Increase Of Heat Source Temperature Research Articles

Multi-objective optimization of the dual-pressure organic Rankine cycle system based on the orthogonal design method under different external conditions

The dual-pressure organic Rankine cycle (DPORC) system can obtain a better temperature match between the heat source and working fluid due to the existence of two evaporation processes, which can significantly improve the utilization rate of the heat source and reduce the irreversible loss. Firstly, single-objective optimization of the DPORC system is conducted based on the orthogonal design method with thermal efficiency, exergy efficiency, electricity production cost (EPC) and annual emission reduction (AER) as the performance indicators, respectively. Then, multi-objective optimization of all performance indicators is carried out based on the comprehensive scoring method. Finally, the contribution rates of the operation parameters and the optimal working conditions under different external conditions are investigated. The results show that condensation temperature, high-pressure evaporation temperature and turbine isentropic efficiency are the most critical parameters for system comprehensive performance. When heat source temperature is 170 °C, thermal efficiency, exergy efficiency, EPC and AER under the optimal working conditions are 11.91%, 48.46%, 2.71 × 10−2$/kWh and 11.17 × 105kg, respectively. With the increase of heat source temperature, condensation temperature and turbine isentropic efficiency always have an important influence on system comprehensive performance. The contribution rates of high-pressure evaporation temperature and low-pressure evaporation temperature increase and decrease, respectively. Better comprehensive performance can be obtained by using HC working fluid.

Experimentally Identifying the Influences of Key Parameters for an Organic Rankine Cycle Using R123

As an efficient energy conversion technology, the organic Rankine cycle (ORC) has been widely applied in medium- and low-grade heat sources. In order to explore the experimental performance of ORC and reveal the effects of operation parameters, an experimental setup was built and R123 was selected as the working fluid. In the experiments, the heat source temperature as well as the mass flow rates of the working fluid and cooling water were controlled. Under the design conditions, the net work and cycle efficiency can, respectively, reach up to 0.55 kW and 8.7%. As for the influences of key parameters, with the increase in heat source temperature from 130 °C to 160 °C, the involved heat has a small increase, while the net work increases from 0.44 kW to 0.55 kW, and the cycle efficiency greatly increases from 6.71% to 8.72% at a mass flow rate of working fluid 25 g/s. As for the mass flow rate of cooling water, it has a similar impact on the cycle performances. The difference is that the effect of the cooling water rate is relatively smaller. At the mass flow rate 25 g/s, when the cooling water rate increases from 0.68 kg/s to 0.83 kg/s, the net work varies from 0.46 kW to 0.55 kW, the cycle efficiency increases in the range 7.41~9.4%. Furthermore, except cycle efficiency, all performances are proportional to the mass flow rate of working fluid. In the test range, the difference of cycle efficiency among different mass flow rates is less than 0.7%.

Thermodynamic Performance of Geothermal Energy Cascade Utilization for Combined Heating and Power Based on Organic Rankine Cycle and Vapor Compression Cycle

A large population and rapid urbanization dramatically promote the heating supply demand, the combined heating and power (CHP) system for energy cascade utilization came into being. However, the research on the recovery and utilization of condensing heat, the exploration of the coupling law between power generation and heating supply, and the influence of heat source parameters on thermo-economic performance are still insufficient. To this end, two combined heating and power (CHP) systems coupled with an organic Rankine cycle (ORC) and vapor compression cycle (VCC) are proposed, and their thermodynamic and economic performances are optimized and analyzed by the laws of thermodynamics. Results show that the increase of the volume flow will increase the power generation and heating supply quantity of the system, and there is an optimal evaporation temperature range of 130–140 °C to optimize the performance of the system. The increase of heat source temperature will improve the economic performance of the system, but it will reduce the exergetic efficiency. Therefore, two factors should be comprehensively considered in practical engineering. There is mutual exclusivity between the net power output of the system and the heating supply quantity, it should be reasonably allocated according to the actual needs of users in engineering applications. In addition, the exergetic efficiency of the two systems can reach more than 60%, and the energy utilization rate is high, which indicates that the cascade utilization mode is reasonable.

How to identify trade-off of thermodynamic and economic performance of the S-CO2 cycle caused by the cycle structures?

Generally, the improvement of thermodynamic performance of supercritical CO2 Brayton cycles is realized by more complex cycle structures at the expense of expensive system cost. How to identify trade-off of the thermodynamic and economic performance of the S-CO2 cycle is a challenging issue because system structure is hard to be optimized with its nature of discrete variable. Therefore, taking the net power output and cost of electricity as the objective functions, this study tries to solve this issue by multi-objective optimization of superstructure of supercritical CO2 Brayton cycle for gas turbine waste heat recovery. Besides discussing the effect of heat source temperature and cooling temperature, the optimization results of the superstructure are compared with the traditional structures. The results show that at different heat source temperatures, the distribution regularities of the cycle structures on the Pareto-front are the same, and the structure of the trade-off solution tends to be the same. With the increase of heat source temperature, the costs of trade-off solutions are reduced by 8.86%, 11.16% and 16.51%, respectively. The change of cooling temperature has a great effect on the structure of the trade-off solution. In addition, superstructures have obvious advantages over the traditional structures in terms of trade-off solution performance and structure selection.

Effects of the distance and test angle on the precision of infrared temperature measurement

The target distance and test angle are the main factors that affect the accuracy of infrared temperature measurement. To study the infrared temperature measurement precision of different heat source intensities at different distances and test angles, a temperature measurement test with built-in heat source within the rod of the insulator was designed. By setting four different heat source temperatures on the heating film, the temperature data were collected by infrared camera at the distances of 3, 6, 9, 12 m and 15 m and three test angles of 0 °, 90° and 180°, respectively, and the variation law of the measurement results was analysed. The main conclusions are as follows. As the distance increases, the measured values basically show a downward trend. When the distance reaches 12 m, the temperature fluctuates significantly. When the angle between the observation direction and the heat source is 0 °, the measurement value is the highest, followed by the 90° direction, and the lowest is the 180° direction, which indicates that the test angle has an obvious influence on the measurement results. With the increase of heat source temperature, the infrared temperature measurement value increases gradually and tends to be saturated. When an infrared device is adopted to measure the temperature of the insulators in service, it is necessary to pay attention to the influence of the distance and angle on the value in engineering practice.

Thermodynamic and techno-economic performance comparison of two-stage series organic Rankine cycle and organic Rankine flash cycle for geothermal power generation from hot dry rock

• The performance of two geothermal energy cascade utilization systems is optimized. • The thermodynamic and techno-economic performance of the systems are compared. • The influence of heat source temperature on the operating condition is studied. • The exergy destruction of each component in the systems is compared and analyzed. To improve the utilization rate of geothermal resource using organic Rankine cycle (ORC), an organic Rankine flash cycle (ORFC) combined with insufficient evaporation and flash process is proposed to reduce the irreversibility of the power generation cycle. The thermodynamic performance and techno-economic performance of ORFC and two-stage series organic Rankine cycle (TSORC) are optimized, respectively. The effects of evaporation temperature, flash temperature and outlet dryness on the performance of two systems are discussed. The results show that with the increase of heat source temperature, the optimal operating condition value of the system increases, which leads to improving the thermodynamic and techno-economic performance significantly. R601a and R601 are the most suitable working fluids for TSORC and ORFC, respectively. The heat exchanger is the main component that causes the exergy destruction of the system, and its improvement potential is the highest in all components. The thermodynamic performance and techno-economic performances of ORFC are better than those of TSORC. The irreversible loss of the system can be reduced by the insufficient evaporation combined with flash separator.

Thermodynamic analysis of double flash organic flash cycle using R600a/R601a mixtures

Double flash organic flash cycle (OFC) exhibits perfect temperature matching during heat absorption and low throttling loss. Zeotropic mixtures could decrease the irreversible loss during the phase change process due to their non-isothermal characteristic. This study combines double flash OFC with R600a/R601a mixtures to efficiently utilize low-grade thermal energy. The high- and low-stage flash pressures are optimized for maximal net power output. The influences of the R600a mole fraction and the heat source temperature on net power output, exergy efficiency, and cycle parameters are analyzed. Optimal mixture compositions and flash pressures are obtained, and the exergy loss distribution is investigated. The proposed system is compared with the basic single flash OFC using R600a/R601a mixtures. Research shows that the optimized flash pressures have upper limits as heat source temperature increases. The net power output decreases with increasing R600a mole fraction when the heat source temperature is high. The proposed system has more net power output than that using pure working fluid for the 100 °C–180 °C heat source, and the relative net power output growth rates are 3.22%–5.24%. Moreover, the net power outputs of double flash OFC are 15.13%–55.70% higher than basic single flash OFC.

Study on screw rotor thermal machining method of single screw compressor

Single screw compressor (SSC) is a type of rotary compressor with excellent performance. However, under high temperature conditions, the hot deformation of the screw rotor and the star wheel cause the change of the gap of the meshing pairs, which seriously degrades the compressor performance. In order to solve the problem of the gap variation of the meshing pairs, a new hot-state machining method is proposed to study the deformation characteristics of the screw rotor in the hot-state machining process, which provides some reference data for the pre-deformation of the rotor in the machining process. Numerical calculation model of thermal machining process for screw rotor was established by using finite element method. With the validated model, the deformation characteristics in the process of hot working were studied by changing the number of heating holes, diameter of heating holes and temperature of heating holes. Results show that screw rotor deformation will increase with the increase of heat source temperature and diameter, and the deformation distribution of the screw rotor is not significantly affected by the heat source temperature and diameter, but will be more uniform with the increase of heat source quantity. The research work in this paper can provide theoretical basis for hot machining of screw rotor for SSC.

Supercritical CO2 Brayton cycle at different heat source temperatures and its analysis under leakage and disturbance conditions

Supercritical carbon dioxide (SCO2) Brayton cycle has been widely used in a variety of industrial settings. In this work, three commonly used SCO2 Brayton cycle dynamic numerical models at different heat source temperatures are built with MATLAB and Simulink software, and the key parameters of three commonly used Brayton cycle models (recompression, reheating and intermediate cooling) are compared when the heat source temperature changes from 813 K to 2,113 K. And The steady-state values of the simulation system and experimental values are verified. Under the same component parameter setting, the recompression of the model cycle efficiency at different heat source temperature is generally the highest, followed the reheating mode, and the lowest in the intercooling model. With the increase of heat source temperature, the efficiency of the recompression model gradually improve. Under 5 % leakage condition, the recycling efficiency of the recompression model increases by 2.58 %, while the efficiency of the reheating model and the intercooling model decreases. Sinusoidal disturbance with the amplitude of 12.5 K and period of 8 s is added at the inlet of HTR hot side, compared with intercooling model and reheating model. The efficiency fluctuation amplitude of the recompression model is large, but the power generation is more stable.

Optimization of Air Cooling System Using Adjoint Solver Technique

Air cooling systems are currently the most popular and least expensive solutions to maintain a safe temperature in electronic devices. Heat sinks have been widely used in this area, allowing for an increase in the effective heat transfer surface area. The main objective of this study was to optimise the shape of the heat sink geometric model using the Adjoint Solver technique. The optimised shape in the context of minimal temperature value behind the heat sink is proposed. The effect of radiation and trapezoidal fin shape on the maximum temperature in the cooling system is also investigated. Simulation studies were performed in Ansys Fluent software using the Reynolds—averaged Navier–Stokes technique. As a result of the simulation, it turned out that not taking into account the radiation leads to an overestimation of temperatures in the system—even by 14 ∘C. It was found that as the angle and height of the fins increases, the temperature value behind the heat sink decreases and the heat source temperature increases. The best design in the context of minimal temperature value behind the heat sink from all analysed cases is obtained for heat sink with deformed fins according to iteration 14. The temperature reduction behind the heat sink by as much as 25 ∘C, with minor changes in heat source temperature, has been achieved.

Exergy Analysis of Two-Stage Organic Rankine Cycle Power Generation System.

Organic Rankine cycle (ORC) power generation is an effective way to convert medium and low temperature heat into high-grade electricity. In this paper, the subcritical saturated organic Rankine cycle system with a heat source temperature of 100~150 °C is studied with four different organic working fluids. The variations of the exergy efficiencies for the single-stage/two-stage systems, heaters, and condensers with the heat source temperature are analyzed. Based on the condition when the exergy efficiency is maximized for the two-stage system, the effects of the mass split ratio of the geothermal fluid flowing into the preheaters and the exergy efficiency of the heater are studied. The main conclusions include: The exergy efficiency of the two-stage system is affected by the evaporation temperatures of the organic working fluid in both the high temperature and low temperature cycles and has a maximum value. Under the same heat sink and heat source parameters, the exergy efficiency of the two-stage system is larger than that of the single-stage system. For example, when the heat source temperature is 130 °C, the exergy efficiency of the two-stage system is increased by 9.4% compared with the single-stage system. For the two-stage system, analysis of the four organic working fluids shows that R600a has the highest exergy efficiency, although R600a is only suitable for heat source temperature below 140 °C, while other working fluids can be used in systems with higher heat source temperatures. The mass split ratio of the fluid in the preheaters of the two-stage system depends on the working fluid and the heat source temperature. As the heat source temperature increases, the range of the split ratio becomes narrower, and the curves are in the shape of an isosceles triangle. Therefore, different working fluids are suitable for different heat source temperatures, and appropriate working fluid and split ratio should be determined based on the heat source parameters.

Thermodynamic improvements of LNG cold exergy power generation system by using supercritical ORC with unconventional condenser

Organic Rankine cycle (ORC) is the most commonly used power generation cycle that is adopted in this paper to make full use of the cold exergy of liquefied natural gas (LNG). As the heat exchangers are mainly responsible for the exergy destruction of the system, two improvement techniques: supercritical system and unconventional condenser, are proposed to decrease the exergy destructions in steam generator and condenser. The performances of ten preselected working fluids are tested by optimizing five key parameters at three heat source temperatures. The results show that using the supercritical system can improve the system efficiency for fluids with low critical temperatures by reducing the exergy destructions in steam generators. Using the unconventional condenser can greatly improve the system efficiency by decreasing the exergy destruction during the LNG regasification process of most fluids, barring a few wet expansion fluids. The improvements offered by both techniques become more obvious as the heat source temperature increases. However, combining the two techniques only improves the performance for fluids with low critical temperatures, and does not work for most fluids. The highest efficiency is always achieved by the subcritical system with an unconventional condenser at each heat source temperature. When the heat source temperatures are 100 °C and 150 °C, R290 obtains the highest efficiency values of 17.89% and 21.26%, respectively. At 200 °C, R600a achieves the highest efficiency of 25.35%.

Study on Heat Transfer Performance and Anti-Fouling Mechanism of Ternary Ni-W-P Coating

Since the formation of fouling reduces heat transfer efficiency and causes energy loss, anti-fouling is desirable and may be achieved by coating. In this work, a nickel-tungsten-phosphorus (Ni-W-P) coating was prepared on the mild steel (1015) substrate using electroless plating by varying sodium tungstate concentration to improve its anti-fouling property. Surface morphology, microstructure, fouling behavior, and heat transfer performance of coatings were further reported. Also, the reaction path, transition state, and energy gradient change of calcite, aragonite, and vaterite were also calculated. During the deposition process, as the W and P elements were solids dissolved in the Ni crystal cell, the content of Ni element was obviously higher than that of the other two elements. Globular morphology was evenly covered on the surface. Consequently, the thermal conductivity of ternary Ni-W-P coating decreases from 8.48 W/m·K to 8.19 W/m·K with the increase of W content. Additionally, it goes up to 8.93 W/m·K with the increase of heat source temperature 343 K. Oxidation products are always accompanied by deposits of calcite-phase CaCO3 fouling. Due to the low surface energy of Ni-W-P coating, Ca2+ and [CO3]2− are prone to cross the transition state with a low energy barrier of 0.10 eV, resulting in the more formation of aragonite-phase CaCO3 fouling on ternary Ni-W-P coating. Nevertheless, because of the interaction of high surface energy and oxidation products on the bare matrix or Ni-W-P coating with superior W content, free Ca2+ and [CO3]2− can be easy to nucleate into calcite. As time goes on, the heat transfer efficiency of material with Ni-W-P coating is superior to the bare surface.

Optimizations and comparison of three two-stage Rankine cycles under different heat source temperatures and NG distribution pressures

Two-stage Rankine cycles draw more and more attention with the increasing trade of LNG (liquefied natural gas) and the recovery of both the cold exergy of LNG and the thermal exergy of low temperature heat source. To figure out the best configuration of two-stage Rankine cycles, three mostly studied configuration, cascade two-stage ORC (organic Rankine cycle), parallel two-stage ORC and two-condensation ORC are optimized and compared under different heat source temperatures and different NG distribution pressures. Ten substances are selected as the working fluids. The evaporation, condensation and expander inlet temperatures of both ORCs and the LNG regasification pressure are optimized to obtain the maximum exergy efficiency. The results show that both the increase of heat source temperature and the decrease of NG distribution pressure can improve the exergy efficiencies greatly. The increase of heat source temperature not only increases the optimal key parameters but also affects the ranking of optimal fluids, while the increase of NG distribution pressure only affects the optimal parameters. Different from conventional Rankine cycles, there is also an optimal condensation temperature to match the heat absorption line of LNG and it increases with increase of the NG distribution pressure. The LNG regasification pressure is a key parameter which determines the proportion of power outputs between ORCs and direct expansion cycles. The thermodynamic performances of parallel two-stage ORC and two-condensation ORC are almost the same, which are obviously better than that of cascade two-stage ORC. Both parallel two-stage ORC and two-condensation ORC with ammonia as the working fluid achieve the maximum efficiency of 30.54% under the heat source temperature of 200 ℃ and the NG distribution pressure of 3 MPa. Two-condensation ORC is the optimum configuration with both good thermodynamic and economic performances. The lowest electricity production cost of two-condensation ORC achieved in this paper is 0.033$/kW·h. The environmental side effect caused by working fluid leakage is negligible compared with the saved CO2 emission via the electricity generation.

Investigation of exergy efficiency of organic Rankine cycle

Organic Rankine cycle (ORC) which recovers waste heat in the temperature range of 80°C-140°C was investigated. Exergy efficiencies of various components and ORC system were paid great attention. The working fluids of R245fa and R600a are used. It is found that, for saturated ORCs, the expander inlet temperature has the optimum value, so the system exergy efficiency is maximum. With the increase of heat source temperature, the optimal inlet temperature of the expander is also increased. And also for saturated ORCs, the exergy efficiencies of evaporator and expander are highest efficiency, when evaporator exergy efficiency is increased with increase of heat source temperatures, the expander exergy efficiency is unchanged. The condenser decreased exergy efficiencies by increasing the heat source temperatures.

Feasibility of a new helical blade structure for a PV integrated wind turbine in a heat-driven swirling wind field

A controllable heat-driven swirling wind turbine system was integrated with a photovoltaics (PV) system for energy generation in a heat-collecting shed. This is a brand-new type of a wind energy generation system; and a helical three-blade structure in a vertical axis was introduced. The stationary pre-rotation vanes have a variable diameter and a helical twist angle of 225°. A numerical simulation was conducted to investigate the feasibility of a wind turbine blade structure for efficient energy output for industrial application. The computational fluid dynamics (CFD) tool OpenFOAM was used to simulate the operating conditions of the wind turbine. The findings illustrated the efficacy of the new system. The new helical blade structure is efficient for wind energy output of the turbine in a swirling wind field. The simulation under different heat source temperatures illustrated that an increase in heat source temperature could increase the output efficiency of the wind turbine energy system. The increment in output efficiency could be up to 19.07% when the temperature rises from 40 K to 80 K. The PV-swirling wind integrated system was shown to be more economical than a single solar photovoltaic system because its investment payoff period could be shortened by 2 years.

Performance Simulation and Benefit Analysis of Ammonia Absorption Cooling and Heating Dual-Supply System Based on Off-Peak Electricity Heat Storage

The energy consumption of urban central heating in northern China is two to four times that in northern Europe and other countries. Beijing has adopted measures, such as ‘coal to gas’ and ‘coal to electricity’, to reduce environmental pollution caused by central heating. Given a peak-to-valley difference in the electricity supply of power plant, which is uneven day and night, this study proposes to store the night-time off-peak electricity in the form of heat energy and drive the ammonia absorption system in the form of steam or hot water during peak or flat electricity. Simulation results of ammonia absorption cooling and heating dual-supply system show that heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases are all beneficial to improve the refrigeration coefficient in the summer cooling condition. In the meantime, heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases are beneficial for increasing the heating coefficient in the winter heating condition. The heating and cooling coefficients of the system are 1.38 and 0.65 in the optimal working condition in winter and summer. Benefit analysis shows that, compared with central heating and cold storage air conditioning, the system can save 576,000 tons of standard coal and 1.417 million tons of carbon dioxide if used in 12% of the cooling and heat supply areas in Beijing. The potential for energy saving and emission reduction is large.

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.

Theoretical and experimental evaluation of thermal interface materials and other influencing parameters for thermoelectric generator system

Thermal interface resistance of Thermoelectric Generator (TEG) plays a vital role in power production. Improving surface finish of contact surfaces, applying pressure between the contact surfaces and use of Thermal Interface Material (TIM) are few methods of reducing thermal resistance and thereby improving the efficiency of TEG. There is a need to evaluate the influence of these methods and use them optimally for TEG system. Experiments were carried out to study the influence of parameters such as thermal conductivity of TIM, contact pressure, surface roughness and heat source temperature on the voltage and power outputs from TEG. Experimental results are validated with simulations using mathematical heat transfer model and COMSOLTM Multiphysics numerical model. Appreciable agreement is seen between the experimental observations and model outputs. Experimental and model results indicate 0.6 W/mK as optimum thermal conductivity for TIM material. Hence, use of costly TIMs like MWCNT (Multi Wall Carbon Nano Tube) and copper nanoparticles may not be required for the selected application. The contact pressure and surface roughness have appreciable influence when air is used as TIM. These factors have insignificant influence for TIMs with higher thermal conductivity. Increase in heat source temperature increases voltage and power output of TEG.

Effects of superheat and internal heat exchanger on thermo-economic performance of organic Rankine cycle based on fluid type and heat sources

The study investigates the comprehensive effects of superheat and internal heat exchanger (IHX) on the thermo-economic performance of organic Rankine cycle (ORC). Exergy efficiency, net power output, and electricity production cost (EPC) are compared based on the working fluid properties and heat sources. The results indicate that under a lower heat source temperature and load, exergy efficiency of IHX-ORC does not always exceed that of simple ORC (S-ORC) when EPC is selected as an objective function, and IHX-ORC exhibits a worse economic performance than S-ORC for all fluids (R161, R1234ze, R152a, cyclopropane, butane, R123, cyclopentane, heptane, and cyclohexane). However, IHX-ORC with dry fluid achieves a better thermo-economic performance than that with wet fluid when the heat source temperature and load increase to a high level. The EPC of IHX-ORC is close to that of S-ORC with the increase in heat source temperature and load, and thus, IHX-ORC exhibits approximately 10–17% higher thermal efficiency and 5–10% higher exergy efficiency than those of S-ORC. With respect to butane and R123, the net power output exhibits approximately 22.5% and 23.5% growth, respectively. In order to evaluate the feasibility of IHX-ORC, a judgement indicator [α > 1.90625 + 0.4258ξ] with respect to six factors is proposed.