Thermal Transport Behavior of Supercritical Fluids

Team: Md Sajedul Islam Sakir, Kaeden Teague, Hailei Wang PhD

Objectives

  • A literature review of the thermal transport behavior of different supercritical fluids
  • Study the effect of different heat transfer parameters (heat flux, mass flux, pressure, buoyancy, test section orientation, etc on heat transfer enhancements and deterioration in supercritical conditions

Introduction

Supercritical Fluid a state of fluid where the temperature and pressure of the fluid are above its critical point

  • For supercritical fluids, density is equal to that of the liquid state, but viscosity and the diffusion coefficient are congruent with those of the gaseous state 1
  • Pseudocritical temperature is the temperature, for a given pressure, at which the specific heat is at a local maximum
  • Thermophysical properties of supercritical fluids vary sharply near the pseudocritical point and therefore affect thermal transport behavior
  • Supercritical fluids are used in ORC for low to medium heat source utilization technology, thermal management systems, nuclear power plants as coolants, w aste heat recovery, and many other applications
Figure 1. Thermo physical property variations of R125 in the function of temperature with different pressure

Figure 1. Thermo physical property variations of R125 in the function of temperature with different pressure

Experimental Set up

Figure 2. Schematic diagram of the experimental loop 5

Figure 2. Schematic diagram of the experimental loop5

Figure 3. Alpha test section 5

Figure 3. Alpha test section5

Figure 4. Beta test section 5

Figure 4. Beta test section 5

Key Findings from Previous Work

Heat transfer enhancement and deterioration

  • Heat transfer enhancement occurs in the vicinity of the fluid pseudocritical region where specific heat capacity and thermal conductivity abruptly increase and viscosity sharply decreases (Figure 1 causing an increase in boundary turbulence intensity and a consequent improvement in heat transfer
  • When the bulk fluid temperature is higher than the pseudocritical point, the enhancement of heat transfer will decrease

Effect of parameters

  • The heat flux plays a significant role in the heat transfer coefficient fluctuations in the pseudocritical point of the bulk fluid
  • Fluid buoyancy force plays a vital role in the inlet region of the test section to increase heat transfer, but there is no significant buoyancy force effect at the middle and end of the test section 7
  • The fluid's larger specific heat capacity close to its pseudocritical temperature and increased turbulence (higher Reynolds number) cause the heat transfer coefficient to rise at higher mass flux 6
  • When pressure is close to critical pressure, a dramatic change in thermophysical property causes an increase in heat transfer coefficient, but when pressure is higher than critical pressure, the variation in thermophysical property is not as strong, leading to a decrease in heat transfer coefficient 2
  • The heat transfer coefficients could not be predicted accurately by the previously developed Nu correlations, likely due to the differences in the conditions of the various fluids As a result, new Nu correlations have been developed to address this issue by using affecting parameters 4
Figure 5. Variation of Wall temperature and Nu with fluid enthalpy for Horizontal flow of R134a 3

Figure 5. Variation of Wall temperature and Nu with fluid enthalpy for Horizontal flow of R134a 3

Figure 6.HTC variation for various mass fluxes in horizontal flow of R 134a at 4.5 Mpa 6

Figure 6. HTC variation for various mass fluxes in horizontal flow of R 134a at 4.5 Mpa 6

Figure 7. Effect of heat flux on (a) wall temperature and (b) heat transfer coefficient in upward flow of R 134a at 4.3 MPa 4

Figure 7. Effect of heat flux on (a) wall temperature and (b) heat transfer coefficient in upward flow of R 134a at 4.3 MPa 4

Figure 8. HTC at different pressure in the horizontal flow of R134a 6

Figure 8. HTC at different pressure in the horizontal flow of R134a 6

Figure 9. Comparison of correlations with test data of R134a in upward flow 4

Figure 9. Comparison of correlations with test data of R134a in upward flow 4

Conclusions & Future Works

  • The heat transfer behavior of the supercritical fluid is influenced by thermophysical properties as well as several thermohydraulic parameters (heat flow, mass flux, pressure, buoyancy, etc
  • A supercritical methanol and ethanol experiment will be conducted in the future in our test facility with heat being transferred from the heat source to the working fluid via metal fins

References

  1. M. Lazova , Characteristics of forced convection heat transfer to R125 at supercritical state in a horizontal tube, Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur (
  2. J. Van Nieuwenhuyse , A. De Meulemeester , S. Lecompte , M. De Paepe , Experimental Investigation of Near and Supercritical Heat Transfer to R125 Flowing in a Horizontal Tube, International Journa l of Heat and Mass Transfer 183 (2022).
  3. Dabiao Wang , Ran Tian , Yue Zhang , LanLan Li , Yuezheng Ma, Lin Shi , Hui Li, Heat transfer investigation of supercritical R134a for trans critical organic Rankine cycle system, ener gy 169 (2019) 542 557.
  4. Siyu Zhang , Hanyang Gu , Xu Cheng , Zhenqin Xiong , Experimental study on heat transfer of supercritical Freon flowing upward in a circular tube, Nuclear Engineering and Desig n 2 80 (2014) 305 315.
  5. Benjamin M. Pepper, Thermodynamic Analysis of a Novel Cycle for Nuclear SMR and Heat Transfer Performance Validation of the R ela ted Supercritical Working Fluids, Utah State University (2022).
  6. Chen Ru Zhao and Pei Xue Jiang. Experimental study of in tube cooling heat transfer and pressure drop characteristics of R134a at supercritical pressure s. Experimental Thermal and Fluid Science, 35(7):1293 1303, 2011
  7. Yan J, Liu S, Guo P, Bai C. Experimental investigation on convection heat transfer of supercritical hydrocarbon fuel in a lon g m ini tube. Experimental Thermal and Fluid Science. 2020 Jul 1;115:110100.