heat conduction analysis on the evaporator in gravity heat pipe of heavy oil wellbore

1、<p>　　Heat Conduction Analysis on the Evaporator in Gravity Heat Pipe of Heavy Oil Wellbore</p><p>　　Abstract: A technology for using petroleum deposit’s energy and the principle of medium’s phase chang

2、e heat transfer to make hollow rod into heat pipe，which transferred heat from bottom to top in wellbore by using it without extra energy is proposed．It can improve the temprature distribution of the fluid at the upper pa

3、rt of wellbore , therefore paraffin deposition and flocculation are improved. In this paper, heat transfer model of liquid film and liquid pool is established by means of the equa</p><p>　　Keywords: gravity

4、heat pipe; evaporator; heat conduction process; heat transfer coefficient </p><p>　　0 Introduction </p><p>　　As the gravity heat pipe with high efficiency, simple structure and low cost advantag

5、es,it is widely used in all kinds of heat transfer and heat recovery equipments[1]. At present,although two phase fluid flow and heat transfer inheat pipe get in-depth research, and has significant progress, but the stud

6、y of the process of evaporation-condensation in super long gravity heat pipe which is made of hollow sucker rod is very little. Numerical simulation is an important method of studing the heat tra</p><p>　　1.

7、Calculation model </p><p>　　1.1 Mathematical model of liquid membrane </p><p>　　We make the process of thermal conductivity in gravity heat pipe evaporator’s liquid membrane into simplification

8、and assumpt that: </p><p>　　(1)The thickness of liquid film is far less than pipe diameter,?internal heat transfer is pure heat conduction, liquid membrane surface is smooth without fluctuation, the internal

9、 temperature is in linear distribution and ignore the convective heat transfer effects; </p><p>　　(2)The state of gas is pure and saturation,the flow rate of interface gas is equal to the average flow veloci

10、ty,?vapor density relative to the liquid density is neglected; 　　(3)The temperature of the liquid film on the gas-liquid interface is equal to the saturation temperature,?ignore the viscous stress of interface steam aga

11、inst liquid film; </p><p>　　(4)The working medium in heat pipe is often property; </p><p>　　(5)Wall temperature distribute uniform. </p><p>　　The basis of filmwise condensation[2] t

12、heory solving is using the flow boundary layer theory which is proposed by Prandtl[3] and the concept of thermal boundary layer which is proposed by Pohlhausen[4], simplify the Navier ? Stokes[5] equation and then get th

13、e differential equation of thermal boundary layer heat transfer is as follows: </p><p>　　In these formulas, μ, u, ρ, g, T, δ, τ, yrepresent the dynamic viscosity, velocity, density, the acceleration of gravi

14、ty, temperature, the shear stress of liquid film thickness and radial coordinate separately; ,, ,in subscript correspond to liquid, wall temperature of evaporation section, the interface of gas-liquid ,and the saturated

15、state. </p><p>　　We can get the relation of velocity and the temperature distribution by integrating formula (4)and (5)on these two boundary conditions above: </p><p>　　The relation of the veloc

16、ity of liquid film ion the interface of gas-liquid uli,the mass flow rate of liquid film on the unit?width qm,the thickness of liquid film δ,the drop height of liquid film X and the shear stress of interface τi can be go

17、t by using the control equations above and boundary conditions: </p><p>　　Cp, hfg,λ in the formula(13)represent specific?heat?capacity,?latent heat of vaporization and thermal?conductivity. </p><p

18、>　　In?the?formulas above,the flow velocity of liquid film on interface uli can be calculated byformula(10),using the gas mass balance on the same interface can get the average flow velocity of gas:uv=4qm/ρvd, The fric

19、tion coefficient Cf is a function of gas-liquid phase to the Reynolds number. </p><p>　　1.2 mathematical model of liquid pool </p><p>　　In the process of heat transfer in fluid pool,the function

20、 of boiling has great influnce on the height of liquid pool and heat transfer coefficient?, in this paper, the function of bubble in liquid pool is taken intio account by introducing the experience formula of the coeffic

21、ient of hollow bubble in drift model : </p><p>　　In this formula,C0 is the distribution coefficient, which is a function of the density of gas-liquid,and the circular tube adopts the following empirical form

22、ula: </p><p>　　Local show velocity of gas can be got by the balance equation of liquid pool: 　　Dimensionless flowing velocity of gas Vvj+ is a function of liquid viscosity Nμf and dimensionless hydraulic di

23、ameter: </p><p>　　When the height of Liquid pool don’t beyond the height of evaporation section,the relation between the average cavitation coefficient of evaporation in liquid pool α and the height of liqui

24、d pool Lp is as follows: </p><p>　　2. The results of numerical simulation in evaporation </p><p>　　In this paper, using ammonia water as the working medium, the length of gravity heat pipe is 10

25、00 meters, the evaporation section is 400 meters, liquid volume is 200 v/m, the operation pressure of the heat pipe is 2.39 MPa, and the pressure coefficient of stratum is 0.15, the temperature of groud is 20 ,the temper

26、ature gradient of stratum is 3/100m. </p><p>　　(1)The thickness of liquid film </p><p>　　The figure can be seen that the thickness of liquid film in evaporation become thin with the increase of

27、the depth of the heat pipe,?and in this process,the thickness change of the liquid is relatively slow, the reasons for this phenomenon lies in the temperature difference of gravity heat pipe wall’s inside and outside is

28、small, and the steam flow rate is faster, the flushing action against the liquid film is larger, thus a large number of droplets are upward with steam to make the liquid film </p><p>　　(2)Flow velocity of st

29、eam and liquid film </p><p>　　Figure 2 illustrates that the average flow velocity of steam is greater than the flow velocity of liquid film in the gas-liquid interface, steam flow is upward from the liquid p

30、ool to the junction of evaporator and condenser ,and the flow velocity raise gradually from 6.562 m/s to 9.728 m/s, this is due to the steam which from the liquid pool upward absorbs the heat of the steam unceasingly, th

31、e gas flow increase gradually, thus increasing speed. Because the carrying capacity ofsteam in evaporat</p><p>　　When the liquid film is laminar membrane, the thickness of liquid film is lesser, heat flow de

32、nsity is low, its heat transfer coefficient at the highest stage. With the increase of heat transfer rate, the thickness of liquid film is increasing, the heat transfer coefficient of the liquid film of evaporator in hea

33、t pipe will reduce with the increase of heat flux, before it into nuclear boiling.Because the effects of changes on liquid film’s thickness will recede after the liquid film completely t</p><p>　　The heat tr

34、ansfer process of liquid film and liquid pool in the evaporation of heat pipe which is made of hollow sucker rod has a decisive effect on the heat transfer performance of heat pipe.In this paper,we establish mathematical

35、 model of the thermal conductivity of liquid film and liquid pool in evaporation section, calculate to get the formula of the mass and heat transfer rate of the two, and get the change rule that their heat transfer rate?

36、changed with the change of heat flow density by a</p><p>　　References </p><p>　　[1]Ma Tongze,Hou Zengqi,Wu Wenxian.Heatpipe[M].Beijing:science publishing company.1983:4-8 </p><p>　　

37、[2]Yang Shiming,Tao Wenquan.Heat transmission science [M].Beijing:Higher education publishing company.1998:331-335 </p><p>　　[3] El-Genk M S, Saber H H.Heat transfer correlations for liquid film in the evapo

38、rator of enclosed, gravity-assisted thermosyphons[J].Journalof Heat Transfer, Transactions ASME, 1998, 120( 2) : 477-484. </p><p>　　[4] Kaminaga F,Okamoto Y,Suzuki T.Study on boiling heat transfer cor-relati

39、on in a closed two-phase thermosyphon[C].Beijing:Proceeding of the 8th International Heat Pipe Conference.1992.317-322. </p><p>　　[5] S.H.Noi.Heat transfer characteristics of a two-phase closed thermosyp[J].