# BLDG 365 lab 2.docx - Objective The objective of this...

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Objective:The objective of this experiment was to determine, through natural convection andradiation, as well as forced convection, the transfer of heat from a cylinder.Introduction:This experiment will look at the effects of convection (both natural and forced) and radiation. Natural convection occurs, for example, when a heated cylinder of diameter D and length L is at a temperature greater than that of the ambient temperature and warms the air around it. When thesurrounding air heats up, it expands causing its density to lower and resulting in the warm air to flow upwards due to buoyancy. As the warm air flows up, it is replaced but cooler air from below, which in turn warms up and the process repeats. Similarly, forced convection heats the airaround the aforementioned cylinder but instead of allowing the buoyancy of the lower density airto determine the direction of flow, a fan for example would decide the direction of flow. In the example above, the transfer of heat is mainly caused by the effects of natural convection, but it also has a contribution from radiation. In this experiment we will be measuring the heat transfer due to natural and forced convection, along with radiative heat transfer. For the natural convection, heat will naturally flow form the bottom of the convection/radiation apparatus and temperatures at different points will be recorded. As for forced convection, heat will flow form the bottom of the apparatus with a fan forcing the warm air up.To determine the heat loss due to natural convection, the following equation can be used:ϕC=hCAs(TSTa)(1)Where, ϕc is the heat loss due to natural convectionhc is the natural convection heat transfer coefficient [W/m2 °C]Asis the surface area [m2]Ts is the surface temperature [°C]Tais the ambient temperature [°C]To calculate the natural convection heat transfer coefficient, use the following equation:hC=1.32(TSTaD)0.25(2)Where, hc is the natural convection heat transfer coefficient [W/m2 °C]Ts is the surface temperature [°C]
Ta is the ambient temperature [°C]D is the diameter of the cylinder [m]To determine the heat loss due to forced convection, the following equation can be used:ϕf=hfAs(TSTa)(3)Where, ϕf is the heat loss due to forced convectionhf is the forced convection heat transfer coefficient [W/m2 °C]Asis the surface area [m2]Ts