Experimental Study on the Starting-Up and Heat Transfer Characteristics of a Pulsating Heat Pipe under Local Low-Frequency Vibrations

Vibrations have attracted much attention as an effective method for enhancing heat transfer in pulsating heat pipes (PHPs). This study mainly investigates and explores the effects of local low-frequency vibrations on the starting-up and heat transfer characteristics of a PHP. The starting-up temperature and average temperatures along the evaporation section of the pulsating heat pipe were experimentally scrutinized, along with thermal performance, under local vibrations on evaporation, condensation and adiabatic sections, respectively. The following important conclusions can be derived by the experimental study: (1) The effect of vibrations at the evaporation section and at the adiabatic section during the starting-up time of the PHP were more significant than that at the condensation section; (2) vibrations at different positions could reduce the starting-up temperature of the PHP—the effect of the vibrations at the evaporation section was the best when heat power was lower, while the effect of vibrations on the adiabatic section was the best when heat power was higher; (3) vibrations at the evaporation and adiabatic sections could reduce the thermal resistance of the PHP, but vibrations at the condensation section had little effect on the thermal resistance of the PHP; (4) vibrations at the evaporation and adiabatic sections could effectively reduce the temperature at the evaporation section of the PHP, but the vibrations at the condensation section had no effect on the temperature at the evaporation section of the PHP. This paper shows that local low-frequency vibrations have positive effects on the heat transfer performances of PHPs.

Experimental Study on the Starting-Up and Heat Transfer Characteristics of Pulsating Heat Pipe Under Local Low-Frequency Vibrations

This study mainly experimentally investigates and explores the effects of local low-frequency vibrations on the starting-up and heat transfer characteristics of the pulsating heat pipe. A micro motors with the vibration frequency of 200 Hz were imposed on the external surface of evaporation, condensation and adiabatic section of the pulsating heat pipe, respectively, and the starting-up temperature and the average temperatures along the evaporation section as well as the thermal performances of the vibrating heat pipe were experimentally scrutinized under the local vibrations of different positions. The following important conclusions can be achieved by the experimental study: 1) The effect of vibrations at the evaporation section and at the adiabatic section on the starting-up time of pulsating heat pipe is more significant than that at the condensation section. 2) The vibrations at different positions can reduce the starting-up temperature of the pulsating heat pipe. The effect of the vibrations at the evaporation section is the best as the heating power is lower, and the effect of the vibration at the adiabatic section is the best as the heating power is higher. 3) The vibrations at the evaporation section and at the adiabatic section can reduce the thermal resistance of the pulsating heat pipe. However, the vibrations at the condensation section have little effect on the thermal resistance of the pulsating heat pipe. 4) The vibrations at the evaporation section and at the adiabatic section can effectively reduce the temperature of evaporation section of the pulsating heat pipe, but the vibrations at the condensation section have no effect on the temperature of evaporation section of the pulsating heat pipe.

Experimental Investigation on Start-up and Isothermal Performance of Thermosyphon with Noncondensable Gas

Steel-water gravity heat pipe has been widely used in industry because of its low cost and wide applicable temperature range. Steel-water incompatibility can produce hydrogen as a non-condensable gas, seriously weakening the heat transfer capacity. In this paper, the start-up and isothermal performance of thermosyphon with noncondensable gas were studied by experimental methods, and the effect of gas ratio on the start-up and isothermal performance was quantitatively analysed. The results show that the larger gas ratio will increase the start-up time and the working temperature. The wall temperature of evaporation section is higher than that of adiabatic and condensation section. The distributions of wall temperature in the evaporator and adiabatic sections are uniform. The non-isothermal phenomenon only occurs in the condenser section.

Experimental Study on a Forced-Circulation Loop Thermosiphon Solar Water Heating System

Wickless gravity loop thermosiphons (LTs) have been widely used in heat collection for distances up to several meters. This two-phase closed device, which is operating under reduced pressure, is useful in solar water heating (SWH) systems because it could address the freezing problem during winter. Compared to the normal type, forced-circulation wickless LTs have significant advantages in the long-distance heat transfer and installation freedom of condensation section. In this study, a pump-forced wickless LT-SWH system with a remolded flat-plate solar collector was put forward. Solar collector acted as the evaporation section of the wickless LT, while the spiral heat exchanger in the water tank acted as the condensation section. R600a was employed as the working fluid, and long-term outdoor experiments were carried out. Results show that the instantaneous and daily average photothermal efficiency of the proposed system can reach 69.54% and 58.22%, respectively. Temperature differences between the top and bottom and the middle and bottom of the evaporation section of the wickless LT were small, and it usually ranged between 1.1 and 3.9°C. Linear fittings of the collector and system overall performance of the pump-forced wickless LT-SWH system demonstrate the promising potential application of the system.

Experimental Investigation on the Heat Transferring of Nanofluid in Self-Exciting Mode Oscillating-Flow Heat

In this article, the heat transferring property of the copper-water nanofluids in self-exciting mode oscillating flow heat pipe under different laser heating power is experimented, as well as is compared with that of the distilled water medium in self-exciting mode oscillating flow heat pipe under same heating condition. The objective of this article is to provide the heat transfer characteristics of Cu-H2O nanofluids in self-exciting mode oscillating-flow heat pipe under different laser heating input, and to compare with the heat transfer characteristics of the same heat pipe with distilled water as working fluids. The SEMOS HP used in this experiment is made of brass tube with 2mm interior diameter, which is consisted of 8 straight tubes with 4 turns’ evaporation section and 12 turns’ condensation section. The heat resource for the evaporation zone is eight channel quantum pitfall diode array semi-conductor laser heater with 940nm radiation wave length, while the radiation power of each channel is changeable within 0–50W and the facular size is 1×30mm2. The condensation section is set in a cooling water tank in which water is from another higher tank. The actual transferring rate could be calculated by the flow rate of the cooling water and the change of the temperature. The change of the temperature of the heat pipe wall is measured by those thermo-couple fixed in different section in the heat pipe and data is collected by a data acquisition. In the heat pipe the fluid filling rate is 43%, the pressure is 2.5×10−3Pa, and the heat pipe inclination angle is 55° while the size of the brass particle in the nanofluids is less than 60nm and volume proportion is 0.5%. In this paper, the particularity of heat transfer rate of the SEMOS heat pipe with Cu-H2O fluid has been experimentally confirmed by changing the proportion of working fluid and Cu nonsocial particles in the heat pipe. By comparing the experimental result of these two different medium in the SEMOS HP, it is shown that the heat transferring rate with brass-water nanofluids as medium is much better than that with distilled water as medium under same volume proportion.

Experimental Study of Gravity Heat Pipe with ECT

Gravity heat pipe’s interior phase change and heat transfer mechanisms are hardly to research, yet significant for strengthening heat transfer and enhancing energy utilization. This paper reports experimental study on the reconstructed images and concentration measurement of liquid (ethanol) at condensation section of gravity heat pipe with electrical capacitance tomography (ECT). Furthermore, signals’ noises collected by ECT have been reduced with Hilbert-Huang transform (HHT). Finally, reconstruction images have been compared with M. Shiraish’s model, and ECT has provided alternative experimental platform for the research of gravity heat pipe’s mechanisms.

Model for Heat Pipe Position Optimization of Transformers Cooled by Heat Pipes

In the view of heat pipe position optimization of transformers cooled by heat pipes, using the thermal equilibrium equation and the empirical formula of heat transfer coefficient of the evaporation and condensation section, applying Newton Iteration, computing the optimal condensation section area, the optimal computation of heat pipes’ position is implemented and the model of heat pipe position optimization of transformers cooled by heat pipes is set up.

Evaluation of a power plant concept for fast ignition heavy ion fusion

The characteristics of a fast ignition heavy ion fusion (FIHIF) power plant are preliminarily evaluated. The reactor chamber consists of two sections: The upper smaller part is the microexplosion section proper; the lower bigger part is the condensation section, in which sprayed jets of coolant are injected. The first surface of the blanket is of generally accepted wetted porous design. The coolant is lithium-lead eutectic with an initial surface temperature of 820 K. The mass of the evaporated coolant just after the explosion is evaluated as 4 kg. Computation of neutronics results in blanket energy deposition with maximum density of the order of 108 J/m3 at the first wall. The heat conversion system consisting of three coolant loops provides a net efficiency of the FIHIF power plant of 0.37.