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Surface Phenomena
Published in Pramod K. Naik, Vacuum, 2018
levels is the work function . The vacuum level corresponds to the potential energy of an electron at rest outside the metal, in the absence of an external field. In the presence of a strong field, the potential outside the metal is deformed along the line AB, so that a triangular barrier is formed. The field electrons can tunnel through this barrier with the most of the electrons escaping from the vicinity of the Fermi level where the barrier is thinnest. Nordheim 84 has established that the current density j in A/cm 2 is given by
Fundamental Quantities in Vacuum Physics
Published in Igor Bello, Vacuum and Ultravacuum, 2017
However, in other cases, atmospheric pressure is set up to be the zero-reference point at which the vacuum level is 0%. Thus, the vacuum level increases in line with the negative value of the pressure until it approaches the negative value of atmospheric pressure –101.325 kPa (–760 Torr) when the vacuum level is 100%. Then, vacuum in percent can be determined from negative pressure values using similar considerations.
Cr2S3(Et2DTC) complex and [Cr2S3-MoS2(Et2DTC)] bilayer thin films: single source stationed fabrication, compositional, optical, microstructural and electrochemical investigation
Published in Environmental Technology, 2021
Shaan Bibi Jaffri, Khuram Shahzad Ahmad, Saba Ifthikhar
Thin films were deposited by PVD in the resistive heating unit (RHU). FTO was chosen as a substrate material and it was sonicated by exposure to the ultrasonic cleaning process. The powered Cr2S3(Et2DTC) complex were placed on the FTO and positioned on the boat-shaped crucibles that are resistive to temperature so kept in the RHU with ease. Diffusion and rotary pump were utilized for the accomplishment of the vacuum (10−5 mbar). Inside the vacuum chamber, the crucibles were arranged between two panels. The vacuum level inside the chamber was measured by means of rough (10−2 mbar) and medium gauge (10−5–10−6 mbar). After vacuum attainment, the process in the RHU was continued by providing a potential of 100 V and 65 A current.
Prediction of Orthotropic Thermal Conductivities Using Bayesian-Inference from Experiments under Vacuum Conditions
Published in Heat Transfer Engineering, 2023
Suraj Kumar, Chakravarthy Balaji
The schematic and photograph of the complete experimental setup are shown in Figures 3 and 4, respectively. To achieve the desired vacuum, a water-cooled diffusion pump with an oil-cooled rotary pump is used. During the experiments, a high vacuum (8.6 × 10−7 mbar) is maintained in the inverted bell jar type vacuum chamber made of stainless steel, eliminating not only convection but also gas conduction effects. Honeycomb materials are frequently utilized in satellite applications, therefore the aim is to replicate a space environment. A set of Pirani–Penning gauges are used to measure the vacuum level. As a conductive sink, an aluminum cold plate (200 × 200 mm) is employed. The cold plate is basically a heat exchanger, with a cold fluid passing across it to keep it as an isothermal sink. A square annular copper ring (180 × 180 with a square hollow of 140 × 140 mm) is inserted between the cold plate and the test sample for three purposes. First, it provides a perfect isothermal sink at the bottom surface of the test sample as the thermal conductivity of copper is much higher than aluminum. Secondly, the copper ring helps the path of conductive heat rejection from the test sample to the cold plate by copper ring itself, thereby it helps to create a much larger in-plane temperature gradient in the test sample, hence the non-uniform temperature zone increases, which is required for successful retrieval of parameters. Third, the copper ring makes it easier to attach temperature sensors on the bottom side of the test sample. The interior of the vacuum chamber used for conducting experiments on both the isotropic and orthotropic test samples is shown in Figure 5. Figure 6 shows the photograph of the orthotropic test sample. A schematic of the test sample setup for the isotropic and orthotropic test samples are shown in Figure 7. The setup consists of the cold plate, SS304 solid plate (isotropic material), SS304 honeycomb plate (orthotropic material), copper ring, heat flux sensor, etched foil type heat, fixtures, and fasteners. The heat flux sensor and foil heater are attached to the center of the top surface of the test samples. A low emittance tape (ϵ = 0.06) is pasted at the top, lateral, and bottom (excluding copper ring) surfaces of the samples to induce adiabatic boundary conditions on the sides. The SS304 solid test sample experiences only conduction heat transfer. However, conduction and radiation (inside the cavities) heat transfer occur in the SS304 honeycomb test sample. A temperature of 27.4 is maintained inside the vacuum chamber. Steady and unsteady-state experiments are performed in a high vacuum chamber for three heat fluxes of 1840, 2516, 2888 and four heat fluxes of 1342, 1890, 2805, 7569 respectively supplied in the SS304 solid (isotropic material) test sample. Unsteady-state experiments on the SS304 honeycomb (orthotropic material) test sample are performed in a high vacuum for four heat fluxes of 794, 1321, 1953, and 2463 For additional details of the experimental setup, refer to [26, 27].