Utilization Of Low-grade Heat Research Articles

Development of an efficient cross-scale model for working fluid selection of Rankine-based Carnot battery based on group contribution method

Rankine-based Carnot battery is promising system with outstanding performances in addressing the challenges of local consumption of renewable energy generation and utilization of low-grade waste heat. A suitable working fluid is fundamental to the Rankine-based Carnot battery cycle and profoundly influences system performance. However, studies on working fluid selection for the Rankine-based Carnot battery are limited to a predefined database. This approach fails to study or design novel working fluids. Therefore, the nine molecular groups used as a set of molecular groups in this paper can cover most organic working fluids in Rankine-based thermodynamic cycle systems. Developing an accurate cross-scale model based on the group contribution method is used in working fluid selection for Rankine-based Carnot battery. Meanwhile, for the sake of testing the accuracy of the proposed model, twenty-one promising organic working fluids were selected to be compared and analyzed with the results calculated by the REFPROP under the typical working conditions of the Rankine-based Carnot battery. The results show that the absolute average relative deviation of the boiling temperature prediction using the multiple linear regression model proposed in this study is only 3.9 %, while the absolute average relative deviation of the critical temperature based on the proposed boiling temperature model is 5 %. Finally, the present work demonstrates excellent accuracy in predicting the thermodynamic performance of this system. The absolute average relative deviation of the coefficient of performance, generation efficiency and power-to-power-efficiency is 4.6 %, 2.0 %, and 6.4 %, respectively.

Module optimization and array design of moisture swing direct air capture based on 2D-3D coupled analysis

Direct Air Capture (DAC) is crucial for offsetting carbon emissions. Moisture Swing Adsorption (MSA), a DAC method switches between adsorption and desorption through humidity adjustment without relying on heat, offering significant energy-saving potential but lacking engineering solutions. Therefore, using a validated 2D-3D coupled model, a moisture swing DAC array was proposed, and multi-dimensional evaluations were used to optimize the system. Unlike the preferred capture rate around 90 % for post-combustion gas, the ultra-low CO2 concentration in the air resulted in a different rate range for DAC. Simulation indicated that although the capture rate of DAC could reach 90 %, the trade-off was energy consumption exceeding 3000 kWh/t CO2 with low adsorbent utilization. Consequently, a detailed evaluation method based on adsorbent utilization, energy consumption and cost analysis optimized the preferred capture rate range to 50–60 %, and the total energy consumption was reduced to 873.55 kWh/t CO2, including 276.33 kWh/t CO2 for capture energy and 597.22 kWh/t CO2 for vacuum-concentration energy. The lowest cost was $209.17/t CO2 at the optimal capture rate of 53.91 %. Afterwards, the Ordos Plateau, as a typical preferred sub-environment with abundant wind resources and dry climate, was choose for DAC system deployment study. Wind field simulation determined the layout of a 10000-ton array occupying only 0.298 km2. Finally, based on savings in capture energy due to prevailing winds, regeneration energy savings from the utilization of low-grade waste heat, and the improved performance of the adsorbent itself, it was found that this DAC unit showed great potential to reduce the energy and capture costs to 564.91 kWh/t CO2 and $140.25/t CO2, and at wind speed exceeding 16.8 m/s, the unit switched to passive adsorption, further reducing energy consumption to 408.89 kWh/t CO2, with the minimum fix investment estimated at 21.71 million USD.

Design of multi-cycle organic Rankine cycle systems for low-grade heat utilisation

Organic Rankine cycles (ORCs) facilitate the utilisation of low-grade heat sources (e.g., geothermal and industrial waste heat) for power generation, thereby improving energy efficiency in industrial processes and expanding the application of renewable energy. Using multiple ORCs instead of a single cycle provides more flexibility in heat integration and can increase the power output. This paper presents a mathematical model for designing multi-ORC systems; the design task involves the determination of ORC configurations and operating conditions whilst synthesising the associated heat exchanger network. Two case studies on geothermal and industrial waste heat ORC applications illustrate the developed optimisation formulation. In the geothermal case study, the maximum net power output for a single regenerative n-butane cycle can increase by 11.2 % as a result of optimising the ORC operating conditions. With two independent n-pentane cycles, a 7.6 % increase in the maximum net power output can be reached by optimising the ORC configurations. In the industrial waste heat case study, a 14.3 % increase in the maximum net power generation is found with a second n-butane cycle, and a further 5.7 % increase with a third. For comparison, the total annual cost and the payback period are also calculated in both case studies.

A novel oscillating flow cycle engine with characteristics of temperature glide heat addition and no regenerator for low-grade heat utilization

In oscillating flow cycle engines such as Stirling engines, nearly isothermal heat additions in heat exchangers will produce irreversibility losses during the heat transfer processes and the regenerator is indispensable and expensive. Thus, it reduces oscillating flow cycle engine’s economic attractions for low-grade heat utilization. In this work, three structures of one-way oscillating flow cycle engine are proposed for overcoming these problems. To assess the feasibility, one structure is chosen for analysis. Then, a one-dimensional computational fluid dynamic model considering various heat transfer and flow friction losses is developed. Based on the validated model, performance analysis is carried out. The temperature glide for heat absorption can reach up to 116 K and can be adjusted. The obtained maximum thermal efficiency is 7.79 %, 12 %, and 14.6 % respectively for low-grade heat’s inlet temperatures of 373 K, 423 K, and 473 K. Furthermore, the maximum specific work output for 1 kg/s hot water is 13.7 kW, 36.9 kW and 64.4 kW respectively at an inlet temperature of 373 K, 423 K, and 473 K, with corresponding maximum exergy efficiency of 42.8 %, 43.7 % and 41.1 % respectively. Thus, the results demonstrate that large temperature glide heat addition can be achieved, and a novel oscillating flow cycle engine without a regenerator is feasible and efficient.

Magnetically assembled flexible phase change composites with vertically aligned structures for thermal management and electromagnetic interference shielding

Phase change material (PCM) is promising in achieving zero-energy thermal management because of its prominent thermal storage capacity and steady phase-change temperature. However, low intrinsic thermal conductivity (TC), liquid leak, and solid rigidity are long-standing bottlenecks for heat-related applications. Here, we report an innovative dual-encapsulation strategy to develop multifunctional phase change composite (FMP) with vertically aligned NdFeB@Ag arrays and styrene-ethylene-propylene-styrene (SEPS) crosslinked network in paraffin (PA). The NdFeB@Ag arrays induced by magnetic-field driven procedure can offer the consecutive/oriented highways for efficient heat-transfer, and an electric/magnetic heterostructure for electromagnetic interference shielding efficiency (EMI SE). The flexible SEPS block copolymer not only ensures the high flexibility of PCM, but also combines with oriented NdFeB@Ag arrays for dual encapsulating PA. This multifunctional FMP can achieve high TC of 2.59 W m−1 K−1, attractive EMI SE of 35.42 dB, prominent enthalpy density of 120 J g−1, and impressive Joule heating performance, together with leakage-proof, dynamic assembly, and salient charging/discharging durability. Furthermore, the FMP-supported device is demonstrated for thermal energy harvesting and utilization. This dual-encapsulation design opens a new avenue for exploiting multifunctional PCMs for thermal management, anti-EM radiation, and low-grade exhaust heat utilization.

Numerical simulation study on erosion characteristics of desulfurization slurry using shell-and-tube heat exchanger for low-grade waste heat utilization

The wet desulfurization yields slurry with a moderate temperature and stable supply and thus holds promise for waste heat utilization. However, the corrosive nature and solid particle content of desulfurization slurry from the wet desulfurization process pose potential erosion challenges in waste heat utilization heat exchangers, which is an aspect scarcely explored in the existing literature. The present study aimed to investigate the erosion characteristics in desulfurization slurry heat exchangers using numerical simulation approaches, which can offer crucial insights for practical application in low-grade energy recovery. The result identified slurry mass flow rate and composition as essential factors of erosion distribution. Higher mass flow rates enhance heat transfer efficiency. Still, paradoxically, lower flow rates lead to more pronounced erosion, with a slurry mass flow rate of 35 kg/s resulting in nearly double the erosion compared to the benchmark condition of 56 kg/s. This phenomenon is ascribed to lower fluid velocities in the heat tubes, where the influence of changed velocity diminishes, but slurry exhibits more stable flow at higher mass flow rates. Furthermore, it is also observed that both elevated solids content and particle size lead to an increase in erosion rates. The difference in erosion caused by solid particles with particle sizes in the range of 200–350 µm is marginal. The heat exchanger structure and arrangement also impact fluid flow and erosion. While the difference in fluid flow between vertically and horizontally arranged heat exchangers is negligible, the erosion was significantly reduced to 1/10 in the vertical arrangement. The no-tube-in-window heat exchangers, designed to minimize vibration, exhibit reduced heat transfer capacity alongside diminished and more uniform erosion. The augmentation of tube passes reduces overall erosion but focalizes severe erosion at the slurry inlet, which presents a potential design solution.

A novel cycle engine for low-grade heat utilization: Principle, conceptual design and thermodynamic analysis

Efficient engine technologies to convert low-grade heat to electricity are urgently desired. In this work, a conceptual structure of engine for a novel cycle or one-way oscillating flow cycle (OOFC), which consists of two isochoric and two adiabatic processes, is described for low-grade heat utilization. Characteristics of OOFC allows for the working fluid temperature glide to be matched to the decrease in temperature of low-grade heat. Then, thermodynamic model is developed for evaluating the performance. Theoretical simulation results show that maximum specific output works are in the range of 12.2 kJ kg−1 – 79.7 kJ kg−1. Compared to Stirling cycle system, maximum specific output work in OOFC system could be improved by 16.2 %–24.8 %. Compared to ideal Carnot cycle engine system, maximum specific output works in OOFC system is nearly the same and 1.8 %–2.6 % lower. As Carnot cycle engine is ideal while thermodynamic cycle loss and heat transfer loss in cold heat exchangers are considered in OOFC engine, the ratios of maximum specific output work demonstrate that OOFC system could be very promising for low-grade heat utilization as a result of well-matched temperature profile in hot heat exchanger.

Experimental study on exhaust internal circulation desiccant wheel evaporative cooling chiller

Evaporative cooling chillers reduce the water temperature by absorbing heat during the evaporation of water without the need for compressor assistance or refrigerants. It is an energy-saving and environmentally friendly cooling technology but it needs necessary improvements in the applicable environmental area and refrigeration performance due to ambient air wet-bulb temperature limitations. To obtain chilled water below the dew-point temperature of the ambient air, an exhaust internal circulation desiccant wheel evaporative cooling chiller is proposed and experimentally investigated. A combination of a heat pipe exchanger, a desiccant wheel, an air cooler and an air heater are applied to reduce the wet-bulb temperature of the ambient air before it passes through the direct evaporative cooler. At the same time, the low-temperature and low-humidity exhaust air from the direct evaporative cooler is used to circulate to improve chiller performance. The experimental results show that the average chilled water temperature of the proposed chiller is 10.2 ℃ lower than that of the direct evaporative cooling chiller under five typical environmental conditions. The wet-bulb efficiency of the proposed chiller is the highest at high temperatures and high humidities (36 ℃ and 80% RH), which is 6 times greater than that of direct evaporative cooling chillers. Therefore, the proposed chiller expands the application range of evaporative cooling technology, which is especially suitable for humid areas with low-grade heat utilization such as solar energy.

Thermodynamic analysis of an ammonia-water double absorption-resorption heat transformer system

Absorption heat transformer (AHT) presents an effective solution for enhancing energy efficiency through the utilization of low-grade industrial waste heat. To reduce the high operating pressures of traditional ammonia AHT and elevate waste heat to a higher temperature level, a novel ammonia-water double absorption-resorption heat transformer (DARHT) incorporating a coupled middle absorber-generator is proposed in this paper. A thermodynamic simulation model of the system is established using MATLAB software to analyze the effects of operating pressures and temperatures on the COP, temperature lift, solution circulation ratio and bypass ratio, thereby determining the optimal operating conditions of the system. The simulation results indicate that there exist optimal PH/PL pairs and middle absorber-generator temperatures which lead to the maximum COP of the system. COP decreases with the increase of absorber and resorber temperatures while increases with the increase of generator and desorber temperatures. When PH/PL pair is 1.5/0.36 MPa, the DARHT system can provide a temperature lift exceeding 70 °C, while the working pressures are significantly lower compared to conventional AHT, thereby reducing the requirements of robust components and enhancing the operational stability of the system.

Performance research of a solution cross-type absorption-resorption heat transformer using NH3/H2O work fluid

Absorption-resorption heat transformer (ARHT) can realize the efficient utilization of low-grade heat under lower operating pressure than traditional absorption heat transformer (AHT), but the application is limited by the low coefficient of performance (COP). In this paper, an ammonia-water solution cross-type absorption-resorption heat transformer is proposed to improve the performance. The rectifier can be eliminated because the component can be balanced with the adjustment of solution's mass flow rate between the absorber and resorber. A thermodynamic model is established to investigate the influences of different parameters on the coefficient of performance. The results reveal that: When the high/low pressure pair is 1.5/0.48 MPa and the temperatures of generator, absorber, resorber and desorber are 105 °C, 80 °C, 80 °C and 4 °C, the COP of the proposed system can reach 0.4049, which is 19 % higher than traditional ARHT, resulting in a corresponding gross temperature lift (GTL) is 25 °C. Besides, the proposed system has wider working temperature ranges than the traditional system. The advantages of the proposed system also include the lower optimal low-pressure values. Therefore, the ammonia-water solution cross-type absorption-resorption heat transformer is appropriate for working in larger pressure differences and makes waste heat recovery more economical and efficient.

Thermodynamic, economic analysis and multi-objective optimization of an improved self-condensing transcritical CO2 Rankine cycle with two-stage ejector for low grade heat utilization

An improved self-condensing transcritical CO2 Rankine cycle (TCRC) with two-stage ejector on the basis of the preliminarily designed one with an ejector is proposed in this study, aiming to enable the condensation of CO2 using conventional cooling source and achieve desirable performance. Thermodynamic and economic mathematical models of the improved self-condensing TCRC are developed, and detailed parametric analysis is carried out to investigate the effect of main parameters on both thermodynamic and economic performances of the system. Then the multi-objective optimization is conducted to examine the potential for performance enhancement. Thereafter, a comparative analysis of the performances between the improved self-condensing TCRC and preliminary self-condensing TCRC is performed. Results show that the improved self-condensing TCRC with two-stage ejector outperforms the preliminary one with an ejector in both thermodynamic and economic aspects, achieving a 3.93% increase in maximum exergy efficiency and a 13.84% reduction in minimum unit net power cost through multi-objective optimization. Under optimal conditions, the exergy efficiency for the improved self-condensing TCRC is 45.48% with a unit net power cost of 0.1241$/kWh.

Techno-economic feasibility study of coupling low-temperature evaporation desalination plant with advanced pressurized water reactor

The increasing demand for freshwater necessitates sustainable desalination solutions, and nuclear power plants offer a promising avenue by utilizing their low-grade waste heat. This study assesses a techno-economic feasibility of coupling a 5 MWth low-temperature evaporation plant with a UAE-based Advanced Pressurized Water Reactor (APR1400). The system addresses freshwater demand, aligning with sustainability goals through low-grade heat utilization. The investigation explores three extraction points for low-grade heat steam, with temperatures ranging from 80 °C to 130 °C. Thermodynamic evaluations using DE-TOP illustrate power requirements and losses, considering variations in maximum brine temperature from 50 °C to 65 °C. Economic analysis using DEEP estimates water production costs. Findings reveal negligible variances in power plant parameters and a minimal reduction in overall efficiency (<0.5 %). The power loss ratio increases proportionally (10 % to 18.6 %) with higher-temperature heat extraction, while the total power requirements for the desalination plant rises by around 30 %, with a negligible power output reduction ratios (0.03 % to 0.07 %). A consistent linear correlation between water production rate and maximum brine temperature doubles water production (∼900 to 1800 m3/day). Applying multiple extraction points across low-grade heat sources demonstrates scalability, reaching three times that of single-point extraction, with marginal increases in power requirements and losses, while maintaining the power reduction ratio below 0.15 %. Economic feasibility indicates competitive water production costs, ranging from 1.53 to 0.87 $/m3 for desalination capacities between 900 and 5400 m3/day. This study provides valuable insights into sustainable water production at the nexus of nuclear energy and desalination, with implications for necessary policy intervention.

Preparation and thermal properties of zeolite/MgSO4 composite sorption material for heat storage

Thermochemical sorption heat storage based on salt hydrates offers the potential advantages such as high energy density, negligible heat loss, small volume change and flexible working modes. Magnesium sulphate (MgSO4) is a high energy density hydrated salt available for the thermochemical sorption heat storage. In this work, different types of zeolites (including 3A, 5A and 13X zeolites) have been selected as mass-transfer-enhancing and structural stabilizing materials, and a series of zeolite/MgSO4 composites have been fabricated. To investigate the thermal energy storage performance of zeolite/MgSO4 composites, the properties of the composites, such as micro-morphology, pore structure, chemical composition and sorption-desorption behavior, have been characterized and analyzed. Results indicated that the mass transfer performance of the composite materials is significantly better than that of the pure zeolites. As the mass fraction of MgSO4 in the composite sorbents increases, the specific surface area and porosity of the composite sorbent decreases, and the sorption performance has been enhanced. Compared with 3A zeolite-based and 5A zeolite-based composites, 13X zeolite/MgSO4 composite materials show the best heat storage performance. At the condition of 25 °C and 60% RH, the 13XM20 has the highest sorption capacity of 0.21 g/g, which is 24% higher than that of pure zeolite 13X. Accordingly, the maximum heat storage density is 438.4 kJ/kg, which exhibits the superior heat storage performance among of the hydrated salt sorbents. The potential of 13X zeolite/MgSO4 as sorption heat storage material in efficient utilization of solar heat and low-grade industrial waste heat has been revealed.

Multi-objective optimization of a biomass microCHP-ORC system under supercritical conditions

ORC cycle is one of the most efficient technologies for the utilization of low-grade heat. ORC systems cover a wide range of heat sources and power outputs. Apart from increasing the overall efficiency, CHP systems contribute to the decentralization of energy production, the conservation of primary fuel, the reduction of the emission of greenhouse gasses and the re-duction of the cost to the final consumer. This justifies the research activity around CHP-ORC systems. In the present paper, a steady-state thermodynamic model for a 50 kWel biomass microCHP-ORC was developed and four candidate fluids were selected: R124, isobutane, R245fa and isopentane. The multi-objective optimization under supercritical conditions was performed using the genetic algorithm. The thermal efficiency, the exergy efficiency and the total heat exchanger surface were selected as single objectives. The evaporation temperature and pressure and the pinch point temperature differences at the heat exchangers were selected as decision variables. Careful examination of the optimal results revealed a systematic ten-dency for high evaporation temperatures and pressures and low recuperator pinch point tem-perature differences. Recuperation was found beneficial in many aspects, especially at higher evaporation temperatures. Also, the use of cogeneration leads to overall system efficiencies that surpass 90%, while simultaneously saving at least 20% fuel. Lastly, isopentane was found to be the best-performing fluid.

Design and optimization of the novel thermally regenerative electrochemical cycle power device based on machine learning

Utilizing low grade heat and waste heat to generate electricity not only mitigates environmental impacts, meanwhile it enhances energy efficiency and lowers energy expenses. Thermal regenerative electrochemical cycles (TREC) can directly convert low grade heat to electricity, and it has a massive potential for low grade heat utilization. The type and design of a TREC system with practical and continuous power output are of paramount importance, and they can directly influence the performance and efficiency of low-grade heat recuperation systems. In this paper, a novel TREC system of a double layers rotating structure was proposed, and the novel optimal design approach employs CFD and machine learning for this system was presented. The results revealed that the height and number of TREC units had a significant impact on the device's performance. The heat to electricity efficiency of TREC device can be up to 7.34% (equivalent to 48.91% of the Carnot cycle efficiency) when the number of units was 12 and the height of unit was 5 mm. The results indicated that the MLP model was the most suitable, with RMSE values of 0.0077, 0.4415, and 0.5091 for heat to electricity efficiency, heat recuperation efficiency, and heat recuperation, respectively. This work established an effective approach for more rapid and precise estimation of the TREC device's performance metrics. The findings from prediction can serve as a practical guide for the design of TREC devices of various sizes. Furthermore, the method can envision the efficiency before the TREC device is manufactured in case of insufficient numerical calculations, reducing the computational and optimized costs.

Novel marine ejector-compression waste heat-driven refrigeration system: Technical possibilities and environmental advantages

A novel combined ejector-compression refrigeration system for provision rooms of merchant ships was conceptualized and analyzed. The principle possibility of recovery of onboard low-grade heat (85–95 °С) of jacket cooling water was confirmed. Two ejectors of different geometries to ensure the ejector stage operation when the seawater temperature varies in a wide range were designed and proposed to install in parallel. The performance of the combined system was compared to a vapor-compression one and the choice of the rational temperatures in the condenser-evaporator tC/Ev was performed. The combined system COPtotal is considerably higher than the vapor-compression system, and it weakly depends on heat source temperature. At condensing temperature tC = 34 °С the decreasing in tC/Ev from 20/15 to 10/5 °С results in increasing of COPtotal up to 13.5 % at generation temperature tG = 80 °С and up to 15.6 % at tG = 90 °С. Utilizing the combined system for the onboard cold production will contribute to fuel savings of 25 to 33 % per voyage (operation and transport) vs. vapor-compression system. The combined system inherent the lower specific CO2 emission per 1 kW h of cooling energy emrefr than the standard system for all considered operation modes. The value of emrefr for combined system at tC/Ev = 10/5 °C, tG = 80 °C and tC = 36 °C or tC = 42 °C is 23.1% or 18.3%, respectively, less than for the vapor-compression one. The approach to analysis proposed can be used for assessment of the feasibility of utilization of low-grade heat and the retrofit of ship refrigeration systems.

Thermophotonic cells in self-sustaining parallel circuits

Thermophotonic (TPX) cells, which integrate a light-emitting diode (LED) and a photovoltaic (PV) cell, offer potential advantages over thermophotovoltaic (TPV) cells for low-grade waste heat utilization. While TPX cells traditionally operate in an independent circuit, which requires an external battery storage unit, the self-sustaining circuit presents an appealing alternative that eliminates the need for the storage unit. In this study, we conduct a comprehensive analysis of TPX cells operating in the self-sustaining circuit. We provide clear expressions for the electrical currents flowing through the LED and PV cell, considering the different bandgaps of the LED and the PV cell. Our results reveal that the bandgap energy of the LED must exceed that of the PV cell for the TPX cell to function in a self-sustaining parallel circuit. Furthermore, we demonstrate that the performance of the TPX cell in the self-sustaining circuit improves with a narrower bandgap energy for the PV cell and a wider bandgap energy for the LED, regardless of the far-field or near-field configurations. While near-field TPX cells exhibit higher power density, they also experience decreased energy efficiency compared to far-field TPX cells. Additionally, we explore the scenario where the bandgaps of the LED and PV cell are the same, analyzing the performance of a closed-structured self-sustaining parallel circuit with multiple LEDs and PV cells in the near-field configuration. We find that the near-field effect has a marginal impact on TPX cells with identical bandgaps, which means that the near-field TPX cell in the self-sustaining circuit will not be useful in practice. The insights gained from this work serve as valuable design guidelines for TPX cells operating in the self-sustaining parallel circuit, enabling practical operation without the need for an external battery storage unit.

High-Performance Thermoelectric Flexible Ag2Se-Based Films with Wave-Shaped Buckling via a Thermal Diffusion Method.

Herein, an n-type Ag2Se thermoelectric flexible thin film has been fabricated on a polyimide (PI) substrate via a novel thermal diffusion method, and the thermoelectric performance is well-optimized by adjusting the pressure and temperature of thermal diffusion. All of the Ag2Se films are beneficial to grow (013) preferred orientations, which is conducive to performing a high Seebeck coefficient. By increasing the thermal diffusion temperature, the electrical conductivity can be rationally regulated while maintaining the independence of the Seebeck coefficient, which is mainly attributed to the increased electric mobility. As a result, the fabricated Ag2Se thin film achieves a high power factor of 18.25 μW cm-1 K-2 at room temperature and a maximum value of 21.7 μW cm-1 K-2 at 393 K. Additionally, the thermal diffusion method has resulted in a wave-shaped buckling, which is further verified as a promising structure to realize a larger temperature difference by the simulation results of finite element analysis (FEA). Additionally, this unique surface morphology of the Ag2Se thin film also exhibits outstanding mechanical properties, for which the elasticity modulus is only 0.42 GPa. Finally, a flexible round-shaped module assembled with Sb2Te3 has demonstrated an output power of 166 nW at a temperature difference of 50 K. This work not only introduces a new method of preparing Ag2Se thin films but also offers a convincing strategy of optimizing the microstructure to enhance low-grade heat utilization efficiency.

INCREASING THE EFFICIENCY OF HEAT PUMP USING CIRCULATING WATER OF POWER PLANTS

In the article analytical studies of the efficiency of heat pumps in the thermal schemes of thermal and nuclear power plants for centralized heating and hot water supply systems taking into account the climatic conditions of Ukraine have been carried out. This task meets the objectives of energy saving and reduces emissions of harmful substances into the environment. The main focus is on improving the efficiency of the heat pump power supply system, which integrates an alternative energy source. An analysis of the exergy parameters of heat pump cycles has been performed, which have made it possible to establish that the most efficient working fluid of the cycle is freon R152a, at which the highest heat pump conversion coefficient and the lowest compressor power indicator are achieved. Ways and methods leading to reduction to underproduction of the electricity by turbine of of power plant and to increasation of the efficiency of a steam turbine cycle are proposed. It is shown that the efficiency of the system is most affected by losses in the evaporator, so the efficiency of this element of the heat pump should be given the most attention when using the energy of circulating water. An additional aspect of the novelty of the proposed method lies in the possibility of further optimization of the technical and economic parameters of the power system. A methodology based on the use of the exergy method of analysis to substantiate the conditions for the rational use of heat pumps for power plants in the utilization of low-grade heat of circulating water for cooling the turbine condensers is proposed, which can be considered as innovative way. Results open the further prospects for the development of heat pump heat supplyhas been proposed.

Thermodynamic and exergoeconomic analysis of a combined cooling, desalination and power system for low-grade waste heat utilization

As a form of sustainable energy, low-grade waste heat has considerable amount to be recovered, but the energy utilization efficiency is still low. In this paper, a novel multi-generation system is proposed to utilize the low-grade waste heat efficiently and meet the needs for cooling, freshwater and power simultaneously, by integrating vapor compression refrigeration (VCR), humidification and dehumidification (HDH) desalination with transcritical organic Rankine cycle (TORC). Thermodynamic and exergoeconomic performances of the multi-generation system with five working fluids are evaluated. Parametric studies are conducted to identify the key operating parameters. Results show that the highest exergy efficiency ηex and the lowest average unit cost of products (AUCP) can be obtained by using R161, while the highest coefficient of performance (COPtot) belongs to R143a. The proportion of the vapor generator in the total exergy destruction is the largest, followed by the condenser. Higher net power output and freshwater production can be achieved by raising the vapor generation temperature and the ratio of mass flow rates of working fluid, and the corresponding ηex and AUCP are also improved. There is an optimal pressure for the lowest AUCP and the highest net power output and ηex. Performance comparison with systems from the literature is conducted as well.