► Extra-long pulsating heat pipes can enhance the performance of solar water heaters. ► PHP mode with FR=70% has better performance compared with other filling ratios. ► In the best case, performance ...is increased by 22% using pulsating heat pipes.
In this study, the aim is to investigate the application of pulsating heat pipes (PHPs) as a heat transfer tool in a solar water heater (SWH). For this purpose, an extra-long pulsating heat pipe (ELPHP) is designed, constructed and installed in a thermosyphon solar water heater. In this work the ELPHPs are made of copper tubes of internal diameter 2.0mm. The number of meandering turns is 6 and the working fluid employed is distilled water. The lengths of condenser and evaporator sections are 0.8 and 0.96m, respectively. The length of adiabatic section varies between 0.7 and 1.8m. Inclination of the ELPHPs varies between 15° and 90° but is 45° for evaporator section. Four different tests are carried out; SWH with thermosyphon cycle, SWH with PHP filling ratio (FR)=30%, FR=50% and FR=70%. The results show that PHP with FR=70% has the most stable and the longest functioning duration. While mean temperature of container water is 35.3°C and 34.5°C for thermosyphon cycle and PHP FR=70%, respectively, the surface area under the container water temperature curve vs. time for thermosyphon is 87.69% of that of PHP FR=70% which indicates the higher heat transfer rate for the ELPHPs. In addition, calculations show efficiency of PHP FR=70% is equal to 53.79% while efficiency of thermosyphon mode is in range of 31% and 36%.
•Convective heat transfer was enhanced by using ferrofluid under laminar conditions.•Alternating magnetic fields along the tube led to heat transfer enhancement.•Heat transfer enhancement was based ...on the disturbance of the thermal boundary layer.•Effects of volume fraction, magnetic field and Reynolds number were examined.
This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations and under different frequencies of the applied magnetic field in detail. The convective heat transfer coefficient for distilled water and ferrofluid was measured and compared under various conditions. The results showed that applying an alternating magnetic field can enhance the convective heat transfer rate. The effects of magnetic field, volume concentration and Reynolds number on the convective heat transfer coefficient were widely investigated, and the Optimum conditions were obtained. Increasing the alternating magnetic field frequency and the volume fraction led to better heat transfer enhancement. The effect of the magnetic field in low Reynolds numbers was higher, and a maximum of 27.6% enhancement in the convection heat transfer was observed.
The application of the solar energy in thermal desalination devices is one of the most beneficial applications of the renewable energies. In this study, a novel solar desalination system is ...introduced, which is benefited from the undeniable advantages of pulsating heat pipe (PHP) as a fast responding, flexible and high performance thermal conducting device. Results show a remarkable increase in the rate of desalinated water production and the maximum production reaches up to 875mL/(m2.h). However, the optimum water depth in basin and the filling ratio of the PHP are measured 1cm and 40%, respectively.
► A novel solar desalination system is introduced, which profits the undeniable advantages of pulsating heat pipe (PHP). ► The maximum production reaches up to 875mL/(m2.h) and occurred in midday (12:30PM–1:30PM). ► The optimal filling ratio of pulsating heat pipe was recorded as 40%. ► Increasing the water depth in basin will decrease the rate of production.
Pulsating heat pipes (PHPs) are one of the new devices used for cooling in several applications such as electronic and aerospace systems. Their low cost, effectiveness at various conditions, being ...equipped for passive energy conversion, and well distribution of temperature compared to conventional heat pipes are among the reasons of their popularity. To investigate the effect of surface tension of the working fluid on the behavior of PHPs, a copper heat pipe is fabricated with inner and outer diameters of 2 mm and 4 mm, respectively. Five different concentrations of cetrimonium bromide (C-Tab) surfactant are dissolved in water and are tested with a filling ratio of 50% (± 1%). A piece of glass is placed in the adiabatic section to make the flow visualizations possible. Thermal resistance and flow visualization results are compared. Visualization of the flow shows that by increasing the surfactant concentration, annular and semi-annular regimes can be observed at lower powers. It is also detected that by increasing the surfactant concentration, thermal resistance will decrease, while the maximum heat flux is reduced. This can be explained by thinner film thickness in the evaporator. The lowest thermal resistance was detected to be 0.44 K/W for the 0.25 g L
−1
C-Tab concentration at 25 W heat input power which shows a significant improve of 77.5% compared to pure water at the same power.
•A new desalination uses a combination of heat pipe and parabolic trough collector.•A twin-glass evacuated tube is used to decrease the thermal losses from heat pipe.•Adding oil into the space ...between heat pipe and tube collector enhances the yield.•The yield and efficiency reach up to 0.933kg/(m2h) and 65.2%, respectively.
The solar collectors have been commonly used in desalination systems. Recent investigations show that the use of a linear parabolic trough collector in solar stills can improve the efficiency of a desalination system. In this work, a combination of a heat pipe and a twin-glass evacuated tube collector is utilized with a parabolic trough collector. Results show that the rate of production and efficiency can reach to 0.27kg/(m2h) and 22.1% when aluminum conducting foils are used in the space between the heat pipe and the twin-glass evacuated tube collector to transfer heat from the tube collector to the heat pipe. When oil is used as a medium for the transfer of heat, filling the space between heat pipe and twin-glass evacuated tube collector, the production and efficiency can increase to 0.933kg/(m2h) and 65.2%, respectively.
Solar energy is turning to one of the important types of clean energies, due to its availability, and its potential for wide range of applications. In this work, a new passive solar desalination ...system is introduced, which benefits from excellences of twin-glass evacuated tube collectors. For the first time, the evacuated tube collector is not only used as the solar thermal collector, but also as a basin to heat the water. Hence, the thermal resistance between the collector and basin is virtually eliminated. Results show a considerable increase in the rate of desalinated water production and the maximum production reaches up to 0.83kg/(m2·h). It was observed that the maximum rate of the production occurs when the tube is in inclination angle of 35°, and filled 80% with water. Moreover, it is seen that filling the tube with a stainless steel wool can enhance the production rate up to 1.01kg/(m2·h). It was observed that optimum inclination angle is 35°, which is the latitude of location of the experiments. Moreover, a theoretical model is presented in order to evaluate the system's efficiency in quasi-steady state conditions.
•A modified desalination uses an evacuated tube collector to directly heat water.•A quasi-steady state theoretical model is presented for this desalination system.•Adding stainless steel wool enhances the heat transfer and increases the yield.•The yield and efficiency reach up to 1.01kg/(m2·hr) and 65.6%, respectively.
In this study, an experimental investigation was conducted from a thermal performance standpoint on closed-loop pulsating heat pipes (CLPHPs) with four different fluids and their water-based binary ...mixtures as working fluids with volume mixing ratios of 3:1, 1:1, and 1:3. Ethanol and acetone as two types of fluids that are soluble in water and, to unprecedentedly compare the behavior of insoluble mixtures with the soluble ones as the working fluids, toluene and hexane as two types that are insoluble in water were used. Additionally, to predict the thermal performance of the pure, soluble binary, and insoluble binary fluids simultaneously for the first time, a correlation was derived.
A desalination system consumes energy for production of freshwater. Since the solar energy is a low-cost, environmentally clean, and available energy throughout the world, it could be the best source ...of energy for such systems. In this work, a modified desalination system is presented which uses advantages of thermosyphon heat pipes as a fast and high performance thermal conducting device, and at the same time, employs the advantages of evacuated tube collectors (ETCs) which are flexible and have high performance in adverse weather conditions. Results show considerable increase in the production rate of desalinated water and system efficiency with a maximum production rate of 1.02 kg/(m2 h) and maximum efficiency of 22.9%. Furthermore, the optimum water depth in the basin is measured to be 2 cm, which is the same as the length of the heat-pipe's condenser section in the basin.
•An efficient solar desalination system is presented which uses heat pipes and ETCs.•Isolated bubbles are generated over the condensers of the heat pipes.•The maximum rate of production was measured as 1.02 kg/(m2 h).•The effect of using different materials for the cover of basin is investigated.•An optimal water depth was measured to be the length of heat-pipe's condenser.
To investigate boiling heat transfer characteristics of nanofluids, transient quenching experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO
2 nanoparticles were ...performed. A silver sphere with a diameter of 10
mm and an initial temperature of 700
°C was quenched in these nanofluids at a temperature of 90
°C. The results showed a considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused the film boiling mode to vanish at lower temperatures depending on the mixture concentration. Calculated heat transfer rates in nanofluids were lower than those in pure water. In the quenching experiments with an unwashed heated sphere, the film boiling mode did not appear and the hot sphere quenched more rapidly through nucleate boiling. In this case the sphere surface was covered by a thin layer of nanoparticles. It was evident that nanoparticle deposition on the sphere surface prevented vapor film from forming around it and resulted in quick quenching of the hot sphere.
