Transient Temperature Response of Variable Flow Heat Exchangers in a Marnoch Heat Engine

Abstract

T ran sien t T e m p eratu re R esponse of V a ria b le Flow H eat Exchangers in a M arnoch H eat EngineWithin a Marnoch heat engine (MHE), a water!glycol mixture transfers heat from the heat source into a set o f variable flow heat exchangers and removes heat from adjoining cold heat exchangers. The compressed dry air is used as the working medium in this heat engine. The MHE has four shell and tube heat exchangers, which operate transient and variable flow conditions. A new transient heat transfer model is developed to predict this transient behavior o f the heat exchangers fo r different flow regimes and temperatures. The results from the model are validated against experimental results from an MHE pro totype. The heat transfer model shows 85% agreement with measured data from the MHE prototype fo r the individual heat exchangers. This model can be used fo r similar shell and tube heat exchangers with straight or U-shaped tubes. The heat transfer model pre dicts the gas temperature on the shell side, when a step change is imposed on the liquid entering the tubes. System DescriptionThe MHE is a recently developed new type of heat engine that creates mechanical work from temperature differences. The pres ent prototype of the MHE is composed of four shell and tube heat Journal of Heat Transfer