Reversible Carnot Cycle Research Articles

Energetic, exergetic and economic analysis of a trans-critical solar hybrid CCHP system

A solar hybrid CCHP (combination of cooling, heating and power) system was proposed to organically integrate the Brayton and reverse Carnot cycle by trans-critical CO2 working medium. The transient thermal storage in a solar hybrid CCHP system (SCCHP) was designed to overcome the energy coupling challenges in regions rich in solar and gas resources. Moreover, the incorporation of an optimally efficient throttling expander in cooling cycle was designed to enhance energy utilization efficiency. The thermodynamic performance of the SCCHP system was systematically evaluated by comparing with the ejector hybrid CCHP system from energetic, exergetic, and economic perspectives. The results suggest that elevating the intake pressure of both the high-pressure compressor from 5.2 kW to 6.4 kW and turbine from 7.3 kW to 7.8 kW, led to an enhancement in the COP of the SCCHP system. Moreover, raising the turbine intake temperatures from 483.15 K to 503.15 K yielded a significant improvement in system energy efficiency from 0.66 to 0.71 and COP from 1.58 to 1.72. Furthermore, in contrast to the ECHP system, the components in the SCCHP system demonstrated not only less exergy efficiency variation to the influence of ambient temperature but also lower hourly economic costs. The SCCHP has an average hourly investment cost that is 5.70 USD (kgh)−1 lower than ECHP, and its economic efficiency improves with higher ambient temperatures.

Experimental investigation on a screw-type air source heat pump system with air heat absorption defrosting

Defrosting is crucial challenge for air-source heat pump operating in cold and humid climates due to its adverse impact on the heating efficiency. Conventional reverse cycle defrosting method has the disadvantages of reduced heating capacity, inefficient defrosting, and unstable heating temperatures. To address this issue, an Air Heat Absorption Defrosting method based on the reverse Carnot cycle principle was proposed to ensure uninterrupted heating during defrosting. To further validate the technical feasibility and energy-saving potential of the proposed system, a 710.0 kW screw-type air–water heat pump prototype was constructed to carry out control experiments under various conditions. Experimental results showed that, the proposed method achieved an average heating capacity of 315.7 kW during the defrosting process. The cyclic equivalent heating capacity and defrosting correction coefficient of the proposed method were 61.8 kW and 14.4 % higher in comparison with conventional reverse cycle defrosting method, respectively. Thus, the temperature fluctuation of supply water during the defrosting process was reduced by 69 %. In addition, the cumulative COP of Air Heat Absorption Defrosting method was 9.3 % higher than reverse cycle defrosting method, which could be attributed to the fact that the defrosting energy mainly came from air heat absorption. These findings highlight the potential of proposed Air Heat Absorption Defrosting method in addressing heat pump defrosting challenges while offering significant energy-saving benefits.

What Is Psychological Spin? A Thermodynamic Framework for Emotions and Social Behavior

One of the most puzzling questions in neuroscience is the nature of emotions and their role in consciousness. The brain’s significant energy investment in maintaining the resting state indicates its essential role as the ground state of consciousness, the source of the sense of self. Emotions, the brain’s homeostatic master regulators, continuously measure and motivate the recovery of the psychological equilibrium. Moreover, perception’s information-energy exchange with the environment gives rise to a closed thermodynamic cycle, the reversible Carnot engine. The Carnot cycle forms an exothermic process; low entropy and reversible resting state turn the focus to the past, causing regret and remorse. The endothermic reversed Carnot cycle creates a high entropy resting state with irreversible activations generating novelty and intellect. We propose that the cycle’s direction represents psychological spin, where the endothermic cycle’s energy accumulation forms up-spin, and the energy-wasting exothermic cycle represents down-spin. Psychological spin corresponds to attitude, the determining factor in cognitive function and social life. By applying the Pauli exclusion principle for consciousness, we can explain the need for personal space and the formation of hierarchical social structures and animals’ territorial needs. Improving intuition about the brain’s intelligent computations may allow new treatments for mental diseases and novel applications in robotics and artificial intelligence.

An Anti-Condensation Radiant Heating Floor System in Buildings under Moistening Weather

In most regions of southern China, condensation frequently occurs on building surfaces during the period from March to April. This phenomenon has been affecting people’s safety and structural properties. This article proposes an innovative anti-condensation floor system based on the reverse Carnot cycle. The evaporation side treats the air and reduces the moisture content, and the heat extracted from the condensation side is recovered by a heat exchanger and transferred to the floor through capillary mats. Simulation studies of the dynamic operation performance have been conducted through the TRNSYS 18 software. The results show that an innovative anti-condensation floor system can effectively keep the floor dry in Guilin. At the same time, regarding the indoor comfort level index, the PMV value is within ±0.5, and the energy consumption of the system is 42% less than that of the cooling dehumidification system. The system also performs well in representative cities where the air moisture content is less than 12 g/kg. This article also provides a reference for the feasibility of radiant floor systems in humid climate areas.

Energy saving potential pre-estimation approach for air-source heat pump usage in China based on thermodynamic irreversibility

Building sector accounts for a substantial part of energy consumption (EC) and carbon emissions, mainly serving for building services engineering systems. As a known advanced high-efficiency equipment, air source heat pump (ASHP) has been increasingly used for indoor heating ventilation and air conditioning (HVAC) for residential and public buildings. Thus how to pre-estimate the energy saving potential (ESP) for given ASHPs under different climatic conditions is of high value for practical engineering application. In this paper, upon thermodynamic perfectibility conception, a simplified ASHP model is proposed to simulate its dynamic thermal performance according to the disparity between real equipment and the ideal reverse Carnot cycle. Moreover, a novel thermodynamic approach is proposed to pre-estimate and compare the seasoning-based ESPs of ASHP used for both heating and cooling. For illustrative examples, a typical public building is chosen, and the AHSP-ESPs are obtained and analyzed for five cities of different climate zones in China (Qiqihar, Beijing, Chengdu, Kunming, and Guangzhou). Preliminary research results show that lower/higher ambient temperatures contribute to higher heating/cooling ESPs respectively. However, the correlation between building EC and thermodynamic perfectibility is in inverse proportion. At first, building EC decreases rapidly with the increase of thermodynamic perfectibility, but as the thermal performance of ASHP gets closer to the corresponding ideal ones, the impact of thermodynamic perfectibility on building EC gradually decreases. This work is of great significance in understanding the regional applicability of ASHP and building EC, and providing application references for real ASHP usage in building sectors.

Wetting hysteresis induces effective unidirectional water transport through a fluctuating nanochannel.

We propose a water pump that actively transports water molecules through nanochannels. Spatially asymmetric noise fluctuations imposed on the channel radius cause unidirectional water flow without osmotic pressure, which can be attributed to hysteresis in the cyclic transition between the wetting/drying states. We show that the water transport depends on fluctuations, such as white, Brownian, and pink noises. Because of the high-frequency components in white noise, fast switching of open and closed states inhibits channel wetting. Conversely, pink and Brownian noises generate high-pass filtered net flow. Brownian fluctuation leads to a faster water transport rate, whereas pink noise has a higher capability to overcome pressure differences in the opposite direction. A trade-off relationship exists between the resonant frequency of the fluctuation and the flow amplification. The proposed pump can be considered as an analogy for the reversed Carnot cycle, which is the upper limit of the energy conversion efficiency.

How the Brain Becomes the Mind: Can Thermodynamics Explain the Emergence and Nature of Emotions?

The neural systems’ electric activities are fundamental for the phenomenology of consciousness. Sensory perception triggers an information/energy exchange with the environment, but the brain’s recurrent activations maintain a resting state with constant parameters. Therefore, perception forms a closed thermodynamic cycle. In physics, the Carnot engine is an ideal thermodynamic cycle that converts heat from a hot reservoir into work, or inversely, requires work to transfer heat from a low- to a high-temperature reservoir (the reversed Carnot cycle). We analyze the high entropy brain by the endothermic reversed Carnot cycle. Its irreversible activations provide temporal directionality for future orientation. A flexible transfer between neural states inspires openness and creativity. In contrast, the low entropy resting state parallels reversible activations, which impose past focus via repetitive thinking, remorse, and regret. The exothermic Carnot cycle degrades mental energy. Therefore, the brain’s energy/information balance formulates motivation, sensed as position or negative emotions. Our work provides an analytical perspective of positive and negative emotions and spontaneous behavior from the free energy principle. Furthermore, electrical activities, thoughts, and beliefs lend themselves to a temporal organization, an orthogonal condition to physical systems. Here, we suggest that an experimental validation of the thermodynamic origin of emotions might inspire better treatment options for mental diseases.

Maximum efficiency of low-dissipation heat pumps at given heating load.

We derive an analytical expression for maximum efficiency at fixed power of heat pumps operating along a finite-time reverse Carnot cycle under the low-dissipation assumption. The result is cumbersome, but it implies simple formulas for tight upper and lower bounds on the maximum efficiency and various analytically tractable approximations. In general, our results qualitatively agree with those obtained earlier for endoreversible heat pumps. In fact, we identify a special parameter regime when the performance of the low-dissipation and endoreversible devices is the same. At maximum power, heat pumps operate as work to heat converters with efficiency 1. Expressions for maximum efficiency at given power can be helpful in the identification of more practical operation regimes.

Simulation and experiment investigation of a heating and power double function system with multi-objective optimization

As conventional organic Rankine cycle (ORC) power generation and reverse Carnot cycle (RCC) heat pump systems have some limitations for a fixed heat source. This study proposed a novel RCC and ORC double function system which can work in the ORC power generation mode and RCC heat pump mode for district heating and power output, respectively. The energy model is firstly established to analyze the system thermal performance and then a test rig is built to verify the performance of the system and validate the mathematical model. The economic and environmental analysis are conducted and the multi-objective optimization (MOP) method has been conducted to solve the conflicting problem between the capital cost and payback period under the different operating conditions. Results indicate that the system has good feasibility and stability which can provide 5.96 kW power output with the thermal efficiency of 5.23 % and 60.02 kW heating capacity with the COP of 2.85. The errors of the experiment to simulation COP and the error of experiment to simulation thermal efficiency value are all less than 10%. The optimization consequences based on the TOPSIS decision-making and NSGA-II technology indicate that the MOP solution has a better performance compared with the single-objective optimization.

Application and analysis of multi-stage flash vaporization process in steam production in high-temperature heat pump system with large temperature difference

The high-temperature heat pump steam system (HTHPS) is an effective way to replace the calcining boiler's steam. However, the large temperature span of the system leads to colossal exergy loss of refrigerant in expansion valves and other components. Therefore, it is hoped to adopt the dual-flash vaporization process to improve the system's steam production performance. In this paper, three thermodynamic models and exergy models of HTHPS with a double flash evaporation process are established. Furthermore, this paper uses the multivariate simulated annealing algorithm to calculate the optimal COP of the system. Then, by comparing the single-stage compression (SC) system and the quasi-two-stage compression (QTC) system, the influence of the dual-flash vaporization process on HTHPS is analyzed. The results show that under the same environment, the COP of the dual-flash vaporization process compression system is 23.8% 44.54% higher than that of the SC system. With the increase of the system temperature span, the flash steam supplemental process brings the system to improved thermodynamic performance. Moreover, the exergy model of the dual-flash system is closest to the reversed Carnot cycle, when the evaporation temperature is 50 °C and the condensing temperature is 110 °C.

Thermodynamic and electrochemical performance analysis for an electrochemical refrigeration system based on iron/vanadium redox couples

Alternative refrigeration systems have been explored due to the limitations of vapor compression refrigeration system on theoretical efficiency and environmental friendliness. In this study, an electrochemical refrigeration system based on the endothermic effect of electrochemical reactions was proposed to realize continuous refrigeration. This electrochemical refrigeration system mainly comprised endothermic and exothermic cell stacks, regenerator, heat exchangers, and pumps. Fe2+/Fe3+ and VO2+/VO2+ redox couples were employed to establish a refrigeration cycle due to their large entropy change and no phase change during reaction processes. A thermodynamic model with polarization loss analysis was established for system performance evaluation. Through quantitative analysis of polarization losses, optimal operating conditions of the system and key factors affecting the system performance were determined. The results indicated that the coefficient of performance (COP) of the system under ideal conditions was close to that of the reverse Carnot cycle. In actual situations, polarization losses led to system performance degradation. The electrochemical refrigeration system achieved comparable or better COP than the vapor compression refrigeration system when the current density was within 60 A m−2. The impact analysis of state of charge (SOC) showed that the actual refrigerating capacity and COP reached the peak values when the SOC was about 0.43 and 0.5, respectively. Increasing the flow rate and operating temperature improved the system performance by decreasing concentration and activation polarization losses, respectively. Furthermore, the activation polarization loss accounted for the largest proportion of system losses. Thus, improving electrode catalysis is critical to enhance the system performance.

The thermodynamics of cognition: A mathematical treatment

There is a general expectation that the laws of classical physics must apply to biology, particularly the neural system. The evoked cycle represents the brain's energy/information exchange with the physical environment through stimulus. Therefore, the thermodynamics of emotions might elucidate the neurological origin of intellectual evolution, and explain the psychological and health consequences of positive and negative emotional states based on their energy profiles. We utilized the Carnot cycle and Landauer's principle to analyze the energetic consequences of the brain's resting and evoked states during and after various cognitive states. Namely, positive emotional states can be represented by the reversed Carnot cycle, whereas negative emotional reactions trigger the Carnot cycle. The two conditions have contrasting energetic and entropic aftereffects with consequences for mental energy. The mathematics of the Carnot and reversed Carnot cycles, which can explain recent findings in human psychology, might be constructive in the scientific endeavor in turning psychology into hard science.

Construction of a quantum Carnot heat engine cycle

The microscopic state description of an irreversible quantum Carnot cycle for a general quantum working medium is investigated. An efficiency lag term, which quantifies the deviation of the irreversible cycle efficiency from the classical Carnot efficiency, is given in terms of the total entropy increase in the universe. The efficiency lag and the total entropy increase in the universe are directly connected to the quantum relative entropy between the density matrices obtained at the end of the quantum adiabatic and the relaxation steps of the cycle. The total entropy increase and the efficiency lag are found to be always nonnegative quantities. Our results give a direct proof that the irreversible cycle efficiency is always smaller than the classical Carnot efficiency. Two interacting spins under an external magnetic field are proposed as the working medium of the irreversible quantum Carnot cycle. The external magnetic field is considered to be quasistatically changed during the steps of the cycle. The coupling between the spins is found to break down the scale invariance and make the quantum Carnot cycle irreversible. It is shown that while the quantum coupling can lower the cycle efficiency monotonically to zero, it can make the irreversible cycle to produce more work than the one obtained from the uncoupled spins. The conditions in which one can always construct a reversible Carnot cycle for the coupled spin working medium are also given.

A History of Thermodynamics: The Missing Manual.

We present a history of thermodynamics. Part 1 discusses definitions, a pre-history of heat and temperature, and steam engine efficiency, which motivated thermodynamics. Part 2 considers in detail three heat conservation-based foundational papers by Carnot, Clapeyron, and Thomson. For a reversible Carnot cycle operating between thermal reservoirs with Celsius temperatures t and , heat Q from the hot reservoir, and net work W, Clapeyron derived , with material-independent. Thomson used to define an absolute temperature but, unaware that an additional criterion was needed, he first proposed a logarithmic function of the ideal gas temperature . Part 3, following a discussion of conservation of energy, considers in detail a number of energy conservation-based papers by Clausius and Thomson. As noted by Gibbs, in 1850, Clausius established the first modern form of thermodynamics, followed by Thomson’s 1851 rephrasing of what he called the Second Law. In 1854, Clausius theoretically established for a simple Carnot cycle the condition . He generalized it to , and then . This both implied a new thermodynamic state function and, with appropriate integration factor , the thermodynamic temperature. In 1865, Clausius named this new state function the entropy S.

Calculation of Thermal and Exergy Efficiency of Solar Power Units with Linear Radiation Concentrators

A calculation and optimization algorithm is proposed for operating modes of composite parabolic trough mirror-concentrating sysetms (MCSs) with allowance for the geometric and optical parameters of the concentrator heat receiver in a wide range of operating conditions, as well as temperature conditions of the system as a whole. The thermal and exergy efficiency (i.e., the reversible thermal Carnot cycle) are estimated, the values of which for the developed linear composite parabolic trough concentrators are 0.4438 and 0.0932, respectively.

Regarding the application limitations of the Carnot, s theorem

The purpose of this article is to perform a comparative study of a reversible heat engine with an ideal or real gas as a working fluid and to determine the change in its efficiency depending on the thermodynamic characteristics of the working fluid. The main research method is the method of thermodynamic potentials, based primarily on the analysis of changes in the free and internal energy of an ideal and real gas in a cyclic process. The theory of thermodynamic potentials is used to consider the Carnot quasistatic heat engine. A comparative analysis of its operation is carried out, for a cycle with both an ideal and a real gas as a working fluid. The possibility of analyzing cyclic processes occurring in heat engines using the method of thermodynamic potentials has been identified and substantiated. The study has shown that the existing formulation of the Carnot’s theorem is valid only for ideal gas as a working fluid. Based on the work carried out, the Carnot’s theorem in the general case can be formulated, for example, as follows: the efficiency of the heat engine ηr, when it operates at the reversible Carnot cycle with real gas as a working fluid, is determined by the following expression:hr= 1 - TB /TA + ε,where TA and TB are the temperatures of the upper and lower isotherms of the Carnot cycle, respectively; ε is the correction term (positive or negative), depending on the thermodynamic properties of a real gas, which tends to zero as the properties of a real gas approach the properties of an ideal gas.

Experimental study on refrigerant maldistribution in a fin-and-tube evaporator for a direct expansion air-conditioning system

In this paper, the design concept of the face split evaporator with a retrofitted suction header and choked flow in the capillary tubes was adopted to improve a direct expansion air-conditioning system with a designed air flow rate of 20,000 m3/h. The novel design of the direct expansion air-conditioning system was experimentally tested and validated. Face split evaporator reduced the refrigerant pressure drop in the suction header and the choked flow design limited the maximum flow rate across each branch circuit, which both contributed to the uniform refrigerant flow distribution of the improved system. Consequently, the cooling capacity and COP of the improved system was 10.5% and 13.4% higher than the original system. With the refrigerant mass flow rate of the improved system varying from 1.33 kg/s to 2.05 kg/s, the measured cooling capacity ranged 240–350 kW and the ratio of the system COP to the ideal COP of the reversed Carnot cycle with the same evaporating and condensing temperatures maintained at 0.72–0.74. The experimental results demonstrated that the improved system performed a relatively uniform refrigerant flow distribution among the branch circuit of the evaporator regardless of the refrigerant mass flow rate. This study is beneficial to the optimization design of the multi-circuit evaporator for a direct expansion air-conditioning system with a large air flow rate in engineering applications.

Cooling principle analysis of HEMS and numerical simulation analysis in cooling effect on Jiahe deep coal mine

At present, deep mine cooling is becoming more and more important because of seriously heat hazard. Based on the research of all cooling technologies in both China and abroad professor He Manchao proposed HEMS cooling technology, and it was applied in Jiahe coal mine successfully. In my paper, the reverse Carnot cycle and working process of HEMS in Jiahe coal mine was analysed. After the project was constructed, we tested temperature of key points on working face. FLUENT was adopted to simulate the heat exchange process in HEMS-II and in roadway. Compared with the monitored data, simulation on HEMS-II and roadway was proved correct. We can predict air temperature in roadway by Fluent simulation and it offers basis for optimization design in future.

Performance investigation of the heat pump and power generation integration system

A novel heat pump and power generation integration system (HPPGIS) using solar energy as a low temperature heat source was presented in this study. This system could be operated in both an organic Rankine cycle power generation (ORC-PG) mode and a reverse Carnot cycle heat pump (RCC-HP) mode. Compared with a single heat pump and power generation system, this system improved the utilization efficiency of solar energy, thus showing potential for the generation of economic benefits. Contrastive analyses of different working fluids using ORC-PG and RCC-HP systems were conducted first, leading to the selection of R142b and R245fa as optimal fluids. Then, an experimental investigation of the system was carried out under different conditions. A heat pump and ORC system model was proposed and validated by comparing experimental and simulated values. The experimental results indicated that the HPPGIS had good feasibility and stability in both modes. In the ORC-PG mode, HPPGIS had a power output of 1.29 kW and a thermal efficiency of 4.71% when the water inlet temperature of the evaporator was 90.03°C. In the RCC-HP mode, HPPGIS had a COP of 3.16 and a heat capacity of 33.24 kW when the water outlet temperature of the condenser was 106.23°C.

Energy, exergy, economic(3E) analysis and multi-objective optimization of a novel dual functional integration system

A novel dual functional heat pump and power generation integration system (DFHPPGIS) using a scroll machine as compressor and expander is proposed in this paper. It can be operated in both reverse Carnot cycle (RCC) heat pump mode and organic Rankine cycle (ORC) power generation mode. Compared with single system, this system can improve the utilization efficiency of geothermal water and generate more economic benefits. Three kinds of ORC and RCC working fluids are compared to select refrigerant R245fa as the most suitable fluid for the system. Then the model of DFHPPGIS is built to analyze its energy, exergy and economic performance as the variation of geothermal water inlet temperature. Results of theoretical calculation show that there is a conflict between total cost and payback period of the system. The system with lower total cost shows high payback period and vice versa. Thus, a multi-objective optimization for the system is conducted to determine the optimal geothermal water inlet temperature based on the ideal point decision making method. Exergy loss of the system under the optimal condition is analyzed to reveal which component has the largest exergy loss. The results indicate that in this proposed system, if the total cost based optimized design is chosen, payback period is 136.4% higher than its minimum value. If the method of payback period based optimized design is selected, total cost is 15.3% higher than its minimum value. The system has a heat capacity of 250.19 kW and a power output of 17.83 kW at the optimal geothermal water inlet temperature of 80℃ as well as the total cost and payback period of the system are 37.31 k$ and 4.87 years. In addition, the scroll machine has the largest exergy loss in both RCC and ORC mode, which is the component that needs to be mostly optimized in the further development.