Effect of variable heat input on the heat transfer characteristics in an Organic Rankine Cycle system

Mahdi Hatf Kadhum Aboaltabooq,Ana-Maria Alexandru,Valentin Apostol,Cristina Ciobanu,Tudor Prisecaru,Gheorghe Popescu,Malina Prisecaru,Elena Pop,Horatiu Pop,Cristian Petcu

doi:10.1051/rees/2016021

Abstract

This paper analyzes the heat transfer characteristics of an ORC evaporator applied on a diesel engine using measured data from experimental work such as flue gas mass flow rate and flue gas temperature. A mathematical model was developed with regard to the preheater, boiler and the superheater zones of a counter flow evaporator. Each of these zones has been subdivided into a number of cells. The hot source of the ORC cycle was modeled. The study involves the variable heat input's dependence on the ORC system's heat transfer characteristics, with especial emphasis on the evaporator. The results show that the refrigerant's heat transfer coefficient has a higher value for a 100% load from the diesel engine, and decreases with the load decrease. Also, on the exhaust gas side, the heat transfer coefficient decreases with the decrease of the load. The refrigerant's heat transfer coefficient increased normally with the evaporator's tube length in the preheater zone, and then increases rapidly in the boiler zone, followed by a decrease in the superheater zone. The exhaust gases’ heat transfer coefficient increased with the evaporator’ tube length in all zones. The results were compared with result by other authors and were found to be in agreement.

Highlights

One of the methods to improve the thermal efficiency of an internal combustion engine is the usage of Organic Rankine Cycle systems (ORCs) to recover waste heat
Engine waste energy is transferred to the organic working fluid by means of an evaporator in an ORC, so the evaporator is an important part of the ORC for an engine waste-heat recovery system
A few studies have dealt with variable heat sources

Summary

Introduction

One of the methods to improve the thermal efficiency of an internal combustion engine is the usage of Organic Rankine Cycle systems (ORCs) to recover waste heat. The available heat which, is called waste heat, is transferred to the organic working fluid by means of an evaporator in an ORC, where the organic working fluid changes from a liquid state to a vapor state under a high pressure. The organic working fluid, which has a high enthalpy, is expanded in an expander, and output power is generated. Many studies analyzing ORC performances have been conducted recently [1,2,3,4,5,6,7]. Most of these studies have dealt with heat source as a stable source for simplicity.

Mathematical model

Results

Conclusions