title: Flow maldistribution in industrial air heaters and its effect on heat transfer

authors: Atkins, Martin John

abstract: Flow maldistribution in cross-flow heat exchangers used for industrial air heaters or recuperators is fairly common and can lead to a number of undesirable effects, one of which is deterioration in the thermal performance. The effect of gross flow maldistribution and the improvement in the thermal performance of flow correction guide vanes is investigated using a laboratory heat exchanger apparatus. The thermal performance deterioration from maldistribution was up to around 30 %. Modest improvements in the overall heat transfer coefficient and heat exchanger effectiveness when vanes were used was found for the range of air-side Reynolds numbers tested. Vanes were found to reduce the deterioration in thermal performance by up to 60 % compared to a perfectly uniform flow situation. Based on the ε-NTU correlations the thermal performance deterioration is predicted to decrease as the number of tube rows (i.e. NTU) increases. The effective heat transfer area and therefore thermal performance of industrial air heaters and recuperators can be improved by using flow correction devices, such as guide vanes.

text: Flow maldistribution in industrial air heaters and its effect on heat transfer Flow maldistribution in cross-flow heat exchangers used for industrial air heaters or recuperators is fairly common and can lead to a number of undesirable effects, one of which is deterioration in the thermal performance. The effect of gross flow maldistribution and the improvement in the thermal performance of flow correction guide vanes is investigated using a laboratory heat exchanger apparatus. The thermal performance deterioration from maldistribution was up to around 30 %. Modest improvements in the overall heat transfer coefficient and heat exchanger effectiveness when vanes were used was found for the range of air-side Reynolds numbers tested. Vanes were found to reduce the deterioration in thermal performance by up to 60 % compared to a perfectly uniform flow situation. Based on the ε-NTU correlations the thermal performance deterioration is predicted to decrease as the number of tube rows (i.e. NTU) increases. The effective heat transfer area and therefore thermal performance of industrial air heaters and recuperators can be improved by using flow correction devices, such as guide vanes.

year: 2014-08-31

title: Distributed Operating Systems on Wireless Sensor Networks

authors: Hunkin, Paul Wade

subjects: Wireless Sensor Networks

abstract: This thesis proposes the use of traditional distributed operating system and distributed systems techniques that are adapted and applied to the wireless sensor network domain. These techniques are applied to the creation of a wireless sensor network operating system that allows complex applications to be created without special programmer knowledge of sensor network programming or architecture. The resulting system is capable of executing a high level user application written in conventional single-system-image form, without the user being aware of the mesh architecture or underlying sensor node hardware.

A wireless sensor network is a collection of battery-powered embedded systems that communicate over low-bandwidth radio. Because of their limited hardware, niche deployments and use of embedded processors, programming techniques for wireless sensor network nodes are generally relatively esoteric compared to most software programming tasks. This can be relatively complex for programmers not familiar with the wireless sensor network domain. A naive approach to writing a wireless sensor network application may well result in considerably reduced battery life due to inefficient use of the limited power resources, requiring an expensive and time-consuming replacement or patching process. 

As a result of this complexity, traditional wireless sensor network applications are written as simply as possible. The majority of these applications simply move passive data readings back across a mesh to a more powerful server. While this is a sufficiently effective approach in some situations, for other sensor network deployments involving large amounts of complex data it is more efficient for the sensor network application to process at least some of the data inside the mesh, saving on unnecessary data transmissions. However in the real world, the complexity of writing such an application in many cases precludes this from being created. An operating system that provides power-efficient distributed processing while presenting a more standard unified single system image to the application developer would provide new possibilities for sensor network application developers in terms of creating dynamic and complex sensor network applications. 

This thesis covers the design decisions, development process and evaluation of the Hydra distributed wireless sensor network operating system, an operating system that provides these services. The system is evaluated in the form of a scenario for monitoring intruders over a large area using accelerometer monitoring -- during this scenario, power efficiency is gained due to the intelligent Hydra operating system services, as the resulting accelerometer data is not moved across potentially multi-hop network links. Application code complexity is also reduced due to the higher-level single system image programming environment.

text: Distributed Operating Systems on Wireless Sensor Networks This thesis proposes the use of traditional distributed operating system and distributed systems techniques that are adapted and applied to the wireless sensor network domain. These techniques are applied to the creation of a wireless sensor network operating system that allows complex applications to be created without special programmer knowledge of sensor network programming or architecture. The resulting system is capable of executing a high level user application written in conventional single-system-image form, without the user being aware of the mesh architecture or underlying sensor node hardware.

A wireless sensor network is a collection of battery-powered embedded systems that communicate over low-bandwidth radio. Because of their limited hardware, niche deployments and use of embedded processors, programming techniques for wireless sensor network nodes are generally relatively esoteric compared to most software programming tasks. This can be relatively complex for programmers not familiar with the wireless sensor network domain. A naive approach to writing a wireless sensor network application may well result in considerably reduced battery life due to inefficient use of the limited power resources, requiring an expensive and time-consuming replacement or patching process. 

As a result of this complexity, traditional wireless sensor network applications are written as simply as possible. The majority of these applications simply move passive data readings back across a mesh to a more powerful server. While this is a sufficiently effective approach in some situations, for other sensor network deployments involving large amounts of complex data it is more efficient for the sensor network application to process at least some of the data inside the mesh, saving on unnecessary data transmissions. However in the real world, the complexity of writing such an application in many cases precludes this from being created. An operating system that provides power-efficient distributed processing while presenting a more standard unified single system image to the application developer would provide new possibilities for sensor network application developers in terms of creating dynamic and complex sensor network applications. 

This thesis covers the design decisions, development process and evaluation of the Hydra distributed wireless sensor network operating system, an operating system that provides these services. The system is evaluated in the form of a scenario for monitoring intruders over a large area using accelerometer monitoring -- during this scenario, power efficiency is gained due to the intelligent Hydra operating system services, as the resulting accelerometer data is not moved across potentially multi-hop network links. Application code complexity is also reduced due to the higher-level single system image programming environment.

year: 2017

title: Water Quality Modelling of Te Waihora/Lake Ellesmere

authors: Hamilton, David P.

abstract: As a component of work to contribute towards the management of water quality of Te Waihora/Lake Ellesmere, the University of Waikato was subcontracted by University of Otago to apply a coupled hydrodynamic-water quality model to the lake. The primary funder for this work was Environment Canterbury (ECAN), Whakaora Te Waihora and the Central Government Freshwater Cleanup Fund. The main modelling tool used in the study to simulate the dynamics of Te Waihora/Lake Ellesmere was the one‐dimensional (1‐D) hydrodynamic-water quality model DYRESM-CAEDYM. The model was used to reproduce observed water column data for a mid-lake station over the period 2011 to 2015. Once a satisfactory level of reproduction of these data had been achieved, an assessment was carried out with the model to examine the impact of various management scenarios on lake water quality. These scenarios involved: (i) projected changes to external nutrient loads to the lake that could be associated with future land management in the catchment and (ii) different lake water level management regimes based around opening of the barrier separating the lake from the ocean. The scenarios are intended here to be a catalyst for further hui and consultations that may adapt and refine additional scenarios, some of which may involve testing of multiple management options. The quantitative output from the model provides a component of the input required to inform strategies for lake management, alongside historical and expert knowledge, as well as analysis of measured data.

text: Water Quality Modelling of Te Waihora/Lake Ellesmere As a component of work to contribute towards the management of water quality of Te Waihora/Lake Ellesmere, the University of Waikato was subcontracted by University of Otago to apply a coupled hydrodynamic-water quality model to the lake. The primary funder for this work was Environment Canterbury (ECAN), Whakaora Te Waihora and the Central Government Freshwater Cleanup Fund. The main modelling tool used in the study to simulate the dynamics of Te Waihora/Lake Ellesmere was the one‐dimensional (1‐D) hydrodynamic-water quality model DYRESM-CAEDYM. The model was used to reproduce observed water column data for a mid-lake station over the period 2011 to 2015. Once a satisfactory level of reproduction of these data had been achieved, an assessment was carried out with the model to examine the impact of various management scenarios on lake water quality. These scenarios involved: (i) projected changes to external nutrient loads to the lake that could be associated with future land management in the catchment and (ii) different lake water level management regimes based around opening of the barrier separating the lake from the ocean. The scenarios are intended here to be a catalyst for further hui and consultations that may adapt and refine additional scenarios, some of which may involve testing of multiple management options. The quantitative output from the model provides a component of the input required to inform strategies for lake management, alongside historical and expert knowledge, as well as analysis of measured data.

year: 2017