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: 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.

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

"Macchine a Fluido", V. Dossina, G. Fermin, P. Caetan, G. Montincao, A. Onorati, G. Persico, CintoStudi

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 of learning consists of an oral examination lasting approximately 45 minutes, during which the student is required to answer two questions: one concerning the part of the course devoted to fluid machinery and one concerning the part devoted to internal combustion engines.

The questions are selected at random from a list of approximately eighty questions covering the entire course syllabus. The list is made available on the VIRTUALE platform during the final lecture of the course. On the same platform, students can also access the PDF files of all lectures and the corresponding video recordings.

The oral discussion of the two questions is intended to assess the achievement of the expected learning outcomes, with particular reference to the Dublin Descriptors.

In particular, the following will be assessed:

• knowledge and understanding of the operating principles of fluid machinery and internal combustion engines, their constructional and operational characteristics, and the main parameters affecting their performance (Dublin Descriptor 1 – Knowledge and understanding);

• the ability to apply the acquired knowledge to the analysis of the operation of fluid machinery and internal combustion engines, correctly interpreting diagrams, characteristic curves, and operating conditions (Dublin Descriptor 2 – Applying knowledge and understanding);

• the ability to make independent assessments by comparing different technical solutions and justifying conclusions on the basis of performance, energy efficiency, and operating conditions (Dublin Descriptor 3 – Making judgements);

• clarity of presentation, command of technical terminology, and the ability to discuss critically the topics covered during the course (Dublin Descriptor 4 – Communication skills).

The final grade is expressed on a scale of 30 and takes into account the following criteria:

• knowledge and understanding of the course topics: 25%;

• ability to apply knowledge and integrate the different topics: 25%;

• critical analysis skills and independent judgement: 20%;

• command of technical terminology and clarity of presentation: 15%;

• ability to explore topics in depth and engage in critical discussion: 15%.

The grade will be higher when the student demonstrates:

• independence in developing and presenting the answers to the two questions;

• completeness and thoroughness in the presentation;

• accuracy in drawing freehand diagrams and explaining their functional operation.

The examination is passed with a minimum grade of 18/30. Honours (Cum Laude) may be awarded in the case of an outstanding performance.

The 6-ECTS course unit Macchine T, together with the 6-ECTS course unit Sistemi Energetici T, constitutes the 12-ECTS integrated course Macchine e Sistemi Energetici T C.I.

The final grade recorded for the integrated course is calculated as the arithmetic mean of the grades obtained in the two course units. If the resulting average has a decimal part of 0.5, the grade is rounded up to the next whole number.

For the purpose of calculating the average, a grade of 30/30 with honours is assigned the numerical value of 31. Consequently, a final grade of 30/30 cum Laude may be awarded in either of the following cases:

• 30/30 cum Laude obtained in both course units;

• 30/30 cum Laude obtained in one course unit and 30/30 in the other.

Nine examination dates are scheduled for 2027, already published on the University of Bologna’s AlmaEsami platform.

Students may register for an examination from seven to two days before the examination date. On the day of the examination, students must present a valid identity document. 

For each examination session, students who have been granted working-student or student-athlete status may request an alternative examination date in place of one of the regular examination dates scheduled within the same session.

The request must be submitted to the lecturer at least 14 days before the first examination date of the session, so that a date compatible with all requests received can be identified.

In accordance with the University Code of Ethics, students are required to act with the utmost integrity during the examination.

Any conduct aimed at improperly altering the outcome of the examination is prohibited, including copying, plagiarism, unauthorised access to materials or online learning resources, and the use of unauthorised artificial intelligence tools or systems.

The possession or use of unauthorised devices or materials during the examination will result in the immediate termination and invalidation of the examination, as well as a report being submitted to the relevant University offices.

Conduct in breach of these provisions may result in disciplinary proceedings and, where it may constitute a criminal offence, in a report to the competent authorities, with the possible initiation of criminal proceedings.

 

Teaching tools

The course will be carried out through the use of:

- Slides and audiovisual supports

Office hours

See the website of Davide Moro