Water flowing at a rate of 0.723 kg.s-1enters the inside of a counter flow heat exchanger at 300K and is heated in an oil stream that enters at 385K at a rate of 3.2 kg.s-1. The heat capacity of the oil and the water is 1.89 kJ.kg-1K-1and 4.192 kJ.kg-1K-1respectively. The overall heat transfer coefficient of the exchanger is 300 W.m-2K-1and the area for heat transfer is 15.4 m2.Calculate the effectiveness of the heat exchanger
performance questions seem capturing up plenty immediately... performance is means out divided with the help of means in, and because perpetual action is thermodynamically not achievable, is continuously lower than one. means in is common if that is source is electric powered, merely V*I for merely resistive lots. If there's a motor in touch, do not forget that there'll be an inductive component of it which will make the means in seem truly larger than it honestly is in case you employ V * I to calculate it - you need to rather use a real watt meter which in reality outputs the fundamental of prompt Vi * Ii. i do not recognize what your effectiveness variables characterize, yet what you want is the flexibility in joules over a era of time or means in watts of the nice and comfy temperature bumped off/extra from the object you're cooling/warming. That divided with the help of means in is your performance.
This is a problem that requires you to balance the change in temperature of the two fluids with the amount of heat being transferred. You assume a set temperature changes for the two fluids and calculate the amount of heat the exhanger can transfer with those temperatures. You also calculate the amount of heat needed to make that change to the two fluids using their specific heats. At good starting point for a counter flow exchanger would be a difference between the inlet of the cold water and the hot oil of 10 to 5 degrees. Vary this difference until you get a heat balance in both calculations.
I happen to keep a programme for heat exchangers that I had used, for educanional purposes, some time ago. Running the programme step by step on your information I got, NTU = 1524.342. The subsequent calculation for the effectiveness (E) shows that, E = 1, which leads to the emergence of water (as steam!!) at 385 K, the same as that of the oil at entry. This not realistic, in assuming no phase change, and I think the problem lies with the very low flow rate of water. If you are only interested in the value of the effectiveness then its value as stated above with the optimum amount of heat transfer. For the heat exchanger to work with water undergoes no phase change the flow of water has to be more than tripled.
