Urgent! Please help calculate what size the area of the following tube heat exchanger should be
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The waste gas adsorption tower uses steam for desorption; the amount of steam generated is 600 kg/h, with a temperature of around 120°C and a pressure of less than 1 Kg. The steam contains approximately 80 kg/h of benzene. For the first stage of cooling, water at 32°C is used, while for the second stage, water at 7°C is utilized. What area is required for a 304 stainless steel tube heat exchanger to be used in the first stage of heat exchange? Is 20 square meters enough? What about level two? Thank you!
Based on the heat transfer calculation formula, it is possible to first determine the heat Q of the steam in the waste gas adsorption tower, namely: Q = mcpΔT, where m is the mass of the steam, c is the specific heat capacity of the steam, and ΔT is the difference between the temperature of the steam and the temperature of the water that needs to be heated. By substituting the values, we get: Q = 600 × 4.18 × (120 – 32) ≈ 149776 J/s. Using the heat conduction equation and the formula for convective thermal resistance, it is possible to calculate the external surface area A of the 304 stainless steel tube, as follows: A = Q / (U × ΔTlm), where U is the thermal conductivity and ΔTlm is the logarithmic mean temperature difference. Based on empirical values, U is taken as 200 W/m·°C, and ΔTlm is taken as 15°C. By substituting the values, we get: A = 149776 / (200 × 15) ≈ 49.9 m². Therefore, the heat exchanger area made of 304 stainless steel tubes using circulating water for the first stage requires approximately 50 square meters. 20 square meters is definitely not enough. The same method can be used to calculate the area of the secondary heat exchanger, by using ΔTlm equal to 7°C. By substituting the values, we get: A = 80 × 4.18 × (120 – 7) / (200 × 7) ≈ 69.1 m². Therefore, the area required for a heat exchanger made of 304 stainless steel with 7-degree water cooling for the second stage is approximately 70 square meters. .
Is the steam heat calculation incorrect? A value of 200w... is that too low?
The heat of steam is mainly latent heat. The heat transfer coefficient during the condensation process is very high. Let’s use software to calculate it instead
Mistake in the calculation. 600 is the value in hours; it needs to be converted to seconds. Using the formula Q = mcpΔT, only a small amount of sensible heat is obtained; to condense the steam, latent heat must be taken into account
200 W/m?·℃ is not the same concept as 200W. This is the heat transfer coefficient, usually denoted by K
Level 1 is 50 square meters, level 2 is 70 square meters; generally, industry doesn’t design things this way.
Please, expert, provide the correct solution process