This study aimed to enhance the thermal characteristics of rice husk biomass through torrefaction conducted in a fixed-bed reactor. A novel approach was employed by circulating the gas produced within the system, instead of using traditional nitrogen. The torrefaction process took place at temperatures ranging from 200 to 320 °C, with different residence times of 10, 20, and 30 min for heat exchange. Quantitative analysis of the torrefied biomass revealed several notable improvements. The higher heating value of the biomass increased significantly, reaching 23.69 MJ/kg at a temperature of 320 °C and a residence time of 30 min. This enhancement indicates the effectiveness of torrefaction in increasing the energy content of the biomass. Furthermore, the torrefied biomass exhibited a remarkable reduction in hygroscopicity, with reduction by as much as 92 wt% compared to raw rice husk biomass. This reduction implies that the torrefied biomass is more resistant to moisture absorption, making it more stable and suitable for various applications. The torrefaction process in the fixed-bed reactor yielded a torrefied biomass with a production yield of 76 wt% (RH-320, RT30). This yield showcases the potential of the employed technique for producing a substantial amount of high-quality torrefied biomass. The resulting biomass holds great promise for diverse applications. It can be utilized for industrial steam production, contributing to the efficient use of biomass resources. Moreover, it could serve as an alternative fuel source for biomass power plants, offering a sustainable energy solution. Overall, this study demonstrates the effectiveness of the proposed torrefaction method in enhancing the thermal characteristics of rice husk biomass. The improved energy content and reduced hygroscopicity make torrefied biomass a valuable resource for various industries, promoting the utilization of biomass as a renewable energy source.

An experimental study was undertaken for investigating the heat transfer enhancement in a channel with baffle turbulators mounted on the lower wall. The baffles with rectangular, triangular, and trapezoidal upper edges were examined. The experiments were conducted in the rectangular channel with aspect ratio AR = 10 and height H = 30 mm, using air as the working fluid for Reynolds numbers between 5100 and 22,500. The effect of a baffle height to channel height ratio (y/H = 0.2, 0.3, and 0.4) on the heat transfer, pressure drop, and thermal enhancement factor characteristics was also investigated. The uniform heat flux condition was applied to the external surface of the lower wall of the channel. The results revealed that the baffles with rectangular upper edges gave a higher Nusselt number and friction factor than the ones with triangular and trapezoidal upper edges. Nusselt number increased while thermal performance factor decreased as a baffle to channel height ratio (y/H) and Reynolds number increased. For the range determined, the maximum thermal performance factor was achieved by using the baffles with trapezoidal upper edges at the smallest baffle to channel height ratio and the lowest Reynolds number, due to the best tradeoff between the increases of heat transfer and friction loss.

The helical oscillating heat pipe (HOHP) is a high heat transfer heat exchanger with high flexibility in its installation and can therefore be used in a wide variety of applications. In this study, the effect of various parameters on the heat transfer rates of HOHP were used to establish a correlation equation for use in the heat flux prediction, the dimensionless parameters studied were rv/rl, Bo, Nu, We, Ja, Pr, Fr, Co, Ga, Bi, Wo, Oh, and Ku. Experiments were conducted to find out their effects on the heat transfer rates of copper HOHP with internal diameters were 2.03, 3.5, and 4.5 mm. The lengths of evaporator and condenser sections were equal at 1500, 2000, and 2500 mm. The pitch coils were 10, 15, and 20 mm. The working fluids used were R134a, ethanol, and water with the filling ratios were 30%, 50%, and 80% of the total internal volume. The temperature of evaporator section were varied between 60, 70, and 80°C within normal operating conditions in a vertical position. The results of the experiment showed that the internal diameter, lengths of evaporator/condenser sections, pitch coil, type of working fluid, filling ratio and temperature of evaporator section affected the heat transfer rates of the HOHP. The results of dimensionless parameters can establish the correlation equation to predict the heat flux for the HOHP as shown in this paper. In addition, the results of this research can be applied in the designing and construction of HOHP heat exchangers.