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日常材料的散热系数


银 429 铜 401 金 317 铝 237 铁 80 锡 67 铅 34.8 各种物质导热系数! material conductivity K (W/m.K) diamond 钻石 2300 silver 银 429 cooper 铜 401 gold 金 317 aluminum 铝 237 各物质的导热系数 物质 温度 导热系数 物质 温度 导热系数 亚麻布 50 0.

09 落叶松木 0 0.13 木屑 50 0.05 普通松木 45 0.08~0.11 海砂 20 0.03 杨木 100 0.1 研碎软木 20 0.04 胶合板 0 0.125 压缩软木 20 0.07 纤维素 0 0.46 聚苯乙烯 100 0.08 丝 20 0.04~0.05 硫化橡胶 50 0.22~0.29 炉渣 50 0.84 镍铝锰合金 0 32.7 硬质胶 25 0.18 青铜 30 32~153 白桦木 30 0.15 殷钢 30 11 橡木 20 0.17 康铜 30 20.9 雪松 0 0.095 黄铜 20 70~183 柏木 20 0.1 镍铬合金 20 12.3~171 普通冕玻璃 20 1 石棉 0 0.16~0.37 石英玻璃 4 1.46 纸 12 0.06~0.13 燧石玻璃 32 0.795 皮棉 4.1 0.03 重燧石玻璃 12.5 0.78 矿渣棉 0 0.05~0.14 精制玻璃 12 0.9 毡 0.04 汽油 12 0.11 蜡 0.04 凡士林 12 0.184 纸板 0.14 “天然气”油 12 0.14 皮革 0.18~0.19 甘油 0 0.276 冰 2.22 煤油 100 0.12 新下的雪 0.1 蓖麻油 500 0.18 填实了的雪 0.21 橄榄油 0 0.165 瓷 1.05 已烷 0 0.152 石蜡油 0.123 二氯乙烷 0.147 变压器油 0.128 90%硫酸 0.354 石油 0.14 醋酸 18

石蜡 0.12 硝基苯 0.159 柴油机燃油 0.12 二硫化碳 0.144 沥青 0.699 甲醇 0.207 玄武岩 2.177 四氯化碳 0.106 拌石水泥 1.5 三氯甲烷 0.121 花岗石 2.68~3.35 氨气* 0.022 丙铜 0.177 水蒸汽* 0.0235~0.025 苯 0.139 重水蒸汽* 0.072 水 0.54 空气* 0.024 聚苯板 0.04 木工板 0.1-0.2 重水 0.559 硫化氢* 0.013 表 2 窗体材料导热系数 窗框材料 钢材 铝合金 PVC PA 松木 导热系数 58.2 203 0.16 0.23 0.17 表 3 不同玻璃的传热系数 玻璃类型 玻璃结构(m) 传热系数 K-w/(m2-k) 单层玻璃 6.2 双层中空玻璃 5×9×5 3.26 5×12×5 3.11 一层中空玻璃 5×9×5×9×5 2.22 ←-- 5×12×5×12×5 2.08 Lhw-E 中空玻璃 5×12×5 1.71

石墨 比热 710 J/(kg·K) 电导率 0.061×10-6/(米欧姆) 热导率 129 W/(m·K

Heat transfer coefficientFrom Wikipedia, the free encyclopediaJump to: navigation, search The heat transfer coefficient, in thermodynamics and in mechanical and chemical engineering, is used in calculating the heat transfer, typically by convection or phase change between a fluid and a solid:

where

q = heat flow in input or lost heat flow , J/s = W h = heat transfer coefficient, W/(m2K) A = heat transfer surface area, m2 ΔT = difference in temperature between the solid surface and surrounding fluid area, K From the above equation, the heat transfer coefficient is the proportionality coefficient between the heat flux, that is heat flow per unit area, q/A, and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ?T).

The heat transfer coefficient has SI units in watts per squared meter -kelvin: W/(m2K).

Heat transfer coefficient is the inverse of thermal insulance. This is used for building materials (R-value) and for clothing insulation.

There are numerous methods for calculating the heat transfer coefficient in different heat transfer modes, different fluids, flow regimes, and under different thermohydraulic conditions. Often it can be estimated by dividing the thermal conductivity of the convection fluid by a length scale. The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). There are also online calculators

Convective Heat Transfer Heat transfer between a solid and a moving fluid is called convection. This is a short tutorial about convective heat transfer Sponsored Links

Heat energy transferred between a surface and a moving fluid at different temperatures is known as convection.

In reality this is a combination of diffusion and bulk motion of molecules. Near the surface the fluid velocity is low, and diffusion dominates. Away from the surface, bulk motion increase the influence and dominates.

Convective heat transfer may take the form of either

?forced or assisted convection ?natural or free convection Forced or Assisted Convection Forced convection occurs when a fluid flow is induced by an external force, such as a pump, fan or a mixer.

Natural or Free Convection Natural convection is caused by buoyancy forces due to dens ity differences caused by temperature variations in the fluid. At heating the density change in the boundary layer will cause the fluid to rise and be replaced by cooler fluid that also will heat and rise. This continues phenomena is called free or natural convection.

Boiling or condensing processes are also referred as a convective heat transfer processes.

?The heat transfer per unit surface through convection was first described by Newton and the relation is known as the Newton's Law of Cooling. The equation for convection can be expressed as:

q = hc A dT

(1)

where

q = heat transferred per unit time (W)

A = heat transfer area of the surface (mo)

hc= convective heat transfer coefficient of the process (W/m2K or W/m2oC)

dT = temperature difference between the surface and the bulk fluid (K or oC)

Heat Transfer Coefficients - Units ?1 W/m2K = 0.85984 kcal/h m2 oC = 0.1761 Btu/ ft2 h oF ?1 Btu/ft2 h oF = 5.678 W/m2 K = 4.882 kcal/h m2 oC ?1 kcal/h m2 oC = 1.163 W/m2K = 0.205 Btu/ ft2 h oF Convective Heat Transfer Coefficients The convection heat transfer coefficient - k - is dependent on the type of media, gas or liquid, the flow properties such as velocity, viscosity and other flow and temperature dependent properties.

In general the convective heat transfer coefficient for some common fluids is within the ranges:

?Free Convection - Air : 5 - 25 (W/m2K) ?Free Convection - Water: 20 - 100 (W/m2K) ?Forced Convection - Air: 10 - 200 (W/m2K) 50 - 10.000 (W/m2K)

?Forced Convection - Water:

?Boiling Water : 3.000 - 100.000 (W/m2K) ?Condensing Water Vapor: 5.000 - 100.000 (W/m2K) Example - Convective Heat Transfer A fluid flows over a plane surface 1 m by 1 m with a bulk temperature of 50oC. The temperature of the surface is 20oC. The convective heat transfer coefficient is 2,000 W/m2oC.

q = (2,000 W/m2oC) ((1 m) (1 m)) ((50oC) - (20oC))

= 60,000 (W)

= 60 (kW)

Convective Heat Transfer Calculator A - surface area (m2)

tsurface - surface temperature (oC)

tair - air temperature (oC)

hc - convective heat transfer coefficient (W/m2K) Heat Transfer = 60000 (W) Convective Heat Transfer Chart


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