The feasibility evaluation of using cyclic thermal effect in the rock-cutting tools during drilling hard rock

The possibility of using cyclic thermal effect in drilling tools for softening of rocks is considered in the article. It is shown that during drilling in the phase of heating, the rock sections can actually be heated to 1000 °C, and it is possible to achieve even higher temperatures with the use of corresponding frictional heating elements. It has been found that the phase of cooling of the heated section of the rock can ensure guaranteed cracking of the rock for subsequent mechanical destruction.

Experimental Study of Uniform and Non-Uniform Transverse Heat Flux Distribution Effect on the Onset of Nucleate Boiling

An experiment study is conducted to investigate the effect of transverse power distribution on the Onset of Nucleate Boiling (ONB) through a one-side heated narrow rectangular channel. Two test section are used to perform the experiment; uniform and non-uniform heated suction. The demineralized water is flowing in upward direction through the coolant channel with a thickness of 2.35 mm, a width of 54 mm, and a length of 300 mm. The experiment is carried out under different thermal power (0.5 kW – 6.5 kW) for the both test section. As well as, a wide variety of inlet subcooling and flow velocity are used as; 65−35 °C and 0.1–1.0 m/s, respectively. The wall temperature distribution of the heated plate is measured by 10 TCs for the uniformly heated test section, and 20 TC for the non-uniformly heated section. On the other hand, the ONB location is visualized via high speed camera, in which the ONB occurs near the edges for the non-uniformly heated section and occurs at the center of the heated surface for the uniformly power distribution. The results of the ONB heat flux and temperature in the non-uniformly heated section are compared against the one in the uniformly heated power. The results show the variety of the ONB location, ONB heat flux with the different power distribution. With the increase of the power, the ONB is shifted toward the inlet. On the other hand, the ONB for the non-uniform power distribution occurs near the edges at power lower than that the one in the uniformly power distribution. Also, the results are compared against the available correlations, such as Bergles and Rohsenow (1965), Jens and Lottes (1951), and Thom et al. (1965), as well as other experimental results done by several research institutes.

Thermal Hydraulic Instability Characteristic in Natural Circulation Parallel Boiling Channels Upflow System Under Low Pressure

Natural circulation BWR actively equipped with passive safety features has been promoted to solve the recent challenges in BWR nuclear power and safety technology. With regard to startup stage, various thermo-hydraulic instabilities might be induced due to an elimination of re-circulation pumps. A lot of studies have been made on the instabilities in evaporated system as well as in a reactor. In the instabilities, geysering accompanied with flow reversal phenomena has been investigated in a vertical closed loop, U-shaped closed loop, twin parallel channels, and so on. However, in twin parallel study the effect of non-heated length on geysering has not been sufficiently clarified. The objective of this research is to experimentally investigate the thermo-hydraulic instabilities, particular in geysering, with a natural circulation loop consisting of parallel boiling channels and the single connection channel, which simulates the basic flow around the reactor core in the system pressure range from atmospheric to 0.7MPa. The parallel boiling channels are consisted of heated and non-heated section. The heated section forms annulus and heated from the inner wall. The input heat flux range of 0 up to 580kW/m2, and inlet subcooling temperatures of 5, 10, and 15K respectively, are imposed in the experiments. In the parallel channels with non-heated risers, three types of thermo-hydraulic instabilities were detected in the following sequence, geysering, natural circulation oscillation, and density wave oscillation. Especially in Geysering, it is induced due to rapid condensation in the non-heated risers and it is not be suppressed even at 0.7MPa though it has a tendency to be suppressed with an increase in the system pressure. On the other hand, in the parallel channels without non-heated risers, sinusoidal oscillation similar to natural circulation oscillation has been detected, and geysering had never observed. The new findings are that the sinusoidal oscillation is induced due to the hydrostatic head fluctuation in the connection channel, where the flow regime is constantly slug flow. The oscillating period is well correlated with the sum of delay time for boiling and passing time of slug bubbles in the connection channel. From the facts described above, it is found that non-heated region in a channel box should be as shorter as possible to prevent geysering from occurring, and sinusoidal oscillation similar to natural circulation oscillation is induced in any configuration of parallel channels.

The Effects of Air Infiltration on a Large Flat Heat Pipe at Horizontal and Vertical Orientations

In the satellite or energy conversion industries flat heat pipes may be utilized to transfer heat to the thermal sink. In this investigation, a large flat heat pipe, 1.22m×0.305m×0.0127m, fabricated from 50 mil Monel 400 metal sheets and Monel 400 screens was videographed at horizontal and vertical orientations with an infrared video camera. The heat pipe evaporator section consisted of a 0.305m×0.305m area (one heated side only) while the side opposite the heated section was insulated. The remaining area of the heat pipe served as the condenser. In the horizontal orientation the heated section was on the bottom. In the vertical orientation the evaporator was aligned below the condenser. The sequence of photographs depicts heat inputs ranging from 200 W to 800 W, and the effect of air infiltration on heat pipe operation for both orientations. For the horizontal orientation, the air is seen to recede towards the small fill pipe as the heat input is increased. For the vertical orientation, the air and water vapor exhibit a buoyant interaction with the result that the air presence inhibits heat transfer by rendering sections of the condenser surface ineffective. The effects depicted in this paper set the stage for future analytical and experimental work in flat heat pipe operation for both normal and variable conductance modes.

A Numerical Investigation of the Heat Transfer in a Parallel Plate Channel With Piecewise Constant Wall Temperature Boundary Conditions

For turbulent flows in ducts, streamwise heat conduction effects within the flow can be important for low Prandtl number fluids (liquid metals). The paper presents a numerical investigation of the influence of axial heat conduction within the flow on the heat transfer for hydrodynamically fully developed flow. The calculations have been carried out for a semi-infinite heated section as well as for a heated section of finite length. Additionally, by considering different models for calculating the turbulent heat flux, the normally used assumption that the eddy diffusivity in axial and normal direction are the same was investigated.

Surface Effects on Deposits From Jet Fuels

Flow experiments in a single-pass heat exchanger using JP-8 and certain additives were initiated under controlled conditions to explore the effects of a metal surface on deposition. The experimental apparatus permitted a unique viewing of the time evolution of deposits at different axial locations under conditions of limited oxygen availability somewhat similar to those in jet aircraft. Scanning electron microscopy was used to examine deposit microstructure. In addition, x-ray photoelectron spectroscopy and Auger electron spectroscopy determined the chemical composition of the deposits. Oxygen concentration measurements in the bulk flow were also performed, and the observed transient oxidation behavior was related to measured time-dependent changes in the deposit. Increasing dissolved oxygen levels and large changes in deposition were characteristic of the induction time. Mechanisms of fouling in the heated and cooled sections were different. Spectroscopic analysis indicated that deposits formed in the heated section had chemical compositions different from those formed in the cooled section. Scanning electron microscopy revealed differences in microstructure between the heated and cooled sections: More uniform deposits formed in the cooled section as a result of once-soluble species becoming insoluble at low temperatures. In addition, the JP-8 additives significantly reduced fouling in the heated section, but their effectiveness in the cooled section, especially after long periods, was unclear.