Augmenting the thermal flux experiment: a mixed reality approach with the HoloLens

M. P. Strzys,1 S. Kapp,1 M. Thees,1 P. Lukowicz,2 P. Knierim,3 A. Schmidt,3 and J. Kuhn1

1Department of Physics, Physics Education Group,University of Kaiserslautern, D–67653 Kaiserslautern, Germany

2DFKI, Embedded Intelligence Laboratory, Trippstadter Str. 122, D–67663 Kaiserslautern, Germany3VIS, University of Stuttgart, Germany

This article may be downloaded for personal use only. Any other use requires prior permission ofthe author and AIP Publishing.The following article appeared in The Physics Teacher 55, 376 (2017) and may be found atdoi: http://dx.doi.org/10.1119/1.4999739

In the field of Virtual Reality (VR) and AugmentedReality (AR) technologies have made huge progress dur-ing the last years [1–3] and also reached the field of ed-ucation [4, 5]. The virtuality continuum, ranging frompure virtuality on one side to the real world on the other[6] has been successfully covered by the use of immersivetechnologies like head-mounted displays, which allow toembed virtual objects into the real surroundings, leadingto a Mixed Reality (MR) experience. In such an envi-ronment digital and real objects do not only co-exist,but moreover are also able to interact with each otherin real-time. These concepts can be used to merge hu-man perception of reality with digitally visualized sensordata and thereby making the invisible visible. As a firstexample, in this paper we introduce alongside the basicidea of this column [7] an MR-experiment in thermody-namics for a laboratory course for freshman students inphysics or other science and engineering subjects whichuses physical data from mobile devices for analyzing anddisplaying physical phenomena to students.

THEORETICAL BACKGROUND

The paradigm experiment for heat conduction in met-als can be realized with a metallic rod, heated on one sidewhile simultaneously cooled on the other [8]. Our setupallows to observe the heat flux through the rod, directlyon the real physical object, using a false-color representa-tion. Moreover, also additional representations as, e.g.,graphs and numerical values, can be included as digi-tal augmentations to the real experiment, allowing for ajust-in-time evaluation of physical processes.

If the rod is perfectly isolated, after some equilibrationtime the system will reach a steady state with a hot endat temperature T1, a cold end at temperature T2, and aconstant spatial gradient along the rod axis, which allowsto calculate the thermal conductivity constant λ of thematerial according to

λ =L

A (T1 − T2)Q, (1)

if the constant heating power Q and the dimensions, i.e.length L and cross-section A, of the rod are known. Here

it is assumed that the full heating power Q applied tothe warm end of the rod will be removed on the cold endby cooling.

If the rod is not isolated, it moreover is possible tocalculate the loss of heat to the environment accordingto h = α2λAL, using the decline factor α extracted froman exponential fit to the experimental data [9].

EXPERIMENTAL DESIGN

Our heat conduction experiment consists of cylindri-cal metal sample rods with a length of L = 26 cm anda diameter of d = 5 cm made of Aluminum and Copper,respectively (cf. Fig. 1.b). The sample is heated at oneend with a cartridge heater and cooled at the other by astandard CPU fan. The isolated version moreover has aPVC insulation layer with a 3 mm slit along the rod, toallow for thermal imaging of the rod inside (cf. Fig. 1.c).The temperature data finally is extracted from thermalimages taken with an infrared camera placed in front ofthe sample. Each pixel of the image along a fixed line inaxial direction yields one temperature value, such thatthe whole spatial distribution can be captured by a singleshot. The data is then passed to the Microsoft HoloLensvia WiFi, where the visualization is done. In the currentstate, an App provides three different representations ofthe data: false-color image of the temperature values pro-jected as “hologram” [10] directly onto the sample cylin-der, numerical values at three pre-defined points and atemperature graph as a function of the position along therod hovering above the setup, cf. Fig. 1.a. The user mayswitch the numerical and graph representation on and offat will; moreover, it is possible to export the data as csv-file at any time for later analysis. These functions can beexecuted with the help of virtual buttons (cf. the threewhite squares in Fig. 1.a) projected at the right end ofthe rod which can be selected by the gaze and triggeredby hand gestures.

The benefit of the MR-experiment setup is the possibil-ity of keeping track of the real physical devices and repre-sentations of the data simultaneously and in real-time asthe representations are continuously updated with new

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FIG. 1: a) Experimental setup (non isolated) with MR ex-perience; augmented representations: false-color representa-tion of temperature along the rod, numerical values at threepoints above the rod, temperature graph; b) Experimentalsetup (non isolated) and user wearing a HoloLens; c) isolatedsetup

data from the camera. The false color representations al-lows to experience an otherwise invisible quantity, like inthis case temperature, with human senses, thus extendingperception to new regimes. Furthermore, direct feedbackis implemented, such that students get an immediate im-pression of effects of the experimental parameters.

EXPERIMENTAL RESULTS

The exported data can be analyzed using standardinstruments like spreadsheet programs. In the isolated

R2 = 0.9938T(x) = ax + T1

T1 = 74.76 Ka = − 199.61 K m

Al − isolated

30

40

50

60

70

0.00 0.05 0.10 0.15 0.20x−Position / m

T /

°C

a)

R2 = 0.9974T(x) = ax + T1

T1 = 42.03 Ka = − 77.44 K m

Cu − isolated

25

30

35

40

0.00 0.05 0.10 0.15 0.20x−Position / m

T /

°C

b)

R2 = 0.9953T(x) = T0 + (T1 − T0)eαx

T1 = 77.68 Kα = − 3.69 m−1

Al − non isolated

40

50

60

70

80

0.00 0.05 0.10 0.15 0.20x−Position / m

T /

°C

c)

R2 = 0.9964T(x) = T0 + (T1 − T0)eαx

T1 = 61.41 Kα = − 4.29 m−1

Cu − non isolated

40

45

50

55

60

0.00 0.05 0.10 0.15 0.20x−Position / m

T /

°C

d)

FIG. 2: Temperature graph after equilibration and linear fitfor an isolated Al-rod (a), Cu-rod (b); Temperature graphafter equilibration and exponential fit for a non-isolated Al-rod (c), Cu-rod (d).

case, the problem reduces to a linear fit of the temper-ature graph, yielding the slope and thus, with the helpof the constant heating power Q = 50 W used in the ex-periments via (1) the thermal conductivity constant λ.In our tests (see Fig. 2.a,b) the isolated setup yielded avalue of λAl = (128 ± 11) Wm−1K−1 for the Aluminumrod and λCu = (329 ± 27) Wm−1K−1 for the Copperrod. As expected, due to the non perfect isolation ofthe samples, these values are smaller than the referencevalues found in literature, λAl,lit = 235 W/(m K) and

λCu,lit = 401 W/(m K), as the effective heat flux Q alongthe rod is reduced by loss to the environment.

With the help of the non-isolated rod the heat trans-fer coefficient h can be determined using the exponentialdecline factor α (see Fig. 2.c,d) yielding hAl = (0.72 ±0.01) WK−1 and hCu = (2.5 ± 0.01) WK−1, respectively.These values are also underestimated for the same rea-sons, however, compared to hAl,lit = (1.32± 0.01) WK−1

and hCu,lit = (3.05 ± 0.01) WK−1, where the literaturevalues for λ were used, they are reasonable regarding thevery simple insulation of the setup.

CONCLUSION

The MR experimental setup for a thermal flux exper-iment presented here, sheds new light on an experimentwell known in physics laboratory courses. The main fo-cus of this design is to visualize the invisible and thusto extend human perception to new regimes, e.g., tem-perature and heat, thereby strengthening the connectionbetween theory and experiment. In this realization theMR setting not only has the advantage of intrinsic con-

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textuality, but also spatial and time contiguity which issupposed to support the learning process of the students[11, 12]. Moreover, the just-in-time evaluation of the datayields the possibility for the students to directly examinethe process itself and the parameter involved, and imme-diately compare the outcome to theoretical predictionswhich we believe to enhance the links between theory andexperiment. Under that perspective the effort to achievepossibly more exact numerical values for quantities likethe thermal conductivity therefore seem to be less impor-tant in this setting. Instead, the technical support duringthe experimental phase will give students the possibilityto thoroughly examine the relationship between causeand effect and thus deepen their physical understanding.

Support from the German Federal Ministry of Educa-tion and Research (BMBF) via the project “Be-greifen”[13] is gratefully acknowledged.

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[8] J. E. Parrot and A. D. Stuckes. Thermal Conductivity ofSolids. Pion Limited, London, 1975.

[9] See additional online material for a derivation and moredetailed discussion.

[10] The HoloLens does not actually use interference-basedholograms but rather projections to the transparenthead-mounted displays of the device. However, the termhologram is used by the manufacturer to describe these.

[11] M.L. Crawford. Teaching contextually: Research, ratio-nale, and techniques for improving student motivationand achievement in mathematics and science. CORDComm, 2001.

[12] R. E. Mayer, editor. The Cambridge Handbook of Multi-media Learning. Cambridge University Press, 2010.

[13] https://www.physik.uni-kl.de/kuhn/

forschungsprojekte/aktuelle-projekte/

be-greifen/