I am encouraging those individuals who knew Professor Leidenfrost from Purdue University to contribute to this web site, by adding short stories about their memories and encounters with Him. For example, such things like jokes, special moments with his students and similar other occasion. Thank you very much.
I met Professor Dr. Wolfgang Leidenfrost for the first time in July 1975 when I was admitted, as a foreign student, to Purdue University. This was the Master of Science program in Mechanical Engineering offered through the School of Mechanical Engineering.
Dr. Ray Cohen, Director of the Ray W. Herrick Laboratories at Purdue, introduced me to Professor Leidenfrost, a full professor in the Mechanical Engineering Department, Heat Transfer Division. After we got acquainted, Ray asked me if I was interested in assisting Professor Leidenfrost with completing a sponsored study that had to be finished by the end of the year.
I accepted the offer to work with Professor Leidenfrost, and for the next 6 months we worked together to finish this project. At first, I had some difficulty understanding him because of our different accents. My accent was Serbo-Croatian and his was German. After a bit of time, this was not a problem anymore. As it turned out, we worked very well together. While conducting my calculations related to this project, we would meet every other week to review my progress. I highly appreciated his remarks and was able to quickly incorporate them in the calculations. We were working on an optimization of a refrigeration system for cooling a battery powered vehicle.
During this time, I learned a lot about Professor Leidenfrost, both from him directly and from our peers. For example, he did not like to be called “Wolf”. He preferred to be called by his full title, “Professor Dr. Wolfgang Leidenfrost”, but to all his colleagues he was simply Wolf since the common practice in the USA was to use nicknames. I could never tell if this was another one of his little jokes, or he really meant it. I always called him “Dr. Leidenfrost”, which he did not mind at all.
In time, I learned that he had a wife named Waltraud, whom he called “Walli”. They had a son named Klaus who was, I think, one year younger than me and who was at that time, I believe, a student of Forest Engineering.
I had originally selected another faculty member as my major professor when I arrived to Purdue in June 1975. After completing work for Professor Leidenfrost, I started working on my M.S.M.E. research project. I dropped this project after 8 months for personal reasons. It looked like I was going to have to continue with my master’s program without the thesis option. But then, guess what happened next!?
One day in August of 1976, Dr. Leidenfrost came to see me at the Ray W. Herrick Laboratories, where I had an office. He told me that he had a funded project that could still result in thesis work for me. We set down and reviewed his proposal. I liked the idea very much and accepted it shortly thereafter. The source material was associated with the early work of Professor Dr. Fran Bosnjakovic. I was familiar with his work because, at the University of Belgrade, his Technical Thermodynamics book was used as reference material to teach the Thermodynamics II course.
Professor Leidenfrost was interested in a specific part of this textbook, dealing with evaporative cooling and the stepwise method of solving heat and mass transfer problems in the presence of thin water films on outside surfaces of the refrigerant condensers. He wanted me to explore theoretical ideas from that book and extend them creatively for practical engineering usage. My tasks also included related computational modeling suitable for practical industrial applications for sizing and rating evaporative condensers.
At this time, I worked closely with Professor Leidenfrost and we were very productive. We successfully completed this initial project in summer 1977, as described in my M.S.M.E. thesis, which I then successfully defended in August 1977. After my M.S.M.E. graduation, Professor Leidenfrost encouraged me to stay at Purdue University and continue working toward a Ph.D. degree. Thanks to his encouragement and my determination, I did stay, and in December 1980 I successfully defended my Ph.D. thesis which was also related to evaporative cooling technologies.
Our work together was so good that we obtained very close correlations between measured and theoretically predicted results from a test apparatus we put together at the Heat Transfer Laboratory in the Mechanical Engineering Building. Professor Leidenfrost had what it took to be both an exceptional engineer and educator: the sense of what is right, and what it takes to mathematically describe real-world technical processes.
During my years at Purdue, I also got to know Dr. Leidenfrost’s beloved wife Walli, who was always nice to me. On many holidays the Leidenfrosts used to invite his graduate students to their home for dinner. I appreciated their efforts during these holiday seasons since I and most of his students were from other countries.
Upon my graduation, we put together a paper related to my Ph.D. thesis and devoted it to Professor Dr. Fran Bosnjakovic for his 80th Birthday. While working with him, I learned that Dr. Leidenfrost authored and co-authored over 100 publications and reports in mechanical engineering, both in the United States and Germany. He also received the Senior U.S. Scientist Award from the Humboldt-Stiftung Foundation in 1977 and 1985.
Professor Leidenfrost was known for his wonderful sense of humor, genuine warmth and great concern for his students. He was never short of ideas and new concepts to try, which could have taken his students many lifetimes to explore. He was very enthusiastic about science and engineering, and he possessed a German sense of accuracy and engineering excellence.
All his students, whom I knew, were very motivated to work with him because he treated them with dignity and at the same time gave them precious scientific knowhow. There were stories about Professor Leidenfrost, I heard from other professors, about a one-of-a-kind thermal physical properties measurement facility built in the ground floor of the Mechanical Engineering Building. It had the ability to measure such properties simultaneously, to ultimate precision. Many thought he would be remembered based on those measurements, more than anything else he had ever done. I believe this to be true to an extent, but wanted to mention that our research on evaporative condensers also produced theoretical results which were very closely approximated to those measured in the laboratory.
Our success with evaporative condenser research was so significant that I was hired upon my graduation by one of the major evaporative cooling companies of a global character. With skills and knowledge gained during my training with Dr. Leidenfrost, I was able to do research and write custom software for all types of closed-type evaporative cooling towers and condensers with the ability to predict their thermal performances under various operating conditions within recognized measurement errors in this kind of industry of +/- 5%.
I stayed in close touch with Dr. Leidenfrost after I left Purdue in December 1980. We wrote several papers together, which were published both in the USA and abroad. For example, we published some results from my M.S.M.E. thesis in Waerme- und Stoffubertragung 12 (1979) pp. 5-23, and others from my Ph.D. thesis in Heat Transfer Engineering, Volume 3, Numbers 3-4, Jan.-June 1982. We also wrote Chapter 33, “Principles of Evaporative Cooling and Heat Transfer Augmentation” in The Handbook of Heat and Mass Transfer, Gulf Publishing Company, 1986. We also published another paper in Energy, vol. 5 (1980), pages 47-61, entitled, “Analysis of Evaporative Condensers by the Second Law of Thermodynamics.”
In 1991, I visited the Leidenfrosts with my wife and daughter when she was just two years old. Though this visit was just for one afternoon, it is a memory that I cherish. I also saw him several times later when I visited Purdue University during the years I spent working in the industry.
One day, I believe it was in 2006, I got a phone call from Dr. Leidenfrost while I was at work. Our previous phone conversations were typically work related with a tone of background humor – all on a positive note. This one was not. He paused for a moment, and then said, “Branko, I was diagnosed with brain cancer.” This was the last thing I expected to hear from him.
One year later, I received a message from Professor Ray Cohen that Dr. Leidenfrost had passed away on July 8, 2007 peacefully at his home in West Lafayette, Indiana – located on Purdue University grounds. His wife Walli passed away two years later, in 2009.
Dr. Leidenfrost will always have a special place in my memory, both as my major professor and my friend. I am honored that I was his graduate student, and that he was my mentor during the 5-1/2 years I spent at Purdue University. Thanks to him, I specialized in evaporative cooling for closed-type industrial cooling towers and evaporative condensers applications and stayed in this business for my entire career. I think he would have been proud to know how much I contributed to the field he proposed to me for my graduate studies.
Branislav Korenic, Ph.D.
President, Korenic Engineering Consulting, LLC
Columbia, Maryland
