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This study aimed to examine how human body thermophysiologically responds to four commonly used cooling strategies (i.e., electric fan cooling [AirFC], evaporative cooling clothing [EvapCC], hybrid cooling, i.e., evaporative cooling clothing combined with electric fan cooling [EvapCC&AirFC] and liquid cooling clothing [LiqCC]) during heatwaves. An adaptive ‘Newton’ manikin was used to predict human physiological responses while using these four cooling systems. Four heatwave conditions were selected, i.e., 36 °C, 33% RH (hot-dry, denoted as HD1), 36 °C, 67% RH (hot-humid, denoted as HH1), 40 °C, 27% RH (extremely hot-dry, denoted as HD2) and 40 °C, 54% RH (extremely hot-humid, denoted as HH2). A metabolic rate of 2.5 METs was used to mimic moderate work while sitting at either home or outdoors. AirFC was only found to bring cooling benefits in HD1 and HH1. EvapCC was effective in both HD1 and HD2. LiqCC showed similar cooling benefits compared to EvapCC in HD1 and HD2, and also displayed cooling benefits in HH1. EvapCC&AirFC was discovered to be most effective cooling strategy in the four studied conditions. Concerning their practical applications, EvapCC&AirFC was recommended to inactive populations while staying indoors during different heatwave conditions, and EvapCC and LiqCC were more suitable for active populations while working/exercising in hot-dry conditions and hot-humid conditions, respectively. [ABSTRACT FROM AUTHOR]

The frequent infiltration through doorways accounts for a very large proportion of the total heat load of cold stores. Understanding the influence factors, along with wider range of experiments, clearly supports the accurate prediction and cuts down the infiltration. This paper provides a series of experimental investigations on the infiltration under different conditions. The experiments take factors of various door opening sizes, temperature differences and on/off of the cooling fans into account. It is observed that the infiltration flow rate stays steady while the indoor temperatures of the local probes change vigorously. The infiltration air volume changes linearly with the door open time, whether the cooling fans are turned on or off. Moreover, the air mixture effect related to the cooling fans can counteract the infiltration process. [ABSTRACT FROM AUTHOR]

Personal cooling systems (PCS) have been developed to mitigate the impact of severe heat stress for humans working in hot environments. It is still a great challenge to develop PCSs that are portable, inexpensive, and effective. We studied the performance of a new hybrid PCS incorporating both ventilation fans and phase change materials (PCMs). The cooling efficiency of the newly developed PCS was investigated on a sweating manikin in two hot conditions: hot humid (HH, 34 °C, 75% RH) and hot dry (HD, 34 °C, 28% RH). Four test scenarios were selected: fans off with no PCMs (i.e., Fan-off, the CONTROL), fans on with no PCMs (i.e., Fan-on), fans off with fully solidified PCMs (i.e., PCM+Fan-off), and fans on with fully solidified PCMs (i.e., PCM+Fan-on). It was found that the addition of PCMs provided a 54∼78 min cooling in HH condition. In contrast, the PCMs only offered a 19–39 min cooling in HD condition. In both conditions, the ventilation fans greatly enhanced the evaporative heat loss compared with Fan-off. The hybrid PCS (i.e., PCM+Fan-on) provided a continuous cooling effect during the three-hour test and the average cooling rate for the whole body was around 111 and 315 W in HH and HD conditions, respectively. Overall, the new hybrid PCS may be an effective means of ameliorating symptoms of heat stress in both hot-humid and hot-dry environments. [ABSTRACT FROM AUTHOR]

With the advantages of lower power consumption and longer lifetime, piezoelectric fans have been widely investigated for use in electronic cooling for many years. However, the application of the piezoelectric fans for LEDs is seldom explored because of its insufficient cooling ability. In this study, a dual-sided multiple fans system with a piezoelectric actuator (“D-MFPA”) is considered for use in the thermal management of LEDs. The obvious advantage is that the D-MFPA only uses one piezoelectric fan to drive eight passive magnetic fans vibrating simultaneously to provide sufficient cooling ability and two-directional air flows. Two 30-W chip-on-board (COB) LED models are adopted to investigate the thermal performance of the D-MFPA. The dimensionless heat convection number for the D-MFPA ( M D ‐ MFPA ) is defined in this study to describe and quantify the thermal performance of the D-MFPA. Moreover, several horizontal orientations ( x / S l ) and vertical orientations ( y / S h ) are examined to investigate the effects of different arrangements. The results indicate that M D ‐ MFPA can be improved to 3.92 under the case of x / S l = 0 and y / S h = 0.033; however, the single piezoelectric fan can only improve M D ‐ MFPA to 2.82. [ABSTRACT FROM AUTHOR]

This paper presents a miniature ionic wind blower for active cooling by embedding the needle electrode into heat dissipation surface. Experiments with applied voltage ranging from 8 kV to 12 kV and with heating source temperature of the surface for 40 °C, 45 °C, and 50 °C are conducted. The observation of the ionic wind flow by using the PIV instrument shows a jet flow pattern that leaving the surface, which help to form a convective flow in the region near to the surface. This effect gives a maximum of 50 % improvement for average heat transfer coefficient of the surface by comparing to the condition of natural convection. Compared with the estimation of a semi-empirical correlation, the measured mass flow rate of the ionic wind blower becomes larger during the applied voltage is larger than 9 kV. This attributes to the air temperature variation that affected by the mass flow rate during the heat transfer process. In other words, the increased mass flow rate leads to a temperature drop of the airflow, which provides more molecules per unit of volume for a better condition of the corona discharge process. This phenomenon indicates a coupling effect between the air temperature and the corona discharge process. The experimental results of this study also provide a flexible way for modularized design of the miniature ionic wind blower. • An ionic wind blower by embedding needle electrode into heat dissipation surface is investigated. • Blower performance is analyzed by considering electrohydrodynamic and heat transfer behaviors. • A semi-empirical correlation to evaluate the mass flow rate of the ionic wind blower is developed. • Coupling effect between heat transfer and corona discharge process is observed. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on the influence of dual vibrating fans on flow and thermal fields through numerical analyses and experimental measurements. Two piezoelectric fans were arranged face to face and were vertically oriented to the heat source. 3D simulation was performed with FLUENT and ABAQUS with the use of code coupling interface MpCCI to calculate the velocity and temperature distribution on the horizontal hot plate. The fans'' motion was described as deformable parts by ABAQUS at their first mode vibration. The effects of vibration phase difference between the fans corresponding to in-phase (Φ=0°) and out-of-phase (Φ=180°) vibrations were explored in terms of transient temperature and flow fields. The purpose is to enhance heat dissipation from the microelectronic component. Comparison with the performance of a single fan is made to assess the significance of the additional fan on thermal performance. Good comparison results were achieved through accurate modeling of the most important features of the fans and through heat transfer. Computed results show that the single fan enhanced heat transfer performance within approximately 2.3 times for the heated surface. By contrast, the dual fans enhanced heat transfer performance within approximately 2.9 for out-of-phase vibration (Φ=180°) and 3.1 for in-phase vibration (Φ=0°). [Copyright &y& Elsevier]

Abstract: A novel technique for increasing computer fan effectiveness, based on introducing acoustic perturbations onto the fan blades to control boundary layer separation, was assessed. Experiments were conducted in a specially designed facility that simultaneously allowed characterization of fan performance and introduction of the perturbations. A parametric study was conducted to determine the optimum control parameters, namely those that deliver the largest increase in fan pressure for a given flowrate. The optimum reduced frequencies corresponded with those identified on stationary airfoils and it was thus concluded that the exploitation of Kelvin–Helmholtz instabilities, commonly observed on airfoils, was responsible for the fan blade performance improvements. The optimum control inputs, such as acoustic frequency and sound pressure level, showed some variation with different fan flowrates. With the near-optimum control conditions identified, the full operational envelope of the fan, when subjected to acoustic perturbations, was assessed. The peak pressure and peak flowrate were increased by up to 40% and 15% respectively. The peak fan efficiency increased with acoustic perturbations but the overall system efficiency was reduced when the speaker input power was accounted for. [Copyright &y& Elsevier]

Abstract: This article describes the findings of an investigation on the failure of a cooling fan gearbox. The failure analysis was aimed at identifying the root cause of the gear damage in order to prevent their reoccurrence. Detailed investigation using several characterisation techniques such as visual and metallographic examinations, hardness testing, and different chemical analyses showed that the gears failed by contact fatigue accelerated by alternating high loads. The failure contributing factors are discussed and identified. Practical corrective actions were suggested in order to avoid similar failures. [Copyright &y& Elsevier]

Abstract: Freezing process efficiency is affected by the required conditions to keep the air flow and temperature at the product surface. The objective of this work was to obtain results on comparative studies with air exhaustion and blowing using an experimental portable forced-air freezing tunnel. The device was designed to improve cooling rates inside storage room without the need for a cooling/freezing tunnel. A heterogeneity factor was proposed for air circulation evaluation and compared with convective heat transfer coefficient (h ef) values. Lower modules of heterogeneity factor values represent smaller temperature differences among samples. Comparing two different air flow processes, heterogeneity factor values were similar for regions where the cooling air could flow without obstructions. However, larger differences were observed for regions with hampered air circulation. Results indicated that the air distribution, as well as the heat transfer, occurs more uniformly around the products in the exhausting process than in the blowing system. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical fluid flow model for the stamped metal cooling fans popularly employed in electric motors. An experimental system is constructed to measure the performance of the cooling fan. The agreements between model prediction and experimental data are reasonably good. Parametric studies with the numerical model indicate that the viscous heating in the fluid and the variation of the air density have negligible effects on the fan performance. The blade edge thickness affects the flow driving capability of the fan. With various pressure differentials, three flow regimes are recognized. The first is the axial component dominated flow. In the second regime, the flow has a forward axial flow and a backward leakage flow. The third one is the leakage flow dominated regime, when the pressure differential across the fan is large. [Copyright &y& Elsevier]