Grantee Research Project Results
Nanoenhanced Phase Change Materials for Advanced Energy StorageEPA Grant Number: FP917371
Title: Nanoenhanced Phase Change Materials for Advanced Energy Storage
Investigators: Warzoha, Ronald J
Institution: Villanova University
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Science & Technology for Sustainability: Green Engineering/Building/Chemical Products & Processes/Materials Development
The low efficiency of most power systems presents a formidable problem for increased energy distribution, and subsequent consumption, in the future. A substantial portion of this low efficiency can be attributed to waste heat. In these systems, heat often is used as a means for power generation. In this case, a greater temperature or an extended generation time corresponds with a more efficient system. A good example might be a solar thermal power system, where longer exposure to heat (or heat retention) might lead to an increase in a system’s capacity to deliver power and an increase in its efficiency. Other systems require a reduction in a steady operating temperature (computers, cell phones, etc.), which often is accomplished by using thermal management systems that must consume power to operate effectively (i.e., fans, pumps, jets, etc.). In either case, the thermal management solutions have continuously required more power consumption as a result of the increased heat transfer constraints. This research project examines the role that phase change materials play in reducing the amount of power required to operate renewable energy power delivery systems and thermal management solutions. Phase change materials have the ability to store thermal energy over extended periods of time without requiring additional power (depending on the mass, volume, heat load and latent heat of fusion values), but suffer from a low thermal conductivity and thus not all of the PCM’s storage capacity can be used when in its raw form. Recent technologies used to increase the thermal conductivity of phase change materials have been fins and foams, which increase total thermal storage capacity. Although some have been successful, many of these designs do not comply with the constraints placed on modern power delivery systems and electronics. Preliminary studies suggest that the addition of several types of nanofibers greatly enhance the thermal energy storage time of PCMs while also complying with the aforementioned constraints. This research now will look into the effect of several different parameters of nanostructures on the thermal energy storage time and delay to steady conditions, including length, diameter, type and weight fraction. Once this has been determined, the nanofibers will be separated using two techniques (surfactants and adding an acidic charge) to determine the most effective way to keep nanofibers separated in the liquid phase. This will complete an effort to create a phase change material that is capable of storing an adequate amount of thermal energy for a variety of power profiles and thus, result in a thermal storage material that is economically feasible to implement in applications to reduce overall power consumptions, including, building walls (increase HVAC efficiency), solar thermal systems and modern electronics.
Approach:The first stage of the research will use standard experimental techniques to characterize the thermal conductivity, specific heat and latent heat of PCMs embedded with a variety of different types, sizes and amounts of nanostructures. The thermal conductivity will be measured using a transient hot-wire apparatus, while the specific heat and latent heat of each composite material will be measured using a differential scanning calorimeter. These properties will be vitally important in determining both the reason for enhanced thermal storage capacity in nanocomposite PCMs and for optimization in later stages of the research. The second stage of this research is to determine the effect of each of these same parameters (nanostructure type, size and amount) on the thermal energy storage capacity in adiabatic thermal containment units, which are most like those that would be implemented in renewable power deliver systems or modern electronics packaging. Finally, this research will investigate the potential for stabilizing the nanofibers and prevent them from aggregating and separating from the PCM after several thermal cycles by examining the effect of a common surfactant vs. an acidic soak, which forms a positive charge on each nanostructure and fosters coulomb repulsion. After this research is completed, it is expected that an economically feasible and sustainable design will be accomplished such that the PCM becomes a driving force for a reduction in power consumption or increase in power capacity for these systems.
These engineered materials will allow thermal engineers to design for precise energy storage performance based on PCM type, nanoadditive type, amount, length and diameter, heat source orientation, nanoadditive suspension and geometric configuration. Although the NovaTherm Laboratory has identified the preliminary potential for nanoadditives in PCMs, the work presented here will investigate and quantify this potential with a substantially broader scope. Upon completion of this work, the design of energy storage modules finally will be possible and recognized as economically feasible with the implantation of nanostructures.
Potential to Further Environmental / Human Health Protection
This research will examine the effect of nanostructure type, amount and size on the thermal energy storage capacity of phase change materials for a reduction in energy consumption in some applications (electronic packaging, building walls for HVAC efficiency enhancement, etc.) and for an increase in energy retention in others (solar thermal power systems, etc.). When PCMs become viable candidates for adequate thermal energy storage in these applications, a large portion of fossil fuel consumption, and overall power consumption, can be substantially reduced as the PCM requires no power to store the thermal energy.