Search Results (4)

This study presents the development and evaluation of a stand-alone solar dryer designed to improve the efficiency of bee bread dehydration. Unlike the electric prototype powered by conventional energy sources, the proposed system operates autonomously, utilizing solar energy as the primary drying agent. The drying chamber is equipped with solar collectors located in its lower section, which ensure convective heating of the product. Active convection is generated by a set of fans powered by photovoltaic panels, maintaining the drying agent’s temperature near 42 °C. The research methodology integrates both numerical simulation and experimental investigation. Simulations focus on the variations in temperature (288–315 K) and relative humidity (1–1.5%) within the honeycomb structure under convective airflow. Experimental trials examine the relationship between moisture content and variables such as bee bread mass, airflow rate, number of frames (5–11 units), and drying time (2–11 h). A statistically grounded analysis based on an experimental design method was conducted, revealing a reduction in moisture content from 16.2–18.26% to 14.1–15.1% under optimized conditions. Linear regression models were derived to describe these dependencies. A comparative assessment using enthalpy–humidity (I–d) diagrams demonstrated the enhanced drying performance of the solar dryer, which is attributed to its cyclic operation mode. The results confirm the potential of the developed system for sustainable and energy-efficient drying of bee bread in decentralized conditions. Full article

Drying food stuffs and other materials belongs to one of the most commonly used feedstock processing techniques, featuring rather high energy consumption. The major disadvantage of conventional electric convective-type household dryers is substantial thermal energy emission into the environment with a wet exhaust, worked-out drying agent. Among other principal disadvantages common to all dryers of this type, the following have to be mentioned: spatial inhomogeneity of heating a product under processing and that of drying agent distribution due to its temperature reduction and relative humidity growth as it moves upwards. A block diagram and a breadboard model of a convective-type thermoelectric dryer employing a thermoelectric heat pump have been designed. In our approach, a product is treated with the help of a drying agent (normally, heated air) with partial exhaust-air recirculation and heat recovery. Laboratory studies of the drying process have been carried out using apple fruits as a test material in order to evaluate the power consumed for evaporation of 1 kg of water in the newly developed convective-type thermoelectric drying unit. Physical parameters of apple fruits before and after drying both in the thermoelectric drying unit and in a conventional series-produced convective-type domestic dryer have been reported. The energy efficiency of the newly designed drying unit has been compared with that of some series-produced samples. It has been found out that, unlike conventional convective-type dryers, the breadboard model of the developed thermoelectric drying unit features a smoother product drying process owing to the presence of side air channels and more effective drying agent path organization in the processing chamber. This conclusion was supported by the results of the carried out tests. Application of thermoelectric heat pumps with the function of the exhaust drying agent heat recovery will make it possible to reduce the drying agent heater installed capacity and the power consumed by the newly designed convective-type thermoelectric drying unit by up to 20% in the course of the drying process, compared to series-produced household convective-type dryers. Full article

This paper proposes an indirect-mode forced convection solar dryer equipped with a PV/T air collector. The PV/T air collector generates both heated air and electrical energy, which are used to force convection in the solar dryer. Experiments were carried out on selected tomato slices for which the temperature and humidity readings as well as the masses of the dried samples were instantaneously recorded for two days. A thermal analysis was performed on the solar drying system to investigate its performance. The PV/T dryer’s air temperature and velocity simulation using CFD modeling were validated by the experimental results for which the drying chamber was empty, without tomato slices. The experimental and numerical results were in good agreement. The difference between the CFD model and the experimental results for air temperature was around 1 °C (3%) and 2 °C (5%) for the solar collector and drying chamber, respectively. The average daily efficiencies of the collector, dryer, and PV panel for the solar drying system were estimated to be 30.9%, 15.2%, and 8.7%, respectively. Full article

Spent grains from microbreweries are mostly formed by malting barley (or malt) and are suitable for a further valorization process. Transforming spent grains from waste to raw materials, for instance, in the production of nontraditional flour, requires a previous drying process. A natural convection solar dryer (NCSD) was evaluated as an alternative to a conventional electric convective dryer (CECD) for the dehydration process of local microbrewers’ spent grains. Two types of brewer’s spent grains (BSG; Golden ale and Red ale) were dried with both systems, and sustainability indices, specific energy consumption (e_C), and CO₂ emissions were calculated and used to assess the environmental advantages and disadvantages of the NCSD. Then, suitable models (empirical, neural networks, and computational fluid dynamics) were used to simulate both types of drying processes under different conditions. The drying times were 30–85 min (depending on the drying temperature, 363.15 K and 333.15 K) and 345–430 min (depending on the starting daytime hour at which the drying process began) for the CECD and the NCSD, respectively. However, e_C and CO₂ emissions for the CECD were 1.68–1.88 · 10⁻³ (kW h)/kg and 294.80–410.73 kg/(kW h) for the different drying temperatures. Using the NCSD, both indicators were null, considering this aspect as an environmental benefit. Full article