Cross flow heat exchangers are a fairly common apparatus employed throughout many industrial processes. For these types of systems, correlations have been extensively developed. However, there have been no correlations done for very high enthalpy flows as produced by Arnold Engineering Development Center’s (AEDC) H2 facility. The H2 facility uses a direct current electric arc to heat air which is then expanded through a converging-diverging nozzle to impart a supersonic velocity to the air. This high enthalpy, high temperature air must be cooled downstream by the use of a cross flow heat exchanger. It is of interest to evaluate the actual performance of the air cooler to determine the effectiveness of possible facility upgrades. In order to characterize cooler effectiveness, a numerical model is built to calculate per-tube-row energy balances using real (temperature and pressure dependent) air and water properties and cross-flow Nusselt number calculations.

One of the most important industrial processes is heat transfer, carried out by heat exchangers in single and multiphase flow applications. Despite the existence of well-developed theoretical models for different heat transfer mechanisms, the expanding need for industrial applications requiring the design and optimization of heat exchangers, has created a solid demand for experimental work and effort. This thesis concerns the use of numerical approaches to analyze and optimize heat transfer and fluid flow in power generation industry, with emphasis on pin fin technology. This research begins with a review on heat transfer characteristics in surfaces with pin fins. Different pin fins shapes with various flow boundaries were studied, and thermal and hydraulic performances were investigated. The impact of parameters such as inlet boundary conditions, pin fin shapes, and duct cross-section characteristics on both flow and heat transfer were examined. Two important applications in power generation industry were considered for this study: power transformer cooling, and condenser for CO2 capturing application in oxy-fuel power plants. Available experimental data and correlations in the literature have been used for models validation. For each case, a model based on current configuration was built and verified, and was then used for optimization and new design suggestions. All numerical modeling was performed using commercial CFD software. A basic condenser design was suggested and examined, supplemented by the use of pin fin technology to influence the condensation rate of water vapour from a CO2/H2O flue gas flow. Moreover an extensive review of numerical modeling approaches concerning this condensation issue was conducted and presented. The analysis results show that the drop-shaped pin fin configuration has heat transfer rates approximating those of the circular pin configuration, and the drop-shaped pressure losses are less than one third those of the circular. Results for the power transformer cooling system show those geometrical defects in the existing system are easily found using modeling. Also, it was found that the installation of pin fins in an internal cooling passage can have the same effect as doubling the radiator’s height, which means a more compact cooling system could be designed. Results show that a condensation model based on boundary layer theory gives a close value to experimental correlations. Considering a constant wall temperature, any increase in CO2 concentration results in lower heat transfer coefficients. This is a subsequence of increased diffusivity resistance between combustion gas and condensing boundary layer. Also it was shown that sensitivity of heat transfer rate to inlet temperatures and velocity values decreased when these parameters increased. The application of numerical methods concerning the condensation process for CO2 capturing required significant effort and running time as the complexity of multiphase flow was involved. Also data validation for the CO2/H2O condenser was challenging since this is quite a new application and less experimental data (and theoretical correlations) exist. However, it is shown that models based on numerical approaches are capable of predicting trends in the condensation process as well as the effect of the non-condensable CO2 presence in the flue gas. The resulting data, conclusions, applied methodology can be applied to the design and optimization of similar industrial heat exchangers, such as oil coolers which are currently working at low efficiency levels. It can also be used in the design of electronic components, cooling of turbine blades, or in other design applications requiring high heat flux dissipation. Finally, the finding on water vapour condensation from a binary mixture gas can be referenced for further research and development in this field.

The purpose of this research project is the design and optimization of complex chemical engineering problems, by employing evolutionary algorithms (EAs). EAs are optimization techniques which mimic the principles of genetics and natural selection. Given their population-based approach, EAs are well suited for solving multiobjective optimization problems (MOOPs) to determine Pareto-optimal solutions. The Pareto front refers to the set of non-dominated solutions which highlight trade-offs among the different objectives. A broad range of applications have been studied, all of which are drawn from the chemical engineering field. The design of an industrial packed bed styrene reactor is initially studied with the goal of maximizing the productivity, yield and selectivity of styrene. The dual population evolutionary algorithm (DPEA) was used to circumscribe the Pareto domain of two and three objective optimization case studies for three different configurations of the reactor: adiabatic, steam-injected and isothermal. The Pareto domains were then ranked using the net flow method (NFM), a ranking algorithm that incorporates the knowledge and preferences of an expert into the optimization routine. Next, a multiobjective optimization of the heat transfer area and pumping power of a shell-and-tube heat exchanger is considered to provide the designer with multiple Pareto-optimal solutions which capture the trade-off between the two objectives. The optimization was performed using the fast and elitist non-dominated sorting genetic algorithm (NSGA-II) on two case studies from the open literature. The algorithm was also used to determine the impact of using discrete standard values of the tube length, diameter and thickness rather than using continuous values to obtain the optimal heat transfer area and pumping power. In addition, a new hybrid algorithm called the FP-NSGA-II, is developed in this thesis by combining a front prediction algorithm with the fast and elitist non-dominated sorting genetic algorithm-II (NSGA-II). Due to the significant computational time of evaluating objective functions in real life engineering problems, the aim of this hybrid approach is to better approximate the Pareto front of difficult constrained and unconstrained problems while keeping the computational cost similar to NSGA-II. The new algorithm is tested on benchmark problems from the literature and on a heat exchanger network problem.

SuperCritical-Water-cooled Reactors (SCWRs) are being developed as one of the Generation-IV nuclear-reactor concepts. SuperCritical Water (SCW) Nuclear Power Plants (NPPs) are expected to have much higher operating parameters compared to current NPPs, i.e., pressure of about 25 MPa and outlet temperature up to 625 oC. This study presents the heat transfer analysis of an intermediate Heat exchanger (HX) design for indirect-cycle concepts of Pressure-Tube (PT) and Pressure-Vessel (PV) SCWRs. Thermodynamic configurations with an intermediate HX gives a possibility to have a single-reheat option for PT and PV SCWRs without introducing steam-reheat channels into a reactor. Similar to the current CANDU and Pressurized Water Reactor (PWR) NPPs, steam generators separate the primary loop from the secondary loop. In this way, the primary loop can be completely enclosed in a reactor containment building. This study analyzes the heat transfer from a SCW primary (reactor) loop to a SCW and Super-Heated Steam (SHS) secondary (turbine) loop using a double-pipe intermediate HX. The numerical model is developed with MATLAB and NIST REFPROP software. Water from the primary loop flows through the inner pipe, and water from the secondary loop flows through the annulus in the counter direction of the double-pipe HX. The analysis on the double-pipe HX shows temperature and profiles of thermophysical properties along the heated length of the HX. It was found that the pseudocritical region has a significant effect on the temperature profiles and heat-transfer area of the HX. An analysis shows the effect of variation in pressure, temperature, mass flow rate, and pipe size on the pseudocritical region and the heat-transfer area of the HX. The results from the numerical model can be used to optimize the heat-transfer area of the HX. The higher pressure difference on the hot side and higher temperature difference between the hot and cold sides reduces the pseudocritical-region length, thus decreases the heat-transfer surface area of the HX. / UOIT

The Marnoch heat engine (MHE) is a new type of power generation device that is under research and development at the University of Ontario Institute of Technology. In this thesis, the transient heat transfer behaviour of the source heat exchanger of the Marnoch heat engine is studied, and its operation for laminar and turbulent flows is modelled. The temperature variations of the working fluid, the heating fluid and the wall, are calculated. The temperature distribution of the fluids and the wall over the length of the heat exchanger is also calculated. It is found that the temperature of the working fluid rises sharply to a peak and then gradually decreases. The wall temperature decreases exponentially, and the temperature of the heating fluid falls sharply, and then gradually decreases. A base model for the step change in the mass flow of the working fluid is developed and compared against past works for the purpose of validation. / UOIT

A new adhesive bonding method is introduced for microlamination architectures, for producing low-temperature microchannel arrays in a wide variety of metals. Sheet metal embossing and chemical etching processes have been used to produce sealing bosses and flow features, resulting in approximately 50% fewer laminae over traditional methods. These lamina designs are enabled by reduced bonding pressures required for the new method. An assembly process using adhesive dispense and cure is outlined to produce leak-free devices. Feasible fill ratios were determined to be 1.1 in general and 1.25 around fluid headers, largely due to gaps between faying surfaces caused by surface roughness. Bond strength investigation reveals robustness to surface conditions and a bond strength of 5.5-8.5 MPa using a 3X safety factor. Dimensional characterization reveals a two sigma (95%) post-bonded channel height tolerance under 10% (9.6%) after bonding. Patterning tolerance and surface roughness of the faying laminae were found to have a significant influence on the final postbonded channel height. Leakage and burst pressure testing on several samples has established confidence that adhesive bonding can produce leak-free joints. Operating pressures up to 413 kPa have been satisfied, equating to tensile pressure on bond joints of 1.9 MPa. Higher operating pressures can be accommodated by increasing the bond area of devices. A two-fluid counterflow microchannel heat exchanger has been redesigned, fabricated and tested to demonstrate feasibility of the new method. Results show greater effectiveness and higher heat transfer rates, suggesting a smaller device than the original heat exchanger. A maximum effectiveness of 82.5% was achieved with good agreement between theoretical and experimental values. Although thermal performance was improved, higher pressure drops were noted. Pressure drops were predicted with a maximum error of 16% between theoretical and experimental values. Much of the pressure drop was found to be in the device manifolds, which can be improved in subsequent designs. Fluid flow simulation results show a 45-65X reduction in fluid leakage velocity past sealing bosses, thereby mitigating adhesive erosion concerns. Theoretical models indicate that the worst-case adhesive erosion rate is 1/12th the rate of aluminum and 1/7th the rate of stainless steel, implying satisfactory reliability in high fluid velocity applications. Economic comparison indicates an 83% reduction in material cost and 71% reduction in assembly cost with the new adhesive bonding process, when compared to diffusion bonding for the recuperator investigated in this study. Adhesive compatibility with common refrigerants is reviewed through literature references, with no adverse compatibility issues noted. The findings of this research suggest a fairly quick path to commercialization for the new bonding method. Future studies required to pursue commercialization are liquid and gas permeability evaluations, and long term strength and performance testing of adhesives in targeted applications. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Mar. 26, 2012 - Mar. 26, 2013

Horizontal ground loop heat exchangers (GLHE) are widely used in many countries around the world as a heat source/sink for building conditioning systems. In Canada, these systems are most common in residential buildings that do not have access to the natural gas grid or in commercial structures where the heating and cooling loads are well balanced. These horizontal systems are often preferred over vertical systems because of the expense of drilling boreholes for the vertical systems. Current practice when sizing GLHEs is to add a considerable margin of safety. A margin of safety is required because of our poor understanding of in situ GLHE performance. One aspect of this uncertianty is in how these systems interact with heterogeneous soils. To investigate the impact of soil thermal property heterogeneity on GLHE performance, a specialized finite element model was created. This code avoided some of the common, non-physical assumptions made by many horizontal GLHE models by including a representation of the complete geometry of the soil continuum and pipe network. This model was evaluated against a 400 day observation period at a field site in Elora, Ontario and its estimates were found to be capable of reaching a reasonable agreement with observations. Simulations were performed on various heterogeneous conductivity fields created with GSLIB to evaluate the impact of structural heterogeneity. Through a rigorous set of experiments, heterogeneity was found to have little effect on the overall performance of horizontal ground loops over a wide range of soil types and system configurations. Other variables, such as uncertainty of the mean soil thermal conductivity, were shown to have much more impact on the uncertainty of performance than heterogeneity. The negative impact of heterogeneity was shown to be further minimized by: maintaining a 50 cm spacing between pipes in trenches; favouring multiple trenches over a single, extremely long trench; and/or using trenches greater than 1 m deep to avoid surface effects.

In modern aircraft, one of the most difficult issues has been how to provide avionics with adequate cooling. Future versions of the fighter aircraft JAS 39 Gripen is equipped with new applications that have increased heat loads. In previous versions of the JAS 39 Gripen avionics was cooled by zero degree air and fuel, but in the next version a liquid loop will be installed to cool the new radar.The fluid in the liquid loop is cooled to proper temperature by pressurized bleed air from the engine which is cooled by ram air. The air to cool the avionics is produced the same way and this is a very expensive process for the airplane which lowers its performance. It is important to minimize the production of cooling air and therefore three new adjustable valves that provide various components of cooling air are installed in the next version of the JAS 39 Gripen. The cooled and pressure controlled air from the engine is distributed between different avionic shelves, each containing a set of components. Depending on the type of tasks performed and current flight mode of the aircraft the requirement of functions which should be active varies and therefore also the cooling demand to avionics. The first part of this thesis studies the overall priority of how the engine bleed shall be used. This part of the thesis results in a decision basis for the distribution of cooling air to be regulated in the absence of full cooling capacity. The amount of cooling which must be distributed to the radar is proportional to its developed power which varies widely depending on the radar’s operational mode. Since the pump which determines the liquid flow velocity operates at a constant speed is the regulation of cooling to the radar is controlled by varying the bleed air flow into the heat exchanger which cools the fluid and thus the temperature of the fluid has when it reaches the radar. This part of the thesis creates a control algorithm for controlling the airflow into the heat exchanger. The regulation keeps the fluid inlet temperature to the radar within the range of +25 ± 5 ˚ C and the gradient of the temperature less than 0.5° C per second. The PI-controller with the feed-forward filter succeeded in controlling the temperature of the liquid as it reached the radar within +25 ± 1° C, the temperature gradient requirement, 0.5° C per second, was also passed in all flight cases which were used to evaluate the controller. The PI-controller with feed-forward has a low convergence time and no static error. It also performs well when the measurement signals contain a lot of noise because of the controllers integrated low pass filter.   The three new adjustable valves saves 12 to 97 g/s of cooling air for the different valve positions studied in this thesis, this corresponds to 9 - 70% of the total amount of controllable air to the avionics. Since the production of cooling air is a costly process for the aircraft, the use of all 3 valves is recommended.

The purpose of this report is to investigate the possibilities with drain water heat recovery (DWHR) in residential buildings. Information and relevant theory has been collected and summarized in this report. Calculations have been done for given scenarios to evaluate profits. DWHR heat exchangers use simple technology and have long life-time. The heat exchanger is connected to outgoing drainage pipe and incoming cold-water supply so countercurrent flow is accomplished. This makes it possible to increase the temperature of the incoming cold-water and thereby decrease the amount of energy used to heat water. There are mainly two types of models on the markets, vertically and horizontally heat exchangers. DWHR can be cost-effective if installed during new constructions or renovation, otherwise installation costs can be quite expensive. An installation of a DWHR-unit means no increasing risks of bacteria growth (legionella). Approximately 20 % of the energy used to heat hot-water can be counted as internal heat gain, with a DWHR heat exchanger the amount increases which will result in less energy consumed in the room heating system. More development of existing models is required to reduce the prices and spread information. A big advantage with DWHR is that the energy need for heating water is quite constant during the whole year compared to other demands, for example room-heating. Results from calculations in this report show that a reduction of 43 % of the heating demand for hot-water could be made in a normal family house and 17 % reduction could be made in a residential building with fifty apartments. / Syftet med arbetet är att undersöka möjligheterna med att återvinna värme från spillvatten i bostäder. Fakta och relevant teori inom området har samlats ihop och sammanfattats i denna rapport. Egna beräkningar har gjorts för att utvärdera hur mycket det är möjligt att återvinna. Tekniken för spillvattenvärmeväxling är enkel och växlarna håller i regel länge och kräver inget underhåll. En spillvattenvärmeväxlare kopplas in så att motströmsvärmeväxling uppnås. En växlare ansluts till utgående spillvattenledning och inkommande kallvattenledning. Ett problem är att de större växlarna för flerbostadshus kan vara platskrävanade och dyra. En installation av en växlare lämpar sig bäst vid nybyggnation för både småhus och flerbostadshus. Vid renoveringar av miljonprogrammen som uppfördes på 1960–70-tal finns det goda möjligheter att installera spillvattenvärmeväxlare då man genom exempelvis en stamrenovering gör ingrepp på befintliga ledningar, detta kan minska installationskostnaderna. Det finns inga tillkommande risker för legionellabakterier med spillvattenvärmeväxlare. Mer utveckling borde ske inom området så att nya modeller tillkommer. För nuvarande är den vertikala växlaren liten och passar bäst i småhus medan den horisontella växlaren passar bättre vid större anläggningar, med utveckling kan modellerna anpassas så de kan fungera oavsett användningsområde. I småhus bör man i första hand titta på andra åtgärder att för att minska energiförbrukningen, exempelvis driftoptimering, tätning av fönster, tilläggsisolering av vind m.m. En spillvattenvärmeväxlare kan istället vara ett alternativ för ett lågenergihus eller passivhus där vanliga åtgärder redan vidtagits. Ungefär 20 % av energiåtgången för tappvarmvatten kan tillgodoräknas som internvärme, med en installerad spillvattenvärmeväxlare ökar denna del vilket är bra då mindre effekt krävs till värmesystemet. En stor fördel som kan ses med spillvattenvärmeväxling är att tappvarmvattenförbrukningen är relativt konstant under året till skillnad från exempelvis värmebehovet. Utifrån givna scenarion visade beräkningarna i denna rapport att 43 % kunde besparas i småhus och 17 % i flerbostadshus.

To increase the efficiency of the engine is one of the biggest challenges for heavy vehicles. One possible method is the Rankine based Waste Heat Recovery. Crucial for Rankine based Waste Heat Recovery is to model the temperature and the state of the working fluid. If the state of the working fluid is not determined, not only the efficiency of the system could be decreased, the components of thesystem might be damaged.A Simulink model based on the physical components in a system developed by Scania is proposed. The model for the complete system is validated against a reference model developed by Scania, and the component models are further validated against measurement data. The purpose of the model is to enable model based control, which is not possible with the reference model. The main focus on the thesis is to model the evaporation and condensation to determine state and temperature of the working fluid. The developed model is compared to a reference model with little differences for while stationary operating for both the components and the complete system. The developed model also follows the behavior from measurement data. The thesis shows that two phase modeling in Simulink is possible with models based on the physical components.