Calculation of heat transfer
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I am working on a design. The density of the hot material is 8.96, its viscosity is 0.724, its specific heat is 1.421, and its thermal conductivity is 0.029. For cooling water, these values are 995.56, 0.698, 4.188, and 0.615 respectively. The inlet and outlet temperatures of the hot material are 180 and 40 degrees respectively, while for water they are 33 and 40 degrees. I would like to ask everyone: how can we calculate the flow rate of materials? This post was last edited by jia717 on 2009-4-3 at 18:33.]
The question posed by the original poster is a bit difficult; I thought that it’s impossible to determine the flow rate of the material based on the conditions mentioned above, and that one can only obtain the ratio of the flow rates of the two streams
The data you provided are incomplete; it is not possible to perform either a mass balance calculation or a heat balance calculation. Only the ratio of the two materials can be calculated, and there are infinite solutions.
In typical heat exchanger design, the flow rate on one side is used to calculate the flow rate on the other side. Since you don’t have the flow rates for either side, it’s impossible to make such calculations
It’s impossible to calculate without these conditions; if the water flow rate can be provided, then it can be calculated
From the perspective of heat exchanger design, the conditions you have provided seem to lack one flow condition (it’s not possible to determine the heat load); by specifying one flow condition, the other can be calculated.
Thank you all for all your help to me. Our supervisor only provided us with one diagram and asked us to derive the relevant formulas; it’s quite difficult. Additionally, the heat exchange area is given as 401.1 m2.
The hardest thing for me right now is not knowing how to calculate that overall heat transfer coefficient
Q=c1*m1*ΔT1=c2*m2*ΔT2. Q=1.421*m1*(180-40)=4.188*m2*(40-33). Therefore, m2/m1=6.786; the mass flow rate ratio of water to the hot material is 6.786.
Based on the conditions given by the poster, the hot material should enter in gas phase; if the outlet temperature is 40 degrees, it should be a condensation condition. In such a case, the latent heat of vaporization is unknown, so it’s not possible to calculate even the flow rate ratio
Everyone has already calculated the logistics ratio; since you know the heat exchange area, you can determine the Q value by adding a margin of 20–50%, and then calculate the flow rate based on the heat capacity of the fluid.
Now that the area is known, it should be possible to determine the flow rate for which this heat exchanger is suitable.