Flow inside pipe, heat transfer

In summary, the heat transferred to the water is used to calculate the wall temperature at a given point in the pipe. The heat flux is constant along the length of the pipe and the inside surface area of the pipe is 0.47 m2.
  • #1
Kqwert
160
3

Homework Statement


A 5m long heated pipe is used heat up water from 15°C to 65°C. Water flow through the pipe is 10liter/min. The heating gives a constant heat flow in all parts of the pipes surface. The inner and outer diameter of the pipe is 30 and 50 mm, respectively. Calculate the heat transferred to the water and the inner surface temperature of the pipe at the end (point where water leaves the pipe at temperature of 65oC)

Homework Equations

The Attempt at a Solution


When calculating the heat transferred to the water I used
Q = m,massflow*Cp*dT.

Cp was taken at the "medium" temperature of 40 celsius. My question is: Can you use the heat transferred to the water, i.e. Q, in calculating the wall temperatures at a given point in the pipe? I would then use Q = h*A,i*(Twall-65) and solve for Twall. h is calculated by using the Reynolds/Nusselt number,
 
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  • #2
Kqwert said:

Homework Statement


A pipe with heating is used to heat up water from 5 celsius to 65 celsius. The volume flow through the pipe is 10L/min. The heated pipe gives a constant heat input over the length of the pipe. Find the effect of the heat exchanger and the temperature of the inner pipe wall at the exit.

Homework Equations

The Attempt at a Solution


When calculating the effect of the heat exchanger I used
Q = m,massflow*Cp*dT.

Cp was taken at the "medium" temperature of 40 celsius. My question is: Can you use the effect of the heat exchanger, i.e. Q, in calculating the wall temperatures at a given point in the pipe? I would then use Q = h*A,i*(Twall-65) and solve for Twall. h is calculated by using the Reynolds/Nusselt number,
What is the exact statement of the problem?
 
  • #3
Chestermiller said:
What is the exact statement of the problem?
I have now edited my first post with the correct problem statement, as well as how I wanted to solve it, as I mixed it with another question while typing..
 
  • #4
Kqwert said:
A 5m long heated pipe is used heat up water from 15°C to 65°C. Water flow through the pipe is 10liter/min. The heating gives a constant heat flow in all parts of the pipes surface. The inner and outer diameter of the pipe is 30 and 50 mm, respectively. Calculate the heat transferred to the water and the inner surface temperature of the pipe at the end (point where water leaves the pipe at temperature of 65oC)
If the heat flux is constant along the length of the pipe, what is the heat flux at the inner surface of the pipe?
 
  • #5
Chestermiller said:
If the heat flux is constant along the length of the pipe, what is the heat flux at the inner surface of the pipe?
It is equal to the heat flux along the length of the pipe?
 
  • #6
No. It is equal to the component of heat flux perpendicular to the wall of the pipe. What is the overall heat load of the pipe?
 
  • #7
Chestermiller said:
No. It is equal to the component of heat flux perpendicular to the wall of the pipe. What is the overall heat load of the pipe?
That would be 34.6kW.
 
  • #8
What is the inside surface area of the pipe? What is the wall heat flux at the inside surface of the pipe?
 
  • #9
Chestermiller said:
What is the inside surface area of the pipe? What is the wall heat flux at the inside surface of the pipe?
The inside surface area of the pipe would be 0.47 m2. The wall heat flux is 34.6 kW / 0.47 m2 ?
 
  • #10
Kqwert said:
The inside surface area of the pipe would be 0.47 m2. The wall heat flux is 34.6 kW / 0.47 m2 ?
Can you please actually state that as a single number with units?
Is the flow (a) laminar or (b) turbulent?
 
  • #11
Sorry. 73.6 kW / m^2 I would say. The flow is turbulent.
 
  • #12
Kqwert said:
Sorry. 73.6 kW / m^2 I would say. The flow is turbulent.
Based on your heat transfer correlation, what is the heat transfer coefficient for the flow inside the pipe?
 
  • #13
Chestermiller said:
Based on your heat transfer correlation, what is the heat transfer coefficient for the flow inside the pipe?
It is 1548 W/m^2*K
 
  • #14
Based on the heat flux and this heat transfer coefficient, what is the temperature difference between the bulk fluid and the wall?
 
  • #15
That is 47 degrees, and Twall is then 112 celsius. Is this correct?
 
  • #16
Is this way of solving the problem only possible because the heating gives a constant heat flow across the length of the pipe? I.e. using the calculated total heat transferred in finding inner wall temperatures at different places across the pipe.
 

1. What is the purpose of studying flow inside pipe and heat transfer?

Understanding flow inside pipes and heat transfer is crucial in a variety of industries, from manufacturing to energy production. It allows us to optimize process efficiency, improve product quality, and design systems that can handle high temperatures and pressures.

2. How does heat transfer occur inside a pipe?

Heat transfer inside a pipe occurs through convection, conduction, and radiation. Convection is the transfer of heat through the movement of fluid particles, while conduction is the transfer of heat through the physical contact between the fluid and the pipe walls. Radiation is the transfer of heat through electromagnetic waves.

3. What factors affect the rate of heat transfer inside a pipe?

The rate of heat transfer inside a pipe is affected by several factors, including the fluid properties (such as viscosity and thermal conductivity), the pipe material, the flow rate, the temperature difference between the fluid and the pipe walls, and the geometry of the pipe.

4. How is the heat transfer coefficient calculated for flow inside a pipe?

The heat transfer coefficient for flow inside a pipe can be calculated using the Nusselt number, which is dependent on the fluid properties, flow conditions, and pipe geometry. The Nusselt number is then used in conjunction with the thermal conductivity of the fluid and the pipe diameter to calculate the heat transfer coefficient.

5. What methods are used to enhance heat transfer inside a pipe?

There are several methods that can be used to enhance heat transfer inside a pipe, such as increasing the flow rate, using fins or turbulators inside the pipe, or adding secondary fluids (such as refrigerants) to the system. These methods can increase the heat transfer coefficient and improve overall system performance.

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