When the liquid phase changes to a gas phase, how is the heat exchange area calculated when the temperature remains constant?
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Liquid carbon dioxide is turned into gaseous carbon dioxide in a vaporizer. Assuming that the temperature remains unchanged and only the state changes, how can we use the formula \"heat transfer power = heat transfer area * (heat transfer coefficient * temperature difference)\") to carry out the calculation?
This can also be taken into account. The inlet and outlet temperatures of the cold flow remain unchanged, but there is a temperature difference for the hot flow. Since the heat load is known, the heat transfer coefficient can be calculated first, and from that, the heat exchange area can be determined.
This post was last edited by kangqiaowuyun1 on 2015-10-13 at 14:44. I am using a water-bath type vaporizer; the water in the shell side is heated by steam. I am unable to determine the temperature difference on the shell side – the carbon dioxide inlet temperature is -30 degrees Celsius, and the outlet temperature is also -30 degrees Celsius; there is only phase change.
This generally relies on empirical values.
It can be calculated using the heat of vaporization of liquid carbon dioxide.
Assuming only a gaseous state, with heat exchange from -30°C to 50°C, where the shell side remains at a constant temperature of 50°C and the flow rate is 1200 KG/H, how is the heat exchange area calculated? The specific heat capacity of CO2 is assumed to be 1 KJ/KG. C: The heat transfer power is 1*80*1200=96000 Kj=26.7 kW. Next, knowing that the thermal conductivity k of the stainless steel heat exchange tube is 17, one condition is still missing: what is the temperature difference on the other side? Q=A*(K*△T). . How to calculate the heat exchange area?
Assuming only a gaseous state, with heat exchange from -30°C to 50°C, where the shell side remains at a constant temperature of 50°C and the flow rate is 1200 KG/H, how is the heat exchange area calculated? The specific heat capacity of CO2 is assumed to be 1 KJ/KG. C: The heat transfer power is 1*80*1200=96000 Kj=26.7 kW. Next, knowing that the thermal conductivity k of the stainless steel heat exchange tube is 17, one condition is still missing: what is the temperature difference on the other side? Q=A*(K*△T). . How to calculate the heat exchange area?
OP, in heat transfer calculations, the temperature difference used is usually the logarithmic mean temperature difference between the two heat exchange surfaces, not the temperature difference between the inlet and outlet of the same medium. Here you have -30°C on one side and 50°C on the other; there is no temperature difference between the inlet and outlet, so it’s simply 30 + 50 = 80°C. At the same time, you cannot consider only the heat conduction of the stainless steel heat exchange tubes; you also need to take into account the convective heat transfer from the water bath and carbon dioxide.
Hello, senior. If convection heat transfer is not taken into account and a temperature difference of 80 degrees is used, the calculation formula yields an heat transfer area of 0.02 square meters, calculated as 26.7 KW = A(17*80). This seems incorrect to me. . . How is convective heat transfer calculated? What is the formula? In a conventional shell-and-tube heat exchanger, there is a tube side and a shell side, with a fluid flowing between them to facilitate convective heat transfer. However, in this case, only the CO2 side has flow; the water in the shell side remains stationary. How should this be calculated? Plate heat exchangers should also have convective heat transfer, right? I earnestly ask for your guidance, senior!
The total heat transfer power is obtained through the latent heat of vaporization and specific heat capacity, but the heat transfer area still cannot be determined using these formulas
First of all, it’s already an evaporator – why did LZ use such a convoluted title? Secondly, the calculation of evaporators is already a well-developed and programmed process.