Master of Science / Department of Mechanical and Nuclear Engineering / Donald L. Fenton / Today air cooled chillers are often used in industrial applications where chilled water is pumped through processes or laboratory equipment. Industrial chillers are used for the controlled cooling of products, mechanisms and factory machinery in a wide range of industries. However, there is limited information on condenser coil design for a simulated model that uses R407c in a process chiller system with a focus on the finned tube condenser design. Therefore, a simulation tool that evaluates the performance of a condenser design, e.g. frontal area, cost, and overall system efficiency would be very useful. An optimization calculator for the air cooled fin-tube condenser design was developed. This calculator allows a user to specifically select the condenser geometric design parameters including the overall condenser length and height, number of rows, number of circuits, row and tube spacing, fin thickness, fin density, tube inner and outer diameters, and the quantity and power of the fan motors. This study applied the calculator finding an optimum condenser design for various frontal areas and cost constraints. The calculator developed is appropriate for engineering designers for use in the process chiller industry.

No description available.

This thesis discusses the design, construction, and debugging of an experimental apparatus to measure fouling in smooth and/or augmented copper alloy condenser tubes. In addition, guidelines and recommendations are made for construction of similar devices. Specification sheets of the system components, detailed design calculations, and photographs of the apparatus are included in the appendices.

Steam distillation is the traditional method used for the extraction of peppermint oil. This process is able to remove approximately 20% of the oils from the leaves of the plant. It is a very costly and un-sustainable process due to the release of carbon emissions. Solvent free microwave extraction promises yields of up to 65% of the "available" oils from the peppermint at 3% less cost (Velasco 2007). It can also reduce carbon emissions because it will be using electricity as a power source instead of fossil fuels, however not all electric companies use renewable energies. In 2009 a SFME pilot plant was assembled in North Carolina to test the efficiency of the microwave process on a larger than lab scale. Results from the experiments showed that the tube and shell condenser was unable to effectively condense the mint oil. The problem was determined to be the addition of air to the mixture due to the open ends of the microwave. However it was discovered that the spray scrubber after the condenser was able to collect a visible amount of oil. This inspired the design of a direct contact condenser (Pommerenck 2012). The direct contact condenser they designed, built, and tested showed vast improvements in steam capturing efficiency when compared to a tube and shell condenser. However due to the materials used for its construction it could not sustain operating temperatures seen in the microwave pilot plant. Using their design a new direct contact condenser was built using materials that would be able to withstand heavy temperatures. The condenser was constructed out of aluminum and contained stainless steel spray nozzles, both for their non-corrosive properties. Tests were conducted using 8 and 16 nozzles and tested over a range of 20-100% steam by mass. Additional tests were completed using the full 24 nozzles but due to the location of some of the nozzles coolant was lost as an aerosol with no way to quantify the loss. Comparing the data to research completed by Pommerenck et al. on efficiency of a tube and shell condenser used for the mint distillation process found that with increasing amounts of air there is a greater loss of heat transfer. This is believed to be the effects of a boundary layer of the noncondensable fluid, air, which forms along the tube and resists condensation from forming (Seunguim 2006). Pommerenck's tube and shell condenser used a coolant flow rate of 24 L/min while the flow rates tested in this research were 18 L/min and 36 L/min. The direct contact condenser showed a considerable increase in performance even with the smaller flow rate compared to the tube and shell unit, indicating removal of the boundary layer. The efficiency tends to follow the maximum theoretical efficiency while the tube and shell condenser lowers in efficiency. The overall goal of this project is to determine the feasibility of the use of a direct contact condenser for implementation in the solvent free microwave extraction of peppermint oil when air is present. / Graduation date: 2012

Στην εργασία αυτή μελετήθηκε η γενική θεωρία των πυκνωτικών μικροφώνων που βρίσκουν εφαρμογή σε MEMS εφαρμογές της ακουστικής και αναλύθηκαν διεξοδικά δύο πυκνωτικά μικρόφωνα, ένα single-backplate και ένα dual-backplate, όσον αφορά τη γεωμετρία και τη συμπεριφορά τους. Επίσης, πραγματοποιήθηκε η υλοποίηση αυτών στο περιβάλλον του SIMULINK με τμηματικό τρόπο ανάλογα με τα φυσικά χαρακτηριστικά που προσομοιώνονται στο κάθε μοντέλο. Στη συνέχεια, προκειμένου να μετατοπιστεί ο θόρυβος αυτών πέρα από τις ακουστές συχνότητες, υλοποιήθηκαν δύο διαφορετικοί ΣΔ διαμορφωτές, ο μεν πρώτος βασισμένος στη βιβλοθήκη Delsig, ο δε δεύτερος στο περιβάλλον του SIMULINK. Και στις δύο περιπτώσεις μέσω κατάλληλου κώδικα γραμμένου στο περιβάλλον της MATLAB, οι εξόδοι των δύο μικροφώνων διαμορφώνονται κάθε φορά και από τους δύο ΣΔ διαμορφωτές, με σκοπό τη βελτίωση αυτών όσον αφορά τους δείκτες των SNR,THD και THD+NOISE. Σκοπός αυτής της εργασίας λοιπόν, είναι η εξακρίβωση της λειτουργίας των δύο ισοδύναμων μικροφώνων και ο σχολιασμός τόσο αυτής όσο και των επιδράσεων που προκαλούν στις εξόδους των δύο μικροφώνων η ΣΔ διαμόρφωση. / Στην εργασία αυτή μελετήθηκε η γενική θεωρία των πυκνωτικών μικροφώνων που βρίσκουν εφαρμογή σε MEMS εφαρμογές της ακουστικής και αναλύθηκαν διεξοδικά δύο πυκνωτικά μικρόφωνα, ένα single-backplate και ένα dual-backplate, όσον αφορά τη γεωμετρία και τη συμπεριφορά τους. Επίσης, πραγματοποιήθηκε η υλοποίηση αυτών στο περιβάλλον του SIMULINK με τμηματικό τρόπο ανάλογα με τα φυσικά χαρακτηριστικά που προσομοιώνονται στο κάθε μοντέλο. Στη συνέχεια, προκειμένου να μετατοπιστεί ο θόρυβος αυτών πέρα από τις ακουστές συχνότητες, υλοποιήθηκαν δύο διαφορετικοί ΣΔ διαμορφωτές, ο μεν πρώτος βασισμένος στη βιβλοθήκη Delsig, ο δε δεύτερος στο περιβάλλον του SIMULINK. Και στις δύο περιπτώσεις μέσω κατάλληλου κώδικα γραμμένου στο περιβάλλον της MATLAB, οι εξόδοι των δύο μικροφώνων διαμορφώνονται κάθε φορά και από τους δύο ΣΔ διαμορφωτές, με σκοπό τη βελτίωση αυτών όσον αφορά τους δείκτες των SNR,THD και THD+NOISE. Σκοπός αυτής της εργασίας λοιπόν, είναι η εξακρίβωση της λειτουργίας των δύο ισοδύναμων μικροφώνων και ο σχολιασμός τόσο αυτής όσο και των επιδράσεων που προκαλούν στις εξόδους των δύο μικροφώνων η ΣΔ διαμόρφωση.

The main objective of this study is to propose and to validate simplified models to simulate the performance of refrigeration systems. The proposed modelling approach of the system is modular: the compressor is modelled by a simple and physical model that takes into account the heat transfers and the un-matching of internal and external pressure ratio for the scroll compressors. The evaporator is modelled as a two zones heat exchanger on the refrigeration side (one for the two phases zone and the other one for superheated gas) and finally the condenser is assumed to be divided into three zones (de-superheating, two-phase and the sub-cooling). The compressor model was already developed by other author; here it is only validated using three scroll compressors and two reciprocating ones. The main differences are the conditions at which these compressors are tested: 20 bar at the supply and 40 at the exhaust. The condenser and evaporator models are the main contribution of this study. These models use the geometry and the correlation from the literature to calculate the global heat transfer coefficient on each zone. In the case of the condenser, a mean void fraction model is used to determinate the condenser subcooling as function of the refrigerant charge or vice-versa. The refrigeration system model is validated with experimental results obtained on each component and the whole system in five different test benches. The results show a very good agreement between the measured and predicted main outputs of the system.

The objective of this investigation was to develop micro/nano-scale temperature sensors for measuring surface temperature transients in multi-phase flows and heat transfer. Surface temperature fluctuations were measured on substrates exposed to phase change processes. Prior reports in the literature indicate that these miniature scale surface temperature fluctuations can result in 60-90 percent of the total heat flux during phase change heat transfer. In this study, DTS (Diode Temperature Sensors) were fabricated with a doping depth of ~100 nm on n-type silicon to measure the surface temperature transients on a substrate exposed to droplet impingement cooling. DTS are expected to have better sensor characteristics compared to TFTs (Thin Film Thermocouples), due to their small size and faster response (which comes at the expense of the smaller operating temperature range). Additional advantages of DTS include the availability of robust commercial micro fabrication processes (with diode and transistor node sizes currently in the size range of ~ 30 nm), and that only 2N wire leads can be used to interrogate a set of N x N array of sensors (in contrast thermocouples require 2 N x N wire leads for N x N sensor array). The DTS array was fabricated using conventional semi-conductor processes. The temperature response of the TFT and DTS was also calibrated using NIST standards. Transient temperature response of the DTS was recorded using droplet impingement cooling experiments. The droplet impingement cooling experiments were performed for two different test fluids (acetone and ethanol). An infrared camera was used to verify the surface temperature of the substrate and compare these measurements with the temperature values recorded by individual DTS. PVD (Physical Vapor Deposition) was used for obtaining the catalyst coatings for subsequent CNT synthesis using CVD (Chemical Vapor Deposition) as well as for fabricating the thin film thermocouple (TFT) arrays using the "lift-off" process. Flow boiling experiments were conducted for three different substrates. Flow boiling experiments on bare silicon wafer surface were treated as the control experiment, and the results were compared with that of CNT (Carbon Nano-Tube) coated silicon wafer surfaces. Similar experiments were also performed on a pure copper surface. In addition, experiments were performed using compact condensers. Micro-scale patterns fabricated on the refrigerant side of the compact heat exchanger were observed to cause significant enhancement of the condensation heat transfer coefficient.

No description available.

This paper starts from the single tube condensation theory of shell side inferred by Nusselt , and then analyzes the coefficient of heat transfer of the shell side and the overall heat transfer coefficient of the tube bundle. Referring to the overall heat coefficient of surface condensers and the calculation means of pressure decrease, the HEI, the most exploited one in the commerce is used by combining the basic theory of condenser heat transfer based on the Delphi function language to develop a set of assistant designing software. The software can be used to evaluate the performance of condensers, calculate the sizes of tube materials, and predict the pressure of condensers when the different tube materials are used. When the units are in using, this software also can calculate the cleanliness factor and determine the suitable time to clean the condenser tubes. There are four common used tube materials to compare their performance. They are Al- Brass tubes, 70-30 Cu-Ni tubes, Sea-Cure tubes and Ti tubes. This paper use the software to analyze the performance of the heat transfer of these four different kinds of tube materials and also to calculate the sizes of tubes .And use research papers to analyze the reason of anti-corrosion of these four. In addition, the HEI method can analyze the anti-vibration ability of these four. After comparing with all the performance of the tube materials, and then choosing the best tube material to provide an example for condenser design of new electricity plants or for old electricity plants to change the tube materials.

This study examined the Lake of Egypt Power Plant operated by Southern Illinois Power Cooperative located on the Lake of Egypt south of Marion, IL. The facility has a 173 MW rated turbine operating on a pulverized coal cyclone boiler and three 33 MW rated turbines operating on an oversized circulating fluidized bed boiler with 120 MW capacity. The first area examined was reduction of auxiliary power consumption possible with the addition of variable frequency drives to the forced draft fan and booster fan motors. Included in this examination was an analysis of the economic and environmental impact of such a reduction. From the analysis an annual savings of 24.4 GWh of electricity is possible. The second area examined was the generation capacity lost due to condenser fouling and the possible reduction in facility emissions with altered condenser treatment. From the analysis an additional 3.0 MW of capacity facility wide is possible or a reduction steam production of 1.5% for each boiler.