In the interests of competitiveness, manufactures of tumble dryers are seeking to reduce both their electricity use and the drying time. This study examines how the cylinder volume of the compressor and the total heat transfer of the condenser influence the drying time and electricity use in a heat pump tumble dryer. A transient simulation model was developed and compared to an experimental set-up with good similarity. The simulations show that increasing the cylinder volume of the compressor by 50% decreases the drying time by 14% without using more electricity.

The results presented in this paper show the possibility to control the outgoing moisture content using the exhaust temperature as a control parameter. A model for heat exchange is used to support visual observations of the spouting quality in the bed. The model is also used in a discussion about the heat and mass transfer coefficients. Two efficiency concepts are defined and experimental results presented. The temperature efficiency is used to present the possibility to integrate a steam dryer into energy systems such as boilers and heat sinks. Energy efficiency is used to show the variation of the recoverable heat and to point out suitable outgoing moisture contents for steam dryers. It is important to keep the temperature after the dryer as low as possible in order to achieve a high temperature efficiency. It is also shown that energy efficiency improves with decreasing outgoing moisture content and increasing inlet steam temperature.