Low Temperature Heat Sources Research Articles

Investigation of the performance of modified organic Rankine cycles (ORCs) and modified trilateral flash cycles (TFCs) assisted by a solar pond

Solar pond is a type of solar collector that stores solar energy in the form of heat. The solar pond can be used as a low-temperature heat source for electricity generation. In this paper, to find the most suitable power cycle for power generation from the solar pond, the performance of the Organic Rankine Cycle (ORC), Trilateral Flash Cycle (TFC) and their modified forms with an open feed liquid heater and an internal heat exchanger for different working fluids was investigated. Water was considered as the heat transfer fluid which transfers the stored heat from the solar pond to the working fluid of the cycle. The results indicate that in all cases, the energy and exergy efficiency of the ORC is higher than those of the TFC. The regenerative ORC with both open feed liquid heater and internal heat exchanger that works with R123, as the working fluid, has the best performance and the highest output power among all the examined cycles. By reducing the mass flow rate of the heat removal working fluid, energy and exergy efficiency of the cycle increased. The optimum mass flow rate in which the maximum power is generated is 0.1082 kg/s and 0.1224 kg/s for the ORCs and the TFCs that work with R123, respectively.

Exergo-economic analysis of different power-cycle configurations driven by heat recovery of a gas engine

In the present work a 34.3 kW stationary gas engine considered as prime-mover of bottoming thermodynamic cycles. The waste heat recovery cycles of engine exhaust gas consist of several configurations of organic Rankine cycle and combination of Rankine/Kalina cycles, also the engine jacket water heat is recovered by trilateral flash cycle. The performance of bottoming cycles was investigated from thermodynamic and thermo-economic points of view. For the organic Rankine cycle, three fluids including Benzene, Toluene and Cyclohexane have been compared. Also, considering that the trilateral flash cycle is a suitable cycle for heat recovery from a low temperature heat source due to its better matching between the temperature profiles of cycle working fluid and heat source fluid, this cycle is considered as bottoming waste heat recovery cycle for engine jacket water. In order to compare different working fluids and cycle configurations, three objective functions including energy efficiency, exergy efficiency and specific investment cost for the 18 studied cases are compared. The results reveal that, energy, exergy efficiency and specific investment cost of all configurations with toluene as working fluid of organic Rankine cycle is the highest and least compared to the other working fluids, respectively. But for configuration Rankine with Open Feed Heater-Kalina-Trilateral Flash Cycle, benzene fluid is better in terms of specific investment cost, however the energy and exergy efficiency of this cycle is also maximal with toluene fluid. Also, the results depict that configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle and Rankine with Open Feed Heater_Kalina_Trilateral Flash Cycle thermodynamically, and configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle and Rankine with Open Feed Heater – Trilateral Flash Cycle exergo-economically show the better performance. In this regard, employing configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle, Rankine with Open Feed Heater-Kalina – Trilateral Flash Cycle and Rankine with Open Feed Heater – Trilateral Flash Cycle in base mode leads to 6.85 kW, 6.48 kW and 6.54 kW increment in net power produced imposing 3318 $/kW, 4090 $/kW and 3377 $/kW specific investment cost, respectively.

Sorption thermal energy storage: Hybrid coating/granules adsorber design and hybrid TCM/PCM operation

A novel adsorber design combining fin-coating and filling of granules between the fins is introduced for closed sorption thermal energy storage. A storage system is designed and assembled, experimental results are presented for charging and discharging, heating and cooling. Considering the use case of the thermal management of the battery in a hybrid vehicle, a total cooling energy of 544(8) Wh in a period of 30 min is measured, which gives an average cooling power of 1.05(8) kW. A novel hybrid operation mode is proposed for discharging the storage for heating purposes, exploiting the features of both phase-change and thermochemical materials simultaneously by allowing water to freeze in the evaporator. The freezing enthalpy can then be exploited as evaporation enthalpy, removing the need for an external low-temperature heat source for the evaporator. This hybrid operation might be beneficial, e.g. in winter in order to preheat the battery before discharging it.

A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle

One of the most crucial challenges of sustainable development is the use of low-temperature heat sources (60–200 °C), such as thermal solar, geothermal, biomass, or waste heat, for electricity production. Since conventional water-based thermodynamic cycles are not suitable in this temperature range or at least operate with very low efficiency, other working fluids need to be applied. Organic Rankine Cycle (ORC) uses organic working fluids, which results in higher thermal efficiency for low-temperature heat sources. Traditionally, new working fluids are found using a trial-and-error procedure through experience among chemically similar materials. This approach, however, carries a high risk of excluding the ideal working fluid. Therefore, a new method and a simple rule of thumb—based on a correlation related to molar isochoric specific heat capacity of saturated vapor states—were developed. With the application of this thumb rule, novel isentropic and dry working fluids can be found applicable for given low-temperature heat sources. Additionally, the importance of molar quantities—usually ignored by energy engineers—was demonstrated.

A cold and power cogeneration system utilizing LNG cryogenic energy and low-temperature waste heat

Abstract A novel cold and power cogeneration system is proposed in this paper. In the system, a “special” absorption refrigeration cycle is designed which is driven by liquefied natural gas (LNG) cryogenic energy with ammonia-water as working fluid. And this system contains two power processes, in which ammonia and natural gas are heated respectively by low-temperature heat source and then expanse in turbines. The thermodynamic performance of the cogeneration system is simulated and analyzed. The results show that the new cogeneration system demonstrations good thermal performance. The exergy efficiency of the system is as high as 36.1%. The coefficient of performance (COP) of the refrigeration cycle is 1.6 and the generating efficiency of power cycle reaches 38.8%. Sensitive analyses are performed to evaluate the effects of key parameters on the performance of the cogeneration system. Some values of the key parameters are recommended and the variations of the main thermodynamic characters are outlined. This new cogeneration system provides a new approach for the efficient utilization of LNG cold energy.

Thermodynamic analysis of ejector-assisted vapour compression–absorption hybrid refrigeration system

ABSTRACT The vapour compression–absorption hybrid refrigeration system (VCAHRS) is a potential alternative refrigeration technology as it economises the use of energy resources. The main issues observed with VCAHRS are low overall COP and large size of system which is mainly due to the poor performance of absorption section. Absorption section, while assisted by an ejector, can improve the overall performance of VCAHRS. It is shown that at low generator temperatures, the ejector-assisted absorption section provides better performance than the conventional absorption system adapted in VCAHRS. Simulation results show that the overall COP of VCAHRS is improved by 22.6%, whereas the COP improvement of 25.2% is observed in the absorption section. The total irreversibility of the system is reduced by 38.8% using ejector at optimum generator temperature which is found to be 92.1°C while varying it from 117.9°C. Therefore, ejector-assisted VCAHRS also permits the utilisation of low temperature heat source.

Results of research into efficiency of a flat solar air heliocollector with a wavy absorbing surface

A new design of the air collector with the airtight and warmed casing and the absorber with the wavy surface that can be used as an additional heating element of the low-temperature heat source was developed. We established a series of generalizing dependences for finding thermal effectiveness of the collector, specifically, the influence of the components of thermal balance of the collector on the drop of temperatures in the heat carrier flow in the collector and the insolation level on heating efficiency.We obtained analytical dependences for determining the components of thermal balance of the collector, distribution of the temperature field along the absorbing panel, which made it possible to improve the mathematical model of the heat exchange process in the developed air collector. The results of the research into the air collector allowed developing the program of numerical computer calculation of the temperature field of thermal flows.It was established that application of the wavy absorbing surface of the absorber in the air heliocollector at the low level of insolation E=377 W/m2 allows increasing efficiency up to η=58.3 %, and at high energy lighting of E=1,000 W/m2, up to η=63.9 %. Performance of the collector was determined by the iterative calculation-quantitative method and made up more than 78–80 %. This is 10–20 % higher than that in flat collectors, and by 5–10 % higher than in cylindrical vacuumed collectors.The obtained results can be used in the development and improvement of the technical facilities of fruit drying, for increasing the technological and energy effectiveness of the process

Investigation of crystallization risk in different types of absorption LiBr/H2O heat transformers

Absorption heat transformers are utilized to upgrade the energy of low-temperature heat sources. When the working fluid in such systems is LiBr/H2O solution, there is a possibility of crystallization phenomenon at their generator outlet. This phenomenon has to be avoided because otherwise it stops the system operation. In the present work, the possibility of crystallization, under different operating conditions such as different temperatures in the condenser, evaporator, absorber and absorbing evaporator temperatures as well as different effectiveness of applied heat exchangers, is investigated. Using engineering equation solver software, the investigation is carried out for three types of heat transformers including single-stage, double-effect and triple-effect for identical values of input heat. The results show that at higher absorber temperatures especially in the double and triple-effect absorption heat transformers, crystallization may occur at the outlet of expansion valves in addition to the generator outlet. Moreover, lower values of the condenser temperature and heat exchangers effectiveness increase the possibility of crystallization risk in all the three types investigated.

Experimental study on a small-scale pumpless organic Rankine cycle with R1233zd(E) as working fluid at low temperature heat source

Experimental study on a small-scale pumpless organic Rankine cycle with R1233zd(E) as working fluid at low temperature heat source

Thermodynamic analysis and optimization of a balanced-type single-stage NH3-H2O absorption-resorption heat pump cycle for residential heating application

Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology in efficient utilization of low-temperature heat for residential heating application. This paper proposes a balanced-type single-stage ARHP cycle based on the unbalanced ARHP cycle by eliminating the rectifier and depending on only one solution circulation pump. The proposed cycle can achieve internal mass and species conservation by changing the ammonia-water solution concentration difference at different pressure levels. A mathematical model is developed to obtain feasible high pressure/low pressure (PH/PL) pairs to enable the cycle. The cycle's coefficient of performance (COP) at different PH/PL pair values is investigated. The maximum COP is 1.51 and the corresponding heat supply temperature reaches 43.4 °C when PH/PL pair value is 1.50/0.48 MPa and heat source temperature is 95 °C. The maximum heat supply temperature can reach 53.4 °C and the minimum ambient air temperature to effect the cycle is −5.8 °C. Other parameters like heat output/inputs, solution circulation ratios, and absorption and desorption concentration gradients in the absorbers and generators are studied. Inner pressure (difference), COP and heat source temperature demand have been compared with those of the conventional absorption heat pump (AHP) cycle and the unbalanced ARHP cycle. The results revealed that the proposed cycle could work at lower heat source temperature (above 82 °C) and within wider heat source temperature range than the conventional AHP cycle, indicating that the proposed cycle is potential in efficient utilization of commonly used solar collectors for space heating. In addition, the proposed cycle could be operated at higher COP values and lower inner pressure differences than the unbalanced ARHP cycle.

Aqua-ammonia-based thermally activated combined power and cooling system

The use of aqua-ammonia-based power generating system is a promising way to utilise low temperature heat sources originating either from a renewable energy resource or industrial process waste heat up to a temperature of 150°C. A thermally activated combined power and cooling system to produce electricity and refrigeration effect simultaneously has been modelled and analysed. The proposed system is a Kalina cycle-based power generating system that utilises aqua-ammonia as working fluid. Refrigeration effect is produced by the working fluid from the turbine exit. The combined system produces mechanical power and as well as cooling effect simultaneously. A simulation study has been conducted to analyse the performance of the proposed system and to develop the optimum operating parameters. Result shows thermal efficiency of 18.20% operating with the source fluid temperature at 135°C. This research work provides a new approach to produce cooling effect from low temperature heat sources.

Aqua-Ammonia based Thermally Activated Combined Power and Cooling System

The use of aqua-ammonia-based power generating system is a promising way to utilise low temperature heat sources originating either from a renewable energy resource or industrial process waste heat up to a temperature of 150°C. A thermally activated combined power and cooling system to produce electricity and refrigeration effect simultaneously has been modelled and analysed. The proposed system is a Kalina cycle-based power generating system that utilises aqua-ammonia as working fluid. Refrigeration effect is produced by the working fluid from the turbine exit. The combined system produces mechanical power and as well as cooling effect simultaneously. A simulation study has been conducted to analyse the performance of the proposed system and to develop the optimum operating parameters. Result shows thermal efficiency of 18.20% operating with the source fluid temperature at 135°C. This research work provides a new approach to produce cooling effect from low temperature heat sources.

Progress in design of adsorption refrigeration systems. Evaporators

Adsorption heat pumps are becoming increasingly popular. Due to their design, they enable application of low-temperature heat sources. Evaporators for adsorption chillers make one of the basic design elements determining the correct operation of these devices. The specificity of operation in low pressures and temperatures is the reason why their design significantly differs from that of conventional evaporators. The pluralities of existing solutions as well as the lack of a systematic review of them cause difficulties in correct evaluation and choice of design. The paper presents the current state of art as well as a review of the existing solutions of evaporators used in adsorption heat pumps. The purpose of the review research is to present various solutions of evaporators as well as indicating their advantages and disadvantages in order facilitate the choice of the optimal design.

Thermodynamic performance analysis of a R245fa organic Rankine cycle (ORC) with different kinds of heat sources at evaporator

The first and the second law analyses of a 20 kWeR245fa organic Rankine cycle (ORC) with low grade temperature heat sources were numerically studied. There were three different heat sources such as hot water, saturated steam, and combined hot water/saturated steam used to supply heat at the ORC evaporator. The heat source temperature was varied in a range of 80–110 °C and the pinch temperature difference between the heat source temperature and the evaporating temperature was in a range of 1–10 °C. The ORC condensing temperature was kept constant at 40 °C. The results revealed that the combined hot water/saturated steam heat source provided a highest second law or exergy efficiency due to less irreversibility generated at the evaporator followed by the saturated steam and the hot water heat sources, respectively. The increase of heat source temperature at a specific pinch could increase the second law efficiency of the cycle. However, the increase of pinch value resulted in lower second law efficiency. In addition, for the below pinch zone, with the hot water/saturated steam heat source, the reduction of the hot water flow rate slightly enhanced the ORC second law efficiency as the exergy destruction below pinch was reduced. However, there was a limit that the flow rate should not be reduced below a specific value otherwise a very high heat exchanger area was needed.

Multi-objective optimization of ORC parameters and selection of working fluid using preliminary radial inflow turbine design

Organic Rankine cycles (ORCs) are used to generate power from low temperature heat sources. In this study, 28 hydro carbon (HC), hydro fluorocarbon (HFC) and hydro fluoroolefin (HFO) working fluids are used for three different heat source temperatures (90, 120 and 150 °C). A 1-D radial-inflow turbine (RIT) design with loss calculations is incorporated into the model to add dynamic turbine stage efficiency. The turbine model is run together with the ORC, and real gas properties are used for the entire system. A genetic algorithm multi-objective optimization is used to design an ORC with minimum thermal conductance per net power output and maximum performance factor (PF). The decision variables are specific speed, condensation pressure, pressure ratio at the turbine stage, degree of superheating and pinch point temperature difference (PPTD) in the evaporator. Pareto frontiers are obtained at the end of the study, and a decision-making method (TOPSIS) is used to select an optimum solution for each working fluid. R1234yf, R1234ze(e) and isobutane are found to be the optimum working fluids at 90, 120 and 150 °C heat source temperatures respectively. For each solution, turbine geometry, fluid velocities and impeller rotational speed are calculated.

Mixed refrigerant as working fluid in Organic Rankine Cycle for hydrogen production driven by geothermal energy

The possibility of utilizing low temperature heat source systems for producing electricity has been significant due to increasing energy demand. In this study, the Organic Rankine Cycle (ORC) integrated with proton exchange membrane (PEM) electrolyzer is analyzed thermodynamically and economically. A mixture of butane, pentane and iso-pentane is selected as working fluid. The results show that utilizing the mixed refrigerant enhances the performance of the system and results in a higher hydrogen production rate because of a glide match of temperature profiles in the heat exchangers. Economic analysis results which are helpful in designing entire the system show that the highest cost component is electrolyzer, followed by the turbine and condenser.

Heat recovery in energy production from low temperature heat sources

Low‐temperature (<100°C) heat sources have the potential to provide renewable and clean energy. Traditional technologies (thermal engines and thermoelectric solid‐state devices) are not economic in this temperature range. Innovative methods have been recently proposed. In some of them, a process of “heat recovery” has been proposed: it consists in the reuse of the heat provided by the heat source more than one time. Here, we perform a thermodynamic analysis of the heat recovery process. We found that, in the considered temperature range, the temperature difference across the heat exchangers has a major impact on the efficiency, being the main cause of entropy production. By evaluating the efficiency and the surface of heat exchangers needed for producing one unit of power, we found that fundamental processes operating on large temperature difference should be preferred, in order to minimize the capital cost and volumetric dimension of the heat recovery system. © 2018 American Institute of Chemical Engineers AIChE J, 65: 980–991, 2019

Experiment on radial inflow turbines and performance prediction using deep neural network for the organic Rankine cycle

The organic Rankine cycle makes it possible to accomplish energy recovery from a low-temperature heat source, which is typically not recovered for economic reasons. As the expander for the organic Rankine cycle, the radial turbine is easy to manufacture and has advantages in terms of size and efficiency. The radial turbine design modeler (RTDM), which was developed from in-house code, is a preliminary design program for radial inflow turbines and is different from the commercially available program RITAL. In this study, an experiment on radial inflow turbines is performed using both RTDM and RITAL. As a result, the output and efficiency of the RTDM and RITAL turbines are 36.04 kW, 80.03% and 35.03 kW, 76.01%, respectively. Experimental results demonstrate that the performance of the RTDM turbine is almost similar to the RITAL turbine. We also perform analysis on performance prediction utilizing a deep neural network with two hidden layers based on the experimental data. As a result, the minimum root mean squared errors of the RTDM turbine and RITAL turbine are estimated to be approximately 1.81 and 1.65, respectively. The deep neural network is able to predict the trends of the experiment for the organic Rankine cycle.

Application of numerical modelling for design and improvement of performance of gas ejector

Ejection system can be driven by free or inexpensive low temperature heat source, either solar or waste heat, as the main source of energy instead of electricity. These systems can be thought as a real alternative to compression devices in air-conditioning technologies. The paper deals with design procedure for the gas ejector based on numerical modelling. Crucial geometry parameters of the ejector and performance lines based on numerical analysis are shown. Also, the velocity and pressure flow fields inside the ejector, temperature and pressure profiles along the ejector are presented and discussed. Effects of geometry modification on the ejector performance are also shown and discussed. Comparison between numerical and experimental results of temperature and static pressure are presented.

Experimental analysis of a micro-ORC driven by piston expander for low-grade heat recovery

In this paper, a full experimental characterization of a micro-scale ORC system is presented. The facility under investigation is driven by a piston expander prototype, made of three cylinders arranged radially around the drive shaft. The system is rated for a thermal input around 30 kW, being suitable for residential, tertiary sector or small industry applications. It is conceived for exploiting low temperature heat sources, such as solar collectors, biomass boilers, geothermal energy or waste heat streams. The facility was provided with an electric boiler as heat source, which warms water up to 90 °C, and cold water at ambient temperature as heat sink. A test campaign was performed varying the hot source temperature and the organic fluid feed pump velocity, in order to characterize the system behavior at different off-design working conditions. The electric consumption of the ORC feed pump was measured, in order to quantify the actual impact of the auxiliaries on the overall efficiency. Moreover, the number of electric loads connected to the generator was varied, changing the equivalent phase impedance value, for evaluating the effect on the expander rotating speed and power output.The experimental analysis demonstrated that small reciprocating expander is suitable for exploiting low enthalpy heat sources, with quite good performances compared to other architectures like scroll and screw expanders, more applied within low temperature sources. The results show that the gross electric power output varied between 250 W and 1150 W, depending on the expander speed and on the number of electric loads activated. The expander total efficiency showed a barely constant trend around 40%. The pump total efficiency varied between 10% and 20%, increasing with the pump rotational speed. The maximum ORC gross and net efficiency were 4.5% and 2.2% respectively, confirming that the auxiliaries impact cannot be considered negligible in such type of systems.