Artificial roughness has been found to enhance the thermal performance from the collector to air in the solar air heater duct. This paper presents the results of experimental investigation on thermal performance of three sides solar air heater roughened with combination of multiple-v and transverse wire. The range of variation of system and operating parameters is investigated within the limits of relative roughness pitch of 10−25, relative roughness height of 0.018−0.042, angle of attack of 30°−75° at varying flow Reynolds number in the of range of 3000−12000 for fixed value of relative roughness width of 6. The augmentation in fluid temperature flowing under three side’s roughened duct is found to be 36.57% more than that of one side roughened duct. The maximum thermal efficiency is obtained at relative roughness pitch of 10 and relative roughness height of 0.042, and angle of attack of 60°. The augmentation in thermal efficiency of three sides over those of one side roughened duct is found to be 46−57% for varying values of relative roughness pitch, 38−50% for varying values of relative roughness height, and 40−46% for varying values of angle of attack.

This paper focuses on the global practical Mittag-Leffler feedback stabilization problem for a class of uncertain fractional-order systems. This class of systems is a larger class of nonlinearities than the Lipschitz ones. Based on the quasi-one-sided Lipschitz condition, firstly, we provide sufficient conditions for the practical observer design. Then, we exhibit that practical Mittag-Leffler stability of the closed loop system with a linear, state feedback is attained. Finally, a separation principle is established and we prove that the closed loop system is practical Mittag-Leffler stable.

The paper presents an original architecture and implementation of 9-bit Linearized Pulse Width Modulator (LPWM) for Class-BD amplifier, based on the hybrid method using STM32 microcontroller and Programmable Tapped Delay Line (PTDL). The analog input signals are converted into 12-bit PCM signals, then are directly transformed into 32-bit LBDD DPWM data of the pulse-edge locations within n-th period of the switching frequency, next requantized to the 9-bit digital outputs, and finally converted into the two physical trains of 1-bit PWM signals, to control the output stage of the Class-BD audio amplifier. The hybrid 9-bit quantizer converts 6 MSB bits using counter method, based on the peripherals of STM32 microcontroller, while the remaining 3 LSB bits - using a method based on the PTDL. In the paper extensive verification of algorithm and circuit operation as well as simulation in MATLAB and experimental results of the proposed 9-bit hybrid LBDD DPWM circuit have been performed. It allows to attain SNR of 80 dB and THD about 0,3% within the audio baseband.