Development of a triple stage heat transformer for the recycling of low temperature heat energy

Absorption heat transformers are thermodynamic systems which are capable of recycling industrial waste heat energy by increasing its temperature. Triple stage heat transformers (TAHTs) can increase the temperature of this waste heat by up to approximately 145˚C. The principle factors influencing the thermodynamic performance of a TAHT and general points of operating optima were identified using a multivariate statistical analysis, prior to using heat exchange network modelling techniques to dissect the design of the TAHT and systematically reassemble it in order to minimise internal exergy destruction within the unit. This enabled first and second law efficiency improvements of up to 18.8% and 31.5% respectively to be achieved compared to conventional TAHT designs. The economic feasibility of such a thermodynamically optimised cycle was investigated by applying it to an oil refinery in Ireland, demonstrating that in general the capital cost of a TAHT makes it difficult to achieve acceptable rates of return. Decreasing the TAHT's capital cost may be achieved by redesigning its individual pieces of equipment and reducing their size. The potential benefits of using a bubble column absorber were therefore investigated in this thesis. An experimental bubble column was constructed and used to track the collapse of steam bubbles being absorbed into a hotter lithium bromide salt solution. Extremely high mass transfer coefficients of approximately 0.0012m/s were observed, showing significant improvements over previously investigated absorbers. Two separate models were developed, namely a combined heat and mass transfer model describing the rate of collapse of the bubbles, and a stochastic model describing the hydrodynamic motion of the collapsing vapour bubbles taking into consideration random fluctuations observed in the experimental data. Both models showed good agreement with the collected data, and demonstrated that the difference between the solution's temperature and its boiling temperature is the primary factor influencing the absorber's performance.

The Irish paradigm on the natural progression of hepatitis C virus infection: an investigation in a homogeneous patient population infected with HCV 1b (Review)

The aetiological agent of chronic hepatitis C is the hepatitis C virus. The hepatitis C virus is spread by parenteral transmission of body fluids, primarily blood or blood products. In 1989, after more than a decade of research, HCV was isolated and characterised. The hepatitis C viral genome is a positive-sense, single-stranded RNA molecule approximately 9.4 kb in length, which encodes a polyprotein of about 3100 amino acids. There are 6 main genotypes of HCV, each further stratified by subtype. In 1994, a cohort of women was identified in Ireland as having been iatrogenically exposed to the hepatitis C virus. The women were all young and exposed as a consequence of the receipt of HCV 1b contaminated anti-D immunoglobulin. The source of the infection was identified as an acutely infected female. As part of a voluntary serological screening programme involving 62,667 people, 704 individuals were identified as seropositive for exposure to the hepatitis C virus; 55.4% were found to be positive for the viral genome 17 years after exposure. Of these women 98% had evidence of inflammation, but suprisingly, a remarkable 49% showed no evidence of fibrosis. Clinicopathology and virological analysis has identified associations between viral load and the histological activity index for inflammation, and, between inflammation and levels of the liver enzyme alanine aminotransferase. Infection at a younger age appears to protect individuals from progression to advanced liver disease. Molecular analyses of host immunogenetic elements shows that particular class II human leukocyte associated antigen alleles are associated with clearance of the hepatitis C virus. Additional class II alleles have been identified that are associated with stable viraemia over an extended period of patient follow-up. Although, investigation of large untreated homogeneous cohorts is likely to become more difficult, as the efficacy of anti-viral therapy improves, further investigation of host and viral factors that influence disease progression will help provide an evidence based approach were realistic expectations regarding patient prognosis can be ascertained.