Parametric study on phenomenon of honey drying using low temperature vacuum drying with induced nucleate boiling / Ahmad Syazwan Bin Ramli

Faculty of Mechanical and Automotive Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2024

Includes bibliographical references

The stingless bee rearing industry is growing due to its high nutritional and antioxidant content of honey, but technical challenges persist. One major issue is honey storage, as its high water content promotes microorganism activity, leading to fermentation and sour taste. To preserve its quality and nutrients, a proposed solution is low-temperature vacuum drying with induced nucleation boiling to remove water content without damaging enzymes or nutrients. This research explored the influence of nucleation boiling as well as the effect of variance heater temperature (40, 45 and 50 °C), surface roughness (0.80, 3.39, 8.82, and 11.33 μm), and initial honey water content (27.5, 24.5 and 22.5%) at the pressure of 5.3 kPa in improving the rate of honey dewatering via this method. 200 g of honey was used for each cycle of the experiment using different combinations of the chosen parameters on an experimental rig specifically built for this research. The collected data was in the form of honey’s water content after the dewatering process, temperature readings at specific locations, and recorded nucleate boiling phenomenon videos. The data was then analyzed using Tracker software, which is a video analysis tool and statistical method. The experiment showed that the higher temperature, surface roughness, and initial moisture content produce a higher dewatering rate. A combination of 27.5% water content at 50 °C and 11.33 μm heater surface roughness has the highest heat flux (87.64 kW/m2 ) and heat transfer coefficient (10.11 kW/m2K), which translates to higher bubble frequency, terminal speed, and diameter. These in turn increased the volume of vaporized water content released from the honey. With this parameter combination, the dewatering performance was able to reach the highest value of 0.42 %/min. The maximumheat transfer coefficient obtained was around 10.11 kW/m2K at this parameter combination. The higher surface roughness produced more nucleation sites, thus increasing the number of bubbles departing from the heater surface. The higher initial water content value contributed to lower viscosity, thus reducing drag and resistance experienced by the nucleation bubbles, thus enhancing a faster dewatering process as well. A simple fluid simulation on nucleate bubble during this process was also done using ANSYS CFX software. The value of the drag coefficient obtained using the software was compared with the experimental data. The results showed that the simulation was able to predict the drag coefficient acting on the bubble with acceptable accuracy of 97%. The experimental data was then fitted with several existing drying models, and any model with an accuracy value of 0.95 and above would be deemed as suitable to describe the process. It was found that the logarithmic drying model has the best fit with 0.98 and is therefore more suitable to describe this process. Further regression was conducted so that the effect of initial water content, surface roughness, and temperature on the logarithmic model’s constants and coefficients could be considered by multiple regression analysis. In conclusion, higher temperature, surface roughness, and initial water content correlated to the enhancement of the dewatering rate of honey. Therefore, by applying a suitable parameter combination for this method, the dewatering process of a heat-sensitive material can be achieved in an efficient manner that can lead to a higher nucleation boiling level, which ultimately leads to a faster honey dewatering rate.