Geometric Design of Micro Scale Volumetric Receiver Using System-Level Inputs An Application of Surrogate-Based Approach

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Geometric Design of Micro Scale Volumetric Receiver
Using System-Level Inputs: An Application of
Surrogate-Based Approach
Tufan Akbaa,b,, Derek K. Bakerc,d, M. Pınar Meng¨ca,b
aDepartment of Mechanical Engineering, Ozyegin University, Istanbul, Turkey
bCenter for Energy, Environment and Economy (CEEE), Ozyegin
University, Istanbul, Turkey
cDepartment of Mechanical Engineering, Middle East Technical
University, Ankara, Turkey
dCenter for Solar Energy Research and Application (GUNAM), Middle East Technical
University, Ankara, Turkey
Abstract
Concentrating solar thermal power is an emerging renewable technology with
accessible storage options to generate electricity when required. Central re-
ceiver systems or solar towers have the highest commercial potential in large-
scale power plants because of reaching the highest temperature. With the
increasing solar chemistry applications and new solar thermal power plants,
various receiver designs require in micro or macro-scale, in materials, and
temperature limits. The purpose of the article is computing the geometry of
the receiver in various conditions and provide information during the concep-
tual design. This paper proposes a surrogate-based design optimization for
a micro-scale volumetric receiver model in the literature. The study includes
creating training data using the Latin Hypercube method, training five dif-
ferent surrogate models, surrogate model validation, selection procedure, and
surrogate-based design optimization. Selected surrogates have over 98% R2
fit and less than 4% root mean square error. In final step, optimization per-
formance compared with the base model. Because of the model complexity,
surrogate models reached better objective values in a significantly shorter
time.
Corresponding author.
Email address: tufan.akba@ozu.edu.tr (Tufan Akba)
Preprint submitted to - October 18, 2022
arXiv:2210.09249v1 [physics.flu-dyn] 17 Oct 2022
Keywords: surrogate modeling, concentrating solar thermal, receiver,
OpenMDAO, optimization
List of Symbols
cpspecific heat at constant pressure [J/kg ·K]
hheat transfer coefficient [W/m2·K]
kthermal conductivity [W/m ·K]
q00 heat flux [W/m2]
rinner radius [m]
Llength [m]
sspecific surface [m1]
Ttemperature [K]
vvolume [m3]
ρdensity [kg/m3]
Subscripts
ffluid
ssolid
rradiation
Acronyms
CST concentrating solar thermal
DOE design of experiments
HCE heat collecting elements
HTF heat transfer fluid
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LHD Latin hypercube design
MDO multidisciplinary design optimization
RBF radial basis function
RMSE root mean square error
SLSQP sequential least squares programming
TES thermal energy storage
1. Introduction
Thermodynamic cycle analysis gives insight into the overall system per-
formance and shows irreversibilities in each process creating the system [1].
For a system design (i.e. power plant, gas turbine, internal combustion en-
gine), thermodynamic cycle analysis is the top-level model and defines the
expected performance of the components as the initial phase. After the
component design is completed, the cycle analysis is performed with the new
values to observe the system-level impact for providing feedback information.
Thermodynamic cycle analysis is the core calculation for systems in different
performance parameters, design limitations, and operation conditions. Fossil
to renewable transition changed the analysis structure and performance pa-
rameters, design limitations, and operation conditions. The known method
from the fossil-fueled systems, fuel is the controlled input for optimization of
the plant efficiency by adjusting the fuel [2, 3, 4]. Unlike fossil fuels, renew-
able energy sources are not controlled inputs. The thermodynamic models
focus on maximizing cumulative power generation by creating multiple op-
eration points instead of optimizing the most efficient configuration [5, 6].
For concentrating solar thermal (CST) power, solar field, auxiliary heater,
thermal energy storage (TES), and power block are the main components of
the plant. The possible combinations of these components define the mul-
tiple operation points of the thermodynamic analysis [7]. Defining design
requirements gets more complex in multiple operation points. System-level
simulations are required for verification of the component design at multi-
ple points. The current study focuses on component design integration in
the thermodynamic cycle analysis. The coupled design (thermodynamic sys-
tem performance and integrated component design) will solve the problem
and satisfy these requirements together. However, coupled modeling requires
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multidisciplinary design optimization (MDO) and requires a problem archi-
tecture rather than solving every step separately [8].
The need for MDO arose to solve multiple subproblems in different dis-
ciplines for complex engineering systems. MDO helps to solve these systems
in two ways. The first is coupling the system with all the interdisciplinary
interactions. The second way is optimizing all the design variables coupled,
and the trade-offs of the subproblem design considerations [9]. The optimiza-
tion problem may diverge because of the computational load while solving
the subproblems simultaneously or due to the structure of the optimization
problem. One alternative to converge the optimization problem is using
an approximate (called surrogate) model that retains sufficient accuracy to
represent model complexity in an error range. Surrogate modeling has ad-
vantages for gradient-based optimization, especially when the model has a
high variation of gradients (i.e. noisy data) [10].
Surrogate models or metamodels are used for simplifying complex en-
gineering models. These models are less accurate but can provide a fast
alternative to original models. The accuracy of the model is estimated be-
fore using the model. A surrogate model is evaluated by its computational
time and accuracy [11]. Several surrogate models can be found in the lit-
erature. Response surface methodology [12] is one the fastest method for
surrogate modeling and kriging [13] is the most common alternative origi-
nating from mining applications. Because of the computational load of the
kriging, first or second order response surfaces created to observe the surro-
gate performance and accuracy of the surrogate model increases using kriging
in most of the cases. Neural networks are another surrogate model method
that provides solution alternatives in the form of chains of simple functions.
These chains are called networks, and each calculation node is called a neu-
ron [14]. The accuracy of the surrogate model is highly dependent on the
sample or training data. The term ”design of experiments (DOE)” focuses
on reflecting the model behavior by screening the required number of samples
called experiments [15]. There are several sampling methods like Latin hy-
percube design (LHD), factorial designs, random selection, orthogonal arrays
and low-discrepancy sequences [16, 17, 11, 10] for training accurate surrogate
models.
One advantage of surrogate modeling is the efficient solution of multifi-
delity problems. It maintains the required model complexity in the design
phase, and the surrogate model transfers the required information for sys-
tem optimization. The effectiveness of this approach was observed in several
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studies in different designs such as battery thermal management system [18],
permanent magnet synchronous motor [19], battery package optimization
[20]. A similar approach is the core idea explained in the article. The ac-
tual model is used for an accurate solution. Training data is generated using
the model for surrogate training and optimization is performed using the
surrogate model.
The current study explains an integrated way of receiver modeling. Re-
ceivers are the solar radiation collecting elements in CST power plants. Sev-
eral receiver models are existing in the literature [21, 22, 23] and ETH’s
receiver model [24] is replicated in this study. The main purpose of the ar-
ticle is to fill the gap in component design in CST technology, especially
in multiple operating conditions, and represent the results for proving that
surrogate modeling is an efficient way of finding the optimum solution in com-
plex design problems. In the article, different surrogate models are trained
and their performances are compared with the base model (replicated model
used cases) for validation purposes. After valid surrogates are selected, op-
timizations are performed with the selected surrogate model and the base
model. Optimization results and the final optimum points are compared as
the output of the study. The content of the article is structured as follows:
In section 2, governing equations of the replicated receiver model and prob-
lem statement are explained. Section 3 focuses on building the surrogate
model and optimization. Performance metrics, other findings, results, and
discussion are in Section 4. The final remarks and conclusion are in Section
5.
2. Problem Statement and Numerical Model
Receivers have three distinct designs: In external receivers, liquid heat
transfer fluid (HTF) passes through the heat collecting elements (HCE) which
are exposed to concentrated solar radiation. In solar tower (or central receiver
system), external receivers are widely used in large-scale power generation
from Solar One, the pilot central receivers system in the late 1970s, to re-
cent state-of-the-art large-scale plants including Gemasolar, Crescent Dunes,
Noor3, Delingha, and others [25]. Internal receivers are enclosed, and solar
radiation is concentrated in an opening. These receivers are selected in solar
tower power plants if the reflector field is directional. HCE are enclosed for
decreasing the ambient losses [26].
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摘要:

GeometricDesignofMicroScaleVolumetricReceiverUsingSystem-LevelInputs:AnApplicationofSurrogate-BasedApproachTufanAkbaa,b,,DerekK.Bakerc,d,M.PnarMenguca,baDepartmentofMechanicalEngineering,OzyeginUniversity,Istanbul,TurkeybCenterforEnergy,EnvironmentandEconomy(CEEE),OzyeginUniversity,Istanbul,Turk...

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