Session: 12-12-01: Gas Turbine Heat Transfer and heat exchanger

Paper Number: 165651

Design of a Direct Contact Heat Exchanger Apparatus 

Introduction

This paper describes the design of an experimental apparatus to study the performance of a direct contact heat exchanger. The thermal efficiency of waste heat recovery (“WHR”) systems for low grade heat sources is limited by heat source temperatures, and the working fluid’s ability to accept it. Despite these limitations, the desire to recover otherwise wasted heat for a useful economic purpose, and to reduce environmental impacts persist. The characteristics of surface type evaporators provide an opportunity for improvement when replaced with direct contact heat exchangers (“DCHE”). The apparatus design described below provides for the study of a DCHE evaporator in an organic Rankine cycle (“ORC”) waste heat recovery system in order to increase heat exchanger efficiency, and reduce size and weight, while not increasing environmental risk in any significant way.  

Contribution to Science and Engineering

A wide scale, multiparametric screening process was performed to find commercially available working fluid(s) with characteristics acceptable for use in conjunction with commercial grade distilled water, under typical steady state combustion engine cooling loop operating conditions.   

The test apparatus itself comprises a complete simple (no recuperator/regenerator) organic Rankine cycle (“ORC”) system: a water-cooled condenser with buffer volume, DCHE evaporator, electric heat sources with water reservoir to provide buffer volume, pumps, a needle valve expander, and instrumentation. Pumped heat source and working fluid loops merge in a simple cylindrical DCHE mixing chamber (evaporator), inclusive of a continuous phase stilling zone and a working fluid demisting/reservoir zone. Cooled liquid working fluid is introduced via a single multi-pore diffuser, and hot water via a single conical nozzle. Temperature measurement along the vertical axis of DCHE allows for determination of thermal gradients to observe the extent to which experimental trajectories and heat transfer vary from the simple first approximation idealization. 

Methodology

Experimental technique, data collection and analysis will be used.  The experimental heat source is set at 3 kW, and the maximum acceptable pressure drop through the mixing chamber is set at 0.5 bar.   To study the performance of the multiphase DCHE, planned test variables include nominal heat source flow rates (120%/100%/80% of calculated ideal) and flow rate ratios; heat source (80°C/100°C/120°C) and working fluid inlet (condenser outlet temperatures (20°C/30°C/40°C); and three working heights. Testing is to be performed with and without ceramic Raschig ring type vessel packing at a single packing volume.  A proxy expander valve is installed in place of a turbine / generator.  Potential work generated from turbine / generator at these parameters will be compared against potential work from an equivalently sized ORC system with a standard heat exchanger.

Preliminary Results  

Direct heat exchange will result in higher efficiency than surface heat exchange.  After data are collected and analyzed based on methods above, the degree of efficiency will be better understood.  However, potentially more interesting might be the current unknowns.  A few of these might be the effective lifespan of the working fluid, and the decrease in efficiency over time. 

Presenting Author: Kurt Adams Lawrence Technological University

Presenting Author Biography: Kurt Adams is a Licensed Professional Engineer in the State of Michigan and is pursuing a Ph.D. at Lawrence Technological University in Southfield, Michigan. Adams earned his Masters Degree from the same university and has 24 years of engineering and design experience at a natural gas transmission and distribution utility. The study of heat transfer and thermal sciences, and how they can be harnessed to improve the lives of people around him has always interested him. Adams considers himself a lifelong learner and is willing to trade experiences and knowledge that might improve someone's life or experience.

Authors:

Kurt Adams Lawrence Technological University
Badih Jawad Lawrence Technological University
Vernon Fernandez Lawrence Technological University
Duane Brow Lawrence Technological University