Abstract:

Cooling processes and refrigeration systems are strongly embedded in the everyday life of each individual. It is therefore not surprising that almost 20% of the electrical energy in developed countries is used for cooling purposes [1]. Nowadays, virtually all cooling systems (and heat pumps) are based on vapour-compression technology, which despite continuous research and development exhibits relatively low efficiency and still uses environmentally unfriendly refrigerants that can leak to the atmosphere causing a large Global Warming Potential (GWP). In the recent years, magnetic refrigeration showed a potential to be applied as an alternative to the vapour-compression technology. It should be noted that two reports on the alternative cooling technologies, one by European Commission from 2016 [2] and one by US Department of Energy from 2014 [3], present magnetocaloric technology as one of the most promising alternative refrigeration technologies in the future. Moreover, due to the high potential of this alternative technology, new standards within DIN are being prepared [4], which will include magnetocaloric refrigeration or heat pumping.

Magnetic refrigeration at room temperature is a relatively new and still developing technology. It is based on the so-called “magnetocaloric effect” (MCE), which appears as a temperature change (adiabatic temperature change) in magnetocaloric materials (MCMs) when a magnetic field change is applied as shown in Figure 1. When the MCM is magnetized, its temperature increases and, vice-versa, when the MCM is demagnetized the temperature decreases. Generally speaking, the MCE is a property of all ferromagnetic materials and is most prominent at their transition from the ferromagnetic to the paramagnetic state, which occurs at a certain temperature.

 

Figure 1: Numerically calculated magnetocaloric effect in gadolinium (left) and La-Fe-Co-Si (right) for different magnetic field changes.

 

Magnetic refrigeration at room temperature is based on Active Magnetic Regeneration (AMR), which was patented by Barclay and Steyert [5] in 1982. One of the important issues relating to existing MCMs is the small MCE (a few Kelvins for a magnetic field density change of 1 T). This is not enough for a sufficient operating temperature span of the magnetic refrigerator. The application of the AMR principle overcomes this problem to some extent, in that the MC material can exploit not only the MC effect, but also the process of heat regeneration. This then leads to certain increase in the operating temperature span.

The temperature span along the length of the AMR is established by the four recurring phases of operation in the magnetic refrigerator, as presented in Figure 2. These four phases of operation represent one thermodynamic cycle of the device and are as follows:

a) Magnetization process; in the presence of a magnetic field the MCM heats up due to the MCE;

b) A cold heat-transfer fluid flows through the heated AMR from the cold heat exchanger (left) to the hot heat exchanger (right); the fluid cools the AMR and transfers heat absorbed from the AMR to the ambient; during this process the AMR is still magnetized;

c) Demagnetization process; the AMR is displaced from the magnetic field and cools down due to the MCE;

d) A hot heat-transfer fluid flows through the cooled AMR from the hot heat exchanger (right) to the cold heat exchanger (left) where the fluid, cooled by the AMR, absorbs heat from the cooled ambient; during this process the AMR is still demagnetized;

 

Figure 2: 4 phases of AMR operation.

 

 

Problem identification, state-of-the-art and survey of the relevant literature

In the past four decades over 60 different magnetocaloric prototypes were built in the world [6]. However, there are still some major challenges that need to be addressed and resolved before the magnetocaloric technology will become commercially available. These issues range from the heat-transfer problems of the AMRs and the heat-transfer fluids, the design issues of the magnet assemblies, to the problems related to the peripheral systems, such as pump and valve systems. Another current obstacle is the high price of rare earth MCMs and permanent magnets.

An important constraint with existing AMR prototypes is the inability to efficiently function at operating frequencies (thermodynamic cycles per unit of time) higher than 5 Hz (for a certain relevant cooling power and temperature span) [7], which is due to the inefficient transfer of heat. Despite the fact that a relatively large number of prototypes have been built worldwide, they are still limited (from the efficiency point of view) to operating frequencies up to 5 Hz for temperature spans of 15 to 20 K and specific cooling powers of up to 200 W/kg (cooling power per mass of MCM) [8-11]. It can be concluded that the operating characteristics, especially the cooling power and the temperature span, are gradually improving. However, the important fact is that large masses of MCM and especially permanent magnets (to establish the magnetic field) are needed to achieve sufficient cooling power at such low operating frequencies. This dramatically increases the cost of magnetic refrigerators. These economic aspects of magnetic refrigeration at room temperature have been addressed in several economic analyses [12, 13, 14]. On the other hand, researchers [7] have shown that present device concepts (AMR) will not be able to operate efficiently above operating frequencies of 5 to 10 Hz. For these reasons, an alternative research approach is emerging in the field of magnetic refrigeration at room temperature. This was proposed in a study [15] relating to alternative approaches to magnetocaloric technology. It involves a whole new concept of the AMR, which would apply so-called thermal switches. The application of thermal switches could lead to drastic improvements in the heat transport from/to the MCM and consequently to higher operating frequencies. With a thermal switch mechanism it is possible to manipulate the direction or even the intensity of the heat flux. Recently a comprehensive review has been published listing a vast number of different possible physical mechanisms, which could be applied as thermal switch mechanisms [16]. Some fields of physics where the principles of thermal switches can be found include thermo-electricity [17], spin-caloritronics [18, 19, 20], thermal rectification [21, 22, 23], as well as microfluidic domains, such as electrohydrodynamics [24, 25, 26, 27, 28], ferro and magnetohydrodynamics [29, 30, 31, 32]. Several studies regarding the new concept of the AMR with thermal switches have been presented in the past few years [33, 34, 35, 36], including our own [37, 38], which was one of the first in the new emerging field. These are all theoretical studies with numerical simulations. Their common conclusion is that thermal switches could indeed drastically improve the operating characteristics, especially the operating frequencies (even above 100 Hz) and consequently the specific cooling powers (even above 10 kWkg^-1). Of course, we need to bear in mind that these are all just theoretical studies and an experimental proof-of-principle is still required.

An interesting domain, to look for thermal switch mechansims, is microfluidics, which has enabled the development of integrated lab-on-chip devices for use in clinical diagnostics, drug discovery, biodefense and environmental monitoring [39]. Although most microfluidic devices are based on a continuous flow of liquids in microchanells, there has been an increasing interest for the past couple of years in devices that rely on manipulation of discrete droplets using surface tension effects. One such technique is ElectroWetting On Dielectric (EWOD), which is based on wettability of liquids on a dielectric solid surface by varying the electrical potential. This method offers certain advantages over conventional continuous flow microfluidic chips, by significantly reducing sample sizes, as well as reconfigurability and scalability of the architecture. EWOD system’s similarity to the digital microelectronic systems has led to the term ‘’digital microfluidics’’ [40]. Among many EWOD applications reported in the literature [41], a new technique is a hotspot cooling for more efficient and target specific thermal management of electronics [42, 43]. In this technique, a controlled or programable array of discrete droplets can be used to actively cool areas of locally high heat flux. As it was shown in the numerical and experimental study by Nahar [44] on EWOD droplet actuation and cooling of the hotspot, a small droplet (diameter of approx. 2 mm) can move over a hotspot well under 100 ms and instantly cooling it by approximately 15 K. In this manner EWOD droplet manipulation seems to be an extremely fast thermal switch mechanism, which could be usefully and efficiently employed in the magnetocaloric cooling process. Moreover, EWOD technique is relatively well documented in the literature, so it is technologically fairly easy accessible and to be implemented for other purposes, such as magnetocalorics. However, since there is still no proof-of-principle of magnetocalorics with implemented thermal switches, building such an experimental set-up would be a great challenge.

Objective of the proposed research project

Generally, the project will answer two leading questions. How to manipulate EWOD principle for the purposes of thermal switching in magnetocalorics? How to apply coupled phenomena of EWOD and MCE to form an efficient cooling principle?

The final goal of the project is to design, build and test the first experimental proof-of-principle of coupled magnetocaloric effect and EWOD droplet actuation as the thermal switch mechanism. Our proposed concept is based on active magnetic regeneration as shown in Figure 3. However, instead of the AMR being completely submerged in the heat transfer fluid, only small liquid droplets are separately positioned along the AMR. In this manner the mass of each droplet is much smaller than the mass of the whole liquid in the AMR, making them (droplets) more submissive to the fast manipulation and change in the flow direction. Each droplet then travels only a certain length in the AMR in a reciprocating manner, which can still cause the heat to regenerate inside the AMR, increasing the temperature span beyond that of the magnetocaloric effect. Moreover, the reciprocating of the droplets can be extremely rapid, which can lead to the increase of the operating frequency, which in turn increases the cooling power and the efficiency of the cooling effect. On the other hand, the discrete droplets are separated between each other, which lowers the unwanted longitudinal thermal conduction between the heat sink and the heat source. Such a concept allows for a miniaturization of the future magnetocaloric cooling devices, which is an imperative step towards the commercialization of this technology in the future.

 

Figure 3: A schematic of  our proposed principle of MCM with EWOD thermal switches (left) and its operation (right).

 

To achieve the final objective of the project the proposed concept of coupled MCM and EWOD thermal switches will be analyzed using electrohydrodynamic and thermomagnetic numerical modelling. First, the electrohydrodynamic modelling of EWOD manipulation will take place. Since the droplets are propelled by means of electrical potential and its change of the liquids surface tension, we will model this phenomenon separately before coupling it thermally with the magnetocaloric material and the magnetocaloric effect. Such a model will be developed in a commercially available CFD simulation tool such as Ansys Fluent. A precondition for a consistent modelling are well-defined liquid and electrical properties of droplets and electrodes used in EWOD. They will be obtained based on the available data in the literature and our own experimental experience to build an operational EWOD platform. The goal of the hydrodynamic modelling is to define the optimal size of the droplets and the size of each electrode to achieve a fast movement of the droplets between spaces. Furthermore, each droplet will need to change the movement direction with the frequency of at least 10 Hz or even more. Findings from this work package will lay a solid foundation for further thermomagnetic modeling of the whole device, since it will show the constraints in the EWOD droplet actuation times and velocities.

The electrohydrodynamic model of EWOD will then be thermally coupled with the magnetocaloric material (as thin plates) and its magnetocaloric effect. For that purpose the previously developed AMR numerical model (in Matlab code) [45, 46] with magnetocaloric properties of MCMs will be applied. The goal of thermomagnetic modelling is to define the optimal geometry of the MC material (thickness, length of the MC plates) and the configuration of the droplets (number of discrete spaces on the MCM, number of droplets) to achieve an efficient and fast heat transfer between MCM and liquid droplets. A comprehensive performance analysis of a MC material with implemented EWOD droplet movement will be performed from operating and cooling characteristics point of view (operating frequency, temperature span, cooling power, efficiency).

The findings of such a hydrodynamic and thermomagnetic numerical analysis will give, as first, an important insight to the transient transport phenomena of the proposed cooling principle and to the thermal interactions between the two phenomena of MCE and EWOD. On the other hand it will give crucial directives to achieve the main objective of designing and developing the first experimental proof-of-principle.

The phases of the project and their realization:

The proposed project consists of the following Working Packages:

1. Characterization of EWOD (4 months)
2. Numerical modelling of the coupled transport phenomena of MCM with EWOD thermal switches (14 months)
   1. Electrohydrodynamic modelling Thermomagnetic modelling
3. Designing and building of the experimental proof-of-principle MCM with EWOD thermal switches (7 months)
4. Analysis of the cooling characteristics of the proof-of-principle (3 months)
5. Dissemination and demonstration of results (throughout the project)

1. Characterization of EWOD

At the first stage of the project we will focus on the selection and characterization of the most promising EWOD fabrication methods. The goal is to construct a preliminary experimental set-up for EWOD testing with the most promising and fast fabrication method. Generally, the EWOD consists of three principal elements: fluid droplets, solid electrodes and a solid dielectric (with hydrophobic surface) between the droplets and the electrodes. A precondition for an effective droplet actuation between two separate electrodes is an optimized geometry of all three.

The process of digital microfluidic (EWOD) application fabrication consists of the following three steps: electrode patterning, dielectric coating and hydrophobic treatment. To implement electrode patterns on a solid surface (in our case MCM) usually the processes of photolithography/etching or vapor depositioning of electrically conductive materials are utilized. The optimal thickness of the electrode should be between 50-100 nm [47]. Therefore, to deposit a thin-film electrode, the vapor deposition is a more suitable procedure. Materials that are commonly used as electrodes can be expensive ones, such as gold, silver, chromium or doped silicone substrate, as well as inexpensive ones, such as copper [48]. As suggested by [49, 50, 51, 52] the optimal spacing between electrodes is between 5 – 100 μm, while the size of the electrode should not be decreased below 1 mm [48]. Above the electrode, a thin layer of dielectric coating is placed. The thickness of the dielectric layer is of great importance, since it influences the amount of voltage that needs to be applied to change surface tension of the droplet. On the other hand, the thinner the dielectric layer, the lower is the breakdown voltage. Therefore, a dielectric material with high dielectric constant is favoured. There are several procedures, and respective materials, of how to apply the dielectric coating, such as vapor deposition of parylene, thermal growth of silicone oxide [50, 51], spin coating of PDMS (dimethylsiloxane) [52], as well as inexpensive thermal annealing of thin plastic [48]. Finally, the dielectric coating should be hydrophobically treated to assure low surface roughness. One of the common procedures is a spin coating of a teflon or some other fluoropolymer [53, 54, 55]. There are several possible fluids to be used in droplet formation, such as water with mixtures of NaCl, KCl or HCl, or liquid metals, such as mercury or galinstan. Non-toxic liquid metal galinstan has a great potential to be used in EWOD, since its thermal conductivity is of two orders higher than that of water. From the practical reasons (size of the electrode ~ 1 mm) the volume of each droplet should not be lower than 50 μl [48].

As it is clear from the literature, the EWOD fabrication procedures and materials are well mastered and defined in the scientific community. However, our proposed principle (coupled MCM with EWOD) is a completely novel approach to EWOD utilization, therefore firstly a separate investigation of EWOD will take place. In this manner a preliminary EWOD experimental set-up will be built for testing purposes. Since our final objective is to thermally couple EWOD with MCM, we will focus on how to fabricate EWOD in a manner to apply the thinnest possible layers of electrodes, dielectric and hydrophobic material. A special consideration will have to be put to the selection of materials and fluids with the highest thermal conductivity. All these information and characteristics will be obtain from the literature and from our own experiments. The main goal at this stage of the project is to lay a solid foundation and obtain important information for the numerical electrohydrodynamic modelling of EWOD, which will take place in the next working package. Furthermore, EWOD experimental set-up will serve as a bench-mark for the verification of the EWOD numerical modelling.

2. Numerical modelling of the coupled transport phenomena of MCM with EWOD thermal switches

Based on the characterization of EWOD in the previous Working Package (WP1), an exstensive numerical modelling of coupled transport phenomena of magnetocaloric material (with its magnetocaloric effect) and EWOD will be performed in this WP. The working package is divided into two sub-packages, namely, electrohydrodynamic (EWOD) and thermomagnetic (MCM + EWOD) modelling. A final coupled numerical model will give us the possibility to investigate in detail the dynamical thermal behavior of the novel cooling principle of MCM + EWOD thermal switches. This will be the first, but extremely important, step to the examination and to deep understanding of the proposed cooling principle.

Based on the findings from numerical analysis we will be able to determine geometrical parameters, as well as operating conditions for an effective operation of the cooling thermodynamic process of the MCM and EWOD thermal switches. With such knowledge obtained in this WP a conceptual experimental set-up will be designed, built and tested in the following Working Packages (WP 3 and 4).

The proposed principle of coupled MCM and EWOD is schematically shown in Figure 3 and its operation explained under section Objective of the proposed research project.

2.1. Electrohydrodynamic modelling

The goal of electrohydrodynamic modelling of EWOD is to find the optimal size of droplets and the size of each electrode to achieve a fast actuation of the droplets between electrode spaces in a manner to be suitable for the later implementation with magnetocalorics. As it is shown in Figure 3 the proposed new cooling principle is based on the active magnetic regeneration. However, instead of the MCM being completely submerged in the fluid, only small droplets are separately positioned at discrete places along the MCM (plate). These small droplets need to move extremely fast back and forth over the MCM plate (with the respective magnetocaloric effect) for a certain length (not the entire plate’s length) to ensure the heat to regenerate, thus inducing the active magnetic regeneration process. This droplet reciprocating movement should be as fast as possible, while still efficiently absorbing or releasing the heat from/to the MCM. However, for the successful modelling of these coupled transport phenomena (in the next sub-package), we will first model only EWOD operation separately. Moreover, we will model such an EWOD operation (movement of the droplets) that will exemplify required movement in the AMR process. 

Electrohydrodynamic modelling of the EWOD will be performed in the commercially available CFD simulation tool, such as Ansys Fluent. To achieve this goal the modelling process will be divided into two tasks. First, the electrostatic modelling of the EWOD will take place. Here we will focus on modelling a single droplet placed over a single and two electrodes. The objective is to model the change in the surface tension (contact angle with surface) of the droplet when the electric potential is applied or turned off. This phenomenon could be mathematically expressed by the so called Young-Lippmann equation [44]. Furthermore, when the droplet is placed partially on an activated and partially on a deactivated electrode, the radius of curvature of the droplet meniscus becomes asymmetric due to the different contacts angles on each side of the droplet. Moreover, this creates a pressure difference on both sides of the droplet, which in turn can lead to the droplet movement. The pressure difference can be mathematically realized through Young-Laplace equation [44]. 

The electrowetting effect in the fluid flow dynamics is then directly introduced through the equations from electrostatics and coupled with the Navier-Stokes equations, respectively. Namely, this transition to the fluid-electro-dynamics will be the second task of the electrohydrodynamic modelling. The main objective here is to model a plate (or series of plates) with a number of electrodes patterned on them and with the number of droplets positioned on the electrodes. Different geometries and electrical properties of electrodes and droplets will be numerically analyzed to find the optimal geometry of both, which will allow for a fast actuation of the droplets.

Throughout the whole modelling procedure, we will be able to implement knowledge gathered from the previous Working Package (WP 1). As stated, we will construct a preliminary experimental EWOD set-up, which will serve as a bench-mark for the EWOD numerical modelling.

2.2. Thermomagnetic modelling

With the goal of analyzing cooling characteristics of the proposed coupled transport phenomena of MCE and EWOD to form the unique AMR principle the thermomagnetic modelling of both effects will be performed. For that purposes our own, previously developed numerical model, originally developed for simulating the active magnetic regenerator operation (in Matlab code) [45, 46], will be applied. The regenerator-based numerical model simultaneously solves 1D, coupled, time-dependent energy equations of the heat-transfer fluid and the solid matrix (made of MCM) using finite difference method. Due to being one-dimensional, the impact of the geometry is considered through appropriate thermo-hydraulic correlations. The model predicts the temperature span, cooling power and the efficiency for various different operating conditions, thermodynamic cycles, magnetic field changes, various geometries and magnetocaloric materials (MCMs). The input work includes the magnetic work of the MCM in the cooling cycle and the work needed to pump the heat-transfer fluid.

The AMR numerical model and EWOD electrohydrodynamic model developed in the previous sub-package 2.1. will be coupled together in order to allow for simulations of the proposed new cooling principle with magnetocaloric material and electrowetting. The previously developed AMR model will have to be modified in order to couple its energy equations of the magnetocaloric material and fluid part with the electrohydrodynamic Navier-Stokes equations of EWOD.

A comprehensive performance analysis of the proposed cooling principle will be performed from a cooling characteristics point of view. One of the main focuses is the operating frequency and how will it affect the cooling characteristics, such as temperature span, cooling power and efficiency.

From a magnetocaloric point of view different magnetocaloric materials will be considered, such as gadolinium based magnetocaloric materials (e.g. Gd, Gd-Y), as well as lanthanum based materials (e.g. La-Fe-Co-Si, La-Fe-Si-H). As a part of our past research of different MCMs used in AMR, we have obtained magnetocaloric data (magnetic entropy change, adiabatic temperature change, magnetic field dependent specific heat) of a number of different MCMs through numerical modelling, our own experimental measurements or measurements from our colleagues in the scientific community. It needs to be pointed out, that in order to conduct quality simulations of the active magnetic regeneration, quality magnetocaloric characteristics data is a precondition and of vital importance. Furthermore, the geometry of the MCM is one of the important parameters in the efficient and fast heat-transfer from/to the MCM. Different thicknesses and lengths of plates will be investigated to find the most effective geometry for the interaction with the droplets in the EWOD actuation.

On the other hand, from the EWOD perspective, the important parameters will be thermal properties and geometry of the electrodes, dielectric and liquid droplets. The electrode and dielectric thickness are crucial parametesr, since they present a certain thermal resistance to the heat transfer between the MCM and the droplets. Furthermore, the choice of the fluid of the droplet is also an important factor. Water based fluids, as well as liquid metals, such as galinstan, will be investigated. As stated, galinstan is a promising fluid, since its thermal conductivity is of two orders higher than that of water.

One of the most important questions that will be answered through the numerical analysis in this Working Package is what is the most effective architecture of the MCM and EWOD to perform an efficient cooling cycle at the highest possible operating frequency. How many droplets (and of what volume) are needed per area of MCM? What is the effective ratio between fluid (droplets) and MCM? How fast could the droplets be actuated in a reciprocating manner to perform the most efficient heat regeneration in the AMR? These are just some questions that are needing the answer. The development of the proposed coupled electrohydrodynamic and thermomagnetic numerical model of the magnetocalorics with EWOD thermal switches will give a great opportunity to deliver those answers, as well as give room to new ideas and questions.

3. Designing and building of the experimental proof-of-principle MCM with EWOD thermal switches

Based on the findings obtained by electrohydrodynamic and thermomagnetic modelling from WP 2 an experimental proof-of-principle of MCM with EWOD thermal switches will be designed and built in this WP. The MCM, which will be chosen based on modelling results, will be obtained mostly from research institutions in the field, since there are only a handful of companies producing different magnetocaloric materials with different geometries. On the other hand, fabrication of the EWOD will have to be outsourced, since the procedures (e.g. vapour deposition) to coat the electrodes and dielectric are quite specific and need a special equipment. However, we have a strong collaboration with the Electronic Ceramics – K5 Department from the Josef Stefan Institute in the field of electrocalorics. At the institute they are developing different electrocaloric materials (with similar effect to MCE). In order for electrocaloric materials to be utilized in exploitation of their electrocaloric effect, a thin film of gold or platinum electrodes need to be deposited on the electrocaloric material. In this manner, all the necessary equipment for such surface treatment is available in that group at Josef Stefan Institute and could be available for the purposes of this project.

A special consideration will have to be put to the design and development of a programmable controller for EWOD and the magnetic field source control and power. A software algorithm will be developed, which will control the cycling process of the AMR operation. Such a software will have to control the complex movement of the droplets on the MCM with a subsequent alternating change of the magnetic field (magnetization/demagnetization) to induce the magnetocaloric effect in the MCM. As it is important that the droplets are actuated rapidly, it is of the same importance that the magnetization and demagnetization occur almost instantaneously. However, for such purposes a couple of different custom designed magnetic field sources were built in our laboratory in the past, which allow for magnetization/demagnetization to occur in approximately 10 ms. Such a design of the magnetic field source is a part of the invention of Micro-magnetocaloric device for which a patent application was filed in 2016 [56] and is now in the process of patenting.

Another two important constituents of the experimental set-up are the heat source and the heat sink, which are crucial for the efficient MCM + EWOD operation in the AMR principle. To absorb or release heat in the heat source/sink, the droplets will have to be translated by means of electrowetting into the heat sink/source from the AMR and back. In this manner a special heat exchangers will have to be designed, which will also have electrodes deposited in the their channels for the purposes of EWOD. The heat exchangers are usually constructed from highly thermally conductive materials, such as copper or aluminum, respectively. However, such materials are also good electric conductors, which is an issue from EWOD point of view, since the EWOD operation needs discrete electrically conductive electrodes placement next to each other. However, some new polymer materials have shown relatively good thermal properties that could be effectively applied as heat sink materials, instead of metals.

Finally, all the needed measuring system will be designed in LabView environment and applied through the National Instruments data acquisition.

4. Analysis of the cooling characteristics of the proof-of-principle

An extensive experimental analysis of the developed proof-of-principle will be performed in this WP. The proposed novel cooling principle will be subjected to testing at various different operating conditions for its cooling characteristics, such as temperature span between heat sink and heat source, cooling power and the efficiency.

The experimental proof-of-principle will be tested at different operating frequencies, different ratios of fluid droplet volume to MCM volume, different temperatures of the heat sink and different temperature spans. Cooling power and the efficiency will be measured at different temperature spans, which will give us an important insight to the cooling characteristics of the tested cooling principle.

Moreover, based on the experimental results we will be able to verify and, if needed, modify the developed coupled electrohydrodynamic and thermomagnetic numerical model of the MCM with EWOD thermal switches according to the experimental findings.

The main objective is to find out, if the proposed cooling principle could efficiently transport heat from the heat source to the heat sink at high operating frequencies (above 10 Hz). If the experimental tests will show such a potential, the research work done in this project will represent a major breakthrough in the field of magnetocaloric energy conversion (and other caloric technologies), as well as in the wider domain of other refrigeration technologies.

5. Dissemination and demonstration of results

The dissemination of results will be held from the beginning of the project, through high quality scientific publications (with high impact factor) and conference contributions. The acquired knowledge and findings will be forwarded to undergraduate and postgraduate students at the Faculty of Mechanical Engineering at University of Ljubljana. The last month of the project will be devoted to the demonstration of the operation of the novel cooling principle with MCM and EWOD thermal switches to the general public and industrial and scientific partners. If possible, patent application on the novel cooling principle will be applied (prior to scientific publications).

Project management: Detailed implementation plan and timetable

The project proposal consists of five WPs, which are sectioned in Table 1 together with Milestones, while the Risk management is presented in Table 2. Each WP has clearly defined tasks:

Duration of the project: 24 Months (M1-M24)

WP 1: Characterization of EWOD – duration: M1-M7

• Task 1.1: Construction of preliminary experimental EWOD set-up by most promising fabrication method
• Task 1.2: Experimental characterization of EWOD operation for later numerical modelling

WP 2: Numerical modelling of the coupled transport phenomena of MCM with EWOD thermal switches – duration: M3-M16

WP 2.1: Electrohydrodynamic modelling – duration: M3-M11

• Task 2.1: Electrostatic modelling of EWOD of single/double droplet/electrode configuration
• Task 2.2: Coupling the electrostatic EWOD model with fluid dynamics to develop electrohydrodynamic numerical model of EWOD
• Task 2.3: Numerical evaluation and selection of the geometry and electrical properties of electrodes (with dielectric) and fluid droplets and verification of the EWOD model with the experimental results from WP 1

WP 2.2: Thermomagnetic modelling – duration: M8-M16

• Task 2.4: Coupling the electrohydrodynamic EWOD numerical model with the AMR numerical model
• Task 2.5: Numerical evaluation and selection of the MC materials and geometry, fluid for EWOD based on thermal properties, thickness of dielectric, number of electrodes and corresponding droplets for effective cooling principle operation
• Task 2.6: Numerical evaluation and selection of effective operating conditions of the proposed cooling principle  

WP 3: Designing and building of the experimental proof-of-principle MCM with EWOD thermal switches – duration: M15-M21

• Task 3.1: Development of the controller for EWOD and magnetic field source for the fast cycling of the AMR process
• Task 3.2: Design and construction of special heat source and heat sink that will allow EWOD operation within them
• Task 3.3: Design and construction of the first experimental proof-of-principle MCM with EWOD thermal switches

WP 4: Analysis of the cooling characteristics of the proof-of-principle – duration: M21-M23

• Task 4.1: Complete analysis of cooling charcteristics, such as temperature span between the heat sink and heat source, cooling power and efficiency of the new cooling principle at various operating conditions
• Task 4.2: Verification of the developed coupled electrohydrodynamic and thermomagnetic numerical model of the novel cooling principle with EWOD thermal switches

WP 5: Dissemination and demonstration of results – duration: M3-M24

• Task 5.1: High level scientific publications throughout the entire project
• Task 5.2: Demonstration of the operation of the novel MCM + EWOD cooling principle to the general public, industrial and scientific partners and to students at the faculty (at the end of the project)