Fluorescence Thermometry for Measuring Wall Surface and Bulk Fluid Temperatures

2010 ◽  
Author(s):  
Myeongsub Kim ◽  
Minami Yoda
Keyword(s):  
Heat Transfer ◽  
Spatial Resolution ◽  
Temperature Sensitive ◽  
Wall Surface ◽  
Bulk Fluid ◽  
Surface Temperatures ◽  
Single Temperature ◽  
Heat Transfer Correlations ◽  
Average Uncertainty ◽  
Fluorescence Thermometry

Cooling the next generation of microelectronics with heat fluxes of more than 1 kW/cm2 over hot spots less than 103 μm2 in area will require new single- and two-phase thermal management technologies with micron-scale addressability. Thermal transport models using heat transfer correlations may be the most efficient approach for the initial design and optimization of such micron-scale heat exchangers which will likely involve arrays of microchannels. It is unclear, however, whether classic macroscale convective heat transfer correlations are applicable to these devices given their complex geometries and the possibility of significant thermal coupling between channels. There is therefore a need for new techniques that can measure both bulk fluid and wall surface temperatures at micron-scale spatial resolution without disturbing the flow of coolant. We report here the use of a nonintrusive technique, fluorescence thermometry (FT), to determine bulk fluid temperatures and, for the first time, wall surface temperatures, with a spatial resolution of O(10 μm) for water flowing through a heated channel. Fluorescence thermometry is typically used to estimate temperature distributions in water flows based on variations in the emission intensity of a fluorophore dissolved in the water. The accuracy of FT can be improved by taking the ratio of the emission signals from two different fluorophores (dual-tracer FT, or DFT) to eliminate variations in the signal due to (spatial and temporal) variations in the excitation intensity. In this work, two temperature-sensitive fluorophores, fluorescein and sulforhodamine B, with emission intensities that increase and decrease, respectively, with increasing temperature, are used to further improve the accuracy of the temperature measurements. Temperature profiles were measured in the steady Poiseuille flow of water at Reynolds numbers of 3.3 and 8.3 through a 1 mm square channel heated with a thin-fim heater. Temperatures in the bulk flow were measured using DFT with an average uncertainty of 0.2 °C at a spatial resolution of 30 μm. Fluid temperatures within the first 0.3 μm next to the wall were measured using evanescent-wave illumination of a single temperature-sensitive fluorophore with an average uncertainty of less than 0.2 °C at a spatial resolution of 10 μm. The results are compared with numerical predictions, which suggest that the fluid temperatures within 0.3 μm are effectively the wall surface temperature.

Extending Fluorescence Thermometry to Measuring Wall Surface Temperatures Using Evanescent-Wave Illumination

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Myeongsub Kim ◽  
Minami Yoda
Keyword(s):  
Water Temperature ◽  
Spatial Resolution ◽  
Evanescent Wave ◽  
Temperature Sensitive ◽  
Wall Surface ◽  
Bulk Fluid ◽  
Surface Temperatures ◽  
Single Temperature ◽  
Average Uncertainty ◽  
Fluorescence Thermometry

Cooling microelectronics with heat flux values of hundreds of kW/cm2 over hot spots with typical dimensions well below 1 mm will require new single- and two-phase thermal management technologies with micron-scale addressability. However, experimental studies of thermal transport through micro- and mini-channels report a wide range of Nusselt numbers even in laminar single-phase flows, presumably due in part to variations in channel geometry and surface roughness. These variations make constructing accurate numerical models for what would be otherwise straightforward computational simulations challenging. There is, therefore, a need for experimental techniques that can measure both bulk fluid and wall surface temperatures at micron-scale spatial resolution without disturbing the flow in both heat transfer and microfluidics applications. We report here the evaluation of a nonintrusive technique, fluorescence thermometry (FT), to determine wall surface and bulk fluid temperatures with a spatial resolution of O(10 μm) for water flowing through a heated channel. Fluorescence thermometry is typically used to estimate water temperature fields based on variations in the emission intensity of a fluorophore dissolved in the water. The accuracy of FT can be improved by taking the ratio of the emission signals from two different fluorophores (dual-tracer FT or DFT) to eliminate variations in the signal due to (spatial and temporal) variations in the excitation intensity. In this work, two temperature-sensitive fluorophores, fluorescein and sulforhodamine B, with emission intensities that increase and decrease, respectively, with increasing temperature, are used to further improve the accuracy of the temperature measurements. Water temperature profiles were measured in steady Poiseuille flow at Reynolds numbers of 3.3 and 8.3 through a 1 mm2 heated minichannel. Water temperatures in the bulk flow (i.e., away from the walls) were measured using DFT with an average uncertainty of 0.2 °C at a spatial resolution of 30 μm. Temperatures within the first 0.3 μm next to the wall were measured using evanescent-wave illumination of a single temperature-sensitive fluorophore with an average uncertainty of less than 0.2 °C at a spatial resolution of 10 μm. The results are compared with numerical predictions, which suggest that the water temperatures at an average distance of ∼70 nm from the wall are identical within experimental uncertainty to the wall surface temperature.

Comparison of Existing Supercritical Carbon Dioxide Heat Transfer Correlations for Horizontal and Vertical Bare Tubes

2012 ◽  
Author(s):  
Prabu Surendran ◽  
Sahil Gupta ◽  
Tiberiu Preda ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Wall Temperature ◽  
Statistical Error ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Correlations ◽  
Supercritical Carbon

This paper presents a thorough analysis of ability of various heat transfer correlations to predict wall temperatures and Heat Transfer Coefficients (HTCs) against experiments on internal forced-convective heat transfer to supercritical carbon dioxide conducted by Koppel [1], He [2], Kim [3] and Bae [4]. It should be noted the Koppel dataset was taken from a paper which used the Koppel data but was not written by Koppel. All experiments were completed in bare tubes with diameters from 0.948 mm to 9 mm for horizontal and vertical configurations. The datasets contain a total of 1573 wall temperature points with pressures ranging from 7.58 to 9.59 MPa, mass fluxes of 400 to 1641 kg/m2s and heat fluxes from 20 to 225 kW/m2. The main objective of the study was to compare several correlations and select the best of them in predicting HTC and wall temperature values for supercritical carbon dioxide. This study will be beneficial for analyzing heat exchangers involving supercritical carbon dioxide, and for verifying scaling parameters between CO2 and other fluids. In addition, supercritical carbon dioxide’s use as a modeling fluid is necessary as the costs of experiments are lower than supercritical water. The datasets were compiled and calculations were performed to find HTCs and wall and bulk-fluid temperatures using existing correlations. Calculated results were compared with the experimental ones. The correlations used were Mokry et al. [5], Swenson et al. [6] and a set of new correlations presented in Gutpa et al. [7]. Statistical error calculations were performed are presented in the paper.

Analysis of Updated SuperCritical Water Heat Transfer Correlations for Vertical Bare Tubes

2010 ◽  
Author(s):  
Sarah Mokry ◽  
Sahil Gupta ◽  
Amjad Farah ◽  
Krysten King ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Thermophysical Properties ◽  
Vertical Tube ◽  
Large Set ◽  
Conservative Approach ◽  
Bulk Fluid ◽  
Heat Transfer Correlations ◽  
Vertical Tubes ◽  
Bare Tube

In support of developing SuperCritical Water-cooled Reactors (SCWRs), studies are currently being conducted for heat-transfer at supercritical conditions. This paper presents an analysis of heat-transfer to SuperCritical Water (SCW) flowing in bare vertical tubes as a first step towards thermohydraulic calculations in a fuel-channel. A large set of experimental data, obtained in Russia, was analyzed. Two updated heat-transfer correlations for forced convective heat transfer in the normal heat transfer regime to SCW flowing in a bare vertical tube were developed. It is expected that the next generation of water-cooled nuclear reactors will operate at supercritical pressures (∼25 MPa) with high coolant temperatures (350–625°C). Currently, there are no experimental datasets for heat transfer from power reactor fuel bundles to the fuel coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations obtained with bare tube data can be used as a conservative approach. The analyzed experimental dataset was obtained for SCW flowing upward in a 4-m-long vertical bare tube. The data was collected at pressures of about 24 MPa for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. The values for mass flux ranged from 200–1500 kg/m2s, for heat flux up to 1250 kW/m2 and inlet temperatures from 320–350°C. The Mokry et al. correlation was developed as a Dittus-Boelter-type correlation, with thermophysical properties taken at bulk-fluid temperatures. Alternatively, the Gupta et al. correlation was developed based on the Swenson et al. approach, where the majority of thermophysical properties are taken at the wall temperature. An analysis of the two updated heat-transfer correlations is presented in this paper. Both correlations demonstrated a good fit (±25% for Heat Transfer Coefficient (HTC) values and ±15% for calculated wall temperatures) for the analyzed dataset. Thus, these correlations can be used for preliminary HTC calculations in SCWR fuel bundles as a conservative approach, for SCW heat exchangers, for future comparisons with other independent datasets and for the verification of computer codes for SCWR core thermohydraulics.

Comparison of Heat-Transfer Correlations Obtained in Supercritical-Water-Cooled Bundles

2017 ◽  
Author(s):  
Hanqing Xie ◽  
Hakim Maloufi ◽  
Andrew Zopf ◽  
William Anderson ◽  
Christian Langevin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Nuclear Power ◽  
Annular Channel ◽  
Bulk Fluid ◽  
Efficient Operation ◽  
Normal Heat ◽  
Flow Geometry ◽  
Heat Transfer Correlations ◽  
Bare Tube

SuperCritical Water-cooled Reactor (SCWR) as one of the six Generation-IV nuclear-power-reactor concepts will have increased thermal efficiency compared to that of current Nuclear Power Plants (NPPs) equipped with water-cooled reactors by operating the reactor coolant at supercritical conditions: Coolant pressure of about 25 MPa, inlet temperatures between 300–350°C, and outlet temperatures between 550–625°C. The major flow geometry inside the reactor core is the bundle flow geometry. For safe and efficient operation of an SCWR heat transfer coefficients should be calculated with minimum uncertainties. Unfortunately, the vast majority of experimental datasets were obtained in vertical bare tubes cooled with SCW. Experiments in a bundle flow geometry are even more complicated and expensive compared to that in bare tubes. Due to this very few experiments have been performed in bundles. According to the abovementioned, the vast majority of heat-transfer correlations are based on bare-tube data, and only one currently known correlation is based on a 7-element bundle cooled with SCW (the so-called, Dyadyakin and Popov correlation (1977)). Rods in this bundle are equipped with four helical ribs to enhance the heat transfer. However, the authors have not provided any dataset(s) associated with this bundle and correlation. In the current paper a number of bare-tube heat-transfer correlations obtained in SCW and the Dyadyakin and Popov correlation were compared with two datasets obtained in an annular channel with the heated central rod and 3-element bundle. The central rod in this annular channel and rods in the 3-element bundle have the same heated length as those in the 7-element bundle tested by Dyadyakin and Popov in 1977, and are also equipped with four helical ribs. The comparison showed that the Jackson correlation (2002) is the most accurate one in predicting Heat-Transfer-Coefficient (HTC) profiles in the annular channel at normal heat-transfer regime. The Dittus and Boelter correlation (1930) is the most accurate in predicting HTC profiles in the 3-element bundle at normal heat-transfer regime. No one correlation is capable to follow closely HTC profiles at the deteriorated heat-transfer regimes in both flow geometries. Aloo, it should be mentioned that bare-tube heat-transfer correlations, which have thermophysical properties based on bulk-fluid and wall temperatures, might have problems with convergence at high heat fluxes, i.e., above the heat flux at which the deteriorated heat-transfer regime starts in bare tubes.

Effect of Bulk Temperature on Formation of Crude Oil Fouling Precursors on Heat Transfer Surfaces

2014 ◽  
Vol 625 ◽  
pp. 482-485 ◽  
Author(s):  
Nitin Shetty ◽  
Marappagounder Ramasamy ◽  
Rajashekhar Pendyala
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Crude Oil ◽  
Crude Oils ◽  
Bulk Temperature ◽  
Bulk Fluid ◽  
Surface Temperatures ◽  
Custom Design ◽  
Oil Fouling

Temperature plays a very important role in the formation of fouling precursors in crude oils which is considered to be the first step before the precursors are either attached to the wall as a deposit or transferred back to the bulk fluid by diffusion. In order to investigate the formation characteristics of fouling precursors in crude oils at different bulk temperatures, a custom-design thin film microreactor is constructed. It is observed during the experiments that tendency to form fouling precursors is higher at higher surface temperatures. The precursor particles once formed continue to grow in size with time at constant surface temperatures. It is also observed that the particles tend to grow in size while it is cooled when the temperatures are below 55 oC.

Improvement of Supercritical Water Heat-Transfer Correlations for Vertical Bare Tubes

2014 ◽  
Author(s):  
Sarah Mokry ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Operating Conditions ◽  
Entrance Region ◽  
Fluid Temperature ◽  
Supercritical Conditions ◽  
Bulk Fluid ◽  
Wide Range ◽  
Heat Transfer Correlations ◽  
Region Effect

Currently, there are a number of Generation IV SuperCritical Water-cooled nuclear Reactor (SCWR) concepts under development worldwide. These high temperature, high pressure reactors will have much higher operating parameters compared to current Nuclear Power Plants (NPPs) (i.e., steam pressures of about 25 MPa and steam outlet temperatures up to 625°C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. In support of developing these SCWRs, studies are currently being conducted for heat transfer at supercritical conditions. Currently, there are no experimental datasets for heat transfer at supercritical conditions from power-reactor fuel bundles to a coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations obtained with bare-tube data can be used as a conservative approach. A number of empirical generalized correlations, based on experimentally obtained datasets, have been proposed to calculate Heat Transfer Coefficients (HTCs) in forced convective heat transfer for various fluids, including water at supercritical pressures. There have been a number of methods applied to correlate heat transfer data. The most conventional approach is to modify the classical Dittus-Boelter correlation for forced convection. The Bishop et al. correlation is an example of this type modification with an addition of an entrance-region term. The Mokry et al. correlation (2009) was developed as a Dittus-Boelter-type correlation with thermophysical properties taken at a bulk-fluid temperature. The derived correlation has shown a good fit for experimental data at supercritical conditions within a wide range of operating conditions in normal and improved heat-transfer regimes. This correlation has an uncertainty of about ±25% for HTC values and about ±15% for calculated wall temperature. However, this correlation does not take into account the entrance-region effect. The objective of this paper is an investigation of the entrance-region effect to be incorporated into the proposed Mokry et al. correlation (2009) in an attempt to further improve its accuracy.

Enhancement of Heat Transfer Performance in Nuclear Fuel Rod Using Nanofluids and Surface Roughness Technique

2015 ◽  
Author(s):  
Kang Liu ◽  
Titan C. Paul ◽  
Leo A. Carrilho ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nuclear Fuel ◽  
Three Dimensional ◽  
Pressurized Water ◽  
Bulk Fluid ◽  
Fuel Rod ◽  
Dimensional Surface

The experimental investigations were carried out of a pressurized water nuclear reactor (PWR) with enhanced surface using different concentration (0.5 and 2.0 vol%) of ZnO/DI-water based nanofluids as a coolant. The experimental setup consisted of a flow loop with a nuclear fuel rod section that was heated by electrical current. The fuel rod surfaces were termed as two-dimensional surface roughness (square transverse ribbed surface) and three-dimensional surface roughness (diamond shaped blocks). The variation in temperature of nuclear fuel rod was measured along the length of a specified section. Heat transfer coefficient was calculated by measuring heat flux and temperature differences between surface and bulk fluid. The experimental results of nanofluids were compared with the coolant as a DI-water data. The maximum heat transfer coefficient enhancement was achieved 33% at Re = 1.15 × 105 for fuel rod with three-dimensional surface roughness using 2.0 vol% nanofluids compared to DI-water.

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