SUBJECT: Ph.D. Proposal Presentation
   
BY: Anne Mallow
   
TIME: Wednesday, March 9, 2016, 2:00 p.m.
   
PLACE: Love Building, 109
   
TITLE: Advanced Heat Exchanger Concepts to Enhance Performance of Conditioning Systems
   
COMMITTEE: Dr. Samuel Graham, Jr., Chair (ME)
Dr. Omar Abdelaziz (ME)
Dr. Kyriaki Kalaitzidou (ME)
Dr. Satish Kumar (ME)
Dr. Jason Nadler (MSE)
 

SUMMARY

Heat exchangers are critical components to space conditioning systems as they absorb or reject heat from the thermodynamic cycle. The performance of such systems often dictates the heating or cooling capacity. Thus, improvements to the heat exchanger design can often be beneficial in the creation of compact or more energy efficient space conditioning systems. One such advancement is the insertion of an energy storage medium into the heat exchanger. Such technology delays the thermal exchange between the hot and cold fluid streams, allowing the exchange to occur on demand or when more expedient for an energy efficient application. A second type of advancement is improving the design of the heat exchanger to maximize the convective heat transfer. Since air cooled heat exchangers are often limited by the air-side heat transfer, redesigning the geometry or using innovative ways to increase convection over the coils can increase the performance of the system.

In this proposal, two advanced heat exchanger concepts are being investigated. The first includes the incorporation of a thermal energy storage medium, specifically a phase change material (PCM) thermal battery, with engineered thermal properties to enhance charging and discharging rates. The second is the use of a rotating heat exchanger to enhance air flow over a heat exchanger coil. PCM composites enhanced with aluminum and graphite foams will be characterized, tested, and modeled under various charging conditions to guide the design of thermal batteries. Several batteries are fabricated to use as the condenser in a vapor compression cycle for personal space conditioning to minimize heat released to the ambient. For the second heat exchanger, a rotating heat exchanger is used to replace the common fin and tube heat exchanger found in vapor compression cycles for conditioning systems. The rotating heat exchanger (RHX), initially developed by Sandia National Laboratories as a high performance cooler, is experimentally investigated for the first time as an evaporator. The performance of the RHX is studied as a function of environmental conditions, followed by an investigation of the frost growth, which can impact the performance of the RHX, convective heat transfer coefficient, and defrost energy consumption. While frost growth occurs in evaporator coils for a freezer, it is not clear how frost forms differently on a rotating surface and how this impacts heat transfer.