Source Inlet Research Articles

Experimental Performance Comparison of High-Glide Hydrocarbon and Synthetic Refrigerant Mixtures in a High-Temperature Heat Pump

Several theoretical studies have predicted that refrigerant mixtures with glides of more than 20 K can yield COP improvements in heat pumps for operating conditions where the temperature difference between the heat source and heat sink is large, but experimental validations and quantifications are scarce. The application of high-glide mixtures (>20 K) in industrial heat pumps in the field is, therefore, still hampered by concerns about the behavior and handling of the mixtures. This study experimentally investigates hydrocarbon (HC) mixtures R-290/600 (propane/butane) and R-290/601 (propane/pentane) and compares them to previously tested mixtures of synthetic refrigerants. Comprehensive evaluations are presented regarding COP, compressor performance, pressure drop, heat transfer, and the possibility of inline composition determination. The mixtures were tested over a range of compositions at a source inlet temperature of 60 °C and a sink outlet temperature of 100 °C, with the heat sink and heat source temperature differences controlled to 35 K. R-290/601 at a mass composition of 70%/30% was found as the best mixture with a COP improvement of 19% over R-600 as the best pure fluid. The overall isentropic compressor efficiency was similar for HC and synthetic refrigerants, given equal suction and discharge pressures. Pressure drops in heat exchangers and connecting lines were equal for synthetic and HC mixtures at equal mass flow rates. This allows higher heating capacities of HC mixtures at a given pressure drop (mass flow rate) due to their wider vapor dome. A previously developed evaporator heat transfer correlation for synthetic refrigerant mixtures was applicable to the HC mixtures. A condenser heat transfer correlation previously fitted for synthetic refrigerants performed significantly worse for HC mixtures. Composition determination during operation and without sampling was possible with a deviation of at most 0.05 mass fraction using simple temperature and pressure measurements and REFPROP for thermodynamic property calculations. Overall, high-glide HC mixtures, just like mixtures of synthetic refrigerants, showed significant COP improvements for specific operating conditions despite a decreased heat transfer coefficient. Potential problems like composition shift or poor compressor performance were not encountered. As a next step, testing high-glide mixtures in pilot-plant installations is recommended.

Thermodynamic analysis of novel mixtures including siloxanes and cyclic hydrocarbons for high-temperature heat pumps

This paper presents the investigation of zeotropic binary fluid mixtures containing cyclohexane (critical temperature above 200 °C) as the base fluid with R600, R600a, R601, R601a, R1336mzz(Z), R1234ze(Z), R1233zd(E) and cyclopropane (critical temperatures between 100 °C and 200 °C). For pure components and their mixtures, the performance of the vapor compression system with an internal heat exchanger was analysed at 50 °C and 80 °C heat source and sink inlet, respectively. Variation of the heat source temperature difference and the internal heat exchanger pinch point temperature difference at supply temperatures (140–170 °C) were also investigated. A pinch point temperature difference of 5 K was maintained for the evaporator and condenser. An increase of 6.59 % in COP was obtained with the zeotropic mixture of cyclohexane/cyclopropane compared to that of pure cyclopropane. The design point analysis showed that increasing the heat source temperature difference and internal heat exchanger pinch point temperature difference reduces the COP. The adopted mixture criteria increased the performance between 3.23 % and 3.91 % with respect to standard working fluids like R1233zd(E) and R601, for a 170 °C supply temperature. With this promising thermodynamic analysis in a subcritical operation, the cyclohexane/cyclopropane mixture has prospect of full integration heat pump design.

Pump-stopping-induced hydraulic oscillations in long-distance district heating system: Modelling and a comprehensive analysis of critical factors

To achieve low-carbon goals, long-distance district heating (LDH) systems are widely applied, which utilize the waste heats from renewable energy power plants and waste incineration plants. The hydraulic oscillations induced by pump-stopping in LDH systems may give rise to critical incidents, such as pipeline ruptures and heating disruptions. The systematic analysis of hydraulic oscillations induced by pump-stopping and the subsequent revelation of critical factors that mitigate their intensity are fundamental prerequisites for ensuring the safety and reliability of LDH system. In this paper, firstly, a pump-stopping hydraulic transient model of the LDH system is established based on the distributed parameter method. Then, combining the method of characteristics (MOC) and the Newton iteration method, the numerical solution scheme for this model is proposed. Finally, taking a 20 km LDH system as an example, the characteristics of hydraulic oscillations induced by pump-stopping is analyzed, and the key factors influencing the intensity of these hydraulic oscillations are investigated. In addition, the differences between hydraulic oscillations induced by pump-stopping and those induced by sudden faults on pipelines are also analyzed. The results indicate that an optimal pump inertia moment value and a properly sized bypass pipe at the pump significantly mitigate hydraulic oscillations, while the influence of constant pressure at the heat source inlet on hydraulic oscillations can be negligible. Our study has important reference value for improving the safe and reliable operation of LDH systems.

Research on geothermal-driven single-effect absorption refrigeration systems with different working fluids: energy and exergy analysis

Abstract Geothermal energy is not only environmentally friendly and has low carbon but also represents a nonintermittent technology. It is anticipated that its utilization in human society will experience rapid growth in the coming decades. Absorption refrigeration can be employed for the recovery of geothermal resources. However, the low performance of absorption refrigeration systems has hindered their development. In order to advance absorption refrigeration technology suitable for geothermal energy recovery, this study developed a mathematical model for an absorption refrigeration system using 55% lithium bromide (LiBr) and 35% lithium chloride (LiCl) solutions as working fluids. The impact of various parameters, including cooling water conditions, chilled water conditions, heat source parameters, and working fluid concentration, on the thermodynamic performance, system efficiency, and exergy efficiency of a single-effect absorption refrigeration system was analyzed. The results reveal that the cooling water inlet temperature and flow, chilled water inlet temperature, heat source inlet temperature, and working fluid concentration are the primary factors affecting the thermodynamic performance and exergy efficiency of the absorption refrigeration system. The coefficient of performance (COP) of the system increases with higher cooling water flow, chilled water inlet temperature, and working fluid concentration, but decreases with higher cooling water inlet temperature. Within a certain temperature range, the COP increases with higher heat source temperature. The effective COP (ECOP) increases with higher cooling water inlet temperature, cooling water flow, chilled water inlet temperature, and working fluid concentration, while it decreases with higher heat source temperature. The highest COP values for the LiBr and LiCl solution single-effect absorption refrigeration systems are 0.795 and 0.785, respectively, while the highest ECOP values are 0.694 and 0.684, respectively.

Performance analysis, multiobjective optimization and working fluid selection for a DPORC system with geothermal source shunting

A dual-pressure ORC system with geothermal source shunting (GSS-DPORC) is proposed. The geothermal source at the outlet of the high-pressure evaporator is shunted so that one portion of it heats the high-pressure preheater and the other portion heats the low-pressure evaporator. Thermodynamic, economic, and environmental performance of the GSS-DPORC system are examined and contrasted with those of the DPORC system under different working fluids and conditions. Further, the EW-GRA-TOPSIS comprehensive evaluation method, which picks the optimal working fluid while attaining the best working conditions, is proposed. It fully assesses the working fluid based on the multiobjective optimization results generated by NSGA-II. The results indicate that the performance metrics of the GSS-DPORC system are superior to those of the DPORC system when the geothermal source inlet temperature is in the range of 373–423 K, the evaporation pressure of high-pressure stage ranges from 740 kPa to 1610 kPa, and the evaporation pressure of low-pressure stage ranges from 540 kPa to 1020 kPa. R227ea has better thermodynamic and economic performance, and R245fa has better economic performance. The R227ea has the best overall performance following a thorough review using the EW-GRA-TOPSIS method, while the R245fa has the poorest performance.

Performance explorations of a novel high temperature heat pump with multi-adjusted compositions of zeotropic mixture

High temperature heat pump has received its invigorated interests in recovering industrial waste heat due to its abilities of improving energy efficiency and reducing carbon emissions. But it is subjected to performance degradation at the varied operating conditions. To tackle this challenge, a novel vapor injected heat pump that ingeniously integrates with a liquid-separation condenser as the separating device and an ejector as the combining device (LEHP) is proposed, and it is featured by actively adjusting of the composition of zeotropic mixture. The mathematical model is established and verified. Six environmentally friendly zeotropic mixtures with different temperature glides are selected as working fluids. Comparison results show that the coefficient of performance of the proposed system is 21.86% higher than that of the conventional heat pumps. Parametrical studies indicate that a decrease in the vapor quality for liquid separation or an increase in the flash tank pressure is beneficial to the system performance and temperature matching in heat transfer processes. Its potentials under various operating conditions are further explored and mapped by using Genetic Algorithm. Propane/Cyclobutene is suitable at the heat source inlet temperature lower than 30 °C, and Cyclopropane/Pentane or Cyclopropane/Hexane is favored as ranging from 40 °C to 50 °C, when it is higher than 50 °C, Butene/Cyclohexane should be selected. Under unique scenarios of equivalent inlet temperatures for heat sink and heat source, Butene/Cyclohexane and Cyclopropane/Hexane demonstrate broad applicability across various operating conditions. The maximum coefficient of performance of 4.72 and exergy efficiency of 68.29% are found when Butene/Cyclohexane is employed.

Comparative analysis and optimization of waste-heat recovery systems with large-temperature-gradient heat transfer

Efficient utilization of waste heat is crucial for reducing waste heat emissions and minimizing environmental impact. Organic Rankine cycle (ORC) systems are commonly employed for waste heat recovery. However, conventional ORC systems have limitations in effectively harnessing waste heat resources because of differences in the pinch point temperature and the relatively small temperature difference between the heat source inlet and outlet. To address this issue, we designed two absorption organic Rankine cycle (AORC) systems in this study based on absorption heat exchangers. We analyzed the energy, exergy, and economy of three ORC system models with heat source temperatures within the range from 363.15 K to 413.15 K. The results indicated that the AORC system represented a optimal waste heat recovery system, capable of reducing the outlet temperature to 298.70 K and achieving a high temperature efficiency of 1.037. Thus, an AORC system can facilitate heat exchange with substantial temperature differences, enabling the efficient utilization of heat sources. The AORC system in this study exhibited a high net power of up to 151.8 kW, and an electrical exergy efficiency of 55.45%. Additionally, the AORC consistently outperformed other systems in terms of economy, as evidenced by its electricity production cost, which was the lowest among all three systems with heat source temperatures lower than 398.15 K.

Parametric analysis and multi-objective optimization of biomass-fired organic Rankine cycle system combined heat and power under three operation strategies

Biomass-fired organic Rankine cycle (ORC) systems for combined heat and power (CHP) generation are a feasible technology to provide carbon-neutral power production. In this study, the parametric analysis and multi-objective optimization of a biomass-fired ORC-CHP system under three operation strategies are conducted. The thermodynamic, exergoeconomic, environmental and sustainability models are established, while the effects of seven operation parameters on exergy efficiency (ηex), unit cost of exergy (UCE), equivalent carbon emission (ECE) and ecological life cycle cost (ELCC) are examined. A further four-objective optimization problem is addressed using NSGA-II and the Pareto-optimal solutions for the three operation strategies are derived and compared. The results indicate that evaporation temperature, condensation temperature and heat source inlet temperature present positive effects on ηex and UCE, whereas opposite effects are imposed by degree of superheat and pinch point temperature difference. System B yields a 0.21% higher ηex and a 0.41 tons higher CO2,eq than system C. The Pareto-optimal solutions of ηex, UCE, ECE and ELCC for system A using TOPSIS decision-making are 12.380%, 0.183 $/kWh, 10.250 tons CO2,eq, and 13.677 × 10−3 $/kWh, respectively. System A may be regarded as the preferred operation strategy for biomass-fired ORC-CHP systems due to its moderate performance.

Off-design performance of an organic Rankine-vapor compression cooling cycle using R1234ze(E)

In this study, a 264 kWth organic Rankine-vapor compression cycle (ORVC) was experimentally tested over a range of conditions to quantify the individual impact of off-design external conditions. The ORVC was designed to recover waste heat at 91°C, reject heat to a liquid condenser stream at 30°C, and produce chilled water at 7°C. The condenser heat rejection temperature was varied from 16.6°C to 32.6°C, the chilled water delivery temperature was varied between 2.1°C and 13.1°C, and the heat input temperature was varied from 91°C to 120°C. As the condenser heat rejection temperature decreased, the coefficient of performance (COP) of the ORVC improved from 0.558 at 30°C to 0.682 at 16.6°C, despite a reduction in compressor isentropic efficiency. Although the chilled water temperature variation had almost no impact on the organic Rankine cycle performance, the compressor efficiency decreased when the delivery temperature was below 7°C. At the highest chilled water temperature, 13.1°C, the COP of the ORVC was 0.643. Compressor stall was noted when the condenser heat rejection temperature was greater than 32.6°C and the chilled water delivery temperature was below 2.1°C. Increasing the driving heat source inlet temperature improved the COP of the ORVC and the thermal efficiency of the organic Rankine power cycle, while decreasing the efficiency of the compressor and the COP of vapor compression cycle. In addition, the integrated part load value of the system was determined through experimentation to be 0.682, which provides a realistic estimate of real-world performance.

Analysis and assessment of a novel organic flash Rankine cycle (OFRC) system for low‐temperature heat recovery

AbstractIn this paper, a novel organic flash Rankine cycle (OFRC) system for low‐temperature heat recovery is analyzed and optimized using the 3E (energy, exergy, and economic) analysis method and particle swarm optimization algorithm, respectively. Five environmentally friendly organic fluids and three typical heat source conditions are simultaneously discussed during the parametric analysis and optimization process, to obtain a comprehensive understanding of the thermo‐economic characteristics of this novel system. The main analysis results show that the biggest exergy loss of the OFRC system is caused by the condenser, followed by the evaporator. About 70% of the specific power cost is caused by the capital investment of the system, and more than 60% of the capital investment is spent on purchasing the high‐pressure and low‐pressure expanders. Under the same operating conditions, the working fluids with high critical temperatures can achieve higher cycle thermal efficiency and lower specific power costs than those with low critical temperatures. The optimization results show that the OFRC system is able to achieve a better thermodynamic performance than the organic Rankine cycle (ORC) and organic flash cycle (OFC) systems, and when the heat source's inlet temperature is set to 100°C, 120°C, and 140°C, R245fa, R290, and R152a are, respectively, recommended as the best working fluid for the OFRC system. Besides this, it is found that the OFC system has the worst thermo‐economic performance, and the ORC system can achieve the lowest specific power cost. A new finding is that, for all three systems, the higher the critical temperature of the working fluid, the lower the specific power cost of the system.

Influence of operating parameters on the COP of an R600 high-temperature heat pump

Process heat supply by high-temperature heat pumps exploiting waste heat is an effective method for enabling the decarbonisation of industrial processes. Key aspects for the application of this technology are the supply temperature levels and efficiencies that can be achieved. This work investigates an R600 (n-butane) high-temperature vapour compression heat pump (HTHP) capable of utilizing waste heat at temperature levels between 40 and 60°C and lifting it to supply temperatures between 110°C in sub-critical and 160°C in trans-critical operation. The HTHP prototype is designed as a single-stage cycle, comprising an inverter-driven suction-gas-cooled reciprocating compressor, low-pressure accumulator and internal heat exchanger (IHX) for suction gas superheating. The influence of the operating parameters high pressure and suction gas superheat (“internal parameters”) plus the heat source temperature, the heat sink inlet and outlet temperatures and the compressor speed (“external parameters”) on the COP and heating capacity are studied using data from both the prototype and the simulation model. The optimum high pressure depends on the operating conditions, an increase of suction gas superheat increases the COP. In sub-critical operation, a heating capacity of 30.7 kW at a COP of 4.4 is reached at a source inlet temperature of 60°C heating the sink from 80 to 110°C. Trans-critical operation enables a heat sink outlet temperature of 160°C, offering a heating capacity of 24.2 kW at a COP of 3.1.

Experimental Analysis of Heat Storage and Release of Binary Methanol Aqueous Solution Pulsating Heat Pipe Phase Change Accumulator

To improve the problems of energy shortage and low utilization rate, this paper designed a set of pulsating heat pipe (PHP) devices coupled with phase change energy storage material. Further, the binary methanol-water solution is proposed as a novel experimental filling medium to enhance the heat transfer performance of the device. The fluid flow model of the PHP was analyzed via experiment and simulation. Besides, the heat storage and release performances of the PHP at different flow rates, different heating temperatures, different filling mediums, and different filling ratios are investigated. The results show that when the filling medium (binary methanol-water solution) possesses the filling ratio of 0.6 (methanol and water are each 0.3), the heat source inlet flow is 0.60 m3/h, the heat source heating temperature is 120°C, and the PHP is at the best heat storage performance. During the exothermic process, the lower the initial temperature of cooling water, the higher the heat recovery rate. Thus, it can be concluded that the selection of an appropriate filling medium and the optimal parameters to enhance heat transfer can have a broader application prospect in the field of waste heat recovery.

Integrated Vapor Compression Chiller with Bottoming Organic Rankine Cycle and Onsite Low-Grade Renewable Energy

The present study offers a scheme to improve the performance of existing large-scale chillers. The system involves raising the temperature of the chiller’s cooling water stream using renewable energy sources by incorporating an organic Rankine cycle (ORC). The thermal analysis was conducted by raising the temperature of one-third of the approximately 200 ton chiller’s cooling water. The investigation was considered for ORC evaporator inlet temperature of 90~120 °C by the step of 10 °C. Various working fluids for the different ORC evaporator inlet temperatures were examined. Sensitivity analyses conducted on the degree of superheating, degree of subcooling, condenser saturation temperature, pinch point temperature differences of the ORC evaporator and condenser, and the mass flowrates of the heating and cooling streams were also reported. Genetic algorithm was employed to carry out the optimization. The best options for the ORC working fluid at the heating source ORC evaporator inlet temperatures of 90 °C was found to be DME, presenting an improvement of 48.72% in comparison with the rated coefficient of performance (COP) value of the VCC, with a renewable energy input requirement of 710 kW. At the heat source temperatures of 100 °C and 110 °C, butene, which presented an improvement in the COP equal to 48.76% and 68.85%, respectively, with the corresponding renewable energy requirements of 789.6 kW and 852 kW, was found to be the ideal candidate. Meanwhile, at the heat source inlet temperature of 120 °C, R1233zd (E), representing an improvement of 140.88% with the renewable energy input of around 1061 kW, was determined to be the most favorable ORC working fluid candidate.

Optimization of a heat pipe-radiator assembly coupled to a recuperated closed Brayton cycle for compact space power plants

• Analysis of recuperated closed Brayton cycle conditions is carried out. • Brayton cycle and heat pipe-radiator models are numerically coupled. • Heat source and cold heat exchanger inlet temperatures are optimized. • The specific mass minimization is used as the objective variable. • Optimization provides cycles with specific masses ranging from 40 to 50 kg/kW. Compact and efficient energy conversion systems for space applications enable the appearance of new mission opportunities and technological discoveries resulted from space exploration. Besides energy availability, another crucial factor of any energy conversion system for space purposes is its total mass and size. Focusing on a recuperated closed Brayton cycle (CBC), thermodynamic modeling of a CBC is proposed. Moreover, a thermal model is carried out to predict the overall properties of the cold side of the system (i.e., heat pipes and radiator) for different CBC conditions. Both models are coupled and their conjunct solution provides operational data for the design of the heat rejection system, such as the number of heat pipes (HP), total assembly mass, length, and second-law efficiency. Furthermore, by means of this coupling, the heat source temperature and the cold heat exchanger (CHE) inlet temperature are defined, using an optimization procedure where the specific mass (i.e., radiator mass to cycle power ratio) is minimized. Based on this objective variable, the optimized heat source temperature of 1200 K is achieved, while the CHE inlet temperature of 513.2 K is obtained. Such temperature conditions ensure the future design of a space energy conversion system that aligns good efficiency and compactness.

Off-design model of an ORC system for waste heat recovery of an internal combustion engine

• ASPEN® HYSYS software, off-design cycle simulations were done to evaluate Organic Rankine Cycle performance; • Economic calculation, CEPCI based, evaluated the feasibility of plant implementation; • A technical and economic analysis for an Organic Rankine Cycle was performed. The exhaust gases of an ICE leave the equipment still with enough temperature to generate more electric power if a proper system is used for that purpose. Therefore, due to this scenario, in this work a study of an ORC system to recovery energy from the flow gases of a stationary diesel engine. The analyses are in three parts: (1) parametric analysis of an ORC system in on-design to determine the cycle's optimal operating point; (2) parametric analysis in off-design condition, to verify the behavior of power production and cycle efficiency when the heat source's flow and temperature are varied; (3) An economic analysis, a CEPCI based model was used. The system design was determined for a working fluid flow rate of 0.09 kg/s, evaporation and condensation pressure of 3,870 kPa and 25 kPa, respectively, and with exhaust gas at 420 °C and 0.1697 kg/s. For the off-design simulations, the evaporation pressure, the working fluid flow and the heat source inlet conditions were varied. A minimum, average, and maximum net power production of 8.56 kW, 15.59 kW, and 26.29 kW, respectively, was verified, while in the design condition it was 14.72 kW, there was also an average increase in exergy of 9.35%. The initial investment for the system's implementation is US$ 23,257.02 and the financial return and rate of return reach an average of 1.5 years and 90%, respectively. The study shows that the system increases the power plant's thermal efficiency and decreases fuel consumption as well as the emission of pollutant gases.

Transient behavior investigation of a regenerative dual-evaporator organic Rankine cycle with different forms of disturbances: Towards coordinated feedback control realization

This study utilizes an innovative regenerative dual-evaporator organic Rankine cycle (RDORC) with R1234ze to recover solid bulk waste heat by using air as heat transfer medium. A comprehensive transient model for RDORC is constructed based on finite volume method. Furthermore, a novel coordinated feedback control system for RDORC including two PI controllers is proposed to remain turbine inlet main vapor and resupplied vapor superheat degrees constant. The transient behaviors of RDORC and simple ORC (SORC) are compared under external disturbances of heat source inlet temperature. The results indicate that under 10 °C step decrease disturbance, the RDORC presents a 0.5 °C larger undershoot and a 164s longer setting time of superheat degree than that of SORC. Compared with SORC, the exergy efficiency enhancement of RDORC increases from initial value 4.13% to final value 4.51% after the step disturbance. Under sinusoidal disturbance with amplitude of 10 °C in RDORC, the peak amplitude of turbine main vapor inlet pressure (3.6%) is far higher than that of turbine resupplied vapor inlet pressure (0.82%). Besides, under random disturbance with variance of 1, the system exergy efficiency and thermal efficiency fluctuate around the design values of 35.67% and 7.65% with maximum deviations of 2.2% and 0.37%, respectively.

Optimal hydrocarbon based working fluid selection for a simple supercritical Organic Rankine Cycle

In this paper, several hydrocarbons' performance as a working fluid for a supercritical Organic Rankine Cycle are studied. Energy, exergy, and exergoeconomic analysis are conducted for the cycle operating with a low-grade waste heat source. Initially, fifteen different working fluids, primarily hydrocarbons, were considered based on their environmental characteristics, global warming potential, ozone depletion potential, flammability, and toxicity. The cycle efficiency for each working fluid was analyzed for different cycle operating pressures and different inlet heat source temperatures from 400 K to 500 K for a constant turbine work output. Three different trends of cycle performance characteristics were observed for various working fluids with the cycle operating at different evaporator pressures and source inlet temperatures. The working fluids that exhibited similar characteristic trends were then categorized into families for further analysis. Three hydrocarbons, i.e., Dimethyl Ether, R1234yf, and Diethyl Ether, were each selected as the representative of their respective family, along with Isobutane as the reference working fluid for comparison. After detailed energy and exergy analyses, Dimethyl Ether and Isobutane were found to be promising working fluids for the range of pressure and source inlet temperatures considered. Finally, the exergoeconomic analysis showed Dimethyl Ether to be the optimal working fluid based on the unit cost of net work produced and the total cost of exergy destruction, which were calculated to be (59.18 ± 0.49) $/MWh and (8.92 ± 0.48) $/h, respectively, when operating at 450 K.

Performance analysis and multi-objective optimization of the high-temperature cascade heat pump system

This paper presents a high-temperature cascade heat pump system with a high compression ratio for recovering the waste heat of the chemical plant and replacing the steam. To analyze the economic and the thermodynamic performance of the high-temperature cascade heat pump, a mathematical model, considering energy, exergy, economy and environment, has been developed under different heat source inlet temperature. The proposed system here indicated good stability and feasibility under various operating conditions according to the simulation results. However, as the heating capacity and the annual net profit were found to be conflicting with each other, a multi-objective optimization method was developed to solve this problem. In addition, the technique for Order of Preference by Similarity to Ideal Solution method was selected as the decision-making method to search for the final optimal result of the system. The optimization results showed that if the optimized heating capacity project was selected, the average heating capacity and the average annual net profit were 2.8% and 6.7% lower than their maximum possible values. At the optimal heat source inlet temperature of 71 °C and condensing temperature of 145 °C, the heating capacity of the system was 498.9 kW and the payback period was 3.9 year.

Dynamic Modeling and Operation Characteristics Analysis of LiBr Absorption Heat Pump

In order to fully exploit the dynamic operation characteristics of absorption heat pump, a dynamic simulation model of LiBr absorption heat pump considering mass transfer and distribution parameters is established. The thermal inertia characteristics of the system are studied, and the thermal performance and crystallization characteristics of the system are analyzed under the conditions of heat source temperature change, cooling water temperature change and refrigerant water temperature change. The results show that: the model can accurately simulate the steady-state and dynamic characteristics of the absorption heat pump; the thermal inertia of the unit is mainly related to the mass of the solution stored in the unit; the upper limit of the heat source inlet temperature is affected by the COP of the system and the crystallization risk, the decrease of the inlet temperature of cooling water can increase the COP of the system, and the lower limit is limited by the crystallization risk, and the cooling water inlet temperature is affected by the crystallization risk , and the lower limit of the inlet temperature of cooling water is limited by the crystallization characteristics. The upper limit of the inlet temperature of refrigerant water is not limited by the crystallization characteristics, but is mainly limited by the user’s energy demand. This provides a reference for the dynamic operation of absorption heat pump.

Performance analysis of compressor-assisted two-stage triple effect absorption refrigeration cycle for power and cooling

Ammonia-water absorption and power cycles offer a viable option for the effective use of low and medium temperature heat sources for sub-zero cooling and power generation. The proposed system is a compressor assisted two-stage triple effect absorption cycle for power and cooling. This system comprises of power sub-system and absorption-compressor sub-system and both systems utilize ammonia-water mixture as the working fluid. The power generated by the cycle is used for the compression required to enhance the performance of the cycle. The mathematical model of the proposed system is analyzed using first and second law of thermodynamics. The engineering equation solver (EES) software is employed to analyze the model. Thermodynamic performance of the combined cycle was evaluated based on the compression ratio and the heat source inlet temperature. The pressure ratio (Prcom) of the integrated compressor is varied between 1.0 and 1.6 to observe the effect on the operation, output, and performance of the system. The simulation result shows that the heat source inlet temperature can be reduced by 50 °C compared to the traditional two-stage triple effect absorption system. The effective energy and exergy efficiencies are 17% and 76% respectively while the cooling load was 165.4 kW. The results also showed that asorber1 and absorber 2 have the highest rate of exergy destruction of 30.91% and 37.32% followed by condenser 1 with 16.3% and solution heat exchanger 2 with 7.89%. It is observed that the proposed system performs better in comparison to its counterparts operated at medium temperature heat sources.