Investigation of heat transfer enhancement for a model 21 Feb 2021.pptx
Investigation of heat transfer
enhancement for a model of
external receiver solar power plant
Mahmoud Sh. Mahmoud
M.Sc. Mech. Eng. / Thermal power (2001)
Asst. Prof. Dr. Ahmed F. Khudheyer
Asst. Prof. Dr. Qusai Jihad Abdul Gafor
Seeking to obtain energy with minimal expenses and
pollution is still a challenge that is being worked on.
Energy production especially in developing countries
like Iraq often falls short of energy requirements
which results in frequent power failure. The grow in
energy consumption is continual, on the other hand
fossil fuel is limited, so it is essential to consider other
energy sources like renewable energy especially solar
power to keep up and try to meet the energy demands
in the future. The present work is conducted by
building up a (CSP) model with a novel receiver
design to enhance the thermal performance of it.
Fig 1: shows that Iraq position in area of over than 3000
hours of bright sunshine yearly .
The renewable energy sources are available and used in many applications
now a days. One of these applications is the power generation. The solar energy is the
most available renewable energy sources used in the world. There are two familiar
ways to convert the solar energy to electricity, direct and indirect. The direct way is
presented by using photovoltaic cells (PV). The indirect way is presented by using the
solar energy as a heating source for the working fluid that is used in power plant. One
of the most common ways to heat the working fluid by solar energy is to concentrate
solar energy. there are many concentration types, like Fresnel reflectors, trough type,
compound parabolic collectors (CPC), and heliostat concentrators.
Concentrated solar power (CSP) thermal systems using heliostats for power
generation shows better capability for improvement in performance as well as
reducing the cost compared to other (CSP) systems.
Aims and Novelty for the present work
The main objectives are to increase the (SPTS) performance:
Increase reflected sun rays from the heliostats toward the solar receiver.
Enhance solar receiver thermal efficiency.
The originality of the present work could be summarized as:
Individual automated dual axis tracking system design to enhance solar plant
A novel solar receiver design consisting of staggered configuration pipes is used to
investigate its effect on the receiver thermal efficiency.
Central tower solar power system is considered for the present study. The main losses
in the traditional solar receiver are due to the presence of gaps between receiver pipes
that lead to losing some of the incident sun rays. Seeking for improving and achieving
the thermal efficiency of the system, sources of losses must be defined and minimized.
Fig 2: (a) Traditional
solar receiver. Fig 2: ( (b) novel
A review of previous researchers and studies investigated the main effecting
parameters on the central tower solar power system performance are shown in the
J. Yellowhair et al. (2015), Testing and optical modeling of novel concentrating solar receiver
geometries to increase light trapping and effective solar absorptance.
N. H. Abu-Hamdeh and K. A. Alnefaie (2016), Design considerations and construction of an
experimental prototype of concentrating solar power tower system in Saudi Arabia.
M. Hazmoune et. al (2016), 3D Simulation Study of a Receiver on a Solar Power Tower.
S. S. Alrwashdeh (2018), The effect of solar tower height on its energy output at Ma’an-
A. K. Khlief et. al (2018), Design a New Receiver for the Central Tower of Solar Energy.
P. Xu et. al (2014), Numerical simulation and experimental study of the tube receiver’s
performance of solar thermal power tower.
D. Potter et. al (2015), Optimized Design of a 1 MWt Liquid Sodium Central Receiver System.
N. Karwa et. al (2016), Receiver shape optimization for maximizing medium temperature CPC
A. Piña-Ortiz (2018), Experimental analysis of a flat plate receiver for measurement of low
thermal power of a central tower solar system.
A. Hall et. al (2012), Solar selective coatings for concentrating.
A. H. Alami et. al (2018), Enhancement of spectral absorption of solar thermal collectors by bulk
graphene addition via high-pressure graphite blasting.
S. A. Sakhaei and M. S. Valipour (2019), Investigation on the effect of different coated absorber
plates on the thermal efficiency of the flat-plate solar
M. M. Arturo and G. P. Alejandro (2010), High-precision solar tracking system.
K. K. Chong and M. H. Tan (2011), Range of motion study for two different sun-tracking
methods in the application of heliostat field.
K. Malan (2014), A heliostat field control system.
S. patil Pratik Pawar et. al (2018), Solar Tracking System Using Arduino.
W. M. Hamanah et. al (2020), Heliostat dual-axis sun tracking system: A case study in KSA.
C. J. Noone et. al (2012), A new computationally efficient model and biomimetic layout.
K. Lee and I. Lee et. al (2019), Optimization of a heliostat field site in central receiver systems
based on analysis of site slope effect.
From the above mentioned studies, it is obvious that there are many studies
that deals with solar central tower.
The present work aims to:
• Fabricate new staggered configuration for the absorber heat exchanger and,
• Design a new dual axes tracking system.
Present Study scope
inc. = IN × AH × NH × ηcos ⋅ ηsha ⋅ ηblo ⋅ ηatt ⋅ ηspil ⋅ ρref
gain = 𝑞
inc. − 𝑞
The governing equations are solved numerically with computational
fluid dynamics (CFD) using ANSYS FLUENT 2019R1 commercial
package, according to the mentioned assumptions and boundary
conditions for the present study.
Higher-order differential governing equations that were
analyzed using the SIMPLE algorithm with (10-15) convergence.
Upwind scheme was used in this model. The initialization was
selected as a hybrid for twenty iterations to save the
initialization values used for running.
ANSYS code validation
For justifying the ANSYSFLUENT 2019R1 commercial package performance, a validation process was carried
out for two different cases
Fig 3: Code validation
Series Parallel Staggered
Solar Tower height
Design considerations conclusions
From analysis of the design consideration, the present study description had been recognized. The outcomes of the
design considerations are listed below:
1. Staggered pipes configuration for the receiver, having totally (54) pipe divided into two rows with dimensions
2. Copper is selected to be the pipe material with (9.5 mm) inner diameter and (0.5 mm) thickness.
3. Heat transfer working fluid is selected to be (water) with variation in thermo-physical properties with bulk
4. Central tower high is (4.5 m).
5. Heliostat reflecting material is glass (4mm) thickness, with dimensions (80*80) cm equipped with automated dual
axis tracking system.
6. Heliostat horizontal radius is (7 m) from tower base.
7. Offset angle between heliostats (opt.) is 30o, axisymmetric arrangement with the central tower normal line.
8. Duel-axes tracking system had been used.
Receiver’s final design
Fig 4: Receiver schematic
Factor Value Recommended Status
Skewness 0.2 0.25 Excellent
Orthogonal element 0.88 0.9 Excellent
Element quality 0.84 0.88 Excellent
Aspect ratio 1.81 2 Excellent
Table 1 Finest mesh metrics factors.
Fig 5: Computational domain mesh
Case No. of elements T (oC)
1 79125 38.58
2 1213250 41.63
3 6174048 47.112
4 7698288 47.161
5 27074104 47.86
Table 2 Mesh independence results.
The boundary conditions for the present study are:
o Location: Al-Nahrain University / Baghdad Latitude (33.28° N) and Longitude (44.38° E).
o Solar radiation (W/m2) reflected per each heliostat is measured during the average recommended day for each
o Inlet temperature (oC) is measured during the average recommended day for each selected month.
o Turbulent flow, mass flow rate = 0.04 kg/s.
o Velocity profile
o Working fluid "Water" with variable properties as a function of temperature.
CFD models validation
Fig. 6: Comparison among CFD models
Design and manufacturing of the experimental rig that had
been used in this study was presented, in addition to
instrumentation, measurements, calibrations, test procedure,
and processing gathered data. The rig was assembled, and
tests were performed at Al-Nahrain University/Baghdad with
Latitude (33.3152°N) and Longitude (44.3661°E) during a
clear sky or partially clouded weather conditions according to
the selected tested dates. The presented work is initialized
from January 2018, utilizing central solar tower south
oriented with heliostat automated duel axis tracking system.
Experimental rig setup
Tower alignment in vertical position.
Casting the tower base using cement and sand mortar.
Experimental rig setup
Locate the tower height and the position (offset angle
and radius) for each heliostat.
Casting the heliostats bases using cement and sand
Experimental rig setup
Connecting the tracking system control board
with each heliostat and setting the LDRs sensors
with auxiliary mirror.
Manually setting the tracking system for both
heliostats to reflect the sun rays toward the
testing board and observe the reflected image
and giving feedback till the accurate positioning
Experimental rig setup
Instilling the receiver on the tower and
connecting the input and output water hoses.
Additional fixing for the receiver using stainless
steel strands to avoid wind effect on it.
Experimental rig setup
Connecting all instrumentations to the system
and prepare it for operating.
Experimental rig setup
System is operated according to the
1. The staggered configuration receiver gave 10.13%, 5.5%, and 1.5% thermal efficiency enhancement compared
with conventional parallel, series, and staggered continuous configurations for the receiver, respectively.
2. The numerical results showed that the Copper pipe used in building up the solar receiver had given the highest
outlet temperature with 361.7K compared with Aluminum, and Steel.
3. Automated dual axes tracking system was selected for the heliostats that provided the highest reflected solar rays
with an average enhancement percent was 49.19%, 26.65%, 71.91%, and 42.28% for May, June, July, and August,
4. Optimization of tower height, heliostat radius, and offset angle were performed, and the results show that 4.5 m,
7m, and 30o respectively are the optimum values.
5. To ensure best thermal performance, a coating process was done to reduce the reflectivity and emissivity as well as
increase the absorptivity of the receiver by using Ebonol C to oxidize the receiver pipes and then coated with
black matt paint, this process had enhanced the thermal performance by 13.97%.
6. The highest thermal efficiency for July at 12:00 noon was 86.88% while minimum value was 75.1% for May.
Thermal efficiency enhancement for June, July, and August with that for May are 11.45%, 15.68%, and 13.32%
respectively. The average error percent between numerical and experimental results for May, June, July, and
August are 1.28%, 1.33%, 1%, and 1.13% respectively.
7. An empirical correlation for Nusselt number had been formulated
𝑁𝑢𝑦 = 1602 ∗ 𝑅𝑒0.024463 ∗ 𝑃𝑟 −2.32751 ∗ 𝑦0.160764
The correlation conditions are, fully developed, turbulent flow (Re > 5500), L/D 3150 and Pr 7.56.
8. The present design thermal efficiency compared with one row and evacuated tube mentioned in previous studies
was increased to 8% and 10.92% respectively.
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