Optimizing and Predicting CHF in Spray Cooling of a Square Surface

1996 ◽  
Vol 118 (3) ◽  
pp. 672-679 ◽  
Author(s):  
I. Mudawar ◽  
K. A. Estes
Keyword(s):  
Flow Rate ◽  
Flux Distribution ◽  
Spray Cooling ◽  
Liquid Volume ◽  
Optimum Configuration ◽  
New Correlation ◽  
Impact Area ◽  
Hot Surface ◽  
The Impact ◽  
Volumetric Flux

Spray cooling of a hot surface was investigated to ascertain the effect of nozzle-to-surface distance on critical heat flux (CHF). Full cone sprays of Fluorinert FC-72 and FC-87 were used to cool a 12.7 × 12.7 mm2 surface. A theoretical model was constructed that accurately predicts the spray’s volumetric flux (liquid volume per unit area per unit time) distribution across the heater surface. Several experimental spray sampling techniques were devised to validate this model. The impact of volumetric flux distribution on CHF was investigated experimentally. By measuring CHF for the same nozzle flow rate at different nozzle-to-surface distances, it was determined CHF can be maximized when the spray is configured such that the spray impact area just inscribes the square surface of the heater. Using this optimum configuration, CHF data were measured over broad ranges of flow rate and subcooling, resulting in a new correlation for spray cooling of small surfaces.

scholarly journals Discharge Flow Rate for the Initiation of Jet Flow in Sky-Jump Spillways

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1814
Author(s):  
Raffaella Pellegrino ◽  
Miguel Ángel Toledo ◽  
Víctor Aragoncillo
Keyword(s):  
Flow Rate ◽  
Direct Determination ◽  
Jet Flow ◽  
Effective Solution ◽  
Discharge Flow Rate ◽  
Impact Area ◽  
Experimental Laboratory ◽  
New Formula ◽  
The Impact

The sky-jump spillway is an economical and effective solution to return water to a river, eventually complemented by a pre-excavated basin. However, an inappropriate design could endanger spillways and even the dam itself. For the design of a sky-jump it is necessary to evaluate the position and dimensions of the potential pre-excavated basin based on the characteristics of the water flow to be evacuated and the geometric configuration of the sky-jump. The jump of the water jet occurs when a certain flow rate is reached. This flow rate for the initiation of the jet flow determines the position of the impact area closest to the spillway. We propose a new formula for the determination of the flow rate for the initiation of the jet flow, which incorporates as a novelty the influence of the curvature of the flip bucket. A methodology for the direct determination of the flow rate for the initiation of the jet flow is also presented. The new formula and methodology, based on experimental laboratory work and numerical modeling, will support the designer to choose the energy dissipation way, in the riverbed or inside the flip bucket, for low and frequent discharge flows.

Experimental Investigation of Heat Transfer Characteristics of Inkjet Assisted Spray Cooling

Volume 3 ◽  
2004 ◽  
Author(s):  
Ratnesh K. Sharma ◽  
Cullen E. Bash ◽  
Chandrakant D. Patel
Keyword(s):  
Heat Transfer ◽  
Power Density ◽  
Heated Surface ◽  
Spray Cooling ◽  
Operating Conditions ◽  
Heat Transfer Characteristics ◽  
Subsequent Formation ◽  
Transfer Characteristics ◽  
The Impact ◽  
Volumetric Flux

Increases in microprocessor power density along with an accompanying spatial variation in power density has been well documented in recent years. These combined factors pose a severe challenge for the provisioning of cooling resources at the microprocessor level. The use of thermal inkjet technology to precisely supply coolant onto the surface of a microprocessor has the potential to address this problem in a chip-scale form factor. By providing coolant when and where it is needed on the surface of a chip or package, very high critical heat fluxes can be obtained in an energy efficient manner in a minimum of physical space. In this paper, the unique heat transfer characteristics of inkjet assisted spray cooling of a heated surface are investigated. Sprays of water are used to cool heated surfaces ranging from 281mm2 to 35mm2. Several experiments are conducted at different nozzle-to-surface distances to measure critical heat flux (CHF) at different flow rates and firing frequencies. The impact of volumetric flux variation on CHF is studied. CHF data, measured over broad range of operating conditions is correlated to volumetric flux and liquid properties. Flow visualization studies are also conducted to understand the vapor-liquid interaction at the heater surface and the intermediate region. Jet breakup length studies are carried out to understand the propagation of Rayleigh instabilities in the spray jets and, subsequent, formation of liquid drops. CHF data combined with fluid flow studies have been used to optimize the nozzle-to-surface clearance. Results obtained from these experiments are invaluable for the design of micro scale spray cooling devices for chips.

Impact Of Transurethral Resection Of Prostate On International Prostate Symptom Score And Peak Urinary Flow Rate

2020 ◽  
Vol 16 (1) ◽  
pp. 11-15
Author(s):  
Md Waliul Islam ◽  
Md Abul Hossain ◽  
Md Nurul Hooda ◽  
Kazi Rafiqul Abedin ◽  
Husne Ara
Keyword(s):  
Flow Rate ◽  
Transurethral Resection ◽  
Urine Volume ◽  
T Test ◽  
Urinary Symptoms ◽  
Urinary Flow Rate ◽  
Transurethral Resection Of Prostate ◽  
Urinary Flow ◽  
Paired Student ◽  
The Impact

Objectives: To evaluate urinary symptoms and quality of life in patient with BPH before and after TURP. To determine the impact of TURP on the urinary symptoms (IPSS) and peak urinary flow rate. Methods: This study is prospective study carried out between 2010 and 2011 in the department of Urology, National Institute of Kidney Diseases & Urology. Total 102 cases were selected purposively according to selection criteria. Each patient was observed and followed up at 8 weeks (1st visit), 16 weeks (2nd visit) 24 weeks (3rd visit) after transurethral resection of prostate (TURP). IPSS score, QOL score also recorded and uroflowmetry was done to see the peak urinary flow rate (Qmax) of urine and voiding time. USG was done to see post voidal residual urine volume and DRE also done in selected cases. Data was complied and statistical analysis were done using computer based software, Statistical Package for Social Science (SPSS), using paired ‘t’ test. A P value <0.05 was taken as significance. Results: Before TURP, IPSS range 17-25 and mean 21.61+2.43, after TURP, range 0-7 and mean 4.27+1.71). Hence a significant improvement of IPSS was found from 2 months to 6 months follow up after TURP. The change was tested using “paired student ‘t’ test”. Before TURP Qmax range 7-12.2 and mean was 9.96+1.69, which became range 18-25 and mean was 22.61+2.28 after TURP and therefore change of mean Qmax was 12.64+2.69. The change was tested using “paired student ‘t’ test”. The change was found significant (P<0.001). Conclusion: Transurethral resection of prostate resolves obstructive symptoms, rapid improvement of urinary flow rate Bangladesh Journal of Urology, Vol. 16, No. 1, Jan 2013 p.11-15

Experimental and Modelling of Aqueous Radioactive Waste Treatment by Ultrafiltration

2018 ◽  
Vol 69 (5) ◽  
pp. 1149-1151
Author(s):  
Laura Ruxandra Zicman ◽  
Elena Neacsu ◽  
Felicia Nicoleta Dragolici ◽  
Catalin Ciobanu ◽  
Gheorghe Dogaru ◽  
...  
Keyword(s):  
Flow Rate ◽  
Suspended Solids ◽  
Waste Treatment ◽  
Operating Pressure ◽  
Feed Flow Rate ◽  
Permeate Flux ◽  
Independent Variables ◽  
Opposite Trend ◽  
Process Factors ◽  
Volumetric Flux

Ultrafiltration of untreated and pretreated aqueous radioactive wastes was conducted using a spiral-wound polysulphonamide membrane. The influence of process factors on its performances was experimental studied and predicted. Permeate volumetric flux and permeate total suspended solids (TSS) were measured at different values of feed flow rate (7 and 10 m3/h), operating pressure (0.1-0.4 MPa), and feed TSS (15 and 60 mg/L). Permeate flux (42-200 L/(m2�h)) increased with feed flow rate and operating pressure as well as it decreased with an increase in feed TSS, whereas permeate TSS (0.1-33.2 mg/L) exhibited an opposite trend. A 23 factorial plan was used to establish correlations between dependent and independent variables of ultrafiltration process.

scholarly journals Model of thermal buoyancy in cavity-ventilated roof constructions

2021 ◽  
pp. 174425912098418
Author(s):  
Toivo Säwén ◽  
Martina Stockhaus ◽  
Carl-Eric Hagentoft ◽  
Nora Schjøth Bunkholt ◽  
Paula Wahlgren
Keyword(s):  
Analytical Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Air Flow ◽  
Wind Pressure ◽  
Air Flow Rate ◽  
Test Set ◽  
Air Cavity ◽  
Thermal Buoyancy ◽  
The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

scholarly journals Aircraft Impact Effects on an Aged NPP

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 816
Author(s):  
Rosa Lo Frano
Keyword(s):  
Nuclear Power ◽  
Military Aircraft ◽  
Residual Resistance ◽  
Plant Safety ◽  
Need To Evaluate ◽  
Target Wall ◽  
Impact Area ◽  
Wall Perforation ◽  
The Impact ◽  
Loss Of Strength

The impact of an aircraft is widely known to be one of the worst events that can occur during the operation of a plant (classified for this reason as beyond design). This can become much more catastrophic and lead to the loss of strength of/collapse of the structures when it occurs in the presence of ageing (degradation and alteration) materials. Therefore, since the performance of all plant components may be affected by ageing, there is a need to evaluate the effect that aged components have on system performance and plant safety. This study addresses the numerical simulation of an aged Nuclear Power Plant (NPP) subjected to a military aircraft impact. The effects of impact velocity, direction, and location were investigated together with the more unfavorable conditions to be expected for the plant. The modelling method was also validated based on the results obtained from the experiments of Sugano et al., 1993. Non-linear analyses by means of finite element (FE) MARC code allowed us to simulate the performance of the reinforced concrete containment building and its impact on plant availability and reliability. The results showed that ageing increases a plant’s propensity to suffer damage. The damage at the impact area was confirmed to be dependent on the type of aircraft involved and the target wall thickness. The greater the degradation of the materials, the lower the residual resistance capacity, and the greater the risk of wall perforation.

scholarly journals Renovation of Public Lighting Systems in Cultural Landscapes: Lighting and Energy Performance and Their Impact on Nightscapes

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 509
Author(s):  
Lodovica Valetti ◽  
Francesca Floris ◽  
Anna Pellegrino
Keyword(s):  
Energy Efficient ◽  
Flux Distribution ◽  
Cultural Landscapes ◽  
Energy Performance ◽  
Luminous Flux ◽  
Landscape Value ◽  
Reduce Energy Consumption ◽  
Lighting Systems ◽  
The Impact ◽  
Positive Effect

The technological innovation in the field of lighting and the need to reduce energy consumption connected to public lighting are leading many municipalities to undertake the renewal of public lighting systems, by replacing the existing luminaires with LED technologies. This renovation process is usually aimed at increasing energy efficiency and reducing maintenance costs, whist improving the lighting performance. To achieve these results, the new luminaires are often characterised by a luminous flux distribution much more downward oriented, which may remarkably influence and alter the perception of the night image of the sites. In this study the implications of the renovation of public lighting systems in terms of lighting and energy performance as well as the effects relating to the alteration of the night image, in historical contexts characterized by significant landscape value, are analysed. Results, along with demonstrating the positive effect that more sustainable and energy efficient lighting systems may have on the lighting performance and energy consumptions of public lighting systems, evidences the impact they may have on the alteration of the nocturnal image.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

scholarly journals Research on the impact of ship traffic flow on the restricted channel segment of the middle Yangtze River based on traffic wave theory

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Ting Liu ◽  
Gabriel Lodewijks
Keyword(s):  
Traffic Flow ◽  
Flow Rate ◽  
Flow Simulation ◽  
Wave Theory ◽  
Flow Density ◽  
List Type ◽  
Ship Traffic ◽  
Traffic Wave ◽  
The Impact ◽  
Channel Segment

Abstract Abstract On the basis of the influence of dry season on ship traffic flow, the gathering and dissipating process of ship traffic flow was researched with Greenshields linear flow—density relationship model, the intrinsic relationship between the ship traffic congestion state and traffic wave in the unclosed restricted channel segment was emphatically explored when the ship traffic flow in a tributary channel inflows, and the influence law of multiple traffic waves on the ship traffic flow characteristics in unclosed restricted segment is revealed. On this basis, the expressions of traffic wave speed and direction, dissipation time of queued ships and the number of ships affected were provided, and combined with Monte Carlo method, the ship traffic flow simulation model in the restricted channel segment was built. The simulation results show that in closed restricted channel segment the dissipation time of ships queued is mainly related to the ship traffic flow rate of segments A and C, and the total number of ships affected to the ship traffic flow rate of segment A. And in unclosed restricted channel segment, the dissipation time and the total number of ships affected are also determined by the meeting time of the traffic waves in addition to the ship traffic flow rate of segments. The research results can provide the theoretical support for further studying the ship traffic flow in unclosed restricted channel segment with multiple tributaries Article Highlights The inflow of tributaries' ship traffic flows has an obvious impact on the traffic conditions in the unenclosed restricted channel segment. The interaction and influence between multiple ship traffic waves and the mechanism of generating new traffic waves are explained. The expression of both dissipation time of queued ships and the total number of ships affected in the closed and unclosed restricted channel segment are given.

Numerical Simulation of Heat Transfer Mechanisms in Spray Cooling

2010 ◽  
Author(s):  
Eelco Gehring ◽  
Mario F. Trujillo
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
Impingement Zone ◽  
Ongoing Work ◽  
Efficient Suppression ◽  
A Cell ◽  
Cooling Behavior ◽  
Free Surface Capturing ◽  
The Impact

A primary mechanism of heat transfer in spray cooling is the impingement of numerous droplets onto a heated surface. This mechanism is isolated in the present and ongoing work by numerically simulating the impact of a single train of FC-72 droplets employing an implicit free surface capturing methodology. The droplet frequency and velocity ranges from 2000–4000 Hz, and 0.5–2 m/s, respectively, with a fixed drop size of 239 μm. This gives a corresponding Weber and Reynolds range of 10–170 and 330–1300, respectively. Results show that the impingement zone is largely free of phase change effects due to the efficient suppression of the local temperature field well below the saturated value. Due in part to the relatively high value of the Prandtl number and the compression of the boundary layer from the impingement flow, a cell size on the order of 1 μm is necessary to adequately capture the heat transfer dynamics. It is shown that the cooling behavior increases in relation to increasing frequency and impact velocity, but is most sensitive to velocity. In fact, for sufficiently low velocities the calculations show that the momentum imparted on the film is insufficient to maintain a near stationary liquid crown. The consequence is a noticeable penalty on the cooling behavior.

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