Evaluation of Heat Transfer Effects on Turbocharger Performance

2011 ◽  
Author(s):  
Borislav Sirakov ◽  
Michael Casey
Keyword(s):  
Heat Transfer ◽  
Cold Test ◽  
Practical Significance ◽  
Apparent Effect ◽  
Work Input ◽  
Low Mass ◽  
Mass Flows ◽  
Heat Transfer Effects ◽  
Low Speeds ◽  
Different Levels

Test data on several small turbochargers with different levels of heat transfer from the turbine to the compressor have been obtained through cooling of the turbocharger center housing and by testing in hot and cold test stands. This data identifies the strong effect of the heat transfer on the apparent efficiency of the compressor and turbine, particularly at low speeds and low mass flows. A simplified theory is used to explain the apparent effect of the heat transfer on the work input and efficiency. The results confirm that conventional performance maps underestimate the efficiency of the compressor stage and overestimate the efficiency of the turbine by as much as 20% points at low speeds. A correction procedure for this effect is defined which converts performance maps obtained with heat transfer to performance maps for adiabatic conditions (for both compressor and turbine) without any prior knowledge or measurement of the heat transfer. The practical significance of the results with regard to turbocharger performance and the relevance to a broader class of turbomachines is discussed.

Evaluation of Heat Transfer Effects on Turbocharger Performance

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Borislav Sirakov ◽  
Michael Casey
Keyword(s):  
Heat Transfer ◽  
Cold Test ◽  
Practical Significance ◽  
Apparent Effect ◽  
Work Input ◽  
Low Mass ◽  
Mass Flows ◽  
Heat Transfer Effects ◽  
Low Speeds ◽  
Different Levels

Test data on several small turbochargers with different levels of heat transfer from the turbine to the compressor have been obtained through cooling of the turbocharger center housing and by testing in hot and cold test stands. This data identifies the strong effect of the heat transfer on the apparent efficiency of the compressor and turbine, particularly at low speeds and low mass flows. A simplified theory is used to explain the apparent effect of the heat transfer on the work input and efficiency. The results confirm that conventional performance maps underestimate the efficiency of the compressor stage and overestimate the efficiency of the turbine by as much as 20% points at low speeds. A correction procedure for this effect is defined which converts performance maps obtained with heat transfer to performance maps for adiabatic conditions (for both compressor and turbine) without any prior knowledge or measurement of the heat transfer. The practical significance of the results with regard to turbocharger performance and the relevance to a broader class of turbomachines is discussed.

On the Efficiency of Compressors With Diabatic Flows

2009 ◽  
Author(s):  
Michael V. Casey ◽  
Thomas M. Fesich
Keyword(s):  
Heat Transfer ◽  
Simple Model ◽  
Practical Application ◽  
Compression Process ◽  
Text Book ◽  
Low Speed ◽  
Work Input ◽  
Low Speeds ◽  
Compressor Efficiency ◽  
Isentropic Efficiency

In most compressors the flow is adiabatic, but in micro-compressors, and in turbochargers at low speeds, the compression process has both heat transfer and work input. The classical adiabatic efficiency definition found in most text books is then incorrect. This paper extends the text book definitions of compressor efficiency to diabatic flows. The paper explains different compressor efficiency definitions in a logical way and identifies fundamental flaws in the use of isentropic efficiency for a diabatic flow. It shows that the polytropic efficiency can be used with or without heat transfer without ambiguities. Other significant advantages of the polytropic efficiency are also summarized, as they are not fully covered in any turbomachinery text books. The advantages of the polytropic approach for a practical application are demonstrated by analyzing the heat transfer in a turbocharger compressor. A simple model of the heat transfer allows a correction for this effect on the polytropic efficiency at low speed to be derived. Compressor characteristics that have been corrected for this surprisingly large effect maintain a much higher efficiency down to low speeds.

The Efficiency of Turbocharger Compressors With Diabatic Flows

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Michael V. Casey ◽  
Thomas M. Fesich
Keyword(s):  
Heat Transfer ◽  
Simple Model ◽  
Practical Application ◽  
Compression Process ◽  
Low Speed ◽  
Work Input ◽  
Low Speeds ◽  
Compressor Efficiency ◽  
Isentropic Efficiency

In most compressors the flow is adiabatic, but in low-speed turbochargers, the compression process has both heat transfer and work input. This paper examines different compressor efficiency definitions for such diabatic flows. Fundamental flaws in the use of the isentropic efficiency for this purpose are identified, whereas the polytropic efficiency can be used with or without heat transfer without ambiguities. The advantage of the polytropic approach for a practical application is demonstrated by analyzing the heat transfer in a turbocharger compressor. A simple model of the heat transfer allows a correction for this effect on the polytropic efficiency at low-speed to be derived. Compressor characteristics that have been corrected for this surprisingly large effect maintain a much higher efficiency down to low-speeds.

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