THE EFFECT OF MICROWAVE IRRADIATION ON THE MECHANICAL PROPERTIES OF KIMBERLITE AND LIMESTONE

THE EFFECT OF MICROWAVE IRRADIATION ON THE MECHANICAL PROPERTIES OF KIMBERLITE AND LIMESTONEAbstract In underground excavation, rock fragmentation can be achieved by blasting with explosive materials or using continuous excavation machinery. The significant challenges with the explosives include noise, vibration, pollution, and potential issues such as damage to nearby structures. A less disruptive method for breaking rocks is using machines such as tunnel boring machine and road header those have the capability of continuous operation and are suitable for autonomous mining. In hard rock applications, the excavation machinery is associated with high equipment wear rates, low penetration rates and consequently high operating costs. This paper investigates the work being undertaken at McGill University on the effect of microwave (MW) irradiation on hard rocks to facilitate continuous mining and improve the production rate while reducing costs. Tuffistic Kimberlite (TK) and limestone rocks were studied in this research. Physical properties of untreated samples were measured, and the rock samples were treated for various exposure times in a multi-mode MW unit at power levels ranging from 2 to 10 kW. The results indicate that MW irradiation reduced the strength of TK and limestone rocks. It was concluded that Brazilian Tensile Strength (BTS) and Uniaxial Compressive Strength (UCS) of samples decayed proportionally with exposure time and power level.Keywords: Kimberlite, Microwave Irradiation, Fragmentation, Mechanical Strength, Rock Excavatio

Numerical Investigation of Heat Transfer Performance of Various Coiled Square Tubes for Heat Exchanger Application

AbstractIn heat exchanger application, working fluid inside the tubes is subjected to considerable temperature changes. In order to improve heat transfer performance, various strategies are proposed and evaluated; one of them is the application of coiled tubes. Coiled tubes have been used widely in heat exchanger application mainly due to the presence of secondary flow which enhances heat transfer considerably. This study addresses heat transfer performance of three configurations of coiled tubes with square cross-section, i.e. in-plane, helical and conical coiled tubes, subjected to large temperature difference. Their heat transfer performance is numerically evaluated and compared with that of a straight tube with identical cross-section and length. A concept of Figure of Merit (FoM) is introduced and utilized to fairly asses the heat transfer performance of the coiled tube configurations. The results indicate that FoM increase as the wall temperature increase. In addition, combination of temperature-induced buoyancy flow and curvature-induced secondary flow considerably affect the flow behavior and heat transfer performance inside the tubes

Performance and potential energy saving of thermal dryer with intermittent impinging jet

In designing an energy efficient impinging jet dryer, it is essential to match the energy demand for drying with the supply of heat by convection to avoid overheating and energy wastage. One way to achieve this is by intermittently supply heat to the drying chamber. By using computational fluid dynamics (CFD) approach, this study numerically investigates the possibility of energy saving by intermittency. First, inlet temperature intermittency is applied. This is conducted by alternately raise it to drying temperature and lowers it to the ambient temperature at certain period. Second, inlet velocity intermittency is applied which is conducted by alternately supplying the hot air to the several drying chamber. One, two, three and four chamber configurations are evaluated. In addition, the intermittency period of 10, 20 and 30 min were examined. The results reveal that the steady impinging jet offers faster drying rate as compared to intermittent impinging jet drying under the same inlet conditions. In addition it was found that drying rate goes down as the number of drying chamber increases. However, the intermittent impinging jet drying offers advantages in term of temperature uniformity and energy conservation. For the same energy usage, the production rate of single drying configuration is only one fourth of the four chamber configuration. This indicates the potential of multi chamber configuration in a real drying application

Optimization of Wavy-Channel Micromixer Geometry Using Taguchi Method

The micro-mixer has been widely used in mixing processes for chemical and pharmaceutical industries. We introduced an improved and easy to manufacture micro-mixer design utilizing the wavy structure micro-channel T-junction which can be easily manufactured using a simple stamping method. Here, we aim to optimize the geometrical parameters, i.e., wavy frequency, wavy amplitude, and width and height of the micro channel by utilizing the robust Taguchi statistical method with regards to the mixing performance (mixing index), pumping power and figure of merit (FoM). The interaction of each design parameter is evaluated. The results indicate that high mixing performance is not always associated with high FoM due to higher pumping power. Higher wavy frequency and amplitude is required for good mixing performance; however, this is not the case for pumping power due to an increase in Darcy friction loss. Finally, the advantages and limitations of the designs and objective functions are discussed in the light of present numerical results

Application of Phase Change Material-Based Thermal Capacitor in Double Tube Heat Exchanger—A Numerical Investigation

In many heat transfer related applications, there is a need for a stable, constant supply temperature. As a result, the integration of intermittent renewable sources of heat into these processes can prove to be challenging, requiring special temperature smoothing devices or strategies. This study focuses on the application of phase change materials integrated into a double tube heat exchanger as a possible thermal smoothing device. The objective of this study is to evaluate the ability of the exchanger to smoothen out temperature variations within the cold stream outlet while the hot stream is subject to oscillating inlet conditions. A computational fluid dynamics approach is used where a numerical model is developed, validated and then used to model the conjugate heat transfer within the heat exchanger. Four organic phase change materials (PCM) with different phase change temperatures were selected for investigation (myristic, octadecane, eicosane, and wax) to study the relationship between melting temperature and stabilization performance. A parametric study was then conducted by varying the Reynolds number of the flow as well as temperature oscillation period and amplitude to study the sensitivity of the system. The results confirm the potential of a phase change material-based thermal capacitor at dampening oscillations across the heat exchanger

A computational study of heat transfer under twin turbulent slot jets impinging on planar smooth and rough surfaces

The flow and heat transfer characteristics of twin turbulent slot jets impinging on planar smooth and rough surfaces are examined using a computational fluid dynamics model. The interaction between jets lowers the heat transfer performance of each jet in the zone where the wall jets collide. A single jet performs better than the equivalent twin jet. The average heat transfer under twin jets which are injected alternately so that each one of the pair of jets behaves like a single jet, is found to be better than twin jets issuing simultaneously. It is proposed that alternating jet flows in the twin jet arrangement is a simple novel way to enhance thermal performance of jet pairs. Along with parametric studies of the key flow and geometric parameters, effects of large temperature differences between the jet air and the target surface being heated, and model roughness of the target surface are also evaluated. Interestingly, roughness can lower the heat transfer performance in the impingement zone as the fluid can get trapped in the valleys in the rough surface

Hybrid Renewable Hydrogen Energy Solution for Application in Remote Mines

Mining operations in remote locations rely heavily on diesel fuel for the electricity, haulage and heating demands. Such significant diesel dependency imposes large carbon footprints to these mines. Consequently, mining companies are looking for better energy strategies to lower their carbon footprints. Renewable energies can relieve this over-reliance on fossil fuels. Yet, in spite of their many advantages, renewable systems deployment on a large scale has been very limited, mainly due to the high battery storage system. Using hydrogen for energy storage purposes due to its relatively cheaper technology can facilitate the application of renewable energies in the mining industry. Such cost-prohibitive issues prevent achieving 100% penetration rate of renewables in mining applications. This paper offers a novel integrated renewable–multi-storage (wind turbine/battery/fuel cell/thermal storage) solution with six different configurations to secure 100% off-grid mining power supply as a stand-alone system. A detailed comparison between the proposed configurations is presented with recommendations for implementation. A parametric study is also performed, identifying the effect of different parameters (i.e., wind speed, battery market price, and fuel cell market price) on economics of the system. The result of the present study reveals that standalone renewable energy deployment in mine settings is technically and economically feasible with the current market prices, depending on the average wind speed at the mine location.Applied Science, Faculty ofNon UBCMining Engineering, Keevil Institute ofReviewedFacult