29674 - Fluid Machines T

Learning outcomes

Students acquire the basic knowledge about volumetric pumps and positive displacement compressors, the cooling systems, the heat pump and the internal combustion engine.

Course contents

Requirements/Prior knowledge

The requirements needed to effectively follow the course are the basics of technical physics (thermodynamic diagrams, first and second law of thermodynamics, gas laws, equation of fluid motion), chemical (balance of elementary chemical reactions) and mechanical drawing (freehand drafts).

Classes are held in Italian.

                                   COURSE CONTENTS

Volumetric pumps

Architecture of the alternative volumetric pump, ideal and real indicator diagram, determination of the ideal and real characteristic curve at varying the number of revolutions, definition of the total efficiency of the machine according to the volumetric and hydromechanical efficiency and their dependence on the rotational speed and the operative difference pressure.

The flow rate of the single-effect alternative pump and its regularization with the alternative double-acting pump and with pneumatic compensator in the suction and delivery ports. Multiple plunger pumps. Reason for the odd number of multiple plunger units.

The different types of volumetric pumps: external and internal gear pumps, vane pumps, diaphragm pumps, peristaltic pumps, screw pumps.

Centrifugal pumps

Study of the flow in a rotor channel: expression of the work through the equation of the kinetic energies and derivation of the Euler equation. Centrifugal pump architecture as a consequence of the work equation through the kinetic energies, suction and delivery speed triangles and its operation. Definition of theoretical prevalence of a centrifugal pump according to the volumetric flow rate processed by the pump and to the output angle of the blades (forward, radial and backward blades). fluidodinamic losses trend in the centrifugal pump and determination of the actual head according to the flow rate. Calculation of prevalence at zero flow. Link between prevalence and pressure increase.

Efficiency of a centrifugal pump: total ,hydraulic and mechanical efficency. Torque and power trends at a given rotor speed.

The hydraulic similitude concept to obtain the characteristic curve of the centrifugal pump at a different rotation speed with respect to the characteristic obtained experimentally.

The problem of priming a centrifugal pump. Calculation of pump suction pressure.

The cavitation phenomenon, the NPSH definition of the pump and the plant, considerations on the conditions for which cavitation occurs and use of the NSH diagram to verify the correct placement of the pump in a circuit.

Elementary design of a centrifugal pump. The passage from the centrifugal pump to the axial pump with the decrease of the prevalence and the increase the flow required by the pump. Axial blades: the speed triangles near the hub and at the end of the blade in the axial pump.

The transition to the multicellular centrifugal pump for high prevalence values. The balancing of the axial thrusts of the impeller assembly in the multicellular pump.

Determination of the operating point of a pump inserted in a hydraulic circuit

Determination of the characteristic curve of pumps arranged in series and in parallel.

Determination of hydraulic resistance of branches arranged in series and in parallel.

Determination of the operating point of a centrifugal pump in a non-elementary hydraulic circuit: simplification of the hydraulic circuit by determining the overall resistant characteristic and the operating point of the pump and identification the flow rates in all branches of the hydraulic circuit.

Test circuit of a pump

The main elements of a pump test circuit: tank, flow measurement, measurement of the difference in pressure between pump delivery and suction, valve for the variation of the circuit characteristic, heat exchanger to control the oil temperature in the case of oleodynamic circuit, necessity of the presence of a pressure limiting valve at the delivery of the volumetric pump.

Operational differences between centrifugal and volumetric pumps.

Comparison between the characteristics of the centrifugal pumps and the volumetric pumps in function of the flow rate to be processed and of the prevalence to be introduced into the fluid.

The different operational fields of centrifugal pumps, multicellular pumps and axial pumps.

Volumetric compressors

Architecture of alternative volumetric compressor, ideal and real indicator diagram, dead volume, volumetric efficiency. Limit on the compression ratio achievable in the single stage of a volumetric compressor. Stage work and specific work of a volumetric compressor stage.

Choice of the optimum stage compression ratio in two-stage compressor and extrapolation to the case of n stages to minimize compression work.

The different architectures of volumetric compressors: single-acting ,double-acting and multi-phase reciprocating compressors, vane compressor, at liquid ring, at screw and Roots.

Internal combustion engines

Introduction to internal combustion engines: architecture and main definitions.

The theoretical thermodynamic cycles. Cycles Otto, Diesel, Sabathè: transformations and efficiency.

From ideal indicator diagrams to real ones. The mean temperature of the exhaust gases.

The engine power expressed via thermal analysis. The lower heating value of the air-fuel mixture. Indicated and effective mean pressure. Simplified expressions of engine power and torque.

Efficiencies that influence the behavior of the engine: combustion, thermodynamic, indicator, volumetric and mechanical. Total and thermal efficiency of the engine, link between thermal efficiency and specific engine consumption.

Relationship between the main geometrical engine parameters: the mean piston speed and the stroke/diameter ratio.

Engine performance curves (torque, power and specific consumption).

Relatioship between single and multi cylinders engine with the same power and with the same total displacement. Limit to the cylinder number in a multi cylinder engine. Different architectures of multi-cylinder engine.

Engine load control: by means of quantity of the mixture in spark-ignition engines and the quality of the mixture in compression-ignition engines. Evaluation of the effects of load control through the expression of the thermal power of the engine.

The combustion process in gasoline and Diesel engines and its influence on the architecture of these types of engines.

Concepts of: combustion speed, flame front, equivalence ratio, auto-ignition delay, stoichiometric air-fuel ratio, knock.

Fuel injection systems for internal combustion engines:

gasoline engines: electronic engine control based on the speed-density system. Architecture of the port injection system: pump, injector and pressure regulator. The direct gasoline injection.

Diesel engines: the evolution of the diesel fuel injection system from the Bosch mechanical injection system to the common rail injection system.

Polluting emissions: formation, control and post-treatment.

Auxiliary systems: the lubrication circuit and solution to limit the absorbed power.

Supercharging in internal combustion engines: systems with centrifugal compressor and systems with volumetric compressor. Intercooler contribution to supercharging.

2-stroke engines: architecture, indicator and performance diagrams.e.

Readings/Bibliography

"Sistemi Energetici" 1 – MACCHINE A FLUIDO, G: Negri di Montenegro, M. Bianchi A. Peretto – Pitagora Editore

"Sistemi Energetici" 2 – COMPLEMENTI, M. Bianchi, F. Melino, A. Peretto – Pitagora Editore

"Internal Combustion Engine Fundamentals", John B. Heywood, Mc Graw Hill

"Motori Endotermici Alternativi", G. Minelli, Pitagora

Teaching methods

The lessons are frontal in the classroom. The teacher, replacing the traditional blackboard, uses a tablet connected to the projector to develop the concepts and to show the supporting teaching material. At the end of the lesson the teacher makes available the material shown in a pdf file, downloadable from the IOL platform.

Attendance is strongly recommended for better learning of concepts and notions, but does not affect the final evaluation process.

Assessment methods

The assessment methods consist of an oral part lasting about 45 minutes, during which the student must answer two questions, randomly extracted from a list of about eighty questions covering the entire program, list given at the last lesson of the course in the same dropbox folder that collects all the material presented during the lessons.

During the exam, with regard to fluid machines, their components and functions, is evaluated the student's ability to:

- use the thermodynamic instruments correctly;

- describe their operation;

- theoretically justify their architecture;

- represent their geometry with a free hand sketch;

- evaluate their performance;

The evaluation, expressed in thirtieths, will be higher the more the student is:

- autonomous in articulating responses to the two questions;

- exhaustive in explaining the arguments;

- precise in representing the functionality of the free-hand sketches.

The teaching of Fluid Machines T (6 CFU) is one of the two modules that, together with the Energy Systems T course (6 CFU), constitutes the integrated course of Fluid Machines and Energy Systems T CI (12 CFU). The vote that will be recorded will be calculated with the arithmetic average of the single votes that the student will have obtained in the two modules. If the result of the average presents the decimal number 0.5, the vote will be rounded in excess. The "30 cum laude" is associated with the number 31. Consequently, in order to obtain the "30 cum laude" final evaluation, the student must be in one of the following two cases:

- have received "30 cum laude" in both modules

- obtaining "30 cum laude" in one form and 30 in the other.

The exam dates are comunicated in advance through the AlmaEsami web platform of the University of Bologna. It is possible to enroll to the exam from 7 to 2 days before the exam date. At the time of the exam the student must carry an identification document.

Teaching tools

The course will be carried out through the use of:

- Slides and audiovisual supports

Office hours

See the website of Davide Moro