Analysis and Optimization of DC Supply Range for the ESP32 Development Board

<div><p>ESP32 is becoming a popular and potential game-changer in the IoT industry. Once a code completed, to take off without a USB power, questions rise about powering it; What’s the feasible external voltage range? What’s the current? Which cell battery? And so on. These questions cannot be quickly resolved by only skimming datasheets.</p><p><br></p><p>This paper went over to clarify the obscure information about the DC supply range for the ESP32 development board, especially ESP32-DevKitC V4. The investigation, calculation, experiments, and LTspice simulation disclosed the result. Starting from getting relevance facts from datasheets of essential components on the board, calculated thermal conditions of the heated element, experimented to confirm the deliberate and get empirical data while code running including GPIO and WiFi, and ended with simulation ensure the data.</p><p><br></p><p>This paper concludes the following result points. The minimum supply voltage is 3.6 V to run an ESP32 module. The supply voltage should be under 10 V for both input capacitor rated voltage and LDO junction temperature rating. The thermal restriction was calculated at an ambient temperature of 25 °C and tried and tested. For a more harsh environment, this way could derate the upper limit voltage. An external power should supply current well over average 100 mA, a good 1 A. In terms of battery, this range reassures that an ESP32 can run with a single cell LiPo. Regarding the USB, both the high power and low power port can supply sufficiently. While an external supply being no less than 5.2 V, both the USB and external sources could work simultaneously.</p></div><div><br></div>

Analysis and Optimization of DC Supply Range for the ESP32 Development Board

<div><p>ESP32 is becoming a popular and potential game-changer in the IoT industry. Once a code completed, to take off without a USB power, questions rise about powering it; What’s the feasible external voltage range? What’s the current? Which cell battery? And so on. These questions cannot be quickly resolved by only skimming datasheets.</p><p><br></p><p>This paper went over to clarify the obscure information about the DC supply range for the ESP32 development board, especially ESP32-DevKitC V4. The investigation, calculation, experiments, and LTspice simulation disclosed the result. Starting from getting relevance facts from datasheets of essential components on the board, calculated thermal conditions of the heated element, experimented to confirm the deliberate and get empirical data while code running including GPIO and WiFi, and ended with simulation ensure the data.</p><p><br></p><p>This paper concludes the following result points. The minimum supply voltage is 3.6 V to run an ESP32 module. The supply voltage should be under 10 V for both input capacitor rated voltage and LDO junction temperature rating. The thermal restriction was calculated at an ambient temperature of 25 °C and tried and tested. For a more harsh environment, this way could derate the upper limit voltage. An external power should supply current well over average 100 mA, a good 1 A. In terms of battery, this range reassures that an ESP32 can run with a single cell LiPo. Regarding the USB, both the high power and low power port can supply sufficiently. While an external supply being no less than 5.2 V, both the USB and external sources could work simultaneously.</p></div><div><br></div>

Conductive concrete made from recycled carbon fibres for self-heating and de-icing applications in urban furniture

This paper presents a broad experimental study performed at laboratory and industrial facilities to develop conductive concrete for self-heating and de-icing applications in urban furniture. Self-heating capacity is achieved by the application of electric current through a highly dense matrix containing recycled carbon fibers and graphite flakes. Prisms and slabs were fabricated with two different conductive concretes and electrode con­figurations to characterize the electrical properties and heating performance. Finally, 3 benches with different electrode disposals were fabricated to assess the heating capacity in real-scale applications. The results presented indicate promising results about the use of recycled carbon fibers for electrothermal concrete applications and identify the electrode configuration that allows the most efficient heat transfer and reduction of temperature gradients within the heated element. Real-scale tests show that the current technology developed is potentially applicable at de-icing applications in climates where temperatures remain within the range of -3 or -5 ºC.

The heat transfer and instabilities results during the onset of flow boiling in minichannels

The paper discusses the results of flow boiling heat transfer in minichannels obtained on the basis of time-dependent experiments. The main interest of the work was to investigate the occurrence of the accompanying instabilities during the boiling incipience. The essential part of the experimental standwas a test section with two minichannels, each of 1.7 mm depth. The heated element for FC–72flowing along the minichannels was a thin foil. In the tested minichannel, the temperature of the outer surface of the foil was measured due to thermoelements. The onset of flow boiling in minichannels was induced by increasing the heat flux supplied to the heater. The main aims of the investigation were to determine the heat transfer coefficient by means of the FEM with time—dependent Trefftz–type basis functions based on the Hermite interpolation and to recognize dynamic instabilities during boiling incipience. The results were illustrated as: the heat transfer coefficient, the mass flow rate and the inletpressure versustime and as boiling curves.

Thermal Bowing of Reinforced Concrete Elements Exposed to Non-Uniform Heating

The paper presents the test description and results of thermal bowing of RC beams exposed to non-uniform heating at high temperature. Bending of a non-uniformly heated element is caused by free thermal elongation of the material it is made of. The higher the temperature gradient, the greater the bending. In the case when an element is exposed to load and high temperature simultaneously, apart from free bending also deformation of the RC element may occur, which is caused by the decrease of the concrete or reinforcing steel mechanical properties. In order to examine the contribution of the deflection caused by thermal bowing to the total deformation of the bent element with a heated tension zone, an experimental study of freely heated (unloaded) beams was performed. RC beams were heated: (1) on three sides of the cross-section or (2) only on the bottom side. Deflection of elements loaded by a substitute temperature gradient was calculated using the Maxwell–Mohr formula. The test results show that deflection of freely heated RC beams (caused by the thermal bowing phenomenon) can be 10 to 20% of the total deflection of loaded RC beams with a heated tension zone.

NUMERICAL STUDY OF COOLING BY TANGENTIAL SYNTHETIC JET

Modern electronics are becoming more compact and with higher processing power, which translates into a demand for higher heat dissipation. Current electronic "coolers," which are based on the combination of fans and heat sinks, are becoming unable to provide sufficient heat dissipation since they rely primarily on generating large volumetric flowrates of air to achieve their results. As an alternative, synthetic jets are under consideration due to their known property to enhance turbulence and heat transfer. Synthetic jets are produced by the oscillation of a membrane in a sealed cavity equipped with an orifice. For this study, a numerical model of channel mounted with a heating element on one surface and a synthetic jet directed to blow along the wall was constructed on ANSYS CFX. Heat dissipation provided by the synthetic jet was analyzed with respect to changes in Reynolds number, pulsing frequency and placement of the heated element. Results were compared to a conventional technique represented by a steady channel flow of equivalent mass flow rate to the average flow induced by the synthetic jet. Results showed that the synthetic jet formed a thin layer of intense vorticity along the targeted surface with cooling greatly outperforming conventional techniques. Synthetic jet cooling was also determined to be most affected by jet velocity and Reynolds number while pulsing frequency and placement of the heated element were not as influential.

Natural Convective Heat Transfer From a Horizontal Rectangular Isothermal Element Imbedded in a Plane Adiabatic Surface With a Parallel Adiabatic Covering Surface

Natural convective heat transfer from a horizontal flat rectangular isothermal heated element imbedded in a flat rectangular adiabatic surface has been numerically studied. The surface of the heated rectangular element is in the same plane as the surface of the surrounding adiabatic material. A rectangular flat horizontal adiabatic surface is mounted parallel to and at a relatively short distance from the heated element. The heated element is facing upwards with the covering surface above the element. For the conditions considered laminar, transitional, and turbulent flows can occur. The flow has been assumed to be steady. Constant fluid properties have been assumed except for the density change with temperature which gives rise to the buoyancy forces. This was dealt with using the Boussinesq approach. To obtain the solution, the commercial CFD solver ANSYS FLUENT© was used to numerically solve the governing equations. The k-epsilon turbulence model was employed with account being taken of buoyancy force effects. The effects of the dimensionless distance of the rectangular covering surface from the heated rectangular element and of the ratio of the side lengths of the rectangular element on the variation of the Nusselt number with Rayleigh number have been examined.

Optimal Architecture of Shack Hartmann Wave-Front Sensor for Microfluidic Applications

Means of measuring temperature and fluid flow in microelectromechanical systems (MEMS) continue to show limitations. This paper discusses the development of a noninvasive optical based temperature mapping technique for use in microsystems. The technique employs the Shack-Hartmann wave-front sensor (SHWFS), with documented accuracy in macroscale applications of ±0.7°C [1]. Microscale models indicate the potential to collect data with the same accuracy. With continued development, fluid flow monitoring by thermally seeding an element of fluid and using the SHWFS to detect the location of this heated element will be possible. This measurement technique can be applied to a variety of microfluidic devices, including biomedical devices, since the temperature "seed" can be small enough to prevent damage to sensitive biological systems.

Natural Convection From Two Thermal Sources in a Vertical Porous Layer

Numerical study of natural convection flow induced by two isothermally heated elements located on adiabatic vertical plate immersed in a Darcian porous medium is carried out in the present article. The natural convection is affected by the Rayleigh number, the separation distance between the elements, their temperature ratio, and the length of the upper element. The numerical results are presented as average Nusselt number versus Rayleigh number for wide ranges of the governing parameters. It is found that the heat transfer from the lower element is not affected by the presence of the upper element for equal temperatures of the elements. The heat transfer from the lower element can be enhanced by increasing the temperature of the upper element due to the suction effect. The average Nusselt number along the upper heated element is found to increase with the increase of any of the governing parameters.