Refrigerant Mass Flow Rate Research Articles

Numerical Prediction of Refrigerant Oil Two-Phase Flow from Scroll Compressor Discharge to the Suction Side via Back Pressure Chamber

Oil lubricates the contact between the orbiting and stationary scroll in the refrigerant scroll compressor, while the sealing between the scrolls is achieved through the refrigerant vapour pressure in the sealed back pressure chamber. The back pressure should be adjusted using the refrigerant oil two-phase flow from the oil separator at the compressor discharge to the back pressure chamber and the refrigerant oil flow from the back pressure chamber to the compressor suction side. Both of the flows are conducted through connecting tubes with corresponding high-pressure and low-pressure nozzles with small diameters. Models for predicting the refrigerant oil critical and subcritical flows through the nozzles were developed and applied in enable the prediction of the back pressure. The models are original, because the slip between the oil and the refrigerant as well as the refrigerant solubility in the oil are taken into account. The critical flow model is validated against the experimental data that are available in the literature. The back pressure is predicted by equating the mass flow rates of refrigerant and oil two-phase mixtures through the high- and low-pressure nozzles. The results show that the critical flow takes place through the high-pressure nozzle, while the subcritical flow through the low-pressure nozzle can also exist in cases with a small pressure difference between the back pressure chamber and the compressor suction side. The refrigerant solubility in the oil has a small influence on the critical and subcritical refrigerant oil mixture mass flow rates, while the influence on the back pressure is more pronounced.

Adiabatic capillary tube flows of n-butane and isobutane

This paper presents an experimental study of n-butane (R600) and isobutane (R600a) flows in adiabatic capillary tubes. In total, 48 experimental data points were gathered spanning the typical conditions of household refrigerators, with capillary inner diameters ranging from 0.53 to 0.79 mm, tube lengths ranging from 2.5 to 3.5 m, inlet pressure ranging from 2.83 to 6.05 bar, exit pressure ranging from 0.3 to 0.9 bar, inlet subcooling ranging from 4.7 to 15.2 °C, and mass flow rates ranging from 0.53 to 2.95 kg h−1. In addition, the accuracy of π-type correlations priorly developed for R600a flows was verified when used with R600 to predict the refrigerant mass flow rate. Also, it was found the mass flow rate predictions of the algebraic model developed by Hermes et al. (2010) for R600a agreed well with the R600 experimental data, with more than 90 % of data points within ±10 % error bands.

A comparative analysis of a new semi-empirical model and the AHRI polynomial model for positive displacement compressors

A semi-empirical model has been proposed to predict the refrigerant mass flow rate, input power, and discharge temperature of positive displacement compressors. The prediction accuracy of the proposed model is compared with the accuracy of the AHRI polynomial model. To examine the generalizability of the models, a resampling methodology is used to compare prediction accuracy that results when smaller data sets are used to fit the models. These results show that the semi-empirical model has similar mass flow rate and input power prediction errors to the AHRI polynomial model and results in more consistent performance when smaller data sets are used to fit the model. The results also show that the AHRI polynomial is not a good choice for the prediction of discharge temperature and that the proposed model is much more suitable for this purpose.

Operational stability influenced by lubricant oil charge in the CO2 automotive air conditioning system

In a vapor compression refrigeration system, the oil enhances the efficiency of the compressor but impairs the performance of the heat exchanger. This paper focuses on the experimental study of the influence of oil quantity on the operational stability of CO2 air conditioning system. The operational stability of the system under different oil charge quantity and operating conditions is studied. The experimental results indicate that when the oil circulation rate increases to a certain value, the adjustment of electronic expansion valve (EXV) opening or the compressor speed will cause system fluctuation and the outlet of evaporator gets close to no superheat. The critical oil circulation rate of the experimental system is about 9.2 %. The analysis of the fluctuation shows that it becomes more severe with the increasing of the refrigerant mass flow rate. When the mass flow rate increases from 210 kg∙h − 1 to 250 kg∙h − 1 at 7000 r min−1 of compressor speed, the fluctuation frequency increases from 0.072 Hz to 0.095 Hz. The occurrence of unstable phenomena has remarkable impact on system performance, the maximum difference of this system in instantaneous cooling capacity and COP during the fluctuation period is respectively 0.5 kW and 0.13.

Performance analysis of dual-evaporator ejector refrigeration system in different configurations: Experimental investigation

This study aimed to assess the effectiveness of an ejector refrigeration cycle, using a laboratory-scale experimental system operating in different configurations. The investigated configurations consisted of a conventional vapour compression refrigeration (CVCR) system and a dual evaporator ejector system (DEES) operated in two modes: DEES with a single thermal expansion valve (DEESA) and DEES with dual thermal expansion valves (DEESB). The findings revealed that the utilization of the ejector enhanced the refrigerant's mass flow rate. Additionally, the DEESA configuration achieved higher cooling capacities compared to the CVCR. Moreover, the DEESA configuration achieved up to 21% higher coefficient of performance (COP) values. On the other hand, when the system was operated in the DEESB configuration, it yielded lower evaporation temperatures and higher superheating degrees in comparison to DEESA. Based on the evaluations, it can be concluded that the ejector operates more efficiently in systems with dual evaporators, thereby making positive contributions to overall system performance.

Development, calibration, and validation of a novel gray-box energy model for residential split air conditioners

Energy models for vapor compression refrigeration in residential air conditioners have been developed through white-box, gray-box, and black-box methods in decades. However, existing white-box and gray-box models require complicated equations with detailed geometries while black-box models require substantial experimental data. This paper aims to develop and validate a simple gray-box steady-state energy model without the need for detailed geometries, which can accurately predict the cooling capacity and electrical power input based on outdoor and indoor air conditions, and supply airflow rates. First three state variables, including the evaporation and condensation temperatures, and refrigerant mass flowrate, are applied to develop the energy model and are solved by three physical equations, including the energy conservations at the evaporator and condenser, and the refrigerant volume-mass flow correlation of the compressor. Secondly, seven performance property functions related to three state variables and three physical equations are identified and calibrated by simple temperature and power measurements. Finally, field experiments are conducted on a residential air conditioner to calibrate these performance property functions and validate the developed model. The validated results reveal the model can accurately predict the cooling capacity and electrical power input, with the normalized root mean square errors of 2.3% and 0.87% respectively.

Theoretical exploration of low GWP refrigerant mixtures as replacement to HFC-134A in a vapour compression refrigeration system

Hydro-fluorocarbons (HFCs) that are not harmful to ozone layer and are used in many appli-cations, including as refrigerants, aerosols, solvents and blowing agents for insulating foams replace chlorofluorocarbons and hydro chlorofluorocarbons (HCFCs). However, some HFCs have a high GWP, which stands for “Global Warming Potential(GWP).” Because of the grow-ing concern over global climate change, researchers are paying closer attention for alternatives to these HFCs. The main focus of this work was on the theoretical analysis of the refrigerant mixtures namely AC5, R430A, and R440A as direct replacements for HFC-134a in a refriger-ator. The performance of the refrigerator may be enhanced using heat exchanger. The com-pressor discharge temperature, COP, VCC, refrigerant mass flow rate, power consumption of a compressor and pressure ratio were used to measure the performance of a home refrigerator. The typical COP of R440A and R430A was about 2.5% and 1.4% higher than that of HFC-134, while the average COP of AC5 was 6.1% lesser than that of HFC-134a. R430A almost has the same VCC (Volumetric Cooling Capacity) as HFC-134a. The results also show that HFC-134a uses more power than AC5, R440A, and R430A. R440A and AC5 have higher compressor outlet temperatures than HFC-134a, which affects the life span of the compressor. In com-parison with all the above refrigerants, R430A gives the best overall performance and used as replacement to HFC-134a in a VCR.

Theoretical Analysis for Condensation Heat Transfer Performance Inside Converging-Shaped Microchannel Under Varying-Gravity Conditions

Abstract The fast increasing heat-dissipation requirements under different working conditions such as varying gravity for aerospace industry is drawing more and more attention. Condensation inside microchannel is proved to be a promising technique to tackle this task. To comprehensively and accurately describe the physical phenomenon, a theoretical method considering both momentum exchange caused by vapor condensation and interface temperature drop is developed in this study. Reliability of our theoretical method is verified with both the Comprehensive Shah Correlation and established data. Condensation heat transfer inside converging-shaped microchannel is investigated and the influences of channel size, refrigerant mass flowrate, gravity variation, and converging angle are considered. Converging-shaped microchannel significantly enhances condensation heat transfer, especially for smaller channel with larger refrigerant mass flowrate. Influence of gravity change on condensation performances of vertically configured microchannels both with converging shape and constant cross-sectional area is small.

Performance evaluation of hot-wall condenser in a domestic refrigerator

In this study, the heat transfer performance of a hot-wall condenser, which is affected by design parameters, is investigated. In this study, the pipe section form (O/D) variation, which has not been examined so far, is used as a design parameter for condenser performance. Incorporating the specified design parameters, 12 different condenser samples were manufactured. Additionally, a simulation model regarding with the thermal effects was designed for comparing the outputs of experimental results. The parameters are outer diameter of the condenser pipe (4.0 and 4.76 mm), condenser pipe pitch (20, 40, and 60 mm), the section form (O/D) of condenser pipe, and the refrigerant mass flow rate in flow. The results revealed significant findings regarding the impact of different design parameters on the heat transfer rate of the condenser. Specifically, increasing the condenser pipe diameter led to an average heat transfer rate increase of 8.9% and 5.2% by increasing flow rates as double, respectively. The pipe pitch was found to have a notable effect on the heat transfer rates, resulting in average increases of 213%, 47%, and 313% for the 20–40 mm, 40–60 mm, and 20–60 mm transitions, respectively. Specifically, the novel output is the transition from O-to-D pipe configuration, resulting in a maximum 3% increase in the total heat transfer rate.

An improved approach to model compressors, condenser/gas cooler and their control system in refrigeration systems with R404A and R744 based on physical principles

This study introduces an improved methodology to evaluate with accuracy the performance of a conventional system with R404A and a Booster system with R744. Reciprocating and scroll compressors are modeled with improved semi-empirical approaches, and their operation is ideally controlled to maintain the required refrigerant mass flow rate with an On/Off and variable speed control system. The R744 gas cooler is modeled with a four-zones model and the R404A condenser with a three-zones model. The R744 condenser is modeled with the superheated zone discretized into eight zones to avoid unrealistic results due to the variation of its thermophysical properties and the two-phase and subcooled zones with one zone respectively. In line with the design, the Booster condenser enters into the pseudo-critical zone at an ambient temperature of 23 °C, while the gas cooler is activated after 31 °C. The compressor models present errors lower than 10%, while the Booster model presents mean deviations lower than 2.3%. The Booster system presents better COPs than the conventional at ambient temperatures lower than 15ºC. At higher ambient temperatures, the COPs of both systems are similar: the conventional system overperforms the Booster up to 6%, being in disagree with the literature results where these differences increase up to 30%. The proposed methodology allows to reduce the overall model error by 3% with respect to a thermodynamic cycle-based model; allowing to improve the comparison between the Booster system with R744 and the conventional one with R404A, which leads to more transparent results than the reported common comparisons.

Evaluation of correlations for mass flow rate of refrigerant through electronic expansion valve in air—water heat pump system using R32

To measure mass flow rate of R32 through EEVs under real operating conditions, a commercially available air-water heat pump (AWHP) system was operated in as wide a range as possible. Measurements showed that the effect of oil circulation on the refrigerant mass flow rate of the test system was negligible. To examine whether they were able to predict refrigerant mass flow rate of R32 in a real operating heat pump systems, previous empirical correlations available in the open literature were compared against these measured data. Previous empirical correlations, except for those of Park et al. (2007), showed poor agreement with the present experimental data, with mean absolute percentage error (MAPE) from 9.1% to 334.5% for EEV#1 (D: 2.40 mm) and from 24.1% to 122.2% for EEV#2 (D: 1.65 mm). These large differences were caused by differences in internal geometry of flow passage and operating conditions due to different refrigerants. A new empirical correlation was developed considering these aspects. The valve opening ratio was considered in terms of the valve flow coefficient variation. The thermodynamic state of refrigerant at the EEV inlet was represented by the enthalpy difference, so as to avoid discontinuity of the mathematical expression at the saturated liquid point. The new correlation showed good agreement with mass flow rate measured through both EEVs, with MAPE values of 9.3% and 14.5% for EEV#1 (D: 2.40 mm) and EEV#2 (D: 1.65 mm), respectively.

Condensation heat transfer and pressure drop of R1234yf/HFC mixtures inside small diameter channels

Hydrofluoroolefin/hydrofluorocarbon mixtures, such as R1234yf/HFC mixtures, have been proposed for the substitution of R134a in refrigeration and air-conditioning applications. Indeed, these fluids present good thermodynamic properties and low environmental impact. Here, the condensation process of two mixtures, R513A (R1234yf/R134a 56/44% by mass) and R516A (R1234yf/R152a/R134a 77.5/14/8.5% by mass), has been investigated inside two channels with inner diameters equal to 0.96 mm and 3.38 mm. Both R513A and R516A are azeotropic mixtures. Condensation heat transfer tests have been conducted at 40 °C saturation temperature and mass flux ranging between 40 kg m−2 s−1 and 600 kg m−2 s−1. In the present study, particular focus is put onto condensation at low mass flux (below 100 kg m−2 s−1). Tests at low mass fluxes are very rare in the literature but of great relevance considering that chillers and heat pumps equipped with variable speed compressors work for most of their lifetime at partial loads, thus reducing the refrigerant mass flow rate in the heat exchangers and the mass flux in each channel as compared to the nominal working conditions. In the 3.38 mm diameter channel, the two-phase flow has been recorded using a high-speed camera and a comparison with two flow pattern maps is presented. The heat transfer coefficient data have been compared with the results of three semi-empirical models and with a specifically developed Artificial Neural Network model.

Fuzzy Logic Controlled Simulation in Regulating Thermal Comfort and Indoor Air Quality Using a Vehicle Heating, Ventilation, and Air-Conditioning System.

Conventional heating ventilation and air-conditioning (HVAC) controllers have been designed to mainly control the temperature of a confined compartment, such as a room or a cabin of a vehicle. Other important parameters related to the thermal comfort and indoor air quality (IAQ) of the confined compartment have often been ignored. In this project, IAQ in the vehicle cabin was represented by its carbon dioxide (CO2) concentration, and the occupants' thermal comfort levels were estimated with the predicted mean vote (PMV) index. A new fuzzy logic controller (FLC) was designed and developed using the MATLAB fuzzy logic toolbox and Simulink to provide a nonlinear mapping between the measured values, i.e., PMV, temperature, CO2, and control parameters (recirculation flaps, blower's speed, and refrigerant mass flow rate) of a vehicle HVAC system. The new FLC aimed to regulate both in-cabin PMV and CO2 values without significantly increasing overall energy consumption. To evaluate the effectiveness of the proposed FLC, a cabin simulator was used to mimic the effects of different HVAC variables and indoor/outdoor environmental settings, which represented the in-cabin PMV and IAQ readings. Results demonstrated that the new FLC was effective in regulating the in-cabin PMV level and CO2 concentration, at desirable levels, by adaptively controlling the opening and closing of the recirculation flap based on in-cabin temperature and CO2 readings, while maintaining an average-to-good energy consumption level. The proposed FLC could be applied to a large variety of HVAC systems by utilizing low-cost sensors, without the need to significantly modify the internal design of the HVAC system.

Experimental Research on the Effect of Oil Charge Ratio on the Cooling Performance of CO2 Air Conditioning System for Electric Vehicles

From the perspective of the engineering application, the influence of the oil charge ratio on the cooling performance of the electric vehicle CO2 air conditioning system is experimentally studied in this paper. An online test device for oil circulation rate is set up on the built CO2 air conditioning system test bench. The experiment is conducted under different ambient temperatures and compressor speeds in the fresh air mode. As the oil charge ratio increases, the oil circulation rate increases as well as the oil mass flow rate, while the refrigerant mass flow rate decreases slightly. Under the refrigerant charge amount of 550 g and ambient temperature of 35 °C and 40 °C, this system reaches its best cooling performance when the oil charge ratio is in the range of 20% and 25%. And the maximum COPs are 2.46 and 2.36, respectively. The increase in the oil charge ratio is beneficial to the improvement of the isentropic efficiency and the volumetric efficiency of the compressor. The change in oil circulation rate has less effect on the pressure drop in the gas cooler than that in the evaporator.

Simulation of air-cooled PV/T air conditioning system for cooling and power cogeneration

The traditional photovoltaic/thermal (PV/T) air conditioning system usually uses a PV/T heat exchanger as the condenser, of which poor heat dissipation performance leads to an undesirable system cooling capacity. This study proposes an air-cooled PV/T air conditioning system, comprising an air-cooled condenser and a PV/T condenser combined in series. Experiments are carried out under daytime and nighttime conditions in summer, and numerical simulations are conducted to analyze the influence of different factors on the system performance. EVAP-COND, FLUENT and EES software are adopted to calculate the air-cooled condenser model, PV/T condenser model and system performance under different weather conditions, respectively. Results show that the heat dissipation rate of system condenser increases with the outdoor wind speed, refrigerant mass flow rate and inlet temperature, while decreases with the solar irradiance and outdoor temperature. Remarkably, the refrigerant mass flow rate has the most significant impact on the heat dissipation performance of system condenser. When the refrigerant mass flow rate increases from 10 kg/h to 50 kg/h, the heat dissipation rate of system condenser increases from 639 W to 3116 W. Moreover, the system cooling performance is better under nighttime conditions, as its COP is 20.0 % and 123.7 % higher than that under cloudy and sunny daytime conditions, respectively.

PERFORMANCE ANALYSIS OF HEAT EXCHANGER FOR COOLING APPLICATIONS UNDER DRY AND WET CONDITIONS

The present study is carried out to compare evaporator coil's performance for dry and wet conditions. Numerical simulations are performed by solving a set of governing equations for the above-mentioned operating conditions (dry and wet). Two typical fin configurations, named plain and corrugated or wavy fins, for the staggered tube arrangements are studied. The model utilizes the conservation equations of mass, momentum, and energy to the physical domain. Only a two-phase condition for the flow within the evaporator tube is considered. The working fluid considered for cooling in the heat exchanger is R134a. Variation of evaporator coil performance for different operating parameters such as air inlet temperature, air inlet relative humidity, refrigerant inlet temperature, and mass flow rates of refrigerant and air is presented in this study. The analysis is performed by solving the sets of equations in a MATLAB environment. It is worth observing that the value rises when the relative humidity, air mass flow rate, and air inlet temperature increase. The values are increased by about 7% and 12% from the dry working condition to the wet working condition for plain and wavy fin configurations, respectively. With increase in refrigerant mass flow rate and evaporation temperature, the UA value increases but it is not as much significant as air mass flow rate and air inlet temperature. The air-side pressure drop is increased by 30% for a wavy fin as compared to a plain fin.

Experimental investigation on split type window Air conditioner using HFC and HC mixture as ecofriendly refrigerant alternate to HCFC-22

This paper reports on an experimental study evaluating a window air conditioner's performance when R152a/R290/R600/R600a refrigerant mixture (by various mass percentages) is used as a possible alternative to R-22. Alternative refrigerants are local, cheap, and environmentally friendly. Unmodified R-22 window AC was charged with R152a/R290/R600/R600a. During the experiment, parameters such as coefficient of performance, refrigeration effect, pressure ratio, compressor discharge temperature, refrigerant mass flow rate, and compressor power are analyzed. The present work shows that R152a-15%/R290-15%/R600-35%/R600a-35% is the best-performing alternative refrigerant. Proposed blends and R22's performance were compared.

EFFECTS OF VAPORIZATION TEMPERATURE AND SUB COOLING VARIATION ON THE PERFORMANCE OF A VAPOUR COMPRESSION REFRIGERATION CYCLE WORKING WITH R134A, MET ON NEWER SHIPS

R134a is a refrigerant met in several marine refrigeration applications, such as fishing vessels, passenger and cargo ships. In 2014, 26% of the international commercial fleet was using R134a. Although R134a shows a null Ozone Depletion Potential, it has a quite high Global Warming Potential (1300). R134a is a greenhouse gas and, even if it is present on newer ships, the future will be marked by its replacement with substitutes having low GWP. Still, because its GWP is less than 2500, R 134a will continue to be used. Due to the fact that vapour compression refrigeration systems are dominant on board the ships and knowing that these technologies are high energy consumers, analysing their performance in the contemporary energetic context, is imperious required. This paper presents a theoretical analysis of a single stage vapour compression cycle, working with R134a, based on the laws of thermodynamics. The analysis will reveal the influence of the evaporator temperature on the Coefficient of performance and on exergy efficiency, and also the influence of sub cooling on these two efficiency terms, on the refrigerant mass flow rate and compression rate. It was considered a variation of the evaporator temperature in the range (-40÷ -10)oC and of the sub cooling in the range (0÷10)oC. The increase of the evaporator temperature will contribute to a COP increment (50%) and an exergy efficiency decrease (34%). The sub cooling will lead to both COP and exergy efficiency increase (11%). Higher sub cooling degree will provide an increment in the refrigerant mass flow (18%) and a decrease of the compression rate (76%) meaning lower work consumption at the compressor.

Simulasi Termodinamika Pengaruh Temperatur Subcooling di Kondensor Terhadap Kinerja Cold Storage

The subcooling temperature in the condenser can affect the overall performance of the refrigeration system. One of the refrigeration systems that plays an important role in the cold chain of fishery products is cold storage. This paper discusses thermodynamic study of the effect of condenser subcooling temperatures on the performance of cold storage that operates based on a vapor compression refrigeration cycle based on the CoolPack software. The subcooling temperatures varied was 5 – 10 Kelvin and the system performance parameters analyzed were refrigerant mass flow rate, heat rejected in the condenser, compressor power and coefficient of performance. The results of this study indicate that as the subcooling temperature increases, the refrigerant mass flow rate decreases so that the compressor power and the rate of heat release in the condenser also decrease. Thus, the performance coefficient of cold storage will increase as the subcooling temperature increases.

Energy and Exergy Analysis of Single Effect Water-LiBr Vapour Absorption Refrigeration System

Vapor absorption refrigeration system (VARS) is one of the emerging technology in thermal-driven refrigeration systems and has too many benefits in comparison with another cooling system as their performance is good and the cost is low. Different mathematical models of various complexities have been developed for performance analysis, optimization, and design of such systems. In this study energy and exergy of a single effect LiBr vapor absorption refrigeration system is analyzed with different mathematical model developed so far. The effect of varying the temperature for each component of the system on the coefficient of performance (COP) and exergetic efficiency (COPex) is briefly discussed. The results show that increasing generator temperature from 86oc to 102oc for constant refrigerant mass flow rate causes COP of the system to increase, due to the decrease in circulation ratio. In another case, increasing the evaporator temperature from 2oc to 14oc for a constant temperature input of the generator has a positive effect on both the first and second law efficiency of the VARS as the load on the generator decrease. From the result, it can also be concluded that increasing absorber temperature has a negative impact on both COP and exergetic efficiency of VARS.