Heat Transfer Calculation Method Research Articles

Simulation of air pipe heat dissipation in civil aircraft water system based on flowmaster

Abstract The water supply method of civil aircraft water system is mainly from the bleed air system to pressurize the water tank. However, the gas temperature from the bleed air system is often too high. The AC-25.863 draft [1] stipulates that the maximum surface temperature of the equipment should be lower than 50°F below the spontaneous combustion point of flammable liquid in the area. Otherwise, it will become the ignition source of flammable materials. In this paper, by establishing the heat transfer model of an air pipeline, a set of air duct heat transfer calculation methods is proposed, and the variation rule of air pipe surface temperature is studied, to verify that the gas temperature from the bleed air system meets the requirements of the system, and the air pipe surface temperature meets the requirements of AC-25.863 draft.

Using Fourier series to obtain cross periodic wall response factors

Wall periodic response factors are a very usual calculation method of transient heat transfer through building envelope elements (walls, roofs …) in steady periodic conditions, used in popular heat load calculation procedures as ASHRAE’s RTS method [Spitler, Jeffrey D., Daniel E. Fisher, and Curtis O. Pedersen. 1997. “The Radiant Time Series Cooling Load Calculation Procedure.” ASHRAE Transactions 103 (2): 503–515]. This response factors, time sampled heat flux responses of a multi-layer wall to a 24h-periodic unit triangle function, can be obtained by means of multiple methods: Laplace’s method, state space method, frequency domain methods, etc. These methods are numerical since there is no analytical way of obtaining these response factors. The aim of this work is, taking advantage of the periodic nature of excitations, use Fourier series to represent boundary conditions, and this way find an easier and less computationally demanding procedure to calculate these response factors. Additionally, the convergence of these Fourier series will be analysed to determine the minimum set of frequencies needed to ensure a fixed admissible error for wall periodic response factors.

Experimental and Numerical Investigations on the Heat Transfer Performance of a New Type of Energy Pile

The ground‐source heat pump heating and cooling system is currently the most important development and utilization method of shallow geothermal resources, but its key component is the ground heat exchanger system. Herein, a new type of ground heat exchanger, the soil‐cement energy pile, is proposed. The similarity model comparison experiments of the soil‐cement energy piles and the soil energy pile in summer and winter were conducted respectively, and the 3D numerical models of heat transfer of the two kinds of energy piles are established, their related thermal properties are verified. Then the heat transfer calculation methods of the soil‐cement energy pile are presented and validated. The research has shown that the soil‐cement energy pile has good thermodynamic performance, which effectively reduces the largest thermal resistance in the heat transfer system of the energy pile, the thermal resistance of pile body material, and the heat transfer per linear meter of the soil‐cement energy pile is 21.20%–55.60% higher than that of the soil energy pile. The soil‐cement energy pile is of great significance to improve the thermal efficiency of the ground‐source heat pump system and can reduces the overall project cost.

Asymmetric Heat Transfer in Aircraft Electrothermal Anti-Icing

Aircraft icing is an important cause of air disasters, and electrothermal anti-icing is a common protection method. In this work, the influence of icing meteorological conditions on the anti-icing was studied through an icing wind tunnel experiment on the fairing. Based on the finite volume method, a transient heat transfer calculation method for electrothermal anti-icing was proposed. The calculated results were compared with the experimental results, and the influence of heating mode and structure layout on the anti-icing effect was analyzed. The results show that the calculated results are in good agreement with the experimental results, and the heat transfer of the anti-icing structure shows obvious asymmetry. First, during heating, the temperature gradient of the structural profile is large, the high temperature is concentrated in the heating layer, and the temperature distribution of the heating layer is relatively uniform. During cooling, the temperature distribution of the structural profile is more uniform, the high temperature is mainly concentrated in the back conduction layer, and the temperature of the outer wall increases first and then decreases from the center to the surroundings. Second, when the spray is turned on, the temperature of the outer wall is significantly reduced, but the temperature of the heating layer hardly changes. Third, the uniform heating mode can simultaneously raise the temperature of the outer wall and reduce the temperature of heating layer. Fourth, while the front conduction layer can significantly affect the temperature of the heating layer and the outer wall, the effect of the back conduction layer is small. However, the back one can be used to control the structural temperature more finely.

Numerical method for gas-liquid two-phase flow with phase change heat transfer considering compressibility using OpenFOAM

The numerical simulation of phase change heat transfer is important for predicting the gas-liquid two-phase flow and heat transfer characteristics and optimizing the phase change heat dissipation system. For the isovolumetric phase change heat transfer process, the compressibility of the gas phase has a significant impact on the simulation accuracy. A numerical simulation method of flow and phase change heat transfer considering gas-liquid two-phase compressibility is established based on VOF method using OpenFOAM in this paper. This method introduces a generalized phase change source term and a compressible source term to improve the isoAdvector geometric reconstruction algorithm and establishes a method for capturing the phase interface of a compressible two-phase flow. The phase change flux based on the phase interface is converted into a phase change source term based on the unit volume by calculating the phase interface density. The compressible term of the governing equation is constructed and its implicit discrete method is proposed. The coupling between velocity and pressure is realized based on the PISO algorithm. A numerical calculation method for phase change heat transfer of compressible two-phase flow is established. The effectiveness and accuracy of the proposed numerical method for predicting the heat transfer characteristics of phase change flows are verified by the simulation of vertical flat film condensation and film boiling. The numerical simulation results are in good agreement with the experiment. Compared with the other numerical simulation methods, the proposed method considering the influence of the compressibility of the gas phase on the flow and heat transfer characteristics in the heat pipe has high accuracy in predicting the gas-liquid two-phase flow, capturing the evolution characteristics of the phase interface and predicting the phase change heat transfer. The numerical simulation method can provide algorithm support for the numerical simulation of compressible two-phase flow phase change heat transfer and the design of a phase change heat dissipation system.

Analysis of Fin Interruptions on the Natural Convection of Heat Sinks

For heat sinks with high fins used in outdoor high-power electronic equipment, this paper proposes a natural convection heat transfer calculation method based on the chimney effect and uses this method and numerical simulation to analyze the heat transfer performance of the heat sinks with interrupted fins. Results show that the interrupted fins effectively improve the convective heat transfer coefficient of the fins by breaking the thermal boundary layer of the fins, and have a significant effect on the air flow between the fins. When the fin interruption length is 1mm and the number of interrupts is 15, the natural convection heat transfer performance of the heat sink is the best. Compared to heat sinks of the same size without interrupted fins, the thermal performance has been improved by 80% while reducing weight by 7%.

Разработка методики для расчета теплопередачи потолочных водяных капиллярных систем низко-температурного отопления

The purpose of this work is development of the heat transfer calculation method of a water low-temperature ceiling capillary heating system for heating rectangular rooms. Recently, such systems have become widespread due to their advantages over traditional heating devices: the use of a coolant with a low temperature potential, high heating speed rate of the internal air, low temperature gradient in the height of the room, absence of noticeable air masses movement and dust flows, ability to work in cooling mode. However, such systems are still incompletely studied, and constructive calculations or calculations of thermal and hydraulic modes are carried out according to formulas obtained empirically, thus, calculations do not always have high accuracy. The paper proposes a heat transfer process calculation method from the considered low-temperature heating system, which allows determination of the heat flow value with high accuracy. It`s revealed that in the considered configuration of the system location (on the ceiling), a significant proportion of heat transfer is infrared radiation, and the convective component is very small. Therefore, it was very important to accurately describe the radiant heat exchange by mathematical equations. The calculation of the radiant component of heat transfer was carried out with the theory of radiation view factors. Experimental test of the studying object was carried out to find the missing values, as well as to verify the results obtained using the proposed calculation method. The calculation results had a slight deviation from the results obtained experimentally (the error was 6 %).

Examination on aerogel based on the heat transfer characteristics of nanotechnology

With the rapid development of global industrialization, the research and development of new thermal insulation materials has great social and economic significance for national development and social progress. Due to the porous network structure of nanotechnology, the porosity of aerogel is 80–99.8%, the thermal conductivity can be as low as 0.013 w/(m k) at room temperature. It is the best insulation material by far, it has important value in the fields of aerospace, petrochemical, electric metallurgy, shipbuilding, precision instruments and so on. This paper is based on aerogel nanotechnology materials at home and abroad. In order to solve the problem of the study on heat transfer characteristics based on nanotechnology is not perfect, and the calculation model of solid phase thermal conductivity coefficient and total thermal conductivity of complex nanotechnology structure is not accurate enough. Through a heat transfer calculation method suitable for nanotechnology to conduct more detailed and in-depth research on these issues, introduces and analyzes the development of the equivalent thermal conductivity calculation model of Novel Aerogel nanotechnology insulation material in recent years. And analyzed The heat transfer characteristics and thermal insulation principle of nanotechnology aerogel by using equivalent thermal conductivity calculation model of aerogel nanotechnology insulation material. Research indicates: For aerogel nanotechnology materials, Use heat transfer calculation method aerogel nanotechnology insulation materials can be well calculated using a heat transfer calculation method that suitable for nanotechnology can calculate the equivalent thermal conductivity of aerogel nanotechnology insulation material very well; nanotechnology particles and aerogel meshes and continuous spatial network structures are reason for the very low thermal conductivity of aerogels; The heat transfer of the material is mainly achieved by convection, radiation and heat transfer. So it is possible to reduce the thermal conductivity from the heat transfer path of the material.

Average Wall Radiative Heat Transfer Characteristic of Isothermal Radiative Medium in Inner Straight Fin Tubes

Abstract Wall radiative heat transfer in inner straight fin tubes is very complex considering the coupling of heat conduction in fins and radiative heat transfer of medium with solid surfaces, influenced by a number of factors such as fin parameters, radiative properties and run conditions. The method of simulation is very inconvenient to design the heat exchanger involving the enhancement of inner straight fins on wall radiative heat transfer in tube, such as ascension pipe heat exchanger and radiant syngas cooler. In this study, a simplified method is used. The average radiative heat transfer between radiative medium and solid surfaces is first studied by simulation with fins supposed have a constant temperature. Then an approximate correlation of this radiative heat transfer coefficient is proposed using the traditional radiative heat transfer calculation method with a view coefficient, which has a little error within 15%. A calculation method of average wall radiative heat transfer coefficient is further derived based on fin theory with an average temperature of fin surface used to consider the varying of the temperature along the fin when the conductivity of fins is finite. Using the predicting method proposed, a method for design calculation of fins in tubes to optimize wall radiative heat transfer is also given with three dimensionless numbers of π/n, 2H/D, and nt/πD representing the structural properties of fins defined. Three cases of (ks = 43 W/(m•K), ɛw = 0.7, Tg = 1073.15 K, Tw = 573.15 K, D = 0.66 m, κD = 1.32), (ks = 162 W/(m•K), ɛw = 0.7, Tg = 1073.15 K, Tw = 573.15 K, D = 0.66 m, κD = 1.32) and (ks = 43 W/(m•K), ɛw = 0.3, Tg = 973.15 K, Tw = 673.15 K, D = 0.66 m, κD = 0.66) are analyzed in detail based on the design calculation method. It is verified that the radiative heat transfer could be enhanced twice by introducing fins. Under the same h0, conductivity and emissivity are two important factors that should be considered to choose the material for fins. The microfins or the special treatments on the tube wall are a best choice for the fin material having a relatively small conductivity.

Modeling Study on Heat Transfer in Marangoni Dropwise Condensation for Ethanol-Water Mixture Vapors

In this paper, a model was developed to predict the heat transfer characteristics of Marangoni dropwise condensation. In accordance with the feature of Marangoni condensation, condensation was treated as dropwise condensation of mixture vapors. The condensation space was divided into two parts: the vapor diffusion layer and the condensate layer. For the condensate layer, the classical heat transfer calculation method of dropwise condensation was imitated to obtain the heat transfer characteristics. For the vapor diffusion layer, the heat transfer characteristics were achieved by solving the conservation equations. These heat transfer characteristics were coupled through the conjunct boundary, which was the vapor-liquid interface. The model was applied to the condensation of water-ethanol mixture vapors. A comparison with the existing experimental data showed that the developed model could basically reflect the influences of vapor-to-surface temperature difference, vapor concentration, vapor pressure, and vapor velocity on heat transfer characteristic of Marangoni condensation. Results showed that some differences existed between the calculation results and experimental results, but the prediction deviation of the model could be acceptable in the range of vapor-to-surface temperature difference where the condensation heat transfer coefficients reached peak values.

Cooling structure design of gas turbine blade by using multi-level highly efficient design platform

In this paper, the internal cooling structure of a second-stage rotor blade is designed by using a multi-level highly efficient design platform. The design process is divided into schematic design and detailed design in sequence. The calculations of pipe-network and heat conduction are presented to preliminary evaluate the cooling structures derived from the schematic design stage. The flow field and heat transfer characteristics of the revised cooling structures are analyzed in the detailed design by using the three-dimensional conjugated heat transfer calculation method. Topological structure, mass flow rate, pressure distribution, heat transfer coefficient and temperature distribution of the cooling channels are presented. It is found that the schematic design results based on one-dimensional to three-dimensional solution method are in good agreement with the detailed design results. Meanwile, the introduction of the schematic design is helpful to shorten the cooling design cycle and reduce the dependence of the design experience. In this work, a five-pass serpentine passage with single cooling air inlet in the cooling system may lead to low flow rate at the trailing edge, which is prone to cause hot gas back-flow and local high heat load. The cooling system with a right-angle channel and a three-pass serpentine channel helps to distribute the flow reasonably and reduce the thermal gradient on the blade surface. The optimal cooling structure meet the requirements well. Compared with the uncooled blade, the average temperature of the blade decrease over 530 K with limited cooling air.

ON A METHOD FOR CALCULATING HEAT TRANSFER IN A MOVING FLUID TAKING INTO ACCOUNT ENERGY DISSIPATION

An approximate analytical solution to a heat transfer problem for a moving fluid in a cylindrical channel is obtained using an additional new function and additional boundary conditions in the heat balance integral method and taking into account energy dissipation under a first-order boundary condition that varies along the longitudinal coordinate. The use of an additional new function that determines the temperature change along the longitudinal variable in the center of the channel makes it possible to reduce the solution of the partial differential equation to the integration of an ordinary differential equation. Additional boundary conditions are found in such a way that their satisfaction for the new solution is equivalent to the satisfaction of the differential equation at boundary points.

The Model and Experiment for Heat Transfer Characteristics of Nanoporous Silica Aerogel

Nanoporous silica aerogel insulation material is both lightweight and efficient; it has important value in the fields of aerospace, petrochemicals, electric metallurgy, shipbuilding, precision instruments, and so on. A theoretical calculation model and experimental measurement of equivalent thermal conductivity for nanoporous silica aerogel insulation material are introduced in this paper. The heat transfer characteristics and thermal insulation principle of aerogel nano are analyzed. The methods of SiO2 aerogel production are compared. The pressure range of SiO2 aerogel is 1Pa-atmospheric pressure; the temperature range is room temperature-900K. The pore diameter range of particle SiO2 aerogel is about 5 to 100 nm, and the average pore diameter range of about 20 ~ 40 nm. These results show that experimental measurements are in good agreement with theoretical calculation values. For nanoporous silica aerogel insulation material, the heat transfer calculation method suitable for nanotechnology can precisely calculate the equivalent thermal conductivity of aerogel nano insulation materials. The network structure is the reason why the thermal conductivity of the aerogel is very low. Heat transfer of materials is mainly realized by convection, radiation, and heat transfer. Therefore, the thermal conductivity of the heat transfer path in aerogel can be reduced by nanotechnology.

The Comparative Analysis of External Heat Transfer Calculation Methods for a Solar Aircraft Spacesuit

This article presents an assessment of the external thermal load on the life support system of a solar aircraft under extreme operating conditions. The calculation was carried out for the maximum and minimum possible heat flows in the key points of the aircraft flight. In this article the conditions on the Earth’s surface and at the operating altitude of the aircraft were taken as calculated. The dependence of the quantitative changes in the heat load on the aircraft from altitude was revealed, taking into account changes of thermal properties of the environment and mechanisms of heat transfer.

Study on calculation method of condensation heat transfer for non-azeotropic hydrocarbon mixtures in helically coiled tubes

In order to study the condensation heat transfer characteristics of non-azeotropic hydrocarbon mixtures in helically coiled tubes for large-scale spiral-wound heat exchangers, a simplified physical model of three-section helical tubes was proposed. Reasonable governing equations and boundary conditions were set up, and the grid independence was verified. Then, the condensation heat transfer characteristics of mixture refrigerants were analyzed. In addition, considering the effect of mass transfer resistance of non-azeotropic mixtures on heat transfer during condensation, a method combining numerical simulation with the Bell and Ghaly correction method was proposed to calculate the condensation heat transfer coefficient of mixtures. By comparing with the experimental results, the accuracy of the calculation model is verified, which provides theoretical support for the design of large-scale spiral-wound heat exchangers.

A heat transfer calculation method and primary verification for high-temperature fluid transmission and distribution network from EAST

High-temperature fluids are widely used in many industrial and scientific fields such as steam power generation, oil extraction and transportation, chemical heating catalysis, high-temperature pasteurization of pharmaceuticals and food products, high-temperature printing and dyeing, residential heating, and especially in the nuclear fusion research (baking and power generation). The high-temperature fluid supply network is a transportation channel that takes the high-temperature working fluid from the heat source to the heated areas or end users. This paper introduces the heat transfer calculation method for high-temperature fluid transmission and distribution networks. This calculation method has been verified by the high-temperature nitrogen baking process of the pipe network at EAST (Experimental Advanced Superconducting Tokamak). With the experimental results showing the method to be more than 98 % accurate. This method can be used to precisely design the flow within the distribution network while simultaneously calculating the flow rate, and temperature of the working fluid as well as safety information such as the pipe and insulation temperature throughout the network. Furthermore, this calculation method is not only suitable for the high-temperature fluid transmission and distribution network but also for that of the low-temperature fluid transmission and distribution network, making this calculation method become a very important component of the Fusion Reactor Thermal Hydraulic Analysis Method (FRTHAM).

Heat transfer calculation methods in three-dimensional CFD model for pulverized coal-fired boilers

Computational fluid dynamics (CFD) has been used extensively to study the combustion characteristics of coal-fired boilers. However, very limited of the boiler CFD studies were used to quantitatively predict the heat transfer distributions in practical boiler applications. This paper presents a systematic description on the heat transfer calculation methods in three-dimensional CFD model for coal-fired boilers. The primary objective is to provide a set of heat transfer submodels that can be easily employed to solve and analyze large scale practical boiler problems. All types of boiler heating surfaces are considered with particular focus on the heat transfer calculation of furnace water wall. It is implemented in the CFD model in terms of a thermal boundary condition (B.C.) describing the energy balance between the boiler’s fire side heat transfer and water side heat absorption. The physical significance of the associated B.C. parameters and their accurate prescription are discussed in detail in this paper. It is found that furnace wall heat transfer is largely affected by the wall ash deposit conditions such that the heat transfer coefficient of furnace wall can be determined based on the thermal properties of ash. Although ash thickness may vary dramatically over furnace wall and is extremely difficult to predict, its thermal conductance was found to only vary within a small range for normally operated coal-fired boilers. Establishing the connection between the thermal conductance of wall ash deposits and the heat transfer calculation of furnace wall bypasses the tremendous difficulty and uncertainty incurred in predicting the ash thickness, and thereby, greatly simplifies the wall heat transfer calculation process. The heat transfer calculation methods introduced in this study embody the key physics associated with boiler’s heat transfer process while making a reasonable balance between the level of model complexity and their applicability to practical boiler problems. In this paper they are illustrated and validated on a 330 MW tangentially-fired subcritical boiler. The results show that the predicted boiler heat transfer distributions are in close agreement with the boiler’s operating data.

Method for heat transfer calculation on fluid flow in single-phase inside rough pipes

In the present technical note a new method is provided for determining the heat transfer in the fluid flow in single-phase inside rough pipes. The model was tested by adjusting it with existing experimental quantities of a total of 33 different fluids, including gases, organic substances, water and air. The method presented is valid for a range of Prandtl number for single-phase from 0.65 to 4.5×104, Reynolds number for single-phase from 2.4×103 to 8.2×106, relative roughness in the interval 0.05≤e/d≤0.00005 and correction values of the viscosity factor between 0.006≤μF/μP≤177. In 868 data analyzed, for Re<1×104, the average error found was 18.51% in the 81.06% of the disposable experimental samples, while for 1×104≤Re, the average error found was 19.06% in 80.54% of the disposable samples.

Study on heat transfer model of capillary exchanger in subway source heat pump system

In order to solve the problem of heat build-up in subway tunnels, a subway heat pump system with capillary network as front-end heat exchanger is proposed. A one-dimensional simplified plate heat transfer calculation method for capillary heat exchanger (CHE) based on surface-heat-source is proposed. Taking into consideration of the changing heat flux during heat transfer, this paper adopts step load, superposition principle, energy conservation and iterative method to establish the heat transfer model of CHE. CHE heat transfer tests were carried out at the Zhiquan Road Station of Qingdao Metro R2 line to prove this model. The results show that the max error of the model is 8.79%. In addition, the impact of such factors as inlet water temperature of CHE, the lining thermal conductivity, the thermal conductivity of surrounding rock and thermal diffusivity of the surrounding rock to the performance of the heat exchanger has been analyzed.

Suggested Method for Heat Transfer Calculation During Film Condensation Inside Pipes with Movable Frontiers

Suggested Method for Heat Transfer Calculation During Film Condensation Inside Pipes with Movable Frontiers