Noise In Tubes Research Articles

Investigation on the noise induced by gas–liquid two-phase flow in a capillary tube

In order to research the noise generated by gas–liquid two-phase flow within capillary tubes in refrigeration systems, this study employs a numerical simulation method based on the volume of fluid model and evaporation-condensation model. The noise of gas–liquid two-phase flows is generated by refrigerant vaporization in capillary tubes under different inlet temperatures and diameters. The results of this study showed that two-phase flow noise in capillary tubes predominantly exists in the frequency range of 0–200 Hz, corresponding to low-frequency noise. Under different inlet temperature and diameter conditions, the total sound pressure level (TSPL) of a two-phase flow noise increased with the increase in the capillary tube diameter. Moreover, when the inlet temperature was 316.6 K, as the diameter increased from 1 to 1.9 mm, TSPL increased from 32.02 to 34.36 dB. In addition, as the inlet temperature gradually decreased, TSPL increased. Furthermore, it was found that the lower the inlet temperature, the greater the increase in TSPL. When the inlet temperatures were 316.6, 313.6, 310.6, and 307.6 K, and the diameter increased from 1 to 1.9 mm, TSPL increased by 2.34, 3.41, 4.1, and 5.38 dB, respectively, corresponding to the relative increase of 7.31%, 10.23%, 11.85%, and 15.34%. Finally, using an orthogonal analysis, a criterion relationship was obtained for predicting the TSPL of gas–liquid two-phase flow noises in capillary tubes under different conditions. This study provides guidance for noise control and structural optimization of capillary tubes considering the gas–liquid two-phase flow.

Application of aerating techniques for noise suppression in capillary tubes

A method for suppressing noise in capillary tubes was developed with aerating techniques. The refrigerant R600a was added to the outlet of a throttling capillary from the end of a transition tube between the capillary and evaporator. To investigate the flow characteristic of R600a in the transition tube, a two-phase flow quasi-steady simulation was performed using the mixture model. The Schnerr–Sauer cavitation model was used, and the turbulence model was realizable k − ɛ. Numerical results show that the local pressure and negative mass transfer rate can both be reduced at the downstream of the capillary where bubbles collapse, when bypass capillaries are used in the aerating model. An experimental system was built to measure the noise in a transition tube with/without a bypass capillary. Results show that the noise sound pressure level decreased by 2 dB on average when aerating techniques were used. This research describes the complex mechanism of the throttling flashing process and provides an effective method to suppress the noise in capillary tubes, which will be beneficial to improve occasional sharp noise in a household refrigerator.

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.

Shot noise: a 100-year history, with applications to lithography

The term “shot effect” (schroteffekt) was coined in 1918 when Walter Schottky studied electrical noise in vacuum tubes. Earlier still, the foundations of shot noise theory go back to Einstein, who in 1905 explained the photoelectric effect as caused by discrete “particles” of light and Brownian motion as caused by discrete particles of matter. When the numbers of particles that affect observable outcomes are large, shot noise effects (variability in number as a fraction of the mean number) become small, and the continuum approximation (energy and matter are continuous) becomes accurate. For most of the history of semiconductor lithography, the continuum approximation has served well. But at small dimensional scales, where the number of discrete particles or events is small, the counting statistics of shot noise can dominate. The 100-year history of shot noise in science and engineering is today playing a role in our understanding of shot noise in lithography.

Simulation of ion noise in microwave tubes by two-dimensional particle-in-cell method

The ion noise in microwave tube is studied using two-dimensional particle-in-cell method. The fluctuation of the ion amount, which is the source of ion noise of the tube, is observed in the simulation process. It is found that the sufficient ions amount in drift tube and beam envelope scalloping appear to be responsible for ion noise after changing the gas pressure, magnetic focusing field, and drift tube length. A great number ions escape radially and their amount is about half of the beam electron when ion noise occurs. The number of secondary electron is less than that of the ion and beam electron; it affects the ion noise very slightly. There are two ways can be used for depressing the ion noise. The first is adjusting or increasing the magnetic focusing field in drift tube. The second is creating static electric field gradient to make the ions leave the interaction space quickly.

Characterization of Relaxation–Oscillation Noise in Continuous-Wave Traveling Wave Tubes

Extremely low noise levels are frequently required in radar and communication systems that utilize microwave tubes. A noise waveform frequently found in continuous-wave (CW) linear-beam microwave tubes is a relaxation-type oscillation that has a period typically on the order of several milliseconds. This paper provides an extensive experimental characterization of this relaxation-oscillation phenomenon by recording the corresponding signal modulations on the output of several solenoid-focused CW traveling wave tubes. The characteristics of these amplitude and phase modulations were studied during systematic variations of tube operating parameters that included magnetic field, cathode voltage, depressed collector voltage, heater filament voltage, and input drive level. A measurement technique was also developed with the capability to obtain detailed information on the growth of the relaxation-oscillation noise waveforms along the beam interaction region by comparing reflected and output noise waveforms.

Electron and ion noise in microwave tubes

In nearly any application of a microwave tube, noise characteristics are important figures of merit. This paper reviews and presents new results of recent studies of such noise. The areas discussed are ion noise in linear beam tubes, one of the oldest studied noise phenomena, and electron noise in gyroklystrons, one of the newest areas of interest.

Theory and simulation of ion noise in microwave tubes

Since there is always some ambient gas in electron beam devices, background ionization is ubiquitous. For long pulse times, the electrostatic potentials associated with this ionization can reach significant levels and give rise to such observed phenomena as phase noise in microwave tubes. This noise is usually associated with the motion of ions in the device; therefore, it is called ion noise. It often manifests itself as a slow phase fluctuation on the output signal. Observations of noise in microwave tubes such as coupled-cavity traveling wave tubes (CC-TWTs) and klystrons have been discussed in the literature. In this paper, a hybrid model is discussed in which the electron beam is described by the beam envelope equation, and the ions generated by beam ionization are treated as discrete particles using the one-dimensional equations of motion. The theoretical model provides good qualitative as well as reasonable quantitative insight into the origin of ion noise phenomena. The numerical results indicate that the model reproduces the salient features of the phase oscillations observed experimentally. That is, the scaling of the frequency of the phase oscillations with gas pressure in the device and the sensitive dependence of the phase oscillations on the focusing magnetic field. Two distinct time scales are observed in simulation. The fastest time scale oscillation is related to the bounce motion of ions in the axial potential wells formed by the scalloping of the electron beam. Slower sawtooth oscillations are observed to correlate with the well-to-well interactions induced by the ion coupling to the electron equilibrium. These oscillations are also correlated with ion dumping to the cathode or collector. As a practical matter, simulations indicate that the low frequency oscillations can be reduced significantly by using a well-matched electron beam propagating from the electron gun into the interaction circuit.

Method for the reduction of signal-induced noise in photomultiplier tubes

A new method to reduce photomultiplier tube detector signal-induced noise (SIN) in a lidar system is successfully demonstrated. A metal ring electrode placed external to the photomultiplier tube photocathode is pulsed during the intense near-field lidar return with a potential between 15 and 500 V, resulting in a significant reduction in SIN. The effect of the metal ring voltage on the decay time constant and the magnitude of a simulated lidar signal is presented. Optimal experimental conditions for the use of this device in lidar receivers, such that the lidar decay time constant is not affected, are determined. Mechanisms for this SIN suppression system are discussed in detail, and data were recorded to show that the voltage on the metal ring functions by altering the photomultiplier electron optics.

On the theory of ion noise in microwave tubes

This work examines from a theoretical perspective recent experimental work regarding ion noise in the CPI continuous wave illuminator (CWI) and also earlier related ion measurements on a CW klystron. The measurements are to a large extent complementary, the former doing only microwave measurement, the latter doing only ion current measurements. The measurements are compared to theory which seems applicable. Many results do agree at least qualitatively with theory.

Instabilities and spurious noise in coupled-cavity traveling-wave tubes

The main concepts of design and operation of a traveling-wave tube are outlined, with a discussion of rf instabilities and the causes of spurious noise. Methods and principles for avoiding rf instabilities in coupled-cavity TWTs are described. Suggestions are included for applying similar principles to minimize unwanted spurious effects in EBIS devices.

Quantum electrodynamical theory of infrared effects in condensed matter: II. Radiative corrections of cross sections and scattering rates and quantum [formula omitted] noise

In this article, we go beyond the results of the preceding paper (I), in that we consider the radiative corrections of the interactions of charge carriers with the quantized electromagnetic field to all orders of perturbation. The radiative contribution of the cross section stemming from the emission (and, or) absorption of soft photons (infraquanta) then shows no divergence down to zero frequency. For a classical electron gas, the results of Yennie et al. are recovered. Extensions for metals and for the presence of a radiative background field are also obtained. The computation of the cross section to all orders provides nearly all ingredients for the slightly more elaborate computation of the scattered current-current correlation function. Slight coarse graining of the radiative contributions, which broadens the diagonal part, leads immediately to the Wiener-Khintchine expression for the convergent 1 f 1−αA noise, with α A being again the infrared coupling constant (order 10 −7). The last part of the paper is devoted to an in detail discussion of quantum 1 f noise. While Handel's basic 1975 result for the fluctuations in the cross section and his 1988 result for the cross correlations of the scattering rates are fully confirmed, we indicate that generalization to emission processes involving other infraquanta are not warranted. Also, no quantum 1 f noise effects are expected for ballistic motion, thus invalidating the semi-classical theories for transit 1 f noise in vacuum tubes and “acceleration quantum 1 f noise” in semiconductors. Alternatives for mobility fluctuations with high Hooge parameter (∼10 −3) are discussed.

Interpretation of Schwantes's experimental data on secondary emission [formula omitted] noise

Handel's theory of quantum 1 ⨍ noise is applied to Schwantes's 1960 data on secondary emission 1 ⨍ noise in Philips EFP60 tubes. It is first evaluated what Handel predicts for this case and then the theoretical and experimental values of S I (⨍) are compared at 10 Hz. Excellent agreement is obtained, which is the more remarkable since the theory does not contain any adjustable parameters. It is therefore concluded that Schwantes's secondary emission 1 ⨍ noise seems to be an example of quantum 1 ⨍ noise.

Acoustic boiling noise in a sodium-water steam generator

The governing factor in the attenuation of the water-boiling noise in the steam generator tubes when the noise is transmitted through the wall into sodium is the acoustic impedance of the medium that depends on volume vapor content. For any values of volume vapor content ranging form 0 to 1, the most promising frequency range for detecting the water leaks into sodium in terms of the minimum influence of the water-boiling noise is the ultrasonic frequency range of 30-200 kHz.

Pulling by Neighbouring Transitions and its Effects on the Performance of Caesium-Beam Frequency Standards

Pulling by the wings of neighbouring field-dependent lines is usually taken into account in accuracy evaluation of caesium-beam frequency standards. Its magnitude is commonly calculated from the observed asymmetry of the neighbouring lines using a well-known formula in which the shape of all the Rabi lines is approximated with Lorentzian profiles of the same width.In this paper it is shown that use of these approximations yields in most cases grossly underestimated results for the pulling, and that the real shape of the Rabi wings must be computed in order to match experimental data.Line shapes far from Lorentzian and different widths for the different lines are obtained if the real rf field profile and the actual velocity distributions for each state are used. Unexpectedly high values are found in this way, which indicate this kind of frequency pulling as possibly the biggest single cause of inaccuracy in commercial caesium beams and a bias to be re-evaluated in primary laboratory standards.Theoretical computations show good agreement with experimental data and suggest that the well-known average frequency difference of about +1 × 10-12 which is shown by the ensemble of all short commercial standards with respect to long primary tubes may be traced to Rabi pulling. The effect turns out to be dependent on modulation type and parameters. Dependence on rf power is also studied, which may be the primary cause of temperature sensitivity and flicker noise in short tubes, and the roles of source temperature and beam optics variations in relation to long-term drift are indicated.

Transient noise in photomultiplier tubes

Measurements are presented of the transient noise in a photomultiplier tube (PMT) resulting from illumination by a short pulse of light of low intensity. It is shown that both for a 9558 and for a 9569 PMT the transient noise is more than two orders of magnitude smaller than has previously been reported (Pettifer and Healey (1974)) for a 56TUVP tube.

Channel noise in nerve membranes and lipid bilayers.

The basic principles underlying fluctuation phenomena in thermodynamics have long been understood (for reviews see Kubo, 1957; Kubo, Matsuo & Kazuhiro 1973 Lax, 1960). Classical examples of how fluctuation analysis can provide an insight into the corpuscular nature of matter are the determination of Avogadro's number according to Einstein's theory of Brownian motion (see, e.g. Uhlenbeck & Ornstein, 1930; Kac, 1947) and the evaluation of the electronic charge from the shot noise in vacuum tubes (see Van der Ziel, 1970).

Noise in solid travelling-wave tubes using coupled-mode analysis†

The main sources of noise in solid travelling-wave tubes (STWT) are presented. The noise figure expression for the STWT is presented in a compact and unified form by making use of normal mode amplitudes. Numerical calculations of the noise figure at conditions of maximum gain are presented.

156. Pre-commutation noise in television pick-up tubes: V L Lentsman,Radiotekh Elektron, 16 (10), 1971, 1927–1935 ( in Russian)

156. Pre-commutation noise in television pick-up tubes: V L Lentsman,Radiotekh Elektron, 16 (10), 1971, 1927–1935 ( in Russian)

Noise in thermionic tubes as a criterion of stability and reliability: J Machovec, Slabopr Obzor, 32 (6), June 1971, 264–270 ( in Czech).

Noise in thermionic tubes as a criterion of stability and reliability: J Machovec, Slabopr Obzor, 32 (6), June 1971, 264–270 ( in Czech).