Heat,work, thermal efficiency problems

In summary, the conversation is about two thermodynamics problems: determining the heat added, work produced, and thermal efficiency of a cycle with given temperature and entropy values, and finding the final temperature, change in enthalpy, and change in internal energy when adding heat to a specific amount of CO2. The person asking for help is struggling with understanding the given values and units in the problems.
  • #1
mocha1209
1
0


This is the question that I can't really answer

1. A cycle looks like an ellipse in the T-S diagram. The maximum and minimum temperatures are 1000K and 400K. The maximum and minimum entropies are 0.705 KJ/K and 0.235 Kj/K. Determine
a. the heat added per cycle, b. the work produced per cycle, c. The thermal efficiency of the cycle.

I'm trying to answer this question but I am pretty confused about having the minimum and maximum values. I don't even know what formua to use.

There is another question:

2. There are added 20 BTU to 5lb of carbon dioxide at constant volume. The initial temperature is 90F. (CV= 0.1565 Btu/lb-R) Determine. a the final temperature b. the change of enthalphy. c. The change of internal energy.

Im trying to answer this but I am getting confused about the BTU added to lb. I don't know how could I get BTU from lb to have it added.

Please help me out. I really need your help. This is a make or break of my grades. Thank you needed your response.:frown:
 
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  • #2
In problem 2) it's 20 BTU of heat added to 5 lbs of CO2. It is analogous to adding 20 kJ of heat to 5 kg of CO2.
 

FAQ: Heat,work, thermal efficiency problems

What is heat and how is it measured?

Heat is a form of energy that is transferred from a hotter object to a cooler object. It is measured in units of joules (J) or calories (cal).

What is work and how is it related to heat?

Work is the transfer of energy that occurs when a force is applied to an object and it moves in the direction of the force. In terms of heat, work can be done to increase the temperature of an object, or work can be gained from the transfer of heat.

How is thermal efficiency calculated?

Thermal efficiency is calculated by dividing the output energy by the input energy and multiplying by 100%. The output energy is the desired result, such as work, while the input energy is the total energy put into the system, including any losses.

What is the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, but it can be transferred or converted from one form to another. This means that the total energy in a closed system remains constant.

How do I solve problems involving heat, work, and thermal efficiency?

To solve these types of problems, you will need to use equations that relate to the specific scenario given. It is important to carefully read and understand the problem, identify the known and unknown variables, and choose the appropriate equation to solve for the desired result. It is also helpful to draw a diagram or visualize the scenario to better understand the relationships between heat, work, and efficiency.

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