传热学简答题中英文版

1. 对流换热表面传热系数的定义，与什么有关。

牛顿冷却公式----------- 对流换热包括热对流和热传导，它与流动状态是层流还是紊流，流体性质，流动性质（自然对流还是强制对流），表面材料形状，面积大小和性质等有关，还与换热是否相变有关。

Newton's cooling equation ----------- include convection heat convection and heat conduction, and its flow is laminar or turbulent state of fluid properties, flow properties (natural convection or forced convection), the surface shape of the material , size and nature, but also on whether the phase change heat related.

2. 角系数

一个表面投射到另一个表面的能量占总投射能的份额。性质：可换性，完整性，可加性。 纯几何因子条件：物体表面是漫反射表面且等强辐射，定向辐射强度与方向无关。 Onto the surface to a surface energy of another share of the total energy of the projection. Nature: interchangeable, integrity, additive.

Pure geometric factor conditions: the surface is diffuse surface and other strong radiation, the radiation intensity and direction of orientation-independent.

3. 边界层中温度变化率的绝对值何处最大，对于一定换热温差的同一流体，为何能用温度

梯度的绝对值大小来判断表面传热系数的大小。

流体壁面处最大。由公式————————在表面积和温差恒定时，温度梯度越大，h 越大。

Fluid wall at maximum. And the surface area by the formula -------- constant temperature difference, the larger the temperature gradient, h is.

4. 解释：暖房的“温室效应”？

答：物体表面的单色吸收率随波长变化的特性称为物体表面对波长（光谱）的选择性。 暖房：当太阳光照射到玻璃上时，玻璃对波长小于2.2μm 的辐射能吸收比很小、穿透比很大，从而使大部分太阳能可以进入到暖房内。暖房中的物体温度低，辐射能绝大部分位于红外区，而玻璃对于波长大于3μm 的辐射能吸收比很大、穿透比很小，阻止了辐射能向暖房外的散失。

The absorption rate of the surface color varies with wavelength selectivity to the surface characteristics of known wavelength (spectrum). Conservatory: When sunlight shines on the glass, the glass is less than 2.2μm wavelength of radiation absorption ratio is small, the penetration ratio is large, so make the most of solar energy can enter into the conservatory. Objects greenhouse temperature is low, the majority located in the infrared region of radiation, while the glass for wavelengths greater than 3μm radiant energy absorption ratio is large, the penetration ratio is small, preventing the loss of radiant energy to the outside of the greenhouse.

5. 由导热微分方程可知，非稳态导热只与热扩散率有关，而与导热系数无关。你认为对吗?

答：由于描述一个导热问题的完整数学描写不仅包括控制方程，还包括定解条件。所以虽然非稳态导热的控制方程只与热扩散率有关，但边界条件中却有可能包括导热系数λ(如第二或第三类边界条件) 。因此上述观点不对。

As the description of a complete mathematical description of heat conduction equations include not only, but also boundary conditions. Therefore, although the equations of unsteady heat conduction and thermal diffusivity only relevant, but there are boundary conditions may include thermal conductivity λ (such as the second or third boundary condition). Therefore, this view is wrong.

6. 什么是黑体，灰体？实际物体在什么样的条件下可以看成是灰体？

吸收比1的物体叫做绝对黑体，简称黑体。

在热辐射分析中，把光谱吸收比与波长无关的物体称为灰体。 对工程计算而言，只要在所研究的波长范围内光谱吸收比基本上与波长无关，则灰体的假定即可成立，而不必要求在全波段范围内为常数

Absorption than the object called a blackbody, referred bold.

In the analysis of thermal radiation, the spectral absorption ratio and wavelength-independent object called a gray body. For engineering calculations, as long as the wavelength range studied spectral absorption ratio is essentially independent of wavelength, it is assumed that the gray body can be established, without requiring the full band in the range of constant

7. 热阻角度分析肋片散热，

应该采取导热系数大的材料做肋片，肋片通过增加换热面积来强化散热，但在增加换热面积的同时，也增加了导热热阻。因此，使用导热系数打的材料，其导热热阻较小，会增加肋片的散热量、

Should be taken to make material having a large coefficient of thermal fins to increase heat transfer through the fins to enhance heat dissipation area, but at the same time increase the heat transfer area, but also increases the thermal resistance. Therefore, the thermal conductivity of a material to play its thermal resistance is small, increase the amount of heat fins,

8. 不凝结气体含量对蒸汽凝结换热的影响。

在工业设备的凝结温度下，蒸汽中所含有的空气等气体是不会凝结的，故称这些气体成分为不凝结气体。当蒸汽凝结时，不凝结气体聚集在液膜附近，远处的蒸汽在抵达液膜表面经行凝结前，必须以扩散的方式穿过这个气体层，这就增加了一个热阻，是气相热阻，对流换热系数变小。

In the condensation temperature industrial equipment, air and other gases contained in the steam is not condensed, so that the gas composition of non-condensable gases. When the steam condenses, noncondensable gas accumulation near the film, before arrival distance steam line film surface by condensation, must pass through the gas diffusion layer of the way, which increases a thermal resistance, the thermal gas-phase resistance, convective heat transfer coefficient becomes smaller.

9、使用集总参数法计算非稳态导热需要满足什么条件？为什么？

需要满足1. 物体的导热系数相当大2. 所讨论物体的几何尺寸很小3. 表面传热系数很小。在这三种条件下，Bi 值将很小，这几种情况下都可以使用集总参数法计算非稳态导热。

Calculated using the lumped parameter method unsteady heat conduction what conditions need to meet ?Why ?

Need to meet one . Thermal conductivity of a large object 2 discussed the geometry of the object is small 3 . Surface heat transfer coefficient is small. In these three conditions , Bi value will be small , in these types of cases can be calculated using the non- steady-state thermal lumped parameter method .

10、高粘度的油类流体，沿平板作低速流动，该情况下边界层理论是否仍然适用？

由速度边界层厚度公式知，要使边界层的厚度远小于流动方向上的尺度，即所说的边界层是一个薄层，就要求雷诺数足够大。因此，对于流体流过平板的情况，满足边界层假设的条件就是雷诺数足够大。由此也就知道，当速度很小，粘性很大时，边界层是无法适用的。

High viscosity oils fluid flow along the flat for low , in which case the boundary layer theory is still applicable ?

Formula known by the speed boundary layer thickness , to make the thickness of the boundary layer is much smaller than the dimension in the flow direction , i.e., a boundary layer of said thin layer requires sufficiently large Reynolds numbers . Thus , the fluid flow through the flat plate , the condition is assumed to satisfy Reynolds boundary large enough . This also means that , when the velocity is small , viscosity is large , the boundary layer is not applicable .

11、什么是灰体？试说明在工程温度范围内，为什么可以将一般物体视为黑体。

在热辐射分析中，通常把单色吸收比与波长无关的物体称为灰体。对于工程温度范围内，大部分辐射能都处于红外波长范围内，此时单色吸收比基本与波长无关，所以绝大多数工程材料都可以近似为漫射灰体。

What is a gray body ? Explain the temperature range within the project , and why objects can be generally regarded as bold.

In the analysis of thermal radiation , usually monochromatic absorption ratio and wavelength independent objects called gray body . For the temperature range of projects , most radiant energy in the infrared wavelength range are in this case has nothing to do with color than the basic absorption wavelength , so the vast majority of engineering materials can be approximated as diffuse gray body .

12. 简单说明日常生活中用的保温瓶用了那里种措施来获得保温的效果?

答：两层镀银玻璃, 反射率很低，中间抽成真空，木头瓶塞。

Two silvered glass,Low reflectivity ,Middleevacuated,Wood cork

13、对管内强制对流换热，为何短管和弯管与相同管径的长直管相比，平均表面传热系数要大。

当管道长度与管内径之比小于60时，这种管道流属于短管流，这时。对于进口段的影响不能忽视。这些影响包括雷诺数、管道入口的几何形状等

当管道流体流经弯管时，由于离心力的作用，在弯管处会形成垂直于流动方向的二次流动，这时，会加强管内流体的扰动，有利于流体间的能量或动量交换，使管内对流换热强度增加 When the ratio of the length and the inside diameter l/d

When fluid flows through the pipe elbow, the centrifugal force in a vertical pipe of the secondary flow will be formed in the direction of flow, in which case, the fluid will enhance the disturbance of the inner tube, the fluid between the beneficial energy or momentum exchange that increase the intensity of convective heat transfer tube

14、写出毕渥数Bi 与努赛尔数Nu 的定义式并说明他们的物理意义，试着解释他们的区别？ 答:Bi=（δ/λ）/(1/h)=δh/λ反映了给定流场的传热热组和对流热阻的比值;

Nu=hL/λ反映了给定流畅的换热能力与其导热能力的对比关系，两者对象不一样。

Bi 的对象是固体，而Nu 是流体。Nu 中的L 是流场的特征尺寸，λ为流体的导热系数。Bi 中δ为固体系流的特征尺寸，λ为为固体的导热系数。

Bi = (δ / λ) / (1 / h) = δh / λ ratio reflects the flow field in a given group and convective heat transfer thermal resistance; Nu = hL / λ reflects the heat capacity given its smooth contrast between the thermal capacity of the two objects are not the same. Bi is a solid object, and Nu is a fluid. The L in Nu is the characteristic size of the flow field, λ is the thermal conductivity of the fluid. δin Bi is solid system flow, λ is the thermal conductivity of solids.

15、善于发射的物体必善于吸收，这个说法是否正确？

不正确。由基尔霍夫定律，物体对黑体投入辐射的吸收比α等于同温度下该物体的发射率ε。即投入辐射必须来自黑体，且达到热平衡。物体发射率越大，其对同温度的黑体辐射吸收比越大。只能说：善发射的物体必善吸收同温度下的黑体辐射。

Incorrect. Kirchhoff's law, the object put on the blackbody radiation absorption ratio α is equal to the same temperature as the object emissivity ε. That investment must come from the blackbody radiation, and thermal equilibrium. The larger the object emissivity, its temperature blackbody radiation absorption ratio with the greater. Only say: good body will launch with good absorption of blackbody radiation temperature.

16、①欧拉数：Eu=Δp/(ρu2) 反映了流场压力降与其动压头之间的相对关系，体现了在流动过程中动量损失率的相对大小。

②雷诺数：Re=ρuL/μ=uL/v表征了给定流场的惯性力与其粘性力的对比关系，即反映了这两种力的相对大小。利用雷诺数可以判别一个给定流场的稳定性，随着惯性力的增大和粘性力的相对减小，雷诺数就会增大，而大到一定程度流场就会失去稳定，而使流动从层流变为紊流。

③贝克莱数：Pe=ρcuL/λ反映了给定流场的热对流能力与其热传导能力的对比关系。 ④普朗特数：Pr=μc/λ=v/α反映了流体的动量扩散能力与其能量扩散能力的对比关系。 ⑤努塞尔数：Nu=hL/λ反映了给定流场的换热能力与其导热能力的对比关系。是无量纲的换热系数。

⑥格拉晓夫数：Gr=gβθL3/υ2反映了流体温差引起的浮升力导致的自然对流流场中的流体惯性力与其黏性力之间的对比关系。

① Euler number : Eu = Δp / (ρu2) reflects the relative relationship between the flow field pressure drop between the indenter and its dynamic , reflecting the relative size of the momentum loss rate in the flow process .

② Reynolds : Re =ρuL/μ= uL /v characterize a given inertial forces to viscous forces with its contrast between the flow field , which reflects the relative size of these two forces . Reynolds can use to determine the stability of a given flow field , and viscous force with increasing relative decrease in the force of inertia , the Reynolds number will increase, but to a certain extent the flow field will lose stability, leaving the flow from layer rheology of turbulence.

③ Berkeley number : Pe =ρcuL /λ reflects the flow field of a given thermal convection heat transfer capacity and its ability to contrast relationships.

④Prandtl number : Pr =μc /λ = v /αreflects the contrast between its energy momentum diffusion capacity diffusion capacity of the fluid.

⑤Nusselt number : Nu = hL /λ reflects the flow field of a given thermal heat capacity and its ability to contrast relationships. Is a dimensionless heat transfer coefficient .

⑥Grashof number : Gr = g βθL3/υ2 reflects the contrast between the natural buoyancy convection fluid flow field caused by the temperature difference caused by the inertial force of the fluid between its viscous force .

17、非周期性的加热或冷却过程可以分为哪两个阶段？他们各自有什么特征？

非周期性的加热或冷却过程可分为初始状况阶段和正规状况阶段。前者的温度分布依然受着初始温度分布的影响，也就是说热扰动还没有扩散到整个系统，系统中仍然存在着初始状态，此时温度必须用无穷级数加以描述。后者却是热扰动已经扩散到整个系统，系统中各个地方的温度都随时间变化，此时温度分布可以用初等函数加以描述。

Aperiodic heating or cooling stages can be divided into the initial position and the regular phase condition. The former is still being affected by the temperature distribution of the initial temperature distribution, that thermal disturbance has not spread to the entire system, the system still exist in the initial state, then the temperature must be described by infinite series. The latter is the thermal disturbance has spread to the entire system, the temperature in various parts of the system are time-dependent, then the temperature distribution can be described by elementary functions.

18、时间常数是从什么导热问题中定义出来的？他与那些因素有关？同一种导热过程中的时间常数是不是不变的? 为什么？同一种物体导热过程中时间常数是不是不变的？为什么？ τ=ρcV/hA由非稳态导热过程中定义出来的，时间常数反映了系统对环境温度变化响应的快慢。时间常数越小，物体的温度变化就越快，物体就越迅速地接近周围流体的温度，对环境温度变化响应越快。（热电偶τc 越小越好。）可见，时间常数与系统的物性、形状、大小相关，而且和环境（换热状况）也密切相关。因此，同一物质不同的形状其时间常数不同，同一物体在不同的环境下时间常数也是不相同。

τ=ρcV/hA is defined by the unsteady heat conduction process out。

The time constant of the system reflects the response to environmental temperature changes speed. The smaller the time constant, the faster the temperature of the object, the more rapidly the temperature of the surrounding fluid approaching object, the faster the response to temperature changes. (Thermocouple τc, the better.) Shows the time constant of the system properties, shape, size-related and environmental (heat position) are also closely related. Therefore, the same shape of the different substances in different time constants, the same object at different time constants is not the same environment.

19、什么是热边界层？能量方程在热边界层中得到简化必须满足的条件是什么？这样的简化有何好处？

固体壁面附近流体速度急剧变化的薄层称为速度边界层，而温度急剧变化的薄层则称为温度边界层。能量方程得以在边界层中简化，必须存在足够大的贝克莱数，即Pe=Te·Pr>>1，也就是具有1/Δ²的数量级，此时扩展项才能够被忽略，从而使能量微分方程变为抛物型偏微分方程，成为可以求解的形式。

The thin solid dramatic changes in the fluid velocity near the wall is called the velocity boundary layer, and a thin layer of rapid temperature change is called the temperature boundary layer.

Energy equation can be simplified in the boundary layer, a sufficient number must exist Berkeley, i.e. Pe = Te·Pr>> 1, that is, having a 1 / Δ² magnitude, then the extension is able to be ignored, so that the energy differential equation becomes parabolic partial differential equations can be solved in the form of becoming.

20、什么是物体表面的黑度？他与哪些因素相关？什么是物体表面的吸收率？它与哪些因素有关？他们之间有什么区别？

黑度 : 物体表面的辐射力与同温度下黑体辐射的辐射力之比。它与物体的种类、表面特征及表面温度相关。物体表面的吸收率是表面对投入辐射的吸收份额，他不仅与物体的种类、表面特征和温度相关，而且与投入辐射的能量随波长的分部相关，也就是与投入辐射的发射体的种类温度和表面特征相关。比较两者的相关因素不难看出他们之间的区别，概括的说黑度是物体表面自身的属性，而吸收率却不仅与自身有关情况有关还与外界辐射的情况紧密相连。Blackness: Radiation force and the same temperature blackbody radiation than the radiation power of the object's surface. It is the object of the species, and the surface temperature of the relevant surface features. The absorption rate of the surface is the surface absorption of radiation on inputs share, he not only the kind of the object, the surface characteristics and temperature dependent, and the radiation energy into segments associated with the wavelength, the radiation is emitted into the body and the type temperature and surface characteristics relevant. Comparison of the two factors is not difficult to see the difference between them, in a nutshell is the blackness of the surface properties of its own, and the absorption rate is not only with itself but also closely related to the circumstances of the case outside radiation.

21、用铝制的水壶烧开水时，尽管炉火很旺，但水壶仍然安然无恙。而一旦壶内的水烧干后，水壶很快就烧坏。试从传热学的观点分析这一现象。

答：当壶内有水时，可以对壶底进行很好的冷却（水对壶底的对流换热系数大），壶底的热量被很快传走而不至于温度升得很高；当没有水时，和壶底发生对流换热的是气体，因为气体发生对流换热的表面换热系数小，壶底的热量不能很快被传走，故此壶底升温很快，容易被烧坏。

When a jug of water, can be well Hudicooling (water on the pot bottom of the convective heat transfer coefficient), heat Hudi was soon pass and will not go up very high temperature; When there is no water when, and Hudi convective heat transfer is occurring gas, because gas generation surface convective heat transfer coefficient is small, the heat can not be quickly transferred Hudi go, therefore Hudi temperature quickly, easily burned.