| dc.description.abstract | Drying is one of the most necessary process and technology in today?s world and it is used, among other things, for food processing. The basic goal is to process the food for consumption by increasing its shelf life, and in order to achieve this moisture must be removed from raw material as moisture, which is the main promoter of biological activity and spoilage of the fresh products. Conventional drying is known for its high energy consumption and therefore it is costly. The conventional drying has also a negative impact on the environment and climate, providing the basis for heat pump drying development to ensure sustainable practice within the food industry.Heat pump drying is a relatively new technology developed at NTNU. It unifies the drying and heat pump cycles in which the heat pump is used to recycle energy, for reheat the air during drying the raw material. By recycling the heat from the dryer exhaust, energy is saved and the total energy input to the system is drastically reduced.In this master thesis a laboratory heat pump dryer is applied for drying green peas. The drying air was set on temperature regimes of 45°C, 35°C and 15°C with three levels of relative humidity: 60%, 40% and 20%, from which temperature regime of 45°C was set on 40% and 20%. Therefore, eight drying tests were performed and each test was done in period of three hours. The drying of green peas was conducted in fluidized bed mode.The results have shown that higher temperatures increase the rate of moisture removal from the green peas. Difference in relative humidity of the drying air also plays an important role in the process although the effect is much less compared to the temperature. The tests performed on heat pump drying of green peas provided the experimental data used for modeling and analysis of mass effective diffusivity, moisture content and ratio. The kinetics for all experiments on heat pump drying of green peas were successfully modeled based on the solution of the transient and three-dimensional general equation. Analysis and discussion were also done on the influence that these factors have on color, water activity, bulk and particle density, as well as particle size.Overall the project has shown that heat pump drying has many advantages in producing a satisfactory quality dried green peas, economy and sustainability. Therefore is justifiable to continue further studies and development of heat pump drying technology. | nb_NO |
