Thesis (PhD)--Stellenbosch University, 1997 / ENGLISH ABSTRACT: An experimental investigation on gas-liquid counterflow in inclined rectangular ducts is conducted. The pressure drop across the sharp-edged gas inlet and the pressure gradient inside the duct are measured. Combinations of water, methanol, propanol, air, argon, helium and hydrogen are tested. The duct height and width are varied from 50 mm to 150 mm and 10 mm to 20 mm respectively. The emphasis is on high void fraction flow, i.e. low liquid flow rates as encountered in air-cooled reflux condensers. At low to moderate gas flow rates the pressure gradient is gas Reynolds number related while it becomes dependent on the superficial densimetric gas Froude number as the gas flow is increased. According to experiment the hydraulic diameter is the required length dimension in the gas Reynolds number while the duct height becomes the characteristic dimension in the Froude number regime. Flooding curves are generated for duct inclinations from close to the horizontal to the vertical. The data correlate in terms of the phase Froude numbers and a dimensionless liquid property parameter containing the hydraulic diameter, density, surface tension and the viscosity. The flooding gas velocity is found to be strongly dependent on the duct height, the phase densities and the duct inclination. The liquid viscosity has a stronger effect than the surface tension. Both these properties however playa secondary role. Flooding is not related to the gas Reynolds number. A theoretical model, based on the phenomenological findings of the adiabatic counterflow investigation, is derived to evaluate the performance of an air-cooled reflux condenser. Field tests are conducted on a full scale reflux condenser and the measured performance is compared to the model prediction. The reflux condenser is found to achieve only 60% of the predicted heat rejection rate due to the existence of so-called cold or dead zones. Indications are that excessive entraiment in the bottom header and the subsequent accumulation of condensate in the finned tubes causes a maldistribution of the steamside flow. In the process noncondensable gases accumulate and form dead zones, causing ineffective performance. Flooding as found in single-ducts does not appear to contribute to the formation of the dead zones. / AFRIKAANSE OPSOMMING: Die teenvloei van gas en vloeistof in reghoekige skuins buise is eksperimenteel ondersoek. Die drukverlies oor die skerp gasinlaat en die drukval in die buis is gemeet vir verskillende kombinasies van water, propanol, metanol, lug, argon, helium en waterstof. Buishoogtes en breedtes van 50 mm tot 150 mm en 10 mm tot 20 mm respektiewelik is getoets. Die klem van die ondersoek is op lae vloeistofvloeitempos soos teenwoordig tydens kondensasie van stoom in lugverkoelde teenvloeikondensors. Vir lae tot matige gasvloeitempos is die drukval afhanklik van die gas Reynolds-getal terwyl die densimetriese gas Froude-getal die heersende parameter word soos die gasvloei toeneem. Die hidrouliese diameter verteenwoordig die dimensie in die Reynolds-getal maar die buishoogte word die karakteristieke dirnensie in die Froude-getal gebied. Vloedingskurwes is vir 'n reeks van buishoeke gegenereer. Die vloedingdata korreleer in terme van die Froude-getal en 'n dimensielose parameter bestaande uit die hidrouliese diameter, oppervlakspanning, vloeistofdigtheid en die vloeistofviskositeit. Die vloeidingsnelheid is primêr van die buishoogte, vloeierdigthede en die buishoek afhanklik. Die vloeistofviskositeit-effek is sterker as die van die oppervlakspanning. Beide die eienskappe speel egter 'n sêkondere rol. Die gas Reynolds-getal beïnvloed nie die vloeidingsproses nie. Die fundamentele bevindinge van die teenvloeiondersoek is toegepas om die werkverigting van 'n lugverkoelde teenvloeikondenser teoreties te modelleer. Werkverigtingstoetse is uitgevoer op 'n volskaal teenvloeikondenser. Die toetsresultate word vergelyk met die teoretiese voorspelling. Die teenvloeikondensor behaal slegs sowat 600% van die voorspelde warmteoordrag omdat van die gevinde buise gedeeltelik by omgewingstemperatuur is. Hierdie verskynsel heet koue of dooie sones. Dit blyk dat die kondensaat in die onderste spruitstuk nie vrylik kan dreineer nie en in die vorm van druppels deur die stoom opgesleur word. Gevolglik versamel kondensaat binne die buise en sodoende kan nie-kondenseerbare gasse nie effektief uit die teenvloeikondensor verwyder word nie. Soos die gasse versamel word koue sones gevorm. Dit blyk dat vloeding soos waargeneem in enkelbuise nie tot die vorming van koue sones bydra nie.

Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations. By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit.

A batch vacuum frying system, which processes fruits and vegetables, includes a frying pan, a surface-condenser, and a vacuum pump. With health and safety issues in mind, this research focused on developing a modified surface-condenser to prevent cavitation of the vacuum pump. The final oil-content was reduced by centrifugal de- oiling of the product under vacuum, which make the product healthier than what is currently available. The de-oiling mechanism consists of a centrifuge with a motor attached to the basket shaft, rotating up to 750 rpm (63 g units). The condenser consists of a (counter- flow) spiral-coil heat exchanger (SHE) connected to a refrigeration system that uses R404a refrigerant. De-oiling for 40 s at 300 and 750 RPM removed up to 67% and 72% of the chip’s surface oil, respectively. At 750 RPM for 10 s, 40 s, and 60 s the oil-content was reduced by 38%, 44%, and 51%, respectively. The convective heat transfer coefficient (h) of the frying oil was determined at 120°C and 140°C using the lumped capacitance method. The h-values were 217±13 W/m2K (120°C) and 258±37 W/m2K (140°C) using a copper-ball thermocouple. The h- values increased to 3.6 times during the boiling period. COMSOLTM Multiphysics was used to model the heat transfer in the vacuum fryer pan. Based on the simulation results, a 1.5 cm thick insulation material was installed in the fryer to reduce the energy losses. The refrigeration system operates at Tevap = -26°C and Tcond = 50°C with 26°C sub-cooling. Sensitivity analysis showed that the system Coefficient of Performance (COP) was about 3.87 at these conditions and compressor power requirement (CPR) was 74 W (85% efficiency) when frying 30 g of potatoes slices. The best results were obtained at Tevap = -10°C and Tcond = 40°C with 26°C sub-cooling and superheat of 5°C. The predicted COP was 4 and the CPR 70 W. The ice-formation on coils reduced the condensation rate. Reducing the refrigerant temperature to -10°C (from -26°C) reduced the condensation rate by 30%. These results show a more effective vacuum frying system for high-quality fruits and vegetables than the system previously used.

It is inevitable to observe that, in an urban field any architectural enterprise is subject to changing political, financial, technological and cultural demands. The pressure of these ever-changing forces attempts to modify and replace the initial program and the activities associated with the architectural product. The lifespan and the success of the resulting edifice depend on its ability to respond to such changes. Nevertheless, these ever-changing forces are naturally ambiguous and unpredictable so that architectural program becomes indeterminate. This thesis claims that in order to deal with the programmatic indeterminacy in an urban context, a strategic approach should be employed throughout the design process. Therefore, the thesis critically analyzes the strategic way of design to understand its working principles via examining the Parc de la Villette competition project of Rem Koolhaas/OMA. The mechanism of strategic way of design, how it works, and how it is constructed are the main focus of the thesis.

Three experimental studies were conducted to quantify the effects of system cycling, evaporator airflow, and condenser coil fouling on the performance of residential air conditioners. For all studies, the indoor dry-bulb (db) temperature was 80°F (26.7°C) db. The cycling study consisted of twelve transient tests conducted with an outdoor temperature of 95°F (35°C) db for cycle times of 6, 10, 15, and 24 minutes. Indoor relative humidities of 40%, 50%, and 60% were also considered. The evaporator airflow study consisted of twenty-four steady-state tests conducted with an indoor condition of 67°F (19.4°C) wet-bulb (wb) for evaporator airflows ranging from 50% below to 37.5% above rated airflow. Outdoor temperatures of 85°F (29.4°C) db, 95°F (35°C) db, and 105°F (40.6°C) db were also considered. The coil fouling study used a total of six condensers that were exposed to an outdoor environment for predetermined amounts of time and tested periodically. Three of the condensers were cleaned and retested during the periodic testing cycles. Testing consisted of thirty-three steady-state tests conducted with an indoor condition of 67°F (19.4°C) wb for outdoor exposure times of 0, 2000, 4000, and 8000 hours. Outdoor temperatures of 82°F (27.8°C) db and 95°F (35°C) db were also considered.

Orientador: Vivaldo Silveira Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-15T20:10:11Z (GMT). No. of bitstreams: 1 ChavezGutierrez_MirkoSalomon_M.pdf: 5850684 bytes, checksum: 9125e38d9fe164c0e08b0242569f71af (MD5) Previous issue date: 2010 / Resumo: Os equipamentos utilizados para refrigeração e condicionamento ambiental têm um potencial significativo de redução de consumo energético, principalmente porque esta pratica utilizam quantidades significativas de energia e são encontrados em todas as residências e indústrias. Neste contexto existem numerosos estudos dirigidos para aumentar a eficiência energética dos sistemas de refrigeração domésticos, utilizando diferentes estratégias tecnológicas. O dispositivo proposto neste trabalho atua como um condensador evaporativo, substituindo o ar,, como meio de troca térmica convencional dos sistemas de refrigeração domésticos, por uma corrente vertical de água em contato com a superfície do condensador, aproveitando desta maneira o calor absorvido pela água na mudança de fase (efeito evaporativo) e diminuindo a temperatura de condensação. O protótipo foi desenvolvido, considerando o principio de funcionamento dos condensadores evaporativos industriais e adaptado numa escala menor, para que possa ser facilmente montado na estrutura de um refrigerador doméstico convencional. Com as mudanças nas condições de condensação, especificamente a temperatura, procura-se aumentar o COP (coeficiente de desempenho) que é um indicador da eficiência do sistema, dado que nessas condições de funcionamento, o efeito frigorífico torna-se maior e o trabalho do compressor torna-se menor durante o ciclo. Estas condições de funcionamento, assim como o consumo de energia elétrica, foram monitorados e comparados com os sistemas de refrigeração convencional, utilizando uma câmara especialmente condicionada para esse propósito. Assim, o desempenho do sistema com as novas condições de condensação, promovidas pelo dispositivo, teve uma maior eficiência global com um COP maior em 24% e, em consequência, um aumento da eficiência energética do sistema, com uma redução de 17% de energia em ensaios padronizados conforme norma ABNT 12888 / Abstract: Los equipos utilizados para refrigeración y condicionamiento ambiental tienen gran potencial de reducción de consumo energético, principalmente porque estos aparatos utilizan cantidades significativas de energía y son encontrados en la mayoría de residencias y en las industrias. Existen numerosos estudios dedicados a aumentar la eficiencia energética de los sistemas de refrigeración domésticos utilizando diferentes estrategias tecnológicas. El dispositivo propuesto en este trabajo actuara como un condensador evaporativo, substituyendo el aire, como medio de intercambio de calor convencional de los sistemas de refrigeración domésticos, por una corriente vertical de agua en contacto con la superficie del condensador, aprovechando de esta forma el calor absorbido por el agua durante el cambio de estado (efecto evaporativo) y disminuyendo la temperatura de condensación. Este prototipo fue desarrollado considerando el principio de funcionamiento de los condensadores evaporativos industriales y fue adaptado a una escala menor, para que pueda ser fácilmente instalado en la estructura de un refrigerador domestico convencional. Con las modificaciones en las condiciones de condensación específicamente, la temperatura, se procura aumentar el COP (coeficiente de desempeño), que es un indicador de la eficiencia del sistema, en vista que en estas condiciones de funcionamiento, el efecto frigorífico se torna mayor y el compresor trabaja menos durante el ciclo. Estas condiciones de funcionamiento, así como el consumo de energía eléctrica son monitoreados e comparados con los sistemas de refrigeración convencional, utilizando una cámara especialmente condicionada para este propósito. De esta manera el desempeño del sistema con las nuevas condiciones de condensación, promovidas por el dispositivo en estudio, tuvo una mayor eficiencia global con un COP superior en 24%, y como consecuencia un aumento de la eficiencia energética del sistema, con una reducción del consumo de energía en 17% durante ensayos homogenizados según la norma Brasileña ABNT 12888 / Mestrado / Mestre em Engenharia de Alimentos

This master‘s thesis deals with the design of a control system for a distillation column. It deals with the issue of distillate production and acquaints the reader with the necessary knowledge that is necessary to understand the purpose of the work. The practical part of the work presents a specific distillation column, the means for its control and the method of implementation of the control system, then the visualization of the control system and the method of control. Part of the work is the evaluation of the results and benefits of the work.

The thesis is focused on the cooling cycles, namely cycles of absorption. The work is divided into several parts, as problems to be solved. The first part deals with the principles and using refrigeration cycles in practice, their involvement and by comparing the working pairs of substances circulating in the absorption unit. The practical part deals with making a proposal for one-and two-level modular absorption cycle of 6 kW, and the subsequent techno-economic comparison with commonly supplied absorption unit

This thesis deals with the calculation procedures for determining the heat transfer coefficient for steam condensers. The first section provides a basic overview for industrial steam condensers and possible procedure for selecting the appropriate type of tube condenser. The next section describes the types of condensation and equations for determining the heat transfer coefficient for various geometries of tubular condensers. In the final section there is performed practical calculation of condenser in Maple software using the above relations. The results obtained in this calculation are compared with the results obtained by professional computational software Chemcad and HTRI.

The aim of this Diploma thesis is calculating the parameters of the heat balance diagram as well as creating balance sheet for winter and summer operation. In one of the first parts, the reader is acquainted with two P&I diagrams containing main accessories, which are also used in the heat scheme, KKS marking system is used to name the acces-sories. The main part of the thesis consists of a detailed calculation of the heat transfer surface of the condenser with design of the tube bundle including the main dimensions of the condenser. Last but not least, the calculations of the hydraulic losses of condenser are included in the thesis.