1. Convection in Horizontal Pipes By Brid Fillion, Aaron Spencer, Marshall Pletcher
Introduction
results
Forced Convection
Excel Linear Regression tool
was used to calculate the
values for C and m
Same assumptions were
applied regarding Film temp
and cross sectional area
Reynolds number now required to account for the moving fluid according to equation
Solving for diameter reveals a much lower value of meters clearly demonstrating the increased effectiveness of a forced convective flow
In this study, three pipes with different diameters were experimented with to see the relationship between free convection and forced convection on each pipe. Reasons for this experiment were to see which convection type had the biggest effect on surface temperature. Different flow rates of air were used to also see the effect of higher and lower flow rates on the surface temperature of each pipe.
background
All three pipes had different diameters ¼”, 3/8”, ½”
Free convection was measured at both voltages of 15 V and 30 V
Forced convection was run only at 30 for 3 different air flows
Figure 5: This is a representation of how two different voltages effected each of the three different diameters surface temperature. The solid bars are the 30 V while the crossed are the 15 V.
Figure 4: This shows the relationship with airflow and surface temperature in all three pipes. Squares= smallest pipe, circle= medium pipe, triangles=largest pipe.
CONCLUSIONS
Figure 1: Diagram showing convection around a long horizontal pipe.
Free convection had a higher surface temperature
As air flow increased surface temperature decreased
Higher voltage resulted in higher temperatures
Air flow cause more noise and fluctuation in measurements data
Air flow comes to steady state faster
objectives
Study free and forced convection and the effects of different variables
Figure 6: This shows the relationship between air flow and ambient temperature in all three pipes. Each pipe is color coded and in order from smallest to largest diameter.
Figure 7:This shows the relationship between the AMP’s and the flow rate. Each pipe is color coded and in order from smallest to largest diameter.
Acknowledgements
Design Problem
Determine heating element dimensions to maintain an endothermic reactions at a temperature of 30℃ for free and forced convection
Natural Convection
Coefficients required for natural convection
were linearized and taken
From the linear regression tool in excel
Film temperature was calculated according to the formula 𝑇 𝑓 = 𝑇 ∞ + 𝑇 𝑤 2
The parameters of the Film temperature were interpolated and used in
conjunction with our experimental data to determine
coefficients to be used in the equation for free convection
The Length was assumed to be equal to the 6 inches determined in the laboratory to allow for the final dimension of diameter to be solved for from the derived cross sectional area
The value allows for a direct solution by formula A=𝜋𝐷𝑙 by solving for D with all other known values from the heat transfer equation q=hA𝚫T
The diameter necessary when assumed the heating element at 80℃ was 0.059meters
The group would like to thank Dr. Adam St. Jean of the Chemical Engineering Department at the University of New Hampshire for the support and lessons in this lab experiment. The group would also like to thank another lab in the Wednesday section for allowing us to use their medium sized pipe data as the apparatus had a system failure on the day of data collection.
Figure 2: Diagram showing the different between free and forced convection.
methods
Amperage is run through a selected pipe at a constant rate heating up the selected pipe
Two thermocouples are used to collect surface temperature (Ts) and the ambient or infinite temperature (Tꚙ)
Acknowledgements
Figure 1: convection-in-comsol-multiphysics/
Figure 2:
Figure 3: Apparatus used to measure surface temperature, ambient temperature, voltage, amps.