Torkningshastighet

Torkningshastighet, a Swedish term meaning drying rate, refers to the speed at which moisture is removed from a material or product. It is typically expressed in terms of mass loss per unit time, such as kilograms of water per kilogram of dry material per hour (kg / kg · h) or weight percent per hour (% / h). The measurement can also be reported in terms of the change in moisture content with respect to time.

The drying rate is influenced by several interrelated factors. Thermal energy supplied to the material increases molecular motion and evaporation rate, while the temperature and humidity of the surrounding air determine the moisture gradient that drives diffusion. The geometry and size of the material, its porosity, and its initial moisture distribution also affect how quickly water can be transported to the surface. Additionally, mechanical agitation or turbulence in the drying medium can enhance mass transfer by reducing the thickness of the boundary layer around the material.

In practical applications, controlling the drying rate is essential for product quality and process efficiency. Rapid drying can trap undesirable compounds or cause thermal degradation, whereas overly slow drying may lead to product spoilage or contamination. Industries such as food processing, pharmaceuticals, and construction materials routinely monitor and adjust drying rates to optimize product attributes such as texture, durability, and shelf life.

The relationship between drying rate and time is often described by dryer curves, which plot moisture content against elapsed time. From these curves, engineers derive drying constants and model the drying process using lumped-capacity or differential equations. Accurate estimation of drying rates is also crucial for energy balance calculations and economic assessments of drying equipment.