Low-temperature System Research Articles

Performance Optimization and Numerical Simulation Study of Sludge Low-Temperature Drying System

Performance Optimization and Numerical Simulation Study of Sludge Low-Temperature Drying System

Thermal conductivity and mechanical properties of polymeric aerogels for cryogenic insulation applications

Non-vacuum insulation systems are frequently applied in the thermal management of low temperature systems as well as for the use and storage of cryogens. Aerogels are known for their low density, high mesoporosity, high surface areas, low thermal conductivity and high acoustic impedance. This study focuses on polymeric aerogels that can be mass produced as large monoliths while maintaining the low thermal conductivity over a wide temperature range. The manufacturing flexibility of polymeric aerogels allows fabrication of monolithic blocks and sheets that can be applied in various configurations to insulate cryogenic and superconducting devices. To measure the thermal conductivity, an immersion calorimeter was developed and has been operated at different cold boundary temperatures. The calorimeter heats a hollow cylinder of insulating material on the inside surface and the surrounding bath maintains a cold boundary. This calorimeter was used to measure the thermal conductivity of commercially available FoamGlass and a hollow cylinder of a polymeric aerogel machined from a cast cylinder. The thermal conductivity of the FoamGlass and the polymeric aerogel are compared at room temperature (290 K), ice bath (273 K), and at liquid nitrogen (80 K) cold boundary temperatures. Room temperature measurements of the modulus of elasticity and yield strength using an optical technique are also reported for flat specimens of the aerogel made from the same stock as the cylindrical specimens tested for thermal conductivity. Mechanical properties of aerogels are also reported under compression and both at room temperature and at cryogenic temperature (Liquid nitrogen).

Multi-scale investigation of heat and momentum transfer in packed-bed TES systems up to 800 K

With the rising cost of energy and the advancement of corporate social responsibility, there is a growing interest in addressing the challenge of recovering and storing high-temperature waste heat. Sensible heat storage in packed beds stands out as a cost-effective and seemingly straightforward solution for high-temperature Thermal Energy Storage (TES). Engineering models developed to design low-temperature TES systems were tentatively used to design this new generation of high-temperature systems. Delving into the physics of coupled heat and mass transfer reveals a lack of validation of this approach. This study seeks to establish a comprehensive bottom-up methodology - from the particle scale up to the system level - to provide informed and validated engineering models for the design of high-temperature TES systems. To achieve this goal, we developed a multi-scale numerical model to explore the physics of heat and momentum transfer in packed-bed TES systems. At the microscopic scale (pore/particle), we consider the flow of a compressible high-temperature gas between the particles, coupled to transient heat conduction within the particles, with particular attention given to incorporating accurate temperature-dependent viscosity for the gas phase and thermal conductivity and density for both solid and gas phases. At the macroscopic scale (engineering), we propose a high-temperature extension of state-of-the-art two-equation TES models. The governing equations considered are the volume-average conservation laws for gas-mass, gas-momentum and energy of both phases. The multi-scale strategy is applied to a randomly packed bed of spherical particles generated with the discrete element method (DEM) software LIGGGHTS. Numerical models for both scales were implemented in the Porous material Analysis Toolbox based on OpenFoam (PATO), which is made available in Open Source by NASA. Microscopic scale simulations were used to infer the effective parameters needed to inform the macroscopic model, namely, permeability, Forchheimer coefficient, effective thermal conductivities, and the heat transfer coefficient. The informed macroscopic model reproduces with excellent accuracy the average temperature fields of the physics-based microscopic model. Pore-scale analysis shows highly three-dimensional flow characterized by reverse flow and strong cross-flow in the packed bed system. Moreover, it indicates the coupling between temperature and velocity fields, where a nonuniform velocity field results in uneven temperature distributions across the fluid and the solid spheres within the packed bed, subsequently affecting the macroscopic heat transfer coefficient. The overall strategy is validated by comparison to available experimental data. This bottom-up methodology contributes to the understanding and opens new perspectives for a more precise design and monitoring of high-temperature TES systems.

Phase diagrams of CoSO4-H2O and CoSO4-H2SO4-H2O systems for CoSO4·nH2O (n = 6,7) recovery by cooling and eutectic freeze crystallization

This paper reports the solid-liquid phase equilibria of the CoSO4-H2O and CoSO4-H2SO4-H2O systems at low temperatures. Binary and ternary phase diagrams, including the stable solid phases CoSO4·6H2O and CoSO4·7H2O were established using experimental data and thermodynamic modeling applying the mixed-solvent electrolyte (MSE) model. The results showed that the addition of H2SO4 shifts the eutectic temperature and concentration to lower values for cobalt sulfate and ice crystallization. The trends obtained from the experimental data and the modeling are consistent for the binary CoSO4-H2O system with good agreement, but the ternary CoSO4-H2SO4-H2O system shows some deviations. In general, the MSE model is shown to be reliable for inferring and establishing the phase diagram of the low-temperature system. The phase diagrams are helpful for designing the pathways of cooling crystallization and eutectic freeze crystallization and assessing the performance of the low-temperature crystallization process in the production of CoSO4 hydrates. In addition, some practical examples of cooling crystallization and eutectic freeze crystallization of CoSO4 solutions are provided.

Experimental study of a novel in-tube spray evaporative condenser for geothermal power generation

To enhance the efficiency of medium to low-temperature geothermal power systems, we designed a novel in-tube spray evaporative condenser. Experimental setups for single-tube heat exchange were devised, examining both water-water and working fluid-water configurations. The study analyzed the impact of air volume and hot water flow rate on heat transfer. Economic comparisons were made in laboratory conditions among the novel evaporative condenser, traditional evaporative condenser, water-cooled condenser, and air-cooled condenser. Results indicated: (1) The novel evaporative condenser exhibited 1.5–1.7 times higher heat flux density and 2.0–2.7 times higher mass transfer coefficient, indicating superior heat transfer performance compared to the traditional one. (2) Variations in hot water flow rate within a certain range had minimal impact on condenser performance when the condenser size was constant, providing valuable insights for condenser selection and structural design. (3) Both total power and water consumption of the novel evaporative condenser were lower than the other three types. Its daily operating cost was approximately 3/4 of the traditional evaporative condenser, 1/2 of the air-cooled condenser, and 1/4 of the water-cooled condenser, demonstrating superior economic feasibility.

Decreasing the Return Temperature in District Heating Networks Thanks to a Switch to Alternative Substation Architectures

District heating networks (DHN) are key systems for managing heating and reducing carbon emissions at a large scale. Therefore, increasing their efficiency is a key to reduce climate change. DHNs with centralized production are supplying hot water to building substations (interface between the DHN and the buildings) for domestic hot water (DHW) production and space heating (SH) using heat exchangers. Colder water is returned to the centralized district heating system by the return pipe. One of the crucial factors to improve the efficiency of DHNs is to decrease the return temperature in the network to keep the same amount of energy transferred to the buildings while reducing the thermal losses and the flow rate, leading to more savings. In this paper, we model and simulate two of the most common DHN substation architectures used in a typical third-generation DHN to identify their flaws and propose new district heating substation architectures that can increase the DHN efficiency. The main result from our study is the consistent reduction in the average return temperature across all scenarios when implementing our proposed architectures. The reduction ranged between 3.7 °C and 10.2 °C. We also found that the lower the heating temperature, the greater the reduction. This is particularly beneficial as buildings are increasingly equipped with low-temperature heating systems, especially new constructions. Moreover, these architectures showed optimal efficiency with new buildings that have a high water heating demand compared to heating demand. This is due to the higher impact of cold water preheating.

Influence of hot water consumption patterns on the viability of low-temperature solar thermal systems in the food industry

The thermal demand in agri-food industries is characterised by its considerable variability, hindering the implementation of Solar Water Heating Systems (SWHS). The main objective of the study is to provide an overview of how consumption patterns influence the profitability and energy savings of SWHS in the sector, while also identifying additional key variables that affect their viability. For this purpose, approximately 1,300,000 cases have been examined, considering a wide range of consumption patterns, economic variables, and locations. Demand seasonality, weekly frequency and energy prices exhibit the greatest impact on the feasibility of SWHS. Uniformity of daily demand, location and investment cost are also determinants. Thus, single-day-per-week consumption patterns make SWHS unviable in most scenarios. However, with only three non-consecutive days, feasibility increases significantly, achieving paybacks of less than 5 years and energy savings of over 40 % when conditions are highly favorable. In strongly seasonal industries, the viability of SWHS is seriously compromised. The payback in patterns with a peak consumption in the early morning can double the value with uniform one (e.g., from 4 to 8 years in the most favorable scenarios at a price of 0.1 €/kWh). The results tables reflecting payback and energy savings in thousands of different scenarios represent a valuable tool for decision-making in industries. By looking for the scenario with the most similar characteristics, it is possible to estimate the profitability and savings of the SWHS in a given industry, as well as the possible variations when changing the assumed variables.

Evaluation on novel Kalina power generation system through exergoenvironmental analysis

First law analysis assesses the performance of the system considered for investigation in the energy aspect. Low-temperature power generation system suitable to recover waste heat from a renewable source is investigated in the present work. The system is adopted to work at hot sink conditions and investigation on performance assessment is carried out in exergy aspect. Exergy analysis in both conventional and advanced methods proposes the system components which need improvements in themselves and associated with other components more properly. Exergoenvironmental analysis using the Life cycle assessment (LCA) method is examined in the system under the same sink conditions. Exergy analysis reveals that the component with a high source will yield more losses resulting in higher irreversibility. Hence turbine and evaporator need investigation in improving the system’s performance. Exergoenvironmental investigation suggests that the highest impact results in the low-temperature regenerator (LTRGN). The improvement in these components' designs and limitations in the characteristics of the material chosen and the manufacturing methods involved will favor a higher performance of the system. LTRGN has resulted in with high relative cost difference value of 23.85 % and seeks improvement. The exergy destruction is in a larger amount in the components evaporator and turbine with 70.66 kW and 30.99 kW respectively. Avoidable exergy destruction value of evaporator, condenser results 51.11 $/hr and 16.64 $/hr respectively. The LTRGN has an environmental effect rate of 54.83 mPts/hr and device-related environmental effects of 45.16 mPts/hr. The (ĖD/ĖP), (Ẏ/ĖP) and (Ż/ĖP), values at 85% pump efficiency results 2.16, 0.00946 and 0.30871.

Paddle design based on continuous low-temperature vacuum drying system in fishmeal production

With the rapid development of aquaculture, fishmeal is gradually processed into high-quality aquafeed, and there is a great demand for fishmeal in China. In order to solve the problems in the traditional processing process, the process research, focusing on the fishmeal processing process of the most critical link - drying paddle research. This paper mainly focuses on the continuous low-temperature vacuum drying equipment research, on the basis of the existing process to improve the design of the paddle structure. Compared with the current process, the fishmeal produced by continuous low-temperature vacuum dryer, under the same raw materials and the same time conditions, the transport capacity of the dryer per unit of time and the drying area of the paddle have been effectively improved.

Possibility assessment of the low-temperature district heating systems implementation in Ukraine

These researches concern the application of renewable energy sources in district heating systems. In Ukraine, district heating systems cover approximately 50% of the demand for thermal energy in the residential and communal sector. District heating systems 2G are most often used, which are characterized by high temperatures of the heat coolant, the lack of accounting for heat energy consumption during transportation of the heat coolant, and the use of fossil fuels. In the countries of the European Union, the introduction of district heating systems is considered one of the key directions for the transition to a decarbonized, environmentally safe and efficient energy system. The development of district heating systems technologies makes it possible to lower the temperature of the heat coolant in heat networks and increase the use of renewable energy sources. Ukraine will eventually become a full-fledged member of the European Union, and this determines the need to find ways to bring Ukraine's heat supply systems to the 4G level, in particular to low-temperature district heating systems with the most efficient use of renewable energy sources and waste heat. This article examines climatic, physical-geographical and social features, regulatory, technical and financial-economic opportunities and barriers to the implementation of low-temperature district heating systems in Ukraine. As a result of analytical studies, it was established that there are prerequisites for the introduction of low-temperature heat supply systems in Ukraine, however, a number of technical, regulatory, social and financial and economic measures need to be implemented to bring district heating systems up to 4G indicators. These studies allow establishing measures that require further research for the possibility of introducing low-temperature district heating systems in particular and environmental safety of heat supply systems in general.

Optimization study of a closed-cycle low-temperature evaporation system based on mathematical model and CFD

Treating high salt and high organic matter wastewater (HHW) generated during rapid socio-economic development is a significant challenge. This study aims to optimize a closed-cycle low-temperature evaporation (CCLE) system using mathematical modelling to be adapted to industrial applications. By using mathematical modelling and computational fluid dynamics (CFD), this study investigated the operating mechanism of the system under different operating conditions. Parametric analysis shows that increasing the compressor evaporation temperature and decreasing the condensation temperature is conducive to improving the performance of the heat pump unit, thereby increasing the wastewater treatment efficiency of the system and that a smaller heat transfer coil windward area is conducive to heat and mass transfer within the humidifier. The unique characteristics of the CCLE system are identified, and the wastewater treatment process under various operating conditions is explained. These findings may provide supporting information for the treatment of HHW by the CCLE system.

Progress in the development of acrylic resin-based powder coatings – an overview

Powder coatings, due to the lack of solvents and volatile organic compounds (VOCs), have gained in importance compared to conventional liquid systems. They fulfill key criteria such as effectiveness, economics, energy efficiency, environmental compliance, and excellent surface finish. Recently, low curing temperature and UV-cured systems have been increasingly used. These techniques offer a lot of advantages such as, application of powder coatings on the heat-sensitive materials and energy savings. Acrylic resins are rarely used in powder systems, mainly due to their price. Nevertheless, they are an attractive alternative in low temperature curing or UV-cured systems (free radical or cationic polymerization) thanks to their chemical structure. The review article focuses on the correlation between the chemical structure of the corresponding monomers in the resin and their properties and application in powder coatings. Moreover, the correlation between the structure of acrylic resin and the powder coating formulation process was described.

Development of the Low-Temperature Inducible System for Recombinant Protein Production in Escherichia coli Nissle 1917.

The pET system is commonly used for producing foreign proteins in Escherichia coli, but its reliance on the costly and metabolically demanding inducer IPTG limits its industrial use. This study engineered a low-temperature inducible system (LTIS) in E. coli Nissle 1917 (EcN) by combining the T7 expression system with the thermal inducible mechanism CI857-λPRPL to generate the new LTIS strain, ENL7P. The strain ENL7P-sfGFP-Km underwent overnight culture at 37 °C for 14-16 h, followed by subculturing at 30 °C for 24 h. This resulted in a notable 5.53-fold increase in the sfGFP induction rate when the strain was cultivated under 37-30 °C conditions. Moreover, gene expression was induced using a two-stage strategy. Initially, the strain was cultured overnight at 39 °C for 14-16 h, followed by a subculture at 30 °C for 6 h, and finally, another subculture at 30 °C for 24 h. This cultivation strategy led to an impressive 158.37-fold induction rate for sfGFP. Similar effects could be achieved through utilization of the LTIS system for inducing the production of thermophilic trehalose synthase from Thermus antranikianii (TaTS). The results of this study proved that the LTIS system has the potential for industrial applications.

Effect of bioaugmentation on gas production and microbial community during anaerobic digestion in a low-temperature fixed-bed reactor.

Low temperature is one of the limiting factors for anaerobic digestion in cold regions. To improve the efficiency of anaerobic digestion for methane production in stationary reactors under low-temperature conditions, and to improve the structure of the microbial community for anaerobic digestion at low temperatures. We investigated the effects of different concentrations of exogenous Methanomicrobium (10, 20, 30%) and different volumes of carbon fiber carriers (0, 10, 20%) on gas production and microbial communities to improve the performance of low-temperature anaerobic digestion systems. The results show that the addition of 30% exogenous microorganisms and a 10% volume of carbon fiber carrier led to the highest daily (128.15 mL/g VS) and cumulative (576.62 mL/g VS) methane production. This treatment effectively reduced the concentrations of COD and organic acid, in addition to stabilizing the pH of the system. High-throughput sequencing analysis revealed that the dominant bacteria under these conditions were Acidobacteria and Firmicutes and the dominant archaea were Candidatus_Udaeobacter and Methanobacterium. While the abundance of microorganisms that metabolize organic acids was reduced, the functional abundance of hydrogenophilic methanogenic microorganisms was increased. Therefore, the synergistic effect of Methanomicrobium bioaugmentation with carbon fiber carriers can significantly improve the performance and efficiency of low-temperature anaerobic fermentation systems.

Investigation of a Hybridized Cascade Trigeneration Cycle Combined with a District Heating and Air Conditioning System Using Vapour Absorption Refrigeration Cooling: Energy and Exergy Assessments

The insufficiency of energy supply and availability remains a significant global energy challenge. This work proposes a novel approach to addressing global energy challenges by testing the supercritical property and conversion of low-temperature thermal heat into useful energy. It introduces a combined-cascade steam-to-steam trigeneration cycle integrated with vapour absorption refrigeration (VAR) and district heating systems. Energetic and exergetic techniques were applied to assess irreversibility and exergetic destruction. At a gas turbine power of 26.1 MW, energy and exergy efficiencies of 76.68% and 37.71% were achieved, respectively, while producing 17.98 MW of electricity from the steam-to-steam driven cascaded topping and bottoming plants. The cascaded plant attained an energetic efficiency of 38.45% and an exergy efficiency of 56.19%. The overall cycle efficiencies were 85.05% (energy) and 77.99% (exergy). More than 50% of the plant’s lost energy came from the combustion chamber of the gas turbine. The trigeneration system incorporated a binary NH3–H2O VAR system, emphasizing its significance in low-temperature energy systems. The VAR system achieved a cycle exergetic efficiency of 92.25% at a cooling capacity of 2.07 MW, utilizing recovered waste heat at 88 °C for district hot water. The recovered heat minimizes overall exergy destruction, enhancing thermal plant performance.

Switched to Low-Temperature Powder Coating System

Switched to Low-Temperature Powder Coating System

Design of an integrated system for electrofuels production through Fischer-tropsch process

There has been a growing recognition in recent years that Electrofuels (e-fuels), also known as renewable and sustainable fuels, which are produced from hydrogen and carbon dioxide as the primary feedstocks, have great potential to reduce carbon footprint and address climate change. In the present study, contrary to most previous studies in which the sources of feedstock's preparation were considered as block boxes, two stand-alone processes are taken into account and incorporated into the e-fuels production system. H2 is obtained by a high-temperature electrolysis system having an overall efficiency nearly twice that of a low-temperature electrolysis system. CO2 is captured from a power plant flue gas stream with a purity of 99.81%. Investigating heat integration potential in such an integrated plant is an up-to-date and interesting topic and has not yet been well explored. Therefore, a heat integration within the three individual processes is implemented to reduce energy consumption. The design of the process-to-process heat transfer section is carried out using pinch design rules. By integrating individual units, approximately 42% of the required cold utility, traditionally supplied by chilled water and refrigerants, is allocated to generate high and medium-pressure steams. Having used the high-temperature steam electrolysis for H2 production, a process that requires less external electricity compared to low-temperature water electrolysis, a power-to-liquid efficiency of 70% is achieved. Furthermore, the results reveal a carbon conversion ratio of 98.6%, indicating the effective converting the carbon from the feedstock into liquid hydrocarbons.

Preparation of aluminum-tin alloy by electrodeposition in low-temperature molten salt system

Preparation of aluminum-tin alloy by electrodeposition in low-temperature molten salt system

Comparative exergy and energy analyses of compression–absorption cascade refrigeration cycles with varied configurations and ejector implementations

This study aims to assess the feasibility and performance, as well as the exergy loss, of utilizing ejectors in absorption–compression cascade configurations for low-temperature refrigeration systems. The coefficient of performance (COP) is used to measure system efficiency, including COP.A (COP of the absorption chiller), COP.C (COP of the compression side) and COP.Ca (COP of the cascade configuration). The results highlight the importance of ejector placement on the absorption side for optimal performance. Configuration D1, with an ejector on the absorption side, demonstrates an 85% improvement in COP.A, approximately 10% in COP.C and nearly 100% in COP.Ca compared to configurations without an ejector. However, in certain cases, using an ejector on the compression side is not feasible from a second-law perspective, particularly for higher compression-side evaporator temperatures. Nonetheless, the study suggests that configuration D0, which includes an ejector on the absorption side coupled with a simple compression cycle, is applicable for these conditions and performs similarly to D1 in other temperature ranges. These findings provide valuable insights for optimizing ejector placement in absorption–compression cascade configurations and advancing the development of more energy-efficient refrigeration systems.

Research on control strategy of rapid preheating for power battery in electric vehicle at low temperatures

Due to cold weather conditions, it is not advisable to use the remaining capacity of the power battery to heat it. Instead, the battery can only be preheated during charging when the battery power is almost consumed up. The traditional positive temperature coefficient (PTC) heating system combines the cockpit air conditioning and heating system with the low-temperature preheating system for the power battery cells. The PTC controller is integrated into the air conditioning control system. However, this integration requires the air conditioning to be activated in order to preheat the power battery. As a result, there is energy waste during the charging process. To address the aforementioned issues, this article proposes a rapid preheating system that utilizes an independent liquid circuit equipped with a high-voltage heater. The system achieves a preheating time of 2000 s for a ternary lithium battery with a capacity of 73kWh and a rated voltage of 770 V. Another important finding is that fluctuations in the current of the battery management system (BMS) occur during the rapid preheating process, leading to uncontrolled battery charging and discharging. The battery rapid preheating control strategy has been redesigned to rapidly heat the battery system by disconnecting the rapid charging relay of the high-voltage circuit, thereby prevents over-discharge and overcharge of the power battery. Experiments have shown that the BMS current increases or decreases in a stepwise manner, as expected by the design. The average temperature of the battery pack during onboard charge module slow charging and direct current fast charging is below 35 °C, and the maximum temperature difference is less than 6 °C. The proposed rapid preheating system and improved battery charging architecture can shorten the charging time and reduce energy consumption. This advancement will open up new possibilities for power battery protection and contribute to the development of lithium-ion batteries for electric vehicles at low temperatures.