Chapter 8, Problem 8.81P

Draw the Temperature & compute the LMTD for CO-CURRENT & COUNTER-CURRENT flow heat exchanger. A single-pass tubular type heat exchanger heats air from 35 C to 80 C. Exhaust gas from DIESEL engine at 350 C is used as heating medium. If the final temperature of exhaust gas leaving the heat exchanger is 140 C, what is the LMTD?

The oil cooler of a ship Diesel engine is a simple counterflow type heat exchanger. Overall be 4. transfer coefficient, U is 0.400 kW/m'K and surface area A is 15 m'. Oil enters at 80C at 3 ke rate and water enters at 20°C at 4 kg/s rate. Find: a. The amount of heat transferred b. Water exit temperature Oil exit temperature C. Caer 4.18 kJ/kg.K, Con = 1.67 kJ/kg.K

4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into saturated steam at 500 kPa. (a) Find the steam flow (kg/s) (b) Determine whether the process is allowed by the second law (Answer: It is not!) (c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You should be able to see the problem if you sketch the air and the water temperature profiles as you move left to right through the exchanger. (Hints: The air will be essentially a straight line, while the water will not. For the water, think about what happens when it is changing phase.) This is called a pinch point violation, and it is a very important design consideration in advanced combined cycle systems and in nuclear power plants. Air 100 kPa 160°C 10 kg/s Saturated Vapor 500 kPa Air: 160°C Steam: 151.8°C Q Air 100 kPa 30°C Liquid Water 500 kPa, 20°C Air: 30°C Water: 20°C

heated from 50 C to 75 C by an oil flowing through the tube.. The oil enters at 115 °C and leaves at 70 °C. The overall heat transfer co-efficient is 340 W/m²K. Water flows at the rate of 65 kg/min through a double pipe counter flow heat exchanger. Water is (Specific heat of water is 4186 J/kg. C, and the specific heat of the oil is 1780 j/kg. °C). calculate the following: 1. Heat exchanger area 2. Rate of heat transfer 3. Mass flow rate of oil

(3) In a counter flow heat exchanger if AT = AT, show that AT = AT = AT. AT is the log mean temperature difference and AT, and AT, is the temperature difference at inlet and outlet respectively.

Answer the Problem 2

S2

PROBLEM # 22.a. mass 1020 kg /min, the temperature of hot water is being decreased from to 212.09 oF using a heat exchanger. at a a pressure = 2at m and flow rate = 248.09°F Reservoir waten u used as W coolant with mass flow rate = 1800 kalmin and inlet temperature = 50.09 of. The minimun allow able surface are a = 270. 17 ft o4 heat ex changer 2. %3D all ow able overall heat = 204.05 btu/ The transfer coefficient of heat exchanger maxi mum %3D 2 The heat to be use d must be capaci ty of inet and outlet temperatures the average value Find the Number of Transfer units (NTU) using effective ness esch anger wsing NTU metho d if the heat being used is heat exchanger parallel - flow double-pipe

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