In Memoriam: Ernest G. Cravalho:
A Pathbreaker for Interdisciplinary Research in Thermal Science—Personal Recollections

Contributed by the Heat Transfer Division of ASME for publication in theJOURNAL OF HEAT TRANSFER. Manuscript received July 29, 2021; final manuscript
received August 11, 2021; published online January 18, 2022. Assoc. Editor: Ram
Devireddy.

Journal of Heat Transfer

willingness and capability to successfully enter new fields ofresearch or rather creating them.
Around 1990, when many of us graduated from Prof. Tien’s
group, the new field of microscale and later nanoscale heat transfer emerged, yielding tremendous benefits, more than 20 years
later after Ernie and Prof. Tien had been inspired for their researchby the problem of vacuum insulation of cryogenic systems.
Only four years after he had joined MIT as an assistant professor, Ernie once again entered a completely new field, part of heatand mass transfer in biotechnology, on which this issue of JHT isfocused. Together with Kenneth R. Diller, Ernie invented a cryomicroscope that made it possible to investigate freezing and thawing in biological cell suspensions between liquid nitrogen androom temperatures [8]. One year later, this experimental approachbore rich fruit: Ken Diller, Ernie, and C. E. Huggins were able toestablish precise boundaries for the cooling rates leading to intracellular ice formation in frozen human erythrocytes [9].
Rereading both papers today, I cannot help but be impressed by
the diligence of the design of the cryomicroscopic apparatus complete with an analog electronic temperature control built fromscratch. Ernie was both an accomplished theoretician and a gifted
experimentalist. In the latter, he was undoubtedly supported by thestrong craftsmanship tradition in the Cryogenic Engineering Laboratory. The second paper shows that Ernie and Ken Diller had to absorb
a vast body of literature on physicochemistry and the properties ofbiological tissues, which was completely new at least for Ernie.
One has to view the situation Ernie was in: As an assistant professor trying to get tenure, the natural approach would have been
to play it safe and continue to work in the field with which he wasfamiliar: cryogenic heat transfer in industrial applications.
When I asked Ernie what had driven him down this riskier path,
he told me that he always yearned to make positive and lasting
contributions to humankind and that he had felt at the time thatentering the biomedical field would be the most direct approachfor him, irrespective of the associated risks.
In this sense, Ernie was a true pathbreaker for many of us who
followed in his footsteps, branching out from heat transfer into–andthe list is far from complete–combustion science, thermal atomic
force microscopy, integrated electronic circuit design, infrared
spectroscopy, heat pipe design, laser analysis and design, nuclear
reactor safety, micro-electromechanical systems, etc. Had the heattransfer field not taken to this path of interdisciplinary research, itwould have become an auxiliary science to other disciplines likeelectrical engineering, aerospace, biotechnology, etc. Furthermore,
I am convinced that the Journal of Heat Transfer as our primaryarchival publication would not have the importance it has today.
Now, from an industrial vantage point, I do believe that we inthe mechanical engineering profession are at a similar juncture
today. The last decade has brought significant advances in data
science, artificial intelligence, and machine learning. Through theapplication of cloud native computing to dynamic control systems,
many industrial fields will be disrupted in the coming years. As
mechanical engineers, once again we must pay attention so that we
do not become an auxiliary field carrying out mechanical tasks
handed to us by the intelligence which is implemented in the algorithms developed by computer scientists. We as a profession mustembrace these new technologies and fuze them with our traditional
mechanical engineering disciplines, just as we did with mechatronicsystems, to create new know-how and applications. Systems designis the hallmark of mechanical engineering. Better than anybody, wemechanical engineers are able to affect real-world benefits based on
new algorithms or neural networks, e.g., in energy efficiency, climate protection, human health, and safety. But in order to achievethis, we must venture into data science just as Ernie ventured into
electrodynamic theory and cryobiology 50 years ago.

C 2022 by ASME
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I first met Ernie in the Fall of 1989, after I had joined the MIT
mechanical engineering department as an assistant professor. We
were assigned to coteach the undergraduate engineering thermodynamics course together with Prof. Joseph L. Smith, based on
the book Ernie and Joe had written about 20 years before.
Ernie had to go out of town at short notice, and the next day I
gave my first lecture in front of 200 impatient students expecting
to be taught by a seasoned professor and not by an inexperienced
guy just out of graduate school! But Ernie trusted me with this,and this was typical of him: He had full confidence in his students
and colleagues, and he showed many of us this trust clearly, which
I found most encouraging.
Ernie (1967) and I (1989) had both received our doctorates
working with Prof. Chang-Lin Tien, with 22 years in between, andErnie had been associated for some time with the Cryogenic Engineering Laboratory founded after the war by Prof. Samuel C. Collins and since 1964 lead by Joe Smith [1]. For Ernie, it was natural
to take me under his wings, and I have greatly benefited from ourassociation, which led to five papers we published together withthe students we cosupervised [2–6]. At that time, we investigatedthe optical properties of superconductors and semiconductors andthe design of devices made from these materials. In addition, Ernie
introduced me to his freshly minted Ph.D. student, Prof. Mehmet
Toner, who today himself is a pre-eminent figure in the biomedical
technology field and whose lifelong friendship I treasure.
Ernie was extremely dedicated to his students, both as a teacher
and a research supervisor. He and his first wife were also highly
engaged housemasters in one of MIT’s undergraduate dormitories.
He gave students his full attention, and they were able to reachhim almost any time. He deeply enjoyed his interactions withthem and drew great personal satisfaction from them.
What really set Ernie apart, however, was his courage and ability to enter entirely new fields based on his strong footing in heattransfer and thermodynamics.
Looking at the paper Ernie had written with Prof. Tien and R.P.
Caren in 1967 [7] based on his doctoral thesis, one can only marvel at the extent to which it was ahead of its time. At that moment,
the mechanical engineering profession had just started to absorb amuch deeper physical understanding in its curricula and engineering practice, in part driven by the tremendous progress inaerospace and other emerging high-tech industries, as well as
demanding defense technology applications. But the majority ofteaching, research, and engineering practice were based on continuum formulations of physical laws.
Most papers in heat transfer at that time dealt with rather traditional
engineering problems related to heat conduction, convection, phasechange, and, to a lesser extent, radiation, with a strong bias towardapplication and much less emphasis on physical fundamentals.
In contrast, Ernie’s paper stands out because it addresses deep
fundamental questions of radiative energy transfer in a situation
where the continuum-based Stefan-Boltzmann radiation law wasinadequate because the wavelength at liquid–helium temperatures
is of the same order of magnitude as the spacing of the dielectricsolids which were studied. This influenced the net energy transfer
through wave interference and radiation tunneling at spacings
below about three wavelengths.
Clearly, Ernie was influenced in this approach by Prof. Tien,
and many of my colleagues, I am sure, have Prof. Tien’s voice
still in their ears: “Go to the extremes—that is where you find new
research problems!” But it was Ernie who carried out the research,and he demonstrated later in his career many times over hisMarkus I. Flik
Flik GmbH,
Stuttgart 70176, Germany

030101-2 / Vol. 144, MARCH 2022

References[1] Smith, J. L., Jr., 2002, “50 Years of Helium Liquefaction at the MIT Cryogenic Engineering Laboratory,” AIP Conf. Proc., 613, pp. 213–224.
[2] Malone, C. G., Choi, B. I., Flik, M. I., and Cravalho, E. G., 1993, “SpectralEmissivity of Optically Anisotropic Solid Media,” ASME J. Heat TransferTrans. ASME, 115(4), pp. 1021–1028.
[3] Malone, C. G., Zhang, Z. M., Flik, M. I., and Cravalho, E. G., 1993,“Optimized Design of Far-Infrared Fabry-Perot Resonators FabricatedFrom YBa2Cu3O7,” IEEE Trans. Appl. Superconduct., 3(1), pp.
2852–2855.
[4] Hebb, J. P., Cravalho, E. G., and Flik, M. I., 1995, “Thermal Radiation
Absorption in Doped Semiconductors Due to Direct Intersubband Transitions,” ASME J. Heat Transfer-Trans. ASME, 117(4), pp. 948–954.
[5] Zhang, Z. M., Le, T. A., Flik, M. I., and Cravalho, E. G., 1994, “Infrared
Optical Constants of the High-Tc Superconductor YBa2Cu3O7,” ASME J.
Heat Transfer-Trans. ASME, 116(1), pp. 253–257.
[6] Malone, C. G., Whale, M. D., Flik, M. I., and Cravalho, E. G., 1993,“Performance of Widely Spaced High-Tc Superconductor Radiation
Shields,” ASME Paper No. 93-WA/HT-64.
[7] Cravalho, E. G., Tien, C. L., and Caren, R. P., 1967, “Effect of Small Spacings on Radiative Transfer Between Two Dielectrics,” ASME J. Heat
Transfer-Trans. ASME, 89(4), pp. 351–358.
[8] Diller, K. R., and Cravalho, E. G., 1971, “A Cryomicroscope for the Study ofFreezing and Thawing Processes in Biological Cells,” Cryobiology, 7(4–6),
pp. 191–199.
[9] Diller, K. R., Cravalho, E. G., and Huggins, C. E., 1972, “Intracellular Freezing in Biomaterials,” Cryobiology, 9(5), pp. 429–440.
[10] Whale, M. D., and Cravalho, E. G., 2002, “Modeling and Performance ofMicroscale Thermophotovoltaic Energy Conversion Devices,” IEEE Trans.
Energy Convers., 17(1), pp. 130–142.
[11] Whale, M. D., and Cravalho, E. G., 1997, “Analysis of the Enhancement ofThermal Radiation Between Closely-Spaced Surfaces Due to Microscale
Phenomena,” ASME HTD, 345(7), pp. 41–50.
[12] Whale, M. D., and Cravalho, E. G., 1997, “Regimes of Microscale Radiative
Transfer for Exchange of Thermal Energy Between Metallic Surfaces,”
ASME HTD, 345(7), pp. 65–72.
[13] MacBride, D. M., Malone, C. G., Hebb, J. P., and Cravalho, E. G., 1997,“Effect of Temperature Variation on FT-IR Spectrometer Stability,” Appl.
Spectrosc., 51(1), pp. 43–50.
[14] Malone, C. G., Cravalho, E. G., Johnson, T. J., and Jackson, R. S., 1998, “ATechnique for Measuring the Far-Infrared Radiative Properties of Metal andSuperconducting Thin Films,” AIP Conf. Proc., 430(1), p. 621.
[15] Whale, M. D., 2021, Personal communication.

Transactions of the ASME

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I do want to close these reflections on a personal note. When I
had to make the hardest decision of my professional life, i.e.,
whether to leave academia, MIT, and the collaborations with myesteemed colleagues for a new career in industry, Ernie supported
me. He stepped in and took over the supervision of my studentsJeffrey P. Hebb, Christopher G. Malone, and MacMurray D.
Whale, who would complete their master (J. P. Hebb, whoobtained his Ph.D. with Klavs Jensen) and doctorate degrees (C.
G. Malone and M. D. Whale) under his supervision. They worked
on microscale radiative transfer as well as on spectroscopy andother optical measuring techniques. Ernie took a great load off myshoulders and relieved me from the concern that my students, who
had come to my group expecting me to be there for them, would
suffer from a decision that I felt I had to take. Also, in this case,
Ernie demonstrated his devotion to the MIT students. I was happy
to see that their collaboration resulted in another five papers they
published together [10–14], and that these students had successfulcareers thereafter, just as the students whose research I supervised
completely myself.
Let me quote Mac Whale [15]: “His lasting legacy was in hisencouragement as a mentor and advisor … His insights still carryweight for me: Whether it’s why and how to do science, how to live
your life with meaning and intention, how to be an effective parent
and mentor students when I was an assistant professor myself, oreven now as a partner in an investment bank: it is people and relationships that matter most. I may have been taught that from my parents,
but it was Ernie who crystallized that to me as a young adult.”
As a teacher, a researcher, a research supervisor, and a humanbeing, Ernie Cravalho remains one of the most outstanding individuals I have come across.