Subatmospheric Pressure Research Articles

Comparative study between vacuum-assisted closure therapy and tetra-silver nitrate in the management of diabetic foot ulcer

Background Diabetes-related foot ulcers are becoming more common. The percentage range is 15 to 25%. Several procedures and dressing agents have been investigated. In the vacuum-assisted closure technique, sub-atmospheric pressure is employed to accelerate the healing process. Aim and objectives In this study, the healing rates of diabetic foot ulcers (DFUs) treated with tetra-silver nitrate dressing were compared with those treated with negative pressure wound care. Patients and methods More than 30 patients were randomly allocated to one of two study groups by the Vascular Surgery department at Aswan University Medical School. Group A received a vacuum-assisted closure (VAC) dressing for a total of 30 patients, while group B received tetra-silver nitrate. Result After 6 weeks, there was a statistically significant difference in wound-healing rates between the two groups. Conclusion Patients who got VAC developed granulation tissue faster than those who received tetra-silver nitrate. VAC treatment is safe and effective in diabetic foot ulcers. Granulation tissue formation accelerates healing and reduces the risk of problems such as infection or amputation.

Experimental study on bubble dynamics and heat transfer of pool boiling at sub-atmospheric pressures

Pool boiling, as an efficient phase-change heat transfer method, has attracted extensive attention in recent years. However, the bubble dynamics behavior (BDB) and heat transfer characteristics of pool boiling at sub-atmospheric pressure (sub-ATM) are significantly different from those at or above standard atmospheric pressure (std-ATM). This paper presents experimental results of BDB and heat transfer characteristics of pool boiling at sub-ATM in the range of 30–120 kPa. High-speed backlight imaging technique was adopted. The results show that with the decrease of boiling pressure, the diameter and near circularity coefficient of bubble departure increase, and the frequency and aspect ratio decrease. With the decline in pressure, the critical heat flux (CHF) of pool boiling on the surface of the electric heater decreases. Specifically, the CHF at 120 kPa is 23.2% higher than that at 40 kPa. At sub-ATM, the boiling heat transfer coefficient (HTC) grows with the increase of liquid height. However, the HTC hardly changes with liquid height at std-ATM and higher.

On the flow-facilitated ignition in a mixture with low Lewis number

The imposed laminar flow has been shown to facilitate ignition under certain conditions in our previous work (Chen et al. 2023). Such flow-facilitated ignition (FFI) was observed only for mixtures with sufficiently large effective Lewis numbers, i.e., Le>>1. It is not clear whether FFI can also occur in a mixture with Le<1 and Le∼1. This study will investigate the occurrence of FFI in a mixture with low Lewis number. We conduct multi-dimensional simulations of forced ignition by a pair of electrodes in both static and flowing hydrogen/air mixtures. A simplified ignition model is used in simulations. The laminar flow direction is perpendicular to the pair of electrodes. We consider different values for equivalence ratio (ϕ=0.4 and 1.0), pressure (P = 0.3–1 atm), electrode gap distance (dgap=0.64–3.88 mm) and flow velocity (Uin=0–10 m/s). The simulation results show that FFI can occur in a fuel-lean (ϕ=0.4) H2/air mixture with Le≈0.43 at sub-atmospheric pressure. This indicates that large Lewis number is not a necessary condition for FFI occurring in simulations considering a simplified ignition model. Here, the favorable conditions for FFI are large critical ignition radius at sub-atmospheric pressure, sufficiently small electrode gap distance and moderate flow velocity. Moreover, the reduction in heat loss to the electrodes by the imposed flow is found to be crucial for FFI. To further understand the boundary conditions of FFI, an ignition mode regime diagram in terms of flow velocity and normalized critical ignition radius (i.e. the ratio of critical ignition radius and electrode gap distance) is proposed. The present study provides insights on the effects of laminar flow on forced ignition of premixed flames.

Heat transfer distribution and pressure drop fluctuations in subcooled flow boiling at subatmospheric system pressure

The transfer of higher heat flux at subatmospheric system pressure is relevant to different applications where the higher surface temperature is a constraint. There is a scarcity of literature on subcooled flow boiling at subatmospheric system pressure. The experiments are performed at 50, 75 and 101 kPa absolute system pressure in an SS-304 tube of 5.85 mm radius, heated length of 1500 mm and 0.5 mm thickness. The mass flux of 90–300 kg/m2s is streamed at the varying heat flux of 48–218 kW/m2. The heat transfer coefficient in single-phase flow is not impacted significantly by the subatmospheric system pressure. The subcooled flow boiling heat transfer coefficient is increased at the lower subatmospheric system pressure. The more nucleation sites due to higher wall superheat are activated at the higher heat flux at subatmospheric system pressure. The surface temperature is radially symmetric at subatmospheric system pressure for all values of the Froude number. The gravitational force is suppressed at subatmospheric system pressure. The onset of nucleation is achieved earlier in the axial direction at the higher heat flux. The mass flux has no significant effect on the subcooled flow boiling heat transfer coefficient. The pressure drop and fluctuations are enhanced at the higher mass flux, higher heat flux and lower subatmospheric system pressure.

Effect of mixed wettability surfaces on flow boiling heat transfer at subatmospheric pressures

Subatmospheric flow boiling heat transfer is a promising method for electronics cooling due to lower saturation temperatures. However, pressure is a crucial parameter that affects surface tension and vapor density. In this study, the effect of surface mixed wettability configuration on bubble dynamics and flow boiling was investigated under atmospheric and subatmospheric pressure conditions. Superhydrophilic, superhydrophobic, and mixed-wettability surfaces were prepared and tested at various heat fluxes and three system pressures of 48 kPa, 68 kPa, and 101 kPa. The channel dimensions were 50 mm × 15 mm, and the channel had a depth of 1 mm. The results showed that biphilic surfaces enhanced the performance up to 28% compared to superhydrophilic surfaces at high heat fluxes for subatmospheric boiling. Flow visualization efforts reveal that mixed-wettability surfaces improve heat transfer by extending the efficient slug regime to higher heat fluxes by preventing dried spot formation. These surfaces benefit from high density nucleation sites at low and medium heat fluxes, resulting in a noticeable performance improvement compared to the superhydrophilic surface. The obtained experimental data in this study will be helpful for the development of thermal-fluid systems operating under subatmospheric conditions.

An Experimental Study on the Combustion Characteristics of a Methane Diffusion Flame within a Confined Space under Sub-Atmospheric Pressure

Gas-fired boilers, gas stoves, and wall-mounted gas boilers are the main consumers of gas fuel, but they generally encounter problems when operating at high altitudes, such as reduced thermal efficiency and increased pollutant emissions. Previous studies on gas combustion characteristics under sub-atmospheric pressure were mostly carried out in a large space, which is quite different from chamber combustion equipment. Therefore, it is insufficient to guide the design and operation optimization of plateau gas equipment. In this paper, experimentations were carried out to explore the characteristics of a methane diffusion flame under sub-atmospheric pressures. The mass flow rates of methane and air remain consistent under different pressure conditions. The centerline temperature (Tc) distribution, flame appearance, smoke point, CO emission, and NOx emission under different pressures (ranging from 61.66 to 97.75 kPa) were examined under both fuel rich and lean conditions. The results show that Tc at the rear and front of furnace variation with pressure is opposite under fuel-lean and -rich combustion. The Tc at the front of furnace decreases with decreasing pressure, whereas Tc at the rear of furnace increases with decreasing pressure. With decreasing pressure, flame length decreases under lean combustion, but increases under rich combustion. The smoke point fuel flow rate, flame length, and residence time increases with decreasing pressure, following the law of negative exponent. The CO emission decreases with decreasing pressure, which indicates that the reduced pressure makes methane combustion more complete. For NO emission, the reduced pressure results in an opposite tendency under fuel-lean and -rich combustion. With decreasing pressure, the NO emission decreases under fuel-lean combustion but increases under fuel-rich combustion.

Dynamic Instrumental and Sensory Methods Used to Link Aroma Release and Aroma Perception: A Review.

Perception of flavor is a dynamic process during which the concentration of aroma molecules at the olfactory epithelium varies with time as they are released progressively from the food in the mouth during consumption. The release kinetics depends on the food matrix itself but also on food oral processing, such as mastication behavior and food bolus formation with saliva, for which huge inter-individual variations exist due to physiological differences. Sensory methods such as time intensity (TI) or the more-recent methods temporal dominance of sensations (TDS) and temporal check-all-that-apply (TCATA) are used to account for the dynamic and time-related aspects of flavor perception. Direct injection mass spectrometry (DIMS) techniques that measure in real time aroma compounds directly in the nose (nosespace), aimed at obtaining data that reflect the pattern of aroma release in real time during food consumption and supposed to be representative of perception, have been developed over the last 25 years. Examples obtained with MS operated in chemical ionization mode at atmospheric or sub-atmospheric pressure (atmospheric pressure chemical ionization APCI or proton-transfer reaction PTR) are given, with emphases on studies conducted with simultaneous dynamic sensory evaluation. Inter-individual variations in terms of aroma release and their relevance for understanding flavor perception are discussed as well as the evidenced cross-modal interactions.

A 3D-printed sub-atmospheric pressure electrospray ionization source for robust, facile, and flexible mass spectrometry analysis.

The operation and performance of electrospray ionization (ESI) is affected by the surrounding environment. In this study, a compact sub-atmospheric pressure ESI (SAP-ESI) source was designed and fabricated using the 3D printing method. This source has a simple structure and is easy to operate, as the sample solution and auxiliary gas are continuously sucked into the source through the pressure difference. The compact and enclosed ionization chamber can reduce the fluctuation of the surrounding gas flow to ensure a remarkably stable (< 3%) electrospray. Moreover, the source can offer variable SAP conditions for ESI analysis. The yield of analyte ions increases with decreasing pressure, while the production of background ions is suppressed under these conditions. In the analysis of protein samples, SAP-ESI can increase the yield and charge state of ions, which may be due to the reduction of proton transfer between charged proteins and surrounding gas. The SAP-ESI source was then used to continuously monitor the extract aqueous solution of tea leaves, and to detect the carbendazim residues on the apple surface by coupling with the liquid extraction surface analysis technique. Experimental results demonstrate that the developed SAP-ESI is a stable, practical, and versatile ionization technique.

Custom 3D-Printed External Cranial Orthotic for Prevention and Treatment of Syndrome of the Trephined.

Syndrome of the Trephined (SoT) is a frequently misunderstood and underdiagnosed outcome of decompressive craniectomy, especially in cases of trauma. The pressure gradient between atmospheric pressure and the sub-atmospheric intracranial pressure results in a sinking of the scalp overlying the craniectomy site. This gradually compresses the underlying brain parenchyma. This parenchymal compression can disrupt normal autoregulation and subsequent metabolism, yielding symptoms ranging from headaches, dizziness, altered behavior to changes in sensation, and difficulty with ambulation, coordination, and activities of daily living. We present a case of SoT treated with a 3D-printed custom polycarbonate external cranial orthotic that allowed us to re-establish this pressure gradient by returning the cranium to a closed system. The patient demonstrated subjective improvement in quality of life and his symptoms. This was consistent with the re-expanded brain parenchyma on CT imaging.

Continuous boilover behaviors of large-scale kerosene pool fires under sub-atmospheric pressure

Accidental fire is a major safety concern in chemical parks, highlighted by the several major fire accidents involving storage tanks in recent years. Boilover is considered as one of the most destructive tank fire scenarios, which occurs when a liquid fuel burning on a water layer, leading to the explosive evaporation of water and consequently a sudden increase of the heat release rate (HRR) and associated flame height due to the splashing of burning fuel. Previous studies on boilover with large-scale pool fires were mostly conducted under normal atmospheric pressure. However, chemical parks are often located in plateau regions, where the effects of reduced pressure on boilover behaviors were rarely examined. Moreover, following the initial boilover, continuous boilover could occur, and its understanding is particularly important in the thermal hazard and risk analysis and firefighting of tank fires. In this study, thin-layer boilover experiments were conducted under sub-atmospheric pressure using aviation kerosene (RP-3) with various initial fuel thicknesses and pool diameters. The burning process, boilover intensity, temperature in the fuel and water layers and associated thermal hazard were analyzed. Experimental results showed that continuous boilover occurred in all test conditions, characterized by a high intensity initial boilover followed by a series of subsequent ones with gradually reduced intensity. The mass burning rate and flame height varied significantly during boilover. It was found that the boilover intensity increases with the initial fuel thickness but decreases with the pool diameter and approaches a nearly constant value when the pan diameter is sufficiently large. The temperature at the fuel/water interface was found to increase from 93 ℃ to around 108 ℃ during boilover, both of which are lower than those observed under normal atmospheric pressure due to reduced water boiling point. The thermal hazard calculated for the initial boilover is highest as expected, and that of subsequent boilovers gradually decreases but could still be higher than that at the steady burning stage. The findings in this work will contribute to risk assessment of continuous boilover in fire accidents.

PIC/MCC simulation for a ns-pulsed glow discharge in nitrogen at sub-atmospheric pressure and analysis of its quasi-steady state physics

The present study investigates the physics of a nanosecond-pulsed microplasma operated at a pressure of 200 mbar with the help of a particle-in-cell simulation with Monte Carlo treatment of collision (PIC/MCC) and (semi-)analytical models. The discharge is ignited in a 1 mm gap between two parallel molybdenum electrodes by applying a voltage in the kV-range for several tens to hundreds of nanoseconds. A PIC/MCC simulation code is developed in order to describe the experiment performed under identical conditions. The simulation includes the external electrical circuit to perform ab-initio calculations of the complete experimental setup. Notable features of the PIC/MCC are (i) the adjustment of super-particle weights to reduce the computational load during drastic changes of the plasma density, which reaches values up to a few , and (ii) the inclusion of dissociative recombination of the ions, which is the key loss process for the charge carriers in the plasma bulk regions. The current and voltage waveforms obtained from the simulation are compared to the experimentally measured ones and good agreement is found. After ignition, the discharge establishes a quasi-steady state exhibiting spatial features similar to a conventional DC glow discharge. Using the PIC/MCC results, reasonable approximations are identified, which allow the development of various analytical fluid models for the individual plasma regions. These models are able to reproduce the key features of the discharge in agreement with the PIC/MCC results. The simplified models for the different discharge regions can be combined to describe the global behaviour of the discharge and—in a next step—might be used to develop computationally efficient global chemistry models that account for the different power dissipation mechanisms along the discharge gap.

Socket-residuum coupling integrity affects perception of external stimuli: Effects of altering the transtibial interface using vacuum-assisted suspension.

Relative movement between the socket and residual limb can impair function in prosthesis users. It is plausible that, in addition to its mechanical effect, the integrity of the socket-residuum interface influences the ability of an individual to sense tactile cues through the prosthesis. Vacuum-assisted suspension (VAS) has been shown to reduce relative movement at this interface, providing a means to test this premise. The purpose of this pilot study was to assess the effects of altering socket-residuum interface integrity through the VAS pressure level on the thresholds of perception of an externally applied vibration stimulus. Seven unilateral transtibial prosthesis users participated. Socket-residual limb integrity was altered using the VAS subatmospheric (vacuum) pressure level. Vibration perception tests were conducted at low, mid, and high vacuum levels, targeting 0, 8, and 19 in Hg respectively, and performed in partially loaded and fully loaded conditions. Vibration intensity was increased using a dial until participants delivered a verbal signal indicating it was perceptible, and the nominal intensity was recorded. Intensity thresholds decreased (ie, sensitivity increased) from low to high vacuum settings when fully loaded ( P = 0.008). Differences when partially loaded were nonsignificant and variable across participants. This study provides preliminary evidence that altering the integrity between the socket and residual limb by modifying the vacuum level affects sensation related to the external environment experienced through the prosthesis, although translation of these findings to real-world stimuli remains to be tested.

The State of the Art of Laminar Burning Velocities of H2-Enriched n-C4H10–Air Mixtures

Currently, hydrogen-enriched n-butane blends present a real interest due to their potential to reduce emissions and increase the efficiency of combustion processes, as an alternative fuel for internal combustion engines. This paper summarises the recent research on laminar burning velocities of hydrogen-enriched n-C4H10–air mixtures. The laminar burning velocity is a significative parameter that characterises the combustion process of any fuel–air mixture. Accurately measured or computed laminar burning velocities have an important role in the design, testing, and performance of n-C4H10–H2 fuelled devices. With this perspective, a brief review on the influence of hydrogen amount, initial pressure and temperature, and equivalence ratio on the laminar burning velocity of hydrogen-enriched n-C4H10–air mixtures is presented. Hydrogen has a strong influence on the combustion of butane–air mixtures. It was observed that a parabola with a maximum at a value slightly higher than the stoichiometric ratio describes the variation in the laminar burning velocity of hydrogen-enriched n-butane–air mixtures with the equivalence ratio. An increase in initial pressure or hydrogen amount led to an increase in this important combustion parameter, while an increase in initial pressure led to a decrease in laminar burning velocity. Overall, these studies demonstrate that hydrogen addition to n-C4H10–air mixtures can increase the laminar burning velocity and flame temperature and improve flame stability. These findings could be useful for the optimisation of combustion processes, particularly in internal combustion engines and gas turbines. However, the literature shows a paucity of investigations on the laminar burning velocities of hydrogen-enriched n-C4H10–air mixtures at initial temperatures and pressures differing from those in ambient conditions. This suggests that experimental and theoretical investigations of these flames at sub-atmospheric and elevated pressures and temperatures are necessary.

Analysis of methane pyrolysis experiments at high pressure using available reactor models

Most batch reactor methane thermal decomposition (MTD) studies have focused on sub-atmospheric pressures. In this study, MTD experiments were performed between 892 K and 1292 K and 4 atm inside a quasi-isothermal quartz batch reactor at residence times ranging from 0 to 300 s. At a given temperature, elevated pressure resulted in higher methane conversion compared with the sub-atmospheric conditions. A zero-dimensional, closed, isochoric, homogeneous gas-phase model was used to compare numerical predictions from available reaction mechanisms in literature to experimental data. It was found that most models accurately predict conversion at low pressure and high temperature and at high pressure and high temperature, but did not accurately predict methane, hydrogen, and intermediate species mole fractions at 4 atm and either 892 K or 1093 K. A reaction path analysis showed the reactions responsible for the delay in hydrogen formation at elevated pressure are 2CH3(+M)⟺ C2H6, C2H6 ＋ CH3⟺ C2H5 ＋ CH4, C2H6 ＋ H ⟺ C2H5 ＋ H2 and C2H5(+M)⟺ C2H4 ＋ H, where M is the collision partner. A gas-phase model accounting for the solid carbon shows that the observed discrepancy is not due to the unavailability of the carbon formation model but to slower reaction kinetics, especially at lower temperatures. The experimental data presented can be used to obtain a methane pyrolysis reaction mechanism suitable for high pressure conditions.

Vacuum pressure imaging solution based on fiber-optic Fabry-Pérot interferometer and optical barcode

Slight variations in vacuum can have a huge impact on industrial, medical, and scientific applications. For sub-atmospheric pressure measurements, conventional demodulation methods for fiber-optic sensors based on the wavelength tracking or power interrogation of the single resonant peak encounter difficulties in the direct vacuum level detection, in addition to cost and sensitivity issues which are one of the key obstacles for further applications of sensing probes. Here we demonstrate a total solution based on a fiber-based Fabry-Pérot interferometer (FPI) and an optical barcode based on Fréchet distance. The vacuum sensing fiber tip based on FPI prepared using the fixed-length cutting and fiber-end grinding techniques address the need for low-cost, high-sensitivity sensing for potential applications. Optical barcoding technique provides direct vacuum information by monitoring the overall behavior of the spectral resonance peaks. This work lays the foundation for the development of a low-cost, compact vacuum pressure sensing solution with direct vacuum reading.

A new experimental setup to measure hydraulic conductivity of plant segments.

Plant hydraulic conductivity and its decline under water stress are the focal point of current plant hydraulic research. The common methods of measuring hydraulic conductivity control a pressure gradient to push water through plant samples, submitting them to conditions far away from those that are experienced in nature where flow is suction driven and determined by the leaf water demand. In this paper, we present two methods for measuring hydraulic conductivity under closer to natural conditions, an artificial plant setup and a horizontal syringe pump setup. Both approaches use suction to pull water through a plant sample while dynamically monitoring the flow rate and pressure gradients. The syringe setup presented here allows for controlling and rapidly changing flow and pressure conditions, enabling experimental assessment of rapid plant hydraulic responses to water stress. The setup also allows quantification of dynamic changes in water storage of plant samples. Our tests demonstrate that the syringe pump setup can reproduce hydraulic conductivity values measured using the current standard method based on pushing water under above-atmospheric pressure. Surprisingly, using both the traditional and our new syringe pump setup, we found a positive correlation between changes in flow rate and hydraulic conductivity. Moreover, when flow or pressure conditions were changed rapidly, we found substantial contributions to flow by dynamic and largely reversible changes in the water storage of plant samples. Although the measurements can be performed under sub-atmospheric pressures, it is not possible to subject the samples to negative pressures due to the presence of gas bubbles near the valves and pressure sensors. Regardless, this setup allows for unprecedented insights into the interplay between pressure, flow rate, hydraulic conductivity and water storage in plant segments. This work was performed using an Open Science approach with the original data and analysis to be found at https://doi.org/10.5281/zenodo.7322605.

Detection of Single Ag Nanoparticles Using Laser Desorption/Ionization Mass Spectrometry.

The detection of a single entity (molecule, cell, particle, etc.) was always a challenging subject. Here we demonstrate the detection of single Ag nanoparticles (NPs) using subatmospheric pressure laser desorption/ionization mass spectrometry (LDI MS). The sample preparation, measurement conditions, generated ions, and limiting experimental factors are discussed here. We detected from 84 to 95% of the deposited 80 nm Ag NPs. The presented LDI MS platform is an alternative to laser ablation inductively coupled plasma mass spectrometry for imaging distribution of individual NPs across the sample surface and has a great potential for multiplexed mapping of low-abundance biomarkers in tissues.

Investigation of the mechanism of global and terminal flame uplifted in subsonic horizontal spray jet flame under sub-atmospheric pressure: From macroscopic to microscopic perspective

This work explored how subsonic horizontal spray flames behave under sub-atmospheric pressure and the mechanisms behind their combustion. For examine a horizontal spray flame with rated air volume flow and equivalence ratio, large eddy simulation (LES) and probability density function (PDF) were employed, based on the discrete phase (DPM) random trajectory model. The simulation results are in good agreement with the previous experiments. Through the micro-analysis of the burning time, burning path, and rate of the burn path of droplets under different atmospheric pressures, the combustion characteristics of the flame have been revealed; as well, a component change analysis was conducted to investigate the combustion mechanisms of the flame. Density distributions in buoyancy plumes can reveal the morphologic mechanisms in the corresponding flame regions. A detailed explanation of the varied mechanisms in horizontal spray flames in low-pressure environments is provided, in conjunction with the results of previous experiments on macroscopic flame morphology. There is also a proposed chain of influence across certain characteristics of horizontal spray flames under low pressure. This improves our understanding of mechanisms governing flame behavior in sub-atmospheric pressure environments by allowing us to theoretically design and regulate flames.

Facile and Robust Production of Ultrastable Micrometer-Sized Foams

Stable foams that can resist disproportionation for extended periods of time have important applications in a wide range of technological and consumer materials. Yet, legislative initiatives limit the range of surface active materials that can be used for environmental impact reasons. There is a need for technologies to efficiently produce multiphase materials using more eco-friendly components, such as particles, and for which traditional thermodynamics-based processing routes are not necessarily efficient enough. This work describes an innovative foaming technology that can produce ultrastable Pickering-Ramsden foams, with bubbles of micrometer-sized dimensions, through pressure-induced particle densification. Specifically, aqueous nanosilica-stabilized foams are produced by foaming a suspension at subatmospheric pressures, allowing for adsorption of the particles onto large bubbles. This is followed by an increase back to atmospheric pressure, which induces bubble shrinkage and compresses the adsorbed particle interface, forming a strong elastoplastic network that provides mechanical resistance against disproportionation. The foam’s interfacial mechanical properties are quantified to predict the range of processing conditions needed to produce permanently stable foams, and a general stability criterion is derived by considering the interfacial rheological properties under slow, unidirectional compression. Foams that are stable against disproportionation are characterized by interfaces whose mechanical resistance to compressive deformations can withstand their tendency to minimize the interfacial stress by reducing their surface area. Our ultrastable nanosilica foams are tested in real-life applications by introducing them into concrete. In comparison to other commercial air entrainers, our microfoam improves concrete’s freeze–thaw resistance while supplying higher material strength, providing an economically attractive, industrially scalable, and durable alternative for use in real-life applications involving cementitious materials. The applicability of our stability criterion to other rheologically complex interfaces and the versatile nature of our foaming technology enables usage for a broad class of materials, beyond the construction industry.

Experimental investigation of pressure drop in helical coil during flow boiling at subatmospheric pressures

Experimental investigation of pressure drop in helical coil during flow boiling at subatmospheric pressures