Abstract
While temperature on the surface of a heat-generating solid body can be easily measured using a variety of methods, very few techniques exist for non-invasively measuring the temperature inside the solid body as a function of time. Measurement of internal temperature is very desirable since measurement of just the surface temperature gives no indication of temperature inside the body, and system performance and safety is governed primarily by the highest temperature, encountered usually at the core of the body. This paper presents a technique to non-invasively determine the internal temperature based on the theoretical relationship between the core temperature and surface temperature distribution on the outside of a heat-generating solid body as functions of time. Experiments using infrared thermography of the outside surface of a thermal test cell in a variety of heating and cooling conditions demonstrate good agreement of the predicted core temperature as a function of time with actual core temperature measurement using an embedded thermocouple. This paper demonstrates a capability to thermally probe inside solid bodies in a non-invasive fashion. This directly benefits the accurate performance prediction and control of a variety of engineering systems where the time-varying core temperature plays a key role.
Highlights
While temperature on the surface of a heat-generating solid body can be measured using a variety of methods, very few techniques exist for non-invasively measuring the temperature inside the solid body as a function of time
Development of a technique with similar capability for non-invasive internal temperature measurement will have a dramatic impact on performance, safety and reliability of engineering systems, each of which are directly affected by the peak temperature, which usually occurs at the core of the cell
Performance optimization of such systems, including Li-ion cells, is often carried out using surface temperature measurement, which may result in significant error, since surface temperature measurement gives very little indication of the core temperature, which may be much higher for heat-generating bodies
Summary
While temperature on the surface of a heat-generating solid body can be measured using a variety of methods, very few techniques exist for non-invasively measuring the temperature inside the solid body as a function of time. A process for aggressively discharging a 26650 Li-ion cell may complete within 6–15 minutes[9], whereas the thermal time constant for the cell is much longer[16] In such a case, the capability of determining the transient core temperature in a non-intrusive fashion will help make real-time decisions to improve performance, safety and reliability. Evolution of temperature of the body in time affects other physical parameters and processes, such as stresses, fatigue, etc.[17] For these reasons, it is very desirable to develop a method to determine the core temperature of a heat-generating solid body as a function of time in a contactless, non-intrusive fashion
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