Passively Cooled Research Articles

Experimental Investigation of the Effect of Heat Pipe Tilting on a Concentrated Photovoltaic/Heat Pipe Passive Cooling System

Abstract To maintain the concentrated photovoltaic systems (CPV) output, effective cooling is necessary. In contrast to costly and complicated active cooling methods, passive cooling is static, simple, and maintenance-free. Among passive techniques, Heat Pipes (HPs) are devices that efficiently transfer heat from the evaporator to the condenser. The inclination angle of wicked, liquid-filled HP's long-axis determines how well it cools, as an effect of the gravitational force acting on the condensed liquid. This study investigates the effect of tilting the HP long-axis on the performance of the different parameters of the CPV, which is passively cooled by thermal attachment to its back side. Two similar HPs except for their lengths were attached alternatively. Different concentrated illumination levels are then allowed to be incident on the CPV. At each illumination level, the inclination of the HP long-axis was varied from −90 deg (completely vertical with condenser up) to 90 deg (completely vertical with condenser down), passing through 0 deg (HP is completely horizontal) with a step of 15 deg. The effect of such variations on the inclinations has been tested on the two systems. The system incorporating the long HP was found to have a higher cooling performance at an angle of −15 deg, compared to the short HP system, which has its highest cooling capacity at an angle of −60 deg, with an increase of about 7% for the maximum power in case of using the former system compared to the latter.

Influence of Gravity on Passively Cooled Heat Sink Using Experimental Data and Finite Element Analysis

This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to evaluate the accuracy of Siemens Flotherm XT 2021.2 simulation software. In order to determine the influence of heat sink orientation, experimental measurements were performed on the resistor and heat sink temperature using thermocouples. Siemens Simcenter Flotherm XT 2021.2 software (Siemens, Munich, Germany) was used to perform finite element simulation. The influence of the heat sink position was evaluated on two setups, one where the resistor is placed directly on the heat sink using screws, and the second one, where a thermal pad was placed between the resistor and the heat sink. Screws were to clamp the parts in both cases. In total, four experiments and simulations were performed with two assemblies with two different gravity orientations for each assembly. In all the cases, the heat sink was placed on a wooden structure to prevent heat transfer through conduction, due to poor thermal conductivity of wood, and to allow unrestricted air flow underneath and around the heat sink. The first simulation was then calibrated for the first scenario, and the rest of the simulations were made using the calibrated one. No other changes in boundary conditions were made. Temperature measurements show an improved cooling when the air speed between the heat sink fins is enhanced due to natural hot air movement generated by the gravity. Gravity has an influence on the cooling regardless of the presence or absence of a thermal interface material. Measured temperatures were reduced up to 8.2 °C due to the rotation of the heatsink. Finite element analysis shows similar temperature values to the measured ones in all the scenarios.

A Study on the Influence of Thermal Interface Material in Passively Cooled Electrical Components with Attached Heatsink

A Study on the Influence of Thermal Interface Material in Passively Cooled Electrical Components with Attached Heatsink

A Review on the Design of Chimney for Air Cooled Condenser

Wind coils were used in the US electricity company in the early 1970s, however the amount of facilities has skyrocketed within last 10-15 years, due mainly to an increasing emphasis on green security. In addition, as the consumption of water grows in both household and commercial settings, more people are interested in using wind condensers. The Passively Cooled Compressor and its Contest is the topic of this article. This monthly bases the components of a wind capacitor.

Effective Passive Cooling During Neonatal Transport.

We retrospectively evaluated the rectal temperature of 297 hypoxic-ischemic encephalopathy (HIE) outborn newborns who were passive-cooling transported by Neonatal Emergency Transport Service (Genoa and Rome, Italy) at their arrival in Neonatal Intensive Care Unit. By a total of 1461 transports, 297 were for suspected HIE. Transferring suspected HIE newborn does not mean with certainty directing him/her to cooling treatment, but rather to monitoring and deepening in the hypothesis of starting hypothermia. This is the main reason why we have chosen 35°C (±0.5°C) as the temperature target to be maintained during transport. Our study demonstrated that 263/297 patients (88.55%) passively cooled during transport were within the target limit of 35°C (±0.5°C), whereas 15 newborns were at rectal temperature >35.5°C (5.05%) and 19 were <34.5°C (6.39%); no patients were <33°C. In our opinion, these are satisfactory results. Overcooling, failed temperature target, and unstable temperature values are the main problems claimed to occur during passive cooling in transport. We would like to conclude underlining that a well-experienced neonatal transport team can use passive cooling expecting appropriate performances.

Study on Passive Ventilation and Cooling Strategies for Cold Lanes and Courtyard Houses—A Case Study of Rural Traditional Village in Shaanxi, China

China’s research on and specific implementation of energy saving for buildings are mainly concentrated in urban areas, but according to 2016 statistics, the rural population accounts for 42.65% of the total population, so rural housing has considerable energy-saving potential. However, the degree of attention to the energy consumption of rural houses needs to be improved. Regarding the research on and implementation of passive energy-saving strategies for residences, compared with centralized urban high-rise residences, rural residences mainly have independent courtyards, with a flexible layout and easier transformation. In this study, a system that uses the common cold lanes in traditional villages and buildings’ exterior walls was constructed, and the indoor spaces of courtyard buildings in southern Shaanxi were completely passively cooled in summer. This system can be completely separated from the supply of artificial energy by relying on the accumulation and buoyancy effects of air in patios and cold lanes and the hot-pressure ventilation in buildings to cool the buildings and greatly improve indoor ventilation efficiency. As the building is ventilated and cooled, the air wall formed in the system can effectively prevent direct contact between the outdoor and indoor temperatures and reduce the impact of thermal wall radiation on the interior. In previous studies on the passive design of courtyard houses, scholars considered the effect of thermal wall radiation on indoor temperature in simulations. Therefore, in this study, we also separately calculated whether to consider the difference between the situation with and without wall heat radiation (WHR) when simulating thermal conversion. The final results show that when the cooling system was adopted, the annual cooling load of the whole building was 4786.494 kW·h without WHR. However, with WHR, the cooling load reduction was 2989.128 kW·h, a difference of 1797.336 kW·h.

Lifetime Analysis of IGBT Power Modules in Passively Cooled Tidal Turbine Converters

Thermal cycling is one of the major reasons for failure in power electronic converters. For submerged tidal turbine converters investigating this failure mode is critical in improving the reliability, and minimizing the cost of energy from tidal turbines. This paper considers a submerged tidal turbine converter which is passively cooled by seawater, and where the turbine has fixed-pitch blades. In this respect, this study is different from similar studies on wind turbine converters, which are mostly cooled by active methods, and where turbines are mostly pitch controlled. The main goal is to quantify the impact of surface waves and turbulence in tidal stream velocity on the lifetime of the converter IGBT (insulated gate bipolar transistor) modules. The lifetime model of the IGBT modules is based on the accumulation of fatigue due to thermal cycling. Results indicate that turbulence and surface waves can have a significant impact on the lifetime of the IGBT modules. Furthermore, to accelerate the speed of the lifetime calculation, this paper uses a modified approach by dividing the thermal models into low and high frequency models. The final calculated lifetime values suggest that relying on passive cooling could be adequate for the tidal converters as far as thermal cycling is concerned.

Thermal State of Charge Estimation in Phase Change Composites for Passively Cooled Lithium-Ion Battery Packs

This paper presents an integrated approach, where a Li-ion battery pack is equipped with a passive thermal management system and an on-board intelligent battery management system. The proposed technique estimates the melt fraction of the phase change composite (PCC) material and its remaining thermal mass, which can be a decisive indicator of how long the battery can maintain safe operation. Furthermore, an on-board temperature and melt fraction map of the battery pack can be generated, which will be valuable in case of asymmetrical designs or modes of operation. The core of this paper is based on monitoring the temperature of the entire test pack to estimate the temperatures on all the cells within the pack. This enables the estimation of thermal state of charge of the PCC in all sections of the pack to accurately monitor and ensure safe operation.

Comparison of Passive and Servo-Controlled Active Cooling for Infants with Hypoxic-Ischemic Encephalopathy during Neonatal Transfers.

Objective The recent availability of servo-controlled cooling equipment on transport makes it possible to commence active cooling at the referral unit for infants with hypoxic-ischemic encephalopathy. This study aimed to compare the temperature and transfer variables in passively and actively cooled babies. Study Design This is a retrospective cohort study comparing two groups-passively cooled (July 2011 to August 2012) versus actively cooled group (September 2012 to June 2013), following introduction of active hypothermia using servo-controlled cooling mattress by the London Neonatal Transfer Service (NTS). Results Seventy-six infants were passively cooled and 69 were actively cooled. There was a significant difference between the temperatures of the two groups at each point in the transfer episode: on arrival of NTS, during stabilization, during transfer, and at the receiving hospital. Median time to achieve target temperature was 30 (95% confidence interval [CI]: 23-37) minutes in actively cooled, significantly shorter in comparison to 130 (95% CI: 83-177) minutes in passively cooled babies. Of the 69 newborns, 62 (90%) had temperature within target range at receiving center in actively cooled group as compared with 30/76 (40%) in passively cooled group. Conclusion The use of active cooling during neonatal transfer achieves target temperature in a shorter period and maintains better temperature stability.

A Numerical Study on Comparing the Active and Passive Cooling of AlGaN/GaN HEMTs

In this paper, the power density capability of AlGaN/GaN high-electron mobility transistors (HEMTs) made on Si, SiC, and diamond substrates were compared with devices on Si and SiC with integrated microchannel cooling. A device temperature limit of 200 °C was used to define the power density. The numerical model accounts for heat transfer from channel of the AlGaN/GaN HEMTs to the heat sink, fluid flow rates, pressure drop, and pumping power required for liquid cooling. The diamond substrate was shown to be superior in reducing the junction temperatures in conventional passive cooling methods employing high thermal conductivity substrates. However, single-phase liquid cooling with microchannels integrated into a SiC substrate showed that it is possible to operate the devices at power densities higher than that on 200- $\mu $ m-thick diamond substrates, considering a maximum operational temperature of 200 °C. Microchannels integrated into the Si substrate also showed a slight increase in the power density compared with passively cooled devices on SiC. Overall, this methodology shows a promising alternative to expensive high thermal conductivity substrates for cooling AlGaN/GaN HEMTs.

Active Versus Passive Cooling During Neonatal Transport

Therapeutic hypothermia is now the standard of care for hypoxic-ischemic encephalopathy. Treatment should be started early, and it is often necessary to transfer the infant to a regional NICU for ongoing care. There are no large studies reporting outcomes from infants cooled passively compared with active (servo-controlled) cooling during transfer. Our goal was to review data from a regional transport service, comparing both methods of cooling. This was a retrospective observational study of 143 infants referred to a regional NICU for ongoing therapeutic hypothermia. Of the 134 infants transferred, the first 64 were cooled passively, and 70 were subsequently cooled after purchase of a servo-controlled mattress. Key outcome measures were time to arrival at the regional unit, temperature at referral and arrival at the regional unit, and temperature stability during transfer. The age cooling was started was significantly shorter in the actively cooled group (46 [0-352] minutes vs 120 [0-502] minutes; P <.01). The median (range) stabilization time (153 [60-385] minutes vs 133 [45-505] minutes; P = .04) and age at arrival at the regional unit (504 [191-924] minutes vs 452 [225-1265]) minutes; P = .01) were significantly shorter in the actively cooled group. Only 39% of infants passively cooled were within the target temperature range at arrival to the regional unit compared with 100% actively cooled. Servo-controlled active cooling has been shown to improve temperature stability and is associated with a reduction in transfer time.

Analysis and Modeling of Heat Generation in Overcharged Li-Ion Battery with Passive Cooling

This paper presents a dynamic model for simulating the heat generation in Lithium batteries and an investigation of the heat transfer as well as the capacity of Phase Change Materials (PCM’s) to store energy inside a battery cell module when the battery is overcharged. The study is performed by coupling a one-dimensional model of the electrochemical processes with a two-dimensional model for the heat transfer in a cross section of a battery pack. The heat generation and subsequent temperature rise is analyzed for different charging currents for the two cases where the cell is air-cooled and passively cooled using a PCM, respectively. As expected, the results show that for high currents, the heat generation and implicitly the temperature increases. However, using a PCM the temperature increase is found to be limited allowing the battery to be overcharged to a certain degree. It is found that for fast charging, the charging time has a lower limit determined by the transport properties in the electrodes.

Passive Cooling during Transport of Babies with Hypoxic Ischaemic Encephalopathy

Background: Perinatal hypoxic ischaemic encephalopathy affects 1-2 per 1000 live births. Therapeutic hypothermia is now a standard treatment shown to reduce the severity of neurological damage in mild to moderate cases. Cooling should be commenced within six hours of birth and the target core temperature is 33-34°C. Currently, the recommended practise is for transfer within Neonatal Networks to a centre with experience of providing therapeutic hypothermia for further management. This requires the provision of passive cooling during transport. Method: We conducted a retrospective case note review to look at the temperature regulation during transfer of the babies in Yorkshire and Humber region. The temperature data is expressed as an interquartile range (IQ1-IQ3) and was analysed using Microsoft Excel. Result: In total the Yorkshire and Humber Infant & Paediatric Transport Service transferred nineteen babies to regional cooling centres during April 2010 and November 2010. All the babies were term (>37week gestation). All the babies were passively cooled and in one baby ice packs were used when referred. The median temperature at referral was 35.4°C (34.7-35.7°C), on arrival of the transport team 34.4°C (33.1- 36.0°C), on departure 33.4°C (33.0-34.4°C), at receiving unit 33.1°C (32.7-33.6°C). In 2 babies the temperature was unrecordable.The target temperature was achieved in only 47% of cases. Conclusion: Maintenance of temperature within the target range is challenging during transport. Following the audit there has been increased awareness about monitoring core temperature while cooling babies. As a service we aim to use active cooling method to achieve target temperature.

Passive and Low Energy Cooling of Office Buildings

In this work, the cooling performance of night ventilation systems and different earth heat exchange technologies were experimentally analysed in three office buildings in Southern Germany. One of the first passive energy standard office buildings in Europe was extensively monitored over a three year period to analyse the summer performance of a highly insulated and well shaded building in which night cooling ventilation was based on stack effect and cross ventilation. This was combined with a mechanical ventilation system incorporating a ground coupled heat exchanger to supply daytime fresh air.For comparison, an energy analysis was made of a mechanically driven exhaust air night ventilation system and a supply and exhaust air system in the other two buildings. The first of these was a passively cooled refurbished building in Tübingen which utilises mechanical night ventilation to effectively discharge ceilings with phase change material. In addition, fresh air cooling is achieved using a horizontal brine-earth heat exchanger. The second comparison building was a low energy office building in Freiburg which uses water based ground coupled heat exchangers for fresh air cooling and an exhaust air ventilation system for night cooling.During a typical German summer, in which the number of hours that the ambient air temperature exceeds 25°C is less than 160, the passively ventilated building performed excellently, even with relatively high internal heat loads of 200 to 400 Wh.m−2.day−1. However, when the ambient air temperature was significantly higher, such as in the summer of 2003 (i.e. 3 K higher than the average summer temperature), nearly 10% of all office hours recorded room air temperatures above 26 °C. In the case of the two buildings that were night cooled by mechanical ventilation, cooling performance was limited by the rather low air exchange rate of 2 h−1. This resulted in overnight room temperature reductions of just 2–3 K during hot summer nights. Also the coefficient of performance (COP) was relatively low for this approach at between 4 to 6.All the earth heat exchangers showed excellent energy performances with COP's between 20 and 50. However, due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removed a small part of the total load.