Heat Transfer and Pressure Drop Characteristics of a Manifold Microgroove Aerospace Condenser
by David L. Boyea
High performance condensers are an essential component in many energy conversion, electronics and process systems. Increased capacity and functionality with less and less available space has been a main driving force for development of smart condensers in energy systems. A literature survey of microchannel condensation shows that microchannels are useful for enhancing condensation heat transfer. Our previous work in this area has demonstrated that manifold microgroove heat exchangers operating in single-phase or two-phase modes offer substantially higher heat transfer performance with a greatly reduced pumping power when compared to state-of-art microchannel heat exchangers. Out previous microchannel condensation experiments was using have involved use of small scale manifold microgroove condensers (7 cm2 base area) and a manifold microgroove condenser of this size and capacity has not been investigated before. The goal is to enhance heat transfer performance while minimizing the pumping power, volume and weight. A compact lightweight manifold microgroove condenser, with 60 x 600 micron microgrooves and cooling capacity of 4kW, was fabricated, assembled and tested using two different manifold designs. Experiments using R134a and R236fa as working fluids and two different refrigerant side manifolds were performed. Overall heat transfer coefficient and the pressure drop across a manifold microgroove condenser were calculated and refrigerant side heat transfer coefficient was determined based on water side heat transfer coefficient. 4kW capacity was achieved with an LMTD of 8C. The manifold geometry was found to have a large effect on pressure drop and heat transfer performance as well as flow distribution. A majority of the pressure drop was found to be in the manifold creating poor flow distribution. Future work should focus on optimization of the refrigerant manifold design to reduce pressure drop, increase heat transfer and flow distribution as well as explore the effect of microchannel geometry. Unfortunately current stage of development CFD optimization techniques does not allow optimization of two-phase flow system. An optimization of the airside surface and manifold geometry of heat exchanger that potentially will be coupled with high performance condenser has been performed. It has been concluded that for high performances of single phase flow manifold flow area has to be comparable to microgrooves flow area.
Master's Thesis
http://hdl.handle.net/1903/14846
Experimental Study of Capillary-Fed Enhanced-Surface Tubular Evaporators - With Applications to Low Grade Energy Conversion
by Josh Fody
A novel capillary feed concept was developed for deployment on an enhanced tubular evaporator intended for low grade thermal energy applications. The concept was applied to both vertical and horizontal evaporator orientations. Empirical testing initially focused on capillary feed development, but the bulk of research was conducted on closed single tube testing using anhydrous ammonia. A 2" one foot long proof of concept evaporator was tested along with two different ¾" five foot long (half-length) aluminum tubes. The target test LMTD was around 2 [K]. Results varied with test conditions, enhancement geometry, refrigerant flow rate, and evaporator orientation. Heat transfer performance of the evaporator, as well as water and refrigerant flow rates and pressure drops are assessed. Test operational constraints and uncertainty limitations are investigated. The capillary feed mechanism advantages and limitations are surveyed, and future works are recommended along with discussions about relevant operational considerations.
Master's Thesis
http://hdl.handle.net/1903/14697
Analysis of a Trigeneration System Through Transient Simulations
by John Hartsog
This thesis develops a transient computer model of a trigeneration system using TRNSYS software. This simulation model can accurately reproduce the results from a real world experiment of a trigeneration system conducted over five days. This model is then applied to an entire cooling season to show the primary energy usage of a trigeneration system using an adsorption chiller to meet the cooling load. These results can then be compared to the primary energy usage of a residence with a traditional grid-powered Vapor Compression System (VCS) air conditioner. In order to evaluate the geographic feasibility of this trigeneration system, four different cities were selected for analysis. The chosen cities had various climate conditions to aid in comparison. An analysis was performed on the primary energy usage, environmental impact, and economic cost of the trigeneration system to demonstrate the feasibility and likely implementation of one form of trigeneration technology.
Master's Thesis
http://hdl.handle.net/1903/14671
Experimental Evaluation of a Multifuntional [sic] Variable Refrigerant Flow System in an Educational Office Building
by Laeun Kwon
The top three end uses - space heating, space cooling, and water heating - accounted for close to 41 percent of site energy consumption in U.S. building primary energy consumption. Therefore, energy efficient heating, ventilating and air-conditioning (HVAC) systems in buildings is essential for energy savings in the building sectors. A multifunctional variable refrigerant flow (MFVRF) system is finding its way into residential and commercial buildings since it can simultaneously provide space cooling, space heating and hot water.
The MFVRF system was installed in an educational office building and fully instrumented to measure the performance of the system under a wide range of outdoor weather conditions. The effects of a part-load ratio (PLR) on the daily performance factor (DPF) and total energy consumption were experimentally investigated in the field performance tests. Although the higher PLR represents a more effective cooling and/or heating the system, the DPF is not always increased with PLR because the system is optimized at a certain range of PLR. Furthermore, the effects of the hot water demand and the heat recovery operation modes on the performance of the system were investigated in a field test for the heating and shoulder seasons.
Integrating the water heating functions into the heat recovery type variable refrigerant flow (HR-VRF) system, not only supplies hot water year-round, it also improves the system performance. As the hot water demand for the MFVRF system increased, the PLR was improved, which resulted in an increase system heating performance. In the heat recovery operation mode, the heat absorbed from the indoor units operating in the cooling mode was transferred to other indoor units operating in the heating mode. The DPF was 2.14 and 3.54 when the ratio of daily total cooling energy to daily total heating energy was 13.0% and 28.4%, respectively, at the similar outdoor weather conditions. This enhancement was attributed to the waste heat recovered during the heat recovery operation mode and the decrease in pressure ratio, which is a result of the improvement of the compressor efficiency.
Energy saving potential of the MFVRF system in a building with high internal heat gains, resulted in a high cooling load for the cooling season and a low heating load for the heating season, was verified through the field performance test. The performance of the MFVRF system for the heating and shoulder seasons was improved by transferring the recovered energy to the indoor space and supplying the hot water.
Master's Thesis
http://hdl.handle.net/1903/14305
Review of Thermal Energy Storage Technologies and Experimental Investigation of Adsorption Thermal Energy Storage for Residential Application
by Gang Li
Thermal energy storage (TES) technologies can reduce or eliminate the peak electric power loads in buildings, and utilize benefits of waste heat recovery and renewable energy. This thesis work consists of TES literature review and experimental investigation of adsorption TES. Review work includes cold storage technologies for air conditioning and subzero applications, and heat storage technologies for residential application. Different technologies involving sensible, latent and sorption TES were compared and resolutions of their issues were summarized. In addition, adsorption TES was experimentally investigated and its energy and exergy flows were analyzed to evaluate the effects of different operating parameters, such as temperature and heat transfer fluid mass flow rate for different chambers on the system performance. Finally, a computer model was developed for the adsorption heat TES system integrated with a vapor compression heat pump to assess its performance. Simulation results showed that overall coefficient of performance (COP) and exergy-based COP are approximately 3.11 and 0.20, respectively.
Master's Thesis
http://hdl.handle.net/1903/14698
Heterogenous Ethylene Polymerization in a Micro Reactor System
by Meera Mahadevan
Micro reactors provide enhanced mass and heat transfer owing to their high surface area to volume ratio. These reactors offer precise control and selectivity and can be used for synthesizing specifically engineered and technically sophisticated olefin polymers. An unsteady state reactor model (using coordination reaction kinetics) was developed to study the concentration profiles of monomer, catalyst, polymer and its molecular weight distribution along the length of the reactor with time. Nano silica particles of diameter 400nm were synthesized as a support for the metallocene catalyst. Heterogeneous ethylene polymerization was carried out in tubular reactors of diameters 800 µm, 1 mm, and 2.37 mm under 2-phase flow conditions. This thesis investigates the effect of operating conditions in a micro reactor on the qualitative and quantitative properties of the polymer. The results can be extended to propose applications for synthesis of polymers with unique morphology using the inherent advantages of these reactors.
Master's Thesis
http://hdl.handle.net/1903/14663
Experimental Performance Evaluation of Desorber in a Hybrid Absorption Vapor Compression System
by Bracha Mandel
A single-effect absorption facility was designed and constructed to experimentally investigate the performance of a 3 kW mini-channel desorber using an R134a/POE32 solution mixture. The facility was fabricated to simulate a hybrid absorption/vapor compression system for an off-grid high temperature application utilizing an air-cooled absorber. Desorber design replicated the utilization of waste heat from a generator source. The effects of temperature, pressure, solution mass flow rate and refrigerant concentration variations on desorber and desorption performance were investigated and analyzed through vapor generation, circulation ratio, poor solution concentration, desorber mean heat transfer coefficient and quality difference. Desorber heat transfer coefficient enhancement was found to be a strong function of solution temperature, rising by up to 75% with a 30°C temperature increase. Due to poor absorber performance, increasing solution temperatures and mass flow rates did not result in a proportional desorber vapor generation enhancement, leading to a reduction in desorber quality difference.
Master's Thesis
http://hdl.handle.net/1903/14852
An Investigation of Void Fraction for Low GWP Refrigerants
by James Daniel Spencer
An experimental facility was designed and fabricated to test the void fraction of fluids. Measurements of the void fraction for R134a, R290, and R1234yf were conducted for low mass flux conditions at air-conditioning evaporator temperatures. Test sections of round tube inner diameters 2.99 and 4.56 mm were tested. Flow visualization was performed on the 4.56 mm test section. Results of the flow visualization revealed similar flow regime transition characteristics among the three refrigerants. Void fraction trends for R134a and R290 were found to be similar, while the void fraction for R1234yf trended higher than R134a for most points. The experimental data was compared to predictions by twelve void fraction correlations. For R134a and R290, the Steiner correlation most accurately predicted the data. For R1234yf, the Baroczy correlation was found to most accurately predict the data.
Master's Thesis
Top