Gas Cooler Outlet Temperature Research Articles

Thermodynamic analysis of rotary pressure exchanger and ejectors for CO2 refrigeration system

Natural refrigerant CO2 has become a viable choice for refrigeration units for land-based and offshore applications due to its environment-friendly nature and compactness. The CO2 transcritical cycle allows operating in colder climates and in elevated ambient temperature conditions and with significant heat recovery. However, the energy efficiency of the system suffers at higher heat rejection conditions mainly due to expansion losses. This work theoretically investigates and proposes the implementation of a new expansion work recovery device, a pressure exchanger (CO2-PX), for the transcritical CO2 cycle. The numerical models are developed in the Engineering Equation solver (EES) to compare the performance of CO2-PX configuration with standard booster-, parallel-, and ejector- configurations for various conditions. The analysis is carried out for the evaporation temperature of 0 ℃ and the gas cooler outlet temperature of 33 ℃ to 37 ℃. The results indicate that the coefficient of performance (COP) is improved by 17.7–23.5%, 16.3–20.3%, and 2.4–5.5% to the standard booster, parallel and ejector configurations, respectively, at the investigated conditions.

Towards sustainable process heating at 250 °C: Modeling and optimization of an R1336mzz(Z) transcritical High-Temperature heat pump

Fossil fuel boilers typically produce high-temperature process heating due to the impossibility of current renewable technologies. Vapour compression heat pump systems have been proposed up to 200 °C with subcritical cycles. To increase the heating production level, this paper proposes heating up to 250 °C through a transcritical high-temperature heat pump (THTHP) using R1336mzz(Z), which is not thermally degraded till this temperature, according to existing data. Computational models of a transcritical vapor compression cycle with and without an internal heat exchanger are developed for this work. The input cycle parameters, such as evaporation, production temperature, gas cooler output temperature, and the superheating degree, have been modified through iteration to consider possible scenarios in different industrial sectors. Moreover, the impact of using waste heat to increase evaporation temperature or superheating degree has been studied to optimize the cycle. The internal heat exchanger has also been considered for superheating the compressor suction. Other relevant parameters, such as compression ratio or volumetric mass flow rate, have also been assessed. The results show that a heat pump is feasible to reach 250 °C temperature using waste heat at 120 °C (evaporation at 100 °C and 20 °C of superheating degree), reaching a COP of 3.3. The variation of evaporator temperature from 80 °C to 140 °C increases COP from 2.5 to 5.9, while the increase of superheating degree from 20 °C to 100 °C increases COP from 3.2 to 7. Waste heat use optimization proves that it is more efficient to prioritize the increase of the evaporation temperature. If the industry requires lower production temperatures, the COP can reach a value of 7.0 at 180 °C. The decrease in gas cooler outlet temperature impacts less the COP than other input parameters. At baseline conditions, an optimum superheating degree with an internal heat exchanger of 45 K produces a maximum COP of 4.0. THTHP emissions are less than gas boilers for the same application, and in countries with greener electricity generation, these emissions can be 50 times lower.

Study on the mechanism of the optimal discharge pressure for a transcritical CO2 system

The optimal discharge pressure is the essential factor affecting the operating performance of the transcritical CO2 system. This paper presents a detailed study on the mechanism of the optimal discharge pressure from the perspective of fixed gas cooler outlet temperature and the heat transfer pinch point. The fixed gas cooler outlet temperature mainly analyzes the mechanism of the optimal discharge pressure from the enthalpy difference of isotherm in the supercritical region. The heat transfer pinch point mainly analyses the optimal discharge pressure at low inlet water temperatures, in which the subcritical region close to the critical point is considered. The effect of different parameters on optimal discharge pressure and system performance is discussed. The results indicate that the unique CO2 physical properties and the pinch point in the gas cooler cause the optimal discharge pressure of the transcritical CO2 system. The physical properties mainly affect the optimal discharge pressure at the high inlet water temperature, while the pinch point mainly affects the optimal discharge pressure at the low inlet water temperature. The inlet and outlet water temperatures are the most significant factors affecting the system's performance.

Thermodynamic Analysis of Comprehensive Performance of Carbon Dioxide(R744) and Its Mixture With Ethane(R170) Used in Refrigeration and Heating System at Low Evaporation Temperature

Abstract In this paper, the system performance of R744 and R744/R170 mixed refrigerants used in a single-stage compression transcritical cycle at low evaporation temperature was studied by simulation method, and the effect of evaporation temperature, outlet temperature of gas cooler, R170 ratio on coefficient of performance (COP), discharge temperature, optimal pressure, and compression ratio were analyzed. The results show that Popt increases and decreases with the increase of outlet temperature and evaporation temperature of gas cooler and increases first and then decreases with the increase of R170 proportion. In the heating system, the maximum and minimum Popt of R744/R170 (25/75) were 1.35 MPa, 3.6 MPa, and 2.6 MPa and 1.23 MPa, 2.93 MPa, and 1.87 MPa lower than that of R170 (0%, 22.4%, and 50%); compared to pure R744, the system pressure of the mixed R744/R170 is lower. The COPe and COPh increase with the increase of evaporation temperature and decrease with the increase of outlet temperature of the gas cooler. With the increase of R170 proportion, they first decrease and then increase; the maximum COPe and COPh of R744 were 22.4%, 29.6%, and 21.2% and 10.3%, 13.8%, and 10.8% higher than those of R170 at 22.4%, 50% and 75%, respectively.

Theoretical investigation of a novel distributed compression cycle for CO2 trans-critical system

Efficient cooling of the trans-critical CO2 vapor compression cycle to improve system performance is a crucial research topic. This paper proposes an innovative approach called distribution compression (DC) to achieve the same effect as subcooling in a trans-critical CO2 thermodynamic cycle. In the DC system, the trans-critical CO2 at the gas cooler outlet is no longer further cooled but subjected to a secondary pressure boost and releases heat in ordinary heat sink conditions as in the gas cooler. Thermodynamics calculated the change in performance of the DC system under different working conditions with different secondary boost ratios. The optimal secondary boost ratio related to evaporation and gas cooler outlet temperatures under optimal discharge pressure based on the baseline system was obtained. The results show that compared with the baseline system, the DC system can effectively improve the system performance, and the maximum refrigeration COP increase is between 8.2 % ∼ 10.76 %, and the maximum heating COP increase is between 5.37 % ∼ 6.34 %. The cooling or heating capacity increase can reach up to about 26 %. The ideal secondary boost ratio in a DC system is not highly demanding, and the increased input power for the second input power for the secondary boost will not exceed 20 % relative to the baseline system. Comparing the COP of the DC system over current systems that only use a single subcooling technology still shows advantages. The DC system provides a new idea to improve the performance of the trans-critical CO2 vapor compression cycle.

Performance analysis of a new mechanical superheat coupled-orc refrigeration system with thermoelectric conversion

This paper proposes a new refrigeration and energy conversion system, namely Expander Mechanical Overheating-Organic Rankine Cycle (EMO-ORC) system. Compared with the existing carbon dioxide (R744) refrigeration system, the new system can not only improve the coefficient of performance (COP) of the system and reduce the discharge pressure, but also effectively recover the waste heat of the system, and convert it into electrical energy. Simulation were conducted to compare its system performance with R744 refrigeration system (with heat exchanger), at the same time, the effect of different factors on the performance of new system is analyzed. The results demonstrate that, at the same evaporation temperature and gas cooler outlet temperature, compared with the system (with heat exchanger), the COP of the new system increased by 8.2% and 8.9% on average, respectively. And the discharge pressure decreased by 0.88% and 0.79%, respectively. In the given superheat degree range, compared with the system(with heat exchanger), the COP of the new system is increased by 4.5% on average, and increased by 10.2% at the highest level. Under the most given working conditions, the cooling capacity of new system is higher than that of the system (with heat exchanger), and the power consumption is lower than that of the system (with heat exchanger). In the new system, the narrow point temperature difference and the outlet temperature of the first stage gas cooler have a greater impact on the COP, with the increase of both, the COP of the new system increases by 5.6% and decreases by13.7%, respectively.

Thermodynamic performance and the exergy destruction of the transcritical CO2 two-stage compression and ejector expansion direct cooling ice making system

The transcritical CO2 direct cooling technology was used for the first time in the indoor venues of the 2022 Beijing Winter Olympic Games. The technology has a series of advantages, such as compact structure, uniform ice temperature, energy saving and environmental protection. In order to further reduce the power consumption and improve the performance, two-stage compression and low-pressure ejector direct cooling ice making system (TCLES) and two-stage compression and intermediate-pressure ejector direct cooling ice making system (TCIES) are studied. The performance of the systems is simulated by constructing a one-dimensional thermodynamic model. The impacts of the gas cooler pressure, gas cooler outlet temperature, evaporation temperature and intermediate pressure on these systems are considered. It is showed that TCLES and TCIES have their own advantages when the system is without and with heat recovery, and found that two-stage compression improves the system performance more than the ejector when only the cooling performance is considered. On this basis, conventional exergy and advanced exergy analysis of both systems are carried out. Advanced exergy analysis shows that exergy destruction can be avoided mainly in low-pressure and high-pressure compressors of both systems. Besides, the influence of gas cooler pressure on exergy destruction characteristics is discussed. When controlling the gas cooler pressure at 9.0 MPa, the avoidable endogenous exergy destruction of compressors and ejector is reduced by a maximum of 4.14% and 13.92% for TCLES and reduced by a maximum of 16.15% and 28.04% for TCIES.

Next generation of ejector-supported R744 booster systems for commercial refrigeration at all climates

The pernicious effects of synthetic refrigerants on different environmental aspects leave natural refrigerants as the only alternative for vapour compressions systems. Among natural refrigerants, CO2 (R744) has become the preferred choice for commercial refrigeration at almost any location and climate. However, efficient R744 refrigeration systems for warm climates have a great level of complexity, implementing technologies such as mechanical subcooling or ejector that increase the investment costs. The goal of the novel hybrid configuration presented in this work is to simplify ejector-supported R744 commercial refrigeration systems while maintaining all the benefits of the ejector implementation in transcritical operation mode. Moreover, utilization of a low-pressure accumulator layout in the subcritical mode removes all the practical challenges related to the booster layout operating at low ambient temperatures. This solution is based on: (i) MT and LT compressor suction groups, (ii) non-superheated MT evaporation with increased evaporation temperature, and (iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'), while it is passive and acts as a check-valve at lower ambient temperatures ('winter mode'). The experimental campaign performed proved that this novel system configuration is more energy efficient than booster systems with parallel compressors at any condition, improving the COP by around 40 % at the most extreme gas cooler outlet temperatures tested, i.e., 40 °C (summer mode) and 10 °C (winter mode).

Energetic and entropy analysis of a novel transcritical CO2 two-stage compression/ejector refrigeration cycle for shipboard cold chamber

The adverse effects of global warming and climate change require critical measures for marine refrigeration technology because of its impact on GHG emissions. A novel transcritical CO2 two-stage compression/ejector refrigeration cycle for shipboard cold chamber is proposed in this research. A comparative analysis was conducted between the basic transcritical CO2 two-stage compression cycle and the cycle equipped with a two-phase ejector considering the COP. Meanwhile, the refrigeration cycle was analyzed using entropy analysis to elucidate the distribution of irreversible losses in each component of the two-stage compression/ejector refrigeration cycle, and the effects of system parameters such as the evaporating and gas cooler outlet temperatures as well as the intermediate and discharge pressures on the cycle were investigated. The results showed that the ejector had the largest power capability loss, accounting for 26.95 % of the overall system, which is followed by the low pressure compressor with 26.06%. The COP of basic and ejector system significantly increase as the gas cooler outlet temperature and intermediate pressure decrease as well as the evaporating temperature increases. Furthermore, the entropy production of the system components decreases gradually with increasing evaporating temperature, with the greatest reduction in the ejector. In addition, the entropy production of the two-phase ejector remains constant with the increase of the high pressure side discharge pressure and gas cooler outlet temperature.

Comprehensive Performance Analysis and Correlation Fitting of R744 and Its Mixture Used in Refrigeration and Heat Pump Systems

Abstract In this paper, the performance of R744 and R744/R170 mixed refrigerants in refrigeration and air source heat pump systems is studied by the simulation method. The change trend of coefficient of performance (COP), refrigeration/heat capacity, power consumption with discharge pressure, and the ratio of R744 is analyzed. In addition, optimal parameters of the system are discussed in detail with the change of evaporation temperature, outlet temperature of the gas cooler, and different proportions of R744. The results show that when the discharge pressure is 8–12 MPa, there is a critical ratio of R744. When the ratio of R744 is less than the critical ratio, the optimal pressure of the system increases with the increase of the ratio of R744, and when the ratio of R744 is higher than critical ratio, the optimal pressure of the system decreases with the increase of the ratio of R744. The change trend of COP with the ratio of R744 is first decreasing and then increasing, the optimal discharge temperature of the system increases with the increase of the ratio of R744, and the change trend of optimal discharge pressure with the ratio of R744 is first increasing and then decreasing. In addition, when the evaporation temperature is 233–253 K and the gas cooler outlet temperature is 308–318 K, the average optimal pressure and temperature of R744/R170 (25/75) are 11.64% and 8.06% lower than R744, respectively. And it is the most suitable refrigerant to replace R744. Finally, the optimal performance parameter correlations of R744, R744/R170 (25/75), R744/R170 (50/50), and R744/R170 (77.6/22.4) under the given conditions are fitted through the simulation data.

Long-term performance evaluation of CO2 heat pump water heater under different discharge pressure control strategies

CO2 heat pump water heater has raised considerable attention as an environmentally efficient technology for hot water production. However, after long-term operation, the deterioration of component performance will not only directly cause system performance degradation, but also lead to a deviation of discharge pressure from the actual optimum under different discharge pressure control strategies, further resulting in additional performance loss. So far, the additional performance loss in the long run has not been in-depth investigated. In this study, based on a validated system model of CO2 heat pump water heater with component performance degradation factors, the long-term additional loss of system performance under eight different discharge pressure control strategies are compared. The results reveal that additional performance loss in the long-term operation can be significant under certain control strategy and working conditions. As for the investigated system, the control strategy with the parameter group of ambient and gas cooler outlet temperatures is favorable for application under the nominal operating condition with long-term degradation of heat exchangers, and the average additional loss of COP (coefficient of performance) can be decreased to 0.62%. As for the compressor degradation, the optimal refrigerant charge management strategy is preferred with an average COP loss as low as 0.05% under certain working conditions. In facing with year-round performance degradation, the control strategy with the parameter group of evaporating temperature and gas cooler outlet temperature shows better robustness, since the average additional annual performance loss can be reduced to only 2.52%.

Thermodynamic performance evaluation of an ejector-enhanced transcritical CO2 parallel compression refrigeration cycle

A parallel compression cycle is one efficient approach to improving the transcritical CO2 refrigeration cycle performance. This paper proposes a modified parallel compression transcritical CO2 refrigeration cycle with an ejector and a sub-cooler to further enhance the cycle performance. The thermodynamic analyses based on the energetic and exergetic analyses are conducted, and the influences of the parameters, including discharge pressure, flash pressure, gas cooler outlet temperature, and evaporation temperature, are discussed. The particle swarm optimization method is used to get the optimal discharge pressure and flash pressure and the temperature reduction in the sub-cooler with respect to the maximum COP. The performance comparisons between the conventional cycle and the modified cycle are presented. The results illustrate that the maximum improvements in COP and volumetric refrigeration capacity reach 15.8% and 17.1%. The utilization of the ejector and sub-cooler could reduce the optimal flash pressure by 16.4–33.0% and the compressor displacement by 11.4% compared with the conventional cycle. The ejector plays a dominant role in performance improvement at a high gas cooler outlet temperature. The exergy destruction analysis shows that the first-largest system exergy destruction ratio of 31.5% in the ejector-enhanced cycle is caused by the gas cooler, and its second-largest exergy destruction is generated in the two parallel compressors instead of the expansion valves in the conventional cycle.

Experimental analysis of a transcritical heat pump system with CO2 refrigerant

Today, it is seen that increasing environmental pollution is getting ahead of the increasing energy need. Therefore, more environmentally friendly and more economical refrigerants are needed. In this context, carbon dioxide appears as a natural refrigerant in cooling systems and heat pump (HP) systems, and it has been widely used in recent years. In this study, a single-stage heat pump system with a CO2 refrigerant, with a transcritical cycle, has been experimentally studied. The system is designed as a water-to-water heat pump. The performance of the system has been determined experimentally. In the system, capillary pipes with a diameter of 2.00 mm and two different lengths are used. It is aimed to create different evaporation pressures with two capillary tubes. The first capillary tube is 2.40 m long and the second is 1.20 m long. Gas cooler pressures, gas cooler and evaporator cooling water mass flow rates were kept the same for both cases. A certain gas charge was made and measurements were made for both cases. Thermodynamic analysis and comparison of the system were made. In the short capillary tube system, it was observed that the COPHP value was 7.2% higher, the CO2 mass flow rate increased by 9.1% to achieve the same gas refrigerant pressure value, and the power consumption in the compressor decreased by 1.8%. In addition, the gas cooler outlet temperature, the evaporator outlet temperature and the change in ambient temperatures, as well as the exergetic destruction and exergetic efficiencies in the system and system components are presented in figures with EES.

Experimental study on the performance of trans-critical CO2 two-stage compression refrigeration system with and without an ejector at low temperatures

A trans-critical CO2 two-stage compression refrigeration system with and without an ejector at low temperatures was set up and the effects of gas cooler pressure, gas cooler outlet temperature, and electronic expansion valve opening on the performance of the gas cooler and the refrigeration system were investigated experimentally. At a gas cooler pressure of 91 bar, an outlet temperature of 33 °C, and an electronic expansion valve opening of 95%, the COP of a trans-critical CO2 ejection-expansion two-stage compression refrigeration system reaches a peak of 0.78, which is 2.28 times higher than that of a trans-critical CO2 two-stage compression refrigeration system under the same operating conditions. This experiment also obtained the optimal operating range of the ejector. The effect of gas cooler pressure on COP is the most obvious under the conditions studied in this paper, followed by the electronic expansion valve opening and finally the gas cooler outlet temperature. However, the higher COP can be obtained for the electronic expansion valve opening condition, and the corresponding ∆COP is higher. There exists both an optimal intermediate pressure and an optimal gas cooler pressure to maximize the COP.

Experimental study on refrigerant charge amount and optimal high pressure of a CO2 heat pump system for an electric bus

In order to investigate the influence of refrigerant charge amount and discharge pressure on a CO2 heat pump system of an electric bus, an experiment setup was built. Tests were carried out in an enthalpy difference chamber to obtain the coefficient of performance and heating capacity of the system at each operating condition. The influence of operation parameters—including refrigerant charge amount, ambient temperature, outlet temperature of gas cooler, and compressor speed—was considered in this experiment. The results showed that the system performance was influenced by charge amount, and the minimum charge amount was 6.8 kg. The charge amount was almost independent of the ambient temperature, but the system performance was more sensitive to the charge amount at low temperatures. The optimal high-pressure relationship for this CO2 heat pump is popt = 0.162Tgc.out − 0.016Tamb + 2.668, which was fitted considering both the outlet temperature of the gas cooler and the ambient temperature. Meanwhile, the low-temperature performance test (–22 °C) showed that this CO2 heat pump system can meet the operation requirements of city buses at low temperature.

Evaluation of the ejector two-stage compression refrigeration cycle with work performance from energy, conventional exergy and advanced exergy perspectives

Low temperature cold chain is the top priority of logistics development at this stage. CO2 (carbon dioxide) refrigeration system is widely used. However, the low efficiency of CO2 refrigeration system is the biggest obstacle to its development. In this research work, EES (Engineering equation solver) is used to simulate the system, which is widely used in thermodynamic modeling and calculation, a novel trans-critical CO2 refrigeration cycle with ejector for low-temperature storage is proposed. The energy and conventional exergy model of the system are established, and the advanced exergy model is established based on the conventional exergy model, and the actual performance of the system is analyzed, and the optimization potential of the system components is analyzed through the commonness of the two exergy analysis methods. The results show that the exergy destruction of each component of the ejector is the largest in the system, and the optimization potential is the highest in both conventional and advanced exergy models. After studying the influence of main parameters in the system cycle on the system performance and performance, it is found that there is an optimum intermediate pressure and gas cooler pressure in the system to maximize the system performance and efficiency. According to the influence of the change of system parameters on the system, it is found that the outlet temperature of gas cooler has the greatest influence on the optimization of ejector.

Experimental and theoretical analysis of the optimal high pressure and peak performance coefficient in transcritical CO2 heat pump

Based on the high performance and the environmentally friendly characteristics, the transcritical CO2 heat pump has attracted much attention in last few decades. The high-pressure control is one of the essential factors determining the coefficient of performance due to the large pressure changes in the transcritical CO2 heat pump system. In this work, the contribution rates of different factors to the optimal high pressure and the peak performance coefficient were analyzed by the method of the analysis of variance. Then, the influences of compressor frequency, inlet water flow rate and inlet water temperature on the optimal high pressure and the peak performance coefficient were experimentally investigated on the basis of theoretical analysis. Finally, a novel discharge pressure deviation was proposed to calculate the optimal high pressure, and the occurrence regularity of optimal high pressure was investigated. The results indicated that the gas cooler outlet temperature was the main parameter influencing on the optimal high pressure, peak performance coefficient and discharge pressure deviation. The calculated discharge pressure deviation can seek the optimal high pressure with the average error of 0.57% and the performance coefficient loss of 0.34%. Additionally, the optimal discharge pressure of the experiment was likely to appear in the descending stage of the gas cooler outlet temperature.

Bi-objective optimization of transcritical CO2 heat pump systems

For the transcritical CO2 heat pump cycle, the gas cooler (GC) pressure can be controlled independently and it can be optimized for optimum COP. Control correlations can be developed offline either based on simulations or experiments or optimization can be done online in real time with continuous pressure and temperature measurements at different locations. The online methods provide more accurate results than the offline correlations, however, they have a long convergence time to the optimum value, especially if the initial GC pressure condition is far away from the optimum. In this paper, we investigate the transcritical cycle as a bi-objective optimization problem where COP and cooling/heating capacity are conflicting objectives with primarily optimizing the GC pressure for maximum cycle COP and maximum cooling or heating capacity which can be useful for transient conditions. The Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used, which generates for different operating conditions the best non-dominated solutions i.e. the Pareto Front that includes the maximum COP, max cooling capacity, and also the intermediate optimum trade-off solutions. The effect on the Pareto Front of each optimization variable; GC outlet temperature, evaporation temperature, evaporator useful superheat, and compressor speed is shown separately, where all except superheat have a significant effect on the Pareto Front. A control methodology is proposed where according to a pre-defined preference, steady-state or transient operation, an optimization parameter is set to either maximize cooling or heating capacity (e.g. obtaining comfort as soon as possible in transient operation), maximize COP (for minimum energy consumption) or operate at a trade-off point as desired. The proposed approach can be applied as an offline control method and it can also be integrated as a hybrid solution with any online optimization method. In both, whenever a new condition is imposed, the offline based bi-objective algorithm will provide a very close estimate of the optimum GC pressure. In a hybrid solution, the online optimizer will then start searching for the true optimum from this very close value and hence reach much faster to the true optimum value. Thus, yielding enhanced capabilities (bi-objective optimization of COP and Q˙c), and in a hybrid solution, additionally further enhanced accuracy (vs offline) with reduced convergence time to the optimum COP and Q˙c (vs online only). A gain to loss ratio in terms of the conflicting objectives (COP and capacity) is presented that can be used as a criteria for deciding whether to move from one solution to another on the Pareto Front.

Investigating the effect of interstage pressure on cooling performance of a real-world CO2 heat pump system

The study reveals the effect of interstage pressure with the consideration of gas cooler outlet temperature on the cooling performance of an operating CO2 heat pump system currently in use at a dairy plant. Based on the numerical model and CO2 properties, it was found that the maximum mass fraction of liquid allocated for cooling can be achieved in the middle of the operating range of interstage pressure when the enthalpy at the location of the gas cooler outlet is between 341 kJ/kg. K and 399 kJ/kg. K (that is, the gas cooler outlet temperature is between 37.34 °C and 43.02 °C with a fixed discharge pressure of 85 bar), however, the maximum liquid fraction can be achieved at the upper limit of the pressure when the enthalpy is less than 341 kJ/kg. K and can be achieved at the lower limit of the pressure when the enthalpy is higher than 399 kJ/kg. K, respectively. In the comparative study on fixed and variable interstage pressure, it was found that there is small difference in cooling COP when the gas cooler outlet temperature is lower than 38.5 °C , while the COPs with variable interstage pressures surpass those with fixed pressures when the gas cooler outlet temperatures are even higher.

Simulation study of heat transfer characteristics of a biomimetic honeycomb CO2 gas cooler

CO2 air source heat pumps are widely used because of their advantages of energy saving, high efficiency and clean. Gas cooler is one of the key components of CO2 heat pump system, while its heat transfer effect will affect the energy efficiency of the whole system. In order to improve the heat transfer efficiency, a biomimetic honeycomb gas cooler is proposed in this paper, the steady-state simulation model of the biomimetic honeycomb gas cooler is established by using MATLAB software, and the reliability of the model is verified by literature data. In addition, the heat transfer performance of the biomimetic honeycomb gas cooler is compared with that of the tube-in-tube gas cooler. The results showed that, under the same working condition, compared with the tube-in-tube gas cooler, the outlet temperature of the biomimetic honeycomb gas cooler with 1st, 2nd and 3rd level increased by 9.7°C, 25.4°C and 27.3°C, and heat transfer can be increased by 55.5%, 205.4% and 220.6% respectively. This research is helpful to provide the reference for the design and optimization of this type of gas cooler, and is conducive to the popularization of CO2 air source heat pump.