Mathematical modelling and life‐cycle energy and financial analysis of solar kilns for wood drying A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy By Mahmudul Hasan B.Sc. (Mechanical Engineering) School of Chemical and Biomolecular Engineering Faculty of Engineering and Information Technologies The University of Sydney, Australia June 2017 Declaration I, Mahmudul Hasan, declare that the entire contents of this thesis are, to the best of my knowledge and belief, original, except where otherwise acknowledged. This thesis contains no material that has been submitted previously, in whole or in part, for the award of any other academic degree or diploma. …………………………. Mahmudul Hasan June 2017 i Dedications Dedicated To My parents and wife who are my inspirations. ii Acknowledgment I would like to express my heartiest gratefulness and indebtedness to my principal supervisor, Professor Timothy Langrish, for his scholastic supervision, inestimable help, proper guidance/suggestions throughout my study and research at The University of Sydney. His constant encouragement, time‐to‐time feedback, and immense knowledge in the research context were the key motivation and inspiration throughout my study. I have been especially fortunate to work with such a great supervisor. I also express my sincere gratitude to my co‐supervisor, A/Prof. Ali Abbas, for his insightful suggestions and valuable advice. As an auxiliary supervisor, he was strong and supportive. I would also like to express my special thanks to Dr. Nawshad Haque (CSIRO, Australia) for his insightful advice and intellectual support. I gratefully acknowledge the financial support from The University of Sydney for this research. I extend my extreme thankfulness to all the members in our research group for their help and valuable support. Finally, I feel highly indebted to my beloved wife, Umma, and other family members for her unconditional support, patience, and love. iii List of publications List of publications Book chapter: 1. Hasan, M. and Langrish, T.A.G. (2017). Solar dryers: A green technology for the Australian agricultural and forest industries. In Rasul, M., Azad, A.K., and Sharma, S. (Eds.), Clean Energy for Sustainable Development. Academic Press, Elsevier, Oxford, United Kingdom. Peer‐reviewed journal papers: 1. Hasan, M., Langrish, T.A.G (2016). Development of a sustainable methodolgy for life‐ cycle performance evaluation of solar dryers. Solar Energy, 135, 1‐13. doi: 10.1016/j.solener.2016.05.036 2. Hasan, M., Zhang, M., Wu, W., and Langrish, T.A.G. (2016). Discounted cash flow analysis of greenhouse‐type solar kilns. Renewable Energy, 95, 404‐412. doi: 10.1016/j.renene.2016.04.050 3. Hasan, M., Langrish, T.A.G. (2016). Time‐valued net energy analysis of solar kilns for wood drying: A solar thermal application. Energy, 96, 415‐426. doi: http://dx.doi.org/10.1016/j.energy.2015.11.081 4. Hasan, M., Langrish, T.A.G. (2015). Embodied energy and carbon analysis of solar kilns for wood drying. Drying Technology, 33 (8), 973‐985. doi: 10.1080/07373937.2015.1010207 iv List of publications 5. Hasan, M., Langrish, T.A.G. (2014b). Performance comparison of two solar kiln designs for wood drying using a numerical simulation. Drying Technology, 33(6), 634‐645. doi: 10.1080/07373937.2014.968254 6. Hasan, M., Langrish, T.A.G. (2014a). Numerical simulation of a solar kiln design for drying timber with different geographical and climatic conditions in Australia. Drying Technology, 32 (13), 1632‐1639. doi: 10.1080/07373937.2014.915556 Conferences/Seminars: 1. Hasan, M. and T.A.G. Langrish. (2014b). Timber drying by solar kilns: A performance comparison. Conference proceedings, Energy Conversion and Clean Energy Technology, paper 0004, BSME‐ICTE, 19‐21 December, 2014, Dhaka, Bangladesh. 2. Hasan, M. (2014a). Mathematical modelling and time‐valued energy analysis of solar kilns for wood drying. A Research Seminar, October 31, 2014, University of Sydney, Australia. v Abbreviations Abbreviations Symbol Description Symbol Description FSP Fibre saturation point Dr reference diffusion (kgkg‐1) coefficient (m2 s‐1) X moisture content (kgkg‐1) DE activation energy (K) Pvd vapour pressure at dry‐bulb E modulus of elasticity (Pa) temperature (Pa) CI instantaneous compliance Pvw vapour pressure at wet‐bulb (Pa‐1) temperature (Pa) EO modulus of elasticity for Yw saturation humidity at dry‐ bone‐dry timber (Pa) bulb temperature (kgkg‐1) Eg Green modulus of elasticity Y bulk‐air humidity (kgkg‐1) (Pa) Td dry‐bulb temperature (K) M thermal mass (J K‐1) Db diffusion coefficient for m Mass (kg) bound water (m2 s‐1) En net energy flow rate (W) D diffusion coefficient (m2 s‐1) Wn net water flow rate (kg s‐1) pv partial pressure of water SG solar gain (W) vapor at local temperature CL convection losses (W) and moisture content (Pa) RL radiation losses (W) C convection heat transfer (W) vi Abbreviations Symbol Description Symbol Description TR thermal radiation heat g acceleration due to gravity transfer (W) (m s‐2) SR solar radiation heat transfer VR venting rate (kg s‐1) (W) z distance through the timber Evap evaporation rate (kg s‐1) thickness (m) Cond condensation rate (kg s‐1) Gr recirculating air mass flow Tp plate temperature (K) rate (kg h‐1) Hvap latent heat of vaporization (J G air mass flow rate (kg h‐1) kg‐1) SLD scaled linear dimension (m) WS water spray rate (kg s‐1) OLD original linear dimension (m) LR leakage rate (kg s‐1) SSA scaled surface area (m2) Q radiation energy flow rate OSA original surface area (m2) (W) SV scaled volume (m3) A surface area (m2) OV original volume (m3) IT total solar radiation (W m‐2) OSV original stack volume (m3) Gcb beam radiation (W m‐2) Ustack stack velocity (m s‐1) Rb ratio of the beam radiation EE Embodied energy (J) on a tilted surface to that on a OE operational energy (J) horizontal surface LCEE life cycle embodied energy Gcd diffuse radiation (W m‐2) (J) h heat transfer coefficient (W LCEC life cycle embodied carbon m2 K‐1) (kg CO2‐e) vii Abbreviations Symbol Description Symbol Description EU European Union NEA net energy analysis ISO International Organization FEV future energy value (J) for Standardization PEV Present energy value (J) LCA life cycle assessment d discount rate (%) AusLCI Australian Life Cycle TPEPV total present energy Inventory production value (J) AIM‐ Australian Impact Method TPECV total present energy CED with Normalization consumption value (J) including Cumulative Energy FEPV future energy production Demand value (J) EoL End of life FECV future energy consumption GWP global warming potential (t‐ value (J) CO2‐e) NPEV net present energy value (J) GHG greenhouse gas TPELV total present energy loss ICE Inventory of Carbon and value (J) Energy NBLR Net benefit to loss ratio LCNE life‐cycle net energy PVEL present value of energy MARR minimum attractive rate of losses (J) return (%) PDEV Present drying energy value MC moisture content (kgkg‐1) (J) n time into the kiln service life PVFE Present value of fan energy (years) (J) viii Abbreviations Symbol Description Symbol Description PVLE Present value of PDEB Present drying energy loading/unloading energy (J) benefits (AUD) PVEE Present value of embodied PFEC Present fan energy costs energy (J) (AUD) DEPP discounted energy payback PLC Present loading/unloading period (years) costs (AUD) IRR Internal rate of return (%) PMLC Present material & labor DCF discounted cash flow costs (AUD) LCCF life‐cycle cash flow Greek symbols FC future cost (AUD) γ the slope angle (radians) FB future benefit (AUD) εs shrinkage strain (mm/mm) PC Present cost (AUD) σ Stress (Pa) PB Present benefit (AUD) Cp specific heat capacity (J kg‐1 DPB discounted present benefits K‐1) (AUD) ρg reflectance of the ground TPB total present benefit (AUD) emissivity of the panel TPC total present cost (AUD) τ transmissivity of cover i inflation rate (%) βp reflectivity of the panel NPCB net present cash benefits βc reflectivity of the cover (AUD) μ dynamic viscosity of the air PELC Present energy losses costs (kg m‐1 s‐1) (AUD) ix Abbreviations Symbol Description Symbol Description thermal expansion Subscripts coefficient (m m‐1 K‐1) f floor pick‐up efficiency (%) air internal air drying efficiency (%) nr north roof first‐day drying efficiency sr south roof (%) na north absorber present drying efficiency (%) sa south absorber k thermal conductivity (W m‐1 intw internal walls K‐1) intf internal floor ρt Density of the timber (kg m‐ int internal 3) w walls Cpt specific heat capacity of the a ambient timber (J kg‐1 K‐1) extsr external south roof ζi free shrinkage of the ith layer intsr internal south roof α the shrinkage coefficient extnr external north roof (m m‐1/kg kg‐1) intnr internal north roof σ Stefan‐Boltzmann constant intsa internal south absorber (W m‐2 K‐4) intna internal north absorber x Abstract Abstract There is a general challenge to improve the designs of solar dryers for the direct drying of various materials through the uses of robust models in conjunction with methods incorporating an appropriately defined set of performance parameters for evaluating the performance of solar kilns. However, the use of prevailing methods is unlikely to provide a sustainable means of comparison between various solar‐kiln designs, unless a whole life‐ cycle perspective is taken into consideration. The key tasks involved in this thesis were to develop a robust mathematical model and its simulation procedure for predicting the performance of solar kilns, to build a life cycle assessment (LCA) model for assessing the embodied energy and embodied carbon of solar kilns, to develop a life‐cycle net energy model and a life‐cycle financial model for assessing the life‐cycle performance of solar kilns, and to illustrate how closely these two perspectives are aligned for the present case and how they can lead to significantly different conclusions for some other cases.