Lab 5
Abstract The objective of this lab was to determine the convective heat transfer coefficient of a heated sphere in an quiescent environment. In the experiment a hot brass sphere was put into water and cooled. The temperature of the sphere was recorded over a time of 600 seconds to see how it cooled and given temperature was recorded every 20 seconds. Results were then calculated at both of the time values 300 and 600 seconds. For the experimental results at time 300 seconds, the Rayleigh number, Ra=2,973.30, Nusselt number, Nu=5.36, and the heat transfer coefficient, h1=11.10. At time 600 seconds the results were; Ra=1,207.22, Nu=4.68, h2=9.70. The experimental heat transfer coefficient was 18.72 ± 2, and the theoretical heat coefficient was 10.40. Once plotting the data on a temperature vs. time graph, the data points at time 300, and 600 seconds were used to find the slope and equation of the graph. The graph had a negative slope and the equation of the line was y= -0.0028x - 0.8692.
Theory
The theory behind this experiment is to investigate the natural convection from a sphere, using lumped system analysis. A lumped system analysis is used to determine the convective heat transfer of lumped objects, having negligible internal resistance as compared to the external flow resistance, the temperature is assumed to be uniform throughout the object and being a function of time only. By graphing the recorded data points of the experiment, the experimental and theoretical heat transfer coefficients can be found, and those are used to understand the natural convection of the sphere. The mass, specific heat of brass, diameter, area, and kinematic viscosity, are all known values and used to calculate the Nusselt number, Raleigh number, and the heat transfer coefficient at a certain point. The following equations were used to calculate the results in the experiment: y = a1X + a0 a_1=(ΣxiΣyi-nΣxiyi)/((Σxi)^2-nΣxi^2 ); slope A = 〖πD〗^2 h_experimental =
Theory
The theory behind this experiment is to investigate the natural convection from a sphere, using lumped system analysis. A lumped system analysis is used to determine the convective heat transfer of lumped objects, having negligible internal resistance as compared to the external flow resistance, the temperature is assumed to be uniform throughout the object and being a function of time only. By graphing the recorded data points of the experiment, the experimental and theoretical heat transfer coefficients can be found, and those are used to understand the natural convection of the sphere. The mass, specific heat of brass, diameter, area, and kinematic viscosity, are all known values and used to calculate the Nusselt number, Raleigh number, and the heat transfer coefficient at a certain point. The following equations were used to calculate the results in the experiment: y = a1X + a0 a_1=(ΣxiΣyi-nΣxiyi)/((Σxi)^2-nΣxi^2 ); slope A = 〖πD〗^2 h_experimental =
References: 1. Hamid, Rahai., MAE300 LABORATORY EXPERIMENTS, Spring 2013. 2. Hamid, Rahai., MAE300 INSTRUMENTATION AND MEASUREMENTS, Spring 2013. 3. Cengel, Y.A., Heat Transfer, A Practical Approach, McGraw Hill, 1st Edition, 1998. 4. Incorpera, F.P., and De Witt, D.P., Fundamentals of Heat and Mass Transfer, John Wiley&Sons, 4th ed., 1996. 5. Holman, J.P., Heat Transfer, 8th ed. McGraw Hill, 1997.