Computer-aided engineering facilitates product development.

Current product and process design is characterized by several factors, including the need to reduce cost and time to market. Design engineers and scientists traditionally construct a physical prototype and test it in the laboratory. But these prototypes have many major drawbacks. They usually are expensive to build and modify, and by their very nature lead to lengthy design cycles. Often, repeatability can be difficult to achieve, since the prototype goes through irreversible changes during testing and usually has to be discarded. In addition, dramatic changes can be harder to conceive.

To streamline the building of physical prototypes, engineers in the past have used simplified physical models and handbook calculations. Such calculations are reasonably quick, but many simplifying assumptions make the results imprecise and of limited applicability.

Computer prototyping is emerging as an alternative to handbook calculations and physical prototyping. In computer prototyping, you build a model that is as close to the physical model as possible. An accurate computer model works like a physical prototype, but its engine is mathematical rather than physical. The model entails solving partial differential equations that precisely describe the physics of the model. Applications for computer modeling include the freezing and thawing of products, the canning of liquid and solid foods, the continuous sterilization of liquids, extrusion and various moisture transfer processes.

Some food processes have been modeled for research purposes in the past. Computer prototyping offers several advantages. The technique provides quick and inexpensive testing of experimental scenarios. This can shorten the design cycle and provide quicker turnaround, leading to reduced costs. The technology can provide insight into complex processes otherwise difficult to understand. In ohmic heating, for example, temperature, voltage and species distributions inside the tube are nearly impossible to determine experimentally, but they can be obtained routinely using a computer model. Computer prototyping provides a clearer understanding of the interactions between physical processes and various operational parameters. This allows the designer to be more creative.

It allows front-end engineering to occur before prototyping, making the prototypes better and reducing their number. It makes possible concurrent design and analysis, shortening the design cycle. While an experiment is underway, results can be used simultaneously to further optimize the process.

Food processes have many unique aspects that make them ideal for modeling. In addition to the temperature changes during heating or cooling, there are biochemical (nutrient, color, flavor) or microbial changes that are important to know about. The moisture in food is constantly undergoing either loss (due to evaporation, especially when heated) or gain (from humid surroundings). The properties of foods, such as density, thermal and electrical conductivity, specific heat, viscosity, permeability and effective moisture diffusivity, are often a function of composition, temperature and moisture content. They keep changing during processing.

While computer modeling and simulation may speed the prototyping and product development process, they cannot substitute for real-life knowledge of the subject. Many such software programs do not contain their own intelligence to determine if a computation is physically reasonable.

Further information. Ashim Datta, Cornell University, Department of Agricultural and Biological Engineering, Riley-Robb Hall, Ithaca, NY 14853; phone: [phone]; fax: [phone]; email: [e-mail].