Yongzhong Liu

The Design of Water-reusing Network with a Hybrid Structure Through Mathematical Programming

A new design method for a water-reusing network, with a hybrid structure, to reduce the complexity of the network and to minimize freshwater consumption, is proposed. The unique feature of the methodology proposed in this article is to control the complexity of the water network by regulation of the control number in a water-reusing system. It combines the advantages of a conventional water-reusing network and a water-reusing network with internal water mains. To illustrate the proposed method, a single contaminant system and a multiple contaminant system serve as examples of the problems.

Theoretical tools for predicting optimal cross-sectional shapes in micro-gas chromatography.

It is meaningful to explore the possibility of improving the micro-GC column performance by adjusting the column cross-sectional shape. The objective of this study was to seek the column cross-sectional shape that results in larger plate number per meter than other shapes with the same cross-sectional area and the same flow resistance coefficient. We applied a model based on the volume averaging method to derive the expression of plate height for columns with arbitrary cross-sectional shapes, and conducted the shape optimization by combining the model and an optimization tool. By varying flow resistance coefficient, we obtained a series of optimal shapes. It is found that, the optimal shape with larger flow resistance coefficient is shallower and the related plate number per meter is larger. We predicted and optimized the performance of a micro-GC column reported in literature. The prediction agrees reasonably with experimental data. More than twice the plate number per meter of the original column was predicted by using a hypothetical column with one optimal cross-sectional shape.

A Simplified Model and Similarity Solutions for Interfacial Evolution of Two-Phase Flow in Porous Media

For two-phase flows of immiscible displacement processes in porous media, we proposed a simplified model to capture the interfacial fronts, which is given by explicit expressions and satisfies the continuity conditions of pressure and normal velocity across the interface. A new similarity solution for the interfacial evolution in the rectangular coordinate system was derived by postulating a first-order approximation of the velocity distribution in the region that the two-phase fluids co-exist. The interfacial evolution equation can be explicitly expressed as a linear function, where the slope of the interfacial equation is simply related to the mobility ratio of two-phase fluids in porous media. The application of the proposed solutions to predictions of interfacial evolutions in carbon dioxide injected into saline aquifers was illustrated under different mobility ratios and operational parameters. For the purpose of comparison, the numerical solutions obtained by level set method and the similarity solutions based on the Dupuit assumptions were presented. The results show that the proposed solution can give a better approximation of interfacial evolution than the currently available similarity solutions, especially in the situation that the mobility ratio is large. The proposed approximate solutions can provide physical insight into the interfacial phenomenon and be readily used for rapidly screening carbon dioxide storage capacity in subsurface formations and monitoring the migration of carbon dioxide plume.

Optimal Design of Heat Exchanger Networks by Using SQP Algorithm Based on GPU Acceleration

Abstract To increase computational efficiency and quality of solutions on large-scale mixed- integer nonlinear programming (MINLP) models of heat exchanger network synthesis (HENs), a paralleled sequential quadratic programming (SQP) algorithm based on graphic process unit (GPU) acceleration is proposed. It features that the HENs model is decomposed into independent nonlinear programming (NLP) sub-problems that are simultaneously solved by paralleled SQP algorithm on CPU-GPU heterogeneous architectures. The estimation formulae of speed-up ratios for single-GPU and multi- GPU are derived, and the acceleration performances of the proposed algorithm are demonstrated by two MINLP problems of HENs. Results present the effectiveness and the advantage to solve large-scale MINLP models of HENs problems.

Interfacial Evolution and Migration Characteristics of Acid Gas Injected into a Saline Aquifer

Abstract Acid gas injection into saline aquifers is one of promising ways to reduce greenhouse gas emissions and to dispose hazardous waste simultaneously. On the basis of Level Set method, an improved mathematical model that described interfacial dynamics of acid gas-brine system in a deep confined saline aquifer was proposed for predicting the propagation of the acid gas plume, which was featured by using Peng-Robinson equation and modified Lucas equation to describe variations of the density and viscosity of acid gas in saline aquifers. The evolutional characteristics of acid gas plume were obtained through numerical simulations using COMSOL Multiphysics 3.5a. The results showed that under intrinsic characteristics of aquifers and operational conditions given, the variation of acid gas density was the major factor that influences the patterns and shapes of the plume. The leading edge position of acid gas plume was intensively dependent on the acid gas composition. Under the scheme of fixed mass flow rate injection, as the molar fraction of H 2 S increased, the position of leading edge advanced gradually towards the injection well. Moreover, the estimation of the storage efficiency of acid gas in saline aquifers was clarified and discussed. The proposed approach and the simulation results will provide insights into the determination of optimal operational strategies and rapid identification of the consequences of acid gas injection into deep confined saline aquifers.

Analytical solutions to dissolved contaminant plume evolution with source depletion during carbon dioxide storage

Volatile contaminants may migrate with carbon dioxide (CO2) injection or leakage in subsurface formations, which leads to the risk of the CO2 storage and the ecological environment. This study aims to develop an analytical model that could predict the contaminant migration process induced by CO2 storage. The analytical model with two moving boundaries is obtained through the simplification of the fully coupled model for the CO2-aqueous phase -stagnant phase displacement system. The analytical solutions are confirmed and assessed through the comparison with the numerical simulations of the fully coupled model. Then, some key variables in the analytical solutions, including the critical time, the locations of the dual moving boundaries and the advance velocity, are discussed to present the characteristics of contaminant migration in the multi-phase displacement system. The results show that these key variables are determined by four dimensionless numbers, Pe, RD, Sh and RF, which represent the effects of the convection, the dispersion, the interphase mass transfer and the retention factor of contaminant, respectively. The proposed analytical solutions could be used for tracking the migration of the injected CO2 and the contaminants in subsurface formations, and also provide an analytical tool for other solute transport in multi-phase displacement system.

Research on the Solution of Heat Exchanger Network MINLP Problems Based on GPU

The optimization of heat exchanger network can be expressed in a Mixed Integer Non-Linear mathematical Programming (MINLP) model. However, it demands huge computing power to solve a realistic heat exchanger network optimize problem. Nowadays graphic processing unit (GPU) can be very powerful for general purpose computation. Based on the CUDA framework, this paper presents a parallel computing framework for solving the MINLP problem. We concentrate on both parallel computing model and specific GPU programming level optimization. Tests on a simple MINLP problem is conducted and the results show the new solution has 40 times faster than the one running serially on CPU.

Exergy-based environmental impact analysis in the industrial processes

Abstract The concept of cumulative exergy consumption for treatment of emissions (CExCT) is proposed based on an acceptable level of the environmental impact. The concept of equivalent cumulative exergy consumption (ECExC) is presented as the objective function for total environmental impact analysis of industrial processes and thus providing information of how effective a process is regarding the consumption of natural resources. The amount of resources and energy required to operate and construct a process can be investigated and quantified from the viewpoint of ECExC. A heat pump distillation process is taken as an example to demonstrate the effectiveness of this method. Moreover, a comparison is made with the results obtained from economic optimization. It appears that this method may be particularly useful for environmental impact minimization of industrial processes.