Heat transfer enhancement in rotary drum dryer by incorporating jet impingement to accelerate drying rate

Abstract

The purpose of this study was to investigate experimentally the effects of impinging jets installed in a conventional rotary dryer for heat transfer enhancement. The metal drum had as insert a jet tunnel at the centerline, and the jets were arranged in an in-line configuration on the jet tunnel. A jet-to-jet (S) and a jet-to-target (H) distances were fixed at S/d = 6 and H/d = 4, respectively. Jet velocity (V_j) was set at V_j = 5, 10 and 15 m/s, while jet temperature (T_j) was 70, 80 or 90 °C. Drum rotation speed (N) was also investigated at N = 0.5, 1, and 3 rpm. The conventional rotary dryer was examined at the same mass flow rate of hot air to compare with the case having impinging jets. All experiments were conducted by batch drying 5 kg of fresh chilies for 8 hours. Results showed that installing jets gave more effective heat transfer, which accelerated water removal over that with the conventional rotary dryer, and the moisture contents were greatly reduced. On using impinging jets, the jet temperature had more influence on heat transfer enhancement than the jet velocity. In comparison, the effect of drum speed was small.

Keywords:

• Rotary drum dryer
• jet impingement
• heat transfer enhancement
• drying

Acknowledgments

We thank Assoc. Prof. Dr. Seppo Karrila for proofreading and editing the manuscript with publication service of Research and Development Office (RDO), Prince of Songkla University (PSU).

Additional information

Funding

This work was supported financially by the Energy Policy and Planning Office (EPPO), Ministry of Energy, Thailand, grant No. MCh. 61-EE 001/02.