Refrigerant Pressure Research Articles

Pengembangan Freeze Vacuum Drying Dengan Sistem Kendali Menggunakan Reverse Valve

The post-harvest handling process for rice aims to reduce the water content of rice grain, one of which is using the drying method. To maintain the quality of grain, evaluation and corrections are needed in handling so that losses can be minimized. Mechanical drying methods such as freeze drying are an effective vacuum solution, because they combine freeze drying and vacuum drying which have advantages in efficiency and quality of results. This vacuum dryer prototype has a maximum capacity of 10 kg of rice, the refrigerant used is R-134a, and the vacuum pressure that can be achieved is 5 bar below atmospheric pressure. This research will use variations in mass of 1 kg, 5 kg, and 10 kg, then the mass of 10 kg will be varied with refrigerant pressure of 14 bar, 15 bar, and 16 bar. The results of this test are that for the mass variation of 1 kg the air content that can be removed is 89% for 12.1 hours, for the mass of 5 kg the air content that can be removed is 85% for 15.3 hours, and for the mass of 10 kg the air content that can be removed is 76% for 17.5 hours. For variations in refrigerant pressure at a pressure of 16 bar 78% of the air content is lost for 19.8 hours, 15 bar 76% of the air content is lost for 19 hours, and 14 bar 62% of the air content is lost for 18 hours

Experimental study on flow boiling and circumferential non-uniform heat transfer characteristics in helically-coiled tube under coupled heat transfer conditions

Experimental study on flow boiling and circumferential non-uniform heat transfer characteristics in helically-coiled tube under coupled heat transfer conditions

An experimental investigation on the role of the operating time of the mist device on the thermal performances of a water-sprayed air-cooled condenser and on the energy consumption of the cooling system

An experimental investigation on the role of the operating time of the mist device on the thermal performances of a water-sprayed air-cooled condenser and on the energy consumption of the cooling system

On the influence of the refrigerant inlet position and circuitry layout on plate-finned tube evaporator performance through the hybrid method

Abstract Multiple factors can impact the performance of a plate-finned tube evaporator in terms of heat transfer rate and refrigerant pressure drops, including the circuitry layout and the position of the refrigerant distributors. In order to assist designers, various circuitry layout alternatives together with different refrigerant inlet positions were examined in this work, using the hybrid method to calculate the evaporator performance. Based on prediction functions coming from the outcomes of either numerical, analytical, or experimental analysis, the hybrid method has the advantage of combining affordable computing costs with accurate findings. Moreover, the refrigerant inlet position can cause uneven vapor quality entering the various circuits. This characteristic, along with the variation in flow rates it implies, was also examined to investigate their influence on the heat exchanger’s performance.

A Comparative Analysis of Machine Learning Techniques for Predicting the Performance of Microchannel Gas Coolers in CO2 Automotive Air-Conditioning Systems

The automotive industry is increasingly focused on developing more energy-efficient and eco-friendly air-conditioning systems. In this context, CO2 microchannel gas coolers (MCGCs) have emerged as promising alternatives due to their low global warming potential (GWP) and environmental benefits. This paper explores the application of machine learning (ML) algorithms to predict the thermohydraulic performance of MCGCs in automotive air-conditioning systems. Using data generated from an experimentally validated numerical model, this study compares various ML techniques, including both linear and nonlinear regression models, to forecast key performance metrics such as refrigerant outlet temperature, pressure drop, and heat transfer rate. Spearman’s correlation was employed to develop performance maps, whereas the R2 and MSE metrics were used to evaluate the models’ predictive accuracy. The linear models gave around 70% forecasting accuracy for pressure drop across the gas cooler and 97% accuracy for refrigerant outlet temperature, whereas the nonlinear models achieved more accurate predictions, with an accuracy ranging from 71% to 99%. This implies that nonlinear regression generally performs better than linear regression models in assessing the overall thermohydraulic performance of microchannel gas coolers. This research brings forth new ideas on how ML methods can be applied to enhance efficiency and effectiveness in gas coolers, contributing to the development of more eco-friendly automotive air-conditioning systems.

An experimental investigation on frosting characteristics and performance of microchannel evaporators with varied aspect ratios

An experimental investigation on frosting characteristics and performance of microchannel evaporators with varied aspect ratios

Experimental study on startup characteristics of instant heat pump water heater with non-azeotropic natural blend

Experimental study on startup characteristics of instant heat pump water heater with non-azeotropic natural blend

Experimental investigation and simulation on dynamic precipitation characteristics of R32-lubricating oil mixture in heat pump systems

Experimental investigation and simulation on dynamic precipitation characteristics of R32-lubricating oil mixture in heat pump systems

Two-phase lubrication characteristics of journal bearing in refrigerant-oil system under high-pressure environment considering gaseous cavitation

Two-phase lubrication characteristics of journal bearing in refrigerant-oil system under high-pressure environment considering gaseous cavitation

Performance evaluation of ecofriendly R1234ze(E) refrigerant in an automotive air conditioning system

AbstractA mathematical model for an air conditioning system used in five‐seater cars is developed with R1234ze(E) and R134a refrigerants, consisting of real system geometry like an evaporator, compressor, condenser, and thermostatic expansion valve. The mathematical model includes refrigerant properties, heat transfer, and pressure loss correlations for two‐phase and single‐phase regions. The performance parameters of a system like evaporator cooling duty, condenser heat loss, compressor power, refrigerant flow rate, and compressor volumetric efficiency obtained from a mathematical model are validated with the results of an experimental facility developed with R134a. The uncertainty analysis performed for the testing facility showed below 11% deviation. The simulation and experimental results showed an overall 10%–15% difference. It is found that the experimental cooling capacity with R134a and numerical cooling capacity with R134a show a 4%–12% variation, experimental cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 7%–20% variation, and numerical cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 5%–15% variation for the given range of compressor speed (500–1500 rpm), and condensing temperature (26–45°C). The study concluded that R1234ze(E) could potentially replace R134a because it has similar thermophysical properties and an average performance difference of up to 10% with R134a. Due to the limitations of the electric motor used to drive the compressor, tests in the current study were conducted at modest compressor speeds (500–1500 rpm). Future research will focus on experiments with high compressor speed (in the range of 1500–4000 rpm) and R1234yf and R1234ze(E) refrigerants for performance evaluation of automobile air conditioning systems.

Recent progress in pool boiling heat transfer of low GWP refrigerants with the effect of POE lubricant oil

Recent progress in pool boiling heat transfer of low GWP refrigerants with the effect of POE lubricant oil

Generalizability of machine learning-based fault classification for residential air-conditioners

Residential air-conditioning systems are subject to soft faults, which can reduce their efficiency, capacity, and life expectancy, without being detected by the occupants. Early detection and diagnosis of faults could potentially be done by using machine learning (ML) on measurable features of the air-conditioner, such as refrigerant temperatures and pressures. This paper describes a novel approach to applying ML, which is to train a fault classifier using data from one system, and apply it to different systems. If this is effective, it can significantly reduce the cost of widescale application of ML fault classification. The support vector machine (SVM) algorithm was used. An additional question for practical application is whether the number of sensors required for input feature measurement can be reduced. This work also tests the feature reduction effect, in combination with applying an ML classifier trained on one system, to classify faults in two other systems. The results are disappointing, showing that fault classification is poor when the SVM classifier is trained on a different system than it is applied to. However, with additional work, this method has potential for improvement, possibly to a point where it can be a viable approach for field deployment.

Improving performance of air conditioning system by using variable-circuit heat exchanger: Based on the Chinese APF standard

Improving performance of air conditioning system by using variable-circuit heat exchanger: Based on the Chinese APF standard

Experimental Study on the Feasibility of Quick Startup of Instant Heat Pump Water Heaters Based on Active Control of Heat Sink Flow Step

The influence of flow step ratio (FSR) on the startup characteristics of instant heat pump water heaters (IHPWHs) with natural mixture M (R744/R290 (12/88)) under nominal conditions was studied experimentally to verify the feasibility of a new quick startup method. The results show that the FSR had a marked effect on the startup time of system performance parameters. Under the optimal FSR of 0.6, the shortest system startup time and available hot water supply time were 700 s and 250 s, respectively, which were markedly shorter than those in the conventional startup. Therefore, rapid startup of the system and rapid production of usable domestic hot water can be realized by controlling the flow step. The influence of flow step on the variation trend of system performance parameters was obviously different, and there was no slow warming section for the heat sink outlet temperature (HSOT) under three FSRs. The HSOT, heating capacity, and high pressure side pressures had the maximum values in the quick startup, and the maximum values were obviously affected by the FSR. The FSR had no marked effect on the minimum suction pressure. The refrigerant pressures and refrigerant temperatures fluctuated markedly in both rapid and conventional starts.

Experimental study of refrigerant condensation heat transfer and pressure drop in horizontal tubes with full and partial coiled wire inserts (CWIs)

Experimental study of refrigerant condensation heat transfer and pressure drop in horizontal tubes with full and partial coiled wire inserts (CWIs)

Development of In Situ Refrigeration Cycle Measurement Method Using Air-Side Data of Air Source Heat Pump

The refrigeration cycle of an air source heat pump system is an important information that reveals critical operating data, such as the cooling capacity, power consumption, and performance of a system during operation. Operating data, such as refrigerant pressure and enthalpy in situ, can be difficult to measure. Therefore, this study developed an in situ refrigeration cycle measurement method using the airside data of an air source heat pump. A method for measuring the refrigeration cycle is proposed using the characteristics of evaporation, compression, condensation, and expansion processes. The distance function was analyzed by normalizing the difference between the refrigerant pressure and enthalpy of the existing and proposed measurement methods. In addition, the distance function for the maximum error of the pressure and enthalpy measurement devices was analyzed and compared with the distance function of the entire data used in the evaluation. All the evaluation data had low distance function values with a maximum difference of 5%, confirming the reliability of the proposed refrigeration cycle measurement method. The power consumption and calculated COP were also evaluated using the proposed method. The Mean Bias Error (MBE) of power consumption and COP were 0.15% and 0.04%, and the coefficient of variation of root-mean-square error (CvRMSE) was 8.967% and 7.14%, respectively.

CO2 reverse cycles equipped with a bladeless turboexpander

CO2 reverse cycles equipped with a bladeless turboexpander

Experimental study on dynamic thermal characteristics of novel thermosyphon with latent thermal energy storage condenser

Experimental study on dynamic thermal characteristics of novel thermosyphon with latent thermal energy storage condenser

Numerical and Experimental Investigation of Flow Characteristics in a Fluid Self-Lubricating Centrifugal Pump with R134a Refrigerant

With the rapid development of information technology, researchers have paid attention to the pump-driven two-phase cooling loop technology for data centers, which imposes requirements on the efficiency and size of the pump. A fluid self-lubricating centrifugal pump with R134a refrigerant was developed to reach a higher rotation speed and oil-free system, resulting in a more diminutive size. Due to the high rotation speed and refrigerant pressure approaching saturated vapor pressure, the internal flow characteristics and cavitating characteristics are critical and complex. This paper focuses on the prototype’s head and cavitation performance based on experimental and numerical data. The experiments indicated that the head coefficient of the pump under design conditions is 0.9881, and the pump’s critical cavitation number and breakdown number are 0.551 and 0.412, respectively. The numerical results can predict the head and cavitation with deviations less than 2.6%. To study changing patterns in flow characteristics under the different operating conditions in the refrigerant centrifugal pump, the numerical model based on a modified Sauer-Schnerr cavitation model was built to analyze the distributions of pressure, temperature, relative velocity, and bubble volume across every hydraulic component and different degrees of cavitation, and proposed the influence of the thermal effect on refrigerant cavitating. The cavitating flow characteristics were obtained with the aim of providing guidance for the hydraulic design of a refrigerant centrifugal pump.

Experimental study of compressor electric current detection for a split-type air conditioner affects energy savings

The paper presents an experimental study that aims to measure the compressor electric current of a split-type air conditioner for analyzing the various abnormal condition of the R-32 refrigerant pressure, especially for detecting compressor electric current while occurring dirt in the evaporator coil and condenser coil. The method was to install sensor devices to measure the temperature and humidity of inlet air and outlet air, and the velocity of the air outlet of the evaporator unit. In condenser unit was to measure the electric current compressor and electric power input. All data from sensors send to the Arduino board and using Parallax Data Acquisition (PLX-DAQ) Excel Macro for the record. The results show physical behavior and the changing of compressor electric current according to the abnormal condition of the refrigerant system, blocking of condenser and evaporator coil.