Tackling Coolant Freezing in Generation-IV Molten Salt Reactors

2017 ◽  
Author(s):  
N. Le Brun ◽  
A. Charogiannis ◽  
G. F. Hewitt ◽  
C. N. Markides
Keyword(s):  
Molten Salt ◽  
Removal Rate ◽  
Heat Removal ◽  
Internal Flow ◽  
Experimental System ◽  
High Heat ◽  
Diagnostic Techniques ◽  
Piping System ◽  
Cold Surface ◽  
Accident Conditions

In this study we describe an experimental system designed to simulate the conditions of transient freezing which can occur in abnormal behaviour of molten salt reactors (MSRs). Freezing of coolant is indeed one of the main technical challenges preventing the deployment of MSR. First a novel experimental technique is presented by which it is possible to accurately track the growth of the solidified layer of fluid near a cold surface in an internal flow of liquid. This scenario simulates the possible solidification of a molten salt coolant over a cold wall inside the piping system of the MSR. Specifically, we conducted measurements using water as a simulant for the molten salt, and liquid nitrogen to achieve high heat removal rate at the wall. Particle image velocimetry and planar induced fluorescence were used as diagnostic techniques to track the growth of the solid layer. In addition this study describes a thermo-hydraulic model which has been used to characterise transient freezing in internal flow and compares the said model with the experiments. The numerical simulations were shown to be able to capture qualitatively and quantitatively all the essential processes involved in internal flow transient freezing. Accurate numerical predictive tools such the one presented in this work are essential in simulating the behaviour of MSR under accident conditions.

scholarly journals Cooling Performance of a Novel Circulatory Flow Concentric Multi-Channel Heat Sink with Nanofluids

Nanomaterials ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 647 ◽  
Author(s):  
Ravindra Jilte ◽  
Mohammad H. Ahmadi ◽  
Ravinder Kumar ◽  
Vilas Kalamkar ◽  
Amirhosein Mosavi
Keyword(s):  
Heat Sink ◽  
Volume Fraction ◽  
Removal Rate ◽  
Heat Removal ◽  
High Heat ◽  
Operating Conditions ◽  
Bottom Surface ◽  
Outlet Temperature ◽  
Cooling Performance ◽  
Heat Rejection

Heat rejection from electronic devices such as processors necessitates a high heat removal rate. The present study focuses on liquid-cooled novel heat sink geometry made from four channels (width 4 mm and depth 3.5 mm) configured in a concentric shape with alternate flow passages (slot of 3 mm gap). In this study, the cooling performance of the heat sink was tested under simulated controlled conditions.The lower bottom surface of the heat sink was heated at a constant heat flux condition based on dissipated power of 50 W and 70 W. The computations were carried out for different volume fractions of nanoparticles, namely 0.5% to 5%, and water as base fluid at a flow rate of 30 to 180 mL/min. The results showed a higher rate of heat rejection from the nanofluid cooled heat sink compared with water. The enhancement in performance was analyzed with the help of a temperature difference of nanofluid outlet temperature and water outlet temperature under similar operating conditions. The enhancement was ~2% for 0.5% volume fraction nanofluids and ~17% for a 5% volume fraction.

scholarly journals Enhancement of Mist Flow Cooling by Using V-Shaped Broken Ribs

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3785
Author(s):  
Kuan-Tzu Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Removal Rate ◽  
Heated Surface ◽  
Heat Removal ◽  
High Heat ◽  
Water Mist ◽  
Droplet Impingement ◽  
Square Channel ◽  
Air Volume ◽  
Mist Flow

Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45°, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1–3.1 W/cm2 and 3.4–9.4 W/cm2 for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow.

The Enhancement of Spray Cooling Performance in Nucleate and Transition Boiling Regimes by Using Saline Water Containing Dissolved Carbon Dioxide

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Lily Das ◽  
B. Munshi ◽  
S. S. Mohapatra
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Saline Water ◽  
Removal Rate ◽  
Heat Removal ◽  
Spray Cooling ◽  
High Heat ◽  
Vapor Bubbles ◽  
Dissolved Carbon ◽  
Dissolved Carbon Dioxide

Abstract In the current work, by using various additives, the spray cooling in the transition boiling regime is significantly augmented due to the vapor film instability enhancing, which helps to overcome the disadvantages reported in the open literature for the attainment of high heat flux in the aforesaid boiling regime. Saline water containing dissolved carbon dioxide produces two favorable conditions for high heat transfer rate: (1) controlled vapor bubble nucleation and (2) low entrapped vapor bubbles coalescence rate. These phenomena are the parameters defining the step-up in the heat transfer rate. Systematic spray cooling (from 900 °C) experiments were conducted on a 6-mm thick AISI 304 steel plate (100 mm × 100 mm). The heat transfer analysis indicates that the heat removal rate in case of soda added water depicts an increasing trend with the rising of the soda concentration up to 40% in water, and further increment in soda water concentration declines the heat removal rate due to the formation of the uncontrolled vapor bubbles undergoing early coalescence. In case of salt added carbonated water spray cooling, the quenching performance indicates step-up in critical heat flux up to 1.7 MW/m2. In addition to the above, the spray cooling performance of the above-stated coolant is compared with other potential coolants such as soda–surfactant–water, soda–alcohol–water and soda–salt–surfactant–water mixtures.

Microfluidic Refrigerant Compression and Pumping by Maxwell Pressure Generated at a Nanoporous Monolith

2009 ◽  
Author(s):  
Hsueh-Chia Chang
Keyword(s):  
High Pressure ◽  
Vapor Phase ◽  
Removal Rate ◽  
Heat Removal ◽  
High Heat ◽  
Electronic Cooling ◽  
Pressure Source ◽  
Two Phase ◽  
Ac Field ◽  
Two Phase Cooling

We introduce a new concept in miniature two-phase cooling with ammonia and other refrigerants. Despite its high heat removal rate density, two-phase cooling has not been attempted for miniature electronic cooling because of the high pressure needed to compress the vapor phase into liquid. We suggest in this short expository that Maxwell pressure generated by an intense DC or AC field across a solid nanoporous monolith can overcome this challenge. The fundamental mechanisms for such miniature pressure source are reviewed and the fabrication challenges discussed.

Thermal Analysis of Plastic Serpentine-Type Microchannel Evaporators

2007 ◽  
Author(s):  
Boris Kosoy ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Removal Rate ◽  
Flow Characteristics ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
High Heat Transfer ◽  
Micro Channels

Recently, microchannel liquid cooling technology showed very high heat transfer coefficients enabling high heat fluxes at allowable wall temperatures. It promises to be a potential solution to high flux electronics. This paper presents result of two related areas in the field of microchannel heat transfer. First, experimental results of serpentine-type fluoroplastic evaporated thermosyphons for microchannel applications are presented. R11 and R113 were used as working fluid, and it was shown that R11 has higher heat removal rate than R113. Flow distribution and flow characteristics (liquid, vapor, mixture etc) are discussed. Later discussion is extended towards key issues in mini and micro channels, and proposed correlations will be discussed. It is our great honor to contribute to Prof. Sadik Kakac symposium to celebrate his 75th birthday. We feel privileged knowing him and learning from his scientific books, papers, and personal discussions. We wish him a happy, healthy, and long life.

STABLE, CALM, AND HIGH-HEAT-FLUX HEAT REMOVAL USING A POROUS-MICRO-CHANNEL

2017 ◽  
Author(s):  
Tomio Okawa ◽  
Junki Ohashi ◽  
Ryo Hirata ◽  
Koji Enoki
Keyword(s):  
Heat Flux ◽  
Heat Removal ◽  
High Heat ◽  
High Heat Flux ◽  
Micro Channel

Thermo-Fluid-Stress-Deformation Analysis of Two-Layer Microchannels for Cooling Chips With Hot Spots

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Abas Abdoli ◽  
George S. Dulikravich ◽  
Genesis Vasquez ◽  
Siavash Rastkar
Keyword(s):  
Heat Flux ◽  
Thermal Stresses ◽  
Hot Spot ◽  
Heat Removal ◽  
High Heat ◽  
Heat Transfer Analysis ◽  
Deformation Analysis ◽  
High Heat Flux ◽  
Cooling Design ◽  
Microchannel Cooling

Two-layer single phase flow microchannels were studied for cooling of electronic chips with a hot spot. A chip with 2.45 × 2.45 mm footprint and a hot spot of 0.5 × 0.5 mm in its center was studied in this research. Two different cases were simulated in which heat fluxes of 1500 W cm−2 and 2000 W cm−2 were applied at the hot spot. Heat flux of 1000 W cm−2 was applied on the rest of the chip. Each microchannel layer had 20 channels with an aspect ratio of 4:1. Direction of the second microchannel layer was rotated 90 deg with respect to the first layer. Fully three-dimensional (3D) conjugate heat transfer analysis was performed to study the heat removal capacity of the proposed two-layer microchannel cooling design for high heat flux chips. In the next step, a linear stress analysis was performed to investigate the effects of thermal stresses applied to the microchannel cooling design due to variations of temperature field. Results showed that two-layer microchannel configuration was capable of removing heat from high heat flux chips with a hot spot.

Fatigue Evaluation for Thermally Stratified DVI Piping

2012 ◽  
Author(s):  
Hwan Ho Lee ◽  
Joon Ho Lee ◽  
Dong Jae Lee ◽  
Seok Hwan Hur ◽  
Il Kwun Nam ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Heat Removal ◽  
Local Stress ◽  
Piping System ◽  
Hydraulic Analysis ◽  
Fatigue Evaluation ◽  
Core Cooling ◽  
Thermal Hydraulic Analysis

A numerical analysis has been performed to estimate the effect of thermal stratification in the safety injection piping system. The Direct Vessel Injection (DVI) system is used to perform the functions of Emergency Core Cooling and Residual Heat Removal for an APR1400 nuclear power plant (Korea’s Advanced Power Reactor 1400 MW-Class). The thermal stratification is anticipated in the horizontally routed piping between the DVI nozzle of the reactor vessel and the first isolation valve. Non-axisymmetric temperature distribution across the pipe diameter induced by the thermal stratification leads to differential thermal growth of the piping causing the global bending stress and local stress. Thermal hydraulic analysis has been performed to determine the temperature distribution in the DVI piping due to the thermal stratification. Piping stress analysis has also been carried out to evaluate the integrity of the DVI piping using the thermal hydraulic analysis results. This paper provides a methodology for calculating the global bending stresses and local stresses induced by the thermal stratification in the DVI piping and for performing fatigue evaluation based on Subsection NB-3600 of ASME Section III.

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