By comparing the heat of combustion for rubber and paper we can see that more energy is produced when burning rubber. This then makes it less effective when recycled and should be incinerated instead. However, paper releases less energy when burned so it is a better candidate for recyling.
In order to look at the heat of combustion of paper we had to concider the fact that paper is composed mostley of cellulose. Cellulose is a carbohydrate that is a polymer composed of glucose. To look at the heat of combustion we followed the same set of equations used to calculate the heat of combustion for rubber. However, instead of looking at the number of carbons we looked at the number of glucose molecules. This was done because glucose can bind with its self to form polyisaccarides. The picture below shows maltose which is a common disaccaride of glucose. Based on the amount of glucose molecules in the polysaccarides present, the heat of combustion changes.
Based on our calculations we were then able to gain a better understaning of how the number of glucose molecules present can change the heat of combusiton. This is shown in the graph below:
The y-axis is the heat of combustion and the x-axis is the number of glucose molecules present.
Rubber is composed of alkanes with the primary ones being methane and ethane. In order to calculate the energy produced when rubber is burned we chose to look at the combustion reactions of both methane and ethane because they are the simplest alkanes present. The reactions were then used to find the heat of combustion using the bond energies. Using the bond energies the heat of combustion per mole was calculated. We then converted this into a heat of combustion per gram in order to use this value for comparison. We then preformed the same calculation for ethane and obtained the heat of combustion per gram. However, because rubber is composed of other alkanes we used the following formula to estimate the total heat of combustion:
From the above equation we then created the following graph. The graph allows us to gain a better understaning of the heat of combustion per mole vs. the number carbons.
For this project we looked at waste paper and rubber to see if it is more efficient to recycle or burn these materials. Through our Maple calculations we discovered that it is more efficient to recycle paper but burn rubber. This is the case because rubber produces more energy when burned than paper. This then makes it more difficult to recycle rubber.
We are Thermodynamics Team D. Our team consists of Lauren O’Dell, Iori Sanada, and Amanda Nothem.The first project that we are going to be working on will be looking at the functions and effectivness of heat pumps, and the second project will be solid waste solutions. Both of these have impacts and value in our everyday lives. Our goal is to present accurate information on the thermodynamic principles, engineering, and environmental impacts involved in both of these areas of research.
In the world today a majority of our residential energy is used in heating and cooling. One of the most efficient ways of performing this transfer of heat is by using a heat pump.
Heat pumps extract heat from a cold thermal reservoir and transfer it to a hotter reservoir.(1) This cannot be performed spontaneously as it going against the flow of equilibrium from hot to cold. In order for this transfer to occur external work needs to be done on the system as shown in the figure below.
Because of the second law of thermodynamics, heat pumps cannot be 100% efficient.(3) This is because the laws says that although work can be converted into heat, it is not reversible as all of the heat cannot be converted back into work. The flow of heat in a heat pump system can be shown by the reverse Carnot cycle.
Figure 2 Reverse Carnot Cycle
Here heat is taken for the cold reservoir, QL, to the hot reservoir, QH, by the addition of work. The work is equal to the area within the curves and the curves are the results of adiabatic and isothermal expansion and compression. The curve from 1 to 2 is the adiabatic compression, from 2 to 3 is the isothermal compression, from 3 to 4 is the adiabatic expansion, and from 4 to 1 is the isothermal expansion.
Heat pumps are highly efficient and renewable energy technology used for heating and cooling. There are three basic types of heat pumps: air source heat pumps, absorption heat pumps, and ground source heat pumps.(3)
Air source heat pumps: The outside air is used to heat or cool a building. The heating process begins when a cold refrigerant is heated from outside air being blown by a fan into refrigerant coils. Then the temperature is increased by compressing the refrigerant through a compressor. Electricity is used to compress a refrigerant. The heated refrigerant is then moved to the other refrigerant coils known as heating coils where a fan blows air to the coils and excerpts the heat from it. After the heated air is distributed through the buildings, the refrigerant passes through the expansion valve that cools it down and the cycle repeats all over again. This process is reversible. (3)
Absorption heat pumps: It uses heated water generated from solar boilers, geothermal resources or natural gas rather than electricity. The difference between an air source heat pump and an absorption heat pump is that an absorption heat pump absorbs ammonia or lithium bromide into water, then a low-power pump pressurizes it instead of compressing a refrigerant. Then the heat source boils the ammonia or lithium bromide out of the water, creating the heat. This process is not reversible. (3)
Geothermal heat pumps move the hat from the ground into the buildings in the winter, and take the heat away from the buildings and discharge it into the ground in the summer. It consists of an earth connection subsystem, heat pump subsystem, and heat distribution subsystem. The earth connection subsystem is a loop of pipes that is buried underground. A fluid, normally water or antifreeze mixture, circulates through these pipes to transfer the heat from the building to the ground. For heating, heat pump subsystem takes away the heat from the fluid, and transfers it to the building. The reversed process is used for cooling. Finally, the heat distribution subsystem distributes heated or cooled air throughout a building. (1)
The goal of a heat pump is to transfer heat from a cold reservoir to a hot one. However, in order to do this an input of work is required. The equation looking at this heat transfer of a heat pump can be written as follows(1):
For a perfect heat engine the efficiency is the reciprocal of the coefficient of performance of a heat pump(1). For this reason the coefficient of performance for a heat pump is 1/Eff. Normally the efficiency of a heat engine has to be less than one so for a heat pump the coefficient of performance is always greater than one. There is always a greater heat transfer than amount of work put into the heat pump(1).
1. Heat pumps and Refrigerators. Boundless learning, 26 June. 2013. Web. 3 Dec. 2013.
This equation shows the efficiency of a perfect engine/ Carnot engine (1). From the equation we can see that with a decrease in Th the overall efficiency would decrease and become smaller. This decrease in efficiency would then mean that the coefficient of performance would increase because it is one over the efficiency (1). This then shows that with a smaller temperature difference you get a greater coefficient of performance causing the heat pump to run more effectively.
1. Heat pumps and Refrigerators. Boundless learning, 26 June. 2013. Web. 3 Dec. 2013.
Geothermal heat pump is a clean source of energy. The EPA announced that geothermal heat pump systems have the lowest emission rate of carbon dioxide and the lowest overall environmental cost. It is also safe and clean to human health because there are no combustion flames, fuels, or odors. It does not pollute ground water sources either. Normally, water-based antifreeze solution is used for the fluid in the ground-loop heat exchangers. (1) The only impact it could have on the environment is the leakage of refrigerant during operation or loss of refrigerant during demolition of heat pumps. The impact on the environment depends on what kind of refrigerant we use. Hydroflourocarbons are the most commonly used refrigerants today. They have no ozone depletion potential but one of the causes of global warming. A lot of research has been done to find a method to calculate the contribution of greenhouse gas emission from heat pumps. The most well-known method is called TEWI (Total Equivalent Warming Impact), which calculates the sum of the direct emissions and indirect emissions of greenhouse gases. (2)