Internal Heat Exchanger Effectiveness Research Articles

Comparison of an absorption-compression hybrid refrigeration system and the conventional absorption refrigeration system: Exergy analysis

This paper presents an exergy analysis considering different operating conditions of an alternative configuration of an ammonia-water hybrid absorption refrigeration system, where part of condensation heat is recovered and supplied to generator (RCHG-ARS). In order to identify and quantify the irreversibilities in each component of the cycle and its variations, the exergy efficiency and the relative exergy loss of the system were evaluated. Moreover, the results obtained were compared with those obtained by the conventional ARS cycle. Furthermore, the effect of the internal heat exchanger effectiveness on the exergy efficiency and relative exergy loss was analyzed. The results indicate that the generation temperature and the exergy efficiency of the RCHG-ARS cycle decrease in 24 °C and 30%, respectively, it in comparison to ARS cycle at the conventional generation pressure (11.67 bar). However, to decrease the generator pressure at 5.94 bar, the evaporation temperature for the RCHG-ARS decreases in 19.3 °C and the exergy efficiency can be 0.20% higher than the obtained with the ARS cycle. It is also revealed that the exergy efficiency for the RCHG-ARS cycle become more significant at lower condensing and evaporating temperatures as well as lower generator pressures and higher internal heat exchanger effectiveness respect to ARS cycle. Moreover, the minimum values of relative exergy losses are obtained at higher generator temperatures or lower evaporating and condensing temperatures in the RCHG-ARS cycle. Finally, it can be concluded that the main components that increase the relative exergy destruction in the RCHG-ARS cycle are the generator, absorber and the compressors.

Effects of Internal Heat Exchanger on Two-Stage Compression Trans-Critical CO2 Refrigeration Cycle Combined with Expander and Intercooling

Because of the limitations of traditional refrigerants, the application of trans-critical CO2 technology in domestic gas conditioners and other fields is becoming increasingly popular. This paper proposes a new CO2 trans-critical refrigeration system. Combining the internal heat exchanger and expander components, as well as the two-stage compression cycle, we analyzed the effectiveness of the expander, internal heat exchanger, and intercooling on system performance under various operating conditions in terms of energy, exergy analysis, and optimal discharge pressure. The system performance can be changed by changing the cycle conditions and internal heat exchanger effectiveness, which reduces system power consumption and the percentage of exergy losses of gas cooler components. Compared to the single-stage compression with expander cycle, the systems cycle power consumption is reduced by 2–15.7% and the maximum system COP is increased by 2.93–6.93%. From the view of energy effectiveness, the system’s maximum COP increases by 3.9% and the percentage of exergy losses of gas cooler decreases by 22.5% with the effectiveness of internal heat exchanger varying. The addition of an internal heat exchanger has resulted in improved system performance, which is important for providing a relevant cycle model for the application.

Energy, exergy and exergoeconomic evaluation of the air source transcritical CO2 heat pump with internal heat exchanger for space heating

• The system performance of CO 2 heat pump with internal heat exchanger is compared. • The system performance is evaluated with energy, exergy and exergoeconomic analysis. • The COP and exergy efficiency is significantly enhanced with the proposed system. • The cost per unit of exergy production is obviously reduced with the proposed system. • The internal heat exchanger effectiveness and sensitivity analysis are conducted. Currently, the air source heat pump is widely used for space heating. Although the CO 2 has great potential in the refrigeration system, the basic transcritical CO 2 heat pump performance is restricted by the huge throttling irreversibility caused by the higher gas cooler outlet temperature. The internal heat exchanger has been investigated extensively from the energetic perspective. However, little information is available about the exergy analysis, let alone the exergoeconomic analysis. In this paper, the transcritical CO 2 heat pump with/without the internal heat exchanger is studied with the energy, exergy, and exergoeconomic analysis. Results show that the optimal coefficient of performance can be increased to 2.96 and 2.17 in the different heating terminals. The enlarged internal heat exchanger effectiveness is also beneficial to reduce the optimal discharge pressure and increased the system coefficient of performance. The throttling valve irreversibility is decreased from 0.067 to 0.145 kW·kW −1 to 0.040–0.071 kW·kW −1 . With total irreversibility decrement, the exergy efficiency can be effectively improved, resulting in the 55.65%-73.42% reduction of the throttle valve cost rate. Considering the CO 2 compressor investment, its total exergy cost rate increment is reached up to 34.06%-50.21%, leading to the higher exergoeconomic factor. However, the sensitivity analysis results show that the cost per unit of exergy production is more sensitive to the electricity price. Moreover, the optimal cost per unit of exergy production reduction is declined by 58.71% with the return water temperature of 30 °C.

Cooling performance enhancement for the automobile transcritical CO2 air conditioning system with various internal heat exchanger effectiveness

• CO 2 system with internal heat exchanger (IHX) were investigated. • An experiment to change IHX under different conditions was designed. • Effects of IHX on system performance and parameters were studied. • Effect of various IHX under a wide working condition was analyzed. • Energy and exergy analyses with different IHX were conducted. Carbon dioxide (CO 2 ) is one of the promising refrigerant substitutes in mobile air conditioning system. To enhance the cooling performance, this paper presented an experimental investigation on the influence of the various internal heat exchanger (IHX) effectiveness on a transcritical CO 2 mobile air conditioning system. An experimental apparatus with regulatable IHX effectiveness was set up and tested. The effects of IHX effectiveness on the cooling capacities and coefficient of performance (COP) were studied under various outdoor air temperatures (30, 35 and 40 ℃) and compressor speeds (2000 to 7000 rev·min −1 ). Optimal discharge pressure and cycle state parameters with various IHX effectiveness were analyzed. Based on exergy perspective, the irreversibility of the main components and the cycle were discussed to give further reference for system optimization. Results showed that using IHX enhanced the COP of CO 2 system by the rates from 14.5% to 18.5% at various outdoor air temperatures. With increasing IHX effectiveness, the COP enhancement decreased, and the discharge temperature easily increased to its restriction value. The compressor and gas cooler occupied the main exergy losses of the system with IHX. The results could provide reference for the design and optimization of the CO 2 mobile air conditioning system.

A comprehensive investigation on the effect of internal heat exchanger based on a novel evaluation method in the transcritical CO2 heat pump system

With the increasing demand for environmental protection, CO2, as a natural refrigerant, has always been environmentally friendly and safe, which makes transcritical CO2 heat pump system attract more attention. The internal heat exchanger is employed to improve the performance of transcritical CO2 heat pump system to match the traditional heat pump circulation system. In this work, two evaluation methods are proposed, one is the actual operation thermal effectiveness of internal heat exchanger, the other is the actual increase rate of COP. Compared with the experimental results, the conclusions can be extracted that the actual increase rate of COP can effectively evaluate the impact of the internal heat exchanger on system performance. In addition, this research deeply analyzes the influence of the internal heat exchanger on exergy efficiency. The results show that the internal heat exchanger greatly reduces the exergy efficiency under the discharge pressure of 7310 kPa and the ambient temperature of 15 °C, and the difference value between the system with and without internal heat exchanger reaches 39%. However, the influence of the internal heat exchanger on exergy efficiency decreases with the increase of discharge pressure and ambient temperature, the minimum difference value is only 0.1% at 11000 kPa and 30 °C.

Multi-objective optimization for a small biomass cooling and power cogeneration system using binary mixtures

This paper aims to find the optimal design for a small-scale cogeneration system using the Organic Rankine cycle (ORC) integrated with an ammonia-water absorption refrigeration cycle. The thermodynamic model included two ORC configurations (with and without an internal heat exchanger) and used eight Siloxanes and their possible mixtures as working fluids. Additionally, the effects of six design parameters were investigated, these being evaporation pressure, superheating, pinch point temperature, condensation pressure, internal heat exchanger effectiveness, and mass fraction in binary mixtures. A multi-objective genetic optimization algorithm (NSGA-II) was employed in order to evaluate the Pareto optimal solutions, maximizing electrical and cooling power and minimizing the overall global conductance, variables that have the greatest influence on the technical and economic performance of the cycle. Pareto optimal solutions present trade-offs between three objective functions, where optimum solutions are found within power generation ranges with overall energy efficiency between 18 and 30%. MM, MM/MD4M, MDM/MD4M and MDM/D5, stand out as the best options for working fluids, with net power output between 700 and 1170 kW, cooling capacity between 80 and 1050 kW, and the product of overall heat transfer coefficient and overall global conductance in the range of 120–620 kW/K.

Optimal discharge pressure in transcritical CO2 heat pump water heater with internal heat exchanger based on pinch point analysis

Abstract In transcritical CO2 heat pump water heater, the pinch point in gas cooler and the utilization of internal heat exchanger (IHX) both have a significant impact on the optimal discharge pressure and system performance. A theoretical model was developed to investigate the effects, and the results demonstrated that when the water inlet temperature was low, the pinch point prevented the gas cooler outlet temperature from approaching the water inlet temperature at low discharge pressure, which impaired the coefficient of performance (COP). The application of IHX could reduce the gas cooler outlet temperature by 4.9 °C when the water inlet temperature was 10 °C and the discharge pressure was 8.5 MPa. In this condition, combining with the subcooling effect of IHX, the COP was accordingly improved by 26.3%. Regardless of the working condition, using IHX lowered the optimal discharge pressure and enhanced corresponding optimal COP. In addition, parametric analyses were conducted, and the results indicated that the augment of water outlet temperature and ambient temperature resulted in the rise of optimal discharge pressure. The increase of water inlet temperature mostly enlarged the optimal discharge pressure as well. Overall, the optimal discharge pressure varied within a range of 8.53 MPa to 13.38 MPa. The reduction of optimal discharge pressure caused by using IHX intensified with the increase of water inlet and outlet temperature. Nevertheless, the effect of ambient temperature was various depending on the working condition. The reduction of optimal discharge could be up to 1.18 MPa when the effectiveness of IHX was 0.6.

Effect of internal heat exchanger to the performance of vapor compression cycle using refrigerant R32

Vapor compression refrigeration cycle generally is used in the Air-Conditioning (AC) system. In order to increase the energy efficiency, the Coefficient of Performance (COP) of the cycle need to be enhanced. Many innovations can be used, one is to utilize internal heat exchanger (IHX). In this work, the effect of IHX in the vapor compression cycle with refrigerant R32 is investigated and compared with refrigerant R22. The analyses are carried out at temperature evaporation of -5°C, 0°C, and 5°C by using software ASPEN PLUS. The results show that effect of IHX in the cycle with refrigerant R22 increases the COP from 22.78% to 25.61%. On the other hand, in the cycle with refrigerant R32 the COP increases from 33.79% to 36.80%. The average increase for the cycle with refrigerant R22 and refrigerant R32 is 24.14% and 37.04%, respectively. This fact reveals that IHX in the cycle with R32 is more effective that the cycle with refrigerant R22.

Theoretical analysis of internal heat exchanger in transcritical CO2 heat pump systems and its experimental verification

Many studies have investigated the effect of internal heat exchanger (IHX) on the transcritical CO2 heat pump (TCHP) system. However, little information is available regarding the length of IHX under various water temperature conditions. In this paper, the theoretical model was established to compare the heating performance with and without IHX. A prototype TCHP test-rig was conducted to validate the model, and the experimental results showed a good agreement. The results show that the effect of IHX on the coefficient of performance (COP) is related with inlet water temperature. The IHX is beneficial for the COP with higher temperature 40 °C. Meanwhile, the optimal discharge pressure is reduced by more than 1 MPa with the IHX length increasing from 0 m to 4 m. Although the longer length is profitable, the discharge temperature will tend to rise 25 °C and easily exceed 145 °C when the ambient temperature depresses to 2 °C. Therefore, the length in this paper is recommended to be approximately 2.5 m considering the conflict between the discharge pressure and discharge temperature.

Energy and exergy performance of the IHX position in ejector expansion refrigeration systems

This paper presents the theoretical analysis of the influence of an internal heat exchanger (IHX) position, on an ejection-compression refrigeration system. The energy and the exergy performance are discussed by placing an IHX in two different positions: 1) Promoting the superheating in the compressor suction EC+IHX-1 and 2) promoting superheating in the suction nozzle EC+IHX-2, which is a novel configuration proposal. Both configurations are compared under air climatization conditions using the refrigerants R134a, R1234ze(E) and R290. The results show that the exergy efficiency is higher when EC+IHX-2 is used for an IHX effectiveness below 60%, and lower irreversibilities occur in the ejector with this configuration for an effectiveness value of IHX below 40%. In both cases, IHX presence promotes a decrease in the coefficient of performance.

The Effect of Internal Heat Exchanger Using R1234ze(E) as an Alternative Refrigerant in a Mobile Air-Conditioning System

The Effect of Internal Heat Exchanger Using R1234ze(E) as an Alternative Refrigerant in a Mobile Air-Conditioning System

Study on energy saving effect of IHX on vehicle air conditioning system

In this paper, the performance of Internal Heat Exchanger (IHX) air conditioning system for R134a is investigated in bench test and vehicle test. Comparison for cooling capacity and energy consumption between IHX air conditioning system and traditional tube air conditioning system are conducted. The suction temperature and discharge temperature of compressor is also recorded. The results show that IHX air conditioning system has higher cooling capacity, the vent temperature decrease 2.3 °C in idle condition. But the suction temperature and discharge temperature of compressor increase 10°C. IHX air conditioning system has lower energy consumption than traditional tube air conditioning system. Under the experimental conditions in this paper, the application of IHX can significantly reduce the energy consumption of air conditioning system. At 25°C of environment temperature, AC system energy consumption decrease 14%, compressor energy consumption decrease 16%. At 37°C of environment temperature, AC system energy consumption decrease 16%, compressor energy consumption decrease 13%.

Drop-in Performance Analysis and Effect of IHX for an Automotive Air Conditioning System with R1234yf as a Replacement of R134a

This paper presents the experimental comparative performance analysis of an automotive air conditioning (AAC) system using R1234yf and R134a. For this purpose, an AAC experiment setup used for R134a was built to obtain the drop-in performance of a new refrigerant R1234yf. Among the low global warming potential (GWP) refrigerants, R1234yf was particularly chosen due to its similar thermo-physical properties with R134a. However, the system with R1234yf could not perform as efficiently as R134a can. Therefore, an internal heat exchanger (IHX) was employed to enhance the performance of the R1234yf system. After that, the performances of R1234yf and R134a were compared under various compressor speeds and air stream temperatures. The results showed that the cooling capacity and COP of the system with R1234yf were 17.1 % and 12.4 %, respectively, lower compared to the one with R134a. However, when the IHX was introduced into the system with R1234yf, the cooling capacity and COP values were significantly enhanced by 7.9 % and 4.1 %, respectively.

Theoretical Performance Analysis of an R1234yf Refrigeration Cycle Based on the Effectiveness of Internal Heat Exchanger

In this paper, the effects of internal heat exchanger (IHX) effectiveness on the performance parameters of the refrigeration cycle with R1234yf were theoretically investigated. For this purpose, a mathematical model was developed based on the energy balance of the cycle. The analysis were performed between -20°C and 0°C evaporation and 40°C and 50°C condensation temperatures based on the effectiveness value of IHX. The cooling capacity, coefficient of performance (COP), subcooling, superheat and compressor discharge temperature of the refrigeration cycle was examined. Finally, the performance results of the cycle with R1234yf were compared with the baseline cycle that utilizes with R134a. As a result, it was determined that the critical effectiveness to supply the same COP with R1234yf was determined 50% in comparison the baseline cycle. Keywords: R1234yf; R134a; Internal heat exchanger; Effectiveness DOI: 10.17350/HJSE19030000044 Full Text:

Effects of internal heat exchanger on performance of transcritical CO 2 heat pump system

Effects of internal heat exchanger on performance of transcritical CO 2 heat pump system

Transient behavior of CO2 in the internal heat exchanger during the start-up of the transcritical refrigeration system

Transient behavior of internal heat exchanger during start-up of transcritical refrigeration system is investigated in this article. The work is focused on the local transient analysis of CO2 thermophysical properties, in order to see how these transient changes affect the heat transfer rate and the effectiveness of internal heat exchanger, as well as the coefficient of performance during the start-up of the system. The study is conducted through a numerical simulation using the commercial computational fluid dynamics (CFD) software Ansys Fluent. Validation of numerical results is carried out by using seven different empirical correlations applied for the Nusselt number. It is observed that the thermophysical properties of the hot CO2 stream experience large changes during the transient period. This instability is accompanied by a decrease in the heat transfer rate. Finally, the change in the internal heat exchanger effectiveness during the start-up results in a loss of about 12% of the coefficient of performance.

Theoretical assessment of an ejector enhanced oil flooded compression cycle

Compressor loss and throttling loss are major thermodynamic losses in basic vapor compression cycle. For this reason, an ejector enhanced oil flooded compression cycle is proposed. To evaluate the performance, a mathematical model is established and the performance of this cycle with R32 as the working fluid is investigated. Furthermore, basic cycle, ejector enhanced basic cycle and oil flooded compression cycle have also been investigated. The comparison results show that the developed cycle has a maximum of 4.3% and 4% COP improvement at the evaporation temperature of −25 °C and the condensation temperature of 45 °C over the oil flooded compression cycle and the ejector enhanced basic cycle respectively. In addition, the effects of internal heat exchanger on the developed cycle are also studied. In comparison to the ejector enhanced basic cycle with 50% efficient internal heat exchanger, the COP improvement of the developed cycle rises up to a maximum of 8.5%. The results show that the proposed cycle has large potential applications for the ejector cycle enhancement.

다양한 냉매를 적용한 내부열교환기 부착 2단 압축 냉동시스템의 성능 분석

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

Performance analysis of an organic Rankine cycle with internal heat exchanger having zeotropic working fluid

In this study, performance of a 50kW organic Rankine cycle (ORC) with internal heat exchanger (IHE) having R245fa/R152a zeotropic refrigerant with various compositions was investigated. The IHE could reduce heat rate at the ORC evaporator and better cycle efficiency could be obtained. The zeotropic mixture could reduce the irreversibilities during the heat exchanges at the ORC evaporator and the ORC condenser due to its gliding temperature; thus the cycle working temperatures came closer to the temperatures of the heat source and the heat sink. In this paper, effects of evaporating temperature, mass fraction of R152a and effectiveness of internal heat exchanger on the ORC performances for the first law and the second law of thermodynamics were considered. The simulated results showed that reduction of R245fa composition could reduce the irreversibilities at the evaporator and the condenser. The suitable composition of R245fa was around 80% mass fraction and below this the irreversibilities were nearly steady. Higher evaporating temperature and higher internal heat exchanger effectiveness also increased the first law and second law efficiencies. A set of correlations to estimate the first and the second law efficiencies with the mass fraction of R245fa, the internal heat exchanger effectiveness and the evaporating temperature were also developed.

Effect of an Internal Heat Exchanger on Performance of the Transcritical Carbon Dioxide Refrigeration Cycle with an Expander

The effect of the internal heat exchanger (IHE) on the performance of the transcritical carbon dioxide refrigeration cycle with an expander is analyzed theoretically on the basis of the first and second laws of thermodynamics. The possible parameters affecting system efficiency such as heat rejection pressure, gas cooler outlet temperature, evaporating temperature, expander isentropic efficiency and IHE effectiveness are investigated. It is found that the IHE addition in the carbon dioxide refrigeration cycle with an expander increases the specific cooling capacity and compression work, and decreases the optimum heat rejection pressure and the expander output power. An IHE addition does not always improve the system performance in the refrigeration cycle with an expander. The throttle valve cycle with IHE provides a 5.6% to 17% increase in maximum COP compared to that of the basic cycle. For the ideal expander cycle with IHE, the maximum COP is approximately 12.3% to 16.1% lower than the maximum COP of the cycle without IHE. Whether the energy efficiency of the cycle by IHE can be improved depends on the isentropic efficiency level of the expander. The use of IHE is only applicable in the cases of lower expander isentropic efficiencies or higher gas cooler exit temperatures for the refrigeration cycle with an expander from the view of energy efficiency.