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.     

Analysis on the Temperature-control Effect of the Particle Improved Roadbed in Qinghai-Tibet Railway

Based on the observerd ground-temperature data of the particle improved roadbed in Beiluhe test site of Qinghai-Tibet railway, the characteristics of the ground temperature to the particle improved roadbed and its temperature-control effect are analyzed ,and compared with other frozen soil protecting means. The result indicated that the ground temperature of the particle improved roadbed changes with the seasons,and its characteristics present as a sinusoidal curve. Compared with the normal roadbed, the paticle improved roadbed has cooling roadbed and the effect of protecting frozen soil in mean annual ground temperature. Compared with the normal duct-ventilation embankment, the cooling effect of the particle improved roadbed in cold season is less than that of the duct-ventilation roadbed,and the thermal shield effect is better than that of the particle improved roadbed in warm season. The ground temperature curve has the better tendency of the frozen soil protection. It is an active means of frozen soil protecton.     

A simulation experiment of the thermal response of steel structures in fires

A standard indoor temperature rising curve is simulated by using a 10 kW electrical furnace. DN20 seamless steel tubes are horizontally placed on top of the electrical furnace. The distances between the bottom of the steel tubes and the mouth of electrical furnace are 0.5 cm, 5 cm, 10 cm and 15 cm, respectively. Experiments regarding the thermal response of an unshielded steel tube, a steel tube with an external fire retardant coating, and a concrete filled steel tube are carried out. When the temperature of lowest point of the bottom of the unshielded steel tube is 400 ℃, the temperature of corresponding points of the steel tube with an external fire retardant coating and the concrete filled steel tube are 215 ℃ and 200 ℃, respectively. It is concluded that the steel tube fire resistance limit exceeds 2 hours when the exterior of a steel tube is coated with fire retardant or if steel tubes are filled with concrete because these modifications improve their thermal insulation and decalescence.     

Experiment for Condensing Heat Transfer Performance in a New Type of Horizontal Three Dimensional Inner Microfin Tubes

A new type of three dimenstional inner microfin tube is devoloped. Under four different pressures and in the range of condensing mass velocities from 33 to 153 kg/m2 . s,and by the experimental study of the three kinds of tubes with different microfin parameters, the performances of the condensation heat transfer for R11 in the horizontal microfin tubes and obtained. The experiments show that the inner microfin tube is a hopeful and nighty effective condensing heat transfer enhancement tube.     

Space-time Distribution Characteristics of Temperature Field During Asphalt Pavement Paving

The temperature of hot asphalt mixture and environment has a significant effect on the quality of asphalt pavement while paving.Influenced by various kinds of factors, the temperature of the hot asphalt mixture and environment are complicate and changeable while paving.The temperature of different space and time around asphalt pavement are measured while paving hot asphalt mixture on Hou-Yun expressway.The space-time distribution characteristics of temperature field while paving through analysis are given.     

THE EFFECTS OF HEAT CONDUCTING CROSS-SECTION AREA AND AXIAL HEAT CONDUCTION ON THE HEAT TRANSFER IN THE TUBE-MOUTH REGION OF THE HIGH TEMPERATURE HEAT EXCHANGE EQUIPMENT

In this paper the heat transfer in the tube-mouth region of the high temperatur heat exchange equipment is deeply analysed. The effect; of the heat conducting cross-section area of the tube-mouth region and axial heat conduction along the tube on the temperature field is emphatically examined by numerical computation, and then the relation of the highest temperature in the tube with the elongated tube length is established. The computed results in this paper are compared with those without taking account of these two factors. It is shown that the effect can not be ignored for the corrosion-protection by controlling temperature.     

Cold Simulated Experiment of Mixed Condition in Boiler Using Gas Reburning for NOx Reduction

The principle of NO x reduction using gas reburning in boiler is analyzed. The experimental device is set up according to the principle of cold simulation. Replacing natural gas with hot air, the cold simulated experiment of mixed condition in boiler has been done. The method reflecting the mixed condition in boiler by means of surveying the uniformity of temperature is put forward on the basis of the similarity of momentum, heat and mass transfer processes. In the meantime, the temperature of different sections in furnace is measured and mean square difference of temperature field is calculated. The effect of flow rate and position of nozzle on the mixed condition in boiler is investigated.     

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.     

Degital Simulation for the Direct Torque Control of Induction Motors Using the Circle Flux Path

This paper introduces the importance of developing the Ground-Source Heat pump and describes the prospects of it.with the method used abroad to acquire the temperature profiles within surrounding soil of the underground heat exchanger with buried tubes, in this paper the line heat source theory and thermal resistance network analysis method were used to set up the heat transfer model.The original temperature of the ground is determined by calculation and is compared with test results. Experiments of running single tube and running three series connection tubes are carried out on the built underground exchangers of vertical buried tube type.And the data which can provide reference for the Ground-Soure Heat pump technique are acquired.     

Researching the effect of industrial workshop’s different aspect ratio on indoor temperature distribution

Taking the effect of industrial workshop’s aspect ratio on indoor temperature distribution as research object,using finite volume numerical method to dispersed solving for mass conservation equation and energy conservation equation.This paper research distribution of streamline and isotherm and variation of Nu in industrial workshop of different aspect ratio with Ra among 10 3~10 6.The results of analysis indicate that when increasing Ra,heat transmission form turns heat conduction into convection heat transfer,the isotherms change from vertical to horizontal gradually.The indoor streamlines form two vortexes around the model boundary,the vortexes are broken up with Ra.It’s separated into two vortexes when B=0.5 or B=1.And it’s separated into three vortexes when B=3 or B=2 with slight turbulent state. Nu increases with the increase of Ra and the related curve presents power exponent.when B=3 Nu is the largest and indicate that the total quantity of heat transfer at most by high temperature wall face cold wall.     

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.     

Analysis of the Effect of Compositive Meteorology Index on Power Load

The four indexes sensory temperature,temperature-humidity index,cold-humidity index,amenity index in biology meteorology are introduced to compositive analyses the effect of meteorologic factor to power load.Take Chongqing for example,the relation between each compositive index and load is analyzed,and the relation curve of power load and compositive index in observation year is also drawn.The analysis indicates: the load amenity index ratio curve is very stable in all axis range,this indicates amenity index can better reflect the change of power load relative to temperature.At the same time,the effect of rainfall to power load is qualitatively analyzed.     

Cold Model Experimental Study Using Reburning Tecnology to Reduce the emissions of NOx

A cold model (its ratio is 1:12.5) of a 50 MW tangentially pulverized coal-fired boiler was built and the mixture characteristic between a simulating gas (hot air) and a main airflow (cold air) were gotten at different ejecting methods and quantities of the simulating gas through measuring the temperature pattern distributing in the furnace of the model. The simulating gas spouted from front and rear walls resulted a more even mixture characteristic, and the tangentially ejected simulating gas is more suitable for the tangentially pulverized coal-fired boiler, and the tangentially ejected OFA is also of advantage to it. The effect of quantities and locations of the simulating gas on the mixture characteristic was also discussed.     

Analysis of coupled heat transfer between freezing soil,water and horizontal heat exchange tube

The research object is the coupled heat transfer effect between freezing soil,water and horizontal heat exchange tube,use finite volume numerical method to dispersed solving for continuity equation and heat transfer equation of unsaturated freezing soil,gives part of the temperature fields and freezing percentage distribution graphs,and analyzes the reason of the coupled heat transfer.The analysis result shows that:the temperature field of freezing soil are some horizontal lines parallelling to the ground surface.The peak value of solid-liquid phase change region appears in the upper part where there is backwater pipe,the low value appears in the place where there isn't horizontal heat exchange tube.The horizontal heat exchange tube makes the freezing front deviate towards the ground surface.The arrangement difference of inlet and outlet position of horizontal heat exchange tube will effect the size and position of the phase change region of freezing soil.Arranging the backwater pipe at one side or middle position is the optimized mode.     

Thermal Dynamic Analysis of Buried Hent Exchanger in Ground-source Heat Pump System in Cold Region

In order to solve the frost-heaving safety problems of buried heat exchanger hydronic in ground-source heat pump, a mathematics mode1 and its contro1 equation were put forward according to heat transfer, filtration theory and mechanics of frozen soil, which is the couplings problem of temperature field, hydronic field and stress field. The temperature field, frost heaving displacement and stress distribution of ground-source heat pump in Daqing oilfield were simulated with finite elements method. The contrast and analyses are carried out according to the different soil depth, the different soil thermal conductivity in backfilled areas, the different spacing of tube foot. The results showed that the least temperature and heat affected zone in soil increases gradually with operating time. At the beginning of operation, the displacement of buried heat exchanger is small because the soil is not frozen. When the soil temperature reaches the phase temperature, soil volume increases in size, and then buried tube deforms. When soil temperature exceeds between -0.75℃ and -0.30℃, buried tube doesnt deform.     

Experimental Analysis of Building Space Constructions on Hot smoke Flow in Residential Fire

Based on the characteristics of spatial structure of residential units, the effect of building space construction on temperature raise and hot smoke flow in residential fire was analyzed on building model with simulating multiple floors and rooms. The raise and distribution of temperature indoors were mainly tested under varied location of fire sources. And, the rule of smoke flow was discussed by using the law of temperature raise, indirectly. The results indicate that the mode of smoke flows is influenced by three spatial factors which include the form of junction terminal room construction; the height of down stand above the door and the relative locations of each room. The diffusion of hot smoke is prevented effectively by the down stand of the room; the temperature difference between indoor and outdoor should be higher than that of the room without down stand. When the open direction of door in non fire room is opposite to that of the door in fire room, there is much more hot smoke.     

Numerical study of airflow distribution in air-conditionedtrain in Qinghai-Tibet Railway

To obtain the influence of outer environmental condition on the indoor airflow distribution for the 25T air-conditioned train in Qinghai-Tibet, the Realizable k-ε model is adopted to numerically analyze the indoor temperature and velocity fields of the running train. The results indicate that solar radiation has great effect on the indoor temperature field and it is meaningful for improving the thermal comfort to adjust the air supply parameters with the outer environmental condition. Under different air supply conditions, it is the conjugating relation between the indoor temperature field and velocity field that leads to different thermal comfort in different regions of the running train. In addition, the operating modes exchange under different outdoor environmental conditions is also discussed and some additional functions of the using air-conditioning system are put forward too.     

A Study on Modification Effect of SBS on Low-temperature Performance of Base Bitumen

There is a popular opinion that SBS can improve both high and low temperature performance of base bitumen. In this study, four kinds of SBS are used to modify three kinds of common domestic bitumen and one kind of foreign one; some final products of SBS modified bitumen are obtained. The rheological properties of SBS modified bitumen after RTFO/PAV are studied by using bending beam Rheometer (BBR), which is one of the test methods of SHRP. The results indicate that the low temperature grade of SBS modified bitumen made by physical method is at the same level as that of base bitumen. In other words, the SBS modification effect on low temperature anti-cracking performance of base bitumen still deserves to study from the meaning of rheology.     

Simulation and experiment for warp characteristic of wet multiple disc clutches

Based on the real size and constrain of the wet clutch, the friction pair of temperature, stress fields coupling model, and the heat convection coefficient model are established. The transient thermal-structural coupling and the thermoelastic instability of the phenomenon of friction discs generated in overload tests are numerically simulated and analyzed with ANSYS/LS-DYNA. Additionally, the distribution of the hot spots in the circle direction and surface of the friction discs are revealed, the distribution of the stress and strain caused by the thermoelastic instability is analyzed and tested. The results show that hot spots and contact pressure are mutual promotion. The thermal expansion and stress concentration caused by temperature gradient lead to steel disc warp. The heat fading caused by the thermoelastic instability leads to steel disc failure.     

Pressure Drop and Evaporative Heat Transfer Characteristics of Air-water Bubbling Flow

A new kind of evaporative heat transfer experiment for the cooling process of condensers is conducted. The test coil is immersed in an air-water bubbling layer. The air-water two-phase flow passes through the heating tubes of the coil. Due to the motion of the air bubbles in the water, a thin water film forms on the surface of the heating tubes. As the air bubbles passing by the tubes the water is evaporated into the air. The tubes of coil reject heat to the water film, and the evaporation of the water film then rejects heat to the air bubble stream. This heat transfer mode significantly increases the heat transfer coefficient between tubes and air. The consumption of the power of a water pump can be decreased. Moreover, the airflow rate required is less than that of an air-cooled condenser.The pressure drop of air through air-water bubbling layer and the heat transfer between the tubes and water are experimentally investigated in the paper. The results show that the factors affecting the pressure drop and the heat transfer coefficient involve the pore geometry of sieve plate, the height of the air-water bubbling layer, the air flow rate through the sieve plate and the heat flux of tubes. The heat transfer coefficient between tube and water is two times larger than that of falling film of water on the outer surface of tube.