The performance of membrane heat exchangers for HVAC total energy recovery systems was evaluated through experimentation and detailed system modelling. The operating principle of the membrane heat exchanger (enthalpy heat exchanger) is based on passing ambient hot and humid supply air over one side of a porous membrane heat exchanger surface and cold and less humid room exhaust air on the other side of the transfer surface. Due to the gradient in temperature and vapour pressure, both heat and moisture are transferred across the membrane surface causing a decrease in temperature and humidity of the supply air before it enters the evaporator unit of the conventional air conditioner. Hence both sensible and latent energy are recovered. In this study, both experimental and numerical investigations were undertaken and mathematical models were developed to predict the performance of the latent heat recovery heat exchangers for use with conventional air conditioning systems. The membrane moisture transfer resistance was determined by a laboratory-scale permeability measurements. It was found that the membrane heat exchanger performance is significantly influenced by the heat exchanger flow profile and shape, heat and moisture transfer material characteristics, air velocity and air moisture content. Improvement of membrane heat exchanger performance requires an in depth study on flow, temperature and moisture distribution in the heat exchanger flow paths. Thus, a commercial CFD package FLUENT is used to model the membrane heat exchanger. However, software of this type cannot model moisture diffusion through the porous transfer boundary. Therefore, two user defined function codes have been introduced to model the moisture transfer in latent energy heat exchangers. The annual energy consumption of an air conditioner coupled with a membrane heat exchanger is also studied and compared with a conventional air conditioning cycle using the HPRate software. Energy analysis shows that in hot and humid climates where the latent load is high, an air conditioning system coupled with a membrane heat exchanger consumes less energy than a conventional air conditioning system. The membrane heat exchanger dehumidifies the air before it enters the air conditioning system, resulting in a decrease in energy consumption in comparison with conventional air conditioning system.

Energy is an essential and critical commodity and our reliance on it has fuelled much of the debate and interest in society and academia alike. Environmental concerns, depleted energy resources and higher energy prices are the main factors that drive this interest. Energy efficiency is one of the main avenues to preserve and better utilize this valuable commodity. The energy exchange by employment of heat exchangers is extensive and tube-fin heat exchangers are widely used in industrial and commercial applications. Smarter designs could not only improve energy efficiency but may also save on material costs. Although mass production and improved manufacturing techniques have reduced manufacturing costs, tube fin heat exchangers have not evolved greatly to take advantage of these improvements. There has been a large range of fin surface enhancements proposed, such as waffled fins or louvres and while limited improvements in capacity have been achieved, this is generally accomplished at a much larger pressure drop penalty. Numerous studies have been performed in order to examine the potential of various surface enhancement geometries on an ad hoc basis. These presumably operate on the basis of enhanced convection due to increased turbulence levels. However very few of these studies examine the actual nature of turbulence that is responsible for convection enhancement. A series of experiments and numerical studies have been conducted to quantify the effect of the turbulence vortex characteristics on the air side heat convection of a tube-fin heat exchanger. Homogeneous, transverse and streamwise vortical structures were investigated. The thermal transfer performance resulting from these flows was compared to that of standard louver fin geometries by considering sensible heat transfer only, applicable to radiator applications. Several novel coils designed to achieve these vortex structures, were developed and their heat transfer characteristics were quantified. These coil designs can be described as the Tube Mesh, Tube Strut and a Delta-Winglet fin surface.The Tube Mesh heat exchanger consisted entirely of horizontal and vertical tubes arranged in an approximate homogeneous turbulence generating grid. While they had a lower heat transfer of between 53% to 63% of that of the louvre fin surface, they had an extremely low pressure drop of 25% to 33%. This has the potential to make them suitable for certain low pressure drop applications, especially if energy saving is a prerequisite. The range of Tube Strut coils consisted of a tube bundle with interconnecting heat conducting struts to form a parallel plate array were also investigated. Three different strut thicknesses and strut spacing were trialled. In general these had similar performance to the tube mesh at 45% to 65% the heat transfer capacity of the louver fin surface. The resulting pressure drop was 38% to 42% of that of the louver fin surface. A delta-winglet design which positioned the deltas in a flow up configuration just in front of the tubes was examined. It was found that this configuration had an almost comparable capacity of 87% to a louver surface having the same fin pitch. On the other hand it had approximately half the pressure drop of 54% of the similar louver fin surface. This particularly low pressure drop makes this design preferable from an energy utilisation perspective. While a slight increase in coil area is required, this is offset by an almost 50% reduction in operating costs by reducing the parasitic energy requirements of the convection fans. The experimental data gathered for this Delta-Winglet design served to validate a succession of numerical simulations which were performed to estimate the performance of other configurations of multiple vortex generators. In addition the performance of combining a delta-wing with a louvred surface was investigated. It was found that increasing the number of delta-winglets or combining deltas with a louvred surface provided little improvement in heat transfer but increased pressure drop substantially. The louvre design itself was examined, and simulations were undertaken to estimate the effect of louvre angle, as well as louvre pitch. A hitherto unexamined concept was to investigate the effect of having louvres with serrated edges. It was found that an increase in louver angle by 5 degrees had negligible effect on heat transfer but increased the pressure drop by 17%. A variation in louver pitch showed a minimal variation in both heat transfer and pressure drop. Surprisingly a serrated louver showed a slight reduction in both heat transfer and pressure drop but this was miniscule. It was established throughout the course of the investigations that the bulk of the coil heat transfer is performed by the first tube row. Therefore the potential for increasing heat transfer by shifting some heat exchange to the down stream rows was examined. This was attempted by having progressively increasing louvre angles from the front of the coil to the rear. While a slight increase in heat transfer performance was achieved, this accomplished at the expense of a 13%-14% increase in pressure drop. The outcomes have shown that substantial net improvement of heat exchanger energy efficiency can be achieved through optimization of the turbulence generation along the fins of a tube fin heat exchanger. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1253254 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2006

In this thesis a novel computer based model is developed which accurately simulates the operation of a plate heat exchanger (PHE). The model allows for the variation of all relevant fluid properties as the temperatures of the fluids vary through the PHE. It is set up in a spreadsheet in such a way that one can observe the variation of fluid properties and heat transfer parameters through the PHE during steady state operation. Although the model could be used for general purpose analysis of PHE's, it is intended to be used in an educational environment, where students can run "virtual lab sessions" with the model and so gain a better understanding of the overall and detailed operation of plate heat exchangers. The model is validated using experimental data representing a range of different PHE sizes, flow configurations, fluid types and flow conditions. Instructions have been provided on how it can be used in an educational environment to assist student to discover more about the general and detailed operation of a PHE.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Bibliography: (leaves [181]-186).

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on January 11, 2008) Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 1990. / Typescript (photocopy). Includes bibliography (leaves 230-239). Also available via the World Wide Web.

Thesis (M.S.)--Ohio University, August, 1983. / Title from PDF t.p.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Garimella, Srinivas; Committee Member: Ghiaasiaan, Seyed Mostafa; Committee Member: Mistree, Farrokh.

Thesis (M.S.)--University of Michigan, 1962. / Project completed June 1961. Degree awarded Feb. 1962.

Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 61).