest of the dimensions for both the tubes were the same. The simulation was accomplished
3
using the volume of fluid (VOF) method in ANSYS Fluent CFD software and a user defined
function was applied to consider the condensation heat and mass transfer. VOF model was used
to capture the liquid-vapor interface in this simulation. For phase change, the mass transfer
model developed by Lee [9] was used which assumes a constant temperature Tsat at the liquid
vapor interface. When the phase change takes place, a mass transfer rate from one phase to
another is defined using this model. For turbulence model, the SST k-Ꞷ turbulent model
propose by Menter [10] was used for both liquid and vapor. It was found from the experimental
results that the local heat transfer coefficients increase with the increasing mass flux, vapor
quality, and helical angle. The heat transfer enhancement due to the microfin tubes is found to
be more at higher mass flux and vapor quality. Swirling flows in the liquid phase were observed
at 18o helical angle [3].
Anil Kumar, Ravi Kumar, and Arup Kumar Das in their paper titled “Comparative thermo-
fluidic analysis of condensation characteristics inside smooth and enhanced tubes” have done
three dimensional simulation to investigate the thermo-fluidic characteristics during the flow
condensation or R134a refrigerant inside smooth and enhanced tubes. Their computational
domain includes a perfectly smooth surface tube, four different surface structures
(hemispherical ribs, conical fins, axial and circumferential protrusions on the inner and outer
surface of the tube. The simulation was carried out for the mass flux ranging from 100 to 200
kgm-2 s-1 and inlet vapor quality of 0.8 at a phase change temperature of 40oC. They have
used a cylinder with diameter 8.92 mm and length of 60mm for the simulation. For meshing
they have used the ICEM CFD software and non-uniform structured mesh was used. Finite
volume based CFD software OpenFOAM, was used to carry out the numerical calculations
and the phaseChangeHeatFoam solver developed by Samkhaniani and Ansari [11-12] was
used and a single set of governing equations maintaining mass, momentum and energy
conservation are solved and the interface between the phases was captured using the volume
of fluid (VOF) method. From the experiment it was found that the hemispherical rib structure
showed the highest heat transfer coefficient among all the tested structures and the tube with
circumferential protrusions resulted in the maximum pressure drop during the flow
condensation. Overall the benefit of heat transfer appeared to be more than the pressure drop
penalty for tubes with conical find and axial tunnels [4].
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R. Rabiee, M. Désilets, P. Proulx, M. Ariana and M. Julien in their paper has worked in the
condensation heat transfer inside a horizontal smooth tube. They developed a mathematical
model with the open source software OpenFOAM to simulate the heat transfer process during
the flow condensation inside a smooth horizontal tube. They modified the already built model
in OpenFOAM 4.0 to take into account the specific nature of flow condensation. A new
coefficient was used called the “condensation area fraction” and a new library was added to the
solver to simulate the wall heat flux during the flow condensation. Finally a new relationship
for the prediction of total heat transfer coefficient of flow condensation was proposed from this
research [5].
Atilla Gencer Devecioğlua and Vedat Oruça in their paper titled “Characteristics of Some New
Generation Refrigerants with Low GWP” did a study and comparison about some
characteristics of new generation low GWP value gases most of which were at the trial stage.
Hydrofluoro-olefin (HFO) based mixed gases were investigated having a low GWP value as
alternatives to four different refrigerants commonly used in refrigeration and air conditioning
equipments. In the study it was found that R450A, R513A, R1234yf and R1234ze (E) gases
were used instead of R134a, DR-33, L40, DR-7 and R448A was used instead of R404A, DR-
5 and R447A was used instead of R410A. Later the refrigerants were compared within their
own groups. It was found from the study that R1234yf, L40, DR-5 and R444B refrigerants can
be good alternatives to R134a, R404A, R410A and R22, respectively [6].
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2.2 RESEARCH GAP
From the literature review it is found that a lot of research work has been done experimentally
on the condensation heat transfer characteristics for smooth and tubes with microfin. But,
numerical research in this field is very limited and so there is a scope to do numerical research
in this field. Moreover, use of nanoparticles with refrigerant is still a research topic and has not
been applied practically in broad scale. So, numerical analysis is the only way to study the
characteristic of nano particle refrigerant. Enhanced tube can help enhance the heat transfer
rate along with nano particles and can induce more turbulence in the flow at higher mass flux.
So, different structure and shape of the enhanced geometry can be analyzed to find the suitable
geometry.
For the above reasons I chose this topic as my research work as it can play a vital role in
developing the future environment friendly and efficient heat exchanger systems.
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CHAPTER III
3.0 METHODOLOGY
3.1 GEOMETRY & MODELING
At first a three dimensional horizontal tube with conical inward finned will be developed by
using the ANSYS Fluent simulation software. The dimensions of the enhanced tube are
mentioned in table 1.
Parameters Value
Inner tube diameter(mm) 8.92
Structure height(mm) 0.5
Longitudinal Pitch(mm) 2.5
Circumferential Pitch(mm) 2.5
Table 1: Dimensions of the enhanced tube
A figure of the model taken from the simulation of Anil Kumar, Ravi Kumar, and Arup
Kumar Das [4] which is similar to the model which will be used for the analysis is given in
figure 3.1.
Fig 3.1 A cross sectional view of the test model. [4]
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3.2 GOVERNING EQUATIONS
The phaseChangeHeatFoam solver added in the OpenFOAM library will be used for simulation
of the condensation inside the tube. Both vapor and liquid phases are assumed incompressible
and immiscible. The volume of fluid method uses a discontinuous scalar function to resolve
the interface among two phases in fixed grids. This scalar function is the ratio of one fluid
volume to the volume of cell, and it is defined as
The thermos physical properties of two-phase flow such as viscosity (µ), density (ρ) and
thermal conductivity (k) are defined as
Here the subscripts L and G denote liquid and vapor phases respectively. The global mass
conservation equation can be expressed in terms of density (ρ) as
Here U is the local velocity vector and t is the time. Using Eq. (2) ρ can be expressed in terms
of αL and the same can be written as
The global continuity equation can be expressed in terms of αL by substituting in equation (4)
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and equation (3). The modified equation is
Therefore the transport equation as a function of phase fraction can be written as ``
⃗ = 0) , but
The continuity equation for the adiabatic two-phase flows can be written as (𝛻 ⋅ 𝑈
during phase change phenomenon, separate local continuity equations for both liquid and
vapor will be important. The same are shown in the below equations
3.3 Boundary Conditions:
The boundary conditions are presented in the table below:
Description Condition
Volume Fraction : αL = 0 ; vapor Internal field αL = 0 (core), 1 (near the wall)
Inlet αL = 0 (core) 1 (near wall for annular
zone)
Temperature Internal field : saturation temperature
Inlet : saturation temperature
Outlet : saturation temperature
Wall : subcooled temperature
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Velocity Internal field: fixed based on mass flux
Inlet: fixed based on mass flux
Wall: zero (no slip and no penetration)
Table 3.2 Boundary Conditions for the simulation
3.4 Work Plan
The work plan is provided with the help of a chart below:
Week 1 2 3 4 5 6 7 8 9 10 11
Methodology
Model
Drawing &
Meshing
Numerical
Validation of
Model
Data
Collection
Result
Analysis
Report Writing
Submission &
Defense
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CHAPTER IV
4.1 References:
[1] Kim MH, Shin JS. Condensation heat transfer of R22 and R410A in horizontal smooth and
microfin tubes. International journal of refrigeration. 2005 Sep 1;28(6):949-57.
[2] Akhavan-Behabadi MA, Kumar R, Mohseni SG. Condensation heat transfer of R-134a inside a
microfin tube with different tube inclinations. International Journal of Heat and Mass Transfer. 2007
Nov 1;50(23-24):4864-71.
[3] Zhang J, Li W, Minkowycz WJ. Numerical simulation of R410A condensation in horizontal microfin
tubes. Numerical Heat Transfer, Part A: Applications. 2017 Feb 16;71(4):361-76.
[4] Kumar A, Kumar R, Das AK. Comparative thermo-fluidic analysis of condensation characteristics
inside smooth and enhanced tubes. Physics of Fluids. 2024 Apr 1;36(4).
[5] Rabiee R, Désilets M, Proulx P, Ariana M, Julien M. Determination of condensation heat transfer
inside a horizontal smooth tube. International Journal of Heat and Mass Transfer. 2018 Sep
1;124:816-28.
[6] Diani A, Brunello P, Rossetto L. R513A condensation heat transfer inside tubes: Microfin tube vs.
smooth tube. International Journal of Heat and Mass Transfer. 2020 May 1;152:119472.
[7] Majgaonkar A. Use of nanoparticles in refrigeration systems: a literature review paper.
[8] Devecioğlu AG, Oruç V. Characteristics of some new generation refrigerants with low GWP. Energy
Procedia. 2015 Aug 1;75:1452-7.
[9] W. Lee, A Pressure Iteration Scheme for Two-Phase Flow Modeling, Hemisphere, Washington, DC,
1980.
[10] F. R. Menter, 2-Equation Eddy-Viscosity Turbulence Models for Engineering Applications, AIAA J., vol.
32, pp. 1598–1605, 1994.
[11] N. Samkhaniani and M. R. Ansari, “Numerical simulation of superheated vapor bubble rising in
stagnant liquid,” Heat Mass Transfer 53(9), 2885–2899 (2017).
[12] N. Samkhaniani and M. R. Ansari, “The evaluation of the diffuse interface method for phase change
simulations using OpenFOAM,” Heat Transfer 46(8), 1173–1203 (2017).
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