Maximum Pressure Variation Research Articles

Quantitative detection of refrigerant charge faults in multi-unit air conditioning systems based on machine learning algorithms

Refrigerant charging discrepancies constitute the predominant malfunctions in air conditioning systems. Achieving the optimal charging level is crucial for system performance, underscoring the importance of precise refrigerant level prediction. This study introduces an algorithm designed for the quantitative detection of refrigerant charging errors by integrating the Markov Transition Field (MTF), Convolutional Neural Networks (CNN), and Multi-head Self-Attention (MSA) mechanisms. A high-precision enthalpy difference chamber was employed to establish a Variable Refrigerant Flow (VRF) refrigerant charging test bench. This setup facilitated the analysis of system parameter sensitivity to charging faults and aided in the creation of a training dataset for the algorithm. Comparative analysis was conducted against Support Vector Machines (SVM), Random Forests (RF), CNN with Self-Attention (AT), and MTF-CNN-MSA. The findings reveal that our method adeptly captures temporal dependencies and dynamic shifts in time series as visual representations, offering novel insights for discerning fault patterns within such data. Notably, the maximum pressure variations at high-pressure and low-pressure points were 0.25 MPa and 0.07 MPa, respectively, with temperature shifts of 12 °C and 3.5 °C at the high and low-temperature points. The high-pressure and high-temperature points are particularly sensitive to changes in refrigerant charging, and parameters from these sections were utilized to construct the dataset. The CNN-MSA algorithm demonstrates consistent performance across various fault types, effectively delineating fault characteristics. The accuracies achieved by SVM, RF, CNN-AT, and MTF-CNN-MSA were 84.38 %, 73.75 %, 88.13 %, and 93.75 %, respectively. In comparison, the CNN-MSA algorithm was able to more accurately detect refrigerant charge faults at different levels.

Numerical simulation of in-vessel steam explosion for China third-generation PWR

In this study, in order to evaluate the Reactor Pressure Vessel (RPV) integrity under in-vessel steam explosion loads for China third-generation Pressurized Water Reactor (PWR), 2D and 3D numerical simulation of in-vessel steam explosion is conducted using MC3D code. The sensitivity analyses for in-vessel steam explosion are performed, including break area, water temperature, water level, melt temperature, and break height. The results show that the premixing stage cannot cause RPV failure and the possibility of the steam explosion blowing the RPV upper head off is almost non-existent. When the break area increases, the maximum pressure and impulse of the RPV inner wall increase obviously first and then generally decrease slightly. With the increase of water temperature, the maximum pressure and impulse first increase and then decrease. When the water level is higher, the maximum pressure variation is small. When the water level is very low, the maximum pressure decreases. The maximum impulse generally decreases with the decrease of the water level. When the melt temperature exceeds 2850 K, the steam explosion is not sensitive to the melt temperature. With the increase of the break height, the maximum pressure and maximum impulse first increase and then decrease. Furthermore, based on the results of sensitivity analysis, two cases of conservative conditions are selected, and the RPV integrity under in-vessel steam explosion loads for China third-generation PWR is considered. The result shows that the integrity of the RPV can be maintained under the in-vessel steam explosion loads for China third-generation PWR with a large margin. These studies provide some reference to improve the severe accident management strategy in China.

Degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy

The thermochemical hydrogen compression properties and cyclic durability of titanium-iron (TiFe) alloy were investigated at various temperatures of 200, 300, 450, and 500 °C by examing the achieved maximum pressure variations and hydrogen storage capacity before and after compression cycles. The cyclic durability of the TiFe alloy-based thermochemical hydrogen compressors was different depending on the operating temperature. Below 350 °C, the TiFe alloy-based hydrogen compressors showed stable thermochemical hydrogen compression properties with constantly achieved hydrogen compression pressure, hydrogen storage capacity, and unchanged phases. On the contrary, the reached maximum pressure with heating was gradually decreased during the compression cycles at 450 and 500 °C, suggesting poor durability and degradation at the higher temperature region. During the cycles, lattice strain and dislocation density of the alloy may be induced and lead to increase plateau pressure (hysteresis) without a change in hydrogen storage capacity. However, temperature increase can cause the disproportionation of TiFe around the formed lattice strain and dislocation. Therefore, after cycles at 500 °C, the hydrogen storage capacity is reduced by 30.4%. Furthermore, phase identification by X-ray diffraction measurements and thermal analysis suggested that TiH2, Fe2Ti, and Ti2Fe phases were disproportionately generated from the initial TiFe phase as irreversible hydrogen absorption states and became the dead volume for the cyclic compression cycles. Interestingly, the recovery of the TiFe alloy phase from the disproportionated phase of TiH2, Fe2Ti, and Ti2Fe can be achieved based on the TG-DTA-MS results. Therefore, based on the above results, the degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy are well understood in this work.

Shearing stress of shoaling internal solitary waves over the slope

The interaction between internal solitary waves (ISWs) and the seabed has been extensively studied, so do the energy loss, sediment resuspension, parameterization criterion and near-bed pressure variation. However, the horizontal and vertical shearing stresses of ISWs have not been directly measured. In this paper, flume experiments were designed to examine the near-bed pressure variation of shoaling ISWs over the slope with a novel device possessing four pressure sensors in different directions. Then the vertical and horizontal shearing stresses of ISWs were analyzed, with the shearing stress of ISWs in the South China Sea predicted based on field observation. The results showed that the maximum pressure variation of shoaling ISWs approximated 20 Pa, with the ISWs' horizontal shearing stress, about 3–6 Pa and the vertical one, about 10 Pa. It was predicted that the horizontal and vertical shearing stresses of ISWs in the open ocean were 5–100 kPa, larger than the maximum critical shearing stress of the sediment. This paper could promote the understanding of the seabed damage caused by ISWs and is expected to provide a reference for future field experiment design for the direct interaction measurement between ISWs and seabed sediments.

Giant barocaloric effect in commercial polyurethane

Barocaloric effect in polymers is barely recognized and limited to a few reports in the literature. This effect consists of a thermal response of the material when a hydrostatic pressure is applied, allowing its application in the field of solid-state cooling. In this study, the barocaloric effect was investigated for a commercial polyurethane rubber (PU) subjected to three heat treatment temperatures (60, 100, and 115 °C) for 16 h to assess the limiting condition for this application. PU presents giant barocaloric effect, reaching adiabatic temperature change between 13 and 15 °C at a maximum pressure variation of 218 MPa, obtained under direct measurement, reaching a normalized refrigerant capacity of 11.07 kJ kg−1 GPa−1 (ΔTh-c = 25 °C, Δp = 174 MPa). Using the obtained data, it was possible to propose a quadratic model to predict the value of the adiabatic temperature variation as a function of the temperature and pressure applied in the PU. The PU characterization included differential scanning calorimetry and mechanical properties. The results obtained indicate a promising research field for the barocaloric effect in rubber polyurethanes.

Continuous Monitoring of Detrusor Pressure in Patients With a Reflex Urinary Bladder After Spinal Cord Injury

In spinal cord injury, the detrusor pressure, as a parameter of urinary bladder dysfunction, is related to incontinence and renal complications. In order to determine the intraindividual variation of maximum pressure and duration of detrusor contractions, in patients with a spinal reflex bladder, the detrusor pressure was registered during 24 hours of physiological filling in 16 patients. Between the bladder contractions the detrusor pressure was low in all patients, indicating high bladder complicance. During contractions the maximum detrusor pressure and its duration varied both inter- and intraindividually. In individual patients, however, mean values during the initial 12 hours correlated with mean values during the final 12 hours. Thus, mean values of a series of contractions appear to be characteristic of each patient and useful in describing the voiding pressure in spinal reflex bladder.

Combustion behavior of granulated and pulverized coal in a PCI rig: combustibility and pressure variation analysis

The effect of the coal volatile matter content and particle size has been investigated in a new lab-scale pulverized coal injection rig (PCI rig) in terms of combustion efficiency and pressure variation. Two coals typically used for blast furnace injection (a high and a low volatile bituminous coal) and their blends experienced combustion under pressurized conditions and extremely high heating rates and short residence times such as those experienced by coal particles in industrial process. Combustion tests were conducted for a low volatile coal prepared in the particle size ranges of 25–75 µm, 105–250 µm and 250–500 µm. Burnouts were lower for the larger particle size sample, but the intermediate particle size sample (105–250 µm) yielded similar conversion to that of the finer sample. The burnouts of the high and low volatile coal, as well as those of their blends were proportional to the volatile matter content of samples in the test conditions. The measurement of pressure variation in the reactor chamber indicated a displacement in the beginning of reactions to longer times as larger was the particle size of coal. The high volatile coal reached the maximum pressure variation earlier than the low volatile one and the combustion of this coal in the blends may have anticipated the reaction of the low volatile coal portion in the blends.

Field study on the interior pressure variations in high-speed trains passing through tunnels of different lengths

As a high-speed train passes through a tunnel, the intense aerodynamic pressure wave outside the train penetrates into the passenger compartments, changing the pressure environment inside the train and causing discomfort to passengers. This phenomenon varies enormously among tunnels of different lengths. To evaluate the real influence of tunnel length on the interior pressure environment of the carriages and ensure passenger comfort, field measurements were conducted on a CRH2A train operating on the Hefei-Wuhan rail line in China; twelve tunnels with lengths ranging from 72 to 10766 m were investigated. Pressure sensors were deployed along the outside and inside train surfaces to investigate the variations in interior pressure with the exterior pressure environment. The results show that the interior pressure curve over time in a short tunnel has a single-trough form, very different from that in a long tunnel. The total variation of interior pressure increases monotonically with tunnel length from 72 to 10766 m, whereas the maximum pressure variation within a 3 s period occurs in the 1080 m tunnel; the variation within a 1 s period is not significantly affected by the tunnel length for tunnel lengths greater than 556 m. There is a delay in the 1 s interior pressure variation in response to an exterior pressure change; this delay is independent of the tunnel length and is approximately 1.2 s in this test. It is found that the reason for passengers’ ear discomfort in very long tunnels, which is mainly an effect of excessive changes in pressure over a long period of time, could be different from that in long or short tunnels.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВОДОРОДА НА НЕРАВНОМЕРНОСТЬ ПРОТЕКАНИЯ ПРОЦЕССА СГОРАНИЯ СЖАТОГО ПРИРОДНОГО ГАЗА В ДВИГАТЕЛЯХ ВНУТРЕННЕГО СГОРАНИЯ НА РЕЖИМАХ ХОЛОСТОГО ХОДА

Deep choke modes that include the no-load conditions are the most long lasting while operating a car in the city environment. However, the efficiency of work process at the deep choke modes remain low due to high intake depression and the large proportion of residual gases. The paper covers the evaluation of the hydrogen influence on the irregularity of compressed natural gas (CNG) combustion behavior in the engine at the no-load conditions through the assessment of change of the polytropic index as the parameter displaying the direction and the intensity of heat-exchange processes. The paper considers the feasibility to determine the quantity of residual gases and their proportion in working mixture. Carried out experimental study of the hydrogen influence on the cycles irregularity at the idle modes of the VAZ-2111 engine showed the decrease of variation of maximum pressure in the engine cylinder when increasing the proportion of hydrogen in gas fuel from 0 up to 6 %. The authors carried out the detailed study of hydrogen influence on the cycles’ irregularity for three stoichiometric ratios of the CNG mixture with the hydrogen proportion of 0, 4 and 6 %, three the most representative successive cycles displaying the irregularity of engine operation were selected for each of them. The study of the polytropic index on the selected cycles allowed determining the quantity of the residual gases and their proportion in working mixture and showed the significant influence of quality of combustion in the previous cycle on the thermodynamic processes behavior within the compression stroke and the combustion process efficiency in the next cycle. The obtained results allow evaluating the influence of hydrogen addition on the CNG combustion process and concluding that the addition of 6 % hydrogen allows better initiating the ignition process, thereby, preventing the ignition failures and decreases significantly the number of incomplete combustion cycles increasing the efficiency of working process at the idle modes.

О МОЖЛИВОСТІ СТВОРЕННЯ НОВИХ ГАЗОВИХ ХОЛОДИЛЬНИХ МАШИН СТІРЛІНГА НА ОСНОВІ ІСНУЮЧИХ КОНСТРУКЦІЙ

In the given paper the possibility of new Stirling refrigerating machine development on the basis of existing design has been considered. For refrigerating machine process analysis the isothermal model of Stirling cycle and method of separate loss analysis were used. Ambient and cooling temperatures were assumed constant in equation for cooling capacity calculation. The dimensionless complexes, namely, ideal cooling capacity and complexes taking into account cooler regenerator losses due to non-ideal heat exchange, hydraulic resistance and axial matrix heat flow have been obtained after mathematical transformation of the governing equations. According to the theory of similarity the pairwise equalities of heat exchanger volume simplexes (targeted volume divided by volume of refrigerator expansion space) and dimensionless complexes is needed for similarity of new and basis Stirling refrigerating machine. The equality of dimensionless complexes is achieved with equal regenerator length for both new refrigerator and basis cooler. For confirmation of this conclusion the basis refrigerator KGM-9000/80-1 with known experimental data and new designed refrigerator with cooling capacity 200 W have been used. For parameters calculation of refrigerators the one-dimensional mathematical model based on structure-module approach was used. The identical effectiveness for both coolers has been obtained. Variation of maximum pressure and working frequency of cycle does not allow creating new similarity Stirling refrigerating machine due to complicated influence of these parameters on dimensionless loss complexes. The procedure of effectiveness and refrigerating capacity increasing while changing the working frequency and maximum pressure for new refrigerator also ha s been shown.

Effects that internal gravity waves from convective clouds have on atmospheric pressure and spatial temperature-disturbance distribution

Experimental data on variations in atmospheric surface pressure in the region of thunderstorm phenomena are analyzed. A relationship between variations in atmospheric pressure at the land surface and those in tropospheric temperature has been found, and the relation between the vertical distribution of tropospheric temperature and variations in atmospheric pressure at the land surface is studied. The propagation of internal gravity waves caused by atmospheric heating due to water-vapor condensation during the formation of a convective cloud is simulated. The results of calculations show that the lifetime of these internal gravity waves may significantly exceed the lifetime of this cloud. It is shown that the form of the disturbance of atmospheric pressure under such a convective cloud is a sequence of minimum and maximum pressure variations and the amplitude of maxima may exceed that of minima.

An Assessment for Hydraulically Efficient Design of Uniformly Sloping Submain Lines

AbstractDetermining the actual pressure head profiles along the submain lines with a uniform slope is very important for proper hydraulic design of water distribution systems. In practice, there are three general pressure head profiles (Type I, Type II, and Type III) along submain lines depending on different uniform line slope situations. Of all types of pressure profiles, the Type IIb profile is considered the optimal (or ideal) pressure profile which can produce the minimum pressure head difference for a given pipe length. This profile occurs when the total energy loss by friction is just balanced by the total energy gain due to uniform downslope. This paper presents a comprehensive analysis based on the energy–gradient ratio (EGR) approach to identify the optimal (or ideal) pressure profile (Type IIb), to achieve the minimal point of the relative maximum pressure variation, ΦH, which can be defined as the ratio of the maximum allowable pressure head difference (∆Hmax) to the total friction drop (hf(L)). This minimal point is regarded as 'the most efficient pressure profile' or 'ideal hydraulic design' in the existing literature. For this purpose, an illustrative figure (Figure 4) was developed to compare values of the relative maximum pressure variation versus the dimensionless EGR (KS = S0/Sf) for all types of pressure profiles. In this figure, the present ϕH curve versus KS values allows the design engineer to make a decision for the best alternative for selecting the KS value, where for a given pipe slope (S0) the KS value can be selected to meet the minimum pressure variation [KS =1, (ϕH)min =0.36] or the range of pressure variation as close to the minimum point as possible. The present design technique may provide a useful decision support tool for achieving a good design solution among hydraulically possible alternatives with minimal pressure head difference, and results in a higher level of water application uniformity along the multi‐outlet pipeline system. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of undiluted bioethanol on combustion and emissions reduction in a SI engine at various charge air conditions

This paper investigates the effects of neat bioethanol combustion on the performance and emission reduction characteristics of a spark ignition (SI) engine at various air temperature conditions. The experiments were carried out for different intake air temperatures and various operating conditions, and the results were compared to those for conventional gasoline fuel. The investigated results show that as intake ambient air temperatures is decreased, the intake flow rates is increased by the increased density of the intake air. The ethanol fuel has a higher volumetric efficiency than gasoline for all engine speeds and ambient temperature conditions. The cylinder pressures are increased with the improvement of volumetric efficiency due to the decrease of intake temperature. In addition, ethanol combustion creates higher combustion pressures than that of gasoline due to the high latent heat evaporation rate and low boiling point. The coefficients of variation of maximum pressure show slightly decreasing trends as the ambient air temperature increases. The concentration of NOx emissions tends to increase proportionally with the increase of ambient air temperature and engine speed for all test conditions. However, the HC, and CO emissions from ethanol combustion are improved than those of gasoline combustion.

Wavelet analysis of cycle-to-cycle pressure variations in an internal combustion engine

Using a continuous wavelet transform we have analyzed the cycle-to-cycle variations of pressure in an internal combustion engine. The time series of maximum pressure variations are examined for different loading and their wavelet power spectrum is calculated for each load. From the wavelet power spectrum we detected the presence of long, intermediate and short-term periodicities in the pressure signal. It is found that depending on the load, the long and intermediate-term periodicities may span several cycles, whereas the short-period oscillations tend to appear intermittently. Knowledge of these periodicities may be useful to develop effective control strategies for efficient combustion.

Analytical solution for venting from a time-dependent cavity volume

The jet flow at the orifice produced by a cavity-pumping device is studied in the present paper. Internal instantaneous pressure is obtained using analytical solution based on assumptions of isothermal condition and incompressible flow. An example of a venting of a cylindrical cavity with initial volume 1.59 × 10−5 m3 and orifice area 1.96 × 10−5 m2 is considered to determine the differential pressure across the orifice under the sinusoidal variation of the cavity volume. Variation of maximum pressure jump across the orifice as function of angular frequency is obtained for a given cavity volume ratio. The analytical solution of time-dependent volume of incompressible flow retains all the geometrical parameters of the synthetic jet actuator, therefore, can be employed to validate numerical solution of compressible flow under the isothermal condition.

A 2D Finite Element Analysis of an Ultrasonic Cleaning Vessel: Results and Comparisons

This paper describes the use of finite element software to provide a two-dimensional time harmonic analysis of cavitational activity within an ultrasonic cleaning vessel as used within hospitals and dental surgeries. A rational for the simulation method utilized and input parameters affecting the model is discussed. Practical affirmation of the model is provided via qualitative methods (the industry standard HTM2030 foil erosion test) and quantitative data are obtained from an ultrasonic cavitational probe. Simulated data from the finite element model and that obtained practically are compared, with both sets of results showing a good level of agreement and indicating a correlation between those areas of maximum pressure variation and cavitational field strength. Limitations and implications of the results are discussed along with future directions for research, including the development of a three-dimensional model to provide a more accurate reflection pattern from the boundary geometries within the ultrasonic cleaning vessel. Quantification of the results of reflections is discussed as a future development plan, as is correlating the field strength predicted to cleaning efficacy via test soil analysis.

鉄筋腐食膨張圧の三次元効果に関する研究

The reinforcing steel in concrete corrodes due to various degradation factors. Since apparent volume of corroded reinforcement is larger than original one, expansive pressure is introduced. The mechanism of spalling of cover concrete and expansion of corrosion has mainly been studied in 2-dimensional sections. However, the 3-dimensional effect should be considered to make clear the spalling mechanism. In this paper, 3-dimensional finite element analysis that covers the 3-dimension effect is conducted. With considering coefficient of variation of maximum pressure in experimental tests, the corrosion length factor (Lemin/k) where the 3-dimensional effect can be ignored is proposed.

Analysis of the Cyclic Variability in SI Engine at Idling

Cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by the pressure parameters, combustion parameters, and flame front parameters. The coefficient of variation in indicated mean effective pressure () defines the cyclic variability in indicated work per cycle, and it has been found that vehicle driveability problems usually result when exceeds about 10%. For analysis of the cyclic variability in SI engines at idling, the results show that cyclic variability by the or the coefficient of variation in maximum pressure can be explained and may be consequently reduced by the help of the optimum spark timings

Analytical study of pressure variation caused by water hammer, considering the effect of head loss.

Allievi's formula is well khown for approximately calculating the maximum pressure rise in a conduit caused by a water hammer. This formula is obtained, neglecting the elasticity of the conduit, the compressibility of the Fluid, linear closure of the valve, and the head loss of the conduit. The object of this paper is to discuss analytically the effect of the head loss of a conduit on the pressure variation. As a result, a formula for linear closure of the valve, and a method approximately calculating the maximum pressure variation caused by a water hammer not only of cases considering the effect of head loss but also for a system having a conduit downstream from the valve, are obtained.

Experimental Study of Diesel Engine Cycle-to-Cycle Variation—Part II: Correlation of Ignition Delay and Cylinder Pressure Variation

Marine diesel engine excitation can occur from the cycle-to-cycle variation in the engine output. The cycle-to-cycle variation in maximum cylinder pressure is often used to represent this variation. Recent tests indicate a poor correlation between the variation in maximum pressure and variation in pressure impulse (PI). This paper summarizes the results of systematic experiments to determine the cycle-to-cycle variation in maximum cylinder pressure, ignition delay (ID), and corresponding ignition pressure in a single-cylinder test diesel engine at various rpm and compression ratios. Comparisons show that there is a high correlation between the cycle-to-cycle variation in ID and PI. Consequently, the variation in the ignition delays should be used instead of the maximum pressure.