A computer-controlled system, based on the design of S. Brown et al. at the Ontario Cancer Institute, Canada, has been developed for uniform heating of mouse tumors. A steady hyperthermic temperature was maintained in the tumor by combining waterbath heating with RF-heating. The RF field was provided by a transmitter which was connected to two steel capacitive plates via a matching circuit. 50% isotonic saline kept at a temperature 2°C below that in the tumor was circulated in the waterbath. The saline prevented overheating of the skin and provided coupling between the RF field and the tumor. A computer program has been written to measure continually the temperature in the tumor with implanted fine thermocouples. The program also controlled the average RF power delivered to the tumor by switching the transmitter on and off at appropriate intervals. The system has been tested on tumor xenografts growing in the thigh of nude mice. A steady temperature of 42° or 44°c has been maintained in the tumor for up to an hour. The system could be used to study the effect of hyperthermia on the uptake of radiolabelled tumor-associated antibodies and the treatment of tumors by such antibodies. / Thesis / Master of Science (MS)

In this research, the impact of solar thermal water heaters on the electric water heating load curve in a residential distribution circuit is analyzed with realistic hot water draw profiles. For this purpose, the electric and solar thermal water heater models are developed in MATLAB and validated with results from GridLAB-D and TRNSYS respectively. The solar thermal water heater model is developed for two types of collectors namely the flat plate and evacuated glass tube collector. Simulations are performed with the climate data from two cities - Madison, WI and Tampa, FL - which belong to two very different climate zones in the United States. Minute-by-minute electric energy consumptions in all three configurations of water heaters are modeled for a single water heater as well as a residential distribution circuit with 100 water heaters for daily as well as monthly time frames. The research findings include: The electric energy saving potential of a solar thermal water heater powered by auxiliary electric element is in the range of 40-80% as compared to an all-electric water heater depending on the site conditions such as ambient temperature, sunshine and wind speed. The simulation results indicate that the energy saving potential of a solar thermal water heater is in the range of 40-70% during winter and 60-80% during summer. Solar thermal water heaters aid in reducing the peak demand for electric water heating in a distribution feeder during sunshine hours when ambient temperatures are higher. The simulation results indicate that the peak reduction potential of solar thermal water heaters in a residential distribution feeder is in the range of 25-40% during winter and 40-60% during summer. The evacuated glass tube collectors save an additional 7-10% electric energy compared to the flat plate collectors with one glass pane during winter and around 10-15% during summer. The additional savings result from the capability of glass tube collectors to absorb ground reflected radiation and diffuse as well as direct beam radiation for a wider range of incidence angles. Also, the evacuated glass tube structure helps in reducing wind convective losses. From the simulations performed for Madison, WI and Tampa, FL, it is observed that Tampa, FL experiences more energy savings in winter than Madison, WI, while the energy savings are almost the same in summer. This is due to the fact that Tampa, FL has warmer winters with higher ambient temperatures and longer sunshine hours during the day compared to Madison, WI while the summer temperatures and sunshine hours are almost the same for the two cities. As expected, the simulation results prove the fact that lowering the hot water temperature set point will result in the reduction of electricity consumption. For a temperature reduction from 120 deg. F to 110 deg. F, electric water heaters save about 25-35% electric energy whereas solar thermal water heaters save about 30-40% auxiliary electric energy for the same temperature reduction. For the flat plate collectors, glass panes play an important role in auxiliary electric energy consumption. Flat plate collectors with two glass panes save about 10-15% auxiliary electric energy compared to those with no glass panes and about 3-5% energy saving compared to collectors with one glass pane. This is because there are reduced wind convective losses with glass panes. However, there are also transmittance losses from glass panes and there are upper limits on how many glass panes can be used. Results and findings from this research provide valuable insight into the benefits of solar thermal water heaters in a residential distribution feeder, which include the energy savings and peak demand reduction. / Master of Science

Šiais laikais sunku įsivaizduoti namus be bendram vartojimui skirto šilto vandens prieigos. Namuose, kurie nėra prijungti prie miesto vandentiekio infrastruktūros šiltas vanduo paruošiamas vietiniuose vandens šildytuvuose. Lietuvoje dažnai naudojami kombinuoti vandens šildytuvai. Šilto vandens paruošimui jie gali naudoti elektros energiją, arba centrinės šildymo sistemos šilumą. Deja tokie šildytuai dažniausiai negali automatiškai pasirinkti optimaliausio energijos šaltinio. Dėl to gaunami prasti ekonominiai rodikliai ir be reikalo švaistoma energija. Šio darbo tikslas yra kombinuoto vandens šildytuvo modernizacija sukuriant paprastą, tačiau galingą valdiklį, suteikiantį, jo vartotojui, galimybę automatizuoti šilto vandens paruošimo sistemos darbą, taip pagerinant ekonominius ir ergonominius pastato rodiklius. / In modern day it is very hard to imagine household without access to general purpose hot water. In buildings, with no access to centralized water distribution system, hot water is prepared in domestic water heaters or boilers. One of the most common types of water heaters in Lithuania is combined water heater. For hot water preparation it can use either electric power or heat from domestic heating system. However these heaters rarely have any capability to automatically choose energy source so this results in poor economy and useless energy losses. The goal of this work is modernization of combined water heater system by creation of simple yet powerful controller, capable of giving its user ability to automate control of water heating system, improve economy and comfort.

abstract: Testing was conducted for a solar assisted water heater and conventional all electric water heater for the purpose of investigating the advantages of utilizing solar energy to heat up water. The testing conducted simulated a four person household living in the Phoenix, Arizona region. With sensors and a weather station, data was gathered and analyzed for the water heaters. Performance patterns were observed that correlated to ambient conditions and functionality of the solar assisted water heater. This helped better understand how the solar water heater functioned and how it may continue to function. The testing for the solar assisted water heater was replicated with the all-electric water heater. One to one analyzes was conducted for comparison. The efficiency and advantages were displayed by the solar assisted water heater having a 61% efficiency. Performance parameters were calculated for the solar assisted water heater and it showed how accurate certified standards are. The results showed 8% difference in performance, but differed in energy savings. This further displayed the effects of uncontrollable ambient conditions and the effects of different testing conditions. / Dissertation/Thesis / Masters Thesis Engineering 2016

Made available in DSpace on 2014-06-11T19:24:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-11-29Bitstream added on 2014-06-13T20:52:17Z : No. of bitstreams: 1 dallantoniajunior_lc_me_botfca.pdf: 464837 bytes, checksum: 17a18aa81cbdc6fc6cee6b24c67e95c7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho descreve a construção de um coletor solar alternativo de concreto de tração simples (areia, cimento e pedra), para aplicações agrícolas e agroindustriais. o coletor é constituído de uma área de absorção 51 m2 com 470m de mangueira de polietileno para o aquecimento da água, e o armazenador da água aquecida. O sistema coletor e armazenador foi submetido a testes experimentais onde foram determinados para as estações verão e inverno, e sob três coberturas de céu aberto, parcialmente nublada e nublada: as temperatura do absorvedor em três profundidades; ganho térmico do fluido; rendimento térmico do coletor, e desempenho do armazenador. Os resultados mostram que a temperatura do absorvedor foi maior na cobertura de céu aberto, decrescendo em seqüência de profundidade 55,74ºC, 52,10C e 49,30C respectivamente, e foi menor na cobertura de céu nublado, 48,30C, 46,20C e 44,60C respectivamente; o ganho térmico do fluido de trabalho no absorvedor foi decrescente em função do aumento comprimento do condutor: o ganho foi maior no verão e em dias de céu aberto, atingindo a temperatura máxima de 52,70C, e foi menor no inverno, em dias céu nublado, atingindo a temperatura máxima de 28,50C; o rendimento térmico do coletor foi maior em dia de céu aberto: no verão 71,4% e inverno 74%; o sistema armazenador térmico, mostrou ótimo desempenho na conservação da temperatura do fluido de trabalho. Nos dias estudados houve uma redução de 10% na temperatura final da água aquecida / This paper describes the construction of an alternative sidewalk-type solar collector made of concrete (sand, cement and stone), for agriculture and agribusiness uses. The collector consists of an absorption area of 51 m2 with 470m polyethylene tubing for water heating, and a storage for warm water. The collector and storage systems were subjected to experimental tests which were determined for summer and winter, three sky conditions: open skies, partly cloudy and overcast; three depths temperature in the absorber; thermal gain of the fluid, thermal efficiency of the collector and performance of the water storage. The temperature of the absorber was higher in open sky conditions: 55,74ºC above it, decreasing in depth sequence of 52,1ºC and 49,3ºC. This temperatures of the absorber were 48,3ºC 46,2ºC and 44,6ºC respectively in a overcast days. The thermal gain of the working fluid in the absorber was decreasing with increasing length of the conductor: the gain was higher in summer and open sky days, reaching a maximum temperature of 52.7 ºC, and lowest in winter cloudy days, reaching a maximum temperature of 28.5 ºC. The collector thermal efficiency was higher in open sky days: 71.4% in summer and 74% in winter. The warm water storage system had excellent keeping temperature performance with 10% loss in the final water temperature

This diploma thesis deals with thermal calculations of fire tube water heater. The first part of the thesis describes different classifications of boilers and water heaters and provides a basic overview for different types of commonly used boilers. The next part describes thermal calculation model created in Maple software, used formulas and algorithm of the model. Subsequently, the model is applied to the experimental water heater in the form of computational rating. In the last part of the thesis the model is applied to the existing operated industrial water heater to evaluate predictive ability of the calculation model by comparing the essential operating parameters obtained from the calculation with real data measured on the water heater.

A steady-state numerical model of a PV/microchannel integrated direct-expansion CO2 heat pump (PV-DXHP) water heater is developed, validated, and analyzed in the present study. To accomplish the objectives, a numerical model of a microchannel evaporator integrated into a CO2 PV DXHP is developed and validated. The effects of evaporator operating parameters on the heat absorption and pressure drop are analyzed. Utilizing the evaporator model, the PV-DXHP model is developed, and the baseline values of the heat pump operating parameters are determined from the evaporator parametric study. The PV-DXHP demonstrates high water heating capability, while maintaining a reasonably high COP. The COP has the highest dependency on the CO2 mass flow rate, while the water outlet temperature has the highest dependency on the water mass flow rate. The results are highly promising and indicate the system has potential to help meet the energy requirements for residential and industrial water heating demands.

A feedwater heater is a typical component in power plants which increases the cycle efficiency. Over the last decade, renewable energies have significantly developed and been employed in the power grid. However, weather conditions are inconsistent and therefore produce variable power. Fossil fuel power stations are often required to supplement the variable renewable energies, which increased the rate of power cycling to an unforeseeable extent over the past decade. Power cycling results in changes in the flow rate, pressure, and temperature of a feedwater heater’s inlet flows. In a tubesheet-type feedwater heater, these transients induce cycling stress in the tubesheet and failures due to thermal fatigue occur. The header-type feedwater is currently employed in high pressure applications as it is more resistant to thermal fatigue compared to the tubesheet-type. However, the tubesheet-type is more cost effective to construct and maintain. It would be advantageous if the cyclic thermal stresses in the tubesheet can be better analysed and alleviated to support the use of the tubesheet-type. A detailed transient temperature distribution of the tubesheet is required to understand the thermal fatigue. Normally, engineers opt towards a full CFD to obtain such results. However, the size and complexity of a feedwater heater is immense and cannot be simulated practically solely using CFD spatial elements. This study developed a multiscale approach that thermally couples 1D network elements, CFD spatial elements, and macroscopic heat transfer correlations to reduce the computational expense substantially. The combination of the various selected techniques and the specific application of this methodology is unique. This approach is capable of obtaining the detailed transient temperature distribution of the tubesheet in a reasonable time, as well as include the effects of the upstream and downstream components within the network model. The methodology was implemented using Flownex and Ansys Fluent for the 1D network and CFD solvers, respectively. The internal tube flow was modelled using 1D network elements, while the steam was modelled with CFD. Thermal discretisation, mapping, and convergence were considered to create a robust methodology not limited to feedwater heaters only. Additionally, a method was developed to analyse flow maldistribution in tube-bundles using the coupled 1D-3D approach. The implementation of the methodology consists of two parts, of which one is for development purposes, and the other serves as a demonstration. The development was done on a simple TEMA-FU heat exchanger which is representative of a feedwater heater. The methodology was tested by varying the primary fluid’s flow rates, changing the fluid media, and conducting transient simulations. The temperature distributions obtained were compared against a full CFD model and corresponded very well with errors less than 4%. A reduction in computational time of more than 40% was achieved but is highly dependent on the specific problem. Improvements to be made in future studies include the accuracy of the laminar case method and the stability of the flow maldistribution algorithm. The methodology was demonstrated by applying it to an existing industrial feedwater heater. No plant data was available to use for input conditions and therefore were assumed. The steam in the DSH was modelled using 3D CFD elements and the tube flow with 1D network elements. The condensing zone’s heat transfer was approximated using an empirical correlation. A steady state case was simulated and the outlet temperatures corresponded well with the manufacturer’s data. The temperature distribution of the tubesheet and surrounding solids were obtained. Finally, assumed sinusoidal transient perturbations to the inlet conditions were imposed. It was evident that the thermal gradients of both sides of the tubesheet were misaligned which highlights the thermal lag and inertia that cause differential temperatures. The 1D-CFD methodology was developed successfully with results that proved to correspond well, for a wide range of conditions, to full CFD. The methodology was applied and can be, in future work, validated with experimental results or extended by modelling upstream and downstream components in the network solver. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2019. / Mechanical and Aeronautical Engineering / MEng (Mechanical Engineering) / Unrestricted

[pt] Tem-se descrito um modelo calculado pelo computador para prognosticar o rendimento térmico de aquecedores de água domésticos por energia solar, em base à circulação termosifónica entre o coletor e o tanque de armazenagem isolado. A intensidade da radiação solar e a temperatura do ar são determinados de modelos reais. Presupõe-se uma situação ideal de não consumo de água durante o dia todo. Os resultados são comparados com resultados experimentais obtidos nos modelos reias. Analisa-se como caso especial o que acontece com o aquecimento inicial da água no coletor, de dez em dez centímetros. / [en] A computer model for predicting the thermal performance of domestic solar water heaters, employing thermosyphon circulation between the collector and the insulated storage tank, is described. The solar radiation intensity and ambient air temperatures have been found from real models. Ideal condition of no drain-off during the day is assumed. Results are compared with experimental results obtained from real models. As special case, what happen with initial water heating each ten centimeters in the absordber plate is analized.

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