Refrigerant Mass Flow Rate Research Articles

Experimental study of R290/R600a mixtures in vapor compression refrigeration system

This paper presents an experimental investigation of the effect of R290/R600a refrigerant mixtures on the performance of variable speed hermetic compressors used in household refrigeration. In this context, a small-capacity compressor test stand is introduced and four different compositions of R290/R600a mixtures are studied in detail. R290 composition in the refrigerant mixture varies between 40–70% by mass weight. Performance outcomes of the mixtures are compared to baseline refrigerant R600a. The influence of R290 composition in refrigerant mixture over COP, refrigerant mass flow rate and power consumption rates are explored in the present study. Moreover, the effect of compressor speed, evaporation and condensation temperature on the compressor performance are studied via steady-state experimental tests. It has been concluded that increasing the mass weight of R290 in the mixture yields higher power consumption rates, yet it has brought a significant increase in the refrigerant mass flow rate, thus enabling a higher COP. The optimum compressor speed is found to be approximately 2100 rpm for the tested hermetic reciprocating compressor. The COP increases with the increments of evaporation temperature and decrements of the condensation temperature. The COP of the refrigeration cycle is 10–20% greater than that of R600a depending on the composition of the refrigerant mixtures and operating conditions.

Evaluation of flow and heat transfer in the condensation of R-406a vapor in circular tubes with extended surface of twisted fins

The present study aimed to conduct an experimental examination of heat transfer increase using tubes with extended surface of twisted fins for the condensation of vapor R-406A in horizontal tubes. The experimental setup comprised a main counter flow double-tube condenser, with water as the cooling fluid. Further, test and secondary condensers were used to reach desired vapor qualities. The tests were conducted on a smooth tube and four different tubes with extended surface of twisted fins and collected for different mass flow rate of refrigerant and in each mass flow rate for six different vapor quality. The refrigerant mass flow, temperature of refrigerant inlet water and condenser outlet water, were measured in each test. Also, the heat transfer coefficients were obtained based on the former data for different states. The results show that for the tubes with extended surface of fins, heat transfer enhanced by decreasing the pitch. The use of tubes with extended surface of fins increased the mean heat transfer coefficient by about 47% compared to the smooth tube. Eventually, a new correlation is defined for examination of the condensation heat transfer coefficient of R-406A in circular tubes with extended surface of twisted fins.

Comparative experimental investigations of pumpless vapour absorption system using high- and low-grade energy

This work presents an experimental investigation of Pumpless Vapour Absorption System (PVAS) by supplying the high-grade (electric power) and low-grade energy (LPG). The work experimentally investigates the behaviour of the PVAS components by using both energy sources. Experimental result shows the generator takes more time to warm up, around 120 and 35 s by supplying high-grade and low-grade energy, respectively. In the evaporator, the rate of decreasing temperature is higher by low-grade than the high-grade energy supply. It takes only 22 min to reach the steady state in low-grade energy input, while in high-grade energy it takes about 34 min. The work further investigated the mass flow rate of refrigerant and heat supplied in the generator with variation of refrigerating effect. Highlights Air conditioning industry consumes around 10–20% of the world energy. Supplying low-grade energy in pumpless vapour absorption system is suitable. Pumpless vapour absorption system is more beneficial in rural areas.

차압 계측에 의한 압축기 토크 연산

Since the engine of an automotive determines the output of the engine torque by compensating a torque corresponding to the compressor torque to drive the refrigerant compressor for an air conditioner, accurately calculating the torque of the air conditioner compressor can improve fuel economy and quietness through optimal engine power control. In this study, a torque calculation based on differential pressure which is a function of refrigerant mass flow rate is proposed by replacing the conventional torque calculation method based on evaporator load condition. Reliability of torque calculation was confirmed through evaluation under an automotive operating condition. In test results, torque calculation error under differential pressure was improved from 0.3~1.0 N·m depending on the condition compared to the previous method.

Impact of suction line on evaporator effectiveness in refrigeration cycle

The effect of suction line on the evaporator performance with the using of R-134a has been investigated experimentally. Three types of suction lines (lateral, concentric, coil) have been used with various refrigerant flow rates and air velocities. The results of the concentric suction line gave the highest values of the coefficient of heat transfer compared to the other types. Moreover, the maximum increase of the internal heat transfer coefficient (hi) and overall heat transfer coefficient (Uo) was achieved for the reference capillary tube as 16% and 50% respectively, when the mass flow rate of refrigerant is 14.87 kg/h and air velocity 3.8 m/s. In addition, the results displayed that the largest values of evaporator effectiveness (ε) have been obtained, when utilized the concentric suction line compared the other types. Thereby, the internal heat transfer coefficient was increased by 9.24% for the concentric suction line with the increasing of air speed from 1.8 m/s to 3.8 m/s at flow rate of the refrigerant is 14.87 kg/h. Finally, the best suction line according to all results such as hi, Uo and ε is the concentric line compared the other types.

Energetic and exergetic performance comparison of an experimental automotive air conditioning system using refrigerants R1234yf and R134a

In this study, the energetic and exergetic performance merits of an automotive air condition-ing (AAC) system using R134a and R1234yf have been investigated. For this aim, a laboratory AAC system was developed and equipped with devices for mechanical measurements. The refrigeration circuit of the system mainly had an evaporator, condenser, liquid receiver, fixed capacity compressor, and thermostatic expansion valve. The tests were performed by changing the compressor speed and air stream temperatures incoming the condenser and evaporator. Based on energy and exergy analysis, various performance parameters of the AAC system for both refrigerants were determined and presented in comparative graphics. It was found that R1234yf resulted in 0.4–10.9% lower refrigeration capacity, 5.5–11.6% lower COP, and 4.7–16.1°C lower compressor discharge temperature, while yielding 9.3–22.3% higher refrig-erant mass flow rate and 1.1–3.5°C higher conditioned airstream temperature in comparison to R134a. Moreover, the components of the R1234yf system usually destructed more exergy, and the total exergy destruction rate per unit refrigeration capacity of the R1234yf system was 4.1–15.3% greater than that of the R134a one.

Experimental studies on transcritical CO2 heat pump system for simultaneous water cooling and heating application

ABSTRACT An in-house transcritical CO2 heat pump experimental facility was developed for simultaneous cooling and heating of water. Hand-operated (Needle) valve is used as an expansion device to control the gas cooler pressure and mass flow rate of refrigerant. The tests were conducted to study the performance of the system and components at various operating conditions. Four independent input operating variables and four output variables are considered for investigation. The factorial experimental design was employed to achieve the optimum set of experiments. Taguchi L9 array is used to design experiments for chosen variables and results were analyzed by using response surface methodology (RSM). It is observed that system charging pressure and degree of expansion valve opening affect the system performance greatly. Maximum cooling and heating output from the system was recorded as 3.8 kW and 6.6 kW, respectively, and the corresponding system COP obtained was 3.1. Empirical correlations are developed employing RSM technique to predict the system performance.

A comparative study of flow characteristics of adiabatic spiral and helical capillary tube in a CO2 transcritical system

Flow characteristics of an adiabatic spiral and a helical capillary tube in a CO2 transcritical system are numerically simulated. A homogeneous two-phase flow model is developed using the mass, energy and momentum conservation equations, taking into consideration the helical and spiral coiling effects of the capillary tubes. Friction factor and viscosity correlations are used from the available literature. Results are compared with conventional subcritical refrigerant R22. Reduction in a mass flow rate of refrigerant is more pronounced in the spiral capillary tube than helical capillary tube effect; about 18% and 11% with CO2 and R22, respectively. Length requirement with a spiral capillary tube is relatively less compared to other chosen configurations for the given mass flow rate and operating conditions.

Experimental performance evaluation of an R1234yf automobile air conditioning system employing an internal heat exchanger

A bench-top automobile air conditioning (AAC) system using a thermostatic expansion valve was developed. The system was equipped with a coaxial internal heat exchanger (HEX) and charged with R1234yf, a new refrigerant used as an alternative to R134a. The system was tested at the compressor speeds ranging between 1000 rpm and 2600 rpm with increments of 400 rpm. For each compressor speed, the air temperatures at the evaporator and condenser inlets were concurrently changed between 30 °C and 40 °C with increments of 5 °C. The system was operated for the cases of employing and not employing the HEX, and totally 30 test runs were performed. Then, the first law of thermodynamics was applied to the system components to evaluate various steady state performance parameters. The considered parameters were the refrigerant mass flow rate, evaporating temperature, cooling capacity, compressor power, coefficient of performance (COP), condenser heat dissipation rate and discharge temperature of the compressor. It was determined that the experimental system employing the HEX yielded on average 0.8 °C lower evaporating temperature, 2.2% higher cooling capacity, 2.0% lower compressor power and 3.0% higher COP values relative to the system not employing the HEX. These findings reveal that the use of HEX causes a better system performance in terms of the cooling capacity, compressor power and COP. Consequently, the performance of R1234yf AAC systems can be improved with the use of HEX, and thus, the AAC systems using R1234yf can be more competitive with those using R134a.

Experimental assessment of a CO2 direct-expansion solar-assisted heat pump operating with capillary tubes and air-solar heat source

This paper presents an experimental study on a direct-expansion solar-assisted heat pump (DX-SAHP) operating with capillary tubes in a transcritical carbon dioxide cycle. An air-solar dual-source evaporator is also proposed as an alternative to mitigate the performance drop in low solar radiation conditions. The experiments followed a factorial design, considering capillary tubes (number 1 and number 2) and operating schemes (Low Solar Radiation, Low Solar Radiation with fan, and High Solar Radiation) as factors. The results showed that altering from Low Solar Radiation (7 W/m2) to High Solar Radiation (969 W/m2) caused an augment on the heating capacity (58%), on coefficient of performance (from 2.19 to 3.12; 42%), on the refrigerant mass flow rate (35%), and on the degree of superheat (from 4.4 K to 30.6 K). Changing from Low Solar Radiation to Low Solar Radiation with fan, a 17% improvement on the heating capacity was found, with no variation on coefficient of performance. Besides the evaporating pressure, the gas cooler pressure was also sensitive to solar radiation variations. It is estimated that for lower levels of solar radiation, up to 570 W/m2, a single capillary tube could be a reasonable choice for a DX-SAHP. This work aims to be the first to experimentally investigate the use of capillary tubes in a DX-SAHP under solar radiation variations greater than 960 W/m2.

Retarding frosting of an air source heat pump by using vapor-bypassed evaporation technique

• Vapor-bypassed evaporation is firstly used to retard frosting for ASHP applications. • A tested ASHP system that contains two operation modes is established. • Frosting characteristics of the two operation modes are investigated in detail. • Vapor-bypassed evaporation is more suitable for high heating capacity conditions. This paper presents a comparative experimental study on the frosting characteristics of an air source heat pump system that contains two operation modes, i.e., the vapor-bypassed evaporation (VB) mode and the conventional operation (CO) mode. For VB mode, a phase separator is installed inside the evaporator refrigerant circuit to bypass vapor refrigerant, which can increase the average evaporation temperature for retarding frosting by reducing refrigerant pressure drop and decreasing the area of refrigerant inferior heat transfer coefficient region (mist flow region). According to the experimental results, under H2 condition (indoor: 20/15 °C; outdoor: 2/1 °C), as the initial refrigerant mass flow rate ranges 35–45 g / s , the VB mode yields 4.30–7.06% lower frost mass, 3.9–7.3% higher average heating capacity and 6.4–10.8% higher coefficient of performance (COP) over CO mode with the frosting duration of 60 min. Moreover, under H3 condition (indoor: 20/15 °C; outdoor: -7/-8 °C), the frosting duration is set as 100 min, and the VB mode obtains 9.67% lower frost mass, 7.0% higher average heating capacity and 13.3% higher COP over CO mode. Generally, the vapor-bypassed evaporation technique has a great application potential in retarding frosting and improving performance of an air source heat pump system especially under high heating capacity or low ambient temperature conditions.

Influence Of Coiled Wire Presence On The Convective Heat Transfer Coefficients In R-600 Condensers

An experimental investigation has been performed to examine the heat transfer enhancement achieved by helically coiled wire inserts during forced convective condensation of R-600 vapor inside horizontal tubes. The experimental setup is a vapor-compression refrigeration cycle. This system includes a main condenser which is a coaxial double-pipe counter-flow heat exchanger with water as a coolant. To reach the favorable vapor qualities, pre-condenser and after-condenser systems were invoked. Experiments were carried out for plain tube and five different coiled wire inserted tubes. At each test, various parameters were measured like refrigerant mass flow rate, inlet and outlet water temperature of the condenser, refrigerant pressure, etc. Using the acquired data, heat transfer coefficients were calculated for different tubes. Investigation of the results showed that increasing the thickness of the wires can augment the heat transfer rate. Also, it is seen that reducing the coil pitch can enhance the heat transfer rate as high as 31.6%. Also, it was seen that employing coiled wire inserts inside the tube, increases the average heat transfer coefficient up to approximately 80% regarding the plain tube results.

Mass flow rate prediction of direct-expansion solar-assisted heat pump using R290 based on ANN model

A direct-expansion solar-assisted heat pump (DX-SAHP) system using R290 (propane) is studied experimentally. A Coriolis mass flow meter is employed to measure the R290 mass flow rate, and the artificial neural network (ANN) model is used to predict it. Based on numerous experiments, the 5 independent variables are chosen as the input parameters of the ANN model, including the ambient temperature, solar radiation intensity, electronic expansion valve (EEV) opening, compressor frequency and water temperature. The appropriate number of the hidden layer neurons is obtained. The results show that the Mean Relative Error (MRE), Root Mean Square Error (RMSE), and Standard Deviation (SD) of the ANN model are 0.0012, 0.4139 kg h−1 and 0.0447, respectively. Above 97% of prediction results agree well with experimental data within a maximum error of 10%. Furthermore, as the ambient temperature increases, the refrigerant mass flow rate increases. As the solar radiation intensity increases, the refrigerant mass flow rate increases on the whole, and the effect of solar radiation intensity is weakened with the increment of ambient temperature. At a higher level of compressor frequency, the variation in the refrigerant mass flow rate is approximately linear with the ambient temperature, solar radiation intensity, EEV opening or water temperature. With the proposed ANN prediction model, the refrigerant mass flow rate of the DX-SAHP system can be quickly got, which will be very useful in system efficient operation.

The difference between vapor injection cycle with flash tank and intermediate heat exchanger for air source heat pump: An experimental and theoretical study

As a widely used technique, vapor injection plays an important role in air source heat pumps (ASHPs) which operate across a wide range of ambient temperatures. The one of primary solutions has been reported to be vapor injection based on flash-tank (FT) and intermediate heat exchanger (IHX) loops respectively. In this paper, vapor injection and its two typical configurations are experimentally investigated in an ASHP prototype. The results show that in the vapor-injection based ASHPs, the performance of FT based ASHPs is better than that of IHX based ones, and injected vapor improves mass flow rate and distribution of working fluid, with a hidden decreasing effect of exhaust entropy. In order to explore theoretical reasons, a whole system model is presented that quantifies performance enhancement potential of FT based and IHX based ASHPs respectively. The calculation results show increased refrigerant mass flow rate, its optimum distribution, and moderate injected vapor entropy contribute to performance improvement of vapor-injection based ASHPs. Further, we also visualize synergy between refrigerant mass flow and injected entropy from perspective of negentropy. At the negentropy level, FT based rather than IHX based loop brings higher heating capacity and efficiency, which is consistent with measurements from experimental research.

An Investigation on Dehumidification and Heat Transfer Characteristics of a Minichannel Heat Exchanger for Heat Pump System of Electric Vehicles

In this paper, a parallel flow minichannel heat exchanger was experimentally and theoretically studied under various operating conditions. A model of heat and mass transfer was developed and utilized to predict the dehumidification and heat transfer performance of the heat exchanger. The results show that under the operating condition of a low refrigerant mass flow rate, the dehumidification rate increases and then decreases with the increasing inlet airflow with a constant inlet air relative humidity. The lower the refrigerant mass flow rate, the higher the enthalpy humidity ratio when the inlet air humidity and inlet airflow are constant. As the refrigerant mass flow rate and the inlet air relative humidity remain unchanged, the enthalpy humidity ratio decreases as the inlet airflow increases. The results predicted by the proposed model agree well with the experimental results. The absolute errors of the predicted heat transfer rate and dehumidification rate concerning the experimental results are within ±4% and ±10%, respectively. The presented model can be employed for the evaluation of dehumidification and heat transfer performance of heat exchangers for the design and optimization of similar heat pump systems and their components.

Experimental Research on Flow and Heat Transfer in Microchannel with Refrigerant HFO1234yf

An experiment was carried out to study the effect of refrigerant mass flow rate, heat flux density, and saturation temperature on boiling heat transfer coefficient and frictional pressure drop in microchannel. Flow patterns are captured by a high-speed camera. HFO1234yf was used in rectangular microchannels with a hydraulic diameter of 0.5 mm. The results showed that there were eight flow patterns in the experiment, and the change of flow pattern is closely related to the change of heat flux and mass flow rate. The higher the heat flux and mass flow rate, the more the flow patterns appear. Different flow patterns have different heat transfer mechanisms. The heat transfer mechanism is mostly nuclear boiling at the region of bubble flow, slug flow, elongated slug flow, and agitated flow; the heat transfer mechanism is film convection boiling at the region of annular flow, and it is vapor convection at the region of dryout flow. When the dryness is about 0.4, the heat transfer mechanism changes from nuclear boiling to film boiling. The friction resistance decreases with the increase of dryness and saturation temperature.

Experimental investigation on the thermal performance of a water-cooled loop thermosyphon system under fan failure conditions

Fan failure of water-cooled loop thermosyphon system (LTS) is a major factor for thermal safety of data center, thus it is necessary to investigate the effects of fan failures on the thermal performance. In this paper, different operating conditions including normal and eight possible fan failure modes of a LTS are tested at various refrigerant filling ratios. The optimal refrigerant filling ratio is ranged from 55.8% to 74.4% under normal operating condition. Compared with the conditions of leakage (Filling ratio = 46.5%) or overcharge (Filling ratio=83.7%), the LTS has better anti-failure capability with an optimal filling ratio. The cooling capacity at 55.8% filling ratio decreases by 8.2–10.1% and 20.8–23.8% under mild and serious fan failure modes, respectively, and the decrements increase with the filling ratio increasing. This is because the additional refrigerant mass flow rate increases with the filling ratio increasing, which increases the total system thermal resistance. However, the cooling capacity at the minimum optimal filling ratio (55.8%) is only 9.6% larger than that at the maximum optimal filling ratio (74.4%) under the worst fan failure condition. Considering the universality of the slight refrigerant leakage in refrigeration systems, it is better to choose a high optimal filling ratio to ensure the good operating performance and anti-failure capability of LTS.

Buhar Sıkıştırmalı Soğutma Sisteminde R22 Alternatifi Soğutucu Akışkanların Termodinamik Analizi

Bu çalışmada, soğutma sistemlerinde yaygın olarak kullanılan R22 soğutucu akışkanına alternatif ve ozon tabakasına dost R417A, R438A, R422A ve R422D soğutucu akışkanlarının performansları termodinamiğin birinci ve ikinci yasasına göre incelenmiştir. Buhar sıkıştırmalı çevrimin tasarımı için Chemours Refrigerant Expert 1.0 programı kullanılmıştır. Yapılan analizlerde yoğuşma sıcaklığı sabit (50 ºC) tutulurken, evaporasyon sıcaklıkları EUROVENT şartlarına göre (0 °C, -8 °C, -25 °C, -31 °C) belirlenmiştir. Farklı evaporasyon sıcaklıklarına göre hesaplanan parametreler, gerekli kompresör gücü, performans katsayısı (COP) ve gerekli soğutucu akışkan kütle akış oranıdır. Sonuçlar, R438A ve R417A soğutucu akışkanlarının COP değerlerinin R22’ye çok yakın olduğunu göstermiştir. R22 soğutucu akışkanına göre COP değerleri, R438A’da %5, R471A’da %6, R422A’da %15 ve R422D’de %10 düşük olmuştur. Bu değerler R422D için %13 ve R422A için ise %17 olarak hesaplanmıştır. Analiz edilen sistemlere ait en yüksek ekserji verimi, -25 °C evaporasyon sıcaklığında R438A için %31.74, R417A için %31 ve R422A için %27.46 ve R422D için ise %29.24 olarak hesaplanmıştır. Çalışmanın sonunda, R22 soğutucu akışkanına alternatif olarak geliştirilen R417A, R438A, R422A ve R422D akışkanlarından, R438A akışkanının daha yüksek COP değerlerine sahip olduğu belirlenmiştir. Ayrıca kondenser ve kompresör yükleri incelendiğinde en iyi sonuçları sırası ile R438A, R417A, R422D ve R422A akışkanlarının verdiği görülmüştür. Genel olarak incelen 4 alternatif akışkandan R438A ve R417A’nın, COP, ekserji verimliliği, ekserji yıkımları açısından R22 için daha iyi bir alternatif olacağı belirlenmiştir

Energy and exergy analysis study of heat exchanger in a refrigeration system with different lengths of capillary tube

An experimental study was conducted to demonstrate the effect of the capillary tube length on the refrigeration system performance by adding heat exchanger. The heat exchanger was designed by welding 70cm of the capillary tube with the suction line laterally, which included different lengths of the capillary tubes are 160, 175, 190cm. Besides, the experimental part has been tested at different refrigerant flow rates and air fan velocities of the condenser for each case of the adiabatic and nonadiabatic capillary tube. The experimental results showed an increase in the system performance by 17.96% with a decrease in capillary tube length from 190 to 160 cm for the nonadiabatic capillary tubes at the mass flow rate was 17.3kg/hr and air velocity 3m/s. In addition, the increase in the air-speed of condenser has led to elevate COP by 17.47% at the mass flow rate of 18.9 kg/hr and the capillary tube length of 190 cm. Finally, at the capillary tube length 190cm and refrigerant mass flow rate 2.4g/s is achieved the maximum enhancement of the refrigeration system performance and exergy efficiency by 6.7% and 35% at airspeed 1m/s and 3 m/s respectively compared to the reference one of the adiabatic capillary tubes.

Study of effect of geometrical and thermodynamic variables on the performance of condenser in an organic rankine cycle

The study focusses on parametric optimization of condenser used in Organic Rankine Cycle (ORC) to recover waste heat from industrial exhaust. The thermal properties of R245fa are obtained from REFROP-9.0 and the calculation as per the mathematical model has been carried out using MATLAB 2019. Effect on variables is studied on the total heat transfer surface area and cost with channel distance, width of channel, length of the plate, mass flow rate and velocity of refrigerant. Furthermore, effect of mass velocity of refrigerant is studied and the trade-off between the two objective function is presented. The trends observed in the results are presented where there is a trade-off between cost and the total area of heat exchanger. The mass flow rate and mass velocity have significant effects on optimizing design of condenser because a small change results in huge changes in the area of heat exchanger and cost, whereas channel distance, channel width, velocity and mass velocity of R245fa have less effect. The mass flow rate of R245fa has a promising effect in optimizing design of condenser for a minimum value of 3.5 kg/s, the change in the value of the area is 90 m2 and 12,500 euros in cost. Similarly, when the parametric factor of mass velocity is around 120 kg/m2 s, minimal cost is attained and the area observed is around 86 m2 whereas maximum cost of 11,800 euros is seen at mass velocity of 40 kg/m2s.