Here are web sites with specific heat of some foods, and general solids. If you don’t find your product there, try a google search for “specific heat” and the name of your product. The metric conversion is easy: 1 cal/g-°C = 1 kcal/kg-°C = 1 BTU/lb-°F!
The equilibrium temperature is a thermodynamic limit; it’s simple arithmetic. Predicting how close a particular system will come to equilibrium is a more complicated question of heat transfer. The heat transfer consists of two parts: conduction, which depends upon the thermal conductivity and size of the conveyed product particles, and convection, which depends on the turbulence and the difference between air and product velocity.
Systems that convey moist product with warm air are influenced by evaporative cooling. When moist product (such as flour) is heated, it’s equilibrium moisture content is lowered. When some of the product’s moisture content evaporates, it absorbs a whopping 1000 BTU per lb …compare that to flour’s 0.38 specific heat! For this reason, systems that convey moist product with warm air have much lower equilibrium temperatures than those conveying dry product.
In general, these factors will cause a system to get closer to equilibrium:
- Less product, more air
- Longer pneumatic conveying line, with more elbows and vertical-up
- Smaller diameter pneumatic conveying line
- Smaller product particles
- Smaller initial temperature difference
