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System Simulation of an Elastocaloric Heating and Cooling Device Based on SMA

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Elastocaloric (EC) cooling uses solid-state NiTi-based shape memory alloy (SMA) as a non-volatile cooling medium and enables a novel environment-friendly cooling technology. Due to the high specific latent heats activated by mechanical loading/unloading, substantial temperature changes are generated in the material. Accompanied by a small required work input, a high coefficient of performance is achievable. Recently, a fully functional and illustrative continuous operating elastocaloric air cooling system based on SMA was developed and realized. To assist the design process of an optimized device with given performance and efficiency requirements, a fully coupled thermo-mechanical system-level model of the multi-wire cooling unit was developed and implemented in MATLAB. The resulting compact simulation tool is qualified for massively parallel computation, which allows fast and comprehensive parameter studies. In this work, the influence of different SMA diameters, rotation frequencies, and airflow rates is investigated. The results are analyzed to find the suited parameter for high efficiency (COP) and temperature span.
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SYSTEM SIMULATION OF AN ELASTOCALORIC HEATING AND COOLING DEVICE BASED ON SMA
Felix Welsch1, Susanne-Marie Kirsch1, Nicolas Michaelis3, Michele Mandolino1, Andreas Schütze3, Stefan
Seelecke1,2, Paul Motzki2, Gianluca Rizzello1
1Intelligent Material Systems Lab, Saarland University, Saarbruecken, Germany
2Intelligent Material Systems Lab, ZeMA gGmbH, Saarbruecken, Germany
3Lab for Measurement Technology, Saarland University, Saarbruecken, Germany
ABSTRACT
Elastocaloric (EC) cooling uses solid-state NiTi-based
shape memory alloy (SMA) as a non-volatile cooling medium
and enables a novel environment-friendly cooling technology.
Due to the high specific latent heats activated by mechanical
loading/unloading, substantial temperature changes are
generated in the material. Accompanied by a small required
work input, a high coefficient of performance is achievable.
Recently, a fully functional and illustrative continuous
operating elastocaloric air cooling system based on SMA was
developed and realized. To assist the design process of an
optimized device with given performance and efficiency
requirements, a fully coupled thermo-mechanical system-level
model of the multi-wire cooling unit was developed and
implemented in MATLAB. The resulting compact simulation tool
is qualified for massively parallel computation, which allows fast
and comprehensive parameter studies.
In this work, the influence of different SMA diameters,
rotation frequencies, and airflow rates is investigated. The
results are analyzed to find the suited parameter for high
efficiency (COP) and temperature span.
  

1. INTRODUCTION
         



        

        


       


      
        

  
        
        

        
     
   




       

         


         


      
        
      
     
       
        
    



2. REALIZED EC-DEVICE
      

       

           
 

Proceedings of the ASME 2020 Conference on Smart Materials,
Adaptive Structures and Intelligent Systems
SMASIS2020
September 15, 2020, Virtual, Online
SMASIS2020-2262
1
Copyright © 2020 ASME
Attendee Read-Only Copy
FIGURE 1:    
   





       
      
     

         



          
         

          
          

     




       

  
         

    
  
  
3. DEVICE SIMULATION TOOL


        

         

         


FIGURE 2:    

3.1. Device model
The load profile represents the central component of the
mechanics, governing the elastocaloric cycle and is modeled as
a piecewise function depending on the rotation angle of the SMA
arrangement.  function is adaptable to different
thermodynamic cycles to optimize the performance of the
device.[5]         


   
        The
fluid transport and temperature evolution in the ducts on the hot
and cold side are implemented as one-dimensional flow with
homogeneous radial and axial temperature distribution. The
outlet temperatures are calculated with the inlet temperatures and
flow velocities by solving the advection-diffusion partial
differential equation for the fluid temperature. The heat
exchange coefficient strongly depends on the SMA wire
diameter, as well as flow velocity and is calculated with the
Churchill-Bernstein Equation [26].
  coupling of the individual loaded
SMA elements is covered by the multiple copies of an SMA
model. The current material composition between martensite and
austenite is calculated with the Mueller-Achenbach-Seelecke
model using Boltzmann statistics on a multi-well free energy
function.[27] The temperature of each SMA element is
calculated by the energy balance in the SMA material, which
links the temperature rate with the heat exchange to the
surrounding fluid and the production or absorption of latent heats
due to phase transformations.
Rot. Frequency
Cam geometry
Inlet temperatures
Flow rate
Channel geometry
Torque
Mechanical power
Efficiency (COP)
Thermal power
Outlet temperatures
Elastocaloric Device
Me chanics
SMA arrangement Fluid
SMA Model
SMA Model
SMA Mode l
SMA Model
SMA
 

 

2
Copyright © 2020 ASME
The interacting modules, enable the calculation of the
coefficient of performance (COP) by dividing the transported
heat from the cold to the hot through the mechanical input
energy. These energies are calculated by integrating the thermal
and mechanical power over the time interval of one rotation after
reaching a stationary temperature distribution in the fluid ducts.
The simulation tool is fully implemented in MATLAB and
solved using a standard ode113 solver, allowing fast and
accurate computation. The short computation time, due to the
 vectorization,
as well as massively parallel computation on multi-core
computers, enables economic comprehensive parameter studies.
      
        



3.2. Parameter study
    
  and 

.Device parameters like mass of SMA material, wire
diameter, rotation frequency, airflow rate represent degrees of
freedom during the design process to reach the best COP. 
          
     

    
 

4. SIMULATION SETUP AND RESULTS

       
         
    
           
       
  
TABLE 1: PARAMETER SWEEP
Rotation
frequency (Hz)
Airflow rate
(m3/h)
0.25
25
0.5
50
1.0
100
2.0
150
4.0
5 steps
4 steps
80 simulations
      
     
          
         

TABLE 2: MATERIAL PARAMETERS OF NITICO#3
Parameter
Value
Unit
Description
EA
53.8
GPa

EM
22.6
GPa

T
0.0246
-
Transformation strain
6317
kg/m3
Mass density
c
463
J/kg/K
Specific heat capacity
H
15.6
J/g
Latent heat
h

W/m2/K
Convection coefficient,
depending on air velocity
T0
295.15
K
Reference temperature
(T0)
542.5
MPa

(T0)
423.3
MPa


7
MPa/K
Temperature dependency
of transformation stress
VLE
510-23
m3
Volume element size
x
0.001
s
Phase transition time constant
        
 
 
 
        
         
           
   
        

            
            



         
         

       
 
        



         
         

        




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 
FIGURE 3:     

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FIGURE 4:    
    
    
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
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 
FIGURE 5: 




        
 
       
        
       


        
 
     


The presented parameter study imposingly illustrates the
advantages of small wire diameter and high flow rates like high
COP at high frequencies, large thermal power, and high
temperature span. However, for the given machine configuration
with 24 bundles of 30 individual wires, a change to 50
wires, while maintaining the mass of SMA material, leads to
480 wires per bundle. For practical reasons, a compromise
between manufacturing effort and high performance is often
found at slightly thicker wire diameters.
5. CONCLUSION




         
        
     

       
        

ACKNOWLEDGMENT
       
    
      



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   
      Nat. Mater.
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 

Sci.
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

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
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Technol. Built Environ.
      
 
  
   

 
       
   Int. J. Refrig.  

 et al.
       
Energy Technol.     

  
     
     
    
      
  Thermag VII    

          
     

ASM Int. - Int. Conf. Shape Mem. Superelastic Technol.
SMST 2019
 et al.

    ASME 2019
Conference on Smart Materials, Adaptive Structures and
Intelligent Systems
  
  
     Refrigeration
Science and Technology    
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 

     Thermag VII

 
    
   ASM Int. - Int. Conf. Shape
Mem. Superelastic Technol. SMST 2019  

  
     
     Int. J.
Refrig.
         
     
    Contin.
Mech. Thermodyn.
 
      
    
  Int. J. Solids Struct.    

        

Acta Mater.
   et al.   
     
     
Contin. Mech. Thermodyn.      

  
     
  
   Refrigeration Science and
Technology
  
     
     
    
Thermag
VII
          
     
     
ASM Int. - Int. Conf. Shape Mem. Superelastic Technol.
SMST 2019
        
     
     
ASME
2019 Conference on Smart Materials, Adaptive
Structures and Intelligent Systems
 et al.
ASME 2018 Conference
on Smart Materials, Adaptive Structures and Intelligent
Systems
       
   
  

       
   
6
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        
      
        J. Heat
Transfer
       
     
Mater. Sci. Eng. A
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... Furthermore, the system's efficiency can be quantified and compared to the theoretical limit given by the properties of the elastocaloric material, enabling the quantification of further optimization potential. In the literature, different approaches of elastocaloric cooling systems have been studied regarding their efficiency with simulations [20][21][22][23]. In this publication, we present a simulation model of the AEH that was validated with experimental data. ...
Article
Full-text available
When it comes to covering the growing demand for cooling power worldwide, elastocalorics offer an environmentally friendly alternative to compressor-based cooling technology. The absence of harmful and flammable coolants makes elastocalorics suitable for energy applications such as battery cooling. Initial prototypes of elastocaloric systems, which transport heat by means of thermal conduction or convection, have already been developed. A particularly promising solution is the active elastocaloric heat pipe (AEH), which works with latent heat transfer by the evaporation and condensation of a fluid. This enables a fast and efficient heat transfer in a compression-based elastocaloric cooling system. In this publication, we present a simulation model of the AEH based on MATLAB-Simulink. The model showed very good agreement with the experimental data pertaining to the maximum temperature span and maximum cooling power. Hereby, non-measurable variables such as efficiency and heat fluxes in the cooling system are accessible, which allows the analysis of individual losses including the dissipation effects of the material, non-ideal isolation, losses in heat transfer from the elastocaloric material to the fluid, and other parasitic heat flux losses. In total, it can be shown that using this AEH-approach, an optimized system can achieve up to 67% of the material efficiency.
... dimensions, density of SMAs and heat exchanging fins, timing, fans and pumps speed, heat recovery), thus demonstrating the massive room for integrated efficient operation. Similarly, in (Welsch et al., 2020), the continuously operating EC ventilation concept presented in (Kirsch et al., 2019) was simulated to predict COP, thermal power, and outlet temperature on account of different SMA size, rotation frequency, and airflow rate. Distinct feature is the power saturation for increasing rotation frequencies (0.25-4 Hz), the inverse proportionality with the EC wire diameter and the beneficial effects of higher flow rates. ...
Article
Refrigerants in vapor-compression systems have a global warming potential thousands of times that of carbon dioxide, yet their spread on the market is unrivalled. Elastocaloric systems, based on solid state cooling, feature among the most promising alternatives. In this paper, an elastocaloric device for air ventilation (ECV) composed by parallel and serial connection of multiple shape memory alloy (SMA) films, is investigated via volume-based finite difference simulation in MATLAB and dynamic building simulation in TRNSYS considering eight cities across the globe. The models assume experimentally demonstrated thermal parameters for the elastocaloric phase transformation around room temperature and a single-storey reference building. The ECV operates according to an optimized, energy-saving logic that includes load partialization and recirculation. Parametric analyses suggest that moderate terminal velocities (∼2 m/s) and a climate-specific design aimed at maximizing the use of the ECV device at nominal cooling capacity are key to reach building cooling needs reductions up to 70% in the considered scenarios. Partialization results in enhanced energy flexibility and conservation, whereas recirculation extends the ECV usability to extreme heat conditions. In absolute terms, the ECV works best under hot climates (e.g. Cairo, Dubai, Brisbane), with monthly cooling load reductions about 2/3-fold compared to cold locations (e.g. Milan, Hobart). The performance is extremely sensitive to the ventilation rate. Thermal zones requiring 1 to 2 air changes per hour are best suited. These findings provide initial insight into design criteria, opportunities and limitations on the use of elastocaloric devices for building ventilation to guide future experimental verification.
Chapter
The urban heat island and urban overheating are the most documented phenomena of climate change. Higher ambient temperatures increase the cooling energy consumption of buildings, affect human health, raise the concentration of urban pollutants, and affect the quality of life of urban citizens. The phenomenon is experimentally documented in more than 450 large cities around the world. The intensity of urban overheating depends on several parameters like the characteristics of the local climate, the landscape, and the features of the city, such as the materials used and the strength of the local sinks and sources. According to the existing data, the average maximum magnitude of urban overheating is close to 5°C, but it may vary up to 10°C. The highest intensities are observed during anticyclonic climatic conditions, low wind speed, and clear sky conditions. In parallel, precipitation tends to decrease the strength of the urban overheating as it increases the thermal admittance of the rural areas.
Conference Paper
Full-text available
Elastocaloric cooling uses solid-state NiTi-based shape memory alloy (SMA) as a non-volatile cooling medium and enables a novel environment-friendly cooling technology without global warming potential. Due to the high specific latent heats activated by mechanical loading/unloading, large temperature changes can be generated in the material. Accompanied by a small required work input, a high coefficient of performance is achievable. Recently, a fully-functional and illustrative continuous operating elastocaloric fluid cooling system based on SMA is developed and realized, using a novel mechanical concept for individual loading and unloading of multiple SMA wire bundles. The fluid-based heat transfer system is designed for efficient heat exchange between the stationary heat source/sink and the SMA elements, operates without any additional heat transfer medium. Rotation frequency and fluid flow-rate are adjustable during operation, which allows adapting the operation point to power- or efficiency-optimized demands. The versatile placement of the in- and outlets allows different duct lengths and counter-flow or parallel-flow experiments. To investigate the air flow parameters at the in- and outlets, as well as the crossflow between the hot and cold side, a measurement system is developed and integrated. In this contribution, the first measurement results of the output temperatures for inlet air flow variation in combination with different rotation frequencies are presented.
Conference Paper
Full-text available
Elastocaloric cooling uses solid-state NiTi-based shape memory alloy (SMA) as a non-volatile cooling medium and enables a novel environment-friendly cooling technology. Due to the high specific latent heats activated by mechanical loading/unloading, substantial temperature changes are generated in the material. Accompanied by a small required work input, a high coefficient of performance is achievable. Recently, a fully-functional and illustrative continuous operating elastocaloric air cooling system based on SMA was developed and realized. To assist the design process of an optimized device with given performance and efficiency requirements, a fully coupled thermo-mechanical system-level model of the multi-wire cooling unit was developed and implemented in MATLAB. The resulting compact simulation tool is qualified for massively parallel computation on modern multi-core computers, which allows fast and comprehensive parameter scans. The comparison of first measurements and simulation results showed differences in the system performance. As the airflow rate influences the thermal power and the outlet temperature significantly, the demonstrator is extended with a spatial airflow measurement system to analyze the crossflow between the hot and cold side. Following, the fluid transport model is advanced by the effect of cross-flow losses, and first modeling results with the variation of airflow rate and rotation frequency are presented.
Conference Paper
Full-text available
The following contribution provides analyses of the air cooling potential of elastocaloric shape memory alloys (SMAs) in form of NiTiCo wires. An essential step consists in developing a scientific test setup, which offers the ability to determine the air-cooling potential under varying conditions like wire geometry, material composition, and process parameters. With the help of this test setup the influence of different airflow rates on the heat transfer from SMA wire to air and the coherent heat transfer coefficients as well as the expectable air temperature ΔT values are determined and presented in this contribution. Analysing these parameters will greatly support the simulation, development and construction of elastocaloric air cooling devices to provide environmentally friendly alternatives to the prevalent vapour compression based cooling principles.
Conference Paper
One of the most important parameters of superelastic shape memory alloys (SMA) to be used in elastocaloric cooling and heating processes is their specific latent heat. Thus, when developing and evaluating new materials for elastocaloric processes the determination of the latent heat is an essential step. Usually, the latent heat of a material is determined by differential scanning calorimetry (DSC) where the material phase transformation is induced thermally. During elastocaloric processes, on the other hand, the latent heats of the material become accessible by stress induced transformation under tensile loading and unloading of the sample. In recent elastocaloric experiments, we observed drastic differences between latent heat values determined in DSC experiments and the ΔT values observed in nearly adiabatic elastocaloric cycles, which reflect the latent heat; in fact, the DSC experiments predicted rather pessimistic values and thus also poor elastocaloric cooling performance. Based on these observations we developed and tested a novel experimental approach to determine the latent heat of superelastic materials directly during in the elastocaloric process. By comparing or combining direct Joule heating with the strain based process we are able to accurately determine the latent heats for both tensile loading and unloading for any elastocaloric heating or cooling process. The approach is based on observing and matching temperature changes which also suppresses the influence of most non-idealities in the process, i.e. heat losses within the experimental setup or to the ambient. Furthermore, the influence of applied maximum strain, strain range and rate as well as material conditioning on the latent heat can be observed in the elastocaloric experiment.
Article
This contribution provides an experimental analysis of relevant parameters to determine the air cooling potential of elastocaloric shape memory alloys (SMAs) in the form of wires. An essential step consists in developing a scientific test setup, which offers the ability to determine these parameters under varying conditions like wire geometry, material composition, and process parameters. With the help of this test setup the influence of different airflow rates on the heat transfer from SMA wire to air and the coherent heat transfer coefficients as well as the approximate air temperature ΔT values are determined and presented in this contribution. Furthermore, the latent heat of the SMA material is experimentally identified with a novel approach based on comparing dynamic temperature changes achieved by elastocaloric phase transformation with direct caloric heating. Analysing these parameters will greatly support the simulation, development and construction of elastocaloric air cooling devices to provide environmentally friendly alternatives to the prevalent vapour compression based cooling principles.
Conference Paper
Elastocaloric cooling is a novel environment-friendly alternative to vapor compression-based cooling systems. This solid-state cooling technology uses NiTi shape memory alloys (SMAs) as cooling medium. SMAs are well known for lightweight actuator systems and biomedical applications, but in addition, these alloys exhibit excellent cooling properties. Due to the high latent heats activated by mechanical loading/unloading, large temperature changes can be generated in the material. Accompanied by a small required work input, this also leads to a high coefficient of performance superior to vapor compression-based systems. In order to access the potential of these alloys, the development of suitable thermodynamic cooling cycles and an efficient system design are required. This paper presents a model-based design process of an elastocaloric air-cooling device. The device is divided into two parts, a mechanical system for continuously loading and unloading of multiple SMA wire bundles by a rotary motor and a heat transfer system. The heat transfer system enables an efficient heat exchange between the heat source and the SMA wires as well as between the SMA wires and the environment. The device operates without any additional heat transfer medium and cools the heat source directly, which is an advantage in comparison to conventional cooling systems. The design of this complex device in an efficient manner requires a model approach, capable of predicting the system parameters cooling power, mechanical work and coefficient of performance under various operating conditions. The developed model consists of a computationally efficient, thermo-mechanically coupled and energy based SMA model, a model of the system kinematics and a heat transfer model. With this approach, the complete cooling system can be simulated, and the required number of SMA wires as well as the mechanical power can be predicted in order to meet the system requirements. Based on the simulation results a first prototype of the elastocaloric cooling system is realized.
Poster
Researche objective Motivation: • Elastocaloric cooling is: • Environment-friendly • No global warming potential • Non volatile refrigerant • Elastocaloric material provides: • Large temperature changes in material • High specific latent heats released at first-order transformation • High coefficient of performance (COP) Goal: • Development and realization of a continuously operating elastocaloric macro scale air cooling device. • Independent variation of process parameters, thermal boundary conditions, and material parameters should provide by the system design
Conference Paper
Elastocaloric cooling based on NiTi exhibits an excellent cooling capability, due to the high specific latent heats activated by mechanical loading/unloading and the small required work input. The work of the current funding period in the DFG Priority Program SPP 1599, is focused on the development and realization of a continuous operating elastocaloric cooling device. This paper presents the development of an efficient simulation tool for predicting the operation behavior of the system to support the building process of the machine. The model describes the mechanical and thermal characteristics, to find the optimized parameter set for a high-efficient, high-performance cooling unit with a large temperature span while using a minimal amount of SMA material. The simulation tool and animated visualization tool combines a parallel computing thermo-mechanical SMA model for multiple elastocaloric SMA elements with a mechanical loading system and heat transfer to the heat transport medium to guide the economic development of an efficient cooling device.
Article
Refrigeration is one of the primary uses for electrical energy and an important contributor to worldwide CO2 emissions. Both of these issues can be mitigated if caloric effects in solid materials are fully utilized. In particular, materials with ferroic phase transitions, which give rise to magneto‐, electro‐, and elasto‐caloric effects, are promising candidates. Because these refrigerants are in the solid state, the corresponding cooling technology also eliminates the need for halo‐carbon refrigerants with high global warming potential. This Special Issue gives an overview on recent breakthroughs in the research on magnetocaloric, elastocaloric, and electrocaloric materials and their implementation in more efficient cooling devices, as obtained within the German Priority Program Ferroic Cooling (SPP 1599). As a brief introduction to the in‐depth Reviews and Full Papers included in the Special Issue, a ferroic cooling cycle is sketched and the influences of magnetic, electric, and stress fields on ferroic materials are summarized in this Editorial. Ferroic cooling: If you are not familiar with this term, this is a must‐read article for you! It gives a brief introduction how a ferroic cycle works and presents the basic ideas behind magnetocaloric, electrocaloric, and elastocaloric refrigeration. WARNING: Reading this article may result in an urge to take a look at the entire special issue!
Article
Solid state cooling is an environment‐friendly, no global warming potential alternative to vapor compression‐based systems. Elastocaloric cooling based on NiTi shape memory alloys exhibits excellent cooling capabilities. Due to the high specific latent heats activated by mechanical loading/unloading, large temperature changes can be generated in the material. The small required work input enables a high coefficient of performance. This paper presents an overview of elastocaloric cooling from basic principles, such as elastocaloric cooling cycles, material characterization, modeling, and optimization, to the design of elastocaloric cooling devices. The paper particularly highlights current work performed within the DFG Priority Program SPP 1599 "Ferroic Cooling", which is focused on the development and realization of a continuously operating elastocaloric cooling device. The cooling device operates in a rotatory mode with wires under tensile loading. The design allows maximization of cooling power by suitable wire diameter scaling as well as efficiency optimization by implementing a novel drive concept. Finally, first CAD models of the discussed solid state air cooling device are presented.