I know the velocity, inlet and outlet temperature of oil flowing through a pipe. Now how to find the heat transfer coefficient of the oil flowing through the pipe? What are the steps?
first calculate Reynold number and decide that, is it turbulent flow or laminar.
accordingly apply the dittus bolter equation which give a relation between
Nu,Re and Pr .now Re and Pr are known to you.so Nu no.can be calculated.and hence find heat transfer coefficient.
note one thing that if temperature of oil is very high then u have to account for viscosity correction .that will give u better result.
first calculate Reynold number and decide that, is it turbulent flow or laminar.
accordingly apply the dittus bolter equation which give a relation between
Nu,Re and Pr .now Re and Pr are known to you.so Nu no.can be calculated.and hence find heat transfer coefficient.
note one thing that if temperature of oil is very high then u have to account for viscosity correction .that will give u better result.
Dear Hakeem,
I recommed a combination of Efstathios and Abhishek answers.
Since you know the inlet and outlet temperatures and the flow rate (Vdot), you can calculate the heat flux (Qdot), which the fluid loses.
Qdot= c * rho * Vdot * (Tin - Tout)
where c is the specific heat capacity of the fluid and rho density. These values change with temperature, use the values at (Tin+Tout)/2.
The heat transfer coefficient (alpha) is defined as
Qdot = alpha * A * (Tsurface - Tambient)
Tambient is the temperature of the room, in which the pipe is located.
Tsurface is the surface temperature of the pipe. You can estimate this, if you know the pipe material. If the pipe is made out of metal, you can assume Tsurface=average of Tin and Tout.
If not, or if the pipe is insulated, then you can either mesure the surface temperature of you should use the Dittus-Boelter equation as Abhishek suggested. If Dittus-Boelter is used, Tin and Tout are not needed for estimation of alpha. Thus, you can use the measured Tin and Tout to validate the heat transfer coefficient.
Hope this helps,
Jure.
Is the oil petroleum based? For petroleum based oils, the viscosity can be taken from Data books. One can refer the book "Process Heat Transfer" by Donald Q Kern, McGraw Hill Publications for all properties. The Prandtl number is to be evaluated at the bulk temperature. The Sider and Tate equation (developed considering the viscosity correction factor) is commonly used. The procedure for estimating the Nusselt number is explained in this book through worked out examples.
The heat transferred at the surface of the tube by conduction in the radial direction is equal to heat absorbed by the fluid by convection i.e., k dT/dr at r=R (surface of the tube) is equal to h (T-Tb). In the conduct of experiments, it is generally difficult to determine the temperature profile. If one can determine the variation of temperature in the radial direction, dT/dr, it is possible to determine heat transfer coefficient h, as k, T and Tb are known. Experiments are undertaken in small diameter tubes and generally difficult to determine the temperature profile. Hence we resort to the use of appropriate regression equations available in literature.
A careful and quantitative measurement of heat transfer is quite complicated and requires reference measurements as well; see our recent paper Merilainen et al., International Journal of Heat and Mass Transfer 01/2013; 61:439 and references therein for details.
the hear transfer in pipe is uaually calculated using : Nu = 0.023(Re^0.8)(Pr^0.33).
try to use this equation for water at the same velocity and temperatures.
then use it for oil with same velocitie and temperatures. The oil nusselt number are close at low velocities but water become higher at hiher velocities. the water heat transfer cofficients is 4 6 times the heat transfer coefficient for oil.
The fluid properties should found from lituratre at the mean temperature which you are going to use them to calculate Re Number. you may find Pr number or you may need to caluate it as well.
This comparison based on work that i am writing paper from it.
These ratios give you an idea as my case is different from yours.
The water heat transfer coefficient is 4 to 6 times the heat transfer for oil.
- Badges
- Science topic
- Similar topics
- Engineering
- Thermal Engineering