Anand, M.

Bowen, J.

Holland, A.

Levin Prabhu, V.

Lim, S.

Morse, A.

English

Open Research Online (OU)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsNumerical modelling of microwave sintering of lunarsimulants under near lunar atmospheric conditionConference or Workshop ItemHow to cite:Lim, S.; Levin Prabhu, V.; Anand, M.; Bowen, J.; Morse, A. and Holland, A. (2018). Numerical modelling ofmicrowave sintering of lunar simulants under near lunar atmospheric condition. In: European Lunar Symposium (ELS)2018, 13-16 May 2018, Toulouse, France.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukNUMERICAL MODELLING OF MICROWAVE SINTERING OF LUNAR SIMULANTS UNDER NEAR LUNAR ATMOSPHERIC CONDITION.  S. Lim1 (sungwoo.lim@open.ac.uk), V. L. Prabhu1, M. Anand1,2, J. Bowen3, A. Morse1, and A. Holland1, 1School of Physical Sciences, The Open University, UK, 2Department of Earth Sciences, The Natural History Museum, London, UK, 3School of Engineering and Inno-vation, The Open University, UK    Introduction:  The Space Instrumentation Group at The Open University has recently started investigating microwave sintering of lunar rego-lith/simulant as a potential fabrication method of 3D printing on the Moon to build lunar habitats. As part of this initiative, we have designed an industrial bespoke microwave heating apparatus. This appa-ratus will allow thorough experimental investigation of the sintering mechanism of lunar rego-lith/simulant in the cavity. The mechanical proper-ties of sintered specimens produced under optimal conditions can then be explored. The experiment will also be validated using COMSOL Multiphysics simulation software.  In this contribution, we discuss the current de-sign of the bespoke microwave heating apparatus, and how COMSOL has been employed to under-stand the different characteristics of lunar simulants when subjected to microwave heating.   Microwave sintering:  Microwave sintering of lunar regolith as a potential fabrication method of lunar habitat construction has become one of the popular topics in recent years [1]. Previous research in this area, however, have been conducted using domestic microwaves. Figure 1 shows our initial work setting (see companion abstract by Levin-Prabhu et al. in this meeting).      Figure 1: Microwave sintering using a kitchen mi-crowave  The picture on the left shows an intrared ther-mometer setting for measuring the surface tempera-ture of specimen, the middle and right pictures show the sintered/melted lunar simulant JSC-1A. Domestic kitchen microwaves are not ideal for sin-tering lunar simulants for the following reasons: (i) they are not capable to withstand temperatures of up to 1,250 °C – the melting point of lunar rego-lith/simulant; (ii) they are not optimised to maxim-ise microwave energy into a single hotspot; (iii) they are not able to mimic lunar atmospheric condi-tion; (iv) it is not possible to measure sample sur-face temperature accurately; and (v) the frequency is fixed at 2.45 GHz which is an optimal frequency to heat water molecules in food products but may not be optimal for inorganic solid materials such as lunar regolith.  Thus, an industrial bespoke microwave heating apparatus has been designed to overcome the cur-rent limitations. Figure 2 illustrates a design of the apparatus which includes two ports for an infrared thermometer probe and an endoscope-type digital camera, one naked-eye viewer window, and a cy-lindrical cavity with a flange for a vacuum pump. The ports can also be connected to a mass spec-trometer, permitting extractation and analysis of volatiles while specimens are heated. Volatiles in regolith can be extracted by heating the regolith bewteen 300 and 900 °C [2, 3]. For example,  tem-perature of 700 °C is sufficient to obtain most of the H2 and He [4]. Thus, the apparatus could also be used for measuring the types and amount of vola-tiles which could be used for propellent and life support (e.g. water). It is expected that the new ap-paratus would allow to (i) maximise microwave energy in a single hotspot; (ii) measure the surface temperature and phase change of specimens under near lunar atmospheric condition with more accura-cy; and (iii) heating specimens of lunar simulant rapidly to be sintered/melted. This first version of apparatus does not support multiple frequencies, however, this feature is planned to be added in a future upgrade.      Figure 2: Industrial bespoke microwave heating apparatus  Numerical Modelling:  While the actual exper-iment will be conducted as soon as the apparatus is installed in our lab, the experiment can also be sim-ulated with a numerical modelling method. We have chosen COMSOL Multiphysics software (ver-sion 5.3a) [5] which has been used previously for a similar purpose [6]. COMSOL requires various pa-rameters of material characteristics to simulate mi-crowave heating phenomenon. Most parameters of lunar simulants have been identified, e.g., Table 1 shows the required material properties of JSC-1A for COMSOL simulation.   Table 1: Minimal material parameters of JSC-1A needed for COMSOL simulation [6] Thermal conductivity k 0.35 W/m × K Specific Heat   Cp 0.85 KJ/Kg × K Density ρ  1.66 g/cm3  Electrical conductivity 𝜎 0 S/m Permittivity  εʹ– εʺ × j 4 – 0.1j Permeability µʹ – µʺ × j 1 – 0.01j  Initially, it was assumed that nanophase iron (np-Fe0) is key to facilitate microwave heating of lunar regolith [7], but later some experiments [8] revealed that np-Fe0 does not play a major role in microwave heating of lunar regolith under low magnetic field conditions and room temperature. The experiment led to another finding that the exist-ing lunar simulants have larger absorption caused by their dielectric properties rather than magnetic properties at room temperature [9] although the finding still needs to be validated at higher tempera-tures.  All existing experiments, however, do not report the dielectric properties of each simulant as a func-tion of temperature. Ideally, it would be best if we have these properties from cryogenic to the melting point of test materials in order to fully mimic the onsite fabrication on the lunar surface. As a starting point, we are measuring the dielectric properties of two lunar simulants JSC-1A and NU-LHT-3M and some powdered lunar meteorites from room temper-ature to 600, 800 and 950 °C; more temperature steps could be added depending upon the initial results guided by the available time and resources. The bulk density of JSC-1A powder was measured as 1.65~1.66 g/cm3 in [6, 9], however, we are mak-ing compacted pellets of simulants for which the bulk density of JSC-1A is around 2.07 g/cm3, ob-tained through our inital measurement of dielectric property of JSC-1A. Thus, the same value will be used for simulation.    Discussion:  Currently, we are creating a virtual cavity of the bespoke microwave apparatus in a COMSOL envi-ronment in order to conduct simulations of micro-wave heating in vacuum cavity with different mate-rials, density, temperature and frequencies. With the identified full set of material data, we will be able to model more thorough mechanism of microwave heating of lunar simulant under near lunar atmos-pheric condition. Expected findings from the planned numerical modelling are (i) verifying the bespoke design of the cavity that could maximise microwave energy to heat specimens; (ii) under-standing the sequence of sintering phenomenon by continual simulation of the surface and internal temperature of specimens; and (iii) identifying the different effects of sintering among frequencies in terms of the time and penetration depth.  The Open University has established three Stra-tegic Research Areas (SRA) one of which is Space. This has enabled us to integrate our existing exper-tise in 3D Concrete Printing [10, 11] and knowledge of lunar science and ISRU potential on the Moon [2] to perform a series of microwave sintering ex-periments aiming to develop a potential fabrication method of an extra-terrestrial construction process.  Acknowledgement: The authors acknowledge funding from the Open University’s Space SRA.   References:  [1] Lim, S., Prabhu V.L., Anand, M. and Taylor, L. (2017) Adv. in Space Research J., 60(7), 1413-1429. [2] Anand, M., et al. (2012). Planet. and Space Sci., 74(1), 42-48. [3] Ethridge, E. and Kauk-ler, W. (2012). Concepts and Approaches for Mars Exploration. [4] Crawford, I. (2015). Progress in Physical Geography, 39, 137-167. [5] http://www.comsol.com. [6] Ethridge, E. and Kauk-ler, W. (2012) 50th AIAA Aerospace Sci. Meeting, AIAA2012-0801. [7] Taylor, L.A. and Meek, T.T. (2005). J. of Aerospace Eng. 18(3), 188-196. [8] Barmatz, M.B., at al. (2011). 42nd Lunar and Plane-tary Sci. Conf., LPI. [9] Barmatz, M.B. et al. (2012). 43rd Lunar and Planet. Sci. Conf., LPI. [10] Lim, S., et al. (2016). Additive Manufacturing, 12(B), 216-230. [11] Lim, S., et al. (2012). Automation in Con-struction, 21(1), 262-268.  

Numerical modelling of microwave sintering of lunar simulants under near lunar atmospheric condition

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Numerical modelling of microwave sintering of lunar simulants under near lunar atmospheric condition

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