Thermal Spray Coatings’ Performance in Phase Change Materials

Despite the high potential of geothermal reservoirs in Meshkinshahr, we only see the government entering the electricity extraction of geothermal energy because the cost of the Meshkinshahr geothermal electricity is higher than the balanced price of the electricity market and the private sector is disadvantaged for entering it. So, the government has adopted a feed in tariff policy for geothermal electricity to encourage private sector investors. This research is aimed at financial appraisal of Maskinshahr geothermal power plant with the assumption of feed in tariff by the government with Equivalent Uniform Annual Worth, Equivalent Uniform Annual Worth, and Equivalent Uniform Annual Cost methods. Equivalent Uniform Annual Benefit is obtained from feed in tariff of government and Equivalent Uniform Annual Cost is determined based on technical and economic components of the geothermal power plant and macroeconomic parameters. The results of the data analysis show that the construction of the geothermal power plant is fully justified with the 14% reduction rate, but if the investor's minimum expected rate exceeds 54%, the construction of the power plant has no economic justification. Also, if the construction of Meshkinshahr geothermal plant takes more than 13 years and 5 months like the government project, the generation of geothermal power is not cost-effective.

This paper presents the work carried out in ‘SEHRENE’ (Horizon Europe Project) to select suitable materials of construction for MgCl2.6H2O-based PCM (phase change material) thermal energy storage system. Commonly used construction materials, such as carbon steels, often have corrosion rates that limit their use in industrial PCMs. Metals that form passivating oxide films, such as Al, may give lower corrosion rates if fluxing of the oxide does not occur in the molten PCM. There have been suggestions to use Al alloy construction materials in PCM-based thermal energy storage (TES) systems where better heat transfer is essential, and carbon steel where structural integrity and cost-effective construction material is more suitable. This philosophy forms the core of the TES design in the above mentioned project. However, galvanic corrosion between the two dissimilar metals is a concern. To understand this further, carbon steel substrates were coated with Al, cut to expose Al-steel interface, and exposed to molten MgCl2.6H2O. The galvanic corrosion performance was determined by examining the cross-sections of specimens post-exposure. The cross-sectional metallographic analysis revealed that corrosion was detectable. However, no significant effect was discernable. The experimental work demonstrated that MgCl2.6H2O could be a potential PCM candidate for thermal energy storage system. The study also indicated coatings, such as thermally sprayed aluminum (TSA), could be considered for such applications to mitigate the corrosion issues based on the ease of application, availability, and cost.

Estimation of efficiency of a geothermal power plant is a subject of debate with regards to the best method that should be applied. In Zarrouk and Moon, (2014) [1] the conversion efficiency of geothermal plants (dry-steam, single and double flash, binary and hybrid steam binary) was analyzed and correlations developed. In this paper, focus is made on binary power plants to further develop the correlation in Zarrouk and Moon, (2014) [1] so as to get a more accurate estimation formula that can be used during prefeasibility studies by taking into consideration the estimated rejection temperatures from the chemical composition of the geothermal fluid. Different methods for efficiency measurements are described and are shown to be dependent on the objective of calculation. During geothermal project development, it may be necessary to use conversion efficiency to get a realistic estimate of electricity production from a given estimate of the reservoir capacity for geothermal systems. Optimization of power plant operations on the other hand may require the use of utilization efficiency to achieve maximum benefit for the power plant operations. Published data from thirty-five (35) binary power plants are used to compare existing correlations and develop a new correlation that can be used to estimate production output from a reservoir during pre-feasibility studies. The results show more accurate conversion efficiency can be generated when the effect of reinjection temperature is taken into account

The Committee on Metallizing of the American Welding Society sponsored a test program to study the corrosion protection afforded by thermal sprayed aluminum and zinc coatings applied to structural at eel. The first panels were exposed in January, 1953. Inspections were made at 1, 3, 6, and 12 year intervals. Reported results examined the performance of the subject metallized coatings in marine atmospheric and seawater environments. Seawater tests included full and half tide immersion in quiet seawater and full immersion in flowing seawater (approximately 3 knots). The subject conditions are highly representative of those found on off-shore structures. The results indicate that low carbon steel can be protected from the corrosive effects of these environments for 18 years or more by the application of flame sprayed zinc or aluminum coatings. INTRODUCTION This paper reports the results of an l8-year study of the corrosion protection afforded by metallized aluminum and zinc coatings applied to low carbon steel. Test sites were selected throughout the United States to provide a wide variety of environmental conditions. These included urban, industrial, salt air, and severe marine atmospheric exposure. Also below mean tide, mean tide, and total seawater immersion conditions were tested. This paper will only be concerned with the marine atmospheric and seawater environments. There were three major program objectives:To determine the life of any given thickness of coating in a specific environment (and the protection afforded the base metal).To determine the effect of various methods of steel preparation on the corrosion protection properties of the flame sprayed coating.To determine the increase in life of the aluminum and zinc flame sprayed coatings with the addition of seal coats. Steel panels, numbering 4,248, were employed in the study; half were coated with commercially pure zinc and the balance coated with commercially pure aluminum. Steel panels for atmospheric exposure were 4 × 6 × 1/8 inch and 4 × 12 × 1/8 inch for seawater exposure. Aluminum and zinc coatings for atmospheric exposure tests were 0.003, 0.006, 0.009 inch. In addition, a coating thickness of 0.018 inch was included in seawater exposure tests. Originally, exposure periods of 1, 3, 6, and 12 years were scheduled. At the end of each of the above periods, a complete set of panels, consisting of three identical panels of each type, was to be removed from the exposure racks for laboratory examination. At the same time, the panels of each type remaining on site were to be inspected and their condition recorded. However early inspections indicated that nearly all coatings would last for more than 12 years, at all exposure sites. Accordingly, the panels intended for removal at 6 years were left on exposure for 12 years, and the 12year set was left exposed for 18 years. Results of the 6- and l2-year inspections are reported in American Welding Society publications C2.8-62 and C2.ll-67, respectively.

Geothermal electric power in Iceland: Development in perspective

The corrosive nature of phase change materials (PCMs) presents a significant obstacle to the long-term reliability of PCM-based thermal energy storage (TES) devices. Carbon and low-alloy steels are typically the preferred construction materials for TES devices due to their mechanical strength, widespread availability, weldability, and cost-effectiveness. Although aluminium alloys have been proposed as alternative materials because of their superior corrosion resistance and heat transfer coefficient, their higher cost often limits their practical adoption in large-scale applications. Consequently, applying aluminium-based coatings onto carbon steel substrates offers a promising compromise between performance and affordability. As part of the SEHRENE project under the Horizon Europe programme, this study investigates the effectiveness of aluminium alloy thermal spray coatings for corrosion protection of carbon steel in Erythritol-based TES devices. The corrosion behaviour of the thermally sprayed aluminium (TSA) was evaluated through macroscopic observation and detailed microstructural analysis using metallography, optical microscopy, and electron microscopy techniques. The study also provided information on the possible galvanic interactions between carbon steel and aluminium in molten erythritol relevant to thermal energy storage applications.

The first part of the review presents information on the scale and specific features of geothermal energy development in various countries. The classification of geothermal power plant (GeoPP) process flow diagrams by a phase state of the primary heat source (a geothermal fluid), thermodynamic cycle, and applicable turbines is proposed. Features of geothermal plants using methods of flashing and steam separation in the process loop and a flowsheet and thermodynamic process of a geothermal fluid heat-to-power conversion in a GeoPP of the most widespread type using a double-flash separation are considered. It is shown that, for combined cycle power units, the specific power-to-consumption geothermal fluid ratio is 20–25% higher than that for traditional single-loop GeoPP. Information about basic chemical components and their concentration range for geothermal fluids of various formations around the world is presented. Three historic stages of improving geothermal energy technologies are determined, such as development of high-temperature geothermal resources (dry, superheated steam) and application of a two-phase wet-steam geothermal fluid in GeoPP power units with one or two expansion pressures and development of binary cycle GeoPPs. A current trend of more active use of binary power plants in GeoPP technological processes is noted. Design features of GeoPP’s steam turbines and steam separating devices, determined by the use of low-potential geothermal saturated steam as a working medium, which is characterized by corrosion aggressiveness and a tendency to form deposits, are considered. Most promising Russian geothermal energy projects are determined. A list of today’s most advanced geothermal turbine performance technologies is presented. By an example of a 25 MW steam turbine design, made by JSC Kaluga Turbine Works, advantages of the internal moisture separation with a special turbine-separator stage are shown.

Motor vehicle traffic is commonly cited as a barrier to walking, but national level perceptions of traffic characteristics that negatively influence walking and potential traffic mitigation strategies remain unclear. The objectives of this study were to describe perceptions of (1) traffic characteristics that make walking unsafe in the United States and (2) potential mitigation strategies to address these concerns among those who report traffic as a barrier to walking. Data were from FallStyles, a nationwide internet panel survey conducted in October 2019 (n = 3,284 adults). Respondents reported if traffic makes walking unsafe where they live; those who answered yes were then asked about traffic characteristics that make walking unsafe (number of vehicles, speed of vehicles, distracted or impaired driving, types of vehicles, and other reasons) and potential mitigation strategies (new or improved sidewalks, crosswalks, pedestrian signals, street lighting, things that slow vehicles down, separating the sidewalk from the road, fewer vehicle lanes, and other). Prevalence of responses was assessed overall and by select sociodemographic and geographic characteristics, and by walking status. Nearly 25% of US adults reported that traffic is a barrier to walking where they live. Of these, 79% selected vehicle speed as a contributing traffic characteristic, and 57% indicated new or improved sidewalks as a potential mitigation strategy. These top responses were shared across all sociodemographic, geographic, and walking behavior subgroups. Speed reduction efforts and built environment enhancements such as sidewalks may alleviate pedestrian safety concerns. Promotion campaigns may be needed to bring awareness to such changes.

This calculator is a handy tool for interested parties to estimate two key life cycle metrics, fossil energy consumption (Etot) and greenhouse gas emission (ghgtot) ratios, for geothermal electric power production. It is based solely on data developed by Argonne National Laboratory for DOE’s Geothermal Technologies office. The calculator permits the user to explore the impact of a range of key geothermal power production parameters, including plant capacity, lifetime, capacity factor, geothermal technology, well numbers and depths, field exploration, and others on the two metrics just mentioned. Estimates of variations in the results are also available to the user.

Latent heat storage systems consisting of phase change materials (PCMs) offer the advantage of a large thermal energy storage density as compared to sensible heat storage systems. Most recent work has focussed on organic and inorganic PCMs which have problems of subcooling and phase segregation. Metallic PCMs are a recent innovation for medium to high temperature applications due to their high thermal conductivities, high volumetric storage capacities and their low degrees of sub-cooling during the release of latent heat. For medium temperature applications like cooking of food, very limited work has been done on metallic PCMs for energy storage. Solder based PCMs have rarely been investigated for medium temperature applications thus it is necessary to carry out an experimental study on the use of a solder as PCM candidate. No work has ever been reported using the eutectic solder (Sn63/Pb37) as a PCM. Its use is justified since it is low cost and locally manufactured solder worldwide. Another recent innovation is cascaded thermal energy storage (TES), whereby two PCMs with different melting temperatures are used in a single storage tank to improve the efficiency of energy storage. No work has also appeared in recent literature involving metallic solders in cascaded systems. In a bid to investigate the suitability of the eutectic solder as a PCM for medium temperature applications, two eutectic solder (Sn63/Pb37) based systems are experimentally evaluated during discharging cycles. The first system is a single PCM system composed of a packed bed of spherically encapsulated eutectic solder capsules. The other system is a two PCM cascaded system comprising of eutectic solder spherical capsules at the top and erythritol spherical capsules at the bottom in a storage ratio of 50 %: 50 %. Discharging experiments are carried with three different discharging flow-rates to investigate the effect of the flow-rate on the thermal performance. The three discharging flow-rates used are 4 ml/s, 6 ml/s and 8 ml/s. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. The single PCM system shows higher energy and exergy rates for most of the discharging duration compared to the cascaded system. An increase in the flow-rate increases the peak energy and exergy discharging rates for the single PCM and the cascaded PCM storage systems. The single PCM system out-performed the cascaded system during the discharging tests possibly due to the lower melting temperature and lower thermal conductivity of the bottom PCM (erythritol) in the cascaded system. However, for the higher flow-rates (6 ml/s, 8 ml/s), the cascaded system shows a slightly better or comparable performance at the start and at end of discharging.

Review on hybrid geothermal and solar power systems

High power density thermal energy storage using additively manufactured heat exchangers and phase change material

Thermal energy storage systems are crucial for reducing dependency on fossil fuels and minimizing CO2 emissions. The building sector is a major sector responsible for producing high levels of CO2 in most countries (including Qatar). Thermal energy storage can be accomplished either by using sensible heat storage or latent heat storage components. Latent heat storage is more attractive than sensible heat storage because of its high storage density with smaller temperature fluctuations.[1] The materials able to utilize latent heat which can undergo phase changes (usually solid to liquid changes) at relatively low temperatures, while absorbing or releasing high amounts of energy are called phase change materials (PCMs).[2] Most promising PCMs are paraffin waxes which contain saturated hydrocarbon mixtures. They are frequently used due to their numerous advantages such as high latent heat of fusion, negligible super-cooling, and chemical inertness.[3,4] In this contribution, thermal properties of the PCMs based on linear low density polyethylene (LLDPE), different types of paraffin waxes with melting points, 25 oC and 42 oC, and expanded graphite (EG) were characterized by unique transient guarded hot plate technique (TGHPT), which allow to identified thermal properties of large sized samples[5] in comparison with commonly used ifferential scanning calorimetry (DSC). It was confirmed that all prepared PCMs were able to store and release huge amount of thermal energy. The 25 % increase of capacity to store and release a thermal energy was observed by PCMs contains paraffin wax with melting point 25 oC in comparison with paraffin wax with melting point 42 oC. Also reproducibility of storage and release heat of the PCMs by repeating of heating and cooling process has been demonstrated. Moreover, the increase of the EG content in the PCMs led to the increase of thermal conductivity from 0.24 W/mK for PCMs without EG to 1.3 W/mK for PCMs contain 15 wt.% of EG. Additionally, life cycle assessment of prepared PCMs has been demonstrated to identify the effects of these new materials on the Qatar environment. Our results indicate that using of PCMs in building industry can reduce emission of CO2 up to 10%.

Thermal energy storage with phase change materials (PCMs) has attracted a lot of attention in the last several decades. Most PCMs do not change phase at a constant temperature but rather in a certain temperature range. It means that the PCM need to transit through its phase change temperature range to fully change phase from the solid state to the liquid state and vice-versa. The situation, in which the phase transition begins and/or ends within the phase change temperature range (in the mushy zone), is usually called a partial phase transition (or a partial phase change). The partial phase transitions occur quite often in real-life thermal energy storage systems with PCMs; especially when a PCM has a wide phase change temperature range. The behavior of PCMs during the partial phase transitions is poorly understood at the moment, because the experimental techniques used for the characterization of PCMs (such as the differential scanning calorimetry – DSC) are difficult to apply for the study of partial phase transitions. The lack of knowledge in this area influences the accuracy of phase change simulation models. The main goal of the experimental investigations, described in the paper, was to obtain data for the development of a simulation model for partial phase changes. The experimental set up for the investigation of partial phase changes of PCMs has been proposed, assembled, and the pilot measurements have been conducted. The experimental set up consists of two water storage tanks (that can be maintained at different water temperatures), a water-PCM concentric tube type heat exchanger and a data acquisition system. The water flows through the central tube of the heat exchanger while the PCM is located in the annular space of the exchanger. The water storage tanks, maintained at the temperatures within the phase change temperature range of a PCM, allow for the investigations of the heat storage cycles consisting of partial phase changes.

Corrosion of metal and metal alloy containers in contact with phase change materials (PCM) for potential heating and cooling applications