Thermal Expansion Valve Research Articles

Numerical modeling of heat transfer mechanism in remote sensing bulb of thermal expansion valves

Thermal management of automotive systems has garnered a lot of focus in recent times to improve the energy efficiency of vehicles and address the challenge of global warming. In combustible fuel vehicles, the heat pump compressor is driven by the engine power which leads to changes in operating condition of the cycle while the vehicle is in motion. In electric vehicles, a combined thermal management strategy handles both cabin and battery pack cooling/heating depending on the ambient conditions and power requirements by adjusting refrigerant flow rates and flow directions with sophisticated valves. Irrespective of the vehicle type, effective variable refrigerant flow control is prerequisite to ensure optimum thermal comfort with minimum energy. Thermal expansion valves (TXV) are the most widely used method for regulating mass flow rate of refrigerant during the expansion step of the vapor compression cycle based on the principle of trying to maintain a fixed degree of superheat at the evaporator outlet. Conventional models of the thermal expansion valve ignore the time lag between fluctuation of temperature at the evaporator outlet and the corresponding change in pressure of the TXV remote sensing bulb, treating the valve as an instantaneous element during transient operation. This paper presents a novel method for determining the temperature profile and time constant of the remote sensing bulb response using numerical methods, in an attempt to capture the dynamics of thermal expansion valve in active heat pump cycle. Finite difference method was used to solve for the conduction heat transfer between the bulb and the heat exchanger outlet tube in perfect thermal contact applying the necessary boundary conditions. This improved modeling approach will be helpful in better prediction of the dynamic behavior of thermal expansion valves and how it influences the evaporative heat exchanger performance during transient operations to determine control algorithm and strategies.

Relationship of flow pattern, vibration, and noise in automobile refrigerant system and flow pattern identification based on convolutional neural network

In recent years, the flow-induced vibration and noise in automotive refrigerant system gradually become the main factor affecting driving comfort. However, the relationship of flow pattern, vibration, and noise is not clear, and pattern identification is not easy but necessary. In this paper, a series of experiments are conducted to investigate the relationship of flow pattern, flow-induce vibration, and noise near the thermal expansion valve in an automobile refrigerant system. The flow pattern, vibration, and noise are closely related to startup processes. Mist flow, which contains more mist two-phase mixture than transition flow and wispy-annular flow, leads to the largest amplitude of vibration and strong broadband hiss noise. Moreover, the increase in compressor speed promotes the pattern transition and the vibration amplitude in time domain but has no effect on the distribution of vibration peaks in frequency spectrum. Finally, a short-time Fourier transform and convolutional neural network combined method for flow pattern identification is developed based on the relationship of flow pattern and flow-induced noise. After using transfer learning and data augmentation, four trained network architectures show relatively high accuracy above 94% for test set. Among them, ResNet34 not only has the highest accuracy of 98.8% but also can recognize each type of flow pattern. The generalization of this method can help engineers to recognize flow patterns in air conditioning without flow visualization but only need to measure sound signals.

Performance Analysis of an Ejector-Enhanced Heat Pump System for Low-Temperature Waste Heat Recovery Using UHVDC Converter Valves

This article proposes a heating method based on heat pump technology to address the large amount of low-grade waste heat generated by a certain type of ultra-high voltage direct current (UHVDC) converter valve. Thermal performance calculations for two systems, a basic vapor compression heat pump system (BVCHPS) based on thermal expansion valve throttling and an ejector-enhanced heat pump system (EEHPS) are analyzed. The research results show that the EEHPS exhibits superior COP and exergy efficiency when generating hot water above 80 °C using a heat source below 50 °C. Additionally, mathematical modeling analysis identifies optimal structural parameters such as nozzle throat diameter, throat area ratio, and nozzle outlet diameter for the ejector in its design state. The low-temperature waste heat recovered from the UHVDC converter valves can be further used in engineering applications such as heating, refrigeration, seawater desalination, and sewage treatment.

A Lab-scale HVAC Hissing-type Noise Characterization with Vehicle System Validation

Heating, ventilation and air conditional (HVAC) system provides a cold ventilation for the comfort of the driver and passengers in a vehicle. However, the vibration induced by the HVAC contributes to a reasonable level of noise emission, and hissing is one of the critical noises. So far, the characterization of hissing noise from the vehicle is least to be reported compared to other type of noises. Hence, this paper investigates the occurrence of hissing noise from several HVAC components. A lab-scale HVAC system was developed to imitate the real-time operations of the vehicle HVAC system. Two engine conditions, namely as ambient and operating conditions, were tested at speed of 850 rpm and 850–1400 rpm, with the blower speed maintained constantly at one level. The result shows that the hissing noise from the labscale HVAC was produced at frequency range of 4000–6000 Hz. The finding also highlights that the main component contributors of noise emission are an evaporator and a thermal expansion valve. The validation with a real vehicle system showed a good consensus whereby the hissing noise was produced at the similar operating frequency ranges. Also, the hissing noise was found to be louder when in an operating condition which could be taken into consideration by the vehicle manufacturers to improve the HVAC design.

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.

Dual-valved skin-interfaced microfluidic device for programmed time-control sweat collection

Biomarkers in human sweat can provide valuable insights into physiological states, identify diseases, and help clinicians understand patients without invasive measurements. However, obtaining accurate long-term data from sweat using current sweat collection methodology raises doubts. Here, we describe a soft-bioelectronic platform that uses a thermal expansion valve to collect sweat under programmed time control. By incorporating expandable microspheres, the skin-interfaced microfluidic device platform merges capillary burst valves and irreversible-thermal expansion valves. An expansion layer below the microfluidic channels expands irreversibly upon heat delivery from underlying microheaters. The thermal expansion valve isolates the collected sweat into separate chambers to minimize internal mixing. The human study demonstrates that our novel time-programmed sweat collection device improved sweat analyte data (sweat volume, pH, lactate, and cortisol) from the conventional sweat collection. In addition, the human study results indicate a correlation between sweat rate and sweat lactate with aerobic and anaerobic exercises. Our approach can be integrated with past and current microfluidic systems and other chemical sensing modalities, such as colorimetric and electrochemical measurements of sweat analytes present in current sweat devices for advanced on-board diagnostics.

Refrigerant overheating in the compression circuit air heat pump

The authors considered the processes of phase transformation of the working fluid in the compression unit of the freon circuit in the section “thermal expansion valve (TEV) - evaporator - compressor”. By adjusting the expansion valve under the conditions of the bubble mode of boiling of the refrigerant, the evaporation process takes place, accompanied by the achievement of a certain excess of steam temperature. Determination of rheological parameters (droplet size, vapor viscosity, refrigerant droplet vaporization rate) is necessary so that when moving from the throttle valve (TEV) to the compressor inlet, they have time to go into the vapor phase or return to the mass of boiling liquid. The article presents the results of an analytical calculation of the parameters of the kinetics of evaporation of Freon droplets as they move in a steam flow. The results of such an analysis make it possible to formulate requirements for the optimal droplet size in the created vapor-liquid mixture in order to ensure their maximum evaporation and the required thermal efficiency of the AHP as a whole. The established patterns of evaporation of refrigerant droplets can be used to select the design and operation of the AHP.

Thermodynamic, economic and environmental assessments of a novel solar-driven combined cooling and power system

The present study investigates an improved design of a solar-driven combined cooling and power system based on energy, exergy, economic and environmental perspectives. It includes evacuated tube collector, thermal energy storage, vapor generator, condenser, evaporator, ejectors, turbine, pump, heat exchanger and expansion valve. It is compared with the same capacity's individual cooling and power system. Effects of operating temperatures, component efficiencies, seasonal climate change and cooling-to-power ratio are also investigated. At the typical operating conditions with isobutene, the novel cycle has a performance index of 0.08 and overall exergy efficiency of 3.05%, which are nearly 33% and 44% higher than the individual cooling and power system, respectively. The specific total cost and equivalent mass of CO2 emission are also lower than the individual cooling and power system by 38% and 26%, respectively. At the higher vapor generator and evaporator temperatures but lower ambient temperature, the performance index is higher, but the specific total cost and equivalent CO2 emission are lower. The performance index and exergy efficiency are maximum for January and minimum for April, whereas specific cost and CO2 emission are minimum for January and maximum for April. The performance index is better, but the specific total cost is lower at a higher cooling-to-power ratio.

Simulation analysis on the operational characteristics of a novel wind-to-heat system

The growing demand for energy and the pressure of carbon emission increase the proportion of renewable energy in the global energy consumption. In the wind-to-heat system, the compressor is utilized to replace the generator in the wind turbine to allow the wind energy driving heat pump directly, which simplifies the energy conversion process. In this study, a dynamic simulation model of the wind-to-heat system is proposed, which consists of the following six parts: wind turbine, compressor, condenser, thermal expansion valve, evaporator, and controller. Validations of this model was conducted by comparing the simulation result with the experimental data from a 100 kW wind-to-heat system. Effects of different operational conditions, such as hot water flow rate, inlet water temperature and types of refrigerants, on the characteristics of the system are explored and analyzed. The conclusion is drawn that the hot water flow rate is optimized as 3 kg/s, lower inlet water temperature led to lower heating capacity and lower COP, R245fa and R717 have good performances in heating production, which is in favor of the further design and optimize of the system. After debugging the simulation model for different design alternatives, different performances will be acquired to improve the efficiency of the design.

A State-of-the-Art Review on Two-Phase Flow-Induced Noise in Expansion Devices

This paper presents a state-of-the-art review of the literature concerning flow-induced noise in expansion devices. The topics covered are theoretical natural frequency models of bubbles with spherical and cylindrical shapes and flow-induced noise in capillary tubes, such as orifice, thermal and electric expansion valve. Several parametric conditions affect the flow-induced noise in capillary tubes, such as outlet capillary geometry, capillary inner diameter and length, flow orientation, outlet vapor quality, mass velocity, pressure drop, in/outlet flow pattern, evaporation temperature, and refrigeration cycle operational conditions. Despite the broad use of orifice, there is a lack of knowledge in the literature of flow-induced noise in these devices. The flow-induced noise seems primarily a function of mass velocity, vapor quality, and flow pattern. It seems that outlet intermittent flow patterns lead to significant noise in capillary tubes and expansion valves. In general, for the noise evaluated outside the expansion device, electric expansion valves exhibited higher sound pressure levels than capillary tubes. Furthermore, the present literature review indicates that efforts should be made to perform tests for a wide range of conditions evaluating the noise within and outside the expansion device, device wall acceleration and flow topology for current and new refrigerants, simultaneously.

Synchronized measurements of noise characteristics and flow regimes near the thermal expansion valve using R134a refrigerant

• Quantitative flow-induced noise prediction model. • Synchronized measurements of flow-induced noise and flow regimes. • Comparison between noise modeling and experimental measurements. • Distinguished flow-induced noise waveforms for different flow regimes. Flow-induced noise in the expansion device can be very disturbing. The thermal expansion valve is usually positioned near the occupants, often resulting in flow-induced noise that can be perceived as annoying. Current studies lack a quantitative relationship between flow characteristics and flow-induced noise. Therefore, in this paper, a noise prediction model is proposed to predict the sound pressure level of flow-induced noise. The study utilizes a pumped R134a loop for synchronized measurements between flow-induced noise and flow regimes. Synchronized high-speed measurements obtained from a microphone and a high-speed camera enable simultaneous investigation of flow-induced noise and flow regimes. In this case, the experimental results find a gurgling noise distributing near 9 kHz. Using the TXV inlet pressure for calculating thermodynamic properties, the gurgling noise sound pressure level prediction error is less than 15%. A hissing noise distributing at around 15 kHz is not as noticeable as the gurgling noise. The error of sound pressure level prediction for hissing noise is less than 40%. Both the experimental results and the modeling results show that the sound pressure level of gurgling noise increases as the vapor mass fraction increases or the system mass flux increases. From the experimental results, the noise waveforms are distinguished. The model can correctly outline the shape of noise waveforms for different flow regimes with the help of visualizations. The model introduced in this paper shows the proper prediction for flow-induced noise except for the annular flow entering the valve.

Validation of Clicking-type Noise and Vibration in Automotive HVAC System

In this study, the characteristics of clicking-type noise and vibration occurring in the automotive heating, ventilation and air conditional (HVAC) systems are investigated. A lab-scale model of HVAC system is developed, and validation is carried out with a vehicle system. A fixed blower speed of 1 (at an airflow of 2.53 m/s) with alternated air conditional (AC) was implied in this study. Three different sensors namely as tachometer, accelerometer, and microphone were used to measure and prove the existing noise in the HVAC system. The study inferred that the compressor contributed significantly to the total vibration and noise in the HVAC system. Other components such as AC pipe, evaporator, and thermal expansion valve (TXV) also contributed to a slight extent. The clicking noise was observed in the operating frequency range of 200 ~ 300 Hz. This noise and vibration issues are partly influenced by the running conditions of the AC and the effect was significant when the AC was turned on. The validation of the findings in the model shows a good agreement with the results obtained in the vehicle system, whereby the clicking noise and vibration can be observed at a similar frequency range.

Exergetic analysis of heat pump units for various climate conditions

The article deals with exergetic analysis of a heat pump for climate of Russian North-West. The dependencies between the parts of the pump and its general characteristic are shown. The influence of ambient temperature, condensation temperature, and low-grade heat source on the working efficiency of heat pump units is analyzed. The changes in thermodynamic characteristics of the heat pump at ambient temperature decreasing form 0°C to –15°C are identified. The coefficient of performance is seen to decrease two times, the coefficient of transformation – by 1.4 times; overall exergetic coefficient of performance increases by 18 %. Working efficiency and coefficient of performance of the unit in general, and the ones of compressor, compensator, evaporator and thermal expansion valve are determined. The results of the research are of use for increasing efficiency of heat pumps.

Thermal performance of ice-making machine with a multi-channel evaporator

ABSTRACTAn experimental investigation is presented in this paper on the vapor compression refrigeration cycle used in an ice-making machine with a multi-channel evaporator. To study the operation performance of the refrigeration system in the ice-making machine, the fluid temperature distribution in multi-channel evaporating coils are tested and the dynamic variations in each cooling loop are investigated during the ice-generating phase. The results show that the external cooling loops have the largest temperature fluctuations caused by the large initial refrigerant injecting mass flow and the external environmental disturbances. For the inner cooling loops, the related temperature profiles of different test points have relative stable variations. To reduce the temperature fluctuations of the outside loops, it is suggested to reduce the initial refrigerant mass flow and adjust the initial opening of the thermal expansion valve. Moreover, it is the normal phenomenon for the slight temperature variations for the temperature curves of different test points, caused by the adjustment of thermal expansion valve. During the ice-making process, both the sensible heat removal phase and latent heat removal phase are experienced successively. To remove the sensible heat of water, the refrigerant system is operating in high efficiency with test points having a rapid linear temperature reduction. While for eliminating the latent heat of ice, it requires much more power supply, the relating test points have a temperature decrease with fluctuations. To improve the operation performance of ice machine, some suggestions and improvements are proposed.

Benefits investigation of electronic expansion valve in electric vehicle thermal system as compared to thermal expansion valve with shut-off valve

Typical electric vehicle thermal management system with air conditioning and battery cooling is introduced with different refrigerant flow control devices. Electronic expansion valve (EXV) and thermal expansion valve integrated with shut off valve (TXV+SOV) are adopted in such a dual evaporators cooling system as refrigerant flow control valve to investigate the benefits of EXV compared to TXV+SOV by testing. Test result shows the EXV has significant benefits of proper refrigerant distribution with less system fluctuation to avoid the dissatisfaction of customer. With the TXV+SOV control, due to mal-distributed refrigerant flow between air conditioner evaporator and battery chiller, air conditioner blow off temperature variation can reach 8 °C which will significantly affect the comfort of passenger cabinet. While with EXV control, air conditioner blow off temperature is very stable. Stable control of EXV also contributes to system efficiency improvement than the TXV+SOV by saving the energy up to 20%.

The Thermal Analysis of a Semi-Open Heat Pump Drying System: An Experimental Investigation

One of the key advantages of heat pump (HP) systems is their ability to recover waste heat energy for useful input. In this study, the thermal performance of a heat pump drying system that recovers heat energy from the hot and moist exhaust air from the dryer was designed, constructed, and examined. The performance of this semiopen air source heat pump system was investigated and analysed by varying the refrigerant charge, the condenser fan speed, and the thermal expansion valve orifice size at ambient temperatures ranging from 23 – 26 C. The results indicated that by increasing the charge in the system, the refrigerant mass flow rate, heating capacity and coefficient of performance (COP) of the system increased to a certain maximum point before maximum charging. By increasing the refrigerant charge, both evaporation and condensation pressures of the system increased with condensation pressure indicating more sensitivity on the charge amount before optimum charging than evaporating pressure. The increase in refrigerant charge was observed to decrease the degree of superheat but increase the sub-cooling degree. At an optimum charge, the heating capacity for thermal expansion valve (TEV) of 0.3 mm diameter orifice is 15% greater than that of 0.2 mm diameter orifice. A system power consumption for O0.3 mm orifice was 3% greater than that of O0.2 mm orifice at the optimum charge amount. However, the COP of O0.3 mm orifice was 18% greater than that of O0.2 mm orifice.

DYNAMICAL BEHAVIOR OF A HEAT PUMP COAXIAL EVAPORATOR CONSIDERING THE PHASE BORDER’S IMPACT ON CONVERGENCE

Using a dynamical mathematical model, we investigated transient behavior of a water-water heat pump’s evaporator. The model consists of time and space dependent partial differential equations of water, pipe wall and refrigerant. Mathematically the thermal expansion valve (TEV) and compressor are described with lumped parameters and represent the boundary conditions. During the numerical solution of this system of equations the problem emerged of divergence of solutions. It was determined that the cause of the divergence solution was in the location of phase change of the refrigerant. The aim of this paper is, firstly, to display and propose a new approach to the elimination of divergence. In addition, it examines dynamic behavior of the heat pumps’ coaxial evaporator.

Non-azeotropic refrigerant charge optimization for cold storage unit based on year-round performance evaluation

This investigation aims at estimating a precise range of non-azeotropic refrigerant charge for medium temperature cooling application through performance test. A sample of cold storage unit originally charged R404A is slightly modified without changing the unit structure and components but adding a parallel thermal expansion valve for charging R407A and R407F. Charging tests are operated on the sample under 4 typical work conditions from high to low ambient temperatures to conduct annual performance evaluation with both unit performance and operation safety considered at the same time. Collecting performance parameters including CC, EER and PI, considering the feedback of sub-cooling degree, super-heating degree and DT and calculating the weight of these 4 working conditions in year-round operation contribute to the concluding recommended range of refrigerant charge and refrigerant mass range in liquid reservoir in cold storage unit charged R404A, R407A and R407F respectively.

Measurement of the Hissing-Type Noise and Vibration of the Automotive HVAC System

Noises such as hissing, humming, air-rush and compressor engagement are the common type of noises that can be induced from the automotive heating and ventilating air conditional (HVAC) system. These noises are basically generated from the effects of vibrational HVAC components. Due to this, the root cause of the noises has to be investigated for any implementation of solution. In this study, the hissing-type of noise is taken into consideration whereby the noise and vibration are measured from various HVAC components such as Evaporator Inlet and Outlet and Thermal Expansion Valve (TXV). Three types of measurement sensors are used in this study which is tri-axial accelerometer for the vibration, tachometer for the engine rpm tracking and microphone for the noise measurement. Two types of operating conditions are taken into consideration, when engine running at 850 rpm (idle) and 850-3000 rpm (tracking) conditions and a constant blower speed is applied for both conditions. the result shows that, the hissing type of noise is determined at the frequency range of 4500-5000 Hz for the both idle and running conditions, whereby the vibration at the Evaporator Inlet is the most significant compared to the Evaporator Core and TVX components. the vibration of the Evaporator Inlet shows the drastic vibration increment between 1000-1500 rpm and getting worse towards 3000 rpm. This result is validated with the 3D colour of noise waterfall analysis, whereby the hissing noise shows the dominant result in the frequency range of 4500-5000 Hz.

Performance of Automotive Air-Conditioning System by Using Ejector as an Expansion Device

An automotive air conditioning system that uses thermal expansion valve (TEV) as an expansion device. The pressure drop from the condenser and evaporator pressure is considered an isenthalpic process (constant enthalpy), where this process causes energy loss (entropy generation) in the expansion process. The ejector recovers energy losses, which was previously lost in the expansion valve, and an ejector can be used to generate isentropic condition in the expansion process. The use of an ejector as an expansion device in this study can reduce power consumption of the compressor and increase cooling capacity of the evaporator. The experiments were conducted with temperature set-points of the conditioned space of 21, 22 and 23°C with internal heat loads of 100, 200 and 400 W. Measurements were taken during the one hour experimental period at a time interval of five minutes. The experiment results indicate that the ejector system is better than TEV and save fuel.