Abstract

Heat pumping is a useful technology in supplying high temperature heat for industrial purpose or district heating by using low temperature heat simultaneously. The absorption heat pump is a rather complex system while the vapor-compression heat pump requires power for compressing the working fluid. In addition, high amounts of waste heat, even at high temperature is available in industrial processes. This article analyzed a novel heat-driven high temperature heat pump with CO2 as working fluid and revealed its performance by a theoretical approach. It is driven by cooling a heat source at 300°C, which may be industrial excess heat. The results showed that the heating capacity supplied by the cycle increases with the increase of the cooled pressure while the temperature shows an opposite trend. The maximum coefficient of performance is 1.54 in the considered conditions.

Abstract

This paper firstly takes Zhongshan City as an example to analyze the feasibility of investment value of household rooftop PV power generation project under carbon trading mode. The results show that the current level of carbon price in Guangdong Province is not enough to promote residents’ investment in rooftop PV. Then, this paper further studies the impact of carbon price on the investment value of household rooftop PV power generation projects. The results show that the higher the carbon price level, the greater the increasing of investment value, and the level of government subsidy required is gradually declining. Finally, based on the research results, this paper puts forward two related conclusions and policy suggestions.

Abstract

Depletion of shallow mineral resources is forcing mining companies to exploit deeper deposits and design more complex mine access tunnels due to sophisticated nature of subsurface mining. Inevitably, this brings more complex mine ventilation networks, associated with higher energy profiles. Also, deep mines (i.e. deeper than 1km) and ultra-deep mines (i.e. deeper than 2.5km) are subjected to other heat loads, sourced by strata heat, auto-compression and equipment heat. These extreme heat loads result in further energy demands for the purpose of mine ventilation and air conditioning which is usually satisfied by grid power (or diesel generation in off-grid applications). Therefore, understanding the performance of mine ventilation and air conditioning systems is a necessity. For mine ambient air conditioning applications, bulk-air-coolers relying on spray cooling systems are commonly used. Although mine ventilation literature provides enough empirical design tools for industrial bulk-air-cooler system design, it still lacks a deeper numerical understanding to attain higher precisions in large-scale designs. Accordingly, this paper aims to provide a valid Computational Fluid Dynamics and Heat Transfer model to better understand the working principles of bulk-air-cooling systems. For this purpose, a previously validated CFDHT model was used to test the applicability of literature-ready, analytically expressed semi-empirical bulk-air-cooler design tools. Present study not only highlights the robustness of the introduced semi-empirical model, but also shows that the design tools used for modern bulk-air-cooler design purposes can capture an experimentally validated CFDHT model within ~7% agreement.

Abstract

A 3D model was established to study the influence of ice formation on the process of gas production during gas hydrate dissociation by depressurization. Considering effects of ice, the temperature field and absolute permeability of the reservoir were analyzed. Additionally, the cumulative gas production was compared with and without ice formation. The results indicated that the temperature change is a process of repeated fluctuations because ice affected the heat transfer in the reservoir. Meanwhile ice formation can reduce the absolute permeability near the production boundary significantly. And then, the permeability can recover from the boundary because of the constant temperature boundary. Moreover, compared to the condition without ice effects, the cumulative gas production with ice formation is more in the initial stage, and then it will become much less. And the gas production rate fluctuates with freezing and melting.

Abstract

CAES using porous geological formations such as sandstones could provide the large storage capacities required in future energy systems largely based on renewable sources. In such systems storage pressure, achievable mass flow and power output have strong interdependencies. Thus, an integrated assessment of the power plant and the geostorage is required, for which a coupling approach is presented. Three generic test cases are constructed, demonstrating an accurate representation during all operational modes.

Abstract

Natural gas is a cleaner fuel source alternative for heavy duty engines. This study discusses the conversion of a single-cylinder diesel research engine to a natural-gas spark-ignited engine with port fuel injection. The conversion to spark-ignited natural-gas operation may be performed with small modifications to the engine. The piston bowl geometry of the converted engine was shown to have a substantial effect on the apparent heat-release rate, showing a double peak for certain spark timings. Peak indicated efficiency was reported at 36 percent for spark timing of -10 CA ATDC, with peak IMEP of 8 bar occurring at -15 CA ATDC. The end of combustion characteristics for the bowl-in-piston engine geometry were strongly influenced by the final flame propagation in the squish band region.

Abstract

The flow behaviour of Vertical Axis Wind Turbine (VAWT) is highly unsteady even at a constant rotor speed and fixed free-stream velocity and therefore predicting the aerodynamic performance accurately is a computational challenge. Our study aims at presenting the comparison of two different mesh strategies (i) Sliding Mesh and (ii) Overset Mesh. Assuming the flow to be 2D, a computational study has been carried out using the commercially available ANSYS Fluent CFD (URANS) code. After ensuring grid independence and numerical stability, simulations are carried out at a fixed wind speed of 9 m/s and a tip speed ratio of 2.33. The turbine configuration chosen is three-bladed H-rotor vertical axis wind turbine having airfoil section NACA0021 and solidity ratio of 0.25 based on the diameter of the turbine. The power coefficient (CP) values obtained from both techniques are compared with the numerical and experimental measurements of Castelli et al. (2011). It is found that at TSR 2.33, the CP for overset mesh is predicted as 0.365 whereas, for the sliding mesh, it is 0.43. The results are in better agreement with the experimental results using the overset grid approach as compared to the sliding mesh approach. This comparison and ease of mesh generation using the overset grid approach will be helpful in analyzing the dual rotor VAWT (D-VAWT) configuration or any other innovative complex configuration which could improve the aerodynamic efficiency of VAWT.

Abstract

The combustion characteristics of biomass in the packed bed is investigated based on the CFD-discrete element method (DEM). During the combustion process, the biomass particle experienced drying, pyrolysis, combustion and cooling. The mass loss leads to the change of particle density and diameter, as the remnant composition is mainly ash. In this work, the shrinkage of packed biomass volume is modelled as the particle diameter is decreased based on DEM. The different effects of compositions in the particle on particle diameter are considered. The simulation results show good agreement with the experimental measurement.

Abstract

The dynamic responses of Solid oxide fuel cell (SOFC) power system across multiple time scales from micro seconds to minutes due to the phenomena of different nature that governing. Mismatching the time scale differences may lead to fuel starving and thermal shock during the fast load following. In this paper, the singular perturbation (SP) theory was introduced for modeling the mutli-time scale system dynamics. The dynamic model of SOFC power system in the coordinates in which slow and fast variables were explicitly defined and exactly separated. The resulting multi-single time scale models facilitate a better understanding of system dynamics, key parameters and their interactions, such as temperature, mass flow rate, current and voltage. Effective SOFC power system controllers can be designed based on these results.

Abstract

In this study, we evaluate the implementation of the concept of wastewater reclamation in the airconditioning system of an educative building located in a hot and arid climate region. In this building, Air conditioning condensates are not reused; a fraction of this condensates is disposed to the municipal sewage network while the other fraction falls into roads causing localized water stagnation that leads to the reproduction of endemic vectors. On the other hand, lawn and garden areas in this building are currently irrigated with potable water. Here, as it has been reported by other authors, we found that the amount and quality of air-conditioning condensates make viable to use it for gardening. Moreover, we describe a renewable alternative to collect, dispose, and transport the air-conditioning condensates for later implementation in lawns and gardens irrigation.