Critical Heat Flux (CHF) and Cold-Flow Pressure Drop Investigations of R-11 in a Vertical Uniformly Heated 5 x 5 Rod Bundle

2005 ◽  
Author(s):  
Asif Salahudidin ◽  
Jamil A. Khan ◽  
L. David Smith ◽  
Chris L. Wilbur
Keyword(s):  
Heat Flux ◽  
South Carolina ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Cold Flow ◽  
Rod Bundle ◽  
Flow Pressure

Experimental and numerical investigations were performed to determine the critical heat flux (CHF) and pressure drop in a vertical uniformly heated 5×5 rod bundle. R-11 is used as the working fluid due to its low latent heat, low critical pressure and well known properties. The experimental investigation was performed at the Westinghouse Nuclear Fuel PWR Product Technologies Test Laboratory in Columbia, South Carolina. Two types of grid designs were tested with Bundle-1 and Bundle-2 respectively. The matrix of DNB test parameters (water equivalent conditions shown in parentheses) includes exit pressure: 317–445 psia (1800–2400), inlet mass flux: 1.725–3.400 Mlbm/hr-ft2 (1.5–2.5 Mlbm/hr-ft2) and inlet temperature: 170–305°F (320–590 Mlbm/hr-ft2). Nominal R-11 conditions for the cold test are 165 psia, and 80°F±10°F. The experimental results were validated using a nuclear thermal hydraulic code VIPRE-01, MOD-02.1. The EPRI-1 correlation was being used to have a gross understanding of the CHF in the Bundles. Subsequently an empirical correlation USC11F was developed with Bundle-1 CHF database which compares favorably with experimental CHF for both the grid designs. Overall mean ratios of experimental to predicted CHF of 0.9984 and 0.9948 with standard deviations of 0.0265 and 0.0338 were obtained for Bundle-1 and Bundle-2 respectively. The predicted cold flow pressure drops also reproduced the experimental values closely. At lower mass flux a slight overprediction was encountered due to the dependability of mixing grid loss coefficient on Reynold’s number.

Experimental Study of Heat Transfer to Supercritical Pressure Water Flowing in a 2×2 Rod Bundle

2014 ◽  
Author(s):  
Han Wang ◽  
Qincheng Bi ◽  
Linchuan Wang ◽  
Haicai Lv ◽  
Laurence K. H. Leung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Pressure Drop ◽  
Wall Temperature ◽  
Mass Flux ◽  
Heat Fluxes ◽  
Outer Diameter ◽  
Square Channel ◽  
Rod Bundle

An experiment has recently been performed at Xi’an Jiaotong University to study the wall temperature and pressure drop at supercritical pressures with upward flow of water inside a 2×2 rod bundle. A fuel-assembly simulator with four heated rods was installed inside a square channel with rounded corner. The outer diameter of each heated rod is 8 mm with an effective heated length of 600 mm. Experimental parameters covered the pressure of 23–28 MPa, mass flux of 350–1000 kg/m2s and heat flux on the rod surface of 200–1000 kW/m2. According to the experimental data, it was found that the circumferential wall temperature distribution of a heated rod is not uniform. The temperature difference between the maximum and the minimum varies with heat flux and/or mass flux. Heat transfer characteristics of supercritical water in bundle were discussed with respect to various heat fluxes. The effect of heat flux on heat transfer in rod bundles is similar with that in tubes or annuli. In addition, flow resistance reflected in the form of pressure loss has also been studied. Experimental results showed that the total pressure drop increases with bulk enthalpy and mass flux. Four heat transfer correlations developed for supercritical pressures water were compared with the present test data. Predictions of Jackson correlation agrees closely with the experimental data.

Experimental Investigation of the CHF Condition During Flow Boiling of Water in Microtubes

2007 ◽  
Author(s):  
Anand P. Roday ◽  
Michael K. Jensen
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Heat Transfer Process ◽  
Working Fluid ◽  
Two Phase ◽  
Flow Boiling Heat Transfer ◽  
C 50 ◽  
Different Diameters

The critical heat flux (CHF) condition sets an upper limit on the flow-boiling heat transfer process. With the growing demand for the use of two-phase flow in micro and nano-sized devices, there is a strong need to understand the CHF phenomenon in channels of such small dimensions. This study experimentally investigates the critical heat flux condition during flow boiling in a single stainless steel microtube of two different diameters—0.427mm, and 0.286 mm. Degassed water is the working fluid. The effects of various parameters—diameter, mass flux (350–1500 kg/m2s), inlet subcooling (2°C–50°C), and length-to-diameter ratio (75–200) on the CHF condition are studied for the exit condition being nearly atmospheric pressure. The CHF increases with an increase in mass flux. The effect of the inlet subcooling on the CHF condition is more complex. With a decreasing inlet subcooling, the CHF decreases until saturated liquid is reached; thereafter, the CHF increases with quality.

Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps

2020 ◽  
Author(s):  
Debora C. Moreira ◽  
Gherhardt Ribatski ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Single Phase ◽  
Bubble Nucleation ◽  
Low Flow ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Inlet Section ◽  
Flow Rates

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Flow Boiling Heat Transfer ◽  
Low Mass

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel-Three-Dimensional Manifold Coolers—Part 2: Parametric Study of EMMCs for High Heat Flux (∼1 kW/cm2) Power Electronics Cooling

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Ki Wook Jung ◽  
Sougata Hazra ◽  
Heungdong Kwon ◽  
Alisha Piazza ◽  
Edward Jih ◽  
...  
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Power Electronics ◽  
Parametric Study ◽  
Three Dimensional ◽  
Working Fluid ◽  
Inlet Temperature ◽  
High Heat Flux ◽  
Dimensional Manifold ◽  
Power Capability

Abstract Thermal management of power electronics modules is one of the limiting factors in the peak power capability of the traction inverter system and overall efficiency of the e-drive. Liquid cooling using embedded microchannels with a three-dimensional (3D)-manifold cooler (EMMC) is a promising technology capable of removing heat fluxes of >1 kW/cm2 at tens of kPa pressure drop. In this work, we utilize computational fluid dynamics (CFD) simulations to conduct a parametric study of selected EMMC designs to improve the thermofluidic performance for a 5 mm × 5 mm heated area with the applied heat flux of 800 W/cm2 using single-phase water as working fluid at inlet temperature of 25 °C. We implemented strategies such as: (i) symmetric distribution of manifold inlet/outlet conduits, (ii) reducing the thickness of cold-plate (CP) substrate, and (iii) increasing fluid–solid interfacial area in CP microchannels, which resulted in a reduction in thermal resistance from 0.1 for baseline design to 0.04 cm2 K/W, while the pressure drop increased from 8 to 37 kPa.

Critical Heat Flux in Microchannels With an Adjustable Inlet Orifice

2012 ◽  
Author(s):  
Brent A. Odom ◽  
Carlos A. Ortiz ◽  
Patrick E. Phelan
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Cooling Capacity ◽  
Hydraulic Diameter ◽  
Low Flow ◽  
Two Phase ◽  
Mass Fluxes ◽  
Inlet Conditions

The benefits of eliminating instabilities in two-phase microchannel flow with inlet orifices come with costs. This study describes the tradeoffs between microchannels with and without inlet orifices, focusing on results from critical heat flux data obtained for various orifice sizes and mass fluxes. An adjustable inlet orifice controlled with a micrometer was placed in front of an array of 31 parallel microchannels each with a hydraulic diameter of 0.235 mm and a length of 1.33 cm. For mass fluxes ranging from 186 kg m−2 s−1 to 847 kg m−2 s−1, critical heat flux (CHF) data were obtained for 7 different orifice sizes. For low flow rates that provided a low quality saturated inlet condition, the difference in CHF values was found to be minimal between open and almost closed orifice conditions. The smallest orifice achieved a CHF value of 5 W cm−2 less than the largest orifice size for a mass flux of 186 kg m−2 s−1, and 7 W cm−2 less for a mass flux of 433 kg m−2 s−1. For mass fluxes higher than 433 kg m−2 s−1, subcooled conditions were present at the orifice inlet, and the highest CHF values occurred with an orifice hydraulic diameter of 35 percent of fully open. For the higher mass flux cases, orifice sizes in the range of 1.8 percent to 28 percent of fully open caused CHF to occur at lower values than less restrictive orifice sizes. This was due to loss of cooling capacity from rapid pressure drop through the orifice. Slightly higher average channel pressures also decrease the refrigerant’s latent heat of vaporization. For the orifice sizes from 35 to 70 percent of unrestricted flow, a very minimal increase in pressure drop over fully open inlet conditions occurred and the general trend was higher CHF values. Very small inlet orifices are beneficial for steady state conditions that do not approach CHF; however, overly restricting the flow at the inlet to microchannels reduces cooling capacity significantly and will cause early onset of CHF. A slightly restrictive inlet orifice will increase CHF.

An Experimental Investigation of Condensation Heat Transfer Coefficients and Pressure Drops of Refrigerants Inside Multiport Mini-channel Tubes

2017 ◽  
Vol 25 (02) ◽  
pp. 1750013 ◽  
Author(s):  
Pham-Quang Vu ◽  
Kwang-Il Choi ◽  
Jong-Taek Oh ◽  
Honggi Cho
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients

The condensation heat transfer coefficients and pressure drops of R410A and R22 flowing inside a horizontal aluminum multiport mini-channel tube having 18 channels are investigated. Experimental data are presented for the range of vapor quality from 0.1 to 0.9, mass flux from 50 to 500[Formula: see text]kg/m2s, heat flux from 3 to 15[Formula: see text]kW/m2 and the saturation temperature at 48[Formula: see text]C. The pressure drop across the test section was directly measured by a differential pressure transducer. At a small scale, the noncircular cross-sections can enhance the effect of the surface tension. The average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux. Under the same test conditions, the heat transfer coefficients of R22 are higher than those for R410A, the pressure drops for R410A are 7–19% lower than those of R22. The lower pressure drop of R410A has an important advantage as an alternative working fluid for R22 in air-conditioning and heat pump systems.

Experimental Study on the Critical Heat Flux of Nanofluid Flow Boiling Under Different Conditions

2018 ◽  
Author(s):  
Y. Wang ◽  
K. H. Deng ◽  
J. M. Wu ◽  
N. N. Yue ◽  
Y. F. Zan ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Heating Surface ◽  
Vertical Tube ◽  
Working Fluid ◽  
Nanofluid Flow ◽  
Sem Images ◽  
Heat Transfer System

Nanofluid has been attracted great attention since it was proposed as a preeminent working fluid. Flow boiling is familiar in heat transfer system and the critical heat flux is a key parameter for the design of thermal hydraulic. In present work, the critical heat flux of nanofluid flow boiling is experimentally investigated in a vertical tube with the consideration of outlet pressure, mass flux, inlet subcooling, heating length and diameter. The results indicate that the critical heat flux of nanofluid flow boiling is enhanced compared with base fluid and the increasing radio is increased with increasing the mass flux, diameter and pressure, and with decreasing the heating length. In addition, the inlet subcooling and concentrations (0.1vol.%, 0.5vol.%) have almost no significant influence. Furthermore, a new mechanism for the enhancement of nanofluid flow boiling critical heat flux was proposed by the SEM images of nanopariticle deposition on the heating surface.

Two-Phase Pressure Drop of Ammonia in a Mini/Micro-Channel

2010 ◽  
Author(s):  
M. Hamayun Maqbool ◽  
Bjo¨rn Palm ◽  
R. Khodabandeh ◽  
Rashid Ali
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Homogeneous Model ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Internal Diameter ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Phase Pressure

Experiments have been performed to investigate two-phase pressure drop in a circular vertical mini-channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. A uniform heat flux is applied to the test section by DC power supply. Two phase frictional pressure drop variation with mass flux, vapour quality and heat flux was determined. The experimental results are compared to predictive methods available in literature for frictional pressure drop. The Homogeneous model and the correlation of Mu¨ller Steinhagen et al. [14] are in good agreement with our experimental data with MAD of 27% and 26% respectively.

Sign in / Sign up

Export Citation Format

Share Document