Unsteady State Heat Transfer
Abstract
The objectives of the Unsteady State Heat Transfer laboratory were to study the rates of heat transfer for different materials of varying sizes, to develop an understanding of the concepts of forced and free convection and to determine the heat transfer coefficients for several rods. These objectives were met by heating several rods and allowing them to cool through free convection in air, free convection in water and forced convection in water- while monitoring their change in temperature over change in time.
Seven heat transfer coefficients were determined during the laboratory for various rods. A copper rod underwent free convection in air, free convection in water and forced convection in water. The measured heat transfer coefficients for the copper trials were 10.13 W/m2K, 438.43 W/m2K and 1715.69 W/m2K, respectively. These results supported theory that convection occurs for quickly in denser mediums and when it has a driving force. Two stainless steel rods underwent forced convection in water; the large rod had an experimental heat transfer coefficient of 1704.42 W/m2K while the small one had 1817.43 W/m2K. The smaller rod was expected to have the larger heat transfer coefficient since it has a smaller surface area. The results of the stainless steel rods therefore also supported theory. The carbon steel rod possessed the smallest heat transfer coefficient for forced convection which was 370.25 W/m2K while the acrylic rod had the largest, 12 602.95 W/m2K.
The heat transfer coefficients were calculated using the Lumped Heat Capacity Method and the Exact Method. The Lumped Heat Capacity Method is only viable for materials with high thermal conductivities and high external thermal resistances. The Exact Method had to be used for the acrylic and stainless steel rods so they were concluded to have low thermal conductivities and low external thermal resistances.
Test Methods
Objectives
The objectives of the Unsteady State Heat Transfer
The objectives of the Unsteady State Heat Transfer laboratory were to study the rates of heat transfer for different materials of varying sizes, to develop an understanding of the concepts of forced and free convection and to determine the heat transfer coefficients for several rods. These objectives were met by heating several rods and allowing them to cool through free convection in air, free convection in water and forced convection in water- while monitoring their change in temperature over change in time.
Seven heat transfer coefficients were determined during the laboratory for various rods. A copper rod underwent free convection in air, free convection in water and forced convection in water. The measured heat transfer coefficients for the copper trials were 10.13 W/m2K, 438.43 W/m2K and 1715.69 W/m2K, respectively. These results supported theory that convection occurs for quickly in denser mediums and when it has a driving force. Two stainless steel rods underwent forced convection in water; the large rod had an experimental heat transfer coefficient of 1704.42 W/m2K while the small one had 1817.43 W/m2K. The smaller rod was expected to have the larger heat transfer coefficient since it has a smaller surface area. The results of the stainless steel rods therefore also supported theory. The carbon steel rod possessed the smallest heat transfer coefficient for forced convection which was 370.25 W/m2K while the acrylic rod had the largest, 12 602.95 W/m2K.
The heat transfer coefficients were calculated using the Lumped Heat Capacity Method and the Exact Method. The Lumped Heat Capacity Method is only viable for materials with high thermal conductivities and high external thermal resistances. The Exact Method had to be used for the acrylic and stainless steel rods so they were concluded to have low thermal conductivities and low external thermal resistances.
Test Methods
Objectives
The objectives of the Unsteady State Heat Transfer
References: Incropera/DeWitt/Bergman/Lavine. Introduction to Heat Transfer (5th edition). Wiley (2007). ChE3424 – Chemical Engineering Laboratory II: Laboratory Manual “Unsteady State Heat Transfer” (2011) Recommendations A recommendation for this lab would be to have a class lecture explaining all of the major concepts prior to the performing the lab. It is more beneficial for students to be applying knowledge they have gained in lecture while in the lab so that they are able to make relations to what they have learned. It is difficult to perform a lab and then interpret the results based on research in a minimal amount of time.