Low Temperature Heat Sources Research Articles

Performance analysis of two-stage CO2 transcritical refrigeration cycles with absorption subcooling and mechanical recooling

Although the two-stage CO2 transcritical refrigeration cycle with dedicated absorption subcooling is favorable for energy saving through employing the heat to reduce the loss of throttling processes, some important issues are essential to address exactly for the performance improvement, e.g., extending the working range of heat sources and enhancing the efficiency for the mid-temperature heat utilization. Thus, the two-stage CO2 transcritical refrigeration cycle with dedicated absorption subcooling and mechanical recooling is presented and studied thermodynamically. Two kinds of the proposed system are considered, e.g., sole-subcooler for the low-temperature heat source (the scheme A) and dual-subcooler for the mid temperature one (the scheme B). The performance of the proposed system and traditional one is compared, and the effect of critical parameters on the novel cycle is analyzed in detail. For the scheme A, the lower limit of heat source temperature is extended from 80 °C to 77 °C, and the compressor power goes down by 3.3%. For the scheme B, the lower limit of heat source temperature is extended from 139 °C to 128 °C, and the power consumption is reduced by 6%. Moreover, the payback period of the scheme A and scheme B is 7.9 years and 6.4 years, respectively. The paper is helpful to increase the performance of two-stage CO2 refrigeration cycle through the heat recovery and utilization, and promote the energy saving of cold storages.

Performance assessment of closed Brayton cycle-organic Rankine cycle lunar base energy system: Thermodynamic analysis, multi-objective optimization

The long lunar night, which cannot be powered by solar energy, brings a huge challenge to the lunar base energy system. Closed Brayton cycle (CBC) system is considered as an effective solution, but cannot be driven by low temperature heat sources. Organic Rankine cycle (ORC) system is used to couple into the CBC system to recover waste heat and produce more electricity. In this paper, a mathematical model of CBC-ORC system driven by collector or heat storage unit is developed, the variation of thermal efficiency, exergy destruction, and Brayton-Rankine rotating unit (BRRU) mass is evaluated during the whole lunar day. Results are as follows: when the helium mole fraction is 0.9, CBC stops on the day of 7.7 at night, which is earlier than the stop time for other helium mole fractions. The maximum power generation can reach 169.21 kW. Thermal and exergy efficiency can reach 34.49% and 31%, respectively. After three-objective optimization, the results of thermal efficiency (30.07%), exergy destruction (169.62 kW) are similar to the basic working condition, and the BRRU mass (720.3 kg) can be extremely reduced by 78.76% compared to the basic working condition, which is essential to the practical applications.

Performance evaluation of a micro partial admission impulse axial turbine in a combined ammonia-water cooling and electricity absorption cycle

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously. This technology holds great promise for its ability to harness low-temperature heat sources more efficiently than production with separate cycles. The integration of a turbine is currently being studied in an experimental ammonia-water absorption chiller at CEA INES. Given the very small mass flow rate and enthalpy drop, a partial admission impulse axial turbine has been selected for the application. Due to lack of experimental data, a 3D model of the impulse turbine was generated and its functioning studied with CFD simulations using pure ammonia. A compressible real gas 1D model of the turbine was later developed in EES® for the ammonia-water mixture and compared to CFD simulation, adjusting loss term parameters to match CFD results, thus achieving an average discrepancy below 7% in the considered range of operating conditions (inlet pressure 14-10 bar, outlet pressure 5 bar, inlet temperature 120 °C and rotational speed of 10–100 thousand RPM). The tuned 1D expander model was then integrated in a previously developed 0D model of the absorption cycle to demonstrate its robustness and potential to be used in the study of complex combined cycles. An overall energy efficiency is introduced and used to map the performance of the cycle for changing operating conditions. Results show the potential of the combined cycle to produce both power and cooling even at small scale, highlighting at the same time, the constraints imposed by this type of expander on the combined cycle.

Compressor-Aid Absorption Chiller Working on Low Grade Temperature Heat Source: A Thermodynamic Analysis

Compressor-Aid Absorption Chiller Working on Low Grade Temperature Heat Source: A Thermodynamic Analysis

Thermodynamic and economic analysis of refrigerant mixture R290/R1234ze used in an ORC-EERC system for low temperature heat sources

In the process of promoting carbon neutrality, heat driven refrigeration technology has been widely concerned due to its ability to make use of low-grade thermal energy and improve energy utilization. A novel combined organic Rankine cycle and ejector expansion refrigeration cycle (ORC-EERC) system is proposed in this study. To lower global warming potential and flammability, refrigerant mixture R290/R1234ze is chosen as the working fluid. The proposed ORC-EERC system with ejector and vapor–liquid separator are compared with those of the traditional organic Rankine cycle and vapor compression refrigeration cycle (ORC-VCC) by thermodynamic and economic analysis. The simulation results show that the ORC-EERC can achieve higher exergy efficiency and produce lower cooling temperature. Under typical conditions, the total coefficient of performance of ORC-EERC increased by 17.32% and its levelized cost of cooling decreased by 10.45% compared with the ORC-VCC. Furthermore, the ORC-EERC can remarkably improve performance at a lower freezing temperature or a higher condensing temperature. The results of the proposed cycle show that the ORC-EERC system has great application potential in freezers.

Utilisation of waste heat from PEM electrolysers – Unlocking local optimisation

Recovery of heat from electrolysers is potentially interesting to increase the total system efficiency, reduce CO2 emissions, and increase the economic feasibility of both hydrogen and heat production. This study examines different designs for the utilisation of (waste) heat from a 2.5 MWel polymer electrolyte membrane (PEM) electrolyser. Redundancy is important in the design, to ensure safe operation regardless of the heat demand of the heat consumer. We analysed cases with local heat consumption (with/without a heat pump) and coupling with a district heating network (DHN). Overall, 14–15% of the electricity input to the stack can be utilised by a heat consumer, increasing the total system efficiency to 90% (HHV) with CO2-savings of 0.08 (DHN)-0.28 (direct use) tonne CO2/MWhheat, used. We performed a first-order techno-economic analysis showing that the levelized costs of the electrolyser heat (8.4–36.9 €/MWh) fall within the range of other industrial heat sources and below lower-temperature heat sources.

Steady-state interconnected cycle modeling and experimental results of a lab-scale ORC

ORC is one of the mature technologies for power generation from low temperature heat sources. In this study, the aim is to develop an accurate ORC model which is validated using reliable steady-state data. For this purpose, tests are carried out at four different heat source temperatures ranging from 80 to 110 °C to obtain data in a repeatable manner. The proposed model considers pressure drop and heat transfer correlations to improve the accuracy of model predictions. Using the refrigerant pump mass flow rate, thermal oil pump volumetric flow rate, cooling water inlet temperature, cooling water volumetric flow rate, the throttle valve outlet set pressure, and refrigerant pump outlet pressure as input, the model predicts the pressure, temperature, and mass flow rate in the cycle. The results show that the steady-state ORC model is significantly accurate, with ±1% deviations in pressure and ±1 °C in temperature, and ±5% in mass flow rate, heat transfer rate and refrigerant pump power predictions. The novel iterative model presented in this study includes pipe losses and significantly improves the simulation accuracy of ORCs with long pipes.

Study on the Influence of the Tube Bundle Arrangement on the Performance of Condenser in Nuclear Power Plant

Nuclear power generation technology is obviously a safe and economical way of generating power in modern society. As the low temperature heat source, the condenser of the nuclear power technology condenses the steam into condensate water and then establishes a certain degree of vacuum at the exhaust port of the turbine. The operation of condenser is critical to the nuclear power generation technology. In this paper, the influences of the arrangement of tube bundles on the condenser of nuclear power generation technology were investigated. Three types of condensers, including the church window type, the centripetal type, and the UT type, were analyzed using Ansys Fluent software. The steam flow velocity distribution, air concentration distribution, temperature distribution, and heat transfer coefficient distribution were studied. Under specific design conditions, the flow velocity in the church window type was large, the exhaust air concentration was small, the maximum flow rate distribution was relatively reasonable, and the air concentration distribution was more concentrated. The performances of the centripetal type and the UT type were slightly worse, and the steam condensation was less. In contrast, the condensation of the church window type was large, the relative performance was high, and the heat transfer performance was better.

Exergoeconomic analysis and multi-objective optimization of ORC configurations via Taguchi-Grey Relational Methods

Recovery of low-grade waste heat in industrial processes is an essential energy management topic. Yet, most low-temperature heat sources discharge their heat directly into the environment. The Organic Rankine Cycle (ORC), which has the benefits of being energy-efficient, enabling investment savings, and being ecologically friendly, is crucial in recycling energy from low-temperature waste heat. Both the application of the optimum cycle design and the provision of optimum working conditions are the issues that need to be focused on efficiently using energy. This study performs the energy, exergy, and exergoeconomic analysis of four different organic Rankine cycle configurations operating with renewable or low grade waste heat. The effect degrees and ratios of selected control factors are calculated using Taguchi and variance analysis methods to compare thermal and exergy efficiencies, total system cost, and unit cost of electricity produced by the system. The objective function of the multi-objective optimization problem is defined, and its solution is realized with the Taguchi-Grey Relational Analysis method. The best thermodynamic and exergoeconomic performance result is calculated for the configuration of ORC with Feed Fluid Heater-Internal Heat Exchanger (IHE–FFH–ORC). As a result of Taguchi and ANOVA analysis, the factors that most affect the thermal efficiency of the system, the exergy efficiency, the total system investment cost, and the unit cost of the electricity produced are, respectively, the evaporation temperature (∼50%), turbine efficiency (∼25%), working fluid (∼20%), subcooling (∼4%), pump efficiency (∼0.05%), and superheating (∼0.05%). As a result of the optimization process, the thermal and exergy efficiencies, the total system cost and the unit cost of produced electricity for the IHE–FFH–ORC power system are calculated as 22.6% and 73.5%, 1.06 $/h, 0.039 $/kWh and 2.9 years, respectively.

Performance investigation and numerical evaluation of a single-effect double-lift absorption chiller

This study deals with innovative integrated absorption refrigeration systems. This cycle could be useful for converting low-temperature energy sources into useful outputs like cooling. The Single Effect Double Lift Absorption Chiller (SE-DL AC) was introduced and energetically evaluated. A detailed modeling based on the first law of thermodynamics is built to investigate the performance of this novel system. This model was initially validated considering a reference SE-DL AC from the Hitachi company with a nominal cooling capacity of 106.1 kW. This system is compared to a conventional single-effect absorption chiller while maintaining the same operating parameters and boundary conditions in both configurations to ensure a fair comparison in terms of the internal and external baseline operating conditions. A parametric study of the driving hot water inlet temperature, the solution mass flow rate, the effectiveness of the solution heat exchanger, and internal and external temperatures on the Coefficient of Performance (COP), Cooling capacity (CC), and Glide Temperature (ΔT) are conducted. The final results demonstrate that the cooling production capability of the SE-DL is increased by an average of about tenfold when compared to the conventional SE AC at a thermal source temperature of 88.7 °C and an inlet hot water mass flow rate of 1 kg/s. The COP results produced under the same operating conditions are quite similar. The cooling generation capability of the SEDL is, on average, 10 times greater than that of the traditional SE AC. This explains that the SEDL-AC is well suited for a wide range of low-temperature heat sources (e.g., solar energy). Furthermore, the SE-DL AC enables efficient use of low-grade heat with a high glide temperature in the driving heat stream of about 10 times (36 °C instead of 3.5 °C). This large temperature difference exemplifies that the SE-DL AC absorption chiller is an alternative for extracting as much heat as possible, thereby improving cold production.

Integration of different organic Rankine and Kalina cycles with compressed refrigeration cycle to reduce the power consumption: a comparative study

The compressed refrigeration cycle (CRC) is one of the popular cooling production cycles, which has important advantages. However, it has high power consumption and significant waste heat. Due to the arising costs of power consumption, the generated heat is very valuable. Moreover, this heat is good enough to be utilized as the heat source of the Organic Rankine cycle (ORC) and Kalina cycle (KC) which are capable of using low-temperature heat sources. In the present work, to improve this integration, the effects of configuration changes for integrating CRC with ORC equipped with a regenerator (system1), ORC equipped with turbine bleeding (system2), KC equipped with a regenerator (system3), and KC equipped with a flash vessel and turbine (system4) are presented. The proposed systems are examined and compared from energy, exergy, economics, environmental, and exergoenvironmental perspectives. If System2 is used, the coefficient of performance is improved 2.05 %, i.e. 14.01 MWh/year and 3.96 ton/year reduction in the power consumption and the CO2 emissions compared to CRC. On the other hand, exergy efficiency and exergoenvironmental impact factor are improved by 16.07 % and 2.46 %, respectively. Meanwhile, the payback period of system2 is obtained as 2.6 years. To find the best system, a scoring method is performed and it is concluded that system2 achieves a higher score even if the priorities change.

Techno-economic evaluation of industrial heat pump applications in US pulp and paper, textile, and automotive industries

Industrial process heat decarbonization through electrification could contribute significantly to climate change mitigation efforts. In the US industry, thermal processes accounted for more than two-thirds of the total final energy demand in 2021. Cross-cutting electrification technologies like industrial heat pumps are suitable for the process heat supply to several industrial unit operations in a sustainable way while also improving overall energy efficiency. This study employs a bottom-up approach to investigate the techno-enviro-economic potentials of deploying high-temperature and steam-generating heat pumps in US textile, pulp and paper, and automotive sectors in different timeframes. The results show that the annual technical potential energy and CO2 savings by electrifying heat supply are 310 PJ (or 36% of the projected energy demand) and 28 MtCO2 (or 71% of the projected CO2 emissions) in 2050 respectively, however, these incur additional costs in each sector (ranging between 5 and 18 $/GJ). The required heating capacity of industrial heat pumps is estimated at 15 GW, which translates roughly into a market of over 6000 heat pump units and an investment volume of $7 billion in the studied processes. Although there may be individual cost-effective opportunities for electrifying heat supply in specific industrial sites, the overall costs are estimated to be high in the three industrial sectors due to the large disparity between electricity and natural gas prices and low heat source temperatures. To overcome the identified techno-economic barriers, comprehensive action plans for different stakeholders are also given. This study provides novel insights that should inform policymakers’ and executives’ decisions about the electrification of the current and future US industrial heat supply in relevant industrial sectors.

Efficiency analysis and operating condition optimization of solid oxide electrolysis system coupled with different external heat sources

Coupling external heat sources effectively reduces energy consumption and improves the efficiency of the solid oxide electrolysis (SOEC) system. While an in-depth analysis of the SOEC systems in different coupling scenarios is still needed. According to the internal heat demand and the temperature of external heat sources, three coupling scenarios are defined in this study, i.e., no heat source coupling (Scenario 1), coupled low-temperature heat source (Scenario 2), and coupled high-temperature heat source (Scenario 3). Firstly, the influence of critical parameters on system efficiency is analyzed from two perspectives, including specific system loss and specific energy consumption. The results present that efficiency η1 mainly increases with the rise of steam utilization. Efficiency η2 is not significantly affected by the parameters and is primarily positively correlated with the fuel electrode steam concentration. Efficiency η3 is negatively related to steam utilization, fuel electrode steam concentration, and fuel electrode flow rate, while positively to stack operating temperature. Meanwhile, for Scenarios 1 and 2, the exothermic state of the stack module should be avoided. Furthermore, the system performance maps and stack operating windows in the three scenarios are obtained by changing multiple operating parameters simultaneously and setting constraints. For Scenarios 1 and 2, high system efficiency, high hydrogen production, and long lifetime cannot be achieved simultaneously, so operating parameters need to be selected at a compromise. For scenario 3, high fuel electrode flow rate and low steam utilization can basically meet the above requirements. Both high stack operating temperature and high fuel electrode steam concentration can improve hydrogen production, while the former is mainly beneficial to efficiency η3, and the latter can improve the three efficiencies. The results obtained can be used not only to choose the optimal working conditions of various external heat sources but also to guide the online control and load regulation during system operation.

STUDY OF A SOLAR ENERGY KALINA CYCLE APPLIED IN BOM JESUS DA LAPA - BAHIA

Modern population’s needs increased demands for electricity in such a way that new energy sources were explored, in search of lower environment impacts and fossil fuels dependency. Renewable energy sources for electricity production, such as solar and wind energy, have significantly attracted attention and places as the west region of Bahia state has a good potential for its application. This location is characterized by high solar irradiance of 2136 kWh/m² a year, already having 4 photovoltaic power plants in operation and 2 more in project phases. Another possible application is the solar thermal energy and Kalina Cycle presents as a good possibility for employing it, since the non-azeotropic mixture of ammonia-water as working fluid allows low temperature heat sources utilization. Based on that, this research proposed the study of a Kalina power cycle, with steady state conditions, using thermal solar energy as low temperature heat source and applied to the solar irradiance of Bom Jesus da Lapa – BA. The thermodynamic cycle was developed and simulated with Engineering Equation Solver (EES®), thermal efficiency was analyzed by varying parameters such as: heat source temperature from 90 °C to 120 °C, high pressure line from 10 to 35 bar and ammonia mass fraction from 0.35 to 0.95. The final cycle presented a superheater before the turbine and a regenerator with poor ammonia-water mixture from the separator (as hot side) and ammonia-water mixture before entering the boiler (as cold side). Results indicated maximum efficiency of ~7.4%, with high pressure side of 35 bar, heat source temperature of 120 °C, superheater heat source temperature of 200 °C and ammonia mass fraction of 0.64 kg/kg.

Compatibility assessment of TEGs arrangement coupled with DC/DC converter to harvest electricity from low-temperature heat sources

Expanding intelligent control systems based on the Internet of Things (IoT) requires powering sensors, actuators, and wireless data transfer, which may be located off-grid or difficult to access. Energy harvesting from industrial excess heat by thermoelectric generators (TEGs) can help to overcome challenges ahead. A fully integrated TEG system, however, remains an obstacle to the effective conversion of heat into electricity for IoT applications. The purpose of this paper is to investigate experimentally the electrical arrangement of TEGs and the design of a DC-DC boost converter in order to optimize the harvesting of electrical power from low-temperature sources of heat in TEG systems. The results of this study provide a guide for selecting a suitable arrangement in a system with several TEGs as well as for the design of matched DC-DC converters with desired electrical generators and consumers. This study shows the impact of specialized arrangement of TEGs in a power generation system to optimize the output power of a DC-DC converter. Accordingly, the most suitable electrical combination of four TEG modules among series, parallel-series, and parallel connections is discussed with heat source temperatures lower than 55 °C, between 55 and 75 °C, and higher than 75 °C. Based on the results of the studied TEG system, it is determined that using inductors and capacitors lower than 0.33 µH and 0.47 µF, respectively in the converter’s circuit decreases the output power dramatically, and delays the startup point to higher heat source temperatures.

Optimizing the discharge process of a seasonal sorption storage system by means of design and control approach

Sorption thermal energy storage systems have higher energy densities and low long-term thermal losses compared to traditional energy storage technologies, which makes them very attractive for seasonal heat storage application. Although they have a lot of potential at material level, its operation and system implementation for residential application requires further study. The performance of a seasonal sorption thermal energy storage system strongly depends on the discharging process during the cold season. The present study analysed through numerical simulations different scenarios to enhance the thermal performance of a solar-driven seasonal water-based sorption storage, which supplied space heating and domestic hot water to a single-family house in a cold climate region. All studied scenarios were analysed under optimal control policy. The results indicated that the sorption storage could increase by 9 % its energy density if conservative and constant discharging temperature set points are considered, due to fewer interruptions during the discharge. The energy density of the sorption storage driven by solar energy was highly impacted by the weather conditions, and by the type and availability of low-temperature heat source. Indeed, the energy density of the sorption storage increased by 22 % using a water tank to assist the evaporator of the sorption storage, instead of a latent storage tank. The use of a dry-heater to assist the evaporator with environmental heat was not suitable for the climate studied due to the low hours of operation. The sorption storage system composed of 20 modules of LiCl-silica gel could obtain an energy density and a COP of 139 kWh/m3 and 0.39, respectively, if a constant low-temperature heat source (i.e, geothermal or waste energy) was available.

Energy comparison based on experimental results of a cascade refrigeration system pairing R744 with R134a, R1234ze(E) and the natural refrigerants R290, R1270, R600a

Refrigeration architectures for low-temperature applications are gaining interest in the Industrial, Commercial and Health fields. One of the most classical architectures is cascade systems, where two mechanical single vapor compression cycles are thermally paired by the cascade heat exchanger (HXcc). The HXcc, acts as condenser for the low temperature cycle and as evaporator for the high temperature cycle. Each cycle is charged with a different refrigerant adapted to the operating conditions. New environmental rules make necessary to find proper refrigerant pairs to get refrigeration plants with high energy efficiency together with environmentally friendly fluids. This experimental work compares the energy performance of a cascade refrigeration system working with the pair R134a/R744 against four alternative refrigerant pairs: R290/R744, R1270/R744, R600a/R744CO2 and R1234ze(E). Laboratory tests were conducted at three heat rejection temperatures: 20, 30 and 40°C, maintaining a fixed low-temperature heat source level (−20°C). The energy analysis shows that R290/R744 and R1270/R744 improve the cooling capacity at low heat sink temperatures, and the pair R290/R744 improves the energy performance at low temperatures. The environmental analysis shows that all the refrigerant pairs achieve a reduction in CO2eq emissions.

Experimental study on high temperature heat pump system with a double heat source cascade

In order to improve the thermal performance of a high temperature heat pump system, to realize the efficient heat recovery of industrial waste heat, and to make the combined utilization of low and medium temperature heat sources, a high temperature heat pump system with a double heat source cascade is proposed, which can absorb heat from industrial waste heat and the system is capable of heating water up to the required high temperature. The performance of the system is tested and analyzed. It is found that the inlet temperature of the medium temperature heat source has a significant impact on the performance of the heat pump system under working mode of the medium and low temperature heat sources. When the inlet temperature of the intermediate temperature heat source rises from 42?C to 53?C, the heating capacity of the cascade heat pump increases by 18.6%, and its performance coefficient increases by 8.9%. This paper provides a reference for the high efficiency of the cascade high temperature heat pump technology.

High temperature cascade heat pump system with double medium and low temperature heat sources

In response to the call for carbon neutrality and control of CO2 emission, this paper proposes a high temperature cascade heat pump system with double medium and low temperature heat sources. Compared with those with a single heat source, the new system has obvious advantages in energy saving and carbon emission. An experiment is designed where the temperature of medium temperature heat source keeps unchanged, revealing that, compared with a single low temperature heat source, the heating capacity of low temperature heat source reduces by 2.9%, the heating capacity of medium temperature heat source increases by 31.1%, the total power consumption of the heat pump increases by 3%, and the heating capacity of the heat pump increases by 4.3%.

Review of Possible Waste Heat Sources from Industrial Facilities and Their Potential Use

The aim of the paper was to review the main reusable sources of heat from industrial facilities and to analyze the most efficient way in which they can be exploited. In order to carry out some case studies, examples were chosen from fields of industry in which energy consumption is very high, namely the energy and mining industries. It was shown that although there are large amounts of energy that can be recovered, they are generally low temperature heat sources. Their efficient recovery can be achieved with the help of heat pumps, but due to the final temperature of the heat source, which is around 70 °C, they can be used mainly as heat sources for heating or hot water. This use greatly limits the research and projects for the reuse of these secondary energy resources, therefore future research should focus on obtaining higher temperatures, but also on the production of steam from these sources. The production of steam would facilitate an increase in projects for the recovery of these secondary energy resources for industrial use, which would lead to a superior valorization of them.