Cold Air Stream Research Articles

Computer Modeling to Predict the Impact of Cold Air Stream on Multi-Chip Memory

RAM was a specialized electronic chip which multiple integrated circuits (ICs), semiconductor or other discrete components were packaged onto a unifying substrate. Facilitating their use as a single component (as though a larger IC). This paper presented model calculated the temperature distribution on four parallel memory modules and studied the effect of running a stream of cooling air . The density of the air domain depended on temperature, and introduced this influence with the ideal gas law. The inlet velocity of the air was given as a parabolic profile with a maximum velocities of 0.20, 0.21,0.22,0.23, 0.24 and 0.25 m/s, at this flow rates the flow will be laminar. This procedure yields average temperatures of 29.2, 32.4, 34.2 and 34.6 °C. The model defined the heat balance in the memory subdomains plus the air subdomain. The temperature field and flux were continued across these subdomains, which mean that there was no need specify any boundaryconditions between the memory and the air subdomain. The model used material properties of the ICpackage material FR4 for the memory modules, and in the surrounding subdomain it used the properties for air.

From Chip to Cooling Tower Data Center Modeling: Influence of Air-Stream Containment on Operating Efficiency1

In the drive to enhance data center energy efficiency, much attention has been placed on the prospect of airflow containment in hot-aisle cold-aisle raised floor arrangements. Such containment prevents airflow recirculation, eliminating the mixing effects of the hot and cold air streams that can cause an undesirable temperature rise at the inlet of the equipment racks. The intuitive assessment of the industry has been that the elimination of such mixing effects increases the energy efficiency of the data center cooling system by enabling delivery of air at higher inlet temperatures, thus reducing the amount of infrastructure cooling required. This paper employs an end-to-end modeling approach to analyze the effect of air stream containment in the computer room and its impact on the holistic system efficiency. Dimensionless heat index parameters are employed to characterize the effects of containment, recirculation, and mixing within the computer room environment. The extent of recirculation is shown to primarily influence the operation of the rack and computer room air conditioning (CRAC) level cooling systems, with the chiller systems also impacted. The overall effect on the complete cooling system performance and data center efficiency requires balancing of these effects. Through this model analysis, it is shown that containment may negatively impact overall energy efficiency in some circumstances, and that recirculation may actually be beneficial to overall energy efficiency under certain system dependent operating thresholds.

The effect of simulated cold weather transport on core body temperature and behavior of broilers

During the winter in Western Canada, broilers are routinely transported in ambient temperatures ranging from 0°C to -40°C, yet there is little research in this area. This study examined the physiology and behavior of broilers undergoing simulated transport at typical Western Canadian winter temperatures. Groups of 15 broilers aged 32 to 33 d were exposed to an air stream regulated to -5, -10, or -15°C. Birds were placed into a typical transport drawer. Following baseline observations, the drawer was placed into a test chamber where cold air was drawn past the birds for 3 h. Three replications were conducted at each temperature. The birds adjusted their position within the drawer based upon the temperature distribution within the drawer. In comparison to the baseline period, exposing the birds to a cold air stream caused them to avoid the front plane (P = 0.003) which was the coldest area within the drawer. The birds did not adjust their usage of the middle (P = 0.308) and rear (P = 0.640) planes, because these were the warmer areas within the drawer. The total amount of space the birds occupied within the drawer did not decrease when exposed to the test chamber (P = 0.669). The core body temperature (CBT) did not vary and was within the known normal range during the normal (P = 0.528), pre-chamber (P = 0.060), and post-chamber (P = 0.285) periods. The CBT of the birds significantly decreased during the in-chamber period (P < 0.001) and then increased during the lairage period (P < 0.001). The shrink loss (P = 0.981) and amount of time to resume feed consumption (P = 0.357) were not affected by exposing the birds to temperatures of -5°C and colder. Exposing birds to temperatures of -5°C and colder had a negative effect on the CBT of the birds. However, the birds demonstrated behaviors which mitigated the negative effect that cold exposure could have on their CBT.

The semi-quantitative assay of neamine and neomycin C in neomycin by thin-layer chromatography

Abstract Thin-layer chromatographic methods are described for the separation and assay of neamine and neomycin C in neomycin sulphate and its preparations. The samples are chromatographed on binder-free silica gel plates using, as developing solvents, a 3·85% w/v ammonium acetate solution to separate neamine from the neomycins and a 3·4% w/v ammonium hydroxide solution to separate neomycin C from neomycin B and neamine. The spots are made visible by spraying with a 1% v/v solution of t-butyl hypochlorite in dichloroethane-acetic acid (9:1), removing the excess reagent in a stream of cold air and spraying with a 0·5% w/v solution of potassium iodide in 0·5% w/v starch mucilage. The size and intensity of the spots produced is compared with standards and the neamine or neomycin C content of the sample estimated. The results obtained for neomycin C are comparable with those given by chromatography on an ion-exchange resin. A possible explanation is offered for the lack of agreement in the case of neamine. The chromatographic systems described are also applied to paromomycin and shown to separate paromamine, paromomycin I and paromomycin II, not only from each other, but also from neamine and the neomycins.

Computational fluid dynamic investigation of liquid rack cooling in data centres

Relying on thermal air management in a data centre is becoming less effective as heat densities from the Information Technology (IT) equipment continue to rise. Direct liquid cooling is more efficient at transferring the waste heat, but requires liquid loops passing as close as possible to the heat source. A new Computational Fluid Dynamics (CFD) strategy is developed for data centre scenarios where a liquid loop heat exchanger is attached at the rear of server racks (back doors), which can avoid the need to separate the cold and hot air streams in traditional hot/cold aisle arrangements. The effectiveness of additional fans in the back door heat exchangers is investigated using the three-dimensional CFD model of a simplified three-aisle, six-rack data centre configuration.

A critical review of temperature separation in a vortex tube

The vortex tube is a simple device used in industry for generation of cold and hot air streams from a single compressed air supply. This simple device is very efficient in separation of air streams of different temperatures and has been the focus of investigation since the tube’s discovery. Different explanations for the phenomenon of the energy separation have been proposed, however there has not been a consensus in the hypothesis. The purpose of this paper is to present a critical review of current explanations on the working concept of a vortex tube. Hypotheses of pressure, viscosity, turbulence, temperature, secondary circulation and acoustic streaming are discussed in the paper, and presumably, future research will benefit from this discussion.

Effect of air freezing, spray freezing, and pressure shift freezing on membrane integrity and viability of Lactobacillus rhamnosus GG

The objective of this work was to assess and compare the impact of three different freezing methods on the physiology of probiotic bacteria based on evaluation of vitality, membrane integrity and special metabolic properties. Lactobacillus rhamnosus GG (LGG) was used as a model strain and was analysed with the plate enumeration method and flowcytometric analyses (FCM) before and after treatment in phosphate buffer saline (PBS) and 20% (w/v) skim milk (RSM), respectively. To get insight into the induced changes in esterase activity and membrane integrity combined staining with carboxyfluorescein diacetate (cFDA) and propidium iodide (PI) was applied. Furthermore the ability of the cells to extract intracellular accumulated cF in presence of glucose was investigated as an indicator for ATP driven membrane transport processes. The freezing methods applied were static air freezing (AF) at −30 °C for 3 h, high pressure shift freezing (PSF) at −21 °C/210 MPa and spray freezing (SF) at −30 °C. Spray freezing was accomplished by spraying the bacteria suspension in a cold air stream using a two fluid atomizer. The atomizing gas was air. After each treatment all samples were stored at −20 °C for one day before they were analysed. Minimum losses in viability occurred when spray freezing LGG in presence of 20% (w/v) RSM whereas air freezing in PBS resulted in the lowest survival rates. For all treatments higher survival rates were achieved when 20% (w/v) RSM was used as protecting media. Comparing the results of live cell count with the FCM data gave evidence for a fraction of viable but not culturable cells. LGG cells frozen by PSF showed viability comparable to AF samples, but physiological characteristics of pressure treated bacteria.

Optimum operational conditions of a rotary regenerator using genetic algorithm

The optimum operational conditions of an air-to-air rotary regenerator (also called air preheater or heat wheel) for air conditioning applications which was designed and manufactured in Energy Systems Improvement Laboratory (ESIL) has been investigated in this paper. The performance of such a rotary regenerator was modeled and the numerical values of modeling output were verified with the experimental data obtained from the equipment testing. In the next step, the optimum operational conditions of the rotary regenerator were obtained using genetic algorithm optimization technique subject to a list of constraints. The objective function in the optimization technique was the thermal effectiveness, while the design parameters (decision variables) were volumetric flow rates of cold and hot air streams, matrix rotational speed, and the exchanger frontal area (heat transfer surface area). The apparatus was tested under the optimized operating conditions and the results were compared with the results obtained numerically applying genetic algorithm optimization. The experimental value for the effectiveness showed an acceptable closeness (2.07%) with the corresponding value obtained from the system modeling and optimization. The economic analysis of energy savings by the designed and manufactured regenerator showed a pay back period about 3 years.

Brayton refrigeration cycle for gas turbine inlet air cooling

In this paper, a new approach to enhance the performance of gas turbines operating in hot climates is investigated. Cooling the intake air at the compressor bell mouth is achieved by an air Brayton refrigerator (reverse Joule Brayton cycle) driven by the gas turbine and uses air as the working fluid. Fraction of the air is extracted from the compressor at an intermediate pressure, cooled and then expands to obtain a cold air stream, which mixes with the ambient intake. Mass and energy balance analysis of the gas turbine and the coupled Brayton refrigerator are performed. Relationships are derived for a simple open gas turbine coupled to Brayton refrigeration cycle, the heat rejected from the cooling cycle can be utilized by an industrial process such as a desalination plant. The performance improvement in terms of power gain ratio (PGR) and thermal efficiency change (TEC) factor is calculated. The results show that for fixed pressure ratio and ambient conditions, power and efficiency improvements are functions of the extraction pressure ratio and the fraction of mass extracted from the air compressor. The performance improvement is calculated for ambient temperature of 45°C and 43.4% relative humidity. The results indicated that the intake temperature could be lowered below the ISO standard with power increase up to 19.58% and appreciable decrease in the thermal efficiency (5.76% of the site value). Additionally, the present approach improved both power gain and thermal efficiency factors if air is extracted at 2 bar which is unlike all other mechanical chilling methods. Copyright © 2007 John Wiley & Sons, Ltd.

Numerical modeling of the formation of aerosol particles in jet engine plumes

The formation of liquid sulfate aerosols in the isobaric axisymmetric plume of a subsonic aircraft is modeled numerically. The specific features of the appearance and evolution of sulfate aerosols attributable to 2D effects, such as the parameter nonuniformity in the initial section (at the nozzle outlet), mixing of the hot engine jet with the cold air stream, and the transverse turbulent diffusion of aerosol particles and gas mixture components. The equations of gas dynamics for a turbulent axisymmetric jet, the equations of chemical kinetics, the equations for the liquid fractions (water and sulfuric acid), and the relations for the binary nucleation, condensation growth and coagulation of aerosol particles are used. The distributions of the parameters determining the formation of the aerosol phase in the exhaust plume of a B-747 aircraft are obtained and the geometry of the nucleation zone in this plume is determined.

Numerical simulation of backdraft phenomena

This paper reports preliminary computational fluid dynamics (CFD) simulations of backdraft observed in an experimental rig at Lund University. The analysis was performed with the CFX software using the Detached Eddy Simulation (DES) turbulence model, a hybrid of Large Eddy Simulation (LES) and RANS, in combination with the EDM combustion model. The DES model uses a RANS formulation in wall proximity to avoid computationally expensive grid resolution that is necessary for realistic LES predictions in wall layers. The preliminary results are qualitatively promising. The simulations began at the instant at which the door opens. A stream of fresh and cold air enters the enclosure as a gravity current. In the rig, ignition was triggered by flammable conditions existing at a wire, which was constantly heated. In the CFD model the ignition time is computed automatically when flammability conditions are reached inside the enclosure, at the wire, as part of the analysis. Subsequently, the fire front is formed. The deflagration expels fuel-rich mixture into environment, and the combustion continues outside the enclosure as a typical ‘secondary’ event. Considering that backdraft is a very complex phenomenon, the outcome is considered by the authors to be encouraging.

The Role of CKIP-1 in Cell Morphology Depends on Its Interaction with Actin-capping Protein

CKIP-1 is a pleckstrin homology domain-containing protein that induces alterations of the actin cytoskeleton and cell morphology when expressed in human osteosarcoma cells. CKIP-1 interacts with the heterodimeric actin-capping protein in cells, so we postulated that this interaction was responsible for the observed cytoskeletal and morphological effects of CKIP-1. To test this postulate, we used peptide "walking arrays" and alignments of CKIP-1 with CARMIL, another CP-binding protein, to identify Arg-155 and Arg-157 of CKIP-1 as residues potentially required for its interactions with CP. CKIP-1 mutants harboring Arg-155 and Arg-157 substitutions exhibited greatly decreased CP binding, while retaining wild-type localization, the ability to interact with protein kinase CK2, and self-association. To examine the phenotype associated with expression of these mutants, we generated tetracycline-inducible human osteosarcoma cells lines expressing R155E,R157E mutants of CKIP-1. Examination of these cell lines reveals that CKIP-1 R155E,R157E did not induce the distinct changes in cell morphology and the actin cytoskeleton that are characteristic of wild-type CKIP-1 demonstrating that the interaction between CKIP-1 and CP is required for these cellular effects.

A Multiwinter Analysis of Channeled Flow through a Prominent Gap along the Northern California Coast during CALJET and PACJET

Abstract Experimental observations from coastal and island wind profilers, aircraft, and other sensors deployed during the California Land-falling Jets Experiment of 1997/98 and the Pacific Land-falling Jets Experiment of 2000/01–2003/04 were combined with observations from operational networks to document the regular occurrence and characteristic structure of shallow (∼400–500 m deep), cold airstreams flowing westward through California’s Petaluma Gap from the Central Valley to the coast during the winter months. The Petaluma Gap, which is the only major air shed outlet from the Central Valley, is ∼35–50 km wide and has walls extending, at most, a modest 600–900 m above the valley floor. Based on this geometry, together with winter meteorological conditions typical of the region (e.g., cold air pooled in the Central Valley and approaching extratropical cyclones), this gap is predisposed to generating westward-directed ageostrophic flows driven by along-gap pressure differences. Two case studies and a five-winter composite analysis of 62 gap-flow cases are presented here to show that flows through the Petaluma Gap significantly impact local distributions of wind, temperature, precipitation, and atmospheric pollutants. These gap flows preferentially occur in pre-cold-frontal conditions, largely because sea level pressure decreases westward along the gap in a stably stratified atmosphere in advance of approaching cold-frontal pressure troughs. Airstreams exiting the Petaluma Gap are only several hundred meters deep and characterized by relatively cold, easterly flow capped by a layer of enhanced static stability and directional vertical wind shear. Airborne air-chemistry observations collected offshore by the NOAA P-3 aircraft illustrate the fact that gap-flow events can transport pollutants from inland to the coast, and that they can contribute to coastally blocked airstreams. The strongest gap-flow cases occur when comparatively deep midtropospheric troughs approach the coast, while the weak cases are tied to anticyclonic conditions aloft. Low-level cold-frontal pressure troughs approaching the coast are stronger and possess a greater along-gap pressure gradient for the strong gap-flow cases. These synoptic characteristics are dynamically consistent with coastal wind profiler observations of stronger low-level gap flow and winds aloft, and greater rainfall, during the strong gap-flow events. However, gap flow, on average, inhibits rainfall at the coast.

Effect of electric field on heat transfer performance of automobile radiator at low frontal air velocity

The effect of electric field on the performance of automobile radiator is investigated in this work. In this experiment, a louvered fin and flat tube automobile radiator was mounted in a wind tunnel and there was heat exchange between a hot water stream circulating inside the tube and a cold air stream flowing through the external surface. The electric field was supplied on the airside of the heat exchanger and its supply voltage was adjusted from 0 kV to 12 kV. From the experiment, it was found that the unit with electric field pronounced better heat transfer rate, especially at low frontal velocity of air. The correlations for predicting the air-side heat transfer coefficient of the automobile radiator, with and without electric field, at low frontal air velocity were also developed and the predicted results agreed very well with the experimental data.

Climatic features of Ljig municipal and its surrounding area

Territory of Ljig municipal is located in Podrinje-Colubara region and belongs to the temperate continental climate with continental rain regime. This is hilly- mountainous area with 848 m altitude (Rajac Mountain) and 723 m relative height, in which are deeply incised (up to 500 m) valleys of Ljig River and its tributaries. These geomorphologic features cause airstreams direction in this territory, and because of that some parts of Ljig municipal have temperate continental climate (like valleys) and some of them have severe continental climate (like Rajac Mountain). The peak of precipitation is at the end of spring and beginning of summer - in May and June, and the driest months are February and October. The great influences on climatic changes in Ljig municipal and its area have north low parts of Panonian area, which are open for penetration of damp and cold air streams from north, northwest and west. This mountain area on south part of Ljig municipal is some kind of dam for cold air streams from south, so they are considerable colder on this territory. On the base of available data in period 1961-1990 from Meteorological Annuals of Republic Hydrometeorological Institute of Serbia climatologic overview is presented.

Identification and Characterization of Keyhole Limpet Hemocyanin N-Glycans Mediating Cross-reactivity with Schistosoma mansoni

Keyhole limpet hemocyanin (KLH) of the mollusc Megathura crenulata is known to serologically cross-react with Schistosoma mansoni glycoconjugates in a carbohydrate-dependent manner. To elucidate the structural basis for this cross-reactivity, KLH glycans were released from tryptic glycopeptides and fluorescently labeled. Cross-reacting glycans were identified using a polyclonal antiserum reacting with soluble S. mansoni egg antigens, isolated by a three-dimensional fractionation scheme and analyzed by different mass spectrometric techniques as well as linkage analysis and exoglycosidase treatment. The results revealed that cross-reacting species comprise approximately 4.5% of released glycans. They all represent novel types of N-glycans with a Fuc(alpha1-3)GalNAc(beta1-4)[Fuc(alpha1-3)]GlcNAc motif, which is known to occur also in schistosomal glycoconjugates. The tetrasaccharide unit is attached to the 3-linked antenna of a trimannosyl core, which can be further decorated by galactosyl residues, a xylose residue in 2-position of the central mannose and/or a fucose at the innermost N-acetylglucosamine. This study provides for the first time detailed structural data on the KLH carbohydrate entities responsible for cross-reactivity with glycoconjugates from S. mansoni.

Evaluation of different temperatures in cold air cooling with pulsed‐dye laser treatment of facial telangiectasia

Cold air cooling is widely used in dermatological laser therapy. We investigated the influence of cold air cooling at different skin temperatures on therapeutic outcome and side effects of pulsed dye laser treatment of facial telangiectasia. From September 2002 to February 2003, 17 patients with previously untreated facial telangiectasia underwent a single treatment session with flash-lamp pulsed dye laser (3.5 J/cm(2), 585 nm, 0.45 milliseconds pulse length, 10 mm beam diameter, Cynosure V). The treatment area was divided into three sub-areas: no cooling, cold air cooling to 20 degrees C and to 17 degrees C skin temperature. The skin temperature was monitored by a prototype infrared sensor system which controlled the temperature of the cold air stream (Cryo5). In a prospective study, we collected data on purpura, pain, clearance, and patient satisfaction on numerical analog scales (NAS) from 0 (meaning "no") to 3 (meaning "high"). Without cooling, purpura (2.53), pain (2.41), and clearance (2.35) were rated medium to high. Cooling to 20 degrees C reduced purpura (1.12) and pain (1.06), whereas the clearance (2.12) was only slightly affected. Cooling to 17 degrees C reduced purpura (0.88) and pain (0.76) even more, the clearance (2.06) was lowered marginally. Most patients preferred cooling to 20 degrees C skin temperature. In dermatological laser therapy of facial telangiectasia, the use of cold air cooling can significantly reduce side effects and increase patient satisfaction while only slightly affecting clearance. Cooling to 20 degrees C skin temperature proved to be a well-balanced middle course. For the practical use of cold air cooling, we thus recommend cooling to a level which the patient can tolerate without problems and to try to increase the energy densities.

Efficient Thermal Management of Data Centers—Immediate and Long-Term Research Needs

Power dissipation within computer rooms or data centers has been steadily increasing over the past decade. With the spread of CMOS technology into microprocessors and memory in the 1980s and 1990s, water-cooled mainframe systems were largely supplanted by lower power air-cooled systems. These systems were typically stacked into 2-m-high racks for efficient use of expensive data center floor space. Data center environmental cooling infrastructures correspondingly evolved into designs that recirculate hot exhaust air from the computer systems into air-conditioning units. The air-conditioning units remove the heat and return the cool air back into the room in a closed-loop fashion. These air-cooled infrastructures are largely open, nonducted environments where hot and cold airstreams are free to mix. The evolution of microprocessor fabrication technology has enabled the construction of high-power processors. The push by business, academia, and consumers for greater processing speed has motivated the design of computer systems that enable the greatest number of processors, and, thus, the greatest processing power, per rack volume. This increase in microprocessor density places a great deal of strain on current computer room environmental control technology. Furthermore, the rate of increase in power density in the data center is outpacing that of HVAC technology improvements. Because of this, computer manufacturers are faced with the choice of either limiting system performance in favor of reduced power consumption or of providing customers with higher performance products that are impractical to deploy. In this paper, we will highlight some of the primary challenges with cooling high-power density data centers. We will demonstrate that existing environmental infrastructures have inherent inefficiencies that can be very costly, and we will explore alternatives. Additionally, the use of numerical modeling to diagnose problems with data center design and layout will be demonstrated, and limitations to its effective use will be discussed. Finally, the high-power densities involved have increased the need for a theoretical treatment of data center thermophysics. We will discuss this need in detail and will suggest ways in which it might be addressed. Throughout the paper, focus will be placed on future directions with the hope of instilling enthusiasm for further research and development by academia and industry in this particular area of HVAC&R that will soon reach a critical point in its continuing evolution.

Critical Heat Flux of Ice Accretion along a Fine Wire Immersed in Cold Air Stream with Water Spray. Digital Simulation on Effects of Droplet Diameter Profile on Critical Heat Flux.

Numerical studies are carried out on the critical heat flux of ice accretion along a horizontal fine wire immersed in cold air stream with water spray. The parameters selects for the investigation are the mean diameter of the droplet, the wire diameter, and the ratio of the former and the latter. The temperature and velocity of a droplet that arrives at a wire are calculated, and based on the results the critical heat flux is estimated using the heat transfer equations previously proposed by other researchers. It is assumed that the droplet diameter distribution is the same as that of Rosin-Rammler. Finally, the characteristics of the critical heat flux are examined by comparing experimental data obtained by the present authors. It is found that the present simulation can successfully explain the experimental results, although it is needed to be modified for wider conditions.

Experimental and numerical analysis of the temperature transition of a suspended freezing water droplet

The objective of this study was to develop a simple experimental and numerical method to study the temperature transition of freezing droplets. One experimental approach and several numerical methods were explored. For the experimental method, a droplet was suspended in a cold air stream from the junction of a thermocouple. The droplet’s temperature transition was able to be accurately measured and the freezing of the droplet observed. The numerical models developed were able to predict the temperature transition and the freezing time of the droplet. Of the numerical methods, a simple heat balance model was determined to be an accurate means of predicting the freezing time of the droplet.