Temperature of the tank in a superheater

[vishnu123]

how can i find the rate of change of temperature of the tank for a superheater? Or is there any relationship between the change in temperature of the tank when it is filled with hot gas?

 

[BvU]

Hello again,

Your question is a bit unclear: are you talking about the 'tank' wall or about the 'tank' contents ?

Usually a superheater is a heat exchanger with a hot gas on the process side and an even hotter gas on the utility side. As such it has a temperature profile, not just 'a temperature'.

 

[vishnu123]

hello once again,
I have modeled electric superheater, but not a heat exchangerand i am talking about the tank wall temperature.so in the equation i need to find the temperature difference of the wall. i know the initial temperature of the tank wall but not the final temperature of the wall. so the initial temperature will be when the tank is completely empty and the final temperature will be the temperature after it is been filled with the gas.

 

[BvU]

This sounds rather strange to me. You have an initial temperature of a tank wall for a (vacuum ?) tank and want to do a dynamic simulation of simultaneously filling (how and with what?) and heating (how and with what ?) ?

In a previous thread you wanted to build an evaporator model. Is this superheater a separate piece of equipment ? Are you describing a continuous flow process or a batch process ?

Could you please specify a complete scenario ? You'll need it anyway for a working model. Also make clear what assumptions and simplifications you make.

 

[vishnu123]

hello @BvU ,
its nothing to do with boiler. Its completely an other task. Its a continuous flow process,but i am jus modelling the individual components and later i need to include all the components in the main model. Here is the equation which i have modeled for superheater
$$m_{a}*C_{p}*\frac{\mathrm{d}T _{a}}{\mathrm{d} t}+\rho _{s}*V_{s}*C_{p}**\frac{\mathrm{d}T _{out}}{\mathrm{d} t}= Q_{ele}+C_{p}*\dot{m}_{in}(T_{in}-T_{out})$$
where
[m][/a] = mass of metal/wall
[C][/p] = Specific heat
[T][/a] = temperature of the metal
[ρ][/s] = density of the steam
[V][/s] = Volume of the steam
[T][/out] = Outlet Temperature of the steam
[Q][/ele] = electrical resistance
mdot = Mass flow rate
[T][/in] = Inlet Temperature of the steam

so in this equation i need to find the rate of change of temperature of the metal. What I need is is there any relation to find the rate of change of metal/wall. I don't know how it works when I implemeted in main model. As of now i am just modelling the individual components with few reference input values.

 

[Chestermiller]

Well, to a first approximation, you can take the metal temperature to be equal to the outlet temperature. Otherwise, you need to include a separate heat balance on the metal, and account for the heat transfer rate between between the vapor and the metal.