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A pipe in a district heating network is transporting over-pressurized hot water (10 atm) at a mass flow of 0.5 kg/s. The pipe is 5 m long, has an inner radius of 50 cm and pipe wall thickness of 50 mm. The pipe has a thermal conductivity of 20 W/m-K, and the inner pipe surface is at a uniform temperature of 110 ºC. The convection heat transfer coefficient of the air surrounding the pipe is 100W/m2 -K. The temperature of the water at inlet of pipe is 130 ºC and the constant pressure specific heat of hot water is 4000 J/kg-ºC. If the temperature of the air surrounding the pipe is 20 ºC, determine the exit temperature of the water at the end of the pipe.

2 Answers

3 votes

Answer:3.6 kg/s 14 w/m-k

Step-by-step explanation:

User Deepakssn
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4 votes

Final answer:

To determine the exit temperature of water from the pipe, the heat transfer from the water as it passes through the pipe is needed. The heat transfer can be calculated using the heat transfer formulas for conduction and convection. Unfortunately, due to missing information, a definitive answer cannot be given.

Step-by-step explanation:

To determine the exit temperature of the water at the end of the pipe, we need to calculate the total heat lost by the water as it flows through the pipe. We can use the formula Q = mc∆T, where Q is the heat transfer, m is the mass flow rate of the water, c is the specific heat capacity of water, and ∆T is the change in temperature. Since we know the mass flow rate (0.5 kg/s), the specific heat capacity of water (4000 J/kg-°C), and the initial temperature of the water (130 °C), we can focus on calculating the heat transferred from the pipe to the surrounding air.

The heat loss through the pipe can be determined using the formula for heat transfer by conduction and convection: Q = U × A × ∆T, where U is the overall heat transfer coefficient, A is the surface area of the pipe, and ∆T is the temperature difference between the pipe surface and the surrounding air. To find U, we'd usually combine the convective heat transfer coefficient of the air and the thermal conductivity of the pipe's material in a series resistive circuit. The surface area (A) would be taken as the external area of the pipe. However, without the details of the outer pipe temperature or the convective resistance on the inner side (due to the hot water), we cannot complete this calculation without assumptions.

Since we do not have all the required information to accurately calculate the heat loss and determine the exit temperature of the water, we're unable to provide the student with a definitive answer.

User Aman Grover
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