Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)

Permanent URI for this collection

https://dspace.lib.cranfield.ac.uk/handle/1826/17865

Browse

Browsing Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT) by Supervisor "Badr, Ossama"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Heat transfer characteristics of heat pipe heat exchangers for low and medium temperature heat recovery
    (1997-07) Kang, Heeyoon; Badr, Ossama
    Heat pipe heat exchangers (HPHEs) offer many advantages over other types of heat exchangers for the recovery of heat from industrial gaseous waste streams in the low and medium temperature ranges. Heat pipes employed in industrial heat exchangers can be made with or without wicks. Although the thermal performances of single heat pipes and HPHEs have been extensively investigated, comparative studies concerning behaviours of HPHE with different types of heat pipes, at the same operating conditions, appear to be very limited. Such studies are useful in evaluating the significance of the parameters pertinent to thermal performance and in selecting the most appropriate HPHE for a particular application. Taking into account previous studies, the present work was focused on comparative studies between heat pipe and thermosyphon, at the same operating conditions, with following the objectives : • Further studying the heat transfer characteristics of heat pipe and thermosyphon to obtain additional information regarding thermal performance, at the same operating conditions. • Providing some guide-lines for HPHEs design which relate to the thermal performance of heat pipe and thermosyphon. To achieve these objectives, two computer models, a ‘Heat Pipe and Thermosyphon Thermal Performance Model’ and a ‘Heat Pipe Heat Exchangers Design Model’, were developed. The former model facilitates the prediction of the axial temperature distributions of the working fluid and the tube wall ; heat transport limitations; and the thermal performances of thermosyphons and heat pipes with different type of wicks. An experimental investigation of the steady-state behaviour of the thermosyphon was carried out to validate this computer model and the results were compared with the corresponding predictions of the computer model developed. According to the experimental results, Nusselt’s film theory for continuous liquid film could not be employed for predicting thermal performances in the condenser and evaporator film region of inclined thermosyphons. Liquid film could only be maintained circumferentially in vertical thermosyphon tubes, even though might not the smooth continuous film. In the evaporator pool region, the change in saturation temperature due to the hydrostatic height of the pool should be considered for predicting the axial temperature distributions. The results of the behaviours of heat pipes and thermosyphons were utilised to develop a ‘Heat Pipe Heat Exchangers Design Model’ to facilitate both the design and the prediction of performances of HPHEs. These models enable the designers of waste-heat recovery systems to choose the most appropriate type of heat-transfer elements and optimise the design parameters of a HPHE for a given application.
  • Thumbnail Image
    ItemOpen Access
    A national energy policy proposal for Trinidad and Tobago: natural-gas cogeneration
    (2002-01) Hosein, Sharaaz; Badr, Ossama
    This thesis looks at energy policy in Trinidad and Tobago (T&T) by focusing on a single policy measure, natural-gas cogeneration, to learn about energy policy in general. It investigates natural gas as it is in the ascendancy, both locally and globally, and because oil is on the decline in T&T. The research further focuses on cogeneration in the industrial sector. It then approximately extrapolates results from the industrial sector to the entire country. The aim can thus be described as assessing natural-gas cogeneration's potential as a policy measure, using the industrial sector as an example. LNG, another major natural-gas use, provides a reference point for locating natural-gas cogeneration in the overall energy policy framework. The industry-wide cogeneration evaluation groups the 1,967 industrial electricity customers in 1998 according to similarity in electricity-use characteristics into 15 subgroups. This allows a study of one or more representatives from each subgroup to apply to the whole subgroup, and thus covers the whole spectrum of industrial electricity customers. This is a fundamental assumption of the research. The research thus essentially becomes a series of cogeneration feasibility studies at individual sites, needing data gathered from extensive fieldwork, and an analysis model constructed in MS Excel, which applies a standard business project-appraisal procedure. The analysis determines that industrial cogeneration in 1998 delivers conservative natural-gas savings of 2.2 billion kWh, or 13.5% of the natural gas used to generate the entire country's electricity in that year. The dollar value of these savings over 20 years is US$0.2 billion, using LNG's natural-gas resource valuation. Considering that a single LNG train uses 48.1 billion kWh natural gas per annum and delivers US$6 billion in revenues over 20 years, cogeneration is a minor policy measure compared to the petrochemical industry, and similarly in an overall natural-gas policy. However, cogeneration's significance to the electricity sector, and its importance in promoting a nationwide natural-gas infrastructure for the future, where the population directly benefits from the resource, renders it an important energy-policy measure.