Heat Transfer Of CO2 Research Articles

Experimental study on the effect of CO2 desublimation on heat transfer

Revealing the influence mechanism of CO2 desublimation on heat transfer is crucial for developing new liquefied natural gas heat exchangers. In this paper, an experimental platform for CO2 desublimation was built to investigate and analyze the intrinsic connection between CO2 desublimation and heat transfer, and systematically elaborated the mechanism of the influence of CO2 desublimation on heat transfer under different operating conditions based on the values of the heat transfer coefficient and CO2 thermal resistance. The results of the study show that CO2 can rapidly start condensation on the cooling surface when the gas flow rate is too fast (60 kg/h), which leads to a weakening and then strengthening of the effect of CO2 condensation on the heat transfer as the gas flow rate increases. In addition, as the cooling temperature drops, the amount of heat exchange between CO2 and the refrigerant decreases, and the magnitude of the changes in the values of the heat exchange coefficient and CO2 thermal resistance increases, with the value of the heat exchange coefficient decreasing by up to 39.9 %. Compared with the gas flow rate, the cooling temperature was the main factor affecting CO2 desublimation, and it has a more significant effect on heat transfer. This experimental study provides a theoretical basis for the design of a new type of liquefied natural gas heat exchanger and provides valuable insights into the mechanism of CO2 desublimation.

Carbon dioxide evaporation heat transfer coefficient prediction in porous media using Machine learning algorithms based on experimental data

The prediction of the internal heat transfer coefficient during evaporation is vital for vapor-compression refrigeration and closed-loop power cycles. Accurate measurements and understanding of CO2 heat transfer in porous evaporators are essential for optimal system design across various operating conditions. This study utilizes a reference dataset derived from previous experiments that investigated the impact of porous evaporators on CO2′s internal heat transfer coefficient under sub-critical conditions, employing gravel sand as the porous medium. The dataset encompasses key factors: gravel sand porosities ranging from 39.8 % to 44.5 %, evaporator inlet pressures between 3700 and 4300 kPa, CO2 mass flow rates from 10.7x10-5–18x10-5kg.s−1, and porous tube effective diameters spanning 1.53 x10-3–3.4x10-3m. Employing three machine learning techniques (SVM, GPR, OBEM), the study predicts the internal heat transfer coefficient using regression models. The models’ predictions are analyzed and compared to expected values for validation, evaluating their performance using four statistical criteria. Results indicate SVM, GPR, and OBEM models achieved RMSEs of 1.5471, 1.8212, and 3.6978, respectively, while MAE errors were 1.1479, 1.2418, and 2.9787, respectively. Comparison with the dimensional analysis method reveals the effectiveness of the proposed models in accurately predicting internal heat transfer coefficients. The models exhibit low uncertainty and maintain prediction quality on an extended dataset without overfitting concerns. Overall, this research contributes valuable insights for designing heat exchangers and systems in vapor-compression refrigeration and closed-loop power cycles.

Dynamic heat transfer characteristics of printed circuit precooler in supercritical CO2 Brayton cycle

The dynamic characteristics of heat exchangers are critical in supercritical CO2 Brayton cycle, especially in the precooler where significant thermophysical property variations occur. However, few studies have comprehensively analyzed the dynamic heat transfer characteristics in precooler, particularly with respect to the detailed flow and thermal field evolution. A three-dimensional numerical model was developed to study the dynamic performance of a printed circuit precooler, with an emphasis on the impact of thermophysical properties. The study examines responses to abrupt changes in CO2 and water inlet temperature, as well as mass flux variations. Results show that the precooler exhibits rapid response characteristics with mild fluctuations in heat transfer parameters and flow structure. Notably, the large specific heat near the critical point results in minimal variation in CO2 outlet temperature despite abrupt increases in CO2 inlet temperature, thereby enhancing system stability. Conversely, a decrease in CO2 mass flux causes a transition from forced convection to mixed flow, with strengthened buoyancy effects and decreased entropy production. These variations lead to significant changes in CO2 outlet temperature, posing potential challenges to system stability under CO2 mass flux step change conditions. The heat transfer shows a relatively lower response rate to parameter changes of water compared to CO2. Although variations in water parameters have a negligible effect on CO2 heat transfer, they influence the overall heat transfer coefficient. The dynamic heat transfer characteristics of the precooler presented in this paper address research gaps left by 1D numerical and experimental studies, which have provided limited information on flow and thermal fields during dynamic processes. These insights are essential for understanding the dynamic behavior of the entire system.

Numerical Investigation on Characteristics of Supercritical CO2 Heat Transfer in Vertical Circular Tubes with Circumferentially Half-Side Heating

Numerical Investigation on Characteristics of Supercritical CO2 Heat Transfer in Vertical Circular Tubes with Circumferentially Half-Side Heating

Fracture Evolution during CO2 Fracturing in Unconventional Formations: A Simulation Study Using the Phase Field Method

With the introduction of China’s “dual carbon” goals, CO2 is increasingly valued as a resource and is being utilized in unconventional oil and gas development. Its application in fracturing operations shows promising prospects, enabling efficient extraction of oil and gas while facilitating carbon sequestration. The process of reservoir stimulation using CO2 fracturing is complex, involving coupled phenomena such as temperature variations, fluid behavior, and rock mechanics. Currently, numerous scholars have conducted fracturing experiments to explore the mechanisms of supercritical CO2 (SC-CO2)-induced fractures in relatively deep formations. However, there is relatively limited numerical simulation research on the coupling processes involved in CO2 fracturing. Some simulation studies have simplified reservoir and operational parameters, indicating a need for further exploration into the multi-field coupling mechanisms of CO2 fracturing. In this study, a coupled thermo-hydro-mechanical fracturing model considering the CO2 properties and heat transfer characteristics was developed using the phase field method. The multi-field coupling characteristics of hydraulic fracturing with water and SC-CO2 are compared, and the effects of different geological parameters (such as in situ stress) and engineering parameters (such as the injection rate) on fracturing performance in tight reservoirs were investigated. The simulation results validate the conclusion that CO2, especially in its supercritical state, effectively reduces reservoir breakdown pressures and induces relatively complex fractures compared with water fracturing. During CO2 injection, heat transfer between the fluid and rock creates a thermal transition zone near the wellbore, beyond which the reservoir temperature remains relatively unchanged. Larger temperature differentials between the injected CO2 fluid and the formation result in more complicated fracture patterns due to thermal stress effects. With a CO2 injection, the displacement field of the formation deviated asymmetrically and changed abruptly when the fracture formed. As the in situ stress difference increased, the morphology of the SC-CO2-induced fractures tended to become simpler, and conversely, the fracture presented a complicated distribution. Furthermore, with an increasing injection rate of CO2, the fractures exhibited a greater width and extended over longer distances, which are more conducive to reservoir volumetric enhancement. The findings of this study validate the authenticity of previous experimental results, and it analyzed fracture evolution through the multi-field coupling process of CO2 fracturing, thereby enhancing theoretical understanding and laying a foundational basis for the application of this technology.

Convective Heat Transfer Analysis of Supercritical CO2 in Artificial Rock Fractures

Geothermal energy has emerged as a promising renewable and sustainable resource. This research article explores the utilization of supercritical CO2 and convective heat transfer in porous rock to enhance geothermal extraction. Artificial cement rock with a smooth and manmade slotted surface fracture was used as a working sample for heat transfer source in the test. Heat transfer characteristics under various flow rates, fluid inlet temperature and pressure, rock initial temperature are analyzed. The results indicate that the geometry characteristics of fracture surface impact the overall heat transfer intensity to a certain extent, whereas lithology has little influence on the heat transfer intensity. In addition, it is found that increasing injection pressure affects the operating temperature and density of the injected fluid, which helps to improve the production effect, to obtain more heat. However, limited by the heat transfer area, low injection flow is required. The maximum error of the heat transfer coefficient model is 7.05% compared with the empirical value and less than 10% compared with the experimental results. By examining the interaction between fluid and porous fractures, we aim to provide insights into the potential of these techniques for maximizing energy efficiency and tapping into deep geothermal resources.

Experimental Study on Convection Heat Transfer of CO2 in C/SiC Composite Porous Material at Subcritical, Transcritical, and Supercritical States

Using C/SiC as the structure for transpiration cooling is prospective for new hypersonic vehicles, based on clarification of heat transfer process in porous media. But there are still gaps due to the complexity of pore structure of C/SiC, together with the effects of capillary force and strong variation of thermophysical properties for subcritical and supercritical flow. In this study, heat transfer analysis for C/SiC with CO2 as the coolant is presented by experiments. Heat transfer characteristics in typical C/SiC sample under various mass flow rates (0.003–0.018 kg/s), inlet fluid temperatures (20–40 °C) and pressures (5.9–10 MPa) are analyzed. Heat transfer and pressure drop correlations have been developed. The results show heat transfer coefficient at supercritical state behaves non-monotonic under varying flow rates caused by the combined effect of sharp increase of specific heat and the change of flow rate. The effect of pressure on heat transfer can be neglected compared to that of flow rate, while for Reynolds number (Re) >100, the pressure drop of supercritical cases are smaller than that of phase-change cases under similar Re, due to the effect of capillary force in C/SiC. This study can provide basic support for further study of transpiration cooling using C/SiC and CO2.

Investigations on cooling heat transfer of CO2-based mixtures in a novel airfoil fin mini-channel at supercritical pressure

Thermal-hydraulic characteristics of three supercritical CO2-based mixtures (CO2/H2S, CO2/Xe and CO2/propane) in an airfoil fin (AFF) mini-channel adopted in the printed circuit heat exchanger (PCHE) under cooling conditions are comprehensively investigated through numerical simulations. The results show that the CO2/H2S mixture, which has higher critical temperature and larger critical pressure than the pure CO2, exhibits the greatest heat transfer performance among three mixtures. This advantage is particularly pronounced at relatively large Reynolds number, with small mass fraction of the H2S and under near-critical conditions. The overall friction loss of mixtures with the additive mass fraction smaller than 0.3 is comparable to that of the pure CO2. The heat transfer coefficient of the mixtures presents fluctuations during the cooling processes, and this goes against the stable and safe operation of the PCHEs. These fluctuations could be mitigated at relatively small mass flow rate and with small mass fraction of the additive. Three widely-recognized buoyancy criteria are employed to predict the onset of the buoyancy effects in the AFF channel, and the superior heat transfer of the CO2/H2S mixture could be attributed to the fiercer buoyancy effects. Considering the buoyancy effects, modified correlations for the flow and heat transfer of pure CO2 and the CO2-based mixtures in the novel mini-channel are proposed. The maximum deviations of the modified Nusselt number and fanning friction factor correlations are ± 25 % and ± 20 %, respectively.

Characterization of supercritical CO2 heat transfer in microporous media under (T/p)-mutability and integrated random function

The thermophysical properties of supercritical carbon dioxide (sCO2) undergo drastic changes under reservoir conditions, which significantly affects transfer characteristics and the storage efficiency. The present work seeks to identity of the heat transfer response of a mutable sCO2 in porous micromodels with integrated Boolean stochastic models. An upgraded variant of Lattice Boltzmann model is used after a thorough validation with literature experiments. The injection conditions of sCO2 are ranged from 295 to 333 K and 8–10 MPa, with a mass flow rate of 0.05–0.20 kg/min. The thermodynamic instabilities are discussed through the joint bonds between temperature and density, local and overall heat transfer, and pressure drop coefficient, under a series of pore-throats dimension from 7.5 to 401.3 μm. The results showed: (i) the remarkable (T/p)-nature of heat transfer capacity of sCO2 to lead the transfer coefficients with a subordinate impact of thermal conductivity near the Widom line, as long as the convective mode primes with increased temperature and pressure; (ii) The heterogeneity of the microporous media promoted the decrease of the transfer capacity while adjusting the spatiotemporal density and the heat transfer orientations inside the pore bodies; (iii) the growth of the pressure drop under increasing temperature has revealed an equilibrium stage where, neither the mutability of sCO2 properties nor the injection intensity can significantly affect the heat transfer of the integrated microporous.

Multi-objective optimization study of airfoil fin printed circuit heat exchanger with tip gap based on machine learning

The printed circuit heat exchanger (PCHE), a compact and highly efficient device, is capable of operating effectively under demanding conditions, which makes it ideal for supercritical CO2 Brayton cycles. In this study, we present a novel airfoil fin PCHE with tip gap, and conduct multi-objective optimization on the tip gap and arrangement of airfoil fins based on the analysis of the supercritical CO2 flow and heat transfer characteristics. We conduct a parameter design using Design of Experiment to examine the impact of the dimensionless design parameters, including the horizontal number (ζh), staggered number (ζs), vertical number (ζv), and gap number (ζg). To forecast the flow and heat transfer performance, we utilize a neural network model called Particle Swarm Optimization-Back Propagation (PSO-BP). We employ the non-dominated sorting genetic algorithm II to obtain the Pareto optimal front by utilizing ζh, ζs, ζv, and ζg as variables for optimization, and the volumetric heat transfer coefficient (hv) and Fanning friction factor (f) as objectives for optimization. The results find that the utilization of tip gap can enhance heat transfer while reducing flow resistance. The PSO-BPNN model exhibits higher prediction accuracy and excellent generalization ability compared with traditional BPNN model. The VIKOR and TOPSIS methods identify compromise schemes with excellent thermal-hydraulic performance. The mechanism of heat transfer enhancement can be elucidated using the principle of field synergy.

Numerical study of CO2 trans-critical process inside micromodel based porous structures under supercritical pressures

Understanding the flow, heat transfer, and trans-critical process of carbon dioxide in porous media is crucial for various applications, including CO2 sequestration, soil remediation and oil and gas recovery, due to its unique physical properties in the critical region. In this study, a porous media model on a microfluidic chip structure was simulated to emphasize the heat transfer and trans-critical process of CO2 under supercritical pressure in porous media. The study aims to observe the behaviors of CO2 during its transition from subcritical to supercritical temperature under supercritical pressure. The main objective is to observe the temperature distribution and pressure change of CO2 in a porous media model under the influence of bottom heating. At the same time, we observe the changes in the position of the critical temperature point of CO2 in porous media and analyze its heat exchange process in porous media. After the flow reaches a steady state, the temperature span near the grains is 1.6 K, and the pressure drop per unit length is 1480.3 Pa/mm. As the flow time progresses, the critical temperature line migrates from outlet region to inlet region, the range of sCO2 narrows from 81.7 % to 84.7 % in the porous media region. Finally, the influence of different working conditions on the trans-critical region is studied. It is hoped that this study will contribute to the understanding of the trans-critical process of CO2 in porous media.

Experimental and numerical investigation on the mechanisms of novel heat transfer deterioration of supercritical CO2 in vertical tubes

Understanding the mechanisms of supercritical CO2 heat transfer deterioration (HTD) has significant importance for ensuring the safety and reliability of supercritical Brayton cycles. Therefore, the effects of mass flux, wall heat flux, and tube diameters on the heat transfer characteristics of supercritical CO2 inside vertical tubes are studied using experimental and numerical methods. Results indicate that the heat transfer performance is positively influenced by an increase in mass flux and heat flux, as well as a decrease in tube diameter. When HTD occurs, the overall heat transfer performance is indeed significantly compromised. When the bulk fluid temperature exceeds Tpc, the thermal acceleration effect amplifies the mainstream velocity, stabilizing the Kelvin-Helmholtz instability between the pseudo-two-phases, thereby causing a new type of HTD that is named Type II HTD in this paper. The so-called post-dryout HTD occurs when the bulk temperature surpasses T+, causing a complete transition from pseudo-liquid to pseudo-gas state and resulting in a pseudo-single-phase flow. The heat transfer capability of the low-density and low-thermal-conductivity pseudo-gas diminishes as the temperature rises, leading to post-dryout HTD. The present work explains the mechanisms of two types of HTD and highlights the similarities between subcritical boiling and supercritical pseudo-boiling flow structures. This study also establishes a theoretical foundation for understanding pseudo-two-phase flow patterns during pseudo-boiling.

Supercritical CO2 flow and heat transfer through tapered horizontal mini-tubes: Parametric analysis and optimization study

One effective method for enhancing heat transfer in tubular heat exchangers involves gradually altering the cross-section of their tubes. While extensive research has been carried out in typical operating conditions, a significant shortage of studies exists that specifically investigate how changes in tube cross-section affect the heat transfer of fluids under critical and pseudocritical conditions. Additionally, the absence of a comprehensive parametric study considering the effect of all operating conditions and geometric parameters, and providing an optimal model in this field, is keenly felt. This paper offers a finite volume-based numerical simulation of steady-state turbulent flow and heat transfer for supercritical CO2 inside circular horizontal mini-tubes with tapered lateral profiles. It is found that the impact of buoyancy on thermal and hydraulic characteristics is more noticeable in the diverging mini-tube than in the converging mini-tube. The results of the parametric study reveal that under the same geometric parameters, the heat transfer coefficient in the diverging mini-tube is higher than that in the converging mini-tube by 5.2–28.6 %, with a simultaneous reduction in pressure drop ranging from 52.1 % to 68.5 %. However, in the case of a high diameter or diameter ratio, the heat transfer coefficient of the converging mini-tube exceeds that of the diverging mini-tube. Subsequently, an optimization study is conducted using BBD-RSM. To achieve the maximum heat transfer coefficient and the minimum pressure drop, an additional 54 cases are investigated, covering diverse ranges of operating conditions and geometric parameters. The results indicate that the mass flow rate and tube diameter are the most influential parameters on thermal and hydraulic characteristics. Additionally, the impact of the diameter ratio on the pressure drop is more pronounced than on the heat transfer coefficient. This research can serve as a foundation for enhancing the design of heat exchange devices within innovative supercritical CO2 power generation cycles.

Experimental verification of the novel transcritical CO2 heat pump system and model evaluation method

This work proposes a novel method for verifying the accuracy of the numerical simulation model of the compression/ejector transcritical CO2 heat pump system using convolutional neural networks. The method focuses on converting the original unequal input conditions into equal input conditions and comparing the simulation results with the experimental prediction results of each component. The validation results reveal the following findings: 1) The root mean square errors of the gas cooler and the water source evaporator are 9.16 °C and 11.47 °C respectively, indicating that future work should focus on correcting of the CO2 heat transfer coefficient calculation method; 2) The verification results of the evaporator indicate that suggesting the need to incorporate an air dynamic change module in the air source input; 3) The root mean square error of the CO2 outlet pressure in the ejector is 462.45 kPa. It can be inferred from the pressure variation trend that the limit pressure ratio of the compressor is the main factor affecting the accuracy of the ejector model. Overall, this article presents a novel and effective method for verifying the accuracy of numerical models.

Experimental investigation of heat transfer to carbon dioxide in parallel rectangular channels under supersonic mainstream

Active cooling using carbon dioxide(CO2) is a promising method for supersonic vehicles' combustion chamber, but few studies have considered CO2 heat transfer under supersonic mainstream conditions. In this paper, the double-wall heat transfer effect of CO2 under supersonic mainstream conditions is investigated by using the direct-connection experimental platform. The double-wall consists of an inner liner and a cooling jacket with parallel rectangular channels. The inlet CO2 parameter conditions range for T (Temperature) = 263.3 ∼ 272.5 K, m (Mass flow rate) = 50 ∼ 205.3 g/s, and P (Pressure) = 3.87 ∼ 8.88 MPa. It has been found that the magnitude of CO2 mass flow rate has a very significant effect on the effectiveness of thermal protection. The CO2 active cooling provides effective thermal protection for the inner liner at inlet parameter m = 199.1 ∼ 205.3 g/s, P = 8.69 ∼ 8.88 MPa, and T = 263.3 ∼ 266.8 K. Moreover, the heat transfer reaches thermal equilibrium quickly. However, it is more effective in thermally protecting the inner liner near the CO2 inlet than near the CO2 outlet at the inlet parameters of m = 50 ∼ 88.6 g/s, P = 3.87 ∼ 7.74 MPa, and T = 263.3 ∼ 272.5 K. In addition, there may be a risk of structural burnout near the CO2 outlet.

Determining of bubble waiting time coefficient, critical Webber number and turbulence model for modeling of subcooled flow boiling heat transfer of CO2 at low temperature

Determining of bubble waiting time coefficient, critical Webber number and turbulence model for modeling of subcooled flow boiling heat transfer of CO2 at low temperature

Simulation study on the coupled heat and mass transfer of CO2 in a heavy oil-water liquid system based on an improved lattice Boltzmann (LB) method

This study investigates the heat and mass transfer when low-temperature CO2 diffuses in a heavy oil–water liquid system based on an improved Lattice Boltzmann (LB) method. First, we determine the CO2 diffusion coefficients in heavy oil and water and the heat transfer coefficients of heavy oil and water using the pressure drop (DP) method and the laser flash (LF) method, respectively. Then, a numerical model that couples the heat and mass transfer in the system is established based on the improved LB method. The effect of low-temperature CO2 on the temperature field of the system and the effect of changes in the temperature field on CO2 diffusion are investigated. Finally, we develop a micro-model reproducing the heat and mass transfer of CO2 in water and heavy oil-saturated porous media to validate the accuracy of the numerical model. The results demonstrate that the CO2 diffusion coefficients in heavy oil and water linearly increase with the temperature increases. The heat transfer coefficients of heavy oil and water are insensitive to the changes in temperature. The heat transfer process has a great impact on the mass transfer of CO2 in the liquid system. The CO2 diffusion velocity slows down as the system temperature decreases because of the heat transfer (from 400 K to 300 K), leading to a reduction percentage of 300 % in the CO2 front movement velocity. Compared to the scenarios neglecting heat transfer, CO2 diffusion distance and amount decrease by 38 % and 50 %, respectively because of the changes in the temperature field of the system.

Rapid 2-Dimensional prediction of supercritical CO2 heat transfer behaviors in inclined tubes based on deep learning

At present, there is a dearth of empirical correlations for the prediction of the inclined supercritical heat transfer. Considering the shortage of the rapid prediction method in the initial design stages for the supercritical fluid heat exchanger with inclined tubes or under inclined conditions, a 2-Dimensional rapid prediction method based on the numerical method combining deep learning method was proposed to reconcile the accuracy and the efficiency of the inclined supercritical heat transfer behaviors prediction. In order to train the deep learning model, 200 numerical cases with 520,000 data were conducted. After that, 7 new cases were chosen to analyze the inclined heat transfer behaviors and validate the current model. The results were indicative of a significant circumferential inner wall temperature difference in the inclined supercritical heat transfer. The temperature difference was larger when the inclined angle was closer to 90°, even though the circumferentially averaged temperature is smooth and acceptable. This potential temperature difference would not only cause large thermal stress which may accelerate fatigue failure, but also increase the risk of over-temperature. Fortunately, the current deep learning model could predict the 2D temperature distribution of these new cases with the max absolute relative error of 16.60%. Therefore, the circumferential inner wall temperature distribution of the inclined supercritical CO2 heat transfer could be evaluated during the initial heat exchanger design. Moreover, the trained model and the relative files are available at Supplementary materials.

Impact of adiabatic entrance length on numerical simulations of supercritical CO2 heat transfer in horizontal circular tubes

Horizontal supercritical carbon dioxide (sCO2) pipe-flow studies in the heat transfer literature commonly use a fixed-length adiabatic hydraulic development section prior to the heat transfer region. It is expected that the length of the adiabatic entrance region is long enough to generate hydrodynamically fully developed flow, such that the influence of the entrance is eliminated. However, despite the criteria for subcritical flows being well established, the criteria defining the adiabatic entrance length for sCO2 flows are not as clear. In this paper, 6-mm-diameter round tubes with heat-flux-to-mass-flux ratios (q/G) equal to 60 J/kg are considered. The tubes have adiabatic entrance lengths between 0 and 1000 mm (0 and 167D), followed by a 500 mm (83D) heat transfer cooling section. An assessment of the effect of adiabatic entrance lengths on flow development and heat transfer behavior is given. An analysis of several flow features such as centerline pressure, centerline velocity, axial velocity profile, wall shear stress, and local heat transfer coefficient are presented. Based on findings for a 6-mm-diameter tube with cooling heat flux boundary conditions and a q/G ratio equal to 60 J/kg, it has been determined that a critical adiabatic length, which is the minimum entrance length necessary to achieve hydrodynamically fully developed flow, of greater than 60D is required.

Supercritical heat transfer of CO2 in horizontal tube emphasizing pseudo-boiling and stratification effects

Here, we investigate supercritical heat transfer of CO2 in a 10.0 mm diameter horizontal tube, covering pressures, mass fluxes and heat fluxes in the ranges of (7.531∼20.513) MPa, (496.7∼1346.2) kg/m2s, and (97.4∼400.3) kW/m2, respectively. It is surprising to find the non-monotonic increase of wall temperatures along the flow direction. Besides, either positive or negative wall temperature differences, ΔT, exist between bottom tube and top tube. The three-regime-model is introduced to explore the mechanisms that trigger the above abnormal findings. The stratified-wavy flow involves a liquid-like (LL) core and a vapor-like (VL) layer on the tube wall. The wavy interface is formed by the two separated phases of LL and VL. The oscillation of wall temperatures is explained by the thermal conduction in the solid wall interacted with the stratified-wavy flow in the tube. Once wall temperatures increase, the local heat flux decreases to decrease the evaporation momentum force, reducing the VL layer thickness to ensure the heat transfer recovery. A regime map clarifies the positive and negative temperature difference runs, and the maximum wall temperature differences are well correlated based on the LL phase Reynolds number, ReLL,ave. In the two-phase-like (TPL) regime, the measured heat transfer coefficients significantly deviate from the predictions based on the single-phase fluid assumption. The strong deviation of hbot/htop from 1 indicates both important effects of pseudo-boiling and stratification in horizontal tubes, where hbot and htop are the heat transfer coefficients at the bottom generatrix and the top generatrix, respectively. Based on this work, the pseudo-boiling theory is recommended to deal with the supercritical heat transfer.