The use of a chevron nozzle/orifice is one of the methods of heat transfer enhancement and noise reduction. In the case of synthetic jets, the number of papers on this topic is small. Therefore, a synthetic jet actuator with three different chevron orifices and one circular orifice is investigated. The aim of this study is to find the impact of orifice shape on centerline velocity (measured with a hot-wire anemometer) and determine if the chevron orifice reduces the generated noise. The sound pressure level was strongly dependent on the input actuator’s power, and only one chevron orifice ensured noise reduction for low power (p = 6; 8 W). At real power p = 12 W, the sound pressure level was lower for each chevron orifice actuator than in the case of the circular orifice actuator. It is shown that the application of a chevron nozzle does not have to provide noise reduction. It is important in the case of the design of new actuators that are to operate in places where noise levels should be limited (e.g., offices).

In this paper, synthetic jet actuators (SJAs) with three different orifice shapes (circular, square, and slot) with the same cross-section area were investigated. The SJA efficiency and the synthetic jet (SJ) Reynolds number were calculated based on the time-mean reaction force measurement. The momentum velocity was measured with hot-wire anemometry and additionally, the sound pressure level (SPL) was measured. The efficiency was equal maximally to 5.3% for each orifice shape, but the square orifice characterized the higher Reynolds number. The compared centerline (axial) velocities and the radial velocity profile at a distance of 112 mm were similar for each orifice type. The SPL measurement results were surprisingly constant in relation to each other. The square orifice generates the lowest SPL, approximately 2.8dB lower than the circular orifice, and approximately 4.2dB lower than the slot orifice, at each investigated real power. Finally, the differences to other papers and limitations of the approach to comparing orifices presented in the present paper were indicated.

This study presents the results of experimental studies on the thermal conductivity of specimens made from selected pure polymer filaments manufactured with the use of FFF 3D-printing technology. The tested samples were made of polylactic acid (PLA), polyethylene terephthalate glycol (PET-G), and acrylonitrile butadiene styrene (ABS). In particular, the effects of the infill patterns and infill density on the tested samples were examined in order to characterize the influence of these parameters on the materials’ effective thermal conductivity. Honeycomb and grid infill patterns of the tested samples with infill densities of 40%, 60%, 80%, and 100% were examined. The influence of temperature on thermal conductivity was studied as well. Thermal conductivity was measured using the guarded heat flow method, according to the ASTM E1530 standard within the defined temperature ranges of 20–60 °C for ABS and PET-G and 20–50 °C for PLA material. Samples of the tested materials were manufactured with the use of the Fused Filament Fabrication method (FFF), and filaments with a uniform black color were used. The obtained results were analyzed in terms of thermal conductivity variation after samples’ infill pattern and infill density modifications, which provides extended thermal property characterization of the polymeric filaments adopted for 3D printing.

The paper presents the experimental research on the thermal management of a 150 W LED lamp with heat sink inside a synthetic jet actuator. The luminous flux was generated by 320 SMD LEDs with a nominal luminous efficacy equal to 200 lm/W mounted on a single PCB. Characteristic temperatures were measured with three different measurement techniques: thermocouples, infrared camera, and an estimation of the junction temperature from its calibrated dependence on the LED forward voltage. The temperature budget between the LED junction and ambient as well as the thermal resistance network was determined and analyzed. The energy balance of the LED lamp is presented along with the values of the heat flow rate and heat transfer coefficient in different regions of the LED lamp surface. For an input power supplied to the SJA equal to 4.50 W, the synthetic jet dissipated approximately 89% of the total heat generated by the LED lamp. The heat from the PCB was transferred through the front and rear surfaces of the board. For the input power of 4.50 W, approximately 91% of the heat generated by LEDs was conducted by the PCB substrate to the heat spreading plate, while the remaining 9% was dissipated by the front surface of the PCB, mostly by radiation. The thermal balance revealed that for the luminous efficacy of the investigated LEDs, approximately 60% of the electrical energy supplied to the LED lamp was converted into heat, while the rest was converted into light.

The synthetic jet actuator (SJA) generated high noise which limits the area of its application. In this paper, the five actuators with different types of soundproofing in the cavity were tested and compared to the classic actuator. The resistance and the sound pressure level (SPL) were measured for real power $P=1, 2, 4$ W, and frequency in a range of 20–150 Hz. The resonant frequency of actuators was designed. Only one type of soundproofing had a significant impact on the resonant frequency. The use of soundproofing in the actuator cavity increased or did not affect the generated noise at a frequency below 120 Hz and only the mineral wool significantly decreased the noise at a frequency above 120 Hz– even 7 dBA. The direction for further investigations was set.

LEDs are widely used light sources. Their main advantages are low power consumption, mechanical strength, high luminous efficacy, and a lifetime exceeding 50 000 hours. However, compared to other light sources, they are more sensitive to high temperatures. Heat is generated by converting electrical energy into radiant energy. The share of heat in this transformation describes the efficiency, but in the case of light sources, efficiency is not one of the basic parameters because only a part of the radiation produced is visible light, which interests the recipients. However, the temperature has a big influence on the properties and lifetime of LEDs. This article presents the results of temperature measurements of the LED lamp.