Wall Heat Transfer Coefficient Research Articles

Numerical parametric study on the burner arrangement design for hydrogen production in a steam methane reformer

A numerical parametric study on the burner arrangement design for a steam methane reforming reactor was conducted under three burner configurations: a single co-axial inside burner (SCIB), a single top burner (STB), and multiple top burners (MTB). The burner combustion gas inlet angle was changed to 25°, 45°, and 90° with respect to the horizontal plane. Moreover, the number of reformer tubes inside the reactor was changed to four, six, and eight tubes arrangements. Furthermore, the models were numerically evaluated for temperature distribution inside the combustion space and hydrogen mole fraction in the reactor by incorporating the Xu and Forment model using a user-defined function (UDF). The results show that the STB configuration is preferable over the SCIB and MTB configuration due to the uniform temperature distribution inside the combustion space and efficient heating from the combustion gas. Furthermore, the standard deviation of the temperature inside the combustion space was found to be lower for the STB arrangement. Moreover, the STB configuration reported a maximum temperature uniformity index of 0.92 for the eight-tubes reformer arrangement. The value of the average wall heat transfer coefficient and wall heat flux at the reformer tube surface for STB configuration was 396.6 W/(m2K) and 21.7 W/m2, respectively. The velocity inlet angle of the burner combustion gas also plays an important role in the methane steam reforming reaction. A burner combustion gas inlet angle of 45° was observed to have better hydrogen conversion than the 25° and 90° inlet angles due to the proper mixing, leading to more effective heat transfer to the reformer tubes.

Parametric Study on Residential Passive House Building in Different Chinese Climate Zones

With the increasing of building energy consumptions, the related issues of energy crisis and environmental pollution become more and more prominent. As an effective energy-saving technology, the passive house (PH) has been widely applied in China to reduce the building energy utilization. However, the design and application of PH vary with different climate conditions. Therefore, it is significant to conduct the parameterization of PH and propose a suitable design zoning of PH in China. In our study, a comprehensive feasibility analysis of the implementation of PH is performed, which chooses 31 representative cities covering 5 climatic regions. The sensitivity analysis firstly filters the key parameters that heavily affect energy consumption. The results indicate that the key parameters include external wall heat transfer coefficient (WU), basement ceiling heat transfer coefficient (BCU), solar heat gain coefficient (SHGC), glass G value (UG), heat recovery efficiency (HERE) and humidity recovery efficiency (HURE). Then, with the multiple regression approach, the values of key parameters are optimized. Based on the determined values of sensitive parameters, the design zoning of PH in China is finally proposed, which can guide the design of PH as well as enhance the application of PH in China.

Efficient Evaluation of Heat Exchangers Behaviour in Nuclear Power Plants

This paper studies the performance of the primary and secondary flow paths of the Heat Exchangers (HEXs) in the Nuclear Power Plants (NPP). Explicit solutions for the wall temperature, primary and secondary wall temperatures of the HEX are presented. Therefore, closed form expressions for wall temperature, primary and secondary wall temperature are proposed. Moreover, performance analysis of HEX is investigated. Curves for the HEX wall temperature are introduced with special emphasis on the initial wall temperature. The various effects of pipe wall heat capacities, perimeter, fluid Heat Transfer (HT) coefficient and wall HT coefficient on the HEX are evaluated. The obtained results confirm that the surface contact between the two fluid passes reduces the temperature to some extent at 5 seconds. Furthermore, it is limited to the pipe length and contact time. As a final point of observation, the distributed temperature through the HEX structure increases with the decrease of perimeter. Since, the wall area decreases with the decrease of perimeter. The proposed work allows more control of the HT process within the HEX. Consequently, the performance of NPPs can be improved.

Effect of Joule heating on the electroosmotic microvortex and dielectrophoretic particle separation controlled by local electric field* *Project supported by the National Natural Science Foundation of China (Grant No. 11572139).

Dielectrophoresis (DEP) technology has become important application of microfluidic technology to manipulate particles. By using a local modulating electric field to control the combination of electroosmotic microvortices and DEP, our group proposed a device using a direct current (DC) electric field to achieve continuous particle separation. In this paper, the influence of the Joule heating effect on the continuous separation of particles is analyzed. Results show that the Joule heating effect is caused by the local electric field, and the Joule heating effect caused by adjusting the modulating voltage is more significant than that by driving voltage. Moreover, a non-uniform temperature distribution exists in the channel due to the Joule heating effect, and the temperature is the highest at the midpoint of the modulating electrodes. The channel flux can be enhanced, and the enhancement of both the channel flux and temperature is more obvious for a stronger Joule heating effect. In addition, the ability of the vortices to trap particles is enhanced since a larger DEP force is exerted on the particles with the Joule heating effect; and the ability of the vortex to capture particles is stronger with a stronger Joule heating effect. The separation efficiency can also be increased because perfect separation is achieved at a higher channel flux. Parameter optimization of the separation device, such as the convective heat transfer coefficient of the channel wall, the length of modulating electrode, and the width of the channel, is performed.

Heat transfer phenomenon and characteristics study of C-shaped tube with nucleate boiling in water tank

The Passive Residual Heat Removal Heat Exchanger (PRHR HX) is an important equipment of the passive safety system in advanced nuclear power plants such as AP1000. Heat transfer phenomenon and characteristics study of the PRHR HX has received more and more attention. However, the research of transient heat transfer under C-shaped tube outside pool boiling condition is insufficient and needs further investigation. An experimental facility was built and a series of experiments were conducted. Distributing and changing tendencies of some important parameters including tank water temperature, tube wall temperature and heat transfer coefficient were obtained and analyzed. This study can provide a reference for the thermal hydraulic design for the PRHR HX in nuclear power plant.

Optimization method for prefabricated restroom envelope energy saving characteristics in hot summer and cold winter zone

In order to reduce the restroom envelope energy consumption, one optimization method on basis of analyzing the influence of heat transfer coefficient on the performance of a prefabricated restroom envelope in a hot summer and cold winter zone was proposed. An energy-consuming model of prefabricated restroom in Nanjing is initially built based on Designer's Simulation Toolkit software. Subsequently, the effect of external walls, rooftops, external windows with various thermal characteristics on the building envelope is analyzed respectively. Simultaneously, a method that only changes the heat transfer coefficient of the prefabricated restroom envelope while keeping other parameters unchanged is adopted. Results show that, for a prefabricated restroom, the optimal range of heat transfer coefficient of the external wall, rooftop, and external window in hot summer and cold winter zone is 0.199∼0.22, 0.16∼0.19, and 3.0∼3.1 W/(m2·K), respectively. When the window-to-wall ratio is less than 0.2, the priority of the wall heat transfer coefficient on building energy consumption is higher than that of the rooftop heat transfer coefficient, simultaneously, the rooftop heat transfer coefficient has priority higher than window heat transfer coefficient. Thus, it is of great significance to optimize the design of the prefabricated restroom envelope in a hot summer and cold winter zone, which provides relative reference for thermal performance improvement of prefabricated restrooms.

The CFD studies on the influence of un-wetted area on the heat transfer performance of the horizontal tube falling film evaporation

This paper discusses about the effect of un-wetted area of tube on the heat transfer performance of horizontal tube falling film evaporation. A 2-D CFD model was developed to perform simulations and investigate the output and validated them with published data available in the literature. In the present study the volume of fluid method is used to track the boundary of the liquid vapour from the contours of volume fraction. Effect of varying tube wall temperature or wall super heat (6-11?C) on un-wetted area, heat transfer coefficients, and mass transfer coefficients of the circular tube were obtained from the simulation model and the results were analysed and reasons were identified and discussed here. The threshold value of wall super heat above which phase change occurs between liquid film and tube surface is identified as 6?C. Also it is noted that mass transfer rate increases and then decreases with increase of wall super heat and heat transfer coefficient showed declining trend.

Wood plastic composites based wood wall's structure and thermal insulation performance

In order to solve the problem of poor thermal insulation in the current wood-plastic building, two kinds of structural wood wall integrated with wood plastic composite (WPC) are designed, and the thermal insulation performances of the walls are studied. The results show that the WPC integrated wall with frame-shear structure has a good stability, and the excellent performance of the WPC can be fully realized. Wall studs and wall panels are important factors affecting the thermal performance of the walls. Wood plastic materials can meet the thermal performance requirements of the walls. The single-layer frame walls and double-layer frame walls integrated with the WPC both have a good thermal performance. According to ‘Design Standard for Energy Efficiency of Public Buildings (GB 50189-2015)’, the heat transfer coefficient of the single-layer frame wall integrated with 20 mm thick WPC wall boards and WPC wall studs is 0.414 W/(m2•K), which can meet the standard of wall thermal level Ⅱt and is suitable for cold areas. The heat transfer coefficient of the double-layer frame wall integrated with 50 mm thick WPC wall panel and WPC wall studs is 0.207 W/(m2•K), which can meet the standard of wall thermal level Ⅰt and is suitable for severe cold areas.

Enhancing public building energy efficiency using the response surface method: An optimal design approach

Today, energy problems are becoming increasingly serious. The direct energy consumption of buildings accounts for 20% of the total energy consumption in a country. There are difficulties in continuing the mode of high energy consumption in the traditional construction industry. Therefore, the future of construction is in the development of green buildings. In the life cycle of a building, the consumption during the construction phase accounts for only approximately 20% of the total energy consumption. Most of the consumption occurs during buildings operations, such as lighting, heating, air conditioning and the running of various electrical appliances. Therefore, this paper focuses on the energy consumed during the building operation period with the aim of optimizing relevant design parameters to reduce total energy consumption. The West Twelfth Teaching Building (WTTB) of Huazhong University of Science & Technology (HUST) is used as a prototype, and Design Builder is used to establish a model of energy consumption and validate the reliability of the model based on the data obtained from the investigation. Based on this model, the study takes the perspective of energy conservation to analyze ten factors that may affect the energy consumption of the building: the heat transfer coefficient of the roof, the amount of fresh air, the heat transfer coefficient of interior walls, the heat transfer coefficient of the floors, the interior temperature, the energy efficiency ratio of the air conditioner, the thickness of the outer wall insulation, the ratio of windows to walls, the natural ventilation starting temperature and the solar heat gain coefficient of the outer windows. Those factors are then ranked according to their energy-saving potential through partial factorial design tests. The six factors with the most potential for energy savings are selected and divided into 2 groups to conduct a response surface optimization analysis of three factors at three levels. The best level of each factor and the optimal combination of all factors are obtained to reduce building energy consumption to the greatest possible extent and to provide a reference for teaching buildings and similar public buildings (PBs) in achieving the goal of “green building.”

Computational fluid dynamic simulations of solidification for enhancing speed of continuous cast copper

In this research experiment computational fluid dynamic (CFD) models were constructed, within Ansys Fluent TM v.R1, to investigate phenomena occurring during the Vertically Upwards Continuous Casting (VUCC) of 8 mm diameter, oxygen free copper (OFCu) for alterations to the casting speed. The simulated influence of heat transported over a 0.1 mm air gap formed within the casting die was investigated and a value for the die wall heat transfer coefficient (hc) of (9.0 ± 0.2) × 104 W/m2K, was extracted. Using this value for hc, simulations of the entire casting crucible and die were made for casting speed settings: pushback motion at 0.06 m/s, average; dwell motion (pause) at 0.05 m/s, average; and continuous motions at 0.022 m/s, 0.015 m/s and 0.008 m/s; and were validated against literature values for measured thermal distribution within the casting die. The fastest casting speed for 8 mm OFCu was investigated and a trend between simulated solidification front and measured grain growth direction was identified, highlighting, the casting motions pushback and dwell yield improved casting conditions. Fluid flow rate was investigated within the casting crucible and showed a small influence on casting due to natural convection relative to flow within the die, 0.001 ± 0.0005 m/s compared with 0.1 ± 0.01 m/s for pushback casting, respectively.

Experimental investigation on heat transfer characteristics of high temperature air in round tube

Air is widely utilized as working fluid in heat exchangers with high heat flux and high temperature, and the empirical correlations for predicting local and total heat transfer coefficients are indispensable for thermal design and optimization of the heat exchange applications. Experimental investigation on heat transfer characteristics of high temperature air in round tube is conducted. The experimental system is designed and constructed. The data processing method for obtaining wall temperature and heat transfer coefficient is introduced. The measured local and total heat transfer coefficients are compared with the widely adopted correlations, including Taylor's correlation and Gnielinski's correlation. The suggested empirical correlations obtained from the experimental data are presented, which may contribute to the design of heat exchangers concerning with high temperature air.

Simulation study of the cooling effect of blood vessels and blood coagulation in hepatic radio-frequency ablation

Purpose Computer simulations of hepatic radio-frequency ablation (RFA) were performed to: (i) determine the dependence of the vessel wall heat transfer coefficient on geometrical parameters; (ii) study the conditions required for the occurrence of the directional effect of blood; and (iii) classify blood vessels according to their effect on the thermal lesion while considering blood coagulation. The information thus obtained supports the development of a multi-scale bio-heat model tailored for more accurate prediction of hepatic RFA outcomes in the vicinity of blood vessels. Materials and methods The simulation geometry consisted of healthy tissue, tumor tissue, a mono-polar RF-needle, and a single cylindrical blood vessel. The geometrical parameters of interest were the RF-needle active length and those describing blood vessel configuration. A simple, novel method to incorporate the effects of blood coagulation into the simulation was developed and tested. Results A closed form expression giving the dependence of the vessel wall heat transfer coefficient on geometrical parameters was obtained. Directional effects on the thermal lesion were found to occur for blood vessel radii between 0.4 mm and 0.5 mm. Below 0.4 mm blood coagulation blocked the flow. Conclusions The closed form expression for the heat transfer coefficient can be used in models of RFA to speed up computation. The conditions on vessel radii required for the occurrence of directional effects on the thermal lesion were determined. These conditions allow the classification of blood vessels. Different approximations to the thermal equation can thus be used for these vessel classes.

CFD-Based Investigation of Lubrication and Temperature Characteristics of an Intermediate Gearbox with Splash Lubrication

In this study, we propose a computational fluid dynamics (CFD)-based method to study the lubrication and temperature characteristics of an intermediate gearbox with splash lubrication. A volume of fluid (VOF) multiphase model was used to track the interface between oil and air. A multiple reference frame (MRF) model was adopted to accurately simulate the movement characteristics of the gears, bearings, and the surrounding flow field. The thermal-fluid coupling computational model of an intermediate gearbox with splash lubrication was then established. Combined with experimental results, we verified that the lubricating oil temperature was below the limit requirement (<110 °C). The numerical results revealed that large amounts of lubricating oil were splashed onto the tooth surfaces near the gear meshing area. A large convective heat transfer coefficient corresponds to a low gear tooth surface temperature. The tooth surface temperature of the driving gear is higher than that of the driven gear. The distribution law of oil volume fraction of the bearing roller was jointly affected by the roller rotation direction and gravity. The convective heat transfer coefficient of the roller wall was largely related to the lubrication environment of the roller, including the oil distribution inside the bearing cavity and the flow rate.

Flow Regime Transition in the Post-CHF Flow Regimes under Subcooled and Low-quality Conditions

Post critical heat flux (post-CHF) heat transfer may occur during loss of coolant accidents (LOCAs) in water-cooled nuclear reactors when makeup water quenches the uncovered portion of fuel rods in the reactor cores. Post-CHF flow regimes include inverted annular film boiling (IAFB), dispersed flow film boiling (DFFB), and a transition regime between these two, i.e., inverted slug film boiling (ISFB) for low mass fluxes or agitated inverted annular film boiling (AIAFB) for high mass fluxes. Flow regime transition is important for modeling heat transfer characteristics in the post-CHF flow regimes. Breakup of the liquid core in the IAFB regime represents the flow regime transition from the IAFB to ISFB/AIAFB regimes. This paper first presents a literature review of previous experimental and theoretical studies of the mechanisms of breakup of the liquid core in the IAFB regime and flow regime transition in the post-CHF regimes. To physically explain the breakup of the liquid core in the IAFB regime, the Weber number is calculated from the experimental data obtained from steady-state post-CHF experiments at subcooled and low-quality conditions and a critical Weber number is obtained to describe the flow regime transition from the IAFB to ISFB/AIAFB regimes. Parametric effects of the inlet subcooling, mass flux, and system pressure on the critical Weber number are then studied, based on which a new correlation for the critical Weber number is proposed to predict the flow regime transition from the IAFB to ISFB/AIAFB regimes. Due to the different flow patterns in the transition regime, i.e., ISFB and AIAFB respectively for low and high mass fluxes, the heat transfer characteristics show different trends. The indication of the flow regime transition from the IAFB to ISFB/AIAFB regimes by the critical Weber number criterion matches well with the trend of the wall heat transfer coefficient.

Enhancing the Thermal Performance of Slender Packed Beds through Internal Heat Fins

Slender packed beds are widely used in the chemical and process industry for heterogeneous catalytic reactions in tube-bundle reactors. Under safety and reaction engineering aspects, good radial heat transfer is of outstanding importance. However, because of local wall effects, the radial heat transport in the vicinity of the reactor wall is hindered. Particle-resolved computational fluid dynamics (CFD) is used to investigate the impact of internal heat fins on the near wall radial heat transport in slender packed beds filled with spherical particles. The simulation results are validated against experimental measurements in terms of particle count and pressure drop. The simulation results show that internal heat fins increase the conductive portion of the radial heat transport close to the reactor wall, leading to an overall increased thermal performance of the system. In a wide flow range (100<Rep<1000), an increase of up to 35% in wall heat transfer coefficient and almost 90% in effective radial thermal conductivity is observed, respectively.

Analysis on Influencing Factors of Energy Consumption of Public Buildings in Cold Areas

DeST-c software was used to build the building model, and the single factor experiment method was used to carry out the simulation study. Under the condition that only single factor was changed and other influencing factors were unchanged, the influence law of each energy influencing factor on energy consumption was analyzed, and the influencing factors were Analysis of the impact degree on energy consumption, the results are as follows: body shape coefficient > outer window heat transfer coefficient > outer wall heat transfer coefficient > south window ratio > roof heat transfer coefficient > north window and wall ratio, namely, body shape coefficient, outer window transmission. The thermal coefficient and the external wall heat transfer coefficient are the main influencing factors of building energy consumption.

A web application for analysis of heat transfer through building walls and calculation of optimal insulation thickness

Controlling heat transfer and managing heat flows in a building has become very important in recent years and is essential to ensure the thermal comfort of occupants, increase energy efficiency, and sustainable development. These measures reduce energy consumption in buildings, save resources and money and at the same time reduce pollution and CO2 emissions into the atmosphere, as the severity of the climate increases. The paper describes the analytical method used to analyse the one-dimensional, steady-state heat transfer through homogeneous walls and composite walls of buildings (wall structure may contain different construction materials, air spaces, insulation, etc.). The web application allows users to analyse one-dimensional and steady-state heat transfer through the building walls and calculate the heat flux density, total heat flux, overall heat transfer coefficient of the building wall, thermal resistance, temperature profile through the wall, the specific thermal resistances and the temperatures at the interface between wall layers. The user can analyse the one-dimensional, steady-state heat transfer through homogeneous and multilayer walls of buildings, being able to analyse a wall composed of a single layer, or one with a maximum of seven layers. The application allows the user, after defining the cross section’s geometry, materials properties, and boundary conditions, to determine the optimal insulation thickness, depending on its placement, on the inner or outer wall surface.

Field Test and Simulation Analysis of Thermal Performance of Bamboo Steel Composite Wall in Different Climate Regions

In this paper, a bamboo steel composite testing building was designed and built to study the thermal performance of a new proposed bamboo steel composite wall. The heat flux meter method was adopted in the field test to measure the heat transfer coefficient of the composite wall. The energy consumption of testing building was measured to verify the validity of the simulation model. Then, the simulation analysis was conducted to study the energy performance of the composite walls compared with reinforced concrete wall in different climate regions. The result showed that the measurement value of heat transfer coefficient matched well with the theoretical calculation value, and both values meet the requirement of the standard. The simulation result showed that the composite walls had better energy performance and had great potential utilization in residential buildings in different climate regions.

Membrane catalyst layer assembly production method and membrane catalyst layer assembly production device

A detailed computational fluid dynamics (CFD) model has been developed in this study for the water gas shift of untreated biogas reformate in both fixed bed and membrane reactors to gain insights into the interaction of 3Ni5Cu/Ce0.5Zr0.33Ca0.17 catalyst with fluid transport phenomena taking place in the reactor. The developed CFD model closely agreed with data from both literature and experiments. An average absolute deviation of 8.59% and 6.32% was obtained when the CFD model was validated with a fixed bed reactor and membrane reactor experiments respectively. The membrane reactor enabled equilibrium conversion at 2.95 gcat.h/mol CO weight-time with equilibrium conversion attained at lower weight-time and steam to carbon ratio of 3.4. Also, it was found that the counter-flow configuration resulted in better enhanced CO conversion, and the wall heat transfer coefficient above 8.6 W/m2/K had negligible on conversion, amounting to only a 1% increase in conversion for both reactors.

Condensation Heat Transfer of R-407C in Helical Coiled Tube Heat Exchanger

The results of an experimental study to evaluate the characteristics of R-407C thermofluid during condensation in a helically coiled copper tube heat exchanger are presented. The effects of saturation temperature (Tsat), and mass and heat fluxes of refrigerant R-407C on thermal performance and pressure drop were determined. The relationship between the refrigerant wall subcooling and heat transfer coefficients was also investigated. This paper reports the effect of the temperature of the water used as cooling medium on the heat transfer rate of condensing R-407C. The study was conducted with mass flux of R-407C in the range of 100–450 kg/m2s, mass flux of the coolant water in the range of 500–5000 kg/m2s and Tsat of 31 °C, 35 °C, and 39 °C. Compared with a straight smooth tube, the use of the helical coiled (helicoidal) tube increased the condensation rate with a corresponding pressure drop that depended on the value of Tsat of the refrigerant and temperature of the coolant.