Onset Of Heat Transfer Deterioration Research Articles

Study on the criterion of the onset of heat transfer deterioration for supercritical CO2 in upward flow

Supercritical fluid heat transfer deterioration (HTD) tends to lower the heat transfer capacity and should be avoided in designing and optimizing heat transfer equipment. It is essential to establish accurate criteria for predicting the onset of HTD. In this study, an experimental investigation of supercritical CO2 in a heated tube with diameters of 8 and 14.5 mm was conducted. By integrating the data obtained from this experiment with experimental data from the published literature, a large dataset covering a wide range of parameters was constructed. Eleven HTD criteria that are only applicable to other fluids and ten HTD criteria that can be applied to supercritical CO2 were compared and evaluated with the experimental dataset. Results show that most of the correlations established for other fluids cannot be directly adapted to CO2. The criteria that only consider mass flux are not accurate for predicting the onset of HTD. With a detailed analysis of the influence pattern of each system parameter on HTD, a new criterion incorporating multiple influencing factors was established. Excellent prediction accuracy of the new criterion was observed from the validation with the experimental dataset.

Study on heat transfer characteristics of supercritical CO2/propane mixtures in vertical tube

The performance optimization of the Brayton cycle could be achieved by further investigation of supercritical CO2/propane mixtures. In this paper, the heat transfer characteristics of supercritical CO2/propane mixtures in a vertical tube are numerically analyzed. The addition of propane could reduce or even eliminate heat transfer deterioration. Compared to CO2, the wall temperature peak of CO2/propane mixtures (α = 7 %) could be reduced by 45.5 K. After the pseudo-critical temperature, the effect of heat flux on the wall temperature of CO2 is more significant than that of mixture. Further, new critical heat flux criterion and Nu correlations are proposed for supercritical CO2/propane mixtures. The correlations could accurately reproduce the trend of Nu and capture the onset of heat transfer deterioration in the upward flow. At Re = 40168–84765 and Pr = 1.2–5.4, the maximum prediction deviation of the new correlations is ±14 %. Approximately 98.4 % of the prediction deviations are within ±10 %.

Onset of heat transfer deterioration caused by pseudo-boiling in CO2 laminar boundary layers

In propulsion and power systems, operating pressures are increasing to improve cycle efficiency, often reaching conditions that approach or exceed the thermodynamic critical pressure of the working fluid. A known phenomenon that occurs at supercritical pressures is supercritical heat transfer deterioration (HTD). Although this phenomenon is well studied, there is still debate about the underlying physics. This paper studies pseudo boiling, the supercritical liquid–gas phase transition, as a possible mechanism that causes HTD, by means of computational fluid dynamics (CFD), boundary layer correlations, and thermodynamic analysis. To this end, we focus on forced laminar convection of supercritical CO2 over a flat plate, excluding alternative factors such as buoyancy or turbulence. In order to accurately represent the strongly non-linear near-critical fluid properties, we use tiny neural networks (TNN) in an interpretable machine learning approach. For use in CFD, TNN combine reference quality accuracy from look-up tables with the memory footprint of equations of state and curve fits. We demonstrate that pseudo boiling theory accurately indicates pressure and temperature regions susceptible to HTD. The simulations show the distinctive boiling curve, with a peak critical heatflux and a Leidenfrost minimum, demonstrating that pseudo boiling is, indeed, a sufficient physical mechanism to cause this effect, in absence of turbulence or boyancy. During HTD, we observe the formation of a supercritical gas film at the wall, with low density, low thermal conductivity, a high compressibility factor, and low viscosity. The boundary of the gaseous film is characterized by a peak in heat capacity, indicative of pseudo boiling, and a sudden transition to a dense supercritical liquid state. This suggests that the subcritical boiling crisis does have a direct representation at supercritical pressures through pseudo boiling, and that pseudo film boiling is a sufficient mechanism to cause HTD.

A dimensionless correlation to predict the onset of heat transfer deterioration of supercritical fluids in upward circular tubes

Heat transfer deterioration (HTD) is extremely dangerous for the supercritical steam generator which has been studied for many years. It is exceedingly crucial to predict the onset of the heat transfer deterioration for the design of the vaporizer. In this study, a dimensionless correlation based on 5662 data from 15 independent references is proposed to predict the onset of heat transfer deterioration of supercritical fluids in vertical circular tubes. Two different criteria of HTD are employed, and the corresponding dimensionless correlations have mean absolute relative deviations of 12.75% and 15.5%, respectively. The new dimensionless correlations not only improve the prediction of HTD for supercritical water compared to the existing correlations, but also have applicability for supercritical CO2 in a proper range.

Heat transfer characteristics of supercritical water in channels: A systematic literature review of 20 years of research

• More experiments are required to validate the existing the turbulence model. • Turbulence model with Algebraic heat flux model (AHFM) may be promising. • Heat transfer peak occurs as the fluid approaches the pseudo-critical temperature. • To achieve the high accuracy, piecewise correlation may be an effective method. • Internally ribbed tube combined with inclined angles may be a research direction. Supercritical water (SCW) is one of the high-profile fluids between scholars, which has great potential in the thermal industry. Therefore, it may serve as a promising fluid utilized in nuclear and boiler systems. This paper presents a comprehensive review in terms of the published literature on supercritical water heat transfer in channels. Three types of heat transfer, involving normal, enhanced and deteriorated heat transfer, are classified in this article. Firstly, the thermo-physical properties of supercritical water are illustrated to explain the reasons for the different heat transfer behavior. Heat transfer enhancement and deterioration appear to have greater potential and draw some researchers’ interest. In short, transformation of geometry or operating conditions, such as, channel structure, mass flux and heat flux, would induce variations of thermo-physical properties. Consequently, heat transfer performance can be significantly affected. The heat transfer characterization and affecting factors were evaluated. Some unusual phenomena were explained. Then, the developed heat transfer coefficients (HTC) were compared with the experimental data available in the open literature. The results indicated that the reliable accuracy could be achieved through these correlations except the pseudo-critical region. Additionally, the mechanism and the onset of heat transfer deterioration were revealed and estimated. Finally, this review also identifies the current challenges regarding this research through analysis and comparison. These challenges deserve to be efficiently solved and optimized to enhance supercritical water heat transfer in the future.

Analysis and prediction of heat transfer deterioration of supercritical pressure cryogenic methane in a vertical tube

Developing a compact vaporizer with high thermal efficiency is of great significance to the storage and usage of Liquid Natural Gas (LNG). Numerical simulations were performed to investigate the flow and heat transfer characteristics of supercritical pressure methane in a vertical tube, and primary focus was to reveal the mechanism of two-peak wall temperatures occurrence. Six turbulent models have been confronted with experimental data, and the Renormalization Group (RNG) k-ε model is adopted. When Heat Transfer Deterioration (HTD) occurs, two-peak wall temperatures appear in the upward flow with high mass flux. The phenomenon of two-peak wall temperatures were explained in detail based on radial distributions of velocity and turbulent kinetic energy at different axial positions. The “M”-shape velocity distribution promotes the generation of turbulence in the core region. The reversal of radial flow direction enhances the mixing between hot and cold fluids. A new criterion was proposed for predicting the critical heat flux which causes the onset of HTD in supercritical pressure methane.

Evaluation of correlations for prediction of onset of heat transfer deterioration for vertically upward flow of supercritical water in pipe

Supercritical water has great potential as a coolant for nuclear reactor. Its use will lead to higher thermal efficiency of Rankine cycle. However, in certain conditions heat transfer may get deteriorated which may lead to undesirable high clad surface temperature. It is necessary to estimate the operating conditions in which heat transfer deterioration (HTD) will take place, so as to establish thermal margins for safe reactor operation. In the present work, the heat flux corresponding to onset of HTD for vertically upward flow of supercritical water in a pipe is obtained over a wide range of system parameters, namely pressure, mass flux, and pipe diameter. This is done by performing large number of simulations using an in-house CFD code, which is especially developed and validated for this purpose. The identification of HTD is based on observance of one or more peak/s in the computed wall temperature profile. The existing correlations for predicting the onset of HTD are compared against the results obtained by present simulations as well as available sets of experimental data. It is found that the prediction accuracy of the correlation proposed by Dongliang et al. is best among the existing correlations.

Heat transfer deterioration mechanism for water at supercritical pressure

Abstract Heat transfer deterioration (HTD) phenomena in supercritical water is one of the most thermal hydraulic critical issues for supercritical reactors. The onset of heat transfer deterioration and bouncy effect have been studied in details, however limited work has been done on the mechanism of HTD occurrence. In this work, three dimensional analysis of velocity and temperature boundary layers under heat transfer deterioration conditions is conducted. The effect of thermo physical water properties changes inside the fluid boundary layer and its effect on the heat transfer coefficient is studied. Analogy between HTD and critical heat flux condition in subcritical boiling is observed and reported. Under HTD conditions, clotting or sudden stopping of the flow inside the tube is predicted due to the severe variation in density and other thermo physical properties in the tubes radial direction.

A new criterion for the onset of heat transfer deterioration to supercritical water in vertically-upward smooth tubes

The heat transfer characteristics of supercritical water, Deteriorated Heat Transfer (DHT) in particular, is crucial to the safety of supercritical devices. It became imperative to develop a new criterion with extensive applicability and high prediction accuracy, to determine whether the operating conditions are safe. To achieve this, a broad-based review was conducted to collect experimental heat transfer data of supercritical water flowing in vertically-upward smooth tubes. The experimental data base consisted of 9705 data points, and the numbers of the Non-DHT and DHT cases were 109 and 64, respectively. Based on the data base, 8 criteria for predicting critical heat flux causing the onset of the DHT (qdht) were assessed and compared thoroughly. It was observed that Yamagata’s criterion showed the best prediction accuracy among the existing criteria. However, Yamagata’s criterion was still insufficient in predicting the DHT conditions. For improvement, further analyses were conducted and the author believed that increasing pressure and decreasing the tube diameter might suppress the occurrence of the DHT under the same conditions, and lead to an increase in qdht. However, the effects of mass flux, pressure and tube diameter on qdht were not considered simultaneously by the earlier researchers. Thus, this paper recognized the need and developed a new criterion which considered the effects of mass flux, tube diameter, and pressure comprehensively. The prediction accuracy of this new criterion for the Non-DHT and DHT were both higher than 90%, and the overall prediction accuracy was 94.25% which was higher than that of existing criteria.

Supercritical “boiling” number, a new parameter to distinguish two regimes of carbon dioxide heat transfer in tubes

The objective of this paper is to develop a criterion to predict the onset of heat transfer deterioration (HTD) for supercritical CO2 heat transfer. A new mechanism is proposed by assuming supercritical pseudo-boiling. Before bulk fluid reaches pseudo-critical temperature (Tpc), the tube cross-section contains a vapor layer and a liquid-like fluid. The saturation temperature interface is defined at T = Tpc, inside and outside which are a vapor layer (T > Tpc) and a subcooled liquid (T < Tpc). The subcritical boiling number is extended to supercritical “boiling” number, defined as SBO = qw/(Gipc), where qw, G and ipc are heat flux, mass flux, and CO2 enthalpy at Tpc, respectively. SBO, by coupling the density ratio between “liquid” and “vapor”, represents the competition between vapor expansion induced momentum force and inertia force. The experiment of supercritical CO2 heat transfer is performed in a 10.0 mm inner diameter tube, covering ranges of P = 7.5–21.1 MPa, G = 488–1600 kg/m2s and qw = 74–413 kW/m2. Surprisingly, the onset of HTD is found to occur at a critical SBO which is 5.126×10−4 and the critical heat flux is expressed as qCHF=5.126×10−4Gipc. It is shown that our new criterion is also suitable for other experiments reported in literature, providing a general guidance to design and operate SCO2 heaters to avoid HTD.

Local heat transfer coefficient measurements using thermal camera for upward flow of Freon 22 in a vertical tube at supercritical conditions and development of correlations

This paper presents experimental results obtained towards characterizing heat transfer behaviour in supercritical fluids employing R22 as a simulant fluid. It is well known that two regimes exist in supercritical heat transfer, viz., heat transfer enhanced regime and heat transfer deteriorated regime and very limited data exist in the heat transfer deteriorated regime. The use of thermal camera has resulted in obtaining high resolution wall temperature data leading to the identification of the bulk enthalpy at which the peak wall temperature occurs. The results bring out the effect of inlet temperature very precisely, on which not much information is available in the literature. Finally the work identifies a criterion for the onset of heat transfer deterioration and correlations to predict the complete heat transfer behaviour exhibited by supercritical fluids. These correlations are shown to predict satisfactorily with a large number of experimental data available in the literature.

Heat transfer deterioration in helically coiled heat exchangers in trans-critical CO2 Rankine cycles

The heat transfer deterioration (HTD) of supercritical CO2 encountered in trans-critical CO2 Rankine cycle is an important issue related the safety of the whole unit. For the purpose, numerical simulations are performed to get a further insight into the mechanism of heat transfer characteristics of supercritical CO2 flow in helically coiled tube (HCT) both in horizontal and vertical orientations with parameters in a range of p = 8 MPa, G = 100–800 kg/m2s and q = 15–140 kW/m2. The Shear-Stress Transport (SST) k–ω turbulence model with enhanced wall treatment method is employed to handle the coupled wall-to-fluid heat transfer. Results show that secondary flow induced by the coil curvature produces a transverse transport of the fluid over the cross section of the pipe and therefore enhances the heat transfer. Additionally, in the vertical oriented HCT, the HTD at supercritical pressure observed in a smooth straight tube (ST) is significantly alleviated. At a higher q/G, the HTD still exists irrespective of coil orientations. But, different from ST, the HTD in HCT is caused by both gravitational and centrifugal buoyancy force. Therefore, the onset of HTD in HCT cannot be predicted by the empirical correlation (q = 0.0002G) derived from analytical and experimental results for ST. Based on numerical calculation, an improved buoyancy parameter is developed to predict buoyancy effect on vertical HCT with an internal upward flow.

An improved correlation on the onset of heat transfer deterioration in supercritical water

On the basis of the supercritical water experimental data, the distribution of onset heat flux is analyzed for the heat transfer deterioration. This study evaluates the performance of empirical correlations for the prediction of heat flux, causing the onset of heat transfer deterioration in vertical tubes of supercritical water. In light of the calculation results, it is shown that the onset of heat transfer deterioration effect is better predicted using the Mokry, Li and Schatte criterion. On the basis of experimental data, a new correlation is developed for predicting the heat flux, which causes the onset of heat transfer deterioration in supercritical water. The new calculation model has considered the influence of mass flux, pipe diameter, pressure and inlet temperature. The newly developed correlation has an average relative error of 0.020837 and an average absolute deviation of 0.1627. The improved criterion is more conducive for the design of supercritical water reactors in the future.

Onset of heat transfer deterioration in vertical pipe flows of [formula omitted] at supercritical pressures

Convective heat transfer to CO2 flowing upward in electrically heated vertical tubes at supercritical pressures was studied for wall heat fluxes within ranges that included values corresponding to the onset of heat transfer deterioration (HTD). The inlet pressure was 8.35 or 7.76 MPa, the mass flux was in the range from 200 to 1500 kg/m2 s and the inlet temperature was in the range from 0 to 40 °C. Wall temperature measurements were collected in three tubular test sections, having inner diameters of 4.6, 8, and 22 mm. The abilities of different HTD identification methods to separate the entire data set into deteriorated and normal heat transfer modes were tested. Measurements show that the minimum heat flux at HTD onset followed power laws of mass flux. For heat flux values that were larger than this minimum, HTD was found to occur only within a limited range of Tin, whose width increased with increasing heat flux.

AN ASSESSMENT OF ROUND TUBE CORRELATIONS FOR CONVECTIVE HEAT TRANSFER AT SUPERCRITICAL PRESSURE

The objective of this study is to evaluate round-tube data-based correlations depending on their applicability conditions including heat transfer mode and fluid. The present assessment of correlations was performed against the round-tube databases for vertical upward flow of water and CO2 from the Canadian Nuclear Laboratories multifluid, multigeometry databank of supercritical heat transfer. To categorize the data according to a representative heat mode, various criteria for onset of heat transfer deterioration were proposed. However, there is no consensus in the literature on a single approach. Two popular, semi-empirical criteria were chosen for screening the data for buoyancy- and acceleration-induced heat transfer deterioration. The experimental conditions of the data were screened for specified ranges of the 2 criteria indicating heat transfer deterioration. However, in many cases, the corresponding heat transfer mode of the experimental data was not appropriately predicted. In light of this inadequ...

Buoyancy effects on turbulent heat transfer of supercritical CO2 in a vertical mini-tube based on continuous wall temperature measurements

Convection heat transfer of supercritical pressure fluid is important in industrial applications such as supercritical power stations, the supercritical CO2 Brayton cycle, Carbon Capture Utilization and Storage, and the thermal protection for rocket thrusters. Previous research has confirmed that there are three heat transfer regions for convection heat transfer of supercritical pressure fluid flowing inside vertical tubes: normal heat transfer, heat transfer deterioration, and heat transfer enhancement. However, existing research still carries inconsistent results, especially regarding the onsets of heat transfer deterioration of supercritical pressure fluid flow in vertical tubes. Here we propose a new view, by estimating the location where local fluid temperature, Tf(r) equals to the pseudocritical temperature, Tpc, in the transversal section inside the tube, then analyzing the relationship between the location where Tf(r)=Tpc and the turbulent boundary layers in the near wall region, to identify buoyancy effects on turbulent heat transfer. By taking advantage of infrared thermometry measurement to achieve continuous wall temperature, theoretical analysis was validated by experiments of supercritical pressure CO2 in a vertical mini-tube with inner diameter of 0.953mm. The experiments were performed for a pressure of 7.6–9.5MPa, inlet mass flux from 255kg/m2s to 685kg/m2s, and heat flux from 12kW/m2 to 63kW/m2. It is found that in contrast with the previous results, when the value of y+ at the location of Tf(r)=Tpc, y+|Tf(r)=Tpc, less than 5, heat transfer enhances for upward and decreases for downward flow due to the buoyancy effect. With the heat flux increasing or mass flux decreasing, the buoyancy effect on the turbulent convection heat transfer characteristics of supercritical pressure fluid in a vertical heated tube is be featured as the following regimes: for the upward flow, from no-effect to slight enhancement, significant reduction, recovery and then enhancement; for the downward flow, from no-effect to slight weaken, and then enhancement. Moreover, the experimental results showed that y+|Tf(r)=Tpc=5 is where there is an onset of heat transfer deterioration for the upward flow in a vertical heated tube induced by buoyancy effects. The results presented provide a better understanding of the special features of the turbulent convection heat transfer of supercritical pressure fluids in mini channels.

Flight Acceleration Effect on Heat Transfer Deterioration of Actively Cooled Scramjet Engines

Heat transfer deterioration produces local wall temperature peaks and may endanger actively cooled scramjet engines. The heat transfer deterioration of supercritical-pressure -decane at different flight accelerations is simulated to represent accelerating hypersonic vehicles. Two types of heat transfer deterioration are observed. The type 1 heat transfer deterioration, which appears at the initial heated section, is due to the formation of the thermal boundary layer. The type 2 heat transfer deterioration, which can be identified with an M-shaped velocity profile, appears because of the reduction of turbulent diffusion. The heat transfer deterioration onset parameter, which is defined as the ratio of heat flux to mass flux in case of incipient heat transfer deterioration, is obtained at both positive and negative flight accelerations. A positive flight acceleration value indicates that the flow direction and the acceleration direction is the same, and a negative value indicates that the two directions are opposite. Both types of heat transfer deterioration onset parameter increase linearly as the positive acceleration increases. The type 2 heat transfer deterioration onset parameter cannot be identified when the negative acceleration is less than a certain value. Correlations for the heat transfer deterioration onset parameter as a function of flight acceleration are fitted and can be adopted in the design of the active cooling system of scramjet engines.

Conditions for the occurrence of heat transfer deterioration in light hydrocarbons flows

Heat transfer deterioration could affect heated channel flows of supercritical pressure fluids in a number of technological applications. Aim of the present study is to analyze the phenomenon onset and to investigate its dependence on the pressure, for three light hydrocarbons: methane, ethane and propane. To this goal a parametric numerical analysis is carried out on uniformly heated straight channels varying, for each different species, the inlet reduced pressure and the enforced heat flux. A parabolized Navier–Stokes solver is used to carry out the simulations, together with Helmholtz energy equation of state and accurate models for the transport properties. Results lead to an unambiguous definition of the threshold value for the ratio between heat flux and specific mass flow rate which identifies the boundary for heat transfer deterioration onset. On the basis of this definition, for assigned inlet reduced temperature, a correlation for the threshold parameter in terms of reduced pressure is presented for the considered species.

Onset of Heat Transfer Deterioration in Supercritical Methane Flow Channels

The deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liquid rocket engines. A threshold value of the ratio between the heat flux and the specific mass flow rate is identified as the main parameter controlling the heat transfer deterioration onset. The threshold parameter depends on the specific thermodynamic conditions of the coolant and in particular on its pressure level. In the present study, a parametric numerical analysis has been carried out on the flow of supercritical methane in heated channels, for an assigned inlet temperature level and varying the inlet pressure. A correlation for the threshold parameter as a function of pressure is then proposed on the basis of the obtained results.

Numerical analysis of supercritical water heat transfer in horizontal circular tube

Heat transfer is numerically investigated of supercritical water for three-dimensional horizontal flows in uniformly heated tube. Three ɛ-type turbulence models are tested and the numerical results are compared with experimental data, and the criteria for onset of buoyancy effect and heat transfer deterioration are analyzed. The results show that: (1) the standard k– ɛ turbulence model with enhanced wall treatment is recommended; (2) the quantity Gr/Re 2.7 gives a capacity to predict the buoyancy effect onset; and (3) correlations developed by Styrikovich et al. and Yamagata et al. can predict the onset of heat transfer deterioration for top and bottom surface, respectively.