Compact Tube Research Articles

Experimental study on flow and heat transfer of High-Pressure helium flow in compact helical tube heat exchanger in HTGR

In this study, experiments were conducted on helium flow within a compact helical tube heat exchanger. High-temperature helium and deionized cooling water, flowing in opposite directions, were allocated to the shell side and tube side, respectively. The Reynolds number of helium ranged from 3 × 103 to 1.6 × 104 under an operational pressure of 2.1 MPa. Measurements were taken for helium temperature, tube outer-surface temperature distribution, pressure, and mass flow rate to illustrate the flow and heat transfer characteristics. Sensitivity analysis of thermal–hydraulic parameters, including heat transfer power and efficiency under various operational conditions, was performed. The convective heat transfer coefficient and pressure drop were calculated. The transition point (Re = 9000) between laminar and turbulent flow of helium on the shell side was identified, and empirical correlations for the Nusselt number and friction coefficient were proposed. The experimental results indicate that the heat transfer performance of helium in the compact helical tube heat exchanger exceeds that of water in large-scale helical tube heat exchanger by approximately 20.75 % under fully developed turbulence, while the flow resistance characteristics remain essentially consistent.

Integrated Couplers of THz Radiation for Helical Slow-Wave Structures.

We have designed an integrated device that couples input and output coaxial horn antennas with a self-assembled helical slow-wave structure cradled in a v-groove on a silicon-on-insulator wafer. These devices will potentially enable the characterization of cold parameters and beam-wave interaction in slow-wave structures on a wafer level, i.e., without having to dice and package individual devices. In addition, such vertically integrated antennas and helical slow-wave structures may form the basis of compact and low-cost traveling-wave tube amplifiers operating at THz frequencies.

Force-displacement relation for lumped plasticity model of compact square concrete-filled steel tube columns

Integration of steel and concrete benefits in square concrete-filled tube columns (SCFTs) makes them be utilized extensively worldwide. To evaluate the seismic behavior of special moment frames having SCFT columns, an accurate macro-modeling tool with little complexity is necessary. Although the fiber section can consider both linear and nonlinear behavior of SCFT, it fails to allow for deterioration, which is vital in assessing a seismic resisting system. This study proposes a new deterioration tool based on the Ibarra-Krawinkler model for compact SCFT columns using artificial neural networks (ANNs) through numerical simulation. Initially, 96 specimens with variations in geometry, material, and axial loading conditions were simulated in ABAQUS and then were analyzed using displacement control loading protocol to obtain hysteretic curves, which were used to prepare the data sets for training, testing, and validating the neural networks. Finally, the performance of ANN models was evaluated by statistical relations such as regression and mean square error. Through FEMA 356 and Ibarra-Krawinkler approaches, parameters defining linear and nonlinear phases of SCFTs behavior were derived. By employing efficiently trained neural networks, equations predicting the parameters of the deterioration model were established, and the obtained results show the accuracy and efficiency of the proposed model.

The serpulid tube worm Laqueoserpula reussi (Weinzettl, 1910) from the Upper Cretaceousof the Bohemian Cretaceous Basin – an alleged gastropodwhich has turned out to be a characteristic faunal elementof marine nearshore high-energy environments

The serpulid tube worm Laqueoserpula reussi (Weinzettl, 1910), originally introduced as a gastropod named Burtinella(?) reussi, is described from the Upper Cenomanian and Lower Turonian of the Bohemian Cretaceous Basin. It had usually been confused with other species and genera before 2008. Comparison with specimens from the type locality of the type species of the genus Laqueoserpula Lommerzheim, 1979 confirms the affiliation of the Bohemian species to this genus. The simple prismatic (SP) ultrastructure of the tube wall of L. reussi agrees with an assignment to the tribe Serpulini Rafinesque, 1815. In the Upper Cretaceous, representatives of Laqueoserpula are exclusively found in nearshore deposits, where they are accompanied by a high diverse marine invertebrate fauna. By its compact, large and robust tube forming a spiral and extremely thick tube wall, L. reussi was well-adapted to live in nearshore high energy environments, where its tube could be encrusted by bryozoans, brachiopods and oysters, and infested by hydroids and borers.

Prediction of Heat Transfer for Compact Tube Heat Exchanger Based on Porous Models

Abstract A prediction method for temperature distributions in compact heat exchangers was developed by modeling the microchannel as porous medium. The study is focused on the mathematical formulas and solution methods for convective heat transfer of heat core. The governing parameters include Reynolds number, longitudinal pitch, transverse pitch, Nusselt number, inertial resistance factor, and effective heat transfer coefficient. First, the correlation mechanisms and laws between the key parameters’ effects and heat transfer were revealed and explained. The results show that the temperature/pressure/velocity contours obtained from the porous-media model are consistent with those of the tube-matrix. When the longitudinal pitch has little effect on flow characteristics and Reynolds number, porous-media model and Zukauskas-correlation are consistent. Transverse pitch has significant effects on the flow characteristics and the Reynolds number. The heat transfer performance and Nusselt numbers obtained from tube-matrix, porous-media model, and Zukauskas-correlation decrease as the transverse pitch increases. Under different pitch conditions, the Nusselt number obtained by Zukauskas-correlation is larger than that of the porous-media model, which is larger than that of the tube-matrix. Second, the simplified model and fast calculation method were developed. Tube bundles of the heat exchanger core were modeled as micro-channels and theoretically as fluid-saturated porous structures. Results show the heat transfer performance predicted by the micro-channels, tube-matrix, and porous-media model is consistent under the same boundary conditions. These results are consistent with the experiment. In addition, the computing cost and time required for the porous-media and micro-channels model is relatively reduced. Especially for the micro-channels model, the calculating time is less than one-tenth of the original. Compared with the time-consuming numerical method, the new analytical solution has the advantages of cost and speed.

Dynamics of unipolar charged particles flowing through a cylindrical tube at high number concentrations

This work provides a theoretical and non-dimensional numerical analysis of the dynamics of gas-borne unipolar charged particles flowing through a cylindrical tube at high number concentrations. It is discovered that above a threshold input particle number concentration, the concentration at the exit of the tube is nearly constant and independent of further increase in the input. Based on a maximum of 2% sensitivity of the system, the threshold input number concentration is quantified for a tube of any length more than 40 × the radius. The theoretical analysis developed in this work is used to derive correlations for the threshold input concentration and the exit concentration, as well as show that the exit particle concentration is lower than the threshold input value by a factor of 20/PD, where PD is the well-known diffusive particle penetration. The analysis demonstrates that a constant concentration can occur if and only if the ratio of non-dimensional electric particle mobility to the Gormley-Kennedy diffusion parameter is above 74, which is a hitherto unexplored regime of charged aerosol flow dynamics. It is shown that the constant concentration can occur in compact tube designs (L/R<100) as long as the mass Peclet number of the particles is high and reducing the mass Peclet number to around 10 or below makes it impossible to obtain an input-independent number concentration. It is also shown that the Reynolds number of the flow has very little effect on the charged transport dynamics, where the order of magnitude of the input-independent number concentration is not highly sensitive to the Reynolds number, provided the system remains laminar. Finally, practical examples for designing instrumentation to generate a constant concentration of charged particles are discussed.

Fiber-Optic Photoacoustic Gas Sensor with Multiplexed Fabry-Pérot Interferometric Cantilevers.

A fiber-optic photoacoustic (PA) gas sensor with multiplexed Fabry-Pérot (F-P) interferometric cantilevers is demonstrated. A compact cylindrical nonresonant PA tube with a volume of only 0.45 mL is designed. The PA signal is measured by two symmetrically installed fiber-optic interferometric cantilever microphones (FOICMs) to improve the signal-to-noise ratio (SNR). For multiplexing the two cantilevers by a single demodulation system, a dual cavity length synchronous measurement method based on total-phase demodulation algorithm with ultrahigh resolution is developed. The PA signal detection is realized by the second-harmonic wavelength modulation spectroscopy (2f-WMS) technique. The sensor performance is verified by conducting the detection of trace acetylene (C2H2). The normalized noise equivalent absorption (NNEA) coefficient is 2.5 × 10-9 cm-1·W·Hz-1/2, and the minimum detection limit (MDL) downs to about 0.2 ppm with an averaging time of 1 s. The fiber-optic PA gas sensor has characteristics of high resolution and immunity to electromagnetic and vibration interference. Furthermore, the technical scheme of the multiplexed cantilever demodulation shows great potential for remote multipoint monitoring of gases in harsh environments.

Proof-of-concept for a thin conical X-ray target optimized for intensity and directionality for use in a carbon nanotube-based compact X-ray tube.

Carbon nanotube-based cold cathode technology has revolutionized the miniaturization of X-ray tubes. However, current applications of these devices required optimization for large, uniform fields with low intensity. This work investigated the feasibility and radiological characteristics of a novel conical X-ray target optimized for high intensity and high directionality to be used in a compact X-ray tube. The proposed device uses an ultrathin, conical tungsten-diamond target that exhibits significant heat loading while maintaining a small focal spot size and promoting forward-directedness of the X-ray field through preferential attenuation of oblique-angled photons. The electrostatic and thermal properties of the theoretical tube were calculated and analyzed using COMSOL Multiphysics software. The production, transport, and calculation of radiological properties associated with the resultant X-ray field were performed using the Geant4 toolkit via its wrapper, TOPAS. Heat transfer analysis of this X-ray tube demonstrated the feasibility of a 200-kV electron beam bombarding the proposed target at a maximum current of 100mA using a 1-ms symmetric duty cycle. The cathode of the X-ray tube was designed to be segmented into nine switchable electrical segments for modulation of the focal spot size from 0.4- to 10.8-mm. After importing the COMSOL-derived electron beam into TOPAS for X-ray production simulations, radiological analysis of the resultant field demonstrated high levels of intrinsic beam collimation while maintaining high intensity. A maximum dose rate of 17,887 cGy/min was calculated for 1-mm depth in water at 7-cm distance. The proposed X-ray tube design can create highly directional X-ray fields with superior fluence compared to that of current commercial X-ray tubes of comparable size.

Non-radioactive electron capture detector based on soft X-ray ionization for gas chromatography - A possible replacement for radioactive detectors

In this paper, we present a new electron capture detector based on a compact X-ray tube (X-ECD) for electron generation by soft X-ray radiation instead of using a radioactive source. ECDs are commonly used in many laboratories as standard GC detectors since their invention in the 1950s, especially for highly sensitive detection of halogenated substances, pesticides or other environmental pollutants. However, due to unsatisfactory alternatives, many ECDs are still used with radioactive β-emitters, which is difficult and expensive in most applications today due to legal restrictions. The new X-ECD contains a small X-ray tube for generating free electrons by ionizing the carrier gas like in radioactive ECDs. Thus, no additional dopants or special gases are required. The X-ECD has limits of detection in the pptv range and shows linearity over a wide concentration range. Furthermore, the used X-ray tube shows good long-term stability. So far, we have operated the X-ray tube continuously for about one year without notable degradation. However, in case of future degradation, the X-ECD can still be operated with the same sensitivity by simple adjusting the set point current in constant current mode. This makes calibration robust against possible degradation of the X-ray tube. In combination with a conventional gas chromatograph, the X-ECD is able to detect halogenated hydrocarbons and even low volatile pesticides without any peak distortion such as tailing. Thereby a minimum detectability in the upper fg/µL range for Lindane was reached, which is similar when compared to radioactive ECDs.

Advancing flow-duct noise control: Examples of innovative silencers

Two examples of innovative silencers for advanced duct noise control are presented. The first example is related to using metamaterials and the so-called ‘slow sound' to create a compact virtual Herschel-Quincke tube [1]. The second example revolves around a concept called the ‘modal filter' [2], which is designed to selectively damp a single propagating mode. For plane waves, optimal propagational damping is achieved by a wall impedance equal to the Cremer impedance. We will demonstrate how to compute the Cremer impedance, even for low frequencies, at which the classical solution is invalid [3]. Such an arrangement efficiently dampens both the plane (0,0) and the first radial mode (0,1). To further dampen the first two circumferential modes (1,0) and (2,0), a section with the Cremer impedance can be combined with a modal filter made of micro-perforated plates. These plates are inserted parallel to the flow direction and positioned at modal velocity maxima in the duct cross-section. We anticipate that both examples can be useful in industries requiring compact noise mitigation solutions in flow ducts. [1] https://doi.org/10.1016/j.jsv.2019.115045. [2] https://doi.org/10.1121/2.0000473. [3] https://doi.org/10.1121/1.5136952

Comparative Experimental Study on Effect of Copper Wire Helical Wound Steel Tube with 2.5” Full Length Insert on Performance of Double Pipe Steel Tube Heat Exchanger

Abstract: A comparative experimental study was conducted to explore the hydrothermal behavior of a double tube heat exchanger with copper wire helical wound steel tubes and plane steel tubes with and without twisted tap inserts of pitch length 2.5 inches. In comparison to helical tubes, corrugated tubes, and many other more compact tube type heat exchangers, straight tube heat exchangers offer advantages since the construction of the heat exchanger tubes is easier. In the current work, the fluid-to-fluid heat exchange is considered, with a flow rate ranging from 15 to 75 liters/hour. Constant wall temperature or constant heat flux ideas are used in the majority of investigations on heat transfer coefficients. The efficiency, overall heat transfer coefficient, and impact of hot water flow rate with constant cold water flow rate for straight steel tube and copper wire helical wrapped steel tube heat exchangers in parallel flow and counter flow configurations were investigated and compared. Utilizing a 2.5" full length clockwise twisted tape insert, both layouts were created. The measurements were carried out in a constant state. When the hot water flow rate is increased while maintaining the cold water flow rate constant, the efficiency of the heat exchanger drops for both the straight steel and the copper wire helical wound steel tube. Compared to a plane steel tube heat exchanger, the copper wire helical wound steel tube heat exchanger has a better efficiency. The test findings demonstrate that inserting inserts causes pressure drop. With 2.5" clockwise twisted tape inserts wrapped in helical copper wire, steel tube was able to transmit heat more quickly than other arrangements.

Design and optimization of Miura-Origami-inspired structure for high-performance self-charging hybrid nanogenerator

A hybrid piezoelectric-triboelectric-electromagnetic nanogenerator (HPTENG-EMG) has been designed meticulously by focusing on material selection, structural design, and performance evaluation. The module can operate using three parts; piezoelectric, triboelectric and an electromagnetic mechanism. The hybrid concept of triboelectric and piezoelectric is achieved by fabricating triboelectric-piezoelectric composite materials working through the TENG mechanism. In the material design part, the composite film between bacterial cellulose (BC) and BaTiO3 nanoparticles (BT-NPs) fabricates and optimizes its properties with a suitable number of BT-NPs. The unique Miura-Origami (MO) hexagonal multilayer shape is applied within the structural design to increase the contact surface area, which enhances the electrical output signal. The third part of the hybrid system incorporates an electromagnetic generator (EMG) by designing a structure of compact and lightweight cylindrical tubes with magnetic levitation structures. The hexagonal multilayer shape of MO composite TENG (MO-CTENG) generates an open-circuit output voltage (VOC) of ∼414 V and short-circuit output current (ISC) of ∼48.3 μA with maximum output power (P) of about ∼6.94 mW. The highest ISC value of ∼38 mA can be promoted in the optimized EMG, which is higher than the MO-CTENG by ∼786 times. The practical application of this technology is demonstrated by human shaking motion for battery charging in the wireless Global Positioning System (GPS). The maximum direct current output voltage (VDC) saturation of 30 V can be achieved within 19 s. This work provides a potential methodology for increasing electrical output performance by capturing more mechanical energy through the conjunction of three phenomena into a single device, which exhibits a promising way of addressing an energy crisis.

Design optimization of compact gas turbine and steam combined cycles for combined heat and power production in a FPSO system–A case study

This case study aims to cover a wide range of relevant aspects related to combined cycle design, mechanical integrity and operational reliability for cogeneration of heat and power in FPSO systems. The methods consist of combined optimization of combined cycle thermodynamic design and geometry of steam generator; vibration analysis for flow induced vibrations; and thermal stress estimation of casings during cold start-stop scenarios. Challenges and opportunities for reliable water treatment systems are explored. The results show that small tubes, a compact tube bundle and a low condensation temperature reduces the once-trough steam generator (OTSG) weight. The vibrations numerical simulations in this work support the standard recommendations of using 35 times tube OD as upper limit for the unsupported tube length, which could be used as a reasonable design criterion. Thermal stresses analysis indicates that the design of beam arrangement, location, and stiffness of beams has a major impact on thermal stresses, and can be optimized to different plate thicknesses in order to avoid fatigue damage. Focus should be on reducing leaks of deaerator, steam turbine and condenser. It is recommended to add Na sensors after condenser and investigating the use of Electrodeionization (EDI) technology for make-up water production from seawater.

Physical design of a compact injector for synchrotron-based proton therapy

A compact room-temperature linear injector has been purposed to accelerate an 18.0 mA proton beam to 7.0 MeV for synchrotron-based proton therapy. The total length is appropriately 5 m. It mainly consists of a 3.01 m radio frequency quadrupole (RFQ) and a 0.82 m compact interdigital H-mode drift tube linac (IH-DTL) structure. Based on a fast-bunching strategy, the RFQ, operated at 325 MHz, accelerates protons to 3.0 MeV. The phase advances have been taken into consideration, and parametric resonance has been carefully avoided by adjusting the vane parameters. After the modulation of the transverse and longitudinal phase advances and a compact external quadrupole triplet, the proton beam is injected into the subsequent IH-DTL. Based on modified Kombinierte Null Grad Strukter (KONUS) beam dynamics, it accelerates protons up to 7.0 MeV, which is composed of a re-bunching section and an accelerating section. The accelerating gradient reaches 4.88 MV/m. The overall dynamic simulation results show that the whole accelerating gradient reaches up to 1.62 MV/m with a transmission efficiency above 95%. The transverse and longitudinal normalized RMS emittances at the exit of the DTL are 0.23 π mm·mrad and 2.216 π keV/u·ns, which meet the synchrotron injection requirements. The details of the specific design of this injector are presented in this paper.

Development of a portable pulsed fast ⩾106 neutron generator based on a flexible miniature plasma focus tube

A plasma focus device is a laboratory fusion device that is used to produce pulsed neutrons for a few tens of ns duration. A compact plasma focus tube (volume ≈ 130 cm3) has been developed, and this was connected to a newly developed capacitor bank using 24 coaxial cables, each 10 m long. The capacitor bank was of compact size and consisted of four energy storage capacitors (each 6 µF, 20 kV, size: 20 cm × 20 cm × 30 cm). The peak discharge current of the capacitor bank was estimated to be 176 kA with a rise time of around 3.6 µs at maximum 4.8 kJ operation energy. The average neutron yield was observed to be maximum (3.1 ± 1.0) × 106 neutrons/pulse with a pulse duration of 15–25 ns at an operating energy of 2.7 kJ (15 kV) and deuterium gas filling pressure of 4 mbar. Long coaxial cables allow only the plasma focus head (neutron source) to be moved as per need, making this a portable pulsed neutron source that is useful in many applications, including in extreme conditions, such as in borehole logging applications for oil and mineral mapping. This report describes the various components of this portable neutron generator together with its neutron emission characteristics.

Novel three-dimensional simplified numerical simulation method of a compact precooler for hypersonic precooled air-breathing engine

The revolutionary thermal cycle of precooled air-breathing engines has led to the application of a compact tubular precooler. A novel three-dimensional simplified numerical simulation method for a compact tube precooler is proposed. The unique aspect of this method is the integration of low-dimensional design method of the precooler with three-dimensional simulation technique. The method includes a segmented model to discretize the precooler into sub-precoolers, with corresponding performance calculation programs for circumferential uniform and non-uniform airflows in the circumferential direction. The heat transfer and pressure drop are then simulated using a combination of the distributed heat source method and porous model. The developed method was verified with previous experiments, and showed good agreement. In addition, the flow and heat transfer characteristics of the precooler were investigated under both circumferential uniform and non-uniform inlet conditions. The results show that the radial total temperature distortion intensity at the outlet of the precooler is 0.087 and 0.073 under uniform and non-uniform inlet conditions, respectively. Additionally, the intensity of circumferential total temperature distortion increases from 0.004 under uniform inlet conditions to 0.029 under non-uniform inlet conditions. Overall, this method provides an accurate evaluation of the precooler during the engineering design phase.

Thermal performance and design analysis of U-tube based vacuum tube solar collectors with and without phase change material for constant hot water generation

Solar water heaters are the most promising technology, and they can be effectively used for hot water generation in cold climatic conditions. The moto of this research is the design and development of two compact vacuum tube solar collectors (VTSCs): (i) modified copper finned U-tube based VTSC filled with PEG6000 as a phase change material (PCM). However, it integrates heat transmission and storage capabilities into a unit (ii) conventional U-tube inserted VTSC without PCM. The developed VTSC with PCM was operated under dual (simultaneous and mid-day charging) modes, and their performance was compared with the conventional system at various flow rates. This study explored the design analysis, working principle, and the outcome of fixed mass flow rates on the system's thermal output. The results display that the daily energy output of the developed collector with PCM is 81.54–89.74 % for simultaneous mode and 78.21–86.52 % for mid-day charging mode. Whereas the daily energy output of conventional solar collector without PCM was 69.31–75.54 % for set mass flow rates. The highest thermal efficiency was around 89.74 % for U-tube inserted VTSC with PCM (simultaneous mode) at a high flow rate (30 LPH). The global heat transfer coefficient (UL) was maximum at a low mass flow rate (10 LPH) for conventional system without PCM, followed by mid-day charging and simultaneously operated VTSC with PCM. After comparing both systems, it is found that using PCM in VTSC improves the daily energy efficiency and increases the operating time for 3–4 more hours than conventional system. This analysis revealed that the developed U-tube inserted VTSC with PCM can substantially supply the hot water demand for domestic applications constantly at night/off sunshine hours.

Preparation of flexible hollow TiO2 fibrous membranes for thermal-insulation applications by coaxial electrospinning

With the increasingly serious issues of energy conservation and emission reduction, hollow fibers have attracted wide attention as materials that have structural advantages in terms of thermal insulation. Herein, we report the preparation of flexible hollow TiO2 fibrous membranes via coaxial electrospinning. To optimize the thermal-insulation performance of the fibers, hollow fibers with different diameters and pore sizes were prepared by adjusting the feeding rate of the core spinning solution. Optimum conditions were achieved at a feeding rate of 2 mL/h for the shell solution and 0.4 mL/h for the core solution. The hollow fibers had a compact tube wall structure and good mechanical properties, and the tensile strength of the fibrous membranes reached 0.652 ± 0.119 MPa. In addition, the hollow fibrous membranes have excellent thermal insulation properties with an average reflectance of more than 89% and a room temperature thermal conductivity of less than 0.0294 ± 0.00015 W m−1K−1. In practical experiments, the temperature can be reduced from 1174.6 to below 273.6 °C using 15-mm-thick fibrous membranes, which confirms its excellent thermal insulation. Flexible hollow TiO2 fibrous membranes have a wide range of insulation applications.

Effect of Pitch Ratio of Tube Banks on Passive Acoustic Properties

Tube banks are common design elements in heat exchangers. The most common tube bank patterns are In-line tube banks and Staggered tube banks. These are characterized by their longitudinal and transverse pitch ratios (pitches to diameters). The tube bank with a pitch ratio of less than 1.25 is considered a compact tube bank and a pitch ratio greater than 2 is considered as widely spaced. In this paper, the attention is focused on the effects of pitch ratio in tube banks on its passive acoustics properties which are experimentally investigated. The flow duct experimentation is performed with and without flow to analyse the passive acoustic properties of tube banks. The Experiment is conducted for both the In-line and Staggered tube banks with pitch ratios from 1.2 to 2.5. Experimental results consist of scattering matrix coefficients and power balance. The results are compared to see the pitch ratio effect.

Vacuum Spin LED: First Step towards Vacuum Semiconductor Spintronics.

Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na2KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics.