Heat transfer problems
Thread Content
I have 2000 kg of gas, with an average specific heat capacity of 6.4 KJ/Kg·°C. It takes 0.6 MPa of steam to heat this gas from 20 degrees to 140 degrees. How many kilograms of steam are required? I’m not sure if it’s because I don’t know how to calculate this, or because I didn’t take all the properties of steam into account; my calculation results differ significantly from those of a colleague. I would appreciate some guidance from someone who knows more about this................ Thank you in advance. When calculating the heat required for steam, should the enthalpy value be used as the basis for the calculation, or the latent heat of vaporization? ? ? Furthermore, is there only one purpose to using steam with high pressure as a heat source? It’s all to raise the temperature of the medium being heated. There’s another question – I would appreciate it if an expert could explain this: The final temperature of the medium being heated in my case reaches 140 degrees; shouldn’t the water coming out of the steam condensation tube be saturated water at that point? It should be steam at 140 degrees, right? So can the latent heat of steam still be used as calculation data? This post was last edited by lcpinging on 2009-2-18 09:13]
It is recommended that you share your calculation process so that everyone can take a look; this might help clarify the reasons better. The enthalpy calculation is relatively accurate. This post was last edited by Albertlu on 2009-2-17 at 22:34.]
The steam coming out of the steam condenser should be at 140 degrees. For 2000 kg of gas with an average specific heat capacity of 6.4 KJ/Kg·°C, the heat required to raise this gas from 20 degrees to 140 degrees is: 2000 x 6.4 x (140 – 20) = 1,536,000 KJ. For steam at a constant pressure of 0.6 MPa, the average specific heat capacity is 4.1868 KJ/Kg·°C; the mass of steam required to cool this steam from 158 degrees to 140 degrees is: 536,000 / 4.1868 / (158 – 140) = 20,382 kg. If system heat losses are taken into account, a coefficient of 1.3 should be applied.
There’s an error in the calculations upstairs; the latent heat at 0.6 MPa and 158 degrees is used in the calculations, while the temperature range from 158 to 140 degrees cannot be taken into account. If heat is supplied using water temperature, it is not economical