Utilizing ultrasonic excitation as an active method for studying the rate of heat transfer has gained considerable attention recently. The present study investigated the effects of ultrasonic excitation on the heat transfer rate in a fin-and-flat tube heat exchanger experimentally. The performance of the heat exchanger was investigated with and without the presence of ultrasonic excitation. A comprehensive parameter study was attempted, so several parameters, including ambient temperature, flow rate, air passing velocity, Reynolds number, and Nusselt number, were studied in a relatively wide range. An adequate uncertainty test, as well as a validation assessment, is provided to certify the credibility of the obtained results and the hired facility. The results revealed that reducing the flow rate, ambient temperature, and air passing velocity on the heat exchanger increased the ultrasonic excitation’s effects. The highest heat transfer enhancement in the present experiment was 70.11%, measured at the lowest air passing velocity and ambient temperature with a Reynolds number 2166. The data presented in this paper will be useful for the optimal design of ultrasonic vibrating fin-and-tube heat exchangers.

In this work, the interaction impacts of solid nanoparticles and magnetic force on the entropy generation rates for three-dimensional forced convection over an inclined step in the presence of Brownian movement are examined. To achieve this goal, analysis of the thermodynamics second law is used. The working fluids in this three-dimensional problem are the ${\mathrm{Al}}_2{\mathrm{O}}_3–{\mathrm{H}}_2\mathrm{O}$ and $\mathrm{CuO}–{\mathrm{H}}_2\mathrm{O}$ nanofluids. To consider the impact of Brownian movement on the effective properties of these both nanofluids, the Koo–Kleinstreuer–Li (KKL) correlation is applied. Impacts of magnetic force $\left(Ha=0–100\right)$ and nanoparticles concentrations $\left(\varphi =0.0–0.06\right)$ on the entropy generation and the flow irreversibility are investigated in details. The predictions present that the ${\mathrm{Al}}_2{\mathrm{O}}_3–{\mathrm{H}}_2\mathrm{O}$ nanofluid is more suitable for the optimal design of the hydrothermal systems. Besides, the highest magnitudes of the total entropy generation number in downstream of step are noted for the case of $Ha=100$ and $\varphi =0.06.$

In this paper, the size-dependent vibration and instability of nanoflow-conveying nanotubes with surface effects using nonlocal strain gradient theory (NSGT) are examined. Hence, based on Gurtin-Murdoch theory, the nonclassical governing equations are derived by extended Hamilton's principle. To study the small-size effects on the flow field, the Knudsen number is applied. Applying Galerkin's approach, the partial differential equations converted to ordinary differential equations. The effects of the main parameters like nonlocal and strain gradient parameters, length to diameter ratio, thickness, surface effects, Knudsen number and different boundary conditions on the eigenvalue and critical fluid velocity of the nanotube are explained.

In this research, a numerical algorithm is employed to investigate the classical Blasius equation which is the governing equation of boundary layer problem. The base of this algorithm is on the development of RCW (Rahmanzadeh-Cai-White) method. In fact, in the current work, an attempt is made to solve the Blasius equation by using the sum of Taylor and Fourier series. While, in the most common numerical methods, the answer is considered only as a Taylor series. It should be noted that in these algorithms which use Taylor expansion, the values of the truncation error are considerable. However, adding the Fourier series to the Taylor series leads to reduce the amount of the truncation error. Nevertheless, the results of this research show the RCW method has the ability to achieve the accuracy of analytical solution. Moreover, it is well illustrated that the accuracy of RCW method is higher than the Runge-Kutta one.