Non-uniform Heat Research Articles

Simultaneous features of nonuniform heat sink/source and activation energy in entropy optimized flow of Sutterby fluid subject to thermal radiation

The applications of nanofluids (NFs) have been comprehensively explored in current years, as they have abundant potential for technical progress and more prominently offer assistances that can be associated with the applications of NFs for several determinations. Nanotechnology can be applied in various technological fields such as medicine, information technologies, food safety and novel materials. Here, novel properties of entropy generation in a mixed convective magneto flow of a Sutterby nanomaterial to an extended surface is scrutinized. Nanofluid model comprises Brownian motion and thermophoresis aspects. The expression of energy depends upon the phenomenon of viscous dissipation and thermal radiation. We formulated the Bejan number and entropy generation. To reduce PDEs into nonlinear ODEs, we use transformation of variables and then the resultant system is solved by bvp4c technique. The influence of the parameters involved, such as thermal radiation, chemical reaction parameter, diffusive variable, magnetic parameter, thermophoresis parameter and Schmidt number for temperature, concentration as well as Bejan number, entropy generation are inspected through tables and graphs.

Effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of riser downcomer circuit of natural circulation boiler

The usual practice of design of riser tubes of natural circulation boilers is with an assumption of uniform furnace heat flux. Using the uniform diameter of riser tubes inside the furnace zone is also very common. The effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of the riser downcomer circuit of a natural circulation boiler is presented here for the first time. As the riser tubes are exposed under substantially high heat flux, the tubes containing water-steam mixture are vulnerable and susceptible to overheating, particularly at high flux zone. From systematic analysis, it is proposed that using different diameters and the number of riser tubes at various sections can overcome the early occurrence of tube dry-out. An appropriate two-phase flow model is developed with flow regime mapping, tube wall temperature calculation, and identification of possible dry-out. The peripheral nonuniform distribution of furnace heat flux is implemented analytically in the model by introducing a distribution parameter estimated from the actual furnace data. Results reveal that with an average heat flux of 150 kW/m2, the dry-out occurs near a riser tube height of 44 m for a typical 210 MW capacity boiler. However, considering the nonuniform heat flux variation, the dry-out appears near a height of 32 m and 73 m for higher and lower heat flux zone, respectively. The present analysis shows that the implementation of larger size and lower size diameter of riser tubes, respectively, in higher and lower heat flux regions has a 9.45 % cost-benefit compared to the usual design practice with a consideration of uniform diameter tube and heat flux. The present work concludes that instead of using uniform tube diameter with average heat flux assumption, the use of different diameter of tubes in different heat flux zone not only avoid the early onset of possible dry-out but also has a cost-benefit.

Advances in material phase change modelling approach for EU-DEMO limiter’s plasma-facing components

Within the EU-DEMO first wall protection framework, work on limiter’s plasma-facing component design has started under plasma disruptive events (Richiusa et al., 2022). Starting from the rationale behind the TARTIFL&TTE software (Richiusa et al., 2022), this companion paper describes the progress on the engineering modelling of the plasma-facing material phase change under high heat flux, with the aid of COMSOL Multiphysics® software. The aim is to develop a reliable technique which can be used by designers for predicting how much of the solid armour undergoes phase change. This helps satisfy requirements for actively cooled components, such as at which armour depth safely locating the cooling system, and if its design can safely handle the heat transfer in the resulting component configuration after the disruption is extinguished. A few changes to the driving idea in Richiusa et al. (2022) will be also highlighted.The multiphysics software allows us to implement a 1D model which can be extended to 2D/3D geometries subjected to both uniform and non-uniform heat flux. It also offers the capability of conjugated heat transfer in solids and liquids by coupling the two different domains. Although this multiphysics approach is also investigated, no effort in melting layer motion modelling is done. Therefore, the equivalent way of validating this approach while reducing its computational time is working with one single solid domain, within which any liquid phase changes are tracked by an apparent heat capacity formulation. The vapour domain is not modelled. The material removal due to the evaporative mass flux is modelled by means of moving mesh frames which push the recessing liquid interface backwards according to gas kinetics-driven boundary conditions. The melt pool is not removed during the transient. Mass balance considerations drive the liquid-to-vapour interface velocity.The 3D Multiphisics implementation (3D-TARTIFL&TTE), is here supported by a benchmark activity and an application to the limiter’s plasma-facing armour, whose preferred chosen thickness is 20 mm.

Transpiration cooling with phase change by functionally graded porous media

Transpiration cooling using liquid coolants is considered one of the most promising thermal protection techniques for new generation aerospace vehicles. The leading edges are subjected to a very high and non-uniform heat flux. Unfortunately, few coolants can flow through the part near the stagnation point using traditional porous structures, which will cause ablation. Unlike conventional fabrication methods, additive manufacturing is capable of directly tailoring porous structures with well-controlled pore features and functional graded pore topology, thereby optimizing the coolant distribution and improving the cooling performance. Smoothly graded pore structures can be fabricated using additive manufacturing technology. We experimentally assessed the transpiration cooling performance of uniform and graded porosity porous plates to compare the coolant distributions, temperature profiles, and features of the two-phase region. Graded porous media exhibited much better cooling performance than uniform pore topology. Through computations, the graded porosity improved the imbalanced coolant distribution and minimized the hot-spot temperature under a non-uniform heat flux. Importantly, the temperature profile at the outlet should match with the local flow resistance in porous media and the heat flux at the outlet. The temperature and phase change zone were highly dependent on the topology of the porous media, heat flux profile applied to the outlet, and coolant mass flow rate.

Unfolding flow features of MHD hybrid nanofluid (Ag–Al2O3–H2O) and mono nanofluid (Al2O3–H2O) flow over exponentially expanded sheet soaked in a Darcy–Forchheimer absorbent medium co-existing non-uniform heat generation/absorption

This study unfolds a comparative flow analysis of a hybrid nanofluid (Ag–Al2O3–H2O) and a single nanoparticle-based mono-nanofluid (Al2O3–H2O) through an exponentially permeable expanded sheet. The sheet is drenched in a non-Darcy absorbent medium under the prevalence of variable magnetic flux and non-uniform heat absorption/generation . Similarity transformations are engaged to the leading system of PDEs to transform the equations into ordinary BVP. To gain the analytical solution, DTM is engaged and numerical solution is produced by fifth-order RKF with shooting process. One of the interesting observations depicts that the fluid velocity for Ag–Al2O3–H2O decreases rapidly in comparison to Al2O3–H2O with the escalation of magnetic field parameter and porosity parameter . Whereas the thermal boundary layer width grows quickly for hybrid nanofluid with the augmentation of the porosity parameter and inertial parameter . Moreover, under the control of space and temperature reliant heat generation parameters the temperature distribution for hybrid nanofluid is better in contrast to mono-nanofluid. Also, it is noteworthy that the rate of heat transport decays by 9.56% for Al2O3–H2O while 11.44% for Ag–Al2O3–H2O as and the rate of shear stress is lessened by 45.71% and 37.93% for Al2O3–H2O and Ag–Al2O3–H2O respectively while varies from 0.0 to 1.6.

Magnetized Cross tetra hybrid nanofluid passed a stenosed artery with nonuniform heat source (sink) and thermal radiation: Novel tetra hybrid Tiwari and Das nanofluid model

Researchers around the planet are attempted to explore the influence of various non-Newtonian fluids with the mono and dihybrid nanoparticles in the status of blood flowing arteries to investigate the heat transference aspect for the cure of various diseases. Current examination is created to investigate the effect of extended novel tetra hybrid Tiwari and Das nanofluid model on blood flow arteries with consideration of Cross non-Newtonian fluid model. Heat transference assessment has been taken with the insertion of impacts like heat source/sink, viscous dissipation, Joules heating as well as nonlinear thermal radiation. PDE are designed to investigate the momentum of blood flowing and temperature analysis. The governing PDE are converted into ODE with the application of similarity conversions and furthermore managed these ODE numerically with the utilization of MATLAB builtin bvp4c scheme. The obtained outcomes are studied numerically as well as graphically in the case of diverse dimensionless variables ranges between 0.5≤M≤2, 0.1≤We≤4, 0.1≤n≤1.5, 0.1≤γ≤2, 0.5≤Rd≤2, 19≤Pr≤22, 0.1≤θw≤1.5, 0.1≤Ec≤2.1, 0.5≤U≤2, 0.5≤W≤2 versus velocity, temperature, wall frictional factor and heat transition rate. From obtained outcomes it is reflected that the surface drag phenomenon weakens by the boost of a Weissenberg number and an increment variation in magneto force provides a resistance against the fluid flow. Temperature within the arteries intensifies by the advantage of a thermal radiation and viscous dissipation.

Thermal Performance of Mini Cooling Channels for High-Power Servo Motor with Non-Uniform Heat Dissipation

Thermal Performance of Mini Cooling Channels for High-Power Servo Motor with Non-Uniform Heat Dissipation

Heat and mass transfer model for pork carcass precooling: Comprehensive evaluation and optimization

In this study, we construct a three-dimensional heat- and mass-transfer model to determine the moisture loss and spatio-temporal distribution of pork carcass temperature during precooling. We consider how convection, evaporation, and radiation affect the heat- and mass-transfer process and compare and analyze how precooling conditions affect the precooling rate, uniformity, and moisture loss of pork carcasses. The results reveal nonuniform precooling between different parts of single carcasses, mainly because of the nonuniform heat transfer on the pork carcass surface. However, for the overall precooling space, no significant difference appears in the rate of temperature decrease between individual carcasses. In addition, the ambient humidity most strongly affects carcass moisture loss, and the precooling temperature most strongly affects temperature uniformity and precooling rate. Finally, by comprehensively evaluating the effects of different precooling conditions on carcass precooling performance, the optimal precooling conditions are determined, namely, the air velocity, precooling temperature, ambient humidity, and initial carcass temperature of 10 m/s, 0 °C, 95 %, and 37 °C, respectively. This study thus provides an important theoretical basis and a useful reference for the determination of optimal precooling conditions and the comprehensive evaluation and optimization of pork carcass precooling.

Heat generation rates and anisotropic thermophysical properties of cylindrical lithium-ion battery cells with different terminal mounting configurations

This paper investigates the variation in the heat generation rates and anisotropic thermophysical properties of cylindrical 18,650 and 21,700 lithium-nickel-manganese-cobalt-oxide (NMC) battery cells when the negative terminal is mounted at different points on the cell surface. We developed a methodology that combines experimental data with a numerical inverse heat transfer (IHT) model to quantify the differences in these properties under two strategies for connecting the negative terminal to the cell surface. In the first, the negative terminal is connected at the top rim of the cell, adjacent to the positive terminal; in the second, the negative terminal is connected at the bottom of the cell, adjacent to the negative current collector. Applying this methodology, we found that the total heat generation over 1000 s for 18,650 and 21,700 cells with the negative terminal at the top rim is higher than that for batteries with the negative terminal at the bottom by up to 4.6 % and 10.7 %, respectively. The additional heat was concentrated in the cell canisters, resulting in non-uniform heat generation across the cell volume. Without considering this non-uniformity in the numerical IHT model, the characterization process yielded 15–22 % discrepancies in the predicted thermal conductivities. By considering the canister and jelly roll of the cell as separate heat generation domains, the discrepancies were reduced below 6 % and 7 % for 18,650 and 21,700 cells, respectively. This work developed an improved battery cell characterization methodology taking into account localized heat generation and extrinsic terminal mounting effects. The results underline the importance of high-fidelity cell characterization in the battery cell design process.

Computational analysis of passive strategies to reduce thermal stresses in vertical tubular solar receivers for safety direct steam generation

When exposed to high non-uniform heat fluxes on the receiving surface, significant temperature gradients develop in the tubes, producing thermal stress and deformations in the receivers. This paper reports a detailed investigation of the thermal and structural performance of a solar tower system that operates with direct steam generation tubes when the fins are added to the internal surface and thickness varies. Six tubes were evaluated, two without fins varying the wall thickness (5 mm and 3 mm) and four with fins under different configurations. The thermal system corresponds to a representative tube of an external tubular receiver of a central tower system. The thermal receiver operates with direct steam generation under a non-uniform concentrated solar flux with a maximum value of 0.93 MW/m2. The best configuration of the tube was with fins on the frontal surface of the tube, maintaining a receiving wall thickness of 3 mm and an adiabatic wall thickness of 5 mm. It could reduce maximum thermal gradients and temperature by 31% and 14%, respectively, maximum thermal stresses by 38%, and maintain vapor mass flow at the output (276 kg/h).

Significance of non-uniform heat source/sink and cattaneo-christov model on hybrid nanofluid flow in a Darcy-forchheimer porous medium between two parallel rotating disks

The suspension of nanoparticles in fluid influences several properties of the resulting fluid. Many production and manufacturing applications need knowledge of the heat transference mechanism in nanofluids. The current paper concerns the influence of non-uniform heat source/sink on (MoS2-Go/water flow) hybrid nanofluid flow and (Go/water flow) nanofluid flow in a Darcy-Forchheimer porous medium between two parallel and infinite spinning disks in the occurrence of radiation. The Cattaneo-Christov model is utilized to analyze heat and mass transmission. The Cattaneo-Christov model introduces the time lag factors in the process of heat and mass transmission, known as the thermal relaxation parameter and solutal relaxation parameter, respectively. The governing equations are numerically solved employing the “bvp4c function in MATLAB.” The effect of the primary relevant parameters on the velocity, temperature, nanoparticle concentration, and is graphically depicted. Finally, a table is drawn to show the relationships of various critical factors on the Nusselt number, and Sherwood number. Results reveal that an increase in the thermal relaxation parameter reduces the heat transmission rate at both the upper and lower plate. Furthermore, an increase in the nanoparticle’s volume fraction causes enhancement in thermal conduction, which increases the heat transmission rate at the upper disk. The results of this study will be helpful to many transportation processes, architectural design systems, enhanced oil recovery systems, medical fields that utilize nanofluids, and so on.

Ultrashort pulsed laser ablation of zirconia toughened alumina: Material removal mechanism and surface characteristics

Zirconia toughened alumina (ZTA) is commonly used in hip joint implants and cutting tools. The difference in material properties of the zirconia and alumina phases makes the composite inhomogeneous at the grain size level. Due to the strong nonlinear laser absorption mechanisms of wide band gap materials under intense laser field, the smaller band gap zirconia phase can absorb a significantly larger amount of laser energy than the alumina phase. The nonuniform energy deposition and lattice heating takes place at a comparable timescale as the laser pulse duration, which is too short for thermal diffusion to play a role. As a result, the temperature in the zirconia phase can be significantly higher than in the alumina phase, leading to a unique selective phase melting phenomenon, i.e. localized melting of the higher melting point zirconia phase (2715 °C) surrounded by a lower melting point alumina phase (2072 °C) which remains solid. This phenomenon makes the material removal mechanism of the nanocomposite significantly different from that of single-phase materials under ultrashort pulsed laser processing. On the basis of experimental analysis and theoretical modelling, material ablation by the disintegration of alumina grains due to the localized melting of the zirconia phase was identified.

Improving radio frequency heating uniformity in milled rice with different packaging shapes by changing temperature of forced air

Radio frequency (RF) treatment is a promising physical method for disinfesting and pasteurizing foods but the non-uniform RF heating is still a major obstacle for industrial applications. In this study, a three-dimensional model was established with COMSOL software to simulate temperature distributions in milled rice with different packaging shapes and experiments using a 6 kW, 27.12 MHz RF system were carried out to evaluate the improvement of heating uniform of sample by changing temperature of forced air. The established model was validated by temperature-time histories at three points in the sample and temperature distributions at the top and bottom surfaces. The results showed that the cold spot of the regular shape sample was found at the part with small thickness, and the RF heating uniformity was improved by increasing temperature of forced hot air. When the temperature of forced hot air increased from 40 to 60 °C, all the sample temperatures were above 50 °C, which might meet the required temperature of disinfestation, and the heating uniformity index decreased from 0.113 to 0.099. For the cuboid shape sample, the corner/edge effect was observed and the heating uniformity index firstly decreased and then increased with reduced temperature of forced cold air. When the temperature of forced air decreased to 10 °C, the best heating uniformity of the cuboid shape sample was obtained. The results of this research can help to select packaging shape and improve the heating uniformity of samples for RF treatment in large-scale applications.

Improvement of uniformity of irradiance on truncated compound parabolic concentrator by introducing the homogenizer ratio

A compound parabolic concentrator (CPC) with a flat absorber is widely used in low-concentrating photovoltaic thermal (CPVT) systems. CPC certainly develops non-uniform heat flux distribution over the absorber surface which is significantly reduced by the integration of homogenizer referred as Elongated CPC (ECPC). The objective of the present work is to analyse the effect of homogenizer ratios, truncation ratios and concentration ratios on the heat flux distribution characteristics of a CPC collector. In this paper, a ray tracing simulation is carried out to obtain the heat flux distribution profiles and the same is incorporated within CFD software to obtain the temperature distribution profiles. As a result, it is observed that the optimum truncation ratio would be 0.7 at which uniformity in flux distribution is improved by 3%, with just 2% reduction of average heat flux value. Furthermore, with optimized homogenizer ratio of −0.35 at concentration ratio of 3, 64% improvement in uniformity of flux distribution has been noticed. From the study, it has been concluded that for different concentration ratios of 1.5, 2, 3, 4, 5, 6, 7 and 8, the optimum homogenizer ratio is observed to be −0.9, −0.55, −0.35, −0.25, −0.2, −0.15, −0.15 and −0.05 respectively.

Thermodynamics second-law analysis in an unsteady conduction and radiation heat transfer system with internal heat source

This paper presents an improved thermodynamic analysis method used to evaluate the irreversibility and efficiency of a coupled conductive-radiative heat transfer process. The exergy analysis of the conductive-radiative process is developed based on the exergy balance equation. In the method, the local entropy generation rates due to the radiative heat transfer and heat conduction processes are calculated. Based on the entropy generation analysis, an exergy analysis is performed, the stored exergy of the system and the exergetic efficiency are determined, and the thermodynamic efficiency of the system is further evaluated. The results are verified by the principle of exergy balance and the exergy generation rate calculated by the method does not deviate from the theoretical value by more than 0.1%. Four heat source distributions are specified in the numerical analysis, which include completely uniform, partially uniform, and non-uniform heat source distributions in the numerical analysis. The effects of heat source distribution, conductive-radiative coefficient and total heat generation rate of medium on entropy generation and stored exergy of system are investigated. The numerical results show that the average temperatures and exergy storage rate of the systems with partially uniform heat source distribution are 5.1–79.7 K and 6.8–49.8% higher than the other distributions, and uniform and centralized heat generation in the internal region of the system is proposed. The total stored exergy of the systems has a tendency to first increase and then decrease, reaching its maximum at N = 1 as the conduction and radiation coefficients increase, and increasing as the total heat generation rate increases.

Spatio-temporal progression and influencing mechanism of local wetting in membrane distillation

Membrane wetting is the bottleneck of membrane distillation (MD) in real applications. However, rare information is attainable on the spatial inhomogeneity and temporal instability of local wetting behavior along the membrane. In current study, the influences of operating conditions (i.e., feed temperature, velocity, and concentration) and membrane hydrophobicity on the spatio-temporal progression of local wetting along the membrane were evaluated using a non-invasive and online monitoring technique – ultrasonic time-domain reflectometry (UTDR). UTDR measurements could successfully distinguish local wetting dynamics and were validated by the off-line characterization of the wetting layer thickness via a scanning electron microscopy with energy-dispersive x-ray spectroscopy. Observations showed that the local wetting depth decreases along the feed flow direction. This wetting heterogeneity would be impaired with increasing surfactant concentration, feed temperature, and crossflow velocity. However, enhancing membrane hydrophobicity obviously reduced the rate of local wetting but hardly affected its nonuniform distribution. The wetting heterogeneous propagation at different locations is dominated by the nonuniform mass and heat transfer characteristics along the membrane based on the computational fluid dynamics (CFD) simulation. Localized wetting prevention near the module inlet is therefore critical to ensure stable MD operation.

Analysis on the Quenching Deformation Characteristics of Light Cast Aluminum Alloy Wheels and Their Control Strategies

The purpose of this paper is to develop a new technology for controlling the quenching deformation of light cast aluminum alloy wheels. First, based on the existing wheel heat treatment process, a gas–liquid–solid multi-phase flow coupling model was established through the ANSYS Workbench platform to analyze the gas–liquid phase change, heat exchange on wheel surface and quenching deformation characteristics during the process of wheel immersion into the water. The results show that heat exchange characteristics of the wheel surface are comprehensively affected by wheel structure, quenching fluid flow field and gas–liquid phase transition. There are a lot of non-uniform heat exchange areas in the outer rim, spoke area and center area, which affect the overall deformation characteristics. Affected by spoke structure, the maximum deformation occurs at the outer and inner rim end faces farthest away from the wheel. Based on the above research, this paper independently develops a new deformation control strategy of spray and water immersion composite step process. Through spraying, the influence of spoke structural stiffness on the overall deformation characteristics of the wheel is effectively reduced, and the wheel deformation control is realized by meeting the mechanical properties of the wheel, with the maximum deformation reduction of 39.2%. This study provides a new option for the integrated control of deformation and mechanical properties of aluminum alloy wheels.

An efficient parametrized optical infrared thermography 3D finite element framework for computer vision applications

Matching infrared thermography (IRT) with deep learning-based computer vision has recently gained a lot of interest for automated defect assessment in materials. One of the remaining bottlenecks concerns the necessity of a large and diverse experimental and/or virtual training dataset in order to achieve a sufficiently generalizable computer vision algorithm. This paper presents a parametrized 3D finite element (FE) framework, implemented in Fortran90, for efficiently simulating optical infrared thermographic inspection of multi-layer anisotropic media and establishing large-scale virtual dataset with sufficient diversity. The interface element is introduced for the modelling of an imperfect thermal contact, allowing to simulate a variety of defect types. The flexibility of the interface element makes it possible to simulate delaminations with different thickness using the same discretized model. Validation is done for two benchmark cases which are representative for a fiber reinforced polymer laminate with delamination-like defects. In order to achieve true-to-nature thermographic simulation data, non-uniform heating conditions are adopted from experiment, and a stochastic morphology generator is introduced for modelling realistic irregular defect geometries. To demonstrate the added value of a large, diverse and true-to-nature virtual database for computer vision applications, a Faster-RCNN model was trained on a generated virtual dataset for the detection of delamination-like defects in fiber reinforced polymer laminates. Application of the trained Faster-RCNN on experimental thermographic data yields excellent inference results, illustrating the high generalization ability of the virtually trained object detector.

Exergetic, Energetic, and entropy production evaluations of parabolic trough collector retrofitted with elliptical dimpled receiver tube filled with hybrid nanofluid

In this paper, a numerical study was performed on a parabolic trough collector receiver tube containing elliptical dimpled fins with different elliptical ratios (ER = 0.66–1.66) under turbulent flow regime. The C++ code was developed to perform a non-uniform heat flux on outside of the receiver tube to get approximation real working conditions. Different mono and hybrid nanofluids and their combinations with different nanoparticle volume fractions (2.0 %TiO2/Syltherm800, 2.0 %Al2O3/Syltherm800, 0.5 %TiO2-1.5 %Al2O3/Syltherm800, 1.0 %TiO2-1.0 %Al2O3/Syltherm800, and 1.5 %TiO2-0.5 %Al2O3/Syltherm800) were used as a working fluid. The study provides a detailed analysis of the hydro-thermal characteristics, exergetic, and entropy production of the parabolic trough collector. 1.5 %Al2O3-0.5 %TiO2/Syltherm800 hybrid nanofluid shows the best increase in results obtained in this study using elliptical ratio of a/b = 5/3. The use of the elliptical ratio of a/b = 5/3, the average Nusselt number increases with 38 % compared to the receiver tube without elliptical dimpled fin. Total entropy generation was reduced up to 16.82 % for the elliptical ratio of a/b = 5/3. With the inserting elliptical dimpled fins of a/b = 5/3, the Performance Evaluation Criterion was detected as 1.81 compared to while the thermal efficiency increases from 74 % to 80 % at the lowest Reynolds numbers.

Numerical Investigation on Two-Phase Water Density Wave Oscillations in a Pipe under Various Heating Conditions

This study utilizes the finite volume method with a two-fluid model to analyze water characteristics in a boiling channel when density wave oscillation occurs. A 2-D numerical model is utilized to characterize both axial and radial mass and energy exchange, as well as the mechanisms involving flow and heat transfer during density wave oscillation under uniform and non-uniform heating conditions. The numerical model was used to predict the heating power threshold values of two-phase water flowing upward in a vertical pipe under type II density wave oscillation at the working pressure and an inlet–outlet pressure difference of 125 kPa, when the average heating power increased from 44.06 kW/m2 at a speed of 0.5 kW/(m2·s). The flow and heat transfer characteristics before and after the type II density wave oscillation were determined and compared to the flow and temperature fields at various moments. Along the pipe axis, the wall heat flux was loaded under uniform, standard-sine, and inverted-sine types, which represent three typical types of wall heat flux arrangements. Flow oscillation appeared the earliest under the inverted-sine-type heat flux with low vapor quality (approximately 0.13) with a void fraction of 0.6 at the outlet.