Performance Investigation of CHP Equipment
by Ji Bian
The Cooling Heating & Power systems for Buildings (BCHP) are attracting more attention due to their advantages as compared to conventional energy systems. As a developing technology, there are still problems to be solved. Fuel flexibility and dynamic response between different machines in the system are two of the main issues to be investigated.
This study presents research conducted on a BCHP system that is composed of a microturbine, an absorption chiller and a solid desiccant unit that are driven by the microturbine's exhaust gas to provide cooling and dehumidification. It demonstrates the feasibility of operating the microturbine that is originally designed for natural gas on propane and analyzes the reasons for the efficiency reduction when operating on propane. It further presents a model that describes the transient behavior of the absorption chiller, which requires a much longer period to reach its steady state compared with the microturbine.
Master's Thesis
http://hdl.handle.net/1903/3085
Experimental and Computational Investigation of Planar Ion Drag Micropump Geometrical Design Parameters
by Vytenis Benetis
To deal with increasing heat fluxes in electronic devices and sensors, innovative new thermal management systems are needed. Proper cooling is essential to increasing reliability, operating speeds, and signal-to-noise ratio. This can be achieved only with precise spatial and temporal temperature control. In addition, miniaturization of electric circuits in sensors and detectors limits the size of the associated cooling systems, thereby posing an added challenge. An innovative answer to the problem is to employ an electrohydrodynamic (EHD) pumping mechanism to remove heat from precise locations in a strictly controlled fashion. This can potentially be achieved by micro-cooling loops with micro-EHD pumps. Such pumps are easily manufactured using conventional microfabrication batch technologies.
The present work investigates ion drag pumping for applications in reliable and cost effective EHD micropumps for spot cooling. The study examines the development, fabrication, and operation of micropumps under static and dynamic conditions. An optimization study is performed using the experimental data from the micropump prototype tests, and a numerical model is built using finite element methods.
Many factors were involved in the optimization of the micropump design. A thorough analysis was performed of the major performance-controlling variables: electrode and inter-electrode pair spacing, electrode thickness and shape, and flow channel height. Electrode spacing was varied from 10 µm to 200 µm and channel heights from 50 µm to 500 µm. Also, degradation of the electrodes under the influence of an intense electric field was addressed. This design factor, though important in the reliability of EHD micropumps, has received little attention in the scientific and industrial applications literature.
Experimental tests were conducted with prototype micropumps using the electronic liquid HFE7100 (3M®). Flow rates of up to 15 ml/min under 15 mW power consumption and static pumping heads up to 750 Pa were achieved. Such performance values are acceptable for some electronic cooling applications, where small but precise temperature gradients are required.
Doctoral Dissertation
http://hdl.handle.net/1903/2671
Heat Transfer Coefficient and Pressure Drop Gas Cooling Measurements for CO2/Oil Mixture in a Micro Channel Tube
by James Phillip Kalinger
An experimental study was conducted to measure the heat transfer characteristics and pressure drop of supercritical Carbon Dioxide (CO2) in gas cooling conditions while flowing through a horizontal micro channel. Five experiments were conducted at operating conditions that included an inlet temperature of 70°, inlet pressures of 8 to 10 MPa, a mass flux of 400 kg/m2s, heat fluxes of 10 and 15 kW/m2, and oil concentration ratios of 6.58 to 10.72 wt.% with ND-8, polyalkylene glycol (PAG) oil. This data revealed trends that CO2 flowing through a micro channel has a reduced heat transfer coefficient and an increased pressure drop with an OCR over 6 wt.% in comparison to the predicted values. The measured heat transfer coefficient for the CO2 was 70% smaller than the predicted value using the Gnielinski correlation. The measured pressure drop for the CO2 was 150% larger than the predicted value using the Darcy-Weisbach correlation.
Master's Thesis
http://hdl.handle.net/1903/2632
Construction of Test Facility to Measure and Visualize Refrigerant Maldistribution in Multiport Evaporator Headers
by John Eric Linde
In a refrigeration cycle, condensed liquid refrigerant is expanded to a two-phase fluid entering the evaporator. In many applications, the evaporator paths are divided into a number of parallel sections to keep the pressure drop across the evaporator within a reasonable range and to maximize overall heat exchanger performance. Since the state of the refrigerant entering the evaporator is two-phase and its quality changes depending upon the operating conditions, the proper refrigerant distribution to individual sections is not an easy task. Nonuniform distribution, or maldistribution, will cause dry out at sections of lesser mass flow by superheating the refrigerant gas. This can result in nonuniform heat exchanger surface temperature distribution. Single-phase heat transfer coefficients (HTCs) are much lower than those of two-phase HTCs. When dryout occurs, both refrigerant-side HTCs and air-side HTCs are lower than those of wet surfaces. In addition to this, the temperature difference between the air and refrigerant decreases due to the increased refrigerant temperature. Therefore, refrigerant maldistribution results in an overall deterioration of heat exchanger performance. The main goal of this work is to construct a test facility to visualize and measure the twophase refrigerant flow through a multiport header of a flat multiport tube (FMT) heat exchanger and to investigate maldistribution. Using a transparent test section, a better understanding of the flow behavior will be obtained. The test facility should also measure the mass and vapor quality distribution in the multiport header, using a combination of energy balances and physical measurements. Most previous two-phase flow distribution studies investigated plate or serpentine exchangers. FMT heat exchangers have different geometries, and need to be studied independently. It is the objective of this work to provide essential design information for FMT evaporators by constructing an experimental setup which measures the effects of geometry, operating conditions, and fluid properties on both the distribution of liquid refrigerant and pressure drop across FMT heat exchangers.
Master's Thesis
http://hdl.handle.net/1903/3045
Experimental and Theoretical Investigation of Integrated Engine Generator - Liquid Desiccant System
by Sandeep M Nayak
Combined heat and power (CHP) involves on-site generation of electricity by using gas-fired equipment along with utilization of waste heat available from the power generation process. This research focuses on the design, installation and analysis of integration options of a modular CHP system involving the integration of a natural gas fired reciprocating engine generator with a liquid desiccant dehumidification system in a medium sized commercial office building. The engine generator provides 75 kW of electrical power fed parallel to the grid while the combined waste heat from the exhaust gases and jacket water from the engine is used to regenerate the liquid desiccant. The liquid desiccant unit dehumidifies the outdoor air and supplies it to the mixed air section of the roof top unit of the building. The experimental part of the research discusses the various aspects involved in the design and installation of the system such as the mechanical design of the structure, the heat recovery loop design and the electrical interconnection with the grid. Extensive testing and data analysis was conducted to characterize the performance of the integrated system and compare the performance with a traditional power plant as well as conventional HVAC systems.
A comprehensive steady state thermodynamic model of the integrated CHP system was coded in Visual Basic .Net. After validation with experimental results, an economic and climate model was integrated into the thermodynamic model with actual electricity and gas prices as well as the climate data for different representative states in the United States to demonstrate the feasibility of the system under different scenarios. This research addresses and assesses the different integration opportunities and issues encountered during the integration of the engine generator - liquid desiccant system with the existing electrical grid and the roof top unit. Based on the hands-on experience gained during the design, installation, operation and maintenance of the integrated system as well as the results obtained from extensive simulation of the system, this research develops valuable design guidelines on the integration and operation of the packaged engine generator-liquid desiccant system in commercial office buildings for future designers and system integrators."
Doctoral Dissertation
http://hdl.handle.net/1903/3140
Advances to a Computer Model Used in the Simulation and Optimization of Heat Exchangers
Robert Andrew Schwentker
Heat exchangers play an important role in a variety of energy conversion applications. They have a significant impact on the energy efficiency, cost, size, and weight of energy conversion systems. CoilDesigner is a software program introduced by Jiang (2003) for simulating and optimizing heat exchangers. This thesis details advances that have been made to CoilDesigner to increase its accuracy, flexibility, and usability.
CoilDesigner now has the capability of modeling wire-and-tube condensers under both natural and forced convection conditions on the air side. A model for flat tube heat exchangers of the type used in automotive applications has also been developed. Void fraction models have been included to aid in the calculation of charge. In addition, the ability to model oil retention and oil's effects on fluid flow and heat transfer has been included. CoilDesigner predictions have been validated with experimental data and heat exchanger optimization studies have been performed."
Master's Thesis
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