Investigation of Thermal Effects of CO 2 on Earth-Atmosphere System Design Team Michel Beguin, Tim Bevins Dan Jakiela, Frank Kuchinski Design Advisor Prof. Yiannis Levendis Abstract This Capstone Project will quantify the effect of the CO 2 concentrations on the temperature of the earth s atmosphere. A twin chamber apparatus has been constructed to allow for a maximum stream of high-quality data. Some features of the apparatus include: ability to test various gases, an automated data acquisition system, and the ability to hold gases at different pressures. All of these features are intended to allow for a variety of tests to be run, as well as collection of data with minimal losses and inaccuracies. This project has yielded a variety of data, which after processing and repeatability studies could support correlations between atmospheric temperatures relative to gas concentrations in the atmosphere. For more information, please contact yal@coe.neu.edu. 36
The Need for Project Rising quantities of greenhouse gasses have created a warming effect on earth s atmosphere and surface. This drives the need for an experiment to quantify the thermal effects of specific gasses. Global warming is the theory that the average temperatures of Earth's surface, oceans and atmosphere are rising. The scientific consensus is that global warming is due to the increase in concentrations of greenhouse gases in the atmosphere, initiated by human activities through burning fossil fuels or deforestation. The main understanding of global warming is that these greenhouse gases are able to trap irradiative heat from the earth. The increase in human population and activities in the past century (i.e. The Industrial Revolution) has resulted in the emission of more greenhouse gases. The Earth s surface temperature has significantly increased, affecting its environment and the species depending on it. This project is primarily focused on the behavior of carbon dioxide in the atmosphere. The above illustration shows the correlation between CO 2 concentration in earth s atmosphere in parts per million with the change in temperature in degrees Celsius from the year 1000 to the year 2000. (IPCC Third Assessment Report 2001, Working Group I, Technical Summary) 37
The Design Project Objectives and Requirements The goal of this project is to develop a device designed to simulate the thermal effects of global warming in the earth s atmosphere. This device attempts to quantify a temperature difference between various gases in the atmosphere. Design Objectives The deliverables of this project include a fully constructed twin chamber apparatus, well documented and derived test rules and methods, automated data acquisition system, and a subsequent base of data that shows the effects of CO 2 on the earth s atmospheric temperature. Design Requirements The most important objective is to obtain a temperature correlation based on rising CO 2 quantities in the atmosphere. It is imperative that a temperature difference between the control substance (Air) and the experimental substance (CO 2 ) be greater than the error in the temperature measurement devices. Design Concepts Considered The main considerations in the design of the apparatus were: chamber length, quantity of chambers, data acquisition, ability to introduce various test gases, and a design that mitigated gas leaks. General Considerations There are a host of basic design features that any chamber constructed would have to incorporate. These included: an automated data acquisition system, the ability to introduce a host of different test gases, a modified light source, and a design that would minimize the opportunity for gas leaks over the lifetime of the chamber. Six Foot Single Chamber with Vacuum Insulation Layer Using the Hottel Correlation, (Incropera, Frank P. Introduction to Heat Transfer. 5th ed. 38
Hobokenm NJ: Wiley, 2007. Print) a semi-empirical formula which describes the effect of a heated surface on local gas temperature, the group determined that with a chamber length of six feet, a measurable differential between air and CO 2 gas temperatures could be achieved (ΔT gas = 40 C). The vacuum insulation layer was considered in order to provide the best possible insulation for the inner test chamber. A vacuum does not allow for convective or conductive heat transfer between the chamber and its surroundings, which make up for most of heat losses. Vacuum Layer Six Foot Twin Chamber A 6-foot twin chamber design was considered in order to be able to actively compare temperatures in the chambers. One chamber will consist of air and the other chamber will consist of the test gas. Also, having two chambers permits the collect a substantial amount of data in a short period of time. Final Prototype A six foot twin chamber device was the primary design concept the team decided on. This concept would meet all of the design goals, double data output, and provide a platform from which further investigations into global Six Foot Twin Chamber The chambers are constructed using four inch diameter acrylic tubing with a length of six feet. The end caps are machined from 6061 aluminum and contain threaded fittings for the introduction and extraction of various gases. The tubes to run the gases are silicone and are connected using a series of 39
warming could be built. ball valves and flow meters which provide complete control of all gas flow over the entire apparatus. Thermocouples are run through the exit gas ports to the underside of the apparatus where they meet with the data acquisition system. Inside the chamber, the thermocouples are shielded behind a small section of PVC pipe. This shielding prevents the tips of the thermocouples from seeing distorted readings from direct radiation from the light source. Chamber Insulation A heat transfer analysis was performed to determine if insulation was needed for this device. The calculations demonstrated that insulation was not necessary. However the experimental results displayed that the room s change in temperature does affect the temperature readings inside the chambers. By using insulation, the experimental data being gathered is unaffected by thermal activity in the surrounding environment, eliminating a major source of error. Need for a Collimated Light Source The current type of light source used on the device scatters too much, thus introducing several types of losses and issues associated with acquiring the best possible data. A collimated light source will focus the energy from the light source directly on the earth plate rather than on inner chamber wall, and 40
decrease general loss of light to the surroundings. This design will better simulate the Earth-Sun relationship the project is focused on. Improved Sealing Plates The new caps were designed specifically to eliminate chamber leaks as well as have tapped holes for the gas delivery system fittings, which allow for gases to be introduced or removed. Latches are used to seal the end caps; they can be adjusted to increase or decrease the seal strength. O-rings were used to seal the cap to the open tube face. Through preliminary testing it was shown that the new chambers can hold pressure in excess of what they will experience during any sanctioned testing. Financial Issues The apparatus had to be constructed of materials that were easily obtained, could be machined in house, and were not price prohibitive. The cost of the device was kept down by machining and assembling all parts of the apparatus in house. Much of the apparatus is constructed of commonly found materials that are available in large enough quantities that the cost is minimal. 41
Recommended Improvements The apparatus is ready for the development of individual pods for the introduction of aerosols and particulates. Improvements for this apparatus include further development into the introduction of particulates, aerosols, and vapors. Testing with such could yield results allowing for a much better understanding of the causes, and their direct effects respect to temperature change, of global warming 42