Ethanol is a renewable energy source that could decrease society's dependence on fossil fuels, while reducing greenhouse gas emissions. Producing ethanol on a small scale on South African farms could provide farmers with the capability of increasing their profits by reducing their input cost. Ethanol can be directly used as fuel and could supply alternative products to their market. This study evaluated the feasibility of using an ammonia/water hybrid heat pump in the ethanol production process. A model for the material and energy balance of a small scale ethanol plant was simulated, to obtain the requirements to which the hybrid heat pump had to adhere. A two stage hybrid heat pump (TSHHP) was then modelled. It is capable of operating at high temperatures and it has high temperature lift capabilities, which are suitable in the production of ethanol. The results from the model demonstrated that the TSHHP could operate at an average temperature lift of 106°C with a maximum temperature of heat delivery as high as 142°C and cooling as low as 9°C. Simultaneous heating and cooling demand in the ethanol production process can be met with the TSHHP. For the TSHHP model, 120 kW of heating and 65 kW of cooling is supplied while maintaining a COP of 2.1. The model accuracy was also verified against another simulation program. Implementation of the TSHHP into the ethanol plant was then discussed, as well as methods to optimize production by energy management. When compared to conventional heating and cooling systems, it was found that the TSHHP provides a more cost effective and energy efficient way of producing ethanol. The economic evaluation demonstrated that the installation cost of the TSHHP would only be 63% of the price of a conventional system. The main advantage is that the TSHHP uses only 38% of the energy used in a conventional system. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.

abstract: Recent literature indicates potential benefits in microchannel cooling if an inlet orifice is used to suppress pressure oscillations that develop under two-phase conditions. This study investigates the costs and benefits of using an adjustable microchannel inlet orifice. The focus is on orifice effect during steady-state boiling and critical heat flux (CHF) in the channels using R134a in a pumped refrigerant loop (PRL). To change orifice size, a dam controlled with a micrometer was placed in front of 31 parallel microchannels. Each channel had a hydraulic diameter of 0.235 mm and a length of 1.33 cm. For steady state two-phase conditions, mass fluxes of 300 kg m-2 s-1 and 600 kg m-2 s-1were investigated. For orifice sizes with a hydraulic diameter to unrestricted hydraulic diameter (Dh:Dh,ur) ratio less than 35 percent, oscillations were reduced and wall temperatures fell up to 1.5 °C. Critical heat flux data were obtained for 7 orifice sizes with mass fluxes from 186 kg m-2 s-1 to 847 kg m-2 s-1. For all mass fluxes and inlet conditions tested, CHF values for a Dh:Dh,ur ratio of 1.8 percent became increasingly lower (up to 37 W cm-2 less) than those obtained with larger orifices. An optimum orifice size with Dh:Dh,ur of 35 percent emerged, offering up to 5 W cm-2 increase in CHF over unrestricted conditions at the highest mass flux tested, 847 kg m-2 s-1. These improvements in cooling ability with inlet orifices in place under both steady-state and impending CHF conditions are modest, leading to the conclusion that inlet orifices are only mildly effective at improving heat transfer coefficients. Stability of the PRL used for experimentation was also studied and improved. A vapor compression cycle's (VCC) proportional, integral, and derivative controller was found to adversely affect stability within the PRL and cause premature CHF. Replacing the VCC with an ice water heat sink maintained steady pumped loop system pressures and mass flow rates. The ice water heat sink was shown to have energy cost savings over the use of a directly coupled VCC for removing heat from the PRL. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2012

No description available.

The CFD simulation of cooling piston compressor Stream, manufactured by Emerson company, is the topic of this diploma thesis. Analysis of moving parts (piston, valves) and refrigerant or physical settings for simulation were based on experimental data provided by Emerson. The goal of the thesis is to test opportunities of Star-CCM+ in simulating the flow inside the compressor. In the end there will be a comparison of experimental data and results from the simulation. The thesis also contains a theoretical background of piston compressors and phenomenon following the operating compressor.

No description available.

[ES] Debido a la crisis climática, es necesario encontrar fuentes alternativas para la climatización de locales y la producción de agua caliente sanitaria (ACS). Las bombas de calor se presentan como una alternativa excelente para sustituir a las calderas y así poder reducir las emisiones de gases contaminantes. En obra nueva, si se dispone de acceso al terreno o a una masa de agua, las bombas de calor agua-agua o salmuera-agua son altamente recomendadas debido a sus numerosas ventajas. El principal problema que presentan las bombas de calor es el refrigerante que contienen, ya que en la actualidad no existe refrigerante que sea a la vez barato, seguro y con propiedades termodinámicas óptimas. La tendencia en el futuro cercano en bombas de calor utilizadas para la calefacción de locales es volver al uso de refrigerantes naturales como los hidrocarburos y las hidrofluorolefinas. Estos refrigerantes presentan problemas de seguridad debido a su inflamabilidad o toxicidad y es por eso que, en caso de carecer de medidas de seguridad adicionales, la cantidad de refrigerante está limitada. En esta tesis se presenta un trabajo experimental sobre una bomba de calor salmuera-agua trabajando con poca cantidad de R290. La campaña experimental fue pensada para obtener resultados beneficiosos sobre cuál es el actual potencial de este tipo de tecnología tras la limitación de la carga de refrigerante, para desarrollar formas de reducción de carga de refrigerante en los sistemas y para mejorar las simulaciones de predicción de la cantidad necesaria de refrigerante. La campaña experimental está dividida en dos partes, cada una enfocada en uno de los siguientes objetivos: la primera en conocer el actual comportamiento anual de esa bomba de calor y la segunda para desarrollar estrategias de reducción de carga de refrigerante. En cada campaña experimental se almaceno tanto los datos de funcionamiento como la cantidad de refrigerante que había en cada uno de los componentes. La instalación estaba equipada con las herramientas necesarias para la toma de datos durante el funcionamiento de la bomba de calor y también era capaz de sectorizarla asilando cada uno de los componentes para poder extraer y pesar el refrigerante y así conocer que cantidad había en cada zona. Con los datos recogidos, se ha podido observar diferencias entre la predicción de carga de refrigerante en los diferentes componentes y la medida experimentalmente, y también se ha encontrado alguna de las causas de esa discrepancia, pudiendo así corregir el modelo. Para ello, se ha desarrollado un modelo de compresor y al modelo existente de intercambiadores de calor se le ha añadido un volumen muerto de refrigerante. Con estos cambios la predicción ha mejorado notablemente en el modelo utilizado y en la actualidad se puede utilizar para conocer una aproximación del refrigerante necesario. / [CA] A causa de la crisi climàtica, és necessari enden fonts alternatives per a la climatització dels locals i la endencia d'aigua calenta sanitaria (ACS). Les bombes de calor es presenten com una alternativa excel·lent per a substituir a les calderes i així poder reduir les emissions de gasos contaminants. En obra nova, si es disposa d'accés al terreny o a una massa d'aigua, les bombes de calor aigua-aigua o salmorra-aigua són endencia recomanades a causa dels seus nombrosos avantatges. El principal problema que presenten les bombes de calor és el refrigerant que contenen, ja que en l'actualitat no existeix refrigerant que siga alhora barat, segur i amb propietats termodinàmiques òptimes. La tendencia actual en bombes de calor utilitzades per a la calefacció d'espais, és tornar a l'ús de refrigerants naturals com els hidrocarburs i les hidrofluorolefines. Aquests refrigerants presenten problemes de seguretat a causa de la seua inflamabilitat o toxicitat i és per això que, en cas de mancar de mesures de seguretat addicionals, la quantitat de refrigerant està limitada. En aquesta tesi es presenta un treball experimental sobre una bomba de calor salmorra-aigua treballant amb poca quantitat de R290. La campanya experimental va ser pensada per a obtindre resultats beneficiosos sobre quin és l'actual potencial d'aquesta mena de tecnologia després de la limitació de la càrrega de refrigerant, per a desenvolupar formes de reducció de càrrega de refrigerant en els sistemes i per a millorar les simulacions de predicció de la quantitat necessària de refrigerant. La campanya experimental està dividida en dues parts, cadascuna enfocada en un dels següents objectius: la primera a conéixer l'actual comportament anual d'aqueixa bomba de calor i la segona per a desenvolupar estratègies de reducció de càrrega de refrigerant. En cada campanya experimental s'emmagatzeme tant les dades de funcionament com la quantitat de refrigerant que hi havia en cadascun dels components. La instal·lació estava equipada amb les eines necessàries per a la presa de dades durant el funcionament de la bomba de calor i també era capaç de sectoritzar-la asilant cadascun dels components per a poder extraure i pesar el refrigerant i així conéixer que quantitat hi havia en cada zona. Amb les dades recollides, s'ha pogut observar diferències entre la predicció de càrrega de refrigerant i la mesura experimentalment, i també s'ha trobat alguna de les causes d'aqueixa discrepància, podent així corregir el model. Per a això, s'ha desenvolupat un model de compressor i al model existent de bescanviadors de calor se li ha afegit un volum mort de refrigerant. Amb aquests canvis la predicció ha millorat notablement i en l'actualitat es pot utilitzar per a conéixer una aproximació del refrigerant necessari. / [EN] Due to the climate crisis, there is a need to find alternative energy sources for space heating, cooling, and domestic hot water (DHW) production. Heat pumps are an excellent alternative to substitute current boilers to reduce gas emissions. A liquid source heat pump is highly recommended in new buildings with access to land or water due to its significant advantages. The main problem with this technology is that it uses a refrigerant inside, and there is no refrigerant with good performance, cheap and safe to handle. The near future trend in heat pumps used for space heating is to use pure refrigerants such as natural refrigerants and HFOs. These refrigerants (except CO2) have safety issues (flammability or toxicity); consequently, a maximum amount of refrigerant is allowed without considering extra safety measures. This PhD presents an experimental work with a ground source heat pump (GSHP) with a low R290 refrigerant amount. This experimental campaign is helpful to know the current achievable performance derived from the limitation of refrigerant amount, to develop refrigerant charge reduction strategies and to improve existing simulation software based on refrigerant charge prediction. The experimental campaign was divided into two parts to focus separately on normal annual behaviour and refrigerant charge reduction strategies. In each test campaign, performance data was recorded during the test, and the refrigerant charge amount in each component was extracted and weighed after the end of each test. The installation had the tools to acquire data from the vapour compression circuit, isolate the components, and extract and weigh the refrigerant to know how much refrigerant was inside each section. With the data collected, it was observed that the differences in refrigerant charge prediction in the components with the software used were significant, and some causes of these differences have been identified, correcting the prediction model. So, a compressor model has been developed, and a dead volume has been added to the refrigerant charge calculation in heat exchangers. With these changes, the refrigerant prediction has greatly improved in the model used and could be a reliable approximation. / Gracias a la Universitat Politècnica de València por brindarme la financiación y los medios a través del programas “Ayudas para movilidad de estudiantes de Doctorado de la Universitat Politècnica de València” y “Programa de Ayudas de investigación y Desarrollo” (PAID-01-17) / Sánchez-Moreno Giner, L. (2023). Research about Refrigerant Charge in Domestic Heat Pumps [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/196786

Heat production accounted in 2021 for 50 % of the energy end use globally, where a strongconnection to fossil sources still exists. Large-scale electrical heat pumps can therefore have akey role in the energy system to enable a decreased reliance on fossil fuels and at the same timecontribute to stable system when incorporating more intermittent renewable sources. To operatea heat pump, a working fluid i.e., refrigerant is required. Historically these substances havebeen ozone depleting with a significant global warming potential. Applied regulations andlegislations have therefore limited the substances possible to implement. This study therefore focuses on investigating potential future refrigerants in LSHPs, by studying both current and potential future legislations and regulations but also the potential performanceof the substances. The performance was evaluated for two operational condition cases wherethe first focused on meeting the supply and demand of a third generation district heating systemwith an evaporation temperature of 0 °C. The second case investigated a middle temperature industrial process with an evaporation temperature of 33 °C. For both cases a two-stage compressor heat pump cycle was considered. Substances available in the database REFPROP were considered, where legislations and regulations, classifications, thermodynamic properties, and the performance were investigated. Substances not fulfilling the set criterions were eliminated. Seven substances were then investigated in depth where e.g., the volume flow rate, performance, operational electricity cost and both footprint and cost of the evaporator were considered. All substances were investigated both with and without an internal liquid-suction HEX, to investigate how such component potentially could affect the performance. The result of the study shows that environmental, safety aspects and thermodynamic propertieshave a large impact on possible refrigerants, with a decrease from 160 available substances to20 possible for each case. If an evaporation pressure in the vacuum range or a transcritical cyclewould have been investigated the number of possible refrigerants would increase. Out of the 20possible substances, seven substances namely isobutane, butane, isobutene, butene, propane,perfluoropentane and isopentane were chosen for further investigation. The performance andelectrical operational cost can be concluded to be fairly similar, with an increase when includingan internal liquid-suction HEX. The performance for case 2, is although slightly higher, whereperfluoropentane performs superior. The high GWP value for perfluoropentane however limitsits possibility to be used. Lastly the size and cost of the evaporator was investigated. It couldbe concluded that case 1 required a smaller design than case 2, related to the size of the HTCvalue.

No description available.

No description available.

An examination of various methods for mass flow rate measurements was undertaken to evaluate their applicability for measuring refrigerant R-134a two-phase mass flow in refrigeration and air-conditioning equipment. An experimental apparatus was constructed to generate the required two-phase flow conditions. A turbine and a venturi flowmeter were used together with either a capacitance transducer or a gamma densitometer to determine the two-phase mass flow rate. The time-averaged void fraction was measured using a capacitance transducer and a gamma densitometer. Their measurements were in good agreement. Hence, for mass flow rate measurements, the capacitance transducer was used as the void fraction meter because of its ease of operation. A number of models were used to combine the output of either the turbine flowmeter or the venturi flowmeter, with the void fraction measurement to estimate the mass flow rate. It was found that, within the range of experimental data tested in the present work, the venturi flowmeter, in conjunction with Chisholm's model, provided the best agreement with the experimental results. / Thesis / Master of Engineering (MEngr)