This study aims to improve the performance of existing indirect evaporative coolers. A new dew point indirect evaporative cooler with counter-current heat/mass exchanger was developed in this research by optimal design, material selection, numerical simulation, experimental investigations and economic, environmental, regional acceptance analysis. A new dew point heat/mass exchanger using a counter-current flow pattern was designed by numerical simulation in terms of material, structure, geometrical sizes and operating conditions. The numerical results indicate that under a typical cooling design condition, i.e., 35oC dry-bulb/24oC wet-bulb temperatures, the heat exchanger could achieve a wet-bulb effectiveness of approximately 1.4. The results of numerical simulation are consistent with some published test data. Based on the numeric results and the material selection determined from a set of related tests, a prototype dew point heat/mass exchanger and the associated air cooler was designed and constructed in laboratory. Testing was carried out to evaluate the performance of the experiment prototype. The results indicate that the wet-bulb effectiveness of the prototype ranged from 55% to 110% for all test conditions. The power consumption of the prototype ranged from 10 to 50 W with energy efficiency (or COP) rated from 3 to 12. It is also found that the water consumption of the prototype was very small which ranged from 0.2-1.3 litre/h. A comparison between the numerical and experimental results was carried out and the reasons for the discrepancy were analysed. This research also investigates the feasibility, economic and environmental potential of using a dew point cooler in buildings in Europe and China. From the related studies in this thesis, it is concluded that the dew point cooler can achieve a higher performance (in terms of effectiveness and energy efficiency) than the typical indirect evaporative coolers without adding too much cost. It is found that the effectiveness and energy efficiency of the heat/mass exchanger in the cooler are largely dependent upon channel geometries, the intake air velocity, temperature, humidity and the working-to-intake air ratio but less on the feed water temperature. To maximise effectiveness and energy efficiency, it is suggested that 1) the channel height and the length of exchanger should be set below 6 mm and 1-1.2 m respectively; 2) the intake channel air velocity should be controlled to 0.5-1 m/s; and 3) the working-to-intake air ratio should be adjusted to 0.4-0.5. It is also concluded that the dew point system is suitable for most regions with dry, mild and hot climate. It is, however, unsuitable for humid regions where the system is used as a stand-alone unit. Compared to the conventional mechanical compression cooling system, the dew point system has a significantly higher potential in saving energy bills and reducing carbon emission. A project to construct an 8 kW commercial dew point cooler is currently under development with the assistance of a Chinese company. By the optimisation of material, structure and geometries, the cooler is expected to achieve a cooling output of 8 kW at the inlet air of 38oC dry-bulb/ 21oC wet-bulb temperatures, with a wet-bulb effectiveness of 1.02 at 1530 m3/h of supply air flow and 1200 m3/h of discharge air flow, whereas the power input of the unit is about 450 W and the energy efficiency (or COP) at 18.5.

No description available.

This thesis presents the experimental investigation of stall in low hub tip ratio industrial fans. Detailed measurements were obtained i four fan configurations. The effects of blade setting angle, solidity, blade profile and OGVs on rotating stall were investigated. The purpose of this work has been to get a better understanding of stall i low hub tip ratio fans. A fan test rig was built specially for this investigation. A three hole pressure transducer probe was made to measure the velocity and pressure at rotating stall conditions. A data acquisition system was developed to ensure the results of better quality. Blade Vibration was also monitored at different flow conditions for two builds. From the results obtained, some important features of rotating stall were observed. For the fans with a low blade setting angle, there was no rotating stall. The overall characteristics were continuous. For the fans with high blade setting angle, rotating stall appeared within a limited flow range. The rotating stall cells i the fans were always a single stall cell, covering part of the rotor tip region. The characteristics were the abrupt type. V A Detailed traverse measurements show that rotating stall has a very strong influence on the flow upstream of the rotor and has little effect on the flow downstream. The effects of space chord ratio, blade profile and OGVs on the stall behaviour have also been investigated. The experimental results also indicate that hub tip ratio has a important effect on the rotating stall behaviour. It is therefore concluded that the stall models based on the observation of high hub tip ratio compressors are not applicable to low hub tip ratio fans. The time averaged measurements show that a large radial shift of streamlines exist i the low hub tip ratio fans. Reverse flow near the hub downstream of the rotor was found in many cases, but reverse flow near the hub does not trigger rotating stall. However, the large low velocity region near the hub will affect the fan steady state performance. A simple streamline curvature program has been used to analyse the endwall boundray layer effect on the fan performance. \ Axisymmetric stall is important i low hub tip ratio fans because it dominates most of the stalled flow conditions. Axisymmetric stall is preferred to rotatíng stall since it gives the continuous type characteristic and it causes less Vibration problem. A set of nonlinear equations is used to simulate axsiyrnmetric stall a well a rotating stall and surge.

An experimental and theoretical investigation has been undertaken into the performance of a small prototype, water-cooled, gas-fuelled engine designed for use as a domestic heat pump prime mover. In light of the application, fuel type and capacity, both experimental and theoretical study of similar engines is at best poorly documented in the literature. A comprehensive engine test facility has been set up, incorporating extensive calorimetry, a separate lubrication system, emissions monitoring and high speed data acquisition for in-cylinder pressure measurement and analysis. Two new experimental cylinder heads have been designed together with new induction and exhaust systems, both to improve performance and to enable further investigation of the combustion process. A preliminary parametric study of the combustion process established that the thermal efficiency and emission levels are strongly dependent on operational and design variables and that a lean, fast-burning combustion process in a slow speed engine coupled with careful control of other operating variables had the potential for improving efficiency, reducing emissions, and lowering frictional losses and noise levels with enhanced durability. Accordingly, new information has been obtained relating to rates of heat release, energy flows and emission levels over a wide range of design and operating conditions with utility for and consistent with an envelope of conditions appropriate to such a lean burn strategy. Modelling techniques have been developed and used as diagnostic tools in conjunction with the experimental data to investigate the influence of operating and design variables on rates of heat release and energy flows. The models have been validated using the experimental data over a wide range of operating conditions and incorporated into a thermodynamic engine model for use as a sub-model in an overall heat pump model. The experimental and theoretical programme has provided a valuable insight into the lean burn strategy and realised a considerable improvement in the performance of the prototype engine. The theoretical study benefits from a new approach to small gas engine design and development.

The wide uses of solar energy technology (solar thermal collector, photovoltaic and heat pump systems) have been known for centuries. These technologies are intended to supply domestic hot water and electricity. However, these technologies still face some barriers along with fast development. In this regards, the hybrid energy system combines two or more alternative technologies to help to increase the total efficiency of the system. Solar assisted heat pump systems (SAHP) and photovoltaic/thermal collector heat pump systems (PV/T-HP) are hybrid systems that convert solar radiation to thermal energy and electricity, respectively. Furthermore, they absorb heat first, and then release heat in the condenser for domestic heating and cooling. The research initially investigates the thermal performance of novel solar collector panels. The experimental results indicate an average daily efficiency ranging from 0.75 to 0.96 with an average of 0.83. Compared with other types of solar collectors, the average daily efficiency of novel solar thermal collectors is the highest. The research work further focuses on the integrated system which combines solar collector and air source heat pump (ASHP). The individual components, configurations and layout of the system are illustrated. Theoretical analysis is conducted to investigate thermodynamic cycle and heat transfer contained in the hybrid system. Laboratory tests are used to gauge the thermal performance of the novel SAHP. A comparison is made between the modelling and testing results, and the reasons for error formation are analysed. The research then considers the specially designed PV/T collector that employs the refrigerant R134a for cooling of PV modules and utilizes the glass vacuum tubes for reducing the heat loss to the ambient air. The PV/T collector consists of 6 glass vacuum tube-PV module-aluminium sheet-copper tube (GPAC) sandwiches which are connected in series. The theoretical analysis and experimental tests all give the satisfactory results of up to 2.9% improvement of electrical efficiency compared with those without cooling. The research finally focuses on the integrated heat pump system where the PV/T collector acts as evaporator. Based on the energy balance of the four main components of the heat pump system, a mathematical model of the heat pump system is presented. When the instantaneous ambient temperature and solar radiation are provided, results are obtained for the spatial distributions of refrigerant conditions, which include temperature, pressure, vapour quality and enthalpy. Detailed experimental studies are carried out in a laboratory. Three testing modes are proposed to investigate the effect of solar radiation, condenser water flow rate and condenser water supply temperature on energy performance. The testing results show that an average coefficient of performance (COP) reached 3.8,4.3 and 4.0 under the three testing modes with variable radiation, condenser water supply water temperature and water flow rate, respectively. However, this could be much higher for a large capacity heat pump system using large PV panels on building roofs. The COP increases with the increasing solar radiation, but decreases as the condenser water supply temperature and water flow rate increases.

The subject of this work is the flow inside an axial pump impeller, which is studied both numerically and experimentally. The aim of the work is to provide a numerical method to predict the three-dimensional flow field within an axial flow pump impeller. The numerical scheme is divided into three basic parts. The first part involves the matrix through flow method to obtain the mainstream flow profiles on various blade-to-blade stream surfaces distributed from hub to tip and for given boundary conditions. In addition these solutions w to obtain a detailed flow field in the region of the leading edge. Furthermore, the transport equations of vorticity are integrated along each streamline to obtain the normal and stream wise components of vorticity.

In the present work, the more important parameters of the heat pump system and of solar assisted heat pump systems were analysed in a quantitative way. Ideal and real Rankine cycles applied to the heat pump, with and without subcooling and superheating were studied using practical recommended values for their thermodynamics parameters. Comparative characteristics of refrigerants here analysed looking for their applicability in heat pumps for domestic heating and their effect in the performance of the system. Curves for the variation of the coefficient of performance as a function of condensing and evaporating temperatures were prepared for R12. Air, water and earth as low-grade heat sources and basic heat pump design factors for integrated heat pumps and thermal stores and for solar assisted heat pump-series, parallel and dual-systems were studied. The analysis of the relative performance of these systems demonstrated that the dual system presents advantages in domestic applications. An account of energy requirements for space and hater heating in the domestic sector in the O.K. is presented. The expected primary energy savings by using heat pumps to provide for the heating demand of the domestic sector was found to be of the order of 7%. The availability of solar energy in the U.K. climatic conditions and the characteristics of the solar radiation here studied. Tables and graphical representations in order to calculate the incident solar radiation over a tilted roof were prepared and are given in this study in section IV. In order to analyse and calculate the heating load for the system, new mathematical and graphical relations were developed in section V. A domestic space and water heating system is described and studied. It comprises three main components: a solar radiation absorber, the normal roof of a house, a split heat pump and a thermal store. A mathematical study of the heat exchange characteristics in the roof structure was done. This permits to evaluate the energy collected by the roof acting as a radiation absorber and its efficiency. An indication of the relative contributions from the three low-grade sources: ambient air, solar boost and heat loss from the house to the roof space during operation is given in section VI, together with the average seasonal performance and the energy saving for a prototype system tested at the University of Aston. The seasonal performance as found to be 2.6 and the energy savings by using the system studied 61%. A new store configuration to reduce wasted heat losses is also discussed in section VI.

No description available.

Natural ventilation is a passive cooling method that has significant potential to reduce building energy consumption and to positively contribute to indoor environmental conditions. Because the window is an important element in naturally ventilated buildings, it can be used to adjust indoor air flow. However, lack of knowledge about occupants‘ window control behaviour and how this relates to different window typology would result in discrepancy between actual and proposed building performance. And also, limit the potential of natural ventilation in the building. This thesis explores the relationship between indoor air velocity, occupants‘ window control behaviour and window design. This study is based on field measurement and occupant comfort survey in four office buildings in a hot and humid climate in South-east China. The field study was carried in September and October of 2012. The indoor and outdoor thermal conditions, indoor air flow speed, window state and effective opening area were monitored. Occupant thermal comfort questionnaires were given to participants four times a day to record their comfort perceptions in the office. The field study gives new insights into the correlation between indoor air speed, occupants‘ window control behaviour and window design. For the research 14400 set of indoor and outdoor temperature and relative humidity data, 174560 indoor air velocity records and 1344 copies of questionnaires were collected. The results of this study defined comfort zone for this climate which is consistent with Givoni‘s comfort zone for a hot and humid climate. The indoor air flow path is identified by measuring the indoor air velocity across different parts of the office and related window opening combinations. Besides, the effective opening area is reduced with decreased indoor air temperature when the indoor air temperature is lower than 25°c. None of the windows is closed when the indoor air temperature is higher than 28°c. During the working hours, the changing of effective opening is related to the air velocity across the desk surface. And measured maximum indoor air velocity measured around the occupant is 1.8m/s which did not result in occupants‘ window changing behaviour to adjust for comfort. In conclusion, this study proved that occupants who live in hot and humid climate can accept higher humidity level. If the air velocity can be avoided across the occupant‘s working surface, then a higher indoor air velocity is still accepted by occupant as within their comfort threshold. So, there are great potentials for occupant to extend their comfort threshold and adapt to the local climate. Besides, window opening type and position has a significant impact on indoor air velocity and pattern. It would also influence convective cooling affect and occupant thermal comfort. This is evident from the indoor air velocity measurement results and the occupant comfort survey results. In addition, accessibility is important to window design. In the naturally ventilated office building, if occupants find it difficult to operate the window, this will have an influence on the natural ventilation potential in the building and cause the occupant discomfort. Thus, the findings of this study will help architects and engineers to design naturally ventilated office buildings in South-east China.

Having outlined the requirements of the heat pump, water and sodium hydroxide are selected as a suitable working fluid and absorbent. The advantages and disadvantages of this particular combination are outlined before dealing with the experimental work. The various components in the system are then discussed with particular attention to the absorber. From the results, suitable improvements to the design are suggested before describing possible alternative absorption systems. The technical details are all presented separately from the main text, in the Appendices.