This paper presents a three-dimensional numerical analysis to study the laminar forced convection heat transfer and flow characteristics of AL2O3-water Nano fluid with Solid particles less than 100 nm through a tube with 1m Length and 25 mm inner diameter and 30mm outer diameter contains circular fins with 30mm inner diameter and 50mm outer diameter with thickness of 2mm , investigated numerically by using finite volume method, models using ANSYS 14.5 Based on the single-phase approach, The flow of fluid is assumed to be incompressible, steady and laminar with various thermo physical properties according to volume concentration of Nano particles The Navies Stokes equations along with the energy equation have been solved by using SIMPLE algorithm Technique. The effects of different parameters such as nanoparticle volume concentration (1%, 3% and 5%), and Reynolds number are varied from (500 - 2100) for various axial locations of tube with AL2O3-water fluids and the effect of different values of velocity at the tube inlet will be studied during this paper. Where the results showed that the coefficient of heat transfer increases when the concentration of Nano fluid increase. The following symbols are used generally throughout the text. Others are defined as and when used.
The following symbols are used generally throughout the text. Others are defined as and when used.
Cp Specific heat at constant pressure J/kg.KCp Specific heat at constant pressure J/kg.K
K Thermal conductivity W/m.K
Nu Nusselt number -
P Pressure Pa
Re Reynolds number -
T Temperature K
V Velocity vector m/sV Velocity vector m/s
X Distance along axis m X Distance along axis m
α Thermal diffusivity m2/s
ϕ Volume fraction -
ρ Density kg/m3
µ Molecular dynamic viscosity N.s/m2
bf Base fluid
f Fluid
nf Nanofluid
s Solid of particle
Heat exchangers are usually used devices that transfer heat from one fluid (gas or liquid) to another without those two fluids mixing. Heat transfer enhancement is the process of enhancing the performance of a heat transfer unit. It is used in heating , air conditioning systems in a household, chemical processing, power production in large plants, There are different methods used to increase the heat transfer rate in compact heat exchangers One of these methods is the use of Extended surfaces “finned tube” Achieving higher heat transfer rate by increasing heat transfer area and increasing flow mixing in the boundary layer is the main goal for these methods and The other method is to increase the thermal conductivity of fluid by used Nano fluid. Proposed the use of Nano fluids which are having extremely impressive and attractive thermal properties [
This study aims to enhance the heat transfer characteristics for heat exchanger with use of Nano fluid and finned tube.
Mathematical Model and numerical analysis:
The basic flow configuration, under study, is shown in Fig. 1. A three dimensional pipe have 1 m length and 25 mm inner diameter and 30mm outer diameter contains circular fins with 30mm inner diameter and 50mm outer diameter and thickness of fins is 2mm and The distance between each fin and the second fin is 48mm was spotted in the simulation. The continuity, momentum and energy equations for a three dimensional incompressible laminar flow has been solved using appropriate boundary conditions by mean computational fluid dynamics technique. Following assumptions have been made: three-dimensional problem, there is no viscous dissipation, no gravity acts, the fluid properties are various according to volume concentration of Nano particles and radiation heat exchange was assumed negligible.
The three-dimensional governing equations for the conservation of mass, momentum and energy and for the single phase are solved using a finite volume approach. The spatial discretization is achieved through a second-order upwind scheme. The SIMPLEC algorithm is selected to overcome the pressure-velocity coupling. All calculations are steady state and three-dimensional.
At steady state conditions using above assumption, the governing equations as given below [
The thermal Conductivity of Nano fluid is determined by the following equation:
Where:
F: Fluid
nf :Nanofluid
s: Solid of particle
Property | Fluid Phase ( |
Nanoparticle (AL2O3) |
ρ (kg/ QUOTE _x0001_ | 998.2 |
3880 |
Cp (J/kg K) | 4182 |
729 |
k (W/m K | 0.6 |
42 |
µ(kg/m.s) | 0.001003 |
___ |
Nano fluid |
| | =1 |
ρ (kg/ QUOTE _x0001_ | 1142.2 | 1084.6 | 1027 |
Cp (J/kg K) | 3595 | 3811 | 4051 |
k (W/m K | 0.69 | 0.65 | 0.61 |
µ(kg/m.s) | 0.001140 | 0.001082 | 0.001028 |
The boundary conditions are specified as follows:
· At the tube inlet: u(y) = 0.12 m/s and T = Ti =350 ºK
· At the tube outlet: pressure outlet boundary P = 0
· At the wall: convection heat transfer on the extended surface with heat transfer coefficient =20 to the environment, T=300K
Through numerical analysis by ANSYS 14.5 on two types of tubes, one of which is smooth tube and the other is finned tube and two types of fluid one of which is pure water and the other is Nano fluid and for the purpose of comparing them, the results showed that The presence of nanoparticles with fluid at work occupies the interstellar distances between the working fluid molecules and will therefore increase the heat transfer as shown in table (
Type of tube | Number of node | Number of element | Velocity value m/s | Type of fluid | Volume concentration | Heat transfer coefficient |
Smooth tube | 26029 | 18957 | 0.08 | Pure water | 0% | 148 |
Nano fluid | 1% | 151 | ||||
3% | 156 | |||||
5% | 161 | |||||
0.12 | Pure water | 0% | 171 | |||
Nano fluid | 1% | 173 | ||||
3% | 180 | |||||
5% | 186 | |||||
Finned tube | 28592 | 53714 | 0.08 | Pure water | 0% | 149 |
Nano fluid | 1% | 151.5 | ||||
3% | 157 | |||||
5% | 162.5 | |||||
0.12 | Pure water | 0% | 172 | |||
Nano fluid | 1% | 174 | ||||
3% | 181 | |||||
5% | 187 |
As the results show, heat transfer through finned tube is better than heat transfer through tubes without fins, as well as the use of nano fluid is better than using pure water.