Effect of Freeze Pipe Eccentricity in Selective Artificial Ground Freezing Applications

Building concentric tubes is one of biggest practical challenges in the construction of freeze-pipes of selective artificial ground freezing (S-AGF) applications for underground mines. In this study, the influence of tubes eccentricity on phase-front expansion (i.e., expansion of the frozen body) and energy consumption of S-AGF systems is analyzed. A 1+1D semi-conjugate model that solves two-phase transient energy conservation equation is derived based on the enthalpy method. The 1+1D model is firstly validated against experimental data and then verified with a fully-conjugate model from our previous work. After that, the 1+1D model is extended to a field-scale of typical underground mines to examine the effect of freeze-pipe eccentricity. The results show that concentric freeze-pipes form the desired frozen ground volume 15% faster than eccentric freeze-pipes. Also, the geometrical profile of the phase-transition-front of the frozen ground is found to be significantly influenced by the freeze-pipe eccentricity. Furthermore, in the passive zone, where S-AGF coolants are isolated from the ground to reduce energy consumption, freeze pipe eccentricity can increase the coolant heat gain by 20%. This percentage can increase up to 200 % if radiation heat transfer is minimized.

Effect of Freeze Pipe Eccentricity in Artificial Ground Freezing Applications

Building concentric tubes is one of biggest practical challenges in the construction of freeze-pipes of artificial ground freezing (AGF) applications for deep underground mines. In this study, the influence of tubes eccentricity on phase-front expansion (i.e., expansion of the frozen body) and energy consumption of AGF systems is analyzed. A 1+1D semi-conjugate model that solves two-phase transient energy conservation equation is derived. The model is firstly validated against experimental data and then verified with a fully-conjugate model from the literature. After that, the model is extended to a field scale of typical deep underground mines to study freeze-pipe eccentricity. The results show that an eccentric freeze pipe can reduce the phase-front expansion by around 25%, as compared with a concentric one. Also, the geometrical profile of the phase-front is significantly influenced by the freeze-pipe eccentricity. Furthermore, in the passive zone, where AGF coolants are isolated from the ground to reduce energy consumption, freeze pipe eccentricity can increase the coolant heat gain by 10%. This percentage can increase up to 200% if radiation heat transfer is minimized.

Skew Gaussian processes for classification

Gaussian processes (GPs) are distributions over functions, which provide a Bayesian nonparametric approach to regression and classification. In spite of their success, GPs have limited use in some applications, for example, in some cases a symmetric distribution with respect to its mean is an unreasonable model. This implies, for instance, that the mean and the median coincide, while the mean and median in an asymmetric (skewed) distribution can be different numbers. In this paper, we propose skew-Gaussian processes (SkewGPs) as a non-parametric prior over functions. A SkewGP extends the multivariate unified skew-normal distribution over finite dimensional vectors to a stochastic processes. The SkewGP class of distributions includes GPs and, therefore, SkewGPs inherit all good properties of GPs and increase their flexibility by allowing asymmetry in the probabilistic model. By exploiting the fact that SkewGP and probit likelihood are conjugate model, we derive closed form expressions for the marginal likelihood and predictive distribution of this new nonparametric classifier. We verify empirically that the proposed SkewGP classifier provides a better performance than a GP classifier based on either Laplace’s method or expectation propagation.

Experimental and Numerical Investigation of Effusion Cooling Effectiveness of Combustion Chamber Liner Plates

This study aims to evaluate adiabatic and conjugate effusion cooling effectiveness of combustion chamber liner plate of gas turbines. Validation of the adiabatic model was done by comparing computational fluid dynamics (CFD) result with the experimental results obtained using the subsonic cascade tunnel facility available at Heat Transfer Lab of Council of Scientific and Industrial Research-National Aerospace Laboratories (CSIR-NAL). Computational simulation of the conjugate model is validated against published numerical results. Numerical simulation for the adiabatic cooling effectiveness is carried out for a 1:3 scaled up flat plate test geometry, while the actual flat plate geometry is considered for the conjugate cooling effectiveness analysis. The test plate has 11 rows of cooling holes, and the holes are arranged in staggered manner with each row containing eight holes. For both adiabatic and conjugate cases, the same mainstream conditions are maintained with the inlet temperature of 329 K, velocity of 20 m/s, density ratio 1.3. The coolant to mainstream blowing ratios (BRs) are maintained at 0.4, 1.15, and 1.6. The coolant temperature is 253 K with the flow rates are according to the BRs. Cooling effectiveness is obtained by using CFD simulation with ANSYS fluent package. From the comparison of adiabatic and conjugate results, it is found that conjugate model is giving superior cooling protection than the adiabatic model and effusion cooling effectiveness increases with increase in BR. Investigations on comparison of angle of injection holes show that, 30 deg model give maximum effusion cooling effectiveness as compared to 45 deg and 60 deg models.