Corrugated Tube Regenerator for an Expansion Engine

Abstract

A regenerative heat exchanger for transferring heat from the exhaust gas to the intake working fluid of a prime mover. Application includes gas turbines for both motor vehicles and distributed electric generation. The heat exchanger employs a rotating matrix, which circulates through working fluid exhaust and intake channels while absorbing and rejecting heat between the two channels. Features include corrugated tubes for enhanced heat transfer, minimally welded low stress construction, quick-detach assembly of standard components, and purge flow sealing using recovered heat. Effectiveness exceeding 95% increases thermal efficiency of low-pressure ratio gas turbines.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to counter flow regenerative heat exchangers for heat recovery in low capacity prime movers. This includes distributed electric generation and vehicle use, and pertains particularly to an improved regenerator for small gas turbine engines. Low capacity gas turbines are generally considered to be impractical, especially in variable speed automotive use, due to very high turbine speed, inefficient turn-down during deceleration and idling, and high exhaust temperature. The rotary regenerator of the present invention with heat transfer enhancing features resolves these issues, enabling efficient low compression operation with effectiveness greater than 95%. Low stress and compact low cost metallic construction withstands high turbine outlet temperature associated with low compression. As a result, cycle efficiency is high within turbine stress limitations imposed by the pressure-speed relation, wherein rotor speed is directl...

AI Technical Summary

Benefits of technology

[0010](e) to provide a rotary regenerator having low seal leakage or increased pressure capability;

[0011](f) to provide a rotary regenerator having heat recovering purge flow for matrix lubrication and low seal leakage without loss of engine efficiency;

Problems solved by technology

Low capacity gas turbines are generally considered to be impractical, especially in variable speed automotive use, due to very high turbine speed, inefficient turn-down during deceleration and idling, and high exhaust temperature.

As a result, cycle efficiency is high within turbine stress limitations imposed by the pressure-speed relation, wherein rotor speed is directly proportional to working fluid flow rate and compression ratio and indirectly proportional to turbine diameter.

In the former case micro-turbines for distributed electric generation are gaining wide acceptance, while in the latter case gas turbine development is ongoing and limited to constant speed proto-types.

It is the most expensive component of the gas turbine system, constructed of high temperature alloys with a large number of closely spaced brazed joints and complex header arrangements.

Both fixed and rotary heat exchangers are subject to design compromise to limit thermal stresses.

The ceramic rotary regenerator matrix can withstand elevated turbine exhaust temperature, but off-design operating conditions may impose excessive thermal stress.

In addition, the latter is subject to erosion / corrosion due to seal leakage and is not conducive to heat transfer enhancement geometry and ring gear attachment.

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