Question

Carbon dioxide (CO2) is used for the gas cooled reactor in shell and tube heat exchanger type steam generator (shown in Figure 2). 90000 kg/h entered to the exchanger under pressure and temperature of 4 bar and 500 OC respectively. The steam saturation temperature is 250 oC when the carbon dioxide leave the generator at 3300C. Presume the formed steam is saturated and dry. Using 25 mm inner diameter and 2 mm wall thickness, a copper tube is designed for CO2 mass flow rate of 350000 kg/m2h. Neglect the thermal resistance of the steam side. (a) Determine number of tubes that should be used (b) Determine the length of the tubes Take the following properties for the carbon dioxide: Cp=1.172 KJ/kg OC;u=0.0000298 Ns/m2; k=0.043 w/m oC; p=3.26 kg/m3 Take k (Copper) = 384 W/m oC VW Water in (cold fluid) = 250°C CO, (hot fluid) in (Im = 500°C) CO, out (4x2 = 330°C) Steam out (- 250°C)

Answer 1

3 As the Reas 4oool pipe flow) – the flow is turbulant The Musselt number relation for turbulent flow of cos through tube is, NuD = De - 0.023 Red 22.4-0.023x 8560.9 X 0.85 04 (Prco2=0.85) (taken from Wikipe dla) INUD 183.097 :: The heat transfer coefficient for con Plow through tube is .. Nuo hx Di ha Nusskor Di kor 183.097x 0.0243 6.025 h=314.93 W/ mer The heat transfer from rate from not cor to the sattracted Steam is calccelated as Qcon = (Thi To 1 & Encholri) x As 20kil where Qcos-fheat transfer rate for single tabe 0.04772 3x 1.172 X 183x (506-330) = (500- 250) + 314.93x ITX 0.029 XL InC00145/oops 21J X 0-043* L L= 22.225m L = 22.225m So, the length of the tubes of heat exchanger are