The Effect of Aspect Ratio on Natural Convection in a Cavity with Discrete Heaters and a Vertical Heat Sink

SIMPLE method is used to study the influence of aspect ratio on the natural convection in an enclosure with five discrete heat sources on a vertical wall and an isothermal heat sink on another vertical wall. The range of aspect ratio is from 3. 0 to 12. 22. At high aspect ratio, multiple secondary flow cells can be found,which enhance heat transfer strongly and cause the highest heat transfer coefficient based on cooling area Nuc. With the decrease of aspect ratio,secondary flow cells become weaker gradually and finally reach the lowest Nuc at H/W = 7. 35. If H/W continues to decrease,natural convection is gradually developed,and heat transfer is improved. At H/W = 3. 67,Nuc becomes stable. Then the decrease of aspect ratio will not affect heat transfer. Besides, A heat transfer correlation including the influence of aspect ratio is .also provided.     

Conjugate Natural Convective Heat Transfer in an Enclosure with Discrete Protruded Heat Sources

The mathematic model on natural convection is proposed in a two-dimensional enclosure cavity with an isothermal heat sink at one vertical wall and five discrete protruded sources. Numerical study is performed to analyze the natural convection in the enclosure with a variety of aspect ratio, the range of which is from 3.0 to 12.22, Ra H is 10 7 and Pr is 30.The computed results show that the total heat transfer effect under the situation with discrete protruded heat sources is prior to that with flat wall heated. Moreover, when the aspect ratio is comparatively large, there is several secondary flow in the enclosure, which enhance the convective heat transfer. On the contrary, when the aspect ratio is small, the secondary flow weakened or disappeared, and the total convective heat transfer drop. Finally, the convective heat transfer criteria in the enclosure is obtained.     

Numerical Study of FLow and Heat Transfer in Rectangular CHannel with Dimpled SUrface

This authors uses a physical model of the rectangular channel with dimpled surface to simulate the flow and heat transfer situation. On the basis of actual flow and heat transfer in the channel, it made the interrelated hypothesizes and built up the math model. They adopted the turbulent model, appliy the algorithm to resolve the pressure-velocity coupling and use the experimental data model to check up the feasibility of the model. By the study, the thesis shows the principle of the flow and heat transfer in narrow channel with a dimple surface and gets the factors and the conditions that affect the flow and heat transfer. The results show that the geometry structure and rank distributing of dimple affect the capability of heat transfer evidently. When Reynolds number is low, the capability of heat transfer becomes better as the number increases, and when Reynolds number is bigger than a critical point, there is a little influence.     

The Mathematical Model of Cooling and Heat Transfer for the Solidification of Thin Slab during Continuous Casting Process

In the established model, the cooling differences are considered between the surface of inner radius and that of outer radius, and in the transverse direction of thin slab. And the conception for the effective coefficient of spraying water in continuous casting is firstly put forward. According to different casting speeds and different cooling zones, different time step lengths are adopted. In this model the heat transfer differences are thought over among vertical and curved zones, wide and narrow surfaces an well as angular zone of mould. The method of the corrected equivalent specific heat is used to deal with latent heat. The influence of forced convection is considered on heat transfer. Therefore, the model has higher accuracy and is consistent with the practice.     

COMBINED HEAT TRANSFER OF TURBULENT NATURAL CONVECTION AND SURFACE RADIATION IN AN OPEN CAVITY

A numerical study is carried out for the combined heat transfer of turbulent natural convection and surface radiation in an two-dimensional open square cavity with only one heated wall. The results show that the radiation significantly affects the velocity and temperature fields,and it can reduce the turbulent natural convection heat transfer as well as enhance it. For different Rayleigh number and temperature difference ratio,the overall heat transfer rates and the portion of radiation present different variation patterns.     

Influence numerical analysis of combustion chamber thermal boundary conditions on unsteady combustion characteristics in micro ICE

To research the influence of combustion chamber thermal boundary conditions on micro combustion characteristics in micro ICE, the laminar flow finite rate model is adopted to simulate the micro combustion process. Firstly, the influence of grid scale, the time step length and the maximum iterations per time step on accuracy of simulation results are explored. The results show that simulation results agree well with experimental results. And then, the influences of heat transfer coefficient, wall thickness and material on combustion characteristics are discussed. The results indicate that heat transfer coefficient has obvious influence on combustion characteristics. The pressure rise rate decreases, the ignition delays and the highest pressure value drops 2 atmospheres as heat transfer coefficient increases from 0 to 55 W/(m 2·K). The wall thickness and material have a little effect on combustion characteristics. This is because that the main heat transfer resistance in the heat flow path from cylinder to external environment lies between the outer wall and environment.     

Analysis for Heat Transfer in Micro-annular Channel with Unsymmetrically Heated Walls in Slip Flow Regime

A theoretical analysis is presented for heat transfer in micro-annular channel with an adiabatic wall and a heated wall with uniform wall temperature in slip flow regime. The energy equations with the boundary conditions of temperature jump are solved for the hydrodynamical and thermal fully developed laminar flow of the incompressible fluid in this microchannel. The influences of the Kn number, the ratio of inner diameter to outer diameter on the heat transfer characteristics are discussed respectively. The results show that the Nusselt number in microchannel decreases with the increasing of Kn number comparing with that in macrochannel.     

The Influence of Width of Flag-type Inserts on the Forced Convection of Oil in a Tube

Experimental study of forced convection heat transfer in a horizontal circulartube with ladder-shaped flag-type insert is performed to investigate the characteristics of fluid flow ,heat transfer and the influence of width of flag insert.The working fluid is 30# turbine oil.Theresult shows that the increase of W/D causes the increase of heat transfer coefficient and resistanceforce of fluid flow. The heat transfer coefficient can be enhanced mainly within the length of ninetimes of inner diameter of tube for oil.In the range of experiment, the value of creteria to evaluatethe combined effect is between 1.13 and 1.59.     

NUMERICAL STUDY OF NATURAL CONVECTION HEAT TRANSFER IN A PARTIAL CAVITY

A numerical analysis is carried out for the unsteady and steady, two-dimensional, laminar natural convection heat transfer in a square partial cavity. The partial cavity consists of two horizontal adiabatic surfaces, a vertical hot surface and a cold surface with varied opening. The results are obtained for Ra = 10~3-10~6 and Y0 = 0.0-1.0. This study shows that the opening size has significant effect on the flow and heat transfer in partial cavity, and the. extent of its effect changes with different Rayleigh numbers.     

Heat Transfer Characteristics of the Melting Process of the Metal Foam/Paraffin Compound Material

In order to enhance the heat transfer in the phase change heat storage device, a rectangular cavity filled with metal foam / paraffin wax is made. The melting heat storage experiment of foam metal / wax composite phase change material was carried out in the transverse wall temperature conditions. The temperature change curve is drawn according to different heating temperatures. Both the effects of natural convection in rectangular cavity on temperature distribution and the impact of heat transfer temperature difference on the thermal storage time are analyzed. The results show that the melting process of the paraffin in the body cavity is reinforced by the high thermal conductivity of copper foam. The remaining solid paraffin is accelerated to melt by the natural convection of the liquid paraffin formed near the heating surface; and the greater the heat transfer temperature difference is, the greater the natural convection is and the shorter the time for heat storage is.     

Investigation on flow and heat transfer characteristics in capillary porous wick based on alkali metal thermal-to-electric converter (AMTEC)

An axial symmetric invariable temperature phase change interface model of capillary porous wick based on alkali metal thermal-to-electric converter (AMTEC) is established to simulate flow and heat transfer characteristics in capillary porous wick and liquid channel by solving the mass and heat transport controlling equations. The effects of the working fluid flow rate, inlet temperature, porous wick thickness, porosity and effective pore diameter on the distributions of pressure, velocity and temperature are analyzed. In addition, the available effective pore size of the porous wick and the measures to improve the performance of the porous wick are given by analyzing the relationship between the maximum available capillary pressure and the loop pressure drop. The results show that the model presented in gives a good agreement with the three dimensional two-phase evaporation model. The flow and heat transfer characteristics of the capillary porous wick with the alkali metal liquid as working fluid are different from that with the traditional working fluid in some ways.     

THE EFFECT OF THE CONVECT1VE HEAT TRANSFER IN THE ENTRANCE REGION OF THE TUBE ON THE HEAT TRANSFER IN THE TRBE -MOUTH REGION OF THE HIGH TEMPERATURE HEAT EXCHANGE EQUIPMENT

The effect of the convective heat transfer in the entrance region of the tube on the temperature field and the maximum temperature of the tube material in the tube -mouth region of the high temperature heat exchange equipment is examined by numerical analysis. The computations on the basis of four different formulas for convection heat transfer coefficient are performed. The computed results indicate that the efect can not be ignored as for heat protection of the tube -mouth region and it is resapnable and secure that the mean convective heat transfer coefficient with taking account of the effect of the entrance region is used in the thermal design of the tube -mouth region.     

Thermodynamic Analysis of River Water Fouling on Constant Wall Temperature Tube of Small Diameter

In order to improve utilization of cold and heat source from river, turbulence theory and entropy generation theory were adopted to analyze the effect of fouling on convective heat transfer performance in small diameter tube of constant wall temperature.It is found that the entropy generation caused by conduction of fouling plays a more important role in total entropy generation of heat transfer process through a duct than that in cveast rate of caused by temperature difference.The entropy generation caused by viscous flow is more than the entropy generation caused by temperature difference in flow with bigger Reynolds and small radius.The increase rate of entropy generation monotonically increase with Reynolds and the generation process of fouling resistance.Thereafter, the effect of fouling resistance on the heat transfer performance of water source heat pump heat exchanger should be paid more attention, when river water are used as the cold and heat source of heat pump.     

Computation Method and for Thermal Transmittance of Glass Curtain walls Appllcation

The heat conduction characteristic of glass curtain wall was investigated. Based on one dimensional steady heat conduction theory, the numerical calculation model of glass system thermal transmittance was set up by using insulating glass as an example. Based on two dimensional steady heat conduction theory and finite element method, both the thermal transfer matrix and temperature load array of 3 DOFs triangular element were derived. Then the revised formulas about the heat transfer matrix and temperature load array under the boundary conditions of constant heat flux, heat convective, radiation and coupled of them were also derived. Then the numerical calculation models of glass curtain wall frame and linear thermal transmittance were set up. The program TJCW based on the Visual C++ and ObjectARX was developed for calculating the thermal transmittance of glass curtain wall and was validated by contrast with the results calculated by thermal software LBNL. Finally, TJCW program was used to calculate and check the thermal transmittance of glass curtain wall in a practical project. The results indicate that the thermal transmittance of glass curtain wall can be calculated correctly by adopting the presented model, and the program based on this model can be used in energy conservation calculation and analysis in the actual projects.     

Numerical Computation of 3-D Laminar Boundary Layer Equations of Natural Convection Heat Transfer

Coordinate transformation and Box method already succeed in solving boundary layer equations of compelling convection heat transfer,but the solution of natural convection heat transfer has not been informed.For examining the compute accuracy of solving natural convection heat transfer by using this method,this paper numerically computes 3 D laminar boundary layer equations of natural convection heat transfer of stand strip by using this method,the computational results agree with the experimental data from the published paper.The results shows that using this method to solve the equations is feasible.     

Numerical analysis of indoor natural convection heat transfer under different heat source location

The research object is indoor natural convection heat transfer under different heat source location,using FVM numerical method to dispersed solving for mass conservation equation and energy conservation equation.Researched distribution of streamline and isotherm and variation of Nu in powerhouse with Ra among 10 3~10 6 when different heat source location.The results of analysis indicate that when Ra=10 3, the isotherms expand outward centring on the heat source and present shapely arcuation.When increasing Ra,isotherm shape changes gradually,thin boundary layers appear on cold wall and hot wall.The streamlines are two symmetrically reverse vortexs.As increasing Ra, the vortexs change in size and move. As Ra=10 3,Nu reaches maximum in the case of D=0. the effect of heat source location on heat transfer quantity is obvious.The curve of Nu is steepest when D=0.5 and smoothest.There is a power relationship between Nu and Ra, the linear correlation fitting 90%.The conclusion provides a theory basis for the research of complex indoor heat transfer mechanism.     

Thermal Radiation Effects on Smoke-flow in Atrium Fires

The field models for smoke flow in atrium, takings into account strong buoyancy, turbulence, radiation exchange and wall heat losses are developed according to the characteristics of the atrium fire. Realistic combustion processes in the burning fuel have not been included. A six-flux radiation model is included in a general mathematical model for fires, which are taking as a volumetric heat source, It is applied to the predictions of fire smoke development in a small-scale atrium. In order to avoid complicated radiation exchange models, radiation heat loss effects are combined to the wall heat loss. A General-purpose compute program PHOENICS has been developed to meet this need. Results of numerical calculations based on the field model are compared with test data for a fire in the small-scale atrium test facility. The resullts indicate that radiation transfer has the minor effects, due to the relatively low temperatures encountered. The method that the effect of radiation is included in the calculation of wall heat transfer losses by using maximum heat transfer coefficient is feasible. The field model used in the present study is not good enough, which a turbulent combustion sub-model must be included.     

Performonce of Fouling Fluidized-Removing and Heat Transfer Enhancement on Sewage Side of Sewage-Source Heat Pump System

High thermal resistance resulted by fouling in heat exchanger restricts the application of sewage source heat pump (SSHP) system. The fouling forming mechanism was applied with solid-liquid fluidized bed technique for fouling prevention and removing of SSHP system. Shearing stress model of solid-liquid fluidized bed heat-exchanger is analyzed, and collision stress model is modified. Preventing and removing fouling mechanisms of solid-liquid fluidized bed technique by shearing stress and collision stress was explained. An experimental study on how to solve the fouling problem (such as fouling prevention and removing, heat transfer enhancement, etc) is discussed. The results of theory and experiment show that solid-liquid fluidized bed technique can be used not only to increase convection coefficient, but also to restrict fouling growing, it can effectively solve the fouling problem in SSHP system.     

HATURAL CONVECTION HEAT TRANSFER JN AN ENCLOSURE WITH A LOCAL INTERNAL HEAT SOURCE

Numerical analysis is made for the unsteady and steady, two-dimensional laminar natural convection in an enclosure caused simultaneously by the external heating and a local internal heat source. The velocities and temperature profiles are given, the average and local Nusselt numbers for the hot and cold surfaces obtained, and the equivalent relative intensity of the internal heat source, the critical equivalent relative intensity of the internal heat source and the transient control regime defined. The results show that there exist five flow patterns with changing the external or internal Rayleigh number, and the heat transfer performance for each flow pattern region is different.     

The Numerical Simulation of Casting Process for Making Metal Matrix Composites

In this paper,a numerical simulation of the casting process for making the MMC.using the PEM, is studied.The convection of liquid metal and the release of latent heat of solidification are taken into account.The algorithm and program for axisymmetric casting model are developed to the problem of coupling between flow and heat transfer,as well as phase change.The variational curves of temperature,the position of flow front and the distrsbutions of volume fraction of solid metal in matrix and their variation with time are obtained.The influences of technological paarmeters to casting are discussed.