Which value should be used for the heat transfer coefficient of the outer surface of the insulation layer?
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This post was last edited by *axuezi on 2016-9-22 15:24. In insulation calculations, the heat transfer coefficient of the outer surface of the insulation layer is often considered, such as when calculating the thickness of the insulation layer or heat losses. Consulting the standards GB50264-2013 and GBT8175-2008, as well as the handbooks on chemical process design, reveals that the specifications for this coefficient vary; it is generally 11.63 for indoor areas, while the formulas used for outdoor areas differ, for example, in GBT8175 it is given as 1.163*（6+3*w^0.5) ； And in the chemical process design manual, when the wind speed w > 5, it is 1.163*（as+6*w^0.5） ； Insulation for heat retention: as=6~7, while insulation for heat preservation is 11 ； The values calculated by the two formulas differ greatly. Which method is used in actual calculations? If we use the values of the radiation coefficient and convection coefficient, then when determining the thickness, we don’t know the outer diameter of the insulation layer – how can we calculate it then?
I’m not quite sure about this either; you can check the relevant manuals or something – maybe you’ll find an answer there
Same question: I also saw calculations using 1.163*（10+6*w^0.5). Which formula should be used?
I also noticed this issue today; after checking the chemical engineering process manual, a=1.163*（as+6*w^0.5) (where as is 6–7 for insulation and 11 for heat retention). When it comes to heat retention, a0 is set to 11; however, in the examples in the manual, the value for as in steam insulation pipes is 7. Why is it based on heat insulation values? Is the manual wrong? Indeed, the calculation formulas for a as defined in GB8175-2008 and those in the chemical process manual are not consistent. Therefore, I would also like to know how to handle this issue when performing actual calculations. I appreciate any guidance from those with more experience!
Does no one know? The calculations in GB50264 are different as well; what should be done? Who has an Excel spreadsheet ready? Please share it