Call number: LD2668 .T4 1978 S24 / Master of Science

In an attempt to reduce the dependence on fossil fuels, a variety of research initiatives has focused on increasing the efficiency of conventional energy systems. One such approach is to use waste heat recovery to reclaim energy that is typically lost in the form of dissipative heat. An example of such reclamation is the use of waste heat recovery systems that take low-temperature heat and deliver cooling in space-conditioning applications. In this work, an ejector-based chiller driven by waste heat will be studied from the system to component to sub-component levels, with a specific focus on the ejector. The ejector is a passive device used to compress refrigerants in waste heat driven heat pumps without the use of high grade electricity or wear-prone complex moving parts. With such ejectors, the electrical input for the overall system can be reduced or eliminated entirely under certain conditions, and package sizes can be significantly reduced, allowing for a cooling system that can operate in off-grid, mobile, or remote applications. The performance of this system, measured typically as a coefficient of performance, is primarily dependent on the performance of the ejector pump. This work uses analytical and numerical modeling techniques combined with flow visualization to determine the exact mechanisms of ejector operation, and makes suggestions for ejector performance improvement. Specifically, forcing the presence of two-phase flow has been suggested as a potential tool for performance enhancement. This study determines the effect of two-phase flow on momentum transfer characteristics inside the ejector while operating with refrigerants R134a and R245fa. It is found that reducing the superheat at motive nozzle inlet results in a 12-13% increase in COP with a 14-16 K decrease in driving waste heat temperature. The mechanisms of this improvement are found to be a combination of two effects: the choice of operating fluid (wet vs. dry) and the effect of two-phase flow on the effectiveness of momentum transfer. It is recommended that ejector-based chillers be operated such that the motive nozzle inlet is near saturation, and environmentally friendly dry fluids such as R245fa be used to improve performance. This work provides critical methods for ejector modeling and validation through visualization, as well as guidance on measures to improve ejector design with commensurate beneficial effects on cooling system COP.

Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Realisation of the depletable nature of fossil fuel has increased the need for its optimal use. Increasing global pressure to reduce the emission of greenhouse gases and other harmful gases that affect the chemical cycles or destroy the greenhouse gases in the tropospheric ozone, has attracted a increased worldwide concern. Waste heat recovery devices have been around for more than 50 years and researches and scientists have been very much involved in identifying the correct type of systems to meet the requireme?ts of industries and mankind more efficiently. Waste heat can be identified in the form of unburned but combustible fuel, sensible heat discharges in drain water, and latent and sensible heat discharge in exhaust gases. In this project the feasibility of a small scale waste heat recovery system has been investigated. Sets of preliminary investigations were performed to evaluate the amount of waste heat that can be extracted from the exhaust gases of typical diesel powered truck engines. A waste heat recovery unit was designed, implemented and evaluated through simulation and experimental investigations. Preliminary calculations were performed usmg the readings presented by Koorts (1998) for a typical 6-litre diesel engine. The calculations showed that it is possible to extract about 77kW of waste heat from the exhaust gases from such an engine. A simple Rankine cycle was then investigated to be operated on the waste heat recovered. The optimal parameters for such a Rankine cycle was determined using a spreadsheet program and was found to be an optimal pressure of 800kPa with a temperature of 227.2°C and a water mass flow rate of 0.0015kgls as the working fluid. For such a Rankine cycle, based on the efficiencies of commercially available pumps, turbines and heat exchangers it was found that it is possible to extract 2782kW of power per unit mass flow rate of water. The next stage of the project was designing and implementing an exhaust gas pipe network from the engine test cells at the Centre for Automotive Engineering (CAE) located on the ground floor to the Energy Systems Laboratory (ESL) at the first floor. This pipe network was equipped with a valve system that can be operated from the ESL and allows the selection of the route of the exhaust gases and two bellows to compensate for thermal expansion. A continuous combustion unit was also linked to the exhaust gas supply pipes as an alternative source of exhaust gases. The waste heat exchanger designed and selected was purchased and linked into the exhaust gas stream after calibration tests were carried out on the same in the wind tunnel. The water supply and a steam separator were then connected to the waste heat exchanger. In the final experimental stage of the project, two sets of tests were carried out. The first set of tests was performed using exhaust gases from the continuous combustion unit and the second using exhaust gases from the internal combustion engines in CAE. Superheated steam was obtained in both cases indicating the possibility of operating a turbine with the dry steam generated. With exhaust gases originating from the continuous combustion unit, an air fuel ratio of9.14:1 was used and exhaust gases at a temperature of 540°C were obtained with an air inflow of 1400kglh and a fuel consumption rate of7.11 kg/h. The exhaust gases degraded to 360°C at the waste heat recovery inlet due to losses through the bare pipes. 11.12kW of energy was extracted from the exhaust gases to the water stream with an efficiency of 98%. With the exhaust gases from the 10-litre diesel internal combustion engine, an exhaust gas flow rate of O.22kgls was used and with a heat transfer efficiency of 89%, 18.5kW of power was extracted at the waste heat recovery unit. This represents a 4.9% of the thermal content of the fuel used. A rate of energy production balance on the internal combustion engine showed that 34% is lost in exhaust gases and 29% in coolant and other losses while only 37% is used produced as shaft power. The results obtained therefore show that there is ample room for further investigation for the use afwaste heat in exhaust gases of typical diesel engines. It can therefore be concluded that the aims of the project that were to set up a testing facility and an exhaust gas pipe network and evaluation of a small scale waste heat recovery apparatus were achieved. The tests performed can still be optimised with more waste heat removal from the exhaust gases of typical diesel truck engines and hence better recovery of waste heat and a reduction of fuel consumption. / AFRIKAANSE OPSOMMING: Met die besef van die kwynende beskikbaarheid van fosielbrandstof het die behoefte vir die optimale benutting van die brandstof toegeneem. Toenemende globale druk om die emissies van groenhuis gasse en ander gevaarlike gasse wat chemiese siklusse beïnvloed in die troposfeer te verrniner, geniet wêreldwye aandag. Oorskotenergie-toestelle is alreeds beskikbaar die afgelope 50 jaar en navorsers en wetenskaplikes was tot op hede betrokke met die identifisering van die korrekte tipe sisteme om meer effektief aan die industrie en samelewing se behoeftes te voldoen. Oorskotenergie bestaan uit onder andere onverbrande maar brandbare brandstof, voelbare warmte in dreinwater, en latente en voelbare warmte in uitlaatgasse. In hierdie projek word die lewensvatbaarheid van 'n kleinskaal oorskotenergie herwinningsisteem ondersoek. Voorlopige ondersoeke was gedoen om die hoeveelheid oorskotenergie te bepaal wat herwin kan word uit die uitlaatgasse van 'n tipiese 6 liter vragmotor dieselenjin. 'n oorskotenergie herwinningseenheid was ontwerp, geïmplimenteer en ge-evalueer deur similasies en eksperimentele ondersoeke. Voorlopige berekeninge was uitgevoer op data wat deur Koorts (1998) saamgestel is vir 'n tipiese vragmotor dieselenjin. Die berekeninge toon dat dit moontlik is om ongeveer 77kW oorskotenergie van die uitlaatgasse van so enjin te onttrek. Die moontlikheid was toe ondersoek om die herwinne energie te gebruik om 'n eenvoudige Rankine siklus aan te dryf. Die optimale parameters vir die Rankine siklus was bereken deur van 'n sigblad program gebruik te maak en dit was gevind dat die optimale druk is 800kPa, die optimale temperatuur is 227.2°C teen 'n water massa vloeitempo van 0.0015kg/s. Vir so 'n Rankine siklus, gebaseer op die effektiwiteit van kommersiële beskikbare pompe, turbines en warmteruilers, was dit gevind dat dit moontlik is om 2782kW drywing per eenheidsmassa vloeitempo van water, te onttrek. Die volgende stadium van die projek was die ontwerp en implimentering van 'n uitlaatgas pypnetwerk vanaf die toetsselle van die Centre for Automotive Engineering (CAE) op die grondvloer na die Energy Systems Laboratory (ESL) op die eerste vloer. Die pypnetwerk was toegerus gewees met 'n kleptstelsel wat vanaf ESL bedryf kan word en wat dit moontlik maak om die roete van die uitlaatgasse te beheer. Twee samedrukbare koppelstukke was ook ingesluit in die lang reguit pypseksie om vir termiese uitsetting te kompenseer. 'n Aaneenlopende verbrandingseenheid was ook gekoppel met die uitlaatgasse toevoerpype as 'n alternatiewe bron van uitlaatgasse. Die oorskotenergie warmteruiier wat ontwerp en geselekteer was, was aangekoop en opgekoppel met die uitlaatgas-stroom nadat kalibrasie toetse op die warmteruiier gedoen was in 'n windtonnel. Die watertoevoer en 'n stoomskeier was gekoppel aan die oorskotenergie warmteruiler. Twee toetse was uitgevoer in die finale eksperimentele stadium van die projek. Die eerste stel toetse was uitgevoer deur gebruik te maak van die uitlaatgasse van die aaneenlopende verbrandingseenheid en met die tweede toets is van die uitlaatgasse van die interne verbrandingsenjins van CAE gebruik gemaak. Oorverhitte stoom was verkry in beide gevalle en wys dus dat daar 'n moontlikheid is om 'n turbine met droë stoom aan te dryf. 'n Lug tot brandstof verhouding van 9.14 : 1 was gebruik gewees in die aaneenlopende verbrandingseenheid om uitlaatgasse te verskaf teen 540°C. Die massavloeitempo van die lug was 1400kg/h en die brandstof 7.11kg/h. Die uitlaatgasse se temperatuur het afgeneem tot 360°C tot voor die oorskotenergie herwinningseenheid as gevolg van hitteverliese vanaf die ongeïsoleerde pypnetwerk. 11.12kW energy was onttrek vanaf die uitlaatgasse en oorgedra aan die waterstroom met 'n effektiwiteit van 98%. Die 10 liter diesel interne verbrandingsenjin het uitlaatgas gelewer met 'n massa vloeitempo van O.22kg/s. 18.5kW energie was herwin gewees met 'n effektiwiteit van 89%. Dit verteenwoording 4.9% van die termiese inhoud van die brandstof gebruik. 'n Energie balans op die interne verbrandingsenjin het getoon dat 34% energie gaan verlore in die uitlaatgasse, 29% word aan die verkoelingsmiddeloorgedra en 37% is bruikbare meganiese drywing. Die resultate wat verkry is, wys daarop dat daar nog groot ruimte is vir verdere ondersoeke in die gebruik van oorskotenergie in uitlaatgasse van tipiese vragmotor dieselenjins. Die gevolgtrekking kan dus gemaak word dat die doelwitte van die projek naamlik die opstel van 'n toetsfasiliteit, installering van 'n uitlaatgasse pypnetwerk en die toets van a kleinskaalse oorskotenergie herwinningseenheid, bereik was. Die toetse wat uitgevoer was kan nog ge-optimeer word om meer energie te herwin vanaf die uitlaatgasse van 'n tipiese vragmotor dieselenjin om sodoende beter brandstofverbruik te bewerkstellig.

This study aims to investigate the effects of ventilation rate, indoor air temperature, humidity and using a heat recovery ventilation system on indoor radon concentration and distribution. Methods employed include energy dynamic and computational fluid dynamics simulation, experimental measurement and analytical investigations. Experimental investigations primarily utilize a continuous radon meter and a detached house equipped with a recovery heat exchanger unit. The results of the dynamic simulation show that the heat recovery unit is cost-effective for the cold Swedish climate and an energy saving of about 30 kWh per  floor area per year is possible, while it can be also used to lower radon level. The numerical results showed that ventilation rate and ventilation location have significant impacts on both radon content and distribution, whereas indoor air temperature only has a small effect on radon level and distribution and humidity has no impact on radon level but has a small impact on its distribution.

This study explores ways to determine the energy efficiency of a pyrometallurgical ore reduction plant and measures to improve it. The feasibility of building a commercial plant - that is more energy efficient, has a low energy cost, and can operate independently and cost-effectively of external electricity supply - is determined. The need for energy efficiency is expanded to three questions: how should the energy efficiency of the plant be determined, what is the efficiency of the existing plant and to what level it can be improved. Literature and other relevant sources were consulted. Twenty potential energy conservation measures were identified through a literature study. A multi-criteria decision-making approach resulted in the selection of ten measures for conceptual implementation. The measures ranged from high-efficiency motors, solar power, heat recovery with thermal oil and various heat engines, to pressure recovery with turbo-generators. A case study approach was followed with the energy efficiency of an existing prototype plant the subject being studied. The energy usage of the existing plant and feasible measures to improve the performance were empirically observed. The impact of these measures was modelled and the results of the conceptual implementation determined. Two measures that were implemented during the study are also described and the results reported. The study found that the energy efficiency of the plant could be determined by the ratio of product exergy to input energy. By incorporating a number of energy conservation measures conceptually the internal efficiency of the prototype plant was conceptually improved from the current 17% to 22% and as a result externally supplied electricity reduced by 47%. The results were extrapolated to a future commercial plant and energy efficiencies of 26% on-grid and 21% off-grid predicted. This study suggests that a significant improvement in energy efficiency and energy cost can be achieved by integrating appropriate energy conservation measures into the existing and future plants. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

Global efforts makes buildings successively more energy efficient. This results in that the percentage of the total energy in the building that is lost to the sewage system, in the form of hot water, is increasing. The characteristics of the wastewater originating from the urban water cycle makes it an attractive heat source which is relatively unexploited. Wastewater heat recovery (WWHR) systems is a group of systems designed to reduce a buildings use of external energy sources by recovering the heat out of the wastewater before it is let out into the sewage.         The focus of this report is a parametric study performed on a WWHR system that utilises thermal storage tanks for accumulation of wastewater and a heat pump equipped with heat exchangers for the heat recovery. The studied variables are the amount of energy that the system is able to recover out of the wastewater and the seasonal average COP of the heat pump. The change of these two variables were analysed both as an affect of parameters dependent of system design and on consumption patterns of the residents of the building. The results showed that by properly designing the system the recovery degree can be increased by 31.5 percentage points reaching values above 90 % and the seasonal average COP can be increased by 13.5 % reaching values of 5.13. However, these two variables stands in contrast to each other were maximising one will reduce the other and it is proposed that it is important to take both into account when evaluating a WWHR system. It is also shown that the consumption related parameters have a relatively big effect on the system. The change in recovery degree as a result of these non-controllable parameter is 14 percentage points and the seasonal average COP changes with 4.2 %.         The system performance as a result of changing the U-value of the heat exchanger connecting the system to the domestic hot water circuit was also analysed. This showed an exponential relation between the U-value and delivered energy from the heat pump. The results showed that an increase of the U-value from 50 W/K to 6000 W/K increased the yearly energy supplied with 37.6 % but an increase from 1000 W/K to 6000 W/K increased the yearly supplied energy with less than 1 %. This result highlights the importance of properly dimensioning the heat exchanger.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Rahmatallah Shoureshi. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1986. / Typescript (photocopy). / Includes bibliographical references (v. 2, leaves 288-292) / A study of the energy system at the Massachusetts State Transportation Building was conducted. This innovative energy system utilizes internal-source heat pumps and a water thermal storage system to provide building heating and cooling. The potential benefits of this type of system include both energy savings and operating and equipment cost savings when compared to more conventional building heating and cooling systems. The study involved monitoring of equipment performance, computer simulation of the building energy system dynamics, and analysis of actual and modelled system efficiency. It was found that the building is presently operating as a 'low energy' building, despite a number of factors which have limited the heat pump system's capability to entirely meet winter heating requirements. Significant additional operation efficiency and cost savings are potentially available if a variety of measures are undertaken, including: stratification of the thermal storage system, utilization of demand management controls, and increased lighting system efficiency. / by Abbe Ellen Bjorklund. / M.S.

Conversion of a scroll compressor to an expander for organic Rankine Cycle: modeling and analysis / UOIT

The Marnoch heat engine (MHE) is a new type of heat engine currently under development at the University of Ontario Institute of Technology. The MHE can use waste or collected heat at temperatures that are currently unusable or not eco- nomically viable to use by conventional technologies. The MHE operates by using a heat source to heat the air in one heat exchanger and cool the air in another. This creates a pressure di erence. This pressure di erence drives a two-way piston connected to a ywheel. A generator connected to the ywheel converts the me- chanical energy of the ywheel into electricity. This thesis presents a simulation of the current MHE prototype. The simulation is designed to be easily customized to allow it to model the performance of future possible MHE installations and predict their performance. The simulation is shown to accurately model the performance of the MHE prototype by running under conditions similar to those found in the lab, and comparing its results to collected data from the prototype. Simulations were also run to show the model's ability to model possible applications with di erent operating conditions and physical components. / UOIT