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The housing of totally enclosed fan-cooled electrical machines is usually finned to maximize the heat dissipation over its surface. Complex models involving heat and fluid flow simultaneously are necessary to evaluate a single design. An optimization over a wide parameter range is, therefore, not possible. In this paper, a novel approach on how to model this particular conjugate heat transfer problem in 2-D without the help of lumped circuits is presented. The proposed method is applied to an optimization process controlled by an evolutionary algorithm. Comparative, more detailed simulations in computational fluid dynamic (CFD) verify the tendencies obtained in the optimization. In another case, the method is used to evaluate the allowable degree of engineering tolerance for a given design. Although the method does not provide results as accurate as CFD, it is very helpful to study a large parameter set and determine the CFD candidates. [ABSTRACT FROM PUBLISHER]

The objective of this work is to introduce and evaluate a new end-of-aisle cooling design which consists of three cooling configurations. The key objectives of close-coupled cooling are to enable controlled cooling of information technology (IT) equipment, flexible and modular design, and the containment of hot air exhaust from the cold air. The thermal performance of the proposed solution is evaluated using computational fluid dynamics modeling. A computational model of a small size data center room has been developed. The room is modeled to be a hot aisle containment setup, i.e., the hot air exhaust exiting for each row is contained and directed within a specific volume. The cold aisle is separated from the hot aisle by means of banks of heat exchangers (HXs) placed on either side of the containment aisle. Based on the placement of rack fans, the design is divided into three subdesigns-- Case 1: passive HXs with rack fan walls; Case 2: active HXs (coupled with fans) with rack fan walls; Case 3: active HXs (coupled with fans) with no rack fans. The cooling performance is calculated based on the thermal and flow parameters obtained for all three configurations. The computational data obtained has shown that the Case 1 is used only for lower system resistance IT. However, Cases 2 and 3 can handle denser IT systems. Case 3 is the design that can consume lower fan energy and handle denser IT systems. The article also discusses the cooling behavior of each type of design under cooling failure conditions with Case 2 showing better cooling redundancy compared with other two cases. [ABSTRACT FROM AUTHOR]

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]

As commonly used forced convection air cooling devices in electronics, cooling fans are crucial for guaranteeing the reliability of electronic systems. In a cooling fan assembly, fan bearing failure is a major failure mode that causes excessive vibration, noise, reduction in rotation speed, locked rotor, failure to start, and other problems; therefore, it is necessary to conduct research on the health assessment of cooling fan bearings. This paper presents a vibration-based fan bearing health evaluation method using comblet filtering and exponentially weighted moving average. A new health condition indicator (HCI) for fan bearing degradation assessment is proposed. In order to collect the vibration data for validation of the proposed method, a cooling fan accelerated life test was conducted to simulate the lubricant starvation of fan bearings. A comparison between the proposed method and methods in previous studies (i.e., root mean square, kurtosis, and fault growth parameter) was carried out to assess the performance of the HCI. The analysis results suggest that the HCI can identify incipient fan bearing failures and describe the bearing degradation process. Overall, the work presented in this paper provides a promising method for fan bearing health evaluation and prognosis. [ABSTRACT FROM AUTHOR]

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]

This paper studies the effects of blades' forward-swept amount in the rotation direction and forward-inclined amount in the intake direction on the flow around the fan blades of a large open-type motor. The authors have previously clarified this flow separation on the blade surface under high ventilation resistance from flow analysis and visualization experiments. To prevent flow separation, they proposed forward-swept and inclined blades, together with reduction of the air path's ventilation resistance. In this study, numerical fluid analyses were performed on the flow around forward-swept and inclined blades of axial fans for large open-type motors. Several combinations of forward-swept and inclined amounts were studied. The relationship between forward-swept and inclined amounts and flow was evaluated quantitatively, and an ideal combination was obtained. The study revealed that an axial fan with this combination showed much higher flow rate than a conventional fan without forward-swept and inclined blades. Furthermore, it significantly decreased fluid noise and axis power. [ABSTRACT FROM AUTHOR]

Due to ever increasing consumer demand, today's marketplace is full of portable computing devices such as notebook computers, gaming machines, personal digital assistants, and smart phones. In each of these technologies, processing power and functionality levels are continuing to increase, resulting in increased thermal management issues. The former of these technologies already use an active cooling solution with a profile of 10-15mm while the latter two are quickly approaching the limits of passive cooling. Since a common characteristic in each of these technologies is the desire to reduce profile height, there exists a need to develop low profile cooling solutions that are capable of supporting this growing market. However, a prerequisite to developing such solutions is an accurate understanding of how the noise level characteristics of the driving fans scale with height. This paper experimentally addresses the acoustic scaling of low profile fans. The rotor heights range from 0.5mm to 15mm with diameters from 15mm to 32mm, giving an aspect ratio of height relative to diameter of 0.03-0.6. The results can be used as a foundation for the development of active cooling in mobile devices where both correlations for noise levels and basic design criteria are identified. [ABSTRACT FROM AUTHOR]

In a warm environment, air movement with elevated velocity is a well-known cooling strategy. The local air movement is typically generated by cooling fans (e.g., ceiling fan, table fans, etc.). Appearance, power input, and price are the main parameters considered today when purchasing cooling fans, while cooling capacity and efficiency of energy use are unknown. To address this knowledge gap, this paper introduces the cooling-fan efficiency (CFE) index, defined as the ratio between the cooling effect (measured with a thermal manikin) generated by the device and its power consumption. The index was determined for a ceiling fan, a desk fan, a standing fan, and a tower fan in a real office at three room air temperatures and at different fan speed levels. The results reveal that the index is sensitive enough to identify differences in the performance of the cooling devices. A standard method for testing fan cooling effect and an index for determining fan efficiency, such as the CFE index proposed in this study, need to be developed. The cooling fans generate a nonuniform velocity field around occupants, which cannot be described with a single air-velocity value. Therefore, it is not clear how to apply in practice the recommended elevated velocities in warm environments presented in the present standards. The standards need to be revised. [ABSTRACT FROM AUTHOR]

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]

Purpose - To investigate the film cooling effectiveness in a flat plate with a single row of rectangular injection holes. Design/methodology/approach - Three injection holes in model are in a single row. The holes are rectangular cross section and they are 9?×?6.5?mm. The injection holes are inclined at 30° along the mainstream direction. The blowing ratios are from 0.5 to 2.0. The experiments and their computational models are established to investigate its effects at the 330 and 335 and 340?K injection temperatures and the different blowing ratios. Findings - Results show that the blowing ratio and injection temperature and momentum flux ratio affect the film cooling effectiveness and to provide a good film cooling performance in both mainstream and lateral direction a suitable blowing ratio should be selected. In this study, the highest effectiveness is determined at a blowing ratio of 0.5. Further increasing this ratio results in reverse effect on the film cooling effectiveness. Originality/value - It is the fist time the film cooling effectiveness is compared at the rectangular injection holes as experimental and numerical. [ABSTRACT FROM AUTHOR]

A hybrid chiller plant employs a combination of chillers that are ‘powered’ by electricity and natural gas. This paper presents an algorithm for determining cooling tower fan settings in hybrid plants in response to loadings on individual chillers. Parameters of the algorithm are evaluated using design information for the chillers and cooling tower fans. In addition to reducing operating costs, use of the open-loop control strategy simplifies the control and improves the stability of the tower control compared with the use of a constant condenser water supply or approach to wet-bulb. Simulated plant cooling costs associated with the algorithm were compared with costs for optimized settings and were within 1% of the minimum costs. The control method is general, in the sense that it also applies to cooling plants that have all electric or all natural gas chillers. [ABSTRACT FROM AUTHOR]

The noise produced by cooling air passing through electronics packages arises from two sources. One source is the noise of the air-moving fan of either an axial or centrifugal type. This noise may have both tonal and random components and is strongly dependent on the way that the fan is placed in the unit and on where its operation is on the fan's operating curve. Often, fans are the dominant noise sources. The flow of air produces random noise due to the turbulence generated throughout the unit. Because the turbulent airflow is also responsible for heat transfer between the components and the air stream, we can regard this part of the noise as the irreducible noise due to cooling. If fan noise were eliminated, this part of the noise would remain. There is a relation, therefore, between the irreducible noise and the cooling of the unit. But the fan noise must also be considered. The relation between total airflow related noise and cooling requirements is developed in this paper for the irreducible noise. [ABSTRACT FROM AUTHOR]

This paper studies the cooling performance by axial fans with forward-swept and inclined blades and a structure with low ventilation resistance for large-capacity open-type motors. The ventilation resistance of axial fans for motors is much greater than that of common fans for creating draughts. Flow separates remarkably on the blades' surfaces and fluid noise is large. We reduced the ventilation resistance inside an electric motor and adopted axial fans with forward-swept and inclined blades. We confirmed by wind tunnel experiment that the flow rate with this combination increases remarkably compared with the conventional ventilation structure and axial fans. Numerical fluid analysis was performed on the flow around the blade at this flow rate. It was confirmed that no flow separation appeared for the air flow along the blade surfaces. This was also observed in a flow visualization experiment. Furthermore, an actual motor with both the low-ventilation-resistance structure and axial fans with forward- swept and inclined blades showed that the flow rate of cooling air increased by 80% compared with that of conventional machines, and the average temperature rise of stator windings decreased by 30%. Thus, the cooling performance was greatly improved. [ABSTRACT FROM AUTHOR]

Nonintrusive load monitoring (NILM) is accomplished by sampling voltage and current at high rates and reducing the resulting start transients or harmonic contents to concise "signatures." Changes in these signatures can be used to detect, and in many cases directly diagnose, equipment and component faults associated with rooftop cooling units. Use of the NILM for fault detection and diagnosis (FDD) is important because (1) it complements other FDD schemes that are based on thermo-fluid sensors and analyses and (2) it is minimally intrusive (one measuring point in the relatively protected confines of the control panel) and therefore inherently reliable. This paper describes changes in the power signatures of fans and compressors that were found, experimentally and theoretically, to be useful for fault detection. [ABSTRACT FROM AUTHOR]

Improving cooling performance is a key factor when developing induction motors in smaller sizes with larger capacities and higher rotational speeds. Doing so, however, requires thermal analysis to discover the major parameters in the cooling design. This study investigates temperature distributions and heat transfer rates in a small, totally enclosed, fan-cooled induction motor with both numerical and experimental methods. Parametric studies show that (1) the frame is of the utmost importance in the design and (2) that cooling the motor close to stator coils is the most effective method for cooling. Quantitative analyses show the relationship between the size of the motor and the rise in coil temperature. The results from transient and steady-state experiments using a real motor show that (1) the hottest spot is in the rotor surface, and (2) the load-side surface has a higher temperature than that of the fan-side. The hottest spot in the stator coils is the outer surface of the load-side endwinding. The coil temperature is also significantly affected by the attached components of the frame, as well as the contact state between the stator iron and the frame. It is recommended that the current outer fan be redesigned to improve cooling performance. [ABSTRACT FROM AUTHOR]