Weight Reduction and Stress Analysis of Air Conditioning Compressor Crankshaft – Mechanical project

Abstract:

The hermetically sealed reciprocating compressor is a major component in any refrigeration and air-conditioning systems. The design depends on the cooling capacity of the system, size, location, type of ac system etc. The compressor mainly consists of two parts, which are called as short-kit and an electric motor used for driving the short-kit (short-kit and electric motor are both called as long kit). The short-kit mainly includes a crank case, piston, connecting rod and crankshaft. Present work mainly deals with the redesigning of a short-kit component i.e., Crankshaft by reducing its weight. Crankshaft is a major part in the system which affect through various working stresses and the only dynamic part which has greater possibility to reduce the weight. The weight of any
component can be reduced in two ways; either by suggesting an alternate material or by redesign. In this project an attempt was made to reduce the weight of the crankshaft by considering their design. As a start of design the shaft is designed according to the specifications of the compressor without considering any other factors. The designed shaft is analyzed and the results obtained are reviewed. The most important factors that are concentrated are stress distribution and deflections. The designed shaft is optimized for its topology. The reviewed design is analyzed and the better design for the minimum weight is considered, According to optimized design parameters the shaft is re built. The future scope of project deals with the alternative materials which equalizes the present material properties.

Air Conditioning
Basic components of air conditioning system:
• Compressor
• Condenser
• Expansion valve
• Evaporator

The basic operation of the air-conditioning cycle is as follows:
1. The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas (red in the diagram above).
2. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid.
3. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas (light blue in the diagram above).
4. This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.

Hermetically Sealed Compressor
In the hermetically sealed compressor, the electric motor and compressor are both in the same airtight (hermetic) housing and share the same shaft.

The advantages of the hermetically sealed unit (elimination of pulleys, belts and other coupling methods, elimination of a source of refrigerant leaks) are offset somewhat by the inaccessibility for repair and generally lower capacity.

Principle parts of hermetically sealed compressors
1. Crankshaft
2. Connecting rod
3. Piston
4. Crankcase

Read More : Refrigerators Compressors -Types Of Compressor used in HVAC

Definition of Problem
This project deals with the Weight reduction of crankshaft which is used in air conditioning compressors. The crankshaft which is optimized and analyzed is being used in many R&A/C compressors. The problem is to reduce its weight. As the project deals with the design optimization of the crankshaft, the previous work is reviewed and the results are taken as a reference for present project work. The main problem is that the crankshaft should be optimized for its
minimum weight and it should be also taken care that stress should not exceed allowable stresses given for the material.

Objectives and Goals

In design optimization we have to state the design variables. The figure shows the design of the crankshaft that to be optimized. The present shaft that is being used in compressor weighs about 938 grams. Now the objective here the desired objective that is to be minimized its weight without sacrificing its function and performance.
The main functioning unit of a hermetically sealed compressor is a shot-kit which consists of all mechanical components viz… Crankcase, piston, connecting rod, crankshaft, out board bearing, thrust plate etc. The short-kit is a reciprocating system where the crank shaft in it is driven by an electric motor. The power obtained from the electric motor is utilized in compressing the Freon refrigerants.

The main part which connects the electric motor and the compressing unit is the crankshaft of the short-kit. The present focus of work is of reducing the weight of the crankshaft in the compressor. Crankshaft is one of the major components of the short-kit and has wider possibilities for design optimization. The crankshaft is to be re-designed for the present working stresses and to make the compressor perform better. 

finite element analysis model of crankshaft
finite element analysis model of crankshaft

Methodology

The project mainly is of two stages where in stage one, the study of the present existing model is done by determining the various properties, loads, material considerations, applications etc. The stage two of the project is dedicated to actual work, where the possible modification of model is done.
In this gives the information about the methods that are used for obtaining the optimized solution. With previous dimensional parameters the shaft is modeled in UNIGRAPHICS software. The modified shaft is also modeled. The models can be meshed for further analysis using a meshing package HYPERMESH or free/mapped mesh in ANSYS. Meshing of the component plays an important role in ansys, as it is basis for the analyzing the
component in any software package which supports finite element techniques. The meshed component is imported into ANSYS software, which is being used broadly for analysis.

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Weight Reduction and Stress Analysis of Air Conditioning Compressor Crankshaft – Mechanical project

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