Heat Transfer in Surface-Cooled Objects Subject to Microwave Heating

Several investigators in microwave bioeffects research have exposed biological preparations to intense microwave fields, while at the same time cooling the sample with flowing water. We examine the heat transfer characteristics of this situation, to estimate the maximum temperature increase and thermal time constants that might be encountered in such an experiment. The sample is modeled as a uniform sphere, cylinder, or slab subject to uniform heating, which is located in an unbounded coolant flow. The heat transfer is determined by the Biot and Reynolds numbers (which reflect the geometry, fluid flow, and material thermal properties of the system) the temperature rise is governed by the heat conduction equation coupled with external convection. The results are expressed in terms of nondimensional quantities, from which the thermal response of a heated object of arbitrary size can be determined. At low coolant flow rates, the maximum temperature rise can be biologically significant, even for relatively small objects (of millimeter radius) exposed to moderate levels of microwave energy (with a SAR of ca. 100 mW/g). The results are valid also where the coolant is a gas or a liquid different from water, the only restriction being on the Reynolds number of the flow. Disciplines Engineering | Mechanical Engineering Comments Suggested Citation: Foster, Kenneth R. et al. (1982) Heat transfer in surface-cooled objects subject to microwave heating. Transactions on Microwave Theory and Techniques. Vol. 30(8). p. 1158-1166. "©1982 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE." This journal article is available at ScholarlyCommons: http://repository.upenn.edu/meam_papers/188 1158 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, vOL. MTT-30, NO. 8, AUGUST 1982 Donald L. Morton, Professor of Surgery and Chief, Divisions of Surgical Oncology and General Surgery, is a graduate of the University of California School of Medicine, San Francisco. As a young medical student at the University of California, he became interested in the newly emerging science of cancer, particularly in the clinical application of immunology to cancer treatment and diagnosis. Following his internship and residency, he joined the National Cancer Institute, Bethesda, MD, where he became Head of the Tumor Immunology Section and Senior Surgeon of the Surgery Branch. There, he performed extensive studies and developed his ideas of immunotherapy, and made a number of important contributions which helped advance the knowledge of the role of the immune system in the body’s defense against cancer. In April, 1971, he came to UCLA and founded the Division of Surgical Oncology at the UCLA School of Medicine. Today, both the doctor and the Division are best known for work in the development and application of immunotherapy involving the stimulation of patients’ immune responses as a treatment for cancer. Dr. Morton is a recognized leader in the field of immunotherapy and has published almost 300 papers and articles advancing the knowledge of cancer, including malignant melanoma, lung cancer, bone and soft tissue sarcomas, breast cancer and colon cancer, Heat Transfer in Surface-Cooled Objects Subject to Microwave Heating KENNETH R. FOSTER, SENIOR MEMBER, IEEE, PORTONOVO S. AYYASWAMY, THIRUMALCHARI SUNDARARAJAN, AND KONERU RAMAKRISHNA Abstract — Several investigators in microwave bioeffects research have exposed biological preparations to intense microwave fields, while at the same time cooling the sample with flowing water. We examine the heat transfer characteristics of this situation, to estimate the maximum temperature increase and thermal time constants that might be encountered in such an experiment. The sample is modeled as a uniform sphere, cylinder, or slab subject to uniform heating, which is located in an unbounded coolant flow. The heat transfer is determined by the Biot and Reynolds numbers (which reflect the geometry, fluid flow, and material thermal properties of the system) the temperature rise is governed by the heat conduction equation coupled with external convection. The results are expressed in terms of nondimensional quantities, from which the thermal response of a heated object of arbitrary size can be determined. At low coolant flow rates, the maximnm temperature rise can be biologically significant, even for relatively small objects (of millimeter radius) exposed to moderate levels of microwave energy (with a SAR of ca. 100 mW/g). The results are valid also where the coolant is a gas or a liquid different from water, the only restriction being on the Reynolds number of the flow. Several investigators in microwave bioeffects research have exposed biological preparations to intense microwave fields, while at the same time cooling the sample with flowing water. We examine the heat transfer characteristics of this situation, to estimate the maximum temperature increase and thermal time constants that might be encountered in such an experiment. The sample is modeled as a uniform sphere, cylinder, or slab subject to uniform heating, which is located in an unbounded coolant flow. The heat transfer is determined by the Biot and Reynolds numbers (which reflect the geometry, fluid flow, and material thermal properties of the system) the temperature rise is governed by the heat conduction equation coupled with external convection. The results are expressed in terms of nondimensional quantities, from which the thermal response of a heated object of arbitrary size can be determined. At low coolant flow rates, the maximnm temperature rise can be biologically significant, even for relatively small objects (of millimeter radius) exposed to moderate levels of microwave energy (with a SAR of ca. 100 mW/g). The results are valid also where the coolant is a gas or a liquid different from water, the only restriction being on the Reynolds number of the flow.