Accelerated Degradation Test on Electric Scroll Compressor Using Controlled Continuous Liquid Slugging

Integrating advanced control technologies to enhance energy efficiency and environmental sustainability in heat pump systems is of growing significance. This article offers a comprehensive review on the utilization of Proportional-Integral-Derivative (PID) control and Variable Frequency Drive (VFD) technology to govern the compressor's operation in a heat pump. The primary objective is to optimize energy consumption and thermal output under varying loads and environmental conditions, thus enhancing the heat pump's performance. The article delves into the fundamental principles of heat pump operations, emphasizing the compressor's pivotal role in maintaining the delicate balance between energy consumption and desired thermal output across applications, spanning residential HVAC to industrial processes. The PID control algorithm is introduced to adapt the compressor's speed and power consumption dynamically. The VFD is incorporated into the control system, enabling variable speed compressor operation for a responsive reaction to load fluctuations. Combining PID and VFD control is explored to achieve peak system performance and energy efficiency. Through practical experiments and simulations, the research investigates the influence of PID and VFD control on energy efficiency, stability, and performance. The results underscore substantial energy savings and environmental impact reduction potential, particularly in scenarios with variable thermal loads and fluctuating environmental conditions. This study advances our understanding of advanced control strategies in heat pump technology and underscores the pivotal role PID and VFD control play in creating energy-efficient heating and cooling solutions. The findings offer practical implications for diverse applications, from residential settings to industrial processes, and provide insights into sustainable heat pump technology use in the context of energy conservation and climate change challenges.

Dehumidification and heating of electric vehicle heat pump systems are of significance in ensuring comfort and safety in winter. This study purposes to investigate the dehumidification and heating performances of a new-designed heat pump system. A numerical model is established and serves for analyzing the ventilation conditions for dew or fog removal of the windshield. Both ventilation conditions of the heat pump and the inner surface temperature of the windshield were investigated as per experimental measurements. Meanwhile, dehumidification rates, effective heating capacity, and coefficients of performance were analyzed under different operating conditions. It is shown that the heat-pump’s air outlet conditions are within the range of suitable ventilation conditions meeting the needs of dew or fog removal. At the same compressor speed, the inlet air humidity of the evaporator inlet decreases, the dew or fog removal is more effective, and the coefficient of performance for heating increases but the coefficient of performance for dehumidification decreases. In the case of the same inlet air humidity, the dew or fog removal effect is better with increasing compressor speed; Meantime, the coefficient of performance for heating and dehumidification both decrease. The lower compressor speed and lower inlet air humidity for the evaporator enable the heat pump system to meet the demand for dew or fog removal of the windshield and ensure thermal comfort in the cabin. This study verifies the effectiveness of heat pump systems for dehumidification and heating and would be valuable to promote heat pump systems.

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1). Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3). The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency. The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions. The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet. The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices. The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.

Experimental study of propane heat pump system with secondary loop and vapor injection for electric vehicle application in cold climate

An automotive air conditioning and heat pump (AAC/AHP) system employing refrigerants R134a and R1234yf was developed and tested in cooling and heating operation modes under broad ranges of compressor speed and air inlet temperature conditions. Using test results, various energetic and exergetic performance parameters of the system were evaluated and compared. The R1234yf system provided on average 5.8% lower cooling capacity, 0.2% higher heating capacity, 11.9% lower COP for cooling and 3.6% lower COP for heating relative to the R134a one. Furthermore, the exergetic efficiency of the R1234yf system were on average 17.6% and 14.7% lower compared to the R134a one in cooling and heating modes, respectively. The major contributor to the exergy destruction in the system is the compressor for both refrigerants and operation modes. These results reveal that R1234yf performs better in heating relative to cooling mode, and it can be used as a replacement for R134a in not only AAC but also AHP systems in expense of slightly lower energy effectiveness.

Micro compressed air energy storage systems are a research hotspot in the field of compressed air energy storage technology. Compressors and expanders are the core equipment for energy conversion, and their performance has a significant impact on the performance of the entire compressed air energy storage system. Scroll compressors have the advantages of small size, low noise, light weight, low vibration, long service life, continuous and stable gas transmission, and reliable operation. This article builds a micro compressed air energy storage system based on a scroll compressor and studies the effects of key parameters such as speed, torque, current, and storage tank pressure on the temperature difference, pressure ratio, energy consumption, and efficiency of the scroll compressor. The experimental results indicate that the power consumption of the scroll compressor shows an increasing trend with the increase in current, torque, and gas storage tank pressure. The isentropic efficiency of a scroll compressor shows a decreasing trend with increasing current, torque, and storage tank pressure. The maximum values of power consumption and isentropic efficiency of the scroll compressor are 3427 W and 90.8%, respectively.

Performance assessment of a range-extended electric vehicle under real driving conditions using novel PCM-based HVAC system

Frequent online water wash of Gas turbine compressor is a critical activity to sustain the site-corrected compressor isentropic efficiency after each offline water wash in dusty environment of Middle East. Higher frequency of online water wash impacts the compressor efficiency, compressor pressure ratio, power output, heat rate, exhaust flow and exhaust temperature of Gas Turbine. At one of the CCPP sites of ACWA Power, HDGT OEM requested to change the online water wash frequency from three times a week to once a week. The reason behind this request was compressor blade erosion due to higher droplet sizes of online water wash spraying circuit. This investigation is an effort to estimate how the frequency of online water wash impacts the isentropic efficiency of the compressor for two different scenarios having different frequencies of online water wash. The first scenario was a one-time online water wash per week with a water rinsing cycle and once a month with detergent cycle. The second scenario was with three-times online water washes per week; two with a water rinsing cycle and one with detergent cycle. Various parameters related to compressor performance were compared e.g. ISO-corrected compressor isentropic efficiency, compressor discharge temperature, compressor pressure ratio, exhaust temperature, exhaust temperature, exhaust temperature, exhaust flow, corrected power output and corrected heat rate. The impact on bottoming cycle due to shift in improved exhaust flow due to better compressor performance was also captured. During the investigation, it was identified that the higher frequency of online water wash contributed to sustaining the compressor efficiency for longer periods. By shifting the frequency of online water washing from once a week to three times a week, the GT output was improved by 2MW at similar operating conditions.

Vapor injection enthalpy-enhanced technology is key to addressing the issues of heating capacity degradation and energy efficiency reduction in heat pumps under low-temperature conditions. Against this backdrop, this paper focuses on resolving the challenge of excessively elevated discharge temperatures in heat pump systems during low-temperature operation. A thermodynamic model is constructed to analyze the influence of vapor injection parameters in superheated and two-phase states on compressor performance. An experimental platform for vapor injection scroll compressors was built. The vapor injection state was regulated using electric heaters, and the system performance under different refrigerant injection state levels was compared and analyzed. This study shows that during superheated vapor injection, with the increase of injection temperature, the main branch flow rate, total mass flow rate, and heating capacity slightly decrease, while the coefficient of performance (COP) increases. During two-phase vapor injection, with the increase of injection quality, the injection mass flow rate increased by 55.87% within the injection quality range of 60%–90%, and the heating capacity increases by 3.72%. Compared with the experimental data, the simulation errors of the two types of vapor injection are controlled within 10% respectively. Additionally, the injection point near the suction chamber enhances mass flow rate and heating capacity but increases power consumption and lowers COP, while the injection point near discharge chamber yields opposite trends. Based on these findings, injection strategies for different application scenarios are also proposed.

Centrifugal compressor plays a vital role in the performance of a turbocharger. The compressor contains an impeller and housing, including the vaneless diffuser and a volute. The high-speed flow from the impeller is diffused in the diffuser and volute, before being delivered to the engine. Hence, the housing flow characteristics affect the compressor performance and operating range. Generally, housing has noticeable surface roughness, especially in the volute. This study evaluates the effect of the volute surface roughness on the compressor performance by experimental and numerical analysis. The experiments are conducted for three different volute surface roughness levels to measure the overall compressor pressure ratio and efficiency. The uncertainty in the efficiency for experimental results is within ±0.5% pts. Also, steady-state numerical simulations are performed to analyse the flow mechanisms causing pressure losses. Then, a numerical analysis is done to understand the effect of roughness of the diffuser hub and shroud walls on the compressor performance. From the experimental results, it is found that the increase in the roughness level of the volute from the smooth surface by circa 900% and 1400% shows a significant reduction in the compressor efficiency at the design speed (N) and off-design speeds (0.87 and 1.13 N). The reductions of efficiency are about 0.5%–1% pts at the near surge point, 1%–1.5% pts at the peak efficiency point and 2%–2.5% pts at the near choke flow point. The CFD analyses show significantly higher near-wall turbulence and wall shear resulting in additional pressure losses. Also, it is found that the pressure losses are more sensitive to roughness of the diffuser shroud-wall than that of the hub-wall. On the other hand, the diffuser hub-wall roughness increases the radial momentum in the diffuser passage which suppress the flow separation at low flow rates.

The performance of a system consisting of a proton exchange membrane (PEM) fuel cell coupled to a centrifugal air compressor is simulated. Two modes of operation of the system are investigated: one in which the speed of the compressor is constant, and the other in which the compressor speed is varied with the electric load on the fuel cell stack. The operating characteristics of the compressor and the PEM fuel cell stack and their influence on the system efficiency are analyzed for a step change in the stack current. The effects of the fuel cell stack back-pressure and the electric load on the compressor power consumption and the system efficiency are studied. It is found that the system efficiency is higher when the fuel cell stack is operated at a constant oxygen gas stoichiometry by varying the compressor speed instead of at a constant compressor speed. The system model can be used to determine the rotation speed of the compressor for various electric loads.

This paper investigates the control-oriented modeling for turbofan engines. The nonlinear equilibrium manifold expansion (EME) model of the multiple input multiple output (MIMO) turbofan engine is established, which can simulate the variation of high-pressure rotor speed, low-pressure rotor speed and pressure ratio of compressor with fuel flow and throat area of the nozzle. Firstly, the definitions and properties of the equilibrium manifold method are presented. Secondly, the steady-state and dynamic two-step identification method of the MIMO EME model is given, and the effects of scheduling variables and input noise on model accuracy are discussed. By selecting specific path, a small amount of dynamic data is used to identify a complete EME model. Thirdly, modeling and simulation at dynamic off-design conditions show that the EME model has model accuracy close to the nonlinear component-level (NCL) model, but the model structure is simpler and the calculation is faster than that. Finally, the linearization results are obtained based on the properties of the EME model, and the stability of the model is proved through the analysis of the eigenvalues, which all have negative real parts. The EME model constructed in this paper can meet the requirements of real-time simulation and control system design.

Experimental performance analysis of a direct-expansion solar-assisted heat pump water heater with R134a in summer

The continuous demand for oil and gas forces the petroleum industry to develop new and cost-effective technologies to increase recovery from new fields and enhance extraction from existing fields. Subsea wet gas compression stands out as a promising solution for increasing production capacity, utilizing remote regions and reducing costs. A prerequisite for successful oil and gas production utilizing subsea wet gas compressors is operability. This includes the system’s ability to cope with operational changes, without having to shut down. One of the fundamental operational changes is the liquid content in the inlet pipe, which may fluctuate considerably at certain time intervals. The current study investigates how changes in liquid content impacts compressor performance. An experimental test campaign has been performed at the Norwegian University of Science and Technology (NTNU). The test facility is an open loop configuration consisting of a single shrouded centrifugal impeller, a vaneless diffuser and a symmetrical circular volute. The main objectives were to document how the presence of liquid impacts the compressor characteristics and further, how the operating point moves within the characteristics when solely subjected to an increase of liquid content. The compressor was exposed to liquid contents ranging from gas mass fraction 1.0 to 0.60. The test reveals that the compressor pressure ratio at wet conditions is higher in comparison to dry conditions. Care should be taken when analysing stability and surge margins at variations in fluid liquid content. Further, the compressor behaves in a predictable manner, revealing several linear trends, when subjected to stepwise changes in liquid content from a fixed operating point.

Helical coils of the Large Helical Device (LHD) are large scale superconducting magnets for fusion plasma experiments. The cooling system was upgraded in 2006 to improve the cryogenic stability of the coils by subcooling supplied helium. After the upgrade, the subcooled helium of designed mass flow rate of 50 g/s at designed temperature of 3.2 K has been supplied to the coils stably during steady state subcooling operations. The supplied helium is subcooled at a heat exchanger in a saturated helium bath. A series of two centrifugal cold compressors are utilized in the subcooling system to reduce the bath pressure and temperature. It is necessary to operate the cold compressors within a range of appropriate mass flow rate in order to escape from surge and choke. When the rotational speed of the cold compressors increased/decreased, the mass flow rate of the cold compressors varied. Thus, it is important to comprehend the transient performance of the cold compressors in those cases and to control the mass flow rate for the purpose of the safe operations. In the present study, the characteristics of the system were investigated and automatic operating methods with a heater in the bath and a bypass valve were developed during the change of the rotational speed of the cold compressors. Consequently, the reliable subcooling operations of the system have been achieved over 6,000 hours for three years.