Heat transfer, reactors immersed coils

A stirred reactor contains a batch of 700 kg reactants of specific heat 3.8 kJ/kg K initially at 290 K, which is heated by dry saturated steam at 170 kN/m2 fed to a helical coil. During the heating period the steam supply rate is constant at 0.1 kg/s and condensate leaves at the temperature of the steam. If heat losses arc neglected, calculate the true temperature of the reactants when a thermometer immersed in the material reads 360 K. The bulb of the thermometer is approximately cylindrical and is 100 mm long by 10 mm diameter with a water equivalent of 15 g, and the overall heat transfer coefficient to the thermometer is 300 W/m2 K. What would a thermometer with a similar bulb of half the length and half the heat capacity indicate under these conditions ... 

The heat transfer requirements of reactors are frequently met by circulating a suitable fluid through either a coil immersed in the reaction mixture or a jacket surrounding the reactor itself. 

Stirred tank reactors are provided with a jacket or immersion coil for heating or cooling the reaction medium. The temperature of the medium inside the tank is generally uniform. The rate of heat transfer depends on the heat transfer area, the difference in the temperature between the reaction medium and heating or cooling fluid and heat transfer coefficient. 

Most of the simulators allow heat input or removal from a plug-flow reactor. Heat transfer can be with a constant wall temperature (as encountered in a fired tube, steam-jacketed pipe, or immersed coil) or with counter-current flow of a utility stream (as in a heat exchanger tube or jacketed pipe with cooling water). 

Both reactions are endothermic and have second-order (reaction 1) and third-order (reaction 2) kinetics. Heat is supplied to the reaction mixture by steam which flows through a coil, immersed in the reactor s content, with a heat transfer area A,. 

Small tubes are commonly employed where the reaction is rapid and/or the heat of reaction must be removed rapidly. The two conventional types of tubular reactors are (1) coils immersed in a constant-temperature bath and (2) a jacketed pipeline in which the inner tube is designed to withstand the reaction pressure. A modification of the conventional jacketed-pipe reactor can be used where it is desirable to minimize the thickness of the inner tube in order to reduce the area required for heat transfer. An example of this type of equipment is the liquid-phase heat exchanger of the Bureau of Mines, in which the outside pipe has an outside diameter of 4 2 ill- wall thickness of 1.005 in. The outside diameter of the inner tube is in., but the wall thickness is only 0.16 in. The worldng... 

Vtty few reactions are thermally neutral (AHr = 0), so it frequently is necessary to either supply heat or remove heat as the reaction proceeds. Ihe most common means to transfer heat is to circulate a hot or cold fluid, either through a coil that is immersed in the reactor, or through a jacket that is attached to the wall of the reactor, or both. 

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