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Abstract To ensure techno-economically suitable installation of ground source heat pump (GSHP) systems, thermal and hydrogeological properties of the subsoil need to be investigated. In this paper, the geothermal potential for three types of GSHP installations in the urban area of Wuhan city is assessed based on preliminary geological investigations. The potential for shallow geothermal energy is evaluated for surface water heat pump systems (SWHP), groundwater heat pump systems (GWHP) and ground coupled heat exchanger heat pump systems (GCHP). The mapped shallow geothermal potentials provide essential information for the installation of GSHPs and for the management of geothermal resources of Wuhan city. Furthermore, the heat transfer rates for some typical configured borehole heat exchanger (BHE) are tested by field Thermal Response Tests (TRT). In order to understand the techno-economic feasibility of the GSHPs, different types of the installed systems are measured and analyzed.

Abstract The vertical pipe intake-outlet plays an important role in the pumped hydro energy storage (PHES), and its main parameters included the orifice height ratio (H∗), the diffuser short semi-axis ratio (a∗), the diffuser long semi-axis ratio (b∗) and the cover plate radius ratio (Rc∗). The aim of this study was to analyse effects of the parameters and obtain the optimal design. An integration method combining computational fluid dynamics (CFD), response surface methodology (RSM) and genetic algorithm was proposed. To evaluate grid independency, the grid converge index was introduced. Based on the validation for the baseline design (H∗ = 0.577, a∗ = 1.087, b∗ = 4.231 and Rc∗ = 1.635), a reliable CFD model was developed to obtain results of sample points. Then RSM models were constructed and assessed, and contribution and interactions of the parameters were analyzed. Finally, the optimal design (H∗ = 0.422, a∗ = 1.177, b∗ = 5.363 and Rc∗ = 2.115) was obtained. The CFD results show that the overall head loss coefficient, the inflow and the outflow velocity distribution coefficient are reduced by 4.687%, 11.765% and 38.596%, respectively. Especially, the negative velocity at the trashrack section in the pump mode is eliminated. The improvement demonstrates that the proposed method achieves significant superiority over the trial-and-error method traditionally adopted in the intake-outlet design.

Abstract Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.

Abstract It has been recognized that oils derived from microorganism and wastewater sludge are comparable replacements of traditional biodiesel production feedstock, which is energy intensive and costly. Energy balance and greenhouse gas (GHG) emissions are essential factors to assess the feasibility of the production. This study evaluated the energy balance and GHG emissions of biodiesel production from microbial and wastewater sludge oil. The results show that energy balance and GHG emissions of biodiesel produced from microbial oil are significantly impacted by the cultivation methods and carbon source. For phototrophic microorganism (microalgae), open pond system gives 3.6 GJ higher energy gain than photo bioreactor system in per tonne biodiesel produced. For heterotrophic microorganisms, the energy balance depends on the type of carbon source. Three carbon sources including starch, cellulose, and starch industry wastewater (SIW) used in this study showed that utilization of SIW as carbon source provided the most favorable energy balance. When oil extracted from municipal sludge is used for biodiesel production, the energy gain is up to 29.7 GJ per tonne biodiesel produced, which is higher than the energy gain per tonne of biodiesel produced from SIW cultivated microbes. GHG emissions study shows that biodiesel production from microbes or sludge oil is a net carbon dioxide capture process except when starch is used as raw material for microbial oil production, and the highest capture is around 40 tonnes carbon dioxide per tonne of biodiesel produced.

Abstract Molten salts are subjected to heating-cooling thermal shock cycle in the operation of concentrating solar power (CSP) plant. In this work, the quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are comparatively studied under different thermal shock conditions. After 500 thermal shock test cycles, morphological and structural analysis of samples are carried out by wavelength dispersive x-ray fluorescence (WD-XRF), Fourier-transform infrared (FTIR), x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Meanwhile, thermos-physical properties of samples are comparatively analyzed. The results show the average melting point and average initial crystal temperature of QNN mixed salt are maximum 135 °C, 82.6 °C lower than that of Solar salt, respectively. The decomposition temperature of QNN mixed salt is maximum 52.1 °C higher than that of Solar salt. The specific heat of QNN mixed salt increases with the increasing of thermal shock temperature. The specific heat and thermal conductivity of QNN mixed salt maximally increase 15.46% and 9.8% compared with its base salt, respectively. Meanwhile, the thermal conductivity and viscosity of QNN mixed salt are slight higher than that of Solar salt. The Solar salt viscosity decreases with the increasing of thermal shock temperature.

Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.

Abstract Water management is a critical issue for proton exchange membrane (PEM) fuel cells, and the use of a microporous layer (MPL) substantially improves the PEM fuel cell performance, reliability and durability through improved water management. In this study, graphene, technically a yet-to-be-developed category of material, is investigated as a potential MPL material, due to its high electrical and thermal conductivity. MPLs made of graphene (G-MPL) have been fabricated and assessed through morphological, microstructural, physical, and electrochemical characterizations and performance testing in a single scaled-up cell. Comparison is also made with MPLs made of a conventional material, Vulcan (V-MPL). The results show that the G-MPL has a unique morphology composed of horizontally packaged graphene flakes that improves water management, in-plane electrical conductivity (up to 2 times), catalyst activity, and platinum (Pt) utilization (up to 10%). The cell with the G-MPL has a better performance than the cell with the V-MPL under both fully (100% RH) and partially (40% RH) humidified conditions, with the peak power densities of 0.98 W cm−2 and 0.60 W cm−2, respectively – these peak power densities are about 7% and 43% higher than those obtained for the cell with the V-MPL at 100% and 40% RH, respectively.

Abstract Desalination of water is essential to supply sufficient good quality water to remote areas to satisfy various needs. Saudi Arabia has enormous amount of deep water and the underground water in many areas of this country is so brackish that it requires extensive pre-treatment. In order to utilise inland reserves of brackish water by the local inhabitants, the Energy Research Institute (ERI) of King Abdulaziz City for Science and Technology (KACST) installed a Photovoltaic (PV) powered water desalination Reverse Osmosis (R.O) plant at Riyadh, Saudi Arabia. The reject brine rate from this plant is very high. Due to the inherent advantages of solar still assemblies, for instance; simple to construct and maintain using locally available material, and high technical feasibility in remote areas, a solar still plant capacity of 5.8 cubic meter distillate per day is proposed to couple with the existing PV-RO plant in order to utilise most of the reject brine instead of throwing on the ground. The estimated cost of product water obtained through this design is found to be Saudi Riyal 1.9 (US$0.50) per cubic meter. The proposed design of the solar still assemblies can be applied to configure a 100% solar powered desalination system for any location and quality of brackish water.

Abstract Xylose is a by-product of lignocellulosic biomass processing for production of second-generation biofuels and could be suitable for bioproduct manufacturing. This paper describes an innovative approach that enables the system to achieve high yielding for hydrogen production. The study compared 4 physicochemical pre-treatments performed in an anaerobic mixed culture (acidic, thermal, acidic-thermal and thermal acidic) to achieve an inoculum with a high-efficiency xylose to hydrogen conversion under mesophilic conditions (30 °C). The acidic pre-treatment was the most efficient to select microorganisms able to produce hydrogen and volatile acid from xylose. Kinetics has shown that acidic pre-treatment had a hydrogen/xylose molar yielding factor of 1.57 (molar base) and a hydrogen maximum production rate of 253 mL H2 h−1. Mass balance considered all possible metabolic pathways using xylose as a substrate. Anaerobic degradation of ethanol was the most active pathway for hydrogen production in all experiments, except for the control. Each pre-treatment performed for the original inoculum resulted in different microbiological profiles, but the genus Clostridium was the most abundant in all assays. Acidic pre-treatment stimulated the growth of organisms from the genera Peptostreptococcaceae, Truepera and Kurthia, which could be related to the better results in hydrogen production found in this condition.