Uniform Heat Flux Distribution Research Articles

An experimental study of the CHF in a square channel with non-uniformly heated rod under low pressure and low flow conditions

Experimental research on critical heat flux (CHF) was carried out in a vertical square channel with non-uniformly heated rod at low pressure and low flow conditions. The influence of inlet subcooling on CHF was also investigated. The results showed that the CHF position of the non-uniformly heat flux distribution mainly appeared in the middle and lower part of the heater rod. More significantly, it was found that CHF was enhanced with the rise of the inlet subcooling. The CHF data measured in this experiment were also assessed with the commonly used CHF empirical correlations suitable for low pressure and low flow. The results indicated that the general correlations predicting for CHF of uniform heat flux distribution were not applicable for prediction CHF of non-uniform heat flux distribution and these correlations usually overestimated the experimental values. In addition, The F-factor approach proposed by Tong was used to predict the experimental data and the error predicted by F-factor were mostly between 30% and 50%. Finally, F-factor was modified based on experimental data and the error between the predicted value and experimental results was between 0 and 30 %, and most of the data was between 0 and 20 %.

Influence of spinning flower structure inserts in the thermal performance of LS-2 model of parabolic trough collector with ternary hybrid nanofluid

Parabolic solar trough collector is the most widely accepted technology to use inexhaustible energy. Present research work proposed LS-2 model of parabolic trough collector with various spinning flower inserts and three particles based nanofluid as a heat-carrying medium. Main intention of this examination is to lower the temperature gradient in fluid flow and provide uniform distribution of heat flux on the receiver's outermost surface. A total of ten cases of PTC are examined in ANSYS 22 Fluent. Nine steady receivers are equipped with spinning flower inserts and one without inserts. Hybrid nanofluids with 1% vol. content are attained by blending aluminum oxide, copper oxide, and graphene oxide with water as base fluid. This evolution focuses on the consideration of spinning inserts in the receiver with a range of speed from 0 to 15 rad/s. The flow rate is from 0.016 kg/s - 0.033 kg/s respectively. Highest enhancement for thermal efficiency and heat transfer coefficient are 30.87% and 98.34% for case-9 at 15 rad/s inserts speed than receiver without inserts using nanofluid-6 at 0.033 kg/s. Under the same condition, the highest increment for the pump work requirement is 21.29% for case-9 than receiver without inserts. This means increment of pump work is insignificant than thermal performance improvements.

Optical modeling of a cylindrical-hemispherical receiver for parabolic dish concentrator

Among all sub-systems of a solar thermal energy system, the receiver plays a significant role when it gets heat energy from the concentrator. The reliability of such systems depends on the amount of solar energy that the receiver collects and other optical parameters like focal length, aperture diameter, surface absorptivity, and slope error. The present paper discusses the optical analysis of a cylindrical-hemispherical receiver coupled with a parabolic dish concentrator having 3-m diameter. The study has been carried out using the SolTrace software by varying the parameters like receiver aperture diameter (Da) ranging from 0.125 to 0.162m, surface error of the concentrator varying from 1.7453 to 34.907 mrad, and also surface absorptivity (α) changing from 75 to 95% for different receiver distances (H) ranging from 1.7 to 1.95m. The simulation results show that the optical efficiency is maximum when the receiver with 0.150-m aperture diameter is placed at a distance of 1.85m from the concentrator. An increase in slope errors from 1.7453 to 17.453 mrad decreases the average optical efficiency by almost 50% for all receiver diameters. It is also noticed that uniform heat flux distribution can be achieved when the receiver's position is maintained at H = 1.85m from the concentrator for 0.150-m receiver diameter and 95% absorptivity of the receiver surface. The simulated results of heat flux intensity on the receiver surface are then compared and validated by the experimental results available in the literature. The simulated optical efficiency of the present receiver is found to be 8% higher when compared with a conventional cylindrical receiver with similar dimensions.

Evaluation of Heat Flux Distribution on Flat Plate Compound Parabolic Concentrator With Different Geometric Indices

AbstractThe Compound Parabolic Concentrator (CPC), when coupled with the photovoltaic system, namely the Concentrated Photovoltaic Thermal System (CPVT), makes utilizing solar energy efficient. The major challenge that hinders the electrical and thermal performance of the CPC–CPVT system is the non-uniform heat flux distribution on the absorber surface. In the present paper, detailed ray-tracing simulations have been carried out to understand the heat flux distribution characteristics of CPC with different geometrical conditions, and those are concentration ratio, truncation ratio, incident angle, and average heat flux on the absorber surface. To have a thorough understanding, the analysis has been carried out in multiple steps. First, it is performed by analyzing the effect of concentration ratio and incident angle on heat flux distribution characteristics at a fixed truncation ratio. Second, investigations have been carried out to understand the heat flux distribution characteristics at different truncation ratios and different incident angles by keeping the concentration ratio constant. Local concentration ratio and non-uniformity index have been employed to quantify the non-uniformity of heat flux distribution on the absorber surface. It has been observed that the 0-deg incidence angle is the most effective angle to achieve uniform heat flux distribution on the absorber surface. This paper sheds insight into the heat flux distribution characteristics on the absorber surface of a CPC–CPVT system which can be used by the research community for designing an effective CPVT system from the perspective of uniform heat flux distribution on the absorber surface.

Thermal Performance Analysis of a Linear Fresnel Concentrating Solar Collector Absorber Tube

Linear Fresnel solar collectors are suitable for a wide range of applications, which include steam generation for power generation, industrial process heat, solar cooling, institutional and domestic hot water production etc. The thermal performance of a linear Fresnel solar collector absorber tube was investigated in this study for different fluid mass flow rates, heat flux intensities, heat transfer fluid inlet temperatures, ambient air temperatures and external loss heat transfer rate. Turbulent flow liquid water heat transfer fluid and uniform circumferential heat flux distribution boundary were considered under steady-state conditions. The fluid flow was considered incompressible. This study was limited to a first order model approximation for thermal performance of a linear Fresnel solar collector absorber tube. The heat transfer fluid and absorber tube material properties were considered constant and independent of temperature. The results indicated that the absorber tube outlet heat transfer fluid temperature decreased with an increase in the Reynolds number and increased with the heat flux intensities. Thermal efficiency increased with an increase in the heat transfer fluid mass flow rate and however, decreased with increase in pressure drop and the consequent pumping power requirement. It was also found that the thermal efficiency of the collector decreased with an increase in the fluid bulk inlet temperature and decreased with an increase in the external loss heat transfer rate.

Designing a novel small-scale parabolic trough solar thermal collector with secondary reflector for uniform heat flux distribution

This paper presents a new stepwise approach to design a medium-temperature solar parabolic trough collector with a secondary reflector, which is the fastest growing technology among concentrated solar power technology. The goal of the design is to have a homogeneous concentrated solar flux distribution with maximal output power over the receiver tube. Tonatiuh, a Monte Carlo ray-tracing based optical simulation software, has been used to conduct the ray-tracing analysis of the secondary reflector. Response surface methodology has been used to examine and select the desirable configuration of the solar collector system, and the findings have been analysed using the analysis of variance. It is found that the use of secondary reflector improves the uniformity of heat flux distribution to 0.58, whereas it is 1.0836 for the solar collector without the secondary reflector. For a target output power of 5.5 kW, the most attractive configuration has a maximum desirability value of 0.974. The computational fluid dynamics analysis has been performed in the configuration with better uniform heat flux and the collector without a secondary reflector, using the flux distribution acquired from the ray-tracing analysis. Results show that the use of secondary reflector significantly reduces the thermal gradient, and the heat flux distribution is found to be homogenous. By determining configurations with the best heat flux distribution against a specific output power, the approach provided in this paper lays the groundwork for future research on the design of parabolic trough solar collector systems with secondary reflectors.

Effects of the Conjugate Heat Transfer and Heat Flux Strength on the Thermal Characteristics of Impinging Jets

A numerical study using the conjugate heat transfer approach has been performed to investigate the effects of boundary heat flux, conduction effect, and working fluid on the thermal characteristics due to the jet impingement process. Air and water are used in this study as working fluids. For the water jet, the volume of fluid method is used to capture and track the interface in the multiphase flow. It is found that the wall conduction may change the fluid-solid interfacial thermal characteristics compared with no conduction or pure convection process. The amount of influence depends on the working fluid, nozzle size, metal thermal conductivity, metal thickness, and boundary heat flux. The conduction inside the solid wall tends to reorganize the uniform heat flux distribution at the boundary to a non-uniform heat flux distribution at the fluid-solid interface. This is mainly attributed to the conjugate effect of the solid. For a given jet Reynolds number and boundary heat flux, the conjugate heat transfer results divulge that the convective heat flux removed from the stagnation point is higher for the air jet than for the water jet. Contrary to the air jet, the effect of thermal boundary on the stagnation Nusselt number profile is negligible for the water jet. The disc material and thickness have no obvious effect on the stagnation Nusselt number profile for both air and water fluids.

Secondary Reflector and Receiver Positions for Uniform Heat Flux Distribution in Parabolic Trough Solar Thermal Collector

Abstract The distributions of heat flux over the circumference of the receiver tubes have an immense influence on the performance and reliability of the parabolic trough solar thermal collectors. The location of the receiver tube and the secondary reflector configuration may largely influence the performance of the system. Therefore, in this study, the effect of receiver tube position and parabolic secondary reflector configuration has been analyzed, and the non-uniformity of solar flux distribution, heat gradient, and power output has been compared. The results of the Monte Carlo ray-tracing analysis to homogenize the receiver tube flux distribution and maximize the output power, making the use of the cutting edge solar optical simulation tool Tonatiuh, has been presented. A parabolic trough collector with a rim angle of 80 deg and aperture area of 40 m2 have been used for the analysis. It has been confirmed that the circumferential heat flux gradient and the local hot spot could be greatly diminished, while the power output tended to reduce slightly due to the shading effect of the secondary reflector. Under the conditions investigated in this work, although the output power decreased by 4.83%, flux gradient reduced significantly, and the non-uniformity of flux distribution has reduced from 0.9757 to 0.5176. A simple design procedure for receiver tube position and secondary reflector configurations to homogenize the receiver tube temperature distribution has also been proposed.

Probing the Accuracy of Experimental Data on Nusselt Numbers Within Miniature Heat Sinks

Abstract Achieving accurate experimental data in conjugate heat transfer studies to calculate Nusselt number can be challenging due to its complex three-dimensional thermal hydraulics nature. This study is devoted to evaluating the accuracy and reliability of experimental approaches used to calculate the Nusselt number in miniature heat sinks. It is observed that three major parameters including (1) axial heat conduction within the solid substrate of heat sinks, (2) thermal contact resistance, and (3) assumed uniform wall temperature, as well as wall heat flux distributions, influence the reported experimental data in the literature. The results obtained from the developed analytical and computational models in this study revealed that the assumptions of local uniform wall temperature and heat flux distributions for small-scale heat sinks result in underestimated Nusselt numbers calculated from experiments. At lower Reynolds number (<200) flows in miniature heat sinks with a high solid to fluid thermal conductivity ratio (>> 1), it is shown that the fluid bulk temperature should be measured away from the heat sink inlet and outlet to minimize the effect of axial heat conduction within the solid substrate of the microscale heat sinks on calculated Nusselt numbers. As the third important parameter, the influence of thermal contact resistance on the Nusselt number calculation in a miniature heat sink is studied where thermal slip length is considered. Finally, the concurrent effects of thermal contact resistance and thermal developing region are considered to explicate the obtained trends in the experimental Nusselt numbers dataset.

Numerical study on preheating process of molten salt tower receiver in windy conditions

In the preheating process of the molten salt tower receiver, the thermal stress is large and the over-temperature problem is prone to occur. The finite volume method and two-dimensional thermoelastic method are combined in this paper to study the preheating process of the receiver tube in windy conditions. The experimental results of a lab-scale receiver verify the numerical model. Then, the influence of heat flux, wind speed, wind direction, ambient temperature and uniformity of heat flux distribution on the preheating process is explored. Finally, the influence of salt filling temperature and salt filling mass flow on the salt circulating is also revealed. The results indicate that the increase in heat flux, decrease in wind speed and increase in ambient temperature decrease the preheating time. The wind in the direction of 30° from the front side of the tube has the greatest influence on the preheating process. Compared with the no-wind condition, the preheating time increases by 177.5%. The maximum tube wall temperature and thermal stress are significantly higher under non-uniform heat flux distribution than those under uniform heat flux distribution. The salt inlet temperature and salt inlet mass flow respectively affect the stable value and reduction rate of thermal stress.

Analysis of thermal stress, fatigue life and allowable flux density for the molten salt receiver in solar power tower plants

Abstract The solar power tower (SPT) receiver design should be able to stand with fatigue damage caused by the passage of clouds, start-up and shut-down. In this paper, to investigate the impacts of incident heat flux distribution and SPT site weather data on the thermal stress, fatigue life and allowable flux density (AFD) of the molten salt receiver, the relationship between the fatigue life and AFD of the tube wall is developed based on the coupled thermal–structural analysis and Miner linear damage theory. The results show that the cosine effect of the circumferential heat flux distribution considered has a significant influence on the location and magnitude of the maximum thermal stress of the tube wall, which lead to the difference in the tube wall fatigue damage. The AFD are, respectively, 829 kW/m2 and 1037 kW/m2 under uniform and cosine circumferential heat flux distributions for the site of Barstow, USA, when the design lifetime of the tube is 30 years. Compared with the SPT site of Barstow, USA, the fatigue damage of the tube wall in Sevilla, Spain, and Delingha, China, are lower under the same conditions due to lower insolation hours of direct normal irradiation in the range of 750–1100 W/m2. The AFD are, respectively, 829 kW/m2, 973 kW/m2 and 997 kW/m2 for the site of Barstow, USA, Sevilla, Spain, and Delingha, China, with 30 years design life. These findings give guidelines for the operation reliability of the SPT molten salt receiver tube.

The effect of circumferentially non-uniform heat flux on flow boiling heat transfer in a horizontal tube

Flow boiling is an important energy transfer mechanism in several thermodynamic power cycles. In direct steam generation concentrated solar power applications, flow boiling occurs under non-uniform heat flux conditions, such as in horizontal tubes which are predominantly heated from below. This can influence the local and average heat transfer coefficient. In this experimental study the heat transfer characteristics of saturated flow boiling under different circumferentially non-uniform heat fluxes were determined. To demonstrate the influence of a non-uniform heat flux, tests were conducted on R245fa in an 8.5 mm inner diameter tube at a mass fluxes of 200 kg/m²s and 300 kg/m²s, at saturation temperatures of 35 °C and 40 °C, for vapour qualities between 0.2 and 0.7, and for an averaged heat flux of approximately 6.8 kW/m2. Eight non-uniform heat flux distributions, including variations of heating from above, from the side and below, were considered and their results were compared against those of a uniform heat flux distribution. In all cases, the same or comparable total heat rate was maintained. It was found that uniform heat flux conditions exhibited the highest inner wall heat transfer coefficients, irrespective of the mass flux, saturation temperature or vapour quality under consideration. Compared to the uniform heat flux cases, non-uniform heat flux conditions exhibited a significantly reduced average heat transfer which became worse at higher vapour qualities. Depending on the heat flux scenario, heat transfer performances reduced by up to approximately 45%, and for conditions where heating was applied from below, a reduction of approximately 25% was observed. Based on the circumferential local heat transfer coefficients, that were solved via an inverse problem model, it was concluded that the applied heat flux distribution needs more attention and research. The overall pressure drop was not affected by the heat flux condition.

Integrated optical-thermal-electrical modeling of compound parabolic concentrator based photovoltaic-thermal system

The main aim of this work is to propose an integrated optical, thermal and electrical model to obtain the overall performance of a concentrated photovoltaic-thermal system (CPV/T). Monte Carlo ray-tracing (MCRT) simulations are done to obtain the flux profile on the absorber of a compound parabolic concentrator (CPC) for various angles of incidence. The obtained heat flux is mapped onto the solar cell in the finite volume method (FVM) to obtain its temperature profile. The modelling is done for both glazed and unglazed compound parabolic concentrator-photovoltaic/thermal (CPC-PV/T) systems using uniform (average heat flux) and non-uniform heat flux distribution. The obtained numerical results are compared with experimental results available in the literature. The results show that the prediction is accurate, with a maximum deviation in solar cell temperature of less than 3%. The deviations obtained when using non-uniform heat flux are much less than when using average heat flux. The temperature contours show that the temperature profile of the photovoltaic module obtained by using local non-uniform heat flux is different from the temperature profile obtained by using average heat flux, and these results will have a greater impact when designing a cooling system.The absorbed radiation from the optical analysis and average cell temperature from the thermal analysis are given to the five parameter electrical model of a solar photovoltaic cell to obtain the electrical power output. With the results of the integrated optical-thermal and electrical model, the overall useful power from both glazed and unglazed CPC-PV/T systems is calculated. The results show that the performance of the unglazed CPC-PV/T system is superior to the glazed CPC-PV/T system in terms of electrical and overall system output. This work demonstrates the need for a local heat flux profile and a coupled multi-physics model to accurately predict the performance of a concentrated photovoltaic/thermal (CPV/T) system.

Experimental Investigation on the Heat Flux Distribution and Pollutant Emissions of Slot LPG/Air Premixed Impinging Flame Array

Experiments were carried out to investigate the heat transfer and pollutants emission characteristics of a slot LPG premixed flame array impinging normally onto a flat plate. The effects of jet-to-jet spacing (S/de), nozzle-to-plate distance (H/de), and jet Reynolds number (Re) on the heat flux and emission index of CO, CO2, and NOx/NO2 were examined. In addition, the thermal and emission characteristics between slot jets and circular jets were compared under identical experimental conditions. The results show that the more uniform heat flux distribution and higher total heat flux can be obtained at moderate jet-to-jet spacing, large jet-to-plate distance, and higher Reynolds number. EICO emissions can be influenced by the combined effects of jet-to-jet spacing, jet-to-plate distance, and higher Reynolds number. For the sake of the better combustion efficiency and lower EICO emission, the moderate jet-to-jet spacing (S/de = 2.5), larger jet-to-plate distance (H/de = 4), and relatively higher Reynolds number (Re = 1500) are preferred for the slot jet flame array. Furthermore, it is found that there exists a trade-off between the EICO and EINOx of the slot LPG flame array. Compared with multiple circular flame jets, multiple slot flames jets have the higher area-averaged heat flux due to the larger heating area and more uniform heat flux distribution, while the higher EICO emission and lower EINOx emission are due to the greater jet interaction suppressing the air entrainment. Thus, it is known that the slot flame array has a better heating performance but relatively higher pollutant emissions than the circular flame array.

Design of an auger thermo-radiation dryer for drying plant-derived pomace

This paper reports the improved model design of an auger thermo-radiation dryer for drying plant-derived pomace under a low-temperature mode (35...80 °C) to the resulting moisture content at the level of 8...13 % of solids. The dryer has an adjustable speed of auger rotation (3...4 min–1), of airflow (0.05...0.09 m/s), and is characterized by the uniform distribution of heat flux. It is equipped with an energy-saving two-circuit complex that utilizes secondary energy to heat primary air from 21.1 °C to 28.9 °C. The use of Peltier elements, installed at the heating technical surface of the dryer's auger, makes it possible to convert thermal energy into a low-voltage supply voltage for the autonomous supercharger and exhaust fans. The duration of pomace drying in the model structure of the auger thermo-radiation dryer has been determined, in particular tomato pomace, with an initial content of 75 % of solids, which is 107 min. For apple pomace whose starting content of solids is 65 %, it is 98 min. For comparison, the duration of the convective drying of tomato pomace (75 % of solids) is 120 minutes. The drying was carried out at a temperature of 60 °C to the resulting moisture content of 10...12 % of solids. Organoleptic evaluation on the example of tomato pomace confirms the effectiveness of structural solutions in the auger dryer compared to the convective technique. The results reported in this study could create conditions for the further design and implementation of the proposed structure of thermo-radiation dryer for drying plant-derived pomace involving an altered heat supply technique and the utilization of secondary energy. The designed structure of the device makes it possible to process and preserve the quality properties of plant-derived pomace, allowing the use of this product for a wide range of foodstuffs

A design method for optimizing the secondary reflector of a parabolic trough solar concentrator to achieve uniform heat flux distribution

Non-uniform solar flux distribution in a parabolic trough concentrator (PTC) causes large temperature gradients on absorber tube surface, making the PTC inefficient and damaged. To solve the problem, a novel method is proposed for designing the additional secondary reflector (SR) in a PTC to improve uniform heat flux distribution on absorber tube surface. In the design, the heat flux between upper and lower surfaces of absorber tube is well balanced by optimizing the location of absorber. Then, the SR with segmented broken-line type composed of multiple plane mirrors is delicately designed with local heat flux compensation strategy. Two case studies are conducted to compare the performances of the newly designed SRs with other existing SR designs. It is shown that the uniformity of heat flux distribution can be improved to over 90% for present SR design, much higher than those for other existing SR designs. Also, the optical efficiency of the PTC with present SR design is also increased as compared with other designs. The results indicate that this proposed method is competent for designing SR in a PTC with uniform heat flux distribution.

Sub-Channel Analysis of a Hexagonal Sub-Assembly: Influence of Blockage and Axial Power Distribution on Critical Heat Flux

Abstract The study of thermal hydraulics of a hexagonal sub-assembly is essential to ensure the safe operation of liquid metal cooled fast reactors. Identifying the dryout location in fuel sub-assembly (FSA) is a precursor to the determination of safe Critical Heat Flux (CHF) margins. In this study, a sub-channel analysis code coupled with a film thickness model is employed to predict the CHF location in a hexagonal sub-assembly. A simple post-CHF heat transfer model is proposed and validated against the experimental data. The nature of flow resistance changes and operating conditions would significantly influence the occurrence of CHF. To this end, the effect of blockage (0.0 ≤ b ≤ 0.3) and axial power distribution (APD) on CHF is systematically investigated in a hexagonal sub-assembly. It was observed that the presence of blockage causes coolant flow maldistribution which results in an early occurrence of CHF for higher mass flux (G > 1500 kgm−2s−1) and lower inlet subcooling (ΔTsub ≤ 30 K) conditions for b = 0.3. Furthermore, a comparative study of uniform and sinusoidal heat flux distributions is performed. It was noticed that sinusoidal APD causes the early occurrence of CHF compared to uniform APD.

Improvement of the performance of parabolic trough solar concentrator using freeform optics and CPV/T design

<abstract> The developmental tendency of parabolic trough collector (PTC) is larger aperture area for energy harvest and novel optical design for higher solar concentration. Larger aperture faces a higher demand in tracking accuracy and lower tolerances with respect to wind loads, quality of mirrors, control, and mounting imprecisions. With the increase of reflection angle, the divergence size of concentrated focal spot gets enlarged on receiving surface, forming a Gaussian distribution. Receiving more energy and making best use of the concentrated solar power have become a key problem. In current study, a novel trough free-form solar concentrator (TFFC) has been developed by extending the aperture size with the aid of freeform optics and combined PV/thermal utilization. The structure model is composed by traditional parabolic trough with thermal tube, and extended freeform reflector with solar panel in slope configuration. The free-form surface is generated by geometric construction method for the sake of uniform heat flux distribution. The optical characteristics are validated by ray tracing method. The advantages will be revealed by compared with traditional system. The sensitivity analysis and error factors would be discussed as well. The initial results are promising and significant for the enhancement of trough type solar concentrator systems. </abstract>

Experimental analysis of heat loss of a non – evacuated parabolic trough collector receiver subjected to uniform and non-uniform wall heat flux condition

ABSTRACT The parameters that largely influence the design and performance of a parabolic trough collector system for delivering process heat are optical efficiency, incidence angle modifier, solar irradiation data, and receiver heat loss. The heat loss and optical properties of a receiver greatly influence the overall efficiency of the solar thermal system. This paper focuses the attention on the experimental investigation of heat loss associated with a non-evacuated receiver subjected to i). Uniform wall heat flux (UWHF) and ii). Non – uniform wall heat flux (NUWHF) boundary condition. A series of heat-loss measurements are carried out in the novel test stand capable of emulating both the boundary conditions, on the indigenous non – evacuated receiver developed for moderate temperature process heat applications. A comparative analysis of natural and forced convection heat loss associated with the bare and glass-covered receiver is performed. The results show that the non – uniform wall heat flux boundary condition has a decisive influence over the forced convection heat loss, especially at higher wind velocities. The work concludes that i) the surface temperature of the receiver associated with natural convection heat loss and subjected to NUWHF boundary condition is1.5– 5% higher than the receiver subjected to UWHF boundary condition. ii) In forced convection mode of heat loss the surface temperature of the receiver is 4–13% higher than the receiver subjected to UWHF. Thus, a more realistic characterization of the thermal behaviour of a non-evacuated receiver for moderate temperature process heat application is possible only by investigating the receiver subjected to non – uniform heat flux distribution. Such a characterization of the receiver will considerably influence the aperture area and thus the cost of the collector to deliver process heat.

Integrated study of flue gas flow and superheating process in a recovery boiler using computational fluid dynamics and 1D-process modeling

Superheaters are the last heat exchangers on the steam side in recovery boilers. They are typically made of expensive materials due to the high steam temperature and risks associated with ash-induced corrosion. Therefore, detailed knowledge about the steam properties and material temperature distribution is essential for improving the energy efficiency, cost efficiency, and safety of recovery boilers. In this work, for the first time, a comprehensive one-dimensional (1D) process model (1D-PM) for a superheated steam cycle is developed and linked with a full-scale three-dimensional (3D) computational fluid dynamics (CFD) model of the superheater region flue gas flow. The results indicate that: (1) the geometries of headers and superheater platens affect platen-wise steam mass flow rate distribution (3%–7%); and (2) the CFD solution of the 3D flue gas flow field and platen heat flux distribution coupled with the 1D-PM affect the platen-wise steam superheating temperature (45%–122%) and material temperature distribution (1%–6%). Moreover, it is also found that the commonly-used uniform heat flux distribution approach for the superheating process is not accurate, as it does not consider the effect of flue gas flow field in the superheater region. These new observations clearly demonstrate the value of the present integrated CFD/1D-PM modeling approach.