![]() The compressor loses heat to the surroundings. Since air can be considered to be a diatomic gas and all the relevant molar volumes are greater than 5 L/mole, it is accurate to consider the gas ideal. The appropriate form of the 1st Law for this compressor is :īecause we know both T 1 and T 2 and we assumed that air behaves as an ideal gas in this process, we can use the ideal gas property tables to evaluate H 1 and H 2. For this compressor, changes in kinetic and potentail energies are negligible and only flowwork and shaft work cross the system boundaries. In order to determine the specific heat transfer for the compressor, we must apply the 1st Law for steady-state, SISO processes. Now, we can plug values into Eqns 3 & 4 to complete the first part of this problem. We can now either evaluate T 2 or use Eqn 3 to eliminate T 2 from Eqn 1. We can determine T 2 using the folling PVT relationship for polytropic processes: We can determine the shaft work for a polytropic process on an ideal gas using: Shaft work and flow work are the only forms of work that cross the system boundary. Kinetic and potential energy changes are negligible. The compressor operates at steady-state. Finish by using W S, H 1 and H 2 to evaluate Q. When the index n is between any two of the former values (0, 1,, or ), it means that the polytropic curve will cut through (be bounded by) the curves of the two bounding indices. The specific work done for a polytropic process is: wb (6a) ws n 1 n ( pf f pi i ) (6b) Where wb is the specific boundary work (see graph & math representation) and ws is the specific shaft work (see graph & math representation). Because the gas is ideal, we can use the ideal gas property tables to evaluate H 1 and H 2. Some examples of the effects of varying index values are given in the following table. ![]() Because the process is polytropic, we can determine T 2 and W S. The key to this problem is the fact that the process is polytropic and that the air can be assumed to be an ideal gas. Assume air is an ideal gas in this process. Calculate the specific work and heat transfer if the air follows a polytropic process path with δ = 1.32. Air is compressed from 1 bar and 310 K to 8 bar. ![]()
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