DEVELOPMENT OF A RANGE OF HEAT PIPE HEAT RECOVERY HEAT EXCHANGERS FOR THE DRYING INDUSTRY

1. DEVELOPMENT OF A RANGE OF HEAT PIPE HEAT RECOVERY HEAT EXCHANGERS FOR THE DRYING INDUSTRY Presented by: N.S Thomas Department of Mechanical and Mechatronic Engineering, University of Stellenbosch Private Bag XI, MATIELAND 7602, South Africa Tel: 083 484 2893 Email: 15818705@sun.ac.za Energy Postgraduate Conference 2013

2. Agenda • Background • Motivation and Objectives of the Project • Heat pipes / thermosyphons • Air driers • Heat pipe heat recovery heat exchanger • Thermal modelling of a Heat pipe • Thermal modelling of an Air drier • Thermal modelling of a Heat exchanger • Computer program algorithm • Future work • Questions????

3. Background: Why energy recovery? Sensible Total (sensible and latent) Temperature and moisture Enthalpy wheels Pros: high face velocities (compact size), low pressure drop, sensible and latent Cons: moving parts, cross contamination Effeciency: 55% - 85% • Energy effeciency, minimising input energy to overall system by exchanging energy from one subsystem to another • Subsystem 1: Waste fluid stream => low grade energy source • Subsystem 2: Incoming stream => preheated • Different devices • Temperature only • Heat pipes, run-around-loop, plate and membrane • Pros: no moving parts, no cross contamination, various orientations • Cons: sensible only, frost control • Effeciency: 50 % – 80 %

4. Motivation and Objectives of the Project • Globally increasing demand for energy savings • HPHRHE’s are simple devices and easy to integrate into any system • Packaging the HE and the air drier as an unit, avoiding retrofitting • Illustrate that the HE can be effectively used in an industrial application • Investigate the effects of packaging the HE and air drier as a unit

5. Heat pipes/ thermosyphons Operation Thermosyphon Heat pipe • Closed evaporator-condensor passive heat pump • Hot waste fluid stream heats and boils liquid in evaporator section • Vapour and heat convected upwards by wick (heat pipe) or gravity (thermosyphon) • Cold incoming stream heated by condensing vapour in condensor section • Cycle repeats • Rate of heat transfer altered by adjusting tilt angle Pictures adapted from A. Meyer, 2003

6. Air dryers Operation Tray dryer • Dependant on material, nature of production, method of energy supply, cost • Material heated to temperature so that pvl(material) exceeds pvl(ambient) • Volume of air exchanged as needed Oven tray dryer Pictures adapted from A. Meyer, 2003 and http://www.google.com

7. Heat pipe heat recovery heat exchanger Operation Commercial HPHRHE’s • HPHRHE is just a bundle of heat pipes • Pipes can be in-line or staggered, like other heat exchangers • Pipes can be finned or unfinned individually or in a bundle • Has supporting structure which can be bolted to adjacent parts Pictures adapted from A. Meyer, 2003 and http://www.heatpipes.co/Heat-Exchanger.html

8. Thermal modelling of a single thermosyphon

9. Air dryer modelling

10. Heat exchanger model Case 2: Plate finned tube bundle • 3 configurations were modelled • Unfinned individual tubes • Plate finned tube bundle • Plain individually finned tube bundle Case 1:Unfinned individual tube model Case 3: Plain individually finned tube bundle

11. Computer program algorithm • Computer program solves for the approriate parameters using an iterative procedure • Algorithm is as follows:

12. Future work • HPHRHE design and integration into industrial dryer • Various experiments, including testing of HPHRHE • Easy-to-use HPHRHE estimation program for various temperature ranges • Thank you for your time, any questions?????