Online Calorimetry
In the kitchen, there are many methods that come down to simple thermodynamics. When deciding how long to bake a cookie, it works reasonably well to start by considering a single dimension - the thickness of the cookie. However, what if you wanted an arbitrarily shaped cookie, with varying thickness? If you've ever tried this, you'll know that this is very difficult to do in a conventional oven, and have probably resorted to building the final product from normal, flat, pre-baked cookies, glued together with frosting.
The design and manufacture of composite material parts (i.e. carbon fiber reinforced polymers CFRP for aircraft) has similar issues. Many of the polymer matrices used in CFRP require curing temperatures that are reached by placing parts inside large ovens. Since it is possible to over-cure areas of the material, this restricts the geometry of the parts to similar dimensions in thickness. For structural reasons, the industry is searching for a process that allows this constraint to be removed. Online Calorimetry presents a potential solution, by replacing the oven with a conformable blanket of heaters and sensors that locally manage the curing process.
Back in the kitchen, this would mean being able to sculpt a cookie of any shape, cover it in a flexible array of heaters/sensors, and have it all get perfectly cooked.
Current industry leading fiber composite manufacturing processes require large investments in both manufacturing time and infrastructure. The commercial aerospace industry is moving towards aircraft designs that have fewer but larger individual fiber composite parts. Conventional manufacturing processes have scaled up, accordingly, which requires molds/tooling (for defining the shape of the part), and ovens/autoclaves (for polymer matrix curing) that are large enough to require new kinds of buildings to contain them. This conventional process involves heating of inhomogeneous parts as slowly as is predicted to be necessary, for the most difficult section of the part, resulting in excess energy expenditure on the rest of the part.
Online Calorimetry provides a solution to these problems that involve integration of heating and sensing into the molds/tooling, and customizing the process across the part with distributed closed loop control. This can reduce time and expense for any manufacturing method involving exothermic or endothermic processes. The vision is to replace the conventional autoclave with active tooling, allowing greater flexibility of part sizes and shapes, robust and adaptive control over cure characteristics, and increased energy efficiency in the production process. The Online Calorimeter consists of a network of very simple discrete units, with low cost per unit, which makes them good candidates for trivial adaptation to various processes for various materials at any scale. Conventional cure sensing technologies (such as dielectric cure monitoring) are very expensive and many, ironically, affect the structural characteristics of the part. Both of these attributes limit the ability to apply them in a distributed manner. Calorimetry, on the other hand, simply monitors the ability of a material to absorb heat, which changes significantly for many materials in manufacturing processes.
Part of the beauty of the Online Calorimeter is the ability to take advantage of the physical properties of certain materials in order to have them perform multiple functions. For example, when producing carbon fiber composite parts, the structural carbon fiber itself may be used as heating elements and temperature detectors, by switching back and forth between modes. This is currently being developed for heating and cure sensing of thermoset polymer resins for aerospace applications, but can have wide ranging applications, such as efficient low-cost fire-proof food cooking devices (that also makes foods that are perfectly cooked, to order!). An egg cooking prototype is shown on the right hand side of the image, above. This invention has been submitted for US and international patents, and ongoing work is in collaboration with Nadya Peek (MIT CBA) and Neil Gershenfeld (MIT CBA), with support from industry partner Spirit Aerosystems. Additionally, this is the subject of a forthcoming paper.