Heat pumps have the potential for several applications across various industrial sectors, showcasing significant promise, especially in sectors such as pulp and paper, food and beverage, chemical, ...non-metallic minerals, and machinery. Envisioning the near future, there is confidence that heat pumps can achieve temperatures above 200 °C, offering substantial potential for utilization in these sectors. Nevertheless, a crucial aspect for the advancement of high-temperature heat pumps is the selection of the fluid. Fluid selection involves considerations of both thermodynamic efficiency and environmental impact, requiring fluids with zero ODP, negligible GWP, and no PFAS. Moreover, it is essential to consider the risks to human health associated with a specific fluid. Despite extensive research, particularly in the realm of vapour compression heat pumps, choosing the most suitable working fluid for these applications is a complex undertaking. Therefore, this paper conducts a theoretical analysis to evaluate potential fluids with suitable thermodynamic properties for high-temperature heat pumps (HTHPs). The comparative results gleaned from this study provide valuable insights for the comprehensive analysis of fluids, showing promise within temperature ranges dictated by specific applications. The metrics employed in the comparison emphasise the merits of fluids in terms of the overall performance, dimensions, and operating ranges of applicable compressor, heat exchange capacity, transport properties, and safety. One noteworthy finding from the analysis is that maintaining a constant HTHP lift (at 40 K) results in having the highest COP across all fluids when the condensing temperature ranges between 85% and 90% of their respective critical temperatures. According to the results of the analysis, natural fluids, including water and alcohols like ethanol or methanol, emerge as particularly compelling candidates.
A comprehensive cost correlation analysis was conducted based on available cost correlations, and new equipment cost correlation models were proposed based on QUE$TOR modeling. Cost correlations for ...various types of equipment such as pumps, compressors, heat exchangers, air coolers, and pressure vessels were generated on the basis of extracted cost data. The models were derived on the basis of robust multivariable regression with the aim of minimizing the residuals by using the genetic algorithm. The proposed compressor models for both centrifugal and reciprocating types showed that the Turton cost estimation for carbon steel compressor and Matche’s and Mhhe’s data were compatible with the generated model. According to the results, the cost trend in the Turton correlation for carbon steel had a somewhat lower estimation than these correlations. Further, the cost trend of the Turton correlation for carbon steel pressure vessels was close to the presented model trend for both bullet and sphere types. The Turton cost trend for U-tube shell-and-tube heat exchangers with carbon steel shell and stainless steel tube was close to the proposed heat exchanger model. Furthermore, the Turton cost trend for the flat-plate heat exchanger using carbon steel was similar to the proposed model with a slight difference.
A Thermo-Electric Energy Storage (TEES) system is proposed to provide peak-load support (1–2 daily hours of operation) for distributed users using small/medium-size photovoltaic systems (4 to 50 ...kWe). The purpose is to complement the PV with a reliable storage system that cancompensate the produc tivity/load mismatch, aiming at off-grid operation. The proposed TEES applies sensible heat storage, using insulated warm-water reservoirs at 120/160 °C, and cold storage at −10/−20 °C (water and ethylene glycol). The power cycle is a trans-critical CO2 unit including recuperation; in the storage mode, a supercritical heat pump restores heat to the hot reservoir, while a cooling cycle cools the cold reservoir; both the heat pump and cooling cycle operate on photovoltaic (PV) energy, and benefit from solar heat integration at low–medium temperatures (80–120 °C). This allows the achievement of a marginal round-trip efficiency (electric-to-electric) in the range of 50% (not considering solar heat integration).The TEES system is analysed with different resource conditions and parameters settings (hot storage temperature, pressure levels for all cycles, ambient temperature, etc.), making reference to standard days of each month of the year; exergy and exergo-economic analyses are performed to identify the critical items in the complete system and the cost of stored electricity.
Geothermal energy is acknowledged globally as a renewable resource, which, unlike solar, wind or wave energy, can be continuously exploited. The geothermal fluids usually have some acid gas content, ...which needs to be precisely taken into account when predicting the actual potential of a power plant in dealing with an effective reinjection. One of the key parameters to assess is the solubility of the acid gas, as it influences the thermodynamic conditions (saturation pressure and temperature) of the fluid. Therefore, an enhanced solubility model for the CO2-H2S-water system is developed in this study, based on the mutual solubility of gases. The model covers a wide range of pressures and temperatures. The genetic algorithm is employed to calculate the correlation constants and corresponding solubility values of both CO2 and H2S as functions of pressure, temperature and the balance of the gas. The results are validated against previously published models and experimental data available in the literature. The proposed model estimates the pure gas solubility, which is also a feature of other models. The more innovative feature of the model is the solubility estimation of each CO2 or H2S in simultaneous presence, such as when the binary gas is injected into the pure water of the geothermal reinjection well. The proposed solubility model fits well with the available experimental data, with a mean deviation lower than 0.2%.
Renewable energies are often subject to stochastic resources and daily cycles. Energy storage systems are consequently applied to provide a solution for the mismatch between power production ...possibility and its utilization period. In this study, a solar integrated thermo-electric energy storage (S-TEES) is analyzed both from an economic and environmental point of view. The analyzed power plant with energy storage includes three main cycles, a supercritical CO2 power cycle, a heat pump and a refrigeration cycle, indirectly connected by sensible heat storages. The hot reservoir is pressurized water at 120/160 °C, while the cold reservoir is a mixture of water and ethylene glycol, maintained at −10/−20 °C. Additionally, the power cycle’s evaporator section rests on a solar-heated intermediate temperature (95/40 °C) heat reservoir. Exergo-economic and exergo-environmental analyses are performed to identify the most critical components of the system and to obtain the levelized cost of electricity (LCOE), as well as the environmental indicators of the system. Both economic and environmental analyses revealed that solar energy converting devices are burdened with the highest impact indicators. According to the results of exergo-economic analysis, it turned out that average annual LCOE of S-TEES can be more than two times higher than the regular electricity prices. However, the true features of the S-TEES system should be only fully assessed if the economic results are balanced with environmental analysis. Life cycle assessment (LCA) revealed that the proposed S-TEES system has about two times lower environmental impact than referential hydrogen storage systems compared in the study.
Even though textile industry is not considered an energy intensive sector, it comprises a large number of plants consuming and wasting a significant amount of energy that could be, at least ...partially, conveniently recovered. The objective of this work is to assess the possibilities and convenience of energy recovery from waste heat of different processes of a dry industrial textile laundry.
The various thermal wastes from the processes were identified and characterised, in order to estimate their potential recovery and conversion into electricity.
A suitable system layout was conceived, in order to exploit the heat deriving from thermal waste of different machinery in the factory, having distinct temperature levels, to an ORC powerplant, which converts the recovered heat into electricity.
The ORC cycle was optimized to maximize the thermoelectric efficiency, comparing different possible working fluids. The best fluid was RC318, from which 92.5 kW power output was achieved, at 9.2% efficiency.
The economic analysis revealed, conservatively, a payback period of 7 years for the whole system, which is potentially very interesting. The amount of electricity produced by the waste heat recovery equipment is well matched to the company's electrical needs, resulting in a significant reduction of electricity consumption, greatly reducing the electrical withdrawal from the grid and the related costs.
The case study, the proposed solutions and the methodology have general aspects and may be extended to a wide range of cases in the sector of industrial textile laundry.
The Tesla turbine is a bladeless expander; which principle of operation is based on the conversion of the viscous forces, developed by the flow while expanding through the rotor, in mechanical ...energy. It is especially suitable for small/micro size distributed energy systems (kW scale), mainly due to its very low cost, which results from the simple structure of the machine. The Tesla turbine works well at relatively moderate expansion ratios. Therefore, it is fit for CO2 power cycles applications that are characterised by small expansion ratio, despite the high pressure involved. In this work, the design and off-design analysis of a Tesla turbine for small/micro power application utilizing CO2 cycles is proposed. The optimized design was targeted for an inlet temperature of 150 °C and an inlet pressure of 220 bar. The final optimized geometry of the expander was defined, achieving a 23.4 W per channel power output with a 63% isentropic efficiency, when working with a 10.1 bar pressure drop at 2000 rpm. Furthermore, the turbine placement on the Baljè diagram was performed in order to understand the direct competitors of this machine. Finally, starting from the design configuration, the maps of efficiency at variable load and flow coefficients and that of reduced mass flowrate at variable pressure ratio were realized. Through the merging of these curves, the off-design maps of the Tesla turbine were obtained, highlighting a very limited sensitivity of the efficiency to variable working conditions, if rotational speed is adequately adjusted.
Ocean Thermal Energy Conversion is an important renewable energy technology aimed at harvesting the large energy resources connected to the temperature gradient between shallow and deep ocean waters, ...mainly in the tropical region. After the first small-size demonstrators, the current technology is focused on the use of Organic Rankine Cycles, which are suitable for operating with very low temperatures of the resource. With respect to other applications of binary cycles, a large fraction of the output power is consumed for harvesting the resource – that is, in the case of OTEC, for pumping the cold and hot water resource. An exergy analysis of the process (including thermodynamic model of the power cycle as well as heat transfer and friction modelling of the primary resource circuit) was developed and applied to determine optimal conditions (for output power and for exergy efficiency). A parametric analysis examining the main design constraints (temperature range of the condenser and mass flow ratio of hot and cold resource flows) is performed. The cost of power equipment is evaluated applying equipment cost correlations, and an exergo-economic analysis is performed. The results allow to calculate the production cost of electricity and its progressive build-up across the conversion process. A sensitivity analysis with respect to the main design variables is performed.
Modern textile stenters are designed to reduce the inefficiency of the process and to recover the flow stream, which still contains a relatively high energetic value. In recent years, research has ...focused on the recovery of the energy content of the low-temperature exhaust flow; nonetheless, another important aspect that may increase the efficiency of the process is the reduction of the ambient air suction. In the present research, an innovative way to improve both machine insulation and energy savings, by using preheated air, was numerically evaluated. The proposed solution utilizes an air stream transverse to the fabric (generally called air curtain), either preheated or not, to create soft gates both at the inlet and at the outlet section of the drying machine. Several valuable advantages can be listed when using this solution: reduction of the dispersion of heat and humid polluted air to the work environment, limitation of air ingestion from outside, and effective heat recovery coupled to a uniform temperature profile around the textile fabric. To analyze the insulation capability of the air curtains in terms of mass and energy transfer, a two-dimensional CFD model of the machine was realized. A test matrix including three possible fabric speeds (20, 40 and 60 m/min), three tilt angles (−15°, 0° and 15°), four mass flow rates (0% with no air curtains and 3%, 5% and 7% of the total flow rate through the machine, where the 5% case is equivalent to the flow rate ingested from the ambient) and two temperatures (15 °C and 70 °C) of the plane jets exiting from the air curtains was considered, thus covering a wide range of possible practical applications. The obtained results demonstrate that warm air curtains at both the inlet and outlet are very effective in a fabric speed range up to 40 m/min; at higher fabric speed, entrainment of warm gases from inside the machine at the fabric outlet becomes relevant, and the adoption of a cold air curtain (capable of better insulation) can be recommended in this position.
This paper describes the current efforts to develop and manufacture a first prototype for a boundary layer pump as a mean to assess future and more complex designs. Following an approach of “learning ...by doing”, a previous design was re-assessed from a mechanical/workshop point of view. Budget constraints and in-house manufacturing capabilities were taken into consideration to deliver a new design, suitable for quick production. Challenges such as disc holding, gap spacing, pump intake, discharge nozzles, and tolerances were addressed. Structural analysis has been conducted; where every single component has been modelled and sized accordingly to standard practices. As a support of structural analysis, FEM analysis was also performed with the aim of identifying, discussing, and fixing any potentially critical issues, particularly regarding the bolts holding together the discs into the power shaft. Finally, modal analysis was performed in order to test the dynamic response of the rotor: its critical frequencies would be far from the working range of the machine. This paper gives an overview of the critical issues to be taken into account during the mechanical design of boundary layer pump prototypes for different working fluids in the field of power generation and thermal management.
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