Comp Assist Des Thermal System
Comp Assist Des Thermal System ME 416
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This 4 page Class Notes was uploaded by Princess Rolfson on Saturday September 19, 2015. The Class Notes belongs to ME 416 at Michigan State University taught by Staff in Fall. Since its upload, it has received 14 views. For similar materials see /class/207539/me-416-michigan-state-university in Mechanical Engineering at Michigan State University.
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Date Created: 09/19/15
ME 416 CAD of Thermal Systems ME 416 Computer Assisted Design of Thermal Systems AirWater Vapor Mixtures Basic De nitions Dry Bulb Temperature T DB This is the temperature of the airwater vapor mixture that would be measured with a standard thermometer It is the temperature that is provided in weather reports Relative Humidity This is the parameter that is provided in weather reports that is indicative of the moisture content of the airwater vapor mixture It is actually the ratio of the partial pressure of water vapor in the mixture to the maximum value of water vapor partial pressure This maximum value is the saturation pressure for water vapor at the temperature of the mixture Hence it is defined by P V Psat at Tmix Humidity Ratio w This is the true indication of the moisture content of the airwater vapor mixture It is nearly the percent by mass of water vapor in the mixture It is defined by mass of water vapor in the mixture mass of dry or pure air in the mixture Wet Bulb Temperature T W3 This is the measurement that is used to obtain the moisture content of an airwater vapor mixture It involves measuring the temperature of a wet object that comes to thermal and mass equilibrium with the surrounding air It is found that this equilibrium temperature depends on the moisture content of the air and has been correlated to the humidity ratio Dew Point Temperature T DP This is the temperature at which water would begin to condense out of an airwater vapor mixture It corresponds to 100 relative humidity and can be found as the saturation temperature that corresponds to the partial pressure of the water vapor in the mixture ME 416 CAD of Thermal Systems Mixture Enthalpy hav This is the enthalpy of the airwater vapor mixture and can be calculated from hav ha at Tmix 0 39 hvat Tmix Mixture Speci c Volume vav This is the specific volume of the airwater vapor mixture All of these properties are interrelated and following the state principle for thermodynamics if any two are specified all the others can be determined A convenient way to represent these relationships is graphically in the psychrometric chart shown below ME 416 Computer Assisted Design of Thermal Systems MATLAB InputOutput Tips There are a variety of ways to do input and output in MATLAB Below are a few tips that might prove useful Prompting the user for information This could be accomplished using the display disp command We begin by assigning a character string variable for our case call str the message we wish to relay to the user For example str Welcome to Steam Turbine Then to display this string we use the display commend as shown dispstr A simple trick to develop a menu with indents is to assign the character strings together and add spaces inside the quotes where needed For example strl Choose a turbine type str2 1 Ideal Turbine str3 2 Adiabatic Turbine and then use display dispstrl dispstr2 dispstr3 Receiving input from the user This could be accomplished using the input input command We simply assign the requested variable the input function For example Tlinput 39 Enter the Inlet Temperature in C 39 Note that this command will both write a prompt to the user as well as receive input Output of results One of the better ways to output nice looking results is to use the display function in conjunction with the sprintf command The sprintf command 1 ME 416 Computer Assisted Design of Thermal Systems Symbolic Manipulation with MATLAB To use the symbolic manipulation capabilities of MATLAB one must first define the pertinent variables as symbolic variables Consider that we wish to perform the following integral in order to produce an equation that will go into an Excel cell T jcPT dT Tu We begin by defining the temperature T as a symbol Tsym T For a string of variables we could use syms T C7 D7 Q Next we assign an expression to the specific heat cp374320020102T100 l517857Tl00 1523688T100 232 Note that we did not have to define cp as a symbolic variable since MATLAB is smart enough to figure this out Next we will want to indefinite integral of cP over T to obtain the internal energy To do the indefinite integral we use hintcpT Next we want to evaluate this at the lower limit of the integral hLsubshToT where To must have been defined preciously as a symbolic variable Then we want to evaluate this at the upper limit of the integral hUsubshD7T
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