In this study, a realistic model for dynamic instability of embedded single-walled nanotubes (SWCNTs) conveying PULSATING FLUID is presented considering the viscoelastic property of the nanotubes using Kelvin-Voigt model. SWCNTs are placed in longitudinal magnetic fields and modeled by sinusoidal shear deformation beam theory (SSDBT) as well as modified couple stress theory. The effect of slip boundary condition and small size effect of nano flow are considered using Knudsen number. The Gurtin-Murdoch elasticity theory is applied for incorporation the surface stress effects. The surrounding elastic medium is described by a visco-Pasternak foundation model, which accounts for normal, transverse shear and damping loads. The motion equations are derived based on the Hamilton's principle. The differential quadrature method (DQM) in conjunction with Bolotin method is used in order to calculate the dynamic instability region (DIR) of visco-SWCNTs induced by PULSATING FLUID. The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, magnetic field, visco-Pasternak foundation, Knudsen number, surface stress and FLUID velocity on the dynamic instability of SWCNTs. The results depict that increasing magnetic field and considering surface effect shift DIR to right. The results presented in this paper would be helpful in design and manufacturing of nano/micro mechanical systems.

An experimental study on PULSATING heat pipe (PHP) is presented in this work. A closed loop PHP with a single U turn is fabricated and tested. The transient and steady state experiments are conducted and operating temperatures are measured. The experiments are carried out for different working FLUIDs, heat input and for different evacuation levels. The derived parameters include thermal resistance and heat transfer coefficient of PHP. The results of these experiments show an intermittent motion of the working FLUID at lower heat input. The temperature difference between evaporator and condenser at steady state is found lower for acetone compared to water, ethanol and methanol. Lower value of thermal resistance and higher value of heat transfer coefficient are observed in case of acetone compared to water, ethanol and methanol. Lower values of temperature difference between evaporator and condenser and thermal resistance and higher value of heat transfer coefficient are observed at atmospheric conditions of operation of PHP compared to evacuation conditions. The Power Spectral Density Analysis is also carried out on the results of these experiments using FFT technique to analyse the PULSATING motion of the FLUID in a PHP. In the Power Spectral Density analysis, the frequency distribution of temperature variation in PHP was observed over a wider range, signifying the periodic motion in the FLUID flow of the liquid slug and vapour plug. This characteristic frequency corresponded to the characteristic time for a couple of adjacent vapour plug and liquid slug passing through a specific local wall surface in a PHP.

In this research, a series of experimental and numerical studies on the thermal performance of a single-turn PULSATING Heat Pipe (PHP) using distilled water as base FLUID and distilled water including micro-coppers were performed. Thermal resistance, average temperatures of the hot region (evaporator), average temperatures of the cold part (condenser), and two-phase flow regime of the system were investigated at the different filling ratios, at input powers (20, 30, 40, 50 and 60W), at a concentration of micro-coppers (0. 0625 g/mL). The oscillating heat pipe was fabricated with a copper capillary tube by choosing the internal and external diameters of 4 mm and 6 mm, respectively. Experiments showed adding micro-coppers into base FLUID improves the main mechanism of the PHP based on the oscillating motion of vapor plugs and liquid slugs. The lowest thermal resistance of the system at a filling ratio of 40%, at a concentration of micro-coppers (0. 0625 g/ml), at heat input (60 W) was 0. 95 deg C/W. Meanwhile, CFD results illustrated adding micro-coppers into base FLUID increases the turbulence intensity of the system especially in the evaporator up to 45% which enhances the heat transfer through the PHP in comparison to base FLUID.

FLUID flow around and heat transfer from a rectangular flat plane with constant uniform heat flux in laminar PULSATING flows is studied, and compared with our experimental data. Quantitatively accurate, second-order schemes for time, space, momentum and energy are employed, and fine meshes are adopted. The numerical results agree well with experimental data. Results found that the heat transfer enhancement is caused by the relative low temperature gradient in the thermal boundary layer, and by the lower surface temperature in PULSATING flows. In addition, the heat transfer resistance is much lower during reverse flow period than that during forward flow period. The flow reversal period is about 180 degree behind the PULSATING pressure waves. Besides, spectrum results of the simulated averaged surface temperature showed that the temperature fluctuates in multiple-peaked modes when the amplitude of the imposed pulsations is larger, whereas the temperature fluctuates in a single-peaked mode when the amplitude of the imposed pulsation is small.

PULSATING Heat Pipes have recently become popular due to their capability in removing heat at higher rates, over short or long distances. Their passive operation and relative ease of manufacturing have been added to their popularity.  In this study, a combination of two flat plate PULSATING heat pipes in series configuration is proposed and their thermo-hydraulic behavior is investigated experimentally in vertical bottom heated mode. The series configuration provides the possibility of heat removal from the heat source within longer distances at acceptable efficiencies. FLUID type, filling ratios, and input powers were the factors chosen to study their influence on the operation of the setup. The results showed that the 60% filling ratio for the water filled channel together with the 40% filling ratio for the methanol filled channel present the lowest thermal resistance in the range of considered input powers. It was observed that for all of the filling ratio combinations used, the methanol channel started oscillation before the water channel and it presented lower thermal resistance as compared with the water channel. The experimental results demonstrated that the dominant hydrodynamic FLUID pattern is slug flow with the pulsation of FLUID columns together with sporadic circulation at higher input power rates.

In this study an analytical model for open loop PULSATING heat pipes (PHPs) is presented. The model predicts the effect of different parameters such as evaporator temperature, length of evaporator, filling ratio, number of turn and tube diameter on PHP's performance. The governing equations in two phase flow including mass, momentum and energy equations are solved for both one dimensional liquid slugs and lumped vapor plugs numerically. The model includes the thin film layer concept which contributes to heat transfer in evaporator and condenser section. A proper model is also investigated to describe the steady oscillatory behavior of device. The results show that this model predicts well the oscillatory behavior of the phenomena. The obtained results are in good agreement with available data and can be properly used for predicting the trend of effective parameters on PHP's performance. It is found that sensible heat transfer has extremely more important role in increasing total heat transfer of PHP. The thermal resistance decreases due to increasing of the latent heat transfer. It can be seen that increasing of the evaporator temperature, while the temperature of the condenser is constant, will increase the total evacuated heat by PHP in specific filling ratio limits. The results show that the PHP's performance increases when the tube diameter increases. In this case, by using a specific non-dimensionalized model, a unique curve for arbitrary number of turn and FR can be obtained. Also it is found that PHP's performance reaches its maximum at filling ratio around 0.6 for different tube diameters.