End Of Tube Research Articles

Analyzing the Influence of Welding Process Selection on Residual Stresses in Tube-to-Tubesheet Welded Joints

Tube-to-tubesheet joints are used in the fabrication of shell and tube type heat exchangers, steam generators, boilers, condensers, and end shields of pressure tube type nuclear reactors like CANDU (Canada Deuterium Uranium) and PHWR (Pressurized Heavy Water Reactor). The weld joints connecting the tubes to the tubesheets are of prime importance as they have a direct impact on equipment safety. In the fabrication of these critical class-1 nuclear components, full penetration weld joints are used. Typically, these full penetration weld joints are created through multi-pass Tungsten Inert Gas (TIG) welding. However, more recent techniques, such as single-pass Electron Beam Welding (EBW) and Laser Beam Welding (LBW), have also been employed for this purpose. The fabrication time of these pieces of equipment containing full penetration weld joints can be drastically reduced if single-pass welding techniques are used compared to multi-pass welding techniques. However, the residual stresses developed in these joints due to the localized heat input and the substantial constraints of the tubesheet are unknown. Different welding processes, such as TIG welding, EBW, or LBW, can lead to varying levels of residual stresses in these joints, subsequently impacting their longevity. Weld residual stress plays a significant role in the initiation of failure modes of these tube-to-tubesheet welded joints, such as stress corrosion cracking, fatigue, and corrosion fatigue.This paper analyzes the residual stresses developed at the tube-to-tubesheet interface resulting from different welding techniques, such as multi-pass TIG welding and single-pass EBW/LBW. A comprehensive three-dimensional coupled thermo-mechanical finite element analysis is employed for this purpose. The findings reveal a significant difference, with single-pass EBW exhibiting up to 32% lower residual stresses compared to multi-pass TIG welding. Additionally, the Heat Affected Zone (HAZ) in EBW is approximately 50% smaller than in TIG welding, and the equivalent distortion in EBW is reduced by 90% compared to multi-pass TIG welding. In summary, this investigation concludes that single-pass EBW offers distinct advantages for tube-to-tubesheet weld joints, including reduced residual stresses, a smaller HAZ, and lower distortions.

Study on the bending mechanical properties of composite tube and metal joint bonding structure

Abstract The study of the mechanical properties of composite adhesively bonded joints is a very important issue, which directly affects the safety and reliability of the structure. This article studies the bending performance of carbon fiber composite tubes and metal joint bonding structures, as well as obtains the structural bearing capacity, influencing factors, and structural failure modes. Through mechanical analysis and static bending load tests, it is shown that the failure model of composite tube adhesively bonded metal joints under bending load is manifested as the first layer peeling or interlayer failure of the composite material in the bonding area between the tube and the joint, leading to local crushing at the end of the tube. There is no gap between the tube and the joint, which has little effect on the bending bearing capacity. The thickness gradient treatment at the end of the joint does not help improve the bending bearing capacity. The adhesive layer is at a 90 ° angle, which makes it easy for the first layer to peel off; it should be avoided. Other angle layers have little impact on load-bearing capacity. The longer the bonding length is, the stronger the bending capacity is. The adhesive J133 or 420 has a similar load-bearing. Wrapping a carbon fiber unidirectional layer around the ends of tubes and joints is helpful in improving their bending load-bearing capacity.

Magnetic navigation-assisted colonoscopic enteral tube placement in swine (with video): a preliminary study

BackgroundColonoscopic enteral tube placement using current methods has some shortcomings, such as the complexity of the procedure and tube dislodgement. The magnetic navigation technique (MNT) has been proven effective for nasoenteral feeding tube placement, and is associated with reduced cost and time to initiation of nutrition. This study attempted to develop a novel method for enteral tube placement using MNT.MethodsThe MNT device consisted of an external magnet and a 12 Fr tube with a magnet at the end. Ten swine were used, and bowel cleansing was routinely performed before colonoscopy. Intravenous anesthesia with propofol and ketamine was administered. A colonoscopic enteral tube was placed using the MNT. The position of the end of the enteral tube was determined by radiography, and angiography was performed to check for colonic perforations. Colonoscopy was used to detect intestinal mucosal damage after tube removal.ResultsMNT-assisted colonoscopic enteral tube placement was successfully completed in all pigs. The median operating time was 30 (26–47) min. No colon perforation was detected on colonography after enteral tube placement, and no colonic mucosal bleeding or injury was detected after the removal of the enteral tube.ConclusionsMNT-assisted colonoscopic enteral tube placement is feasible and safe in swine and may represent a valuable method for microbial therapy, colonic drainage, and host-microbiota interaction research in the future.

A novel optical acoustic fabric based on intensity-modulated flexible air-filled fiber adapter for sound sensing

This study proposes and demonstrates an optical acoustic fabric design method to detect sound, which is based on intensity-modulated flexible air-filled fiber adapter (FAFFA). A FAFFA was woven into the weft center of the polyamide fabric as weft, and the FAFFA was realized by connecting polymer optical fibers at each end of an flexible tube. The principle of the optical acoustic fabric is to allow the flexible tube to deform with the resonance of the polyamide fabric, subsequently changing the light intensity in the FAFFA. The macro-scale finite element method and ray tracing optical simulation investigated the operating principle of optical acoustic fabric and performance of FAFFA structures, and the influence of fabric parameters was evaluated by meso-scale finite element simulation. The yarn of the optical fiber acoustic fabric has low Young’s modulus and high flexibility. The proposed FAFFA structure is simple to prepare and has good maneuverability, which breaks away from the constraints of the traditional optical acoustic sensor membrane structure. This proposed optical acoustic fabric is easy to prepare, simple in principle and highly flexible. Along with wireless devices, the use of the optical acoustic fabric can be further extended to “hearing aids” for special individuals in wearable applications.

Experimental investigation and numerical simulation of swaging process of tubes for oil country tubular goods

AbstractPremium integrated seamless pipes made from high strength low alloy steels are used to produce oil country tubular goods. Operational requirements of these pipes in petroleum industry lead to an adequate tube end connection with better mechanical strength and sealing properties. Therefore a cold swaging process or calibration of pipe end is necessary for the mechanical threading process of the tube. Applications of typical calibration mandrels result in heavy wear due to higher swaging loads and the optimal necessary geometry of end tube could not be achieved. In this study, a new mandrel geometry with a finished surface was developed to modify the pipe end profile and reduce the wear tool. The investigated pipe made from P110- pipe steel was plastically preformed using a cold swaging process. Experimental measurements of the pipe end geometry after swaging process resulted an increase of the inner tube diameter of approximately 4.9% and an outer tube diameter of 3.7% respectively. Furthermore, a rather constant tube wall thickness was also observed. An Abaqus plug-in was developed to characterize the swaging process of pipe ends. The influence of friction between tool and pipe surfaces on the final geometry of pipe ends and residual stresses in pipe ends due to preforming were numerically predicted. The new designed swaging process resulted a better final pipe end geometry and low tool wear during the preforming of pipe end. The presented plug-in in this work could be used for tool optimization and characterization of swaging process of pipes in oil and gas industries.

Application of placing the anterior end of endotracheal tube at the glottis in laryngeal mask airway positive ventilation during general anesthesia: A prospective, randomized, controlled trial.

Glottic contraction and closure causes ventilation obstruction and laryngeal mask airway (LMA) leakage during positive pressure ventilation using LMA. This study aimed to assess the effect of placing the anterior end of the endotracheal tube (ET) at the glottis through the LMA ventilation conduit on treating LMA leakage following glottic contraction and closure. In this prospective, randomized, controlled trial, patients with non-minor surgery using LMA ventilation were randomly allocated to the i-gel group (group L) and the i-gel combined with ET group (group LE). The tip of ET was placed 2 cm under glottis guided by fiberoptic bronchoscope through i-gel ventilation conduit in group LE. The perioperative incidence of i-gel leakage, the changes of systolic blood pressure (SBP) and heart rate (HR) following artificial airway insertion, and adverse events were recorded. Perioperative i-gel leakage was observed in 7 of 48 patients (14.6%) in group L and 1 of 49 patients (2.0%) in group LE. There was significant difference in the incidence of leakage between the 2 groups (P = .031). SBP and HR after ET insertion in group LE increased significantly compared to those in group L (P < .05/5). The values of both SBP and HR after ET insertion did not exceed the basic values in group LE (P > .05/4). There were no significant differences in the incidence and severity of postoperative sore pain and hoarseness, cough during i-gel and ET removal between the 2 groups (P > .05). Placing the anterior end of ET at the glottis reduced LMA air leakage related to glottic contraction and closure in non-minor surgery. The ET placing had low stress response and did not significantly increase postoperative complications.

A study of histomorphological features of fallopian tube and immunohistochemical stains for p53 &amp; ki67 of the fimbrial end of fallopian tube

A study of histomorphological features of fallopian tube and immunohistochemical stains for p53 &amp; ki67 of the fimbrial end of fallopian tube

Tracheal gas insufflation for refractory hypercapnia

A 65 year male patient got admitted to ICU after alleged intake of ~ 250 ml of Chlorpyrifos (Organophosphate insecticides which cause cholinergic toxidrome) and cypermethrin (Synthetic pyrethroid) and presented with cholinergic toxidrome with severe hypercapnia (supercarbia). All conventional and advanced modes of ventilation failed to ventilate the patient because of severe bronchospasm and a prolonged expiratory time constant with high airway pressures and high auto-peep. As a last resort, we resorted to unconventional modes, as the patient could not afford ECMO. Tracheal gas insufflation was done using a coaxial flow of humidified oxygen at 8 lpm with a suction catheter and ventilator parameter were adjusted to match the added gas flows. Tracheal gas insufflation can be delivered by a thin catheter placed through the endotracheal tube (terminating within 1 to 2 cm of the main carina) or via a modified endotracheal tube with channels embedded in the walls of the tube. Tracheal gas insufflation flow can be forward (toward the alveoli) or reversed in direction toward the proximal end of the endotracheal tube. Keywords: TGI, Hypercapnia, organophosphate toxicity

Dynamic plain abdominal film provides simple and effective diagnosis of delayed shunt insufficiency caused by abdominal adhesions after VP shunt

BackgroundMany complications may occur after placement of the ventriculoperitoneal shunt (VP shunt) for hydrocephalus, and delayed shunt insufficiency (DSI) is among the most common. It is often caused by abdominal adhesions, which increases the difficulty of diagnosis. This study aimed to explore the clinical value of dynamic plain abdominal radiography (DPAR) as a simple diagnostic method for patients with DSI due to terminal adhesion of the peritoneal shunt after VP surgery.MethodsA total of 30 patients with high suspicion of DSI due to abdominal adhesions after VP surgery were included. DPAR was used for prospective assessment. The interval between the first and second PAR was 4–6 h before surgery. If two plain abdominal radiography at different times indicated that the end of the shunt tube in the abdominal segment was fixed, it was diagnosed as DSI due to adhesion of the shunt tube at the abdominal end. The peritoneal end of the shunt tube was surgically repositioned. Postoperative DPAR was repeated to evaluate the distance of the shunt outlet within the abdominal segment.ResultsAll cases showed clinical symptoms or imaging findings of shunt insufficiency. The diagnostic accuracy of DPAR was 96.67% (29/30). The end of the shunt tube in the abdominal segment of the preoperative group was fixed with abdominal plain film twice with a mean difference of 1.74 ± 1.18 cm. The mean postoperative change in the position of the end of the shunt tube in the abdominal section was 9.36 ± 2.64 cm, showing a significant difference compared with the preoperative group (P < 0.001). The mean postoperative EVANs index (0.37 ± 0.08) was significantly lower than the preoperative (0.42 ± 0.08) (P = 0.007), Glasgow coma scale score (12.8 ± 2.69) was higher than the mean preoperative score (11.36 ± 2.43) (P = 0.013).ConclusionDPAR is a simple and effective method for the diagnosis of shunt insufficiency caused by delayed abdominal end adhesion after VP shunt.

Capillarity-powered and CRISPR/Cas12a-responsive DNA hydrogel distance sensor for highly sensitive visual detection of HPV DNA

The rapid and specific identification and sensitive detection of human papillomavirus (HPV) infection is critical for preventing cervical cancer, particularly in resource-limited regions. In this work, we hope to propose a capillarity-powered and CRISPR/Cas12a-responsive DNA hydrogel distance sensor for point-of-care (POC) DNA testing. Using the thermal reversibility of DNA hydrogel and capillarity, the novel DNA hydrogel distance sensor can be rapidly and simply constructed by loading an ultra-thin CRISPR/Cas12a-responsive DNA-crosslinked hydrogel film at the end of the capillary tube. The target DNA-specific recombinase polymerase reaction (RPA) amplicons activate the trans-cleavage activity of the Cas12a enzyme, cleaving the crosslinked DNA in hydrogel film, and causing an increase of hydrogel's permeability. As a result, a sample solution containing target DNA travels into the capillary tube at a longer distance compared to the negative samples. Reading the solution traveling distance in capillary tubes, the novel sensor realizes target DNA detection without any special equipment. Benefiting from the exponential target amplification of RPA and multiple turnover response of trans-cleavage of CRISPR/Cas12a, the developed sensor can visually and specifically detect as low as 1 aM HPV 16 DNA within 30 min. These outstanding features, including exceptional sensitivity and specificity, simple and portable design, mild measurement conditions, quick turnaround time, and user-friendly read-out, make the novel distance sensor a promising option for POC diagnostic applications.

Modeling study of the energy separation effect of a control valve structure on a vortex tube

This paper compares the effect of different angles of triangular conical and truncated conical regulating valves on the heat and cold separation of vortex tubes. Numerical simulation and experimental studies show that60° truncated cone regulating valve has better cooling effect. The inlet pressure is in the range of 0.2MPa–0.4 MPa, and the temperature rate change at the cold end of the vortex tube is larger and the numerical change is smaller. Under the same circumstances, the temperature at the cold end of the vortex tube is connected to the area of cold-heat exchange in the tube at the hot end, as well as to the location of the fluid's stagnation point. The vortex merging rate is related to the angle and form of the regulating valve. The experimental data and the simulation results are in relative agreement with each other, with the maximum temperature difference being 4.41 % and the minimum difference being 3.52 %. The numerical simulation is validated by the house validation method using the theoretical model and experimental study, and the change of the angle of the control valve has the same trend with the numerical change of the theoretical model.

An Experimental Investigation Of Local Thermo-Fluidic Heat Transfer In A U-Shaped Mini-Channel Sink

This study investigates experimentally a heated U-shaped mini-channel heat sink using Infrared Thermography and Particle Image Velocimetry for a water coolant flow of Reynolds numbers of 280, 650, and 1350 (based on the hydraulic channel diameter). The choice of this cell geometry is based on its role as a simplified unit of a serpentine heat exchanger, which is proved to be one of the most promising for cooling processes. The use of the infrared camera allows the detection of temperature fields on top of the external surface of the cell. Therefore, aiming to derive the temperature distribution on the channel roof, a dedicated transfer function is implemented. Moreover, we employed the lumped capacitance model for thermal analysis on both infrared measurements and thermocouple data. The latter are recorded to capture the cooling process of the aluminium base and water temperature at the end of the outlet tube. As a result, thermal transient rate, cooling magnitude and equilibrium temperature are obtained. These parameters indicate that higher Reynolds numbers correspond to increased thermal transient rates, enhanced cooling effects, and lower equilibrium temperatures. A non-uniform distribution of heat transfer along the channel is reported, with the most efficient cooling area localized close to the first 90-degree corner. These findings are consistent with numerical simulations and previous experimental observations. PIV results reveal the presence of two fluid acceleration zones following both 90-degree corners, which contribute to improve the water cooling ability in their respective regions. Additionally, the formation of two recirculating bubbles is reported at the inner wall from corners vertices, whose intensity is dependent on Reynolds number, pushing the main flow towards the outer channel wall and reducing the local heat transfer. Turbulent kinetic energy distributions are also investigated, pointing out the presence of intense areas that better match with regions of minimum equilibrium temperature than maximum velocity zones. This suggests the presence of local turbulent unsteadiness and three-dimensional phenomena, which contributes significantly to cooling enhancement.

Generation of cutting heat and simulation of core tube wall temperature during coring in primary structure coal seam

When the drilling core method is used to determine the coalbed gas content, the cutting heat generated by the core bit cutting coal will increase the core tube temperature, and the excessively high core tube temperature will have an heating effect on the coal core, which will accelerate the coal core gas desorption rate and increase the gas loss amount. The generation of cutting heat of core bit and the measurement of core tube temperature are the basis for grasping the gas desorption law of coal core and projecting the amount of gas loss. Firstly, the self-developed core tube temperature measurement device was used to conduct on-site core temperature measurement experiments at different cutting speeds. Then, the cutting temperature of core bit was solved by establishing thermodynamic model for cutting coal and heat transfer model of cutting edge. Finally, based on the thermal conductivity characteristics of the core tube, the core tube temperature at different cutting speeds was simulated, and the simulated temperature was compared with the on-site measured temperature to verify the reliability of the model. The results show that when coring in primary structural coal, the temperature change trend of core tube wall temperature measurement point at different cutting speeds is basically consistent, the temperature measurement point at the front end of the core tube mainly goes through a relatively stable period in the drilling process, a sharp rising period in the cutting process, a slow rise and cooling period in the withdrawal process. However, the temperature measurement point at the back end of the core tube wall mainly goes through a relatively stable phase and a slowly increasing phase. The temperature rise of the core bit and the core tube wall are significantly positively correlated with the cutting speed. When coring in hard coal seam and the core depth is not large, the cutting heat generated by the core bit and the coal body is the dominant factor for the temperature rise of the core tube. The core tube wall temperature calculated using the model matches well with the field measured temperature, and the error is small, which fully shows that the coring thermodynamic model is feasible. This study provides a basis for further research on the dynamic distribution characteristic of coal core temperature during coring, which is of profound significance to calculate the gas loss and coalbed gas content.

Research and design of automatic cutting machine for propellant NDSI-2K and FCG-2.B41M

This article introduces the results of research on a new solution in the process of cutting and selecting propellants used for the double-based tubular propellant production line of Factory Z195/General Department of Defense Industry. The traditional method is usually manual, using the foot pedal force of the worker through a mechanical drive system to pull the cutting knife down to cut the propellant. It takes a lot of time, labor and product quality is not high. After cutting it is necessary to lathe the ends of propellant tube to meet technical requirements. With the new solution, the propellant is cut automatically, quickly, safely and accurately and the selection of the propellant is carried out through a weighing conveyor system based on the principle of classification by weight. The entire working process is controlled by a sensor systemand PLC programerthrough a monitoring computer located in the control room. Processing data can be stored and periodically exported for report purposes.

Hybrid FRP-concrete-steel prestressed double-skin wind turbine towers: Concept, design considerations and research needs

The past decade has seen rapid development of offshore wind energy around the world. Furthermore, to improve the efficiency of power generation, wind turbine development has been trending towards increasingly large and tall turbines. These developments call for innovations in the form of wind turbine towers to address the challenges faced by existing tower forms (e.g., steel tubular towers and prestressed concrete towers) in structural adequacy, construction efficiency and/or maintenance. This paper presents a new form of hybrid wind turbine towers which possesses many important advantages over the existing tower forms and are particularly suitable for large offshore wind turbines. The new hybrid towers, termed herein hybrid FRP-concrete-steel prestressed double-skin wind turbine towers or PDSWTs, are prefabricated in segments and then assembled on site. The PDSWT segments are a variation of hybrid FRP-concrete-steel double-skin tubular members (DSTMs), and they consist of an outer confining tube made of fibre-reinforced polymer (FRP), a thin steel inner tube with welded shear studs, prestressed concrete between the two tubes, and flanges welded at the ends of the steel tube. The onsite assembly of the tower involves mainly connecting the steel flanges of two adjacent segments using high-strength bolts, and installing prestressed tendons through the whole tower. In this paper, the rationale behind the development of PDSWTs is first explained, followed by a discussion of the design considerations and future research needs to facilitate the practical applications of the new tower form.

The burnt gas flow stability of limit flames in vertical tubes

Stability of the gas flows generated by steady near-limit flames propagating in vertical tubes is studied numerically. Basic scenarios of the burnt gas flow evolution are identified in relation to the thermal gas expansion parameter and the normal flame speed. It is shown that the realization of specific scenario essentially depends on the stagnation zone width as well as on the distance travelled by the gas from the flame front to the tube end. In particular, it is found that for sufficiently short distances, the burnt gas flows are stable provided that the stagnation zone width is less than half the tube diameter. Otherwise, an unstable flow evolution can lead to the appearance of recirculation domains and acoustic perturbations.

Nature of spontaneous signal and detection of radiation emitted from hydrogen Rydberg matter

In this article, we report on laser-induced radiation and spontaneous radiation emitted from a chamber containing hydrogen Rydberg matter. The emitted isotropic radiation penetrates a 3-mm-thick steel wall and several meters of air. The radiation can be detected using a simple photoelectric multiplier (PM) detector with aluminum foil covering the front end of the PM tube. The experimental setup, how to initiate the radiation, and radiation detector construction are discussed in this article. In addition, the detector stability and time development of detector response when the chamber is activated by gas loading and laser excitation are reported. Gamma-ray sensitivity, x-ray sensitivity, and pulse shape are further examined to characterize the emitted radiation. The results presented herein have been recorded for the past 4 years. The extensive and extended research shown in this work verifies that when hydrogen enters an iron oxide Rydberg state catalyst containing potassium, the catalyst will eventually emit penetrating radiation that behaves as x rays. The radiation can easily be detected using several detector methods. The spontaneous signal shows all indications of being x-ray radiation in character. The findings of this study regarding hydrogen’s behavior in materials have not been previously reported and require additional investigation by other research teams.

PRODUCTION OF Ni-HARD ALLOY POWDERS BY GAS ATOMIZATION

Ni-Hard cast iron materials are frequently used in equipment where high wear resistance is required in industrial applications. Generally, Ni-Hard is produced by conventional casting techniques. In this study, it was aimed to produce Ni-Hard powders to produce Ni-Hard cast iron materials with additive manufacturing techniques. To produce spherical and fine raw materials for additive manufacturing techniques, the gas atomization technique with a close-coupled nozzle system was preferred for the production of Ni-Hard powders. Ni-Hard alloy was melted in a high-frequency 10kW induction furnace under a protective atmosphere integrated into the gas atomization system. During the atomization process, 150 °C superheating was applied to prevent the liquid metal from freezing and clogging the melt delivery tube. In terms of the continuity of the atomization process, the negative pressure (aspiration pressure) values formed at the end of the melt delivery tube at different gas pressures were measured. An aspiration pressure of -50 mbar was obtained under an atomization pressure of 35 bar. Particle size distributions, hall flow behaviour and angle of repose properties of the produced powders were determined. Finally, the characterization of the powders was carried out by scanning electron microscopy. It was determined that the powders obtained as a result of atomization exhibited a spherical morphology and a narrow size range. The Hall flow rate test result of Ni-Hard powders was measured as 22 seconds for 50 g.

SAFE PERFORMANCE OF WORKS IN CONSTRUCTION AND HOUSING AND COMMUNAL SERVICES USING THE ORIGINAL SCAFFOLDING DESIGN

Our development relates to construction, namely scaffolding and scaffolding used when working at height. It is intended for fencing the work area when carrying out various types of work, for example, when performing brickwork from scaffolding. In construction, where safety and efficiency play a crucial role, the correct selection and use of scaffolding are integral to every successful project. We have proposed a patent-protected solution. It is a scaffolding railing consisting of vertical support posts hinged with horizontal crossbars, characterised by the fact that each support post is made in the form of a telescopic connection of pipes of different diameters with the possibility of extending them from each other and is fixed with the help of an existing locking device. The hinge connection of horizontal crossbars with them, except the upper row of such bars that are railing, is made in random order, for example, by attaching a hinge to the upper end of the upper tube of the smallest diameter, and is carried out using additional ring elements mounted on the corresponding telescopic connecting tubes. The inner diameter of each of these annular elements, exceeding the outer diameter of the tube on which it is mounted, is less than the outer diameter of the next subordinate telescopic tube. Thus, it can move only vertically in a telescopic connection within this and above pipes. It makes it possible to support each of the ring elements with horizontal crossbars attached to them under their weight at a certain level of height of the vertical support post, determined by the height of the underlying tube of the telescopic connection. At the same time, the lower horizontal crossbar is hinged to the ring element of the largest diameter, put on the lower tube of the telescopic connection, and rested directly on the working flooring made in the form of a sideboard. The proposed device is not technically complex to implement. Its use increases the workers’ productivity, improves the working conditions, and ensures the safety of various construction works. Keywords: safety, construction, ease of use, prototype, fencing, scaffolding.

Dense Multibutterfly Spots-Enhanced Miniaturized Optical Fiber Photoacoustic Gas Sensor.

A miniaturized optical fiber photoacoustic gas sensor enhanced by dense multibutterfly spots is reported for the first time. The principle of space light transmission of neglecting paraxial approximation is theoretically analyzed for designing a dense multibutterfly spots-based miniature multipass cell. In a multipass photoacoustic tube with a diameter of 16 mm, the light beam is reflected about a hundred times. The light spots on the mirror surfaces at both ends of the photoacoustic tube form a dense multibutterfly distribution. The volume of the micro multipass gas chamber is only 5.3 mL. An optical fiber cantilever based on F-P interference is utilized as a photoacoustic pressure detector. Compared with that of the single-pass structure, the gas detection ability of the photoacoustic system with dense multibutterfly spots is improved by about 50 times. The proposed miniaturized sensor realizes a detection limit of 3.4 ppb for C2H2 gas with an averaging time of 100 s. The recognized coefficients of minimum detectable absorption (αmin) and normalized noise equivalent absorption are 1.9 × 10-8 cm-1 and 8.4 × 10-10 W cm-1 Hz-1/2, respectively.