Thermophysical Properties and Supercritical Heat Transfer Characteristics of R515A

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternative to replace conventional R134a, which can be beneficial for climate change. A considerable suggestion is R515A which possesses considerably lower global warming potential. The present simulations are designed to study supercritical fluid R515A under cooling conditions in horizontal position. The effect of pressure, mass flux, heat flux and tube diameter were considered for horizontal tube in the vicinity of pseudo critical temperature. Numerical investigations on heat transfer characteristics of supercritical fluid R515A were performed using widely used shear-stress transport (SST) model. Moreover, heat transfer correlations were developed and suggested to accurately predict Nusselt number within 10% accuracy. The simulation results showed about 3.98% average absolute deviation.

Numerical Investigation on the Heat Transfer Characteristics of Supercritical Water in a Non-Uniformly Heated Tube for a Supercritical CFB Boiler

In this paper,a numerical model was built by ANSYS FLUENT to investigate the heat transfer performances of supercritical water in a circumferential non-uniformly heated vertical tube.The Shear Stress Transport(SST)k-ωmodel was adopted for describing turbulence.The operating parameters are chosen according to a 660 MW ultra-supercritical CFB boiler.The heat transfer performances under different operating parameters,such as boiler load,flow direction and heat flux distribution are analyzed.The temperature and heat flux on inner wall varies along the circumference and show symmetric distributions.The overall heat transfer performances at each cross section are better than the local heat transfer performance of midpoint of heating side.Flow direction has a great influence on heat transfer performance;it changes the radial distribution of axial velocity and then affects the turbulence distribution.Therefore,upward flow condition shows a better heat transfer performance.Smaller heat flux improves both the overall and local heat transfer performances.Reducing the heat flux area is not conducive to the overall heat transfer,but does not affect the local heat transfer at the midpoint of heating side.Finally,a new correlation is fitted based on the simulated results of supercritical water heat transfer with circumferential non-uniform heat flux distributions.

Convective Heat Transfer of Molten Salt in Receiver Tube with Axially and Circumferentially Non-Uniform Heat Flux

Convective heat transfer characteristics of molten salt in receiver tube under axially and circumferentially non-uniform(ACN)heat flux were experimentally investigated under Reynolds number of 16000 to 58000 and Prandtl number of 4.6 to 7.5.The results showed that flow rate,flow direction and non-uniform heat flux directly affected molten salt transfer.As coating thickness and flow velocity increased,the difference of outer wall temperature in coating side and molten salt temperature dropped.The average Nusselt number in entrance section was larger than that in middle and end sections for higher Prandtl number.The axial wall temperature difference in coating side with counter-flow heating was lower than that with parallel-flow heating,and receiver tube with counter-flow heating will cause smaller axial thermal stress.From experiment measurement and Sieder-Tate correlation,heat transfer correlation of molten salt in tube under ACN heat flux was obtained by using circumferential heat flux ratio and axial heat flux ratio,and it fit with experimental data with maximum deviation of 5%.

Experimental study of primary and secondary side coupling natural convection heat transfer characteristics of the passive residual heat removal system in AP1000

Passive residual heat removal heat exchanger(PRHR HX),which is a newly designed equipment in the advanced reactors of AP1000 and CAP1400,plays an important role in critical accidental conditions.The primary and secondary side coupling heat transfer characteristics of the passive residual heat removal system(PRHRS)determine the capacity to remove core decay heat during the accidents.Therefore,it is necessary to investigate the heat transfer characteristics and develop applicable heat transfer formulas for optimized design.In the present paper,an overall scaled-down natural circulation loop of PRHRS in AP1000,which comprises a scaleddown in-containment refueling water storage tank(IRWST)and PRHR HX models and a simulator of the reactor core,is built to simulate the natural circulation process in residual heat removal accidents.A series of experiments are conducted to study thermal-hydraulic behaviors in both sides of the miniaturized PRHR HX which is simulated by 12 symmetric arranged C-shape tubes.For the local PRHR HX heat transfer performance,traditional natural convection correlations for both the horizontal and vertical bundles are compared with the experimental data to validate their applicability for the specific heat transfer condition.Moreover,the revised natural convection heat transfer correlations based on the present experimental data are developed for PRHR HX vertical and lower horizontal bundles.This paper provides essential references for the PRHRS operation and further optimized design.

Heat transfer characteristics in a rotating AR=4:1 channel with different channel orientations at high rotation numbers

In order to reveal the effect of channel orientations on rotational heat transfer performance,this paper presents an experimental model of AR=4:1 smooth rectangular channel.The stationary and rotational heat transfer characteristics of the channel are studied in the range of Re=10,000-40,000 and Ro=0-1.23 under the channel orientation of 90°and 135°,which represent the basic one and realistic one,respectively.The experimental results indicate that for the trailing wall,the 90°channel shows a typical large range enhancement of rotational heat transfer,while the rotational effect becomes negative in most areas at 135°case.As the rotation number exceeds 0.7,the heat transfer of the trailing surface is greatly improved by rotational effect in 90°channel.When the channel was orientated at 135°,the leading surface heat transfer is more sensitive to rotation under the low rotation number(Ro<0.3),and 20%-30%worse than non-rotating cases.The averaged Nusselt ratios correlations under the channel orientation of 90°and 135°have been developed for further engineering applications.