Читать книгу Fundamentals of Heat Engines - Jamil Ghojel - Страница 65

1 1.6 The following nondimensional parameters are suggested for graphical representation of compressor characteristics:where is the mass flow rate, R is the gas constant, T is the gas temperature, D is the impeller diameter, and p is the gas pressure. Verify whether these parameters are truly nondimensional. If they are not, suggest a corrected form of the parameters.

2 1.7 Dimensional analysis has identified the following function for the pressure loss in a pipe:whereCheck if these two groups are nondimensional, and suggest remedies if they are not.Determine the actual correlation for flow of water in a 1500 mm long pipe with 12.5 mm diameter using experiments conducted at 20 °C with the following results:C, m/s0.3750.5940.8871.7803.3925.1577.1148.757Δp, Pa3007471 4805 07515 75332 60657 45682 832The water is at 20 °C, the density ρ = 998.2 kg/m3, and the dynamic viscosity is

3 1.8 Air is drawn into engine cylinder as the piston moves away from top dead centre (TDC) during the induction stroke, as shown in the following figure. Determine the pressure drop in the induction manifold for these conditions:Ambient pressure pa = 0.1 MPa.Flow velocity at the inlet Ca is negligible, and at the valve throat C = 56 m/s.Loss head at the valve restriction is given by hloss = βC2/2g, where the loss factor β = 7.Density of air ρa = 1.21 kg/m3. (Due to the small pressure drop during the induction process, air can be treated as incompressible fluid.)

4 1.9 In a frictionless cylinder and piston device, the piston is forced against a gas by a spring, which exerts a force directly proportional to the gas volume. In addition, the atmospheric pressure of 101.3 kPa acts on the outer face of the piston.Considering the gas as a system, calculate the work for the process from an initial state of 0.2 MPa, 0.1 m3 to final volume of 0.3 m3.If the spring is taken as a system, find the work for the same process.Explain the difference in work terms for the two systems in (a) and (b).