Master of Science (M.S.), University of Dayton, 2018, Mechanical Engineering

A two-phase pumped refrigerant (R-134a) loop was developed. An energy balance experiment was performed for the preheater, where calculated refrigerant volumetric flow rates differed by no more than 5% from measured flow rates. An energy balance was performed as well for the entire system, and calculated water volumetric flow rates differed by no more than 14% from measured flow rates. A model of the preheater and its power input was constructed and compared to experimental power inputs. The model time constant was 224 seconds and the experimental time constant was 194 seconds. Specified operating conditions were 5 kW heat input to the cold plate with a 96.6 psia discharge pressure. System operating boundaries for this setup were plotted as cold plate inlet subcooling and discharge quality both as functions of preheater input power and pump speed. Preheater power inputs ranged from 0 to 95% full-scale power (0 to 782 W) and pump speeds ranged from 60 to 100% full-scale speed (0.41 to 0.73 GPM). Within operating boundaries, vapor quality was kept at a value of 0.8 or lower. It is very useful to know the boundaries for the system, which could be used for future two-phase pumped loop systems.

Committee: Jamie Ervin Ph.D. (Advisor); Larry Byrd Ph.D. (Committee Member); Scott Stouffer Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, Miami University, 2017, Physics

Ni2MnGa is a Heusler alloy that exhibits a first order martensitic phase transition near 200 K upon cooling. Recent study showed that when Mn was partially replaced with Cr in Ni2Mn1-xCrxGa, the martensitic transformation temperature increased with increasing Cr concentration. At the same time, a sharp drop in electrical resistivity was observed in the system, and the magnitude of the drop increased with increasing Cr content. In an attempt to better understand these observations, in this thesis a series of Heusler alloys that include Ni2-xCrxMnGa, Ni1.75Cr0.25Mn0.75Co0.25Ga, Ni1.9Cr0.1Mn0.75Co0.25Ga, and Ni2.15Cr0.1MnGa have been investigated. The samples were fabricated by conventional vacuum arc melting technique in argon atmosphere. The characterization of the samples were performed by x-ray diffraction, dc magnetization, differential scanning calorimetry, and electrical resistivity measurements. The experimental results revealed interesting properties of the alloys that include existence of multiple magnetic and structural phases, coupled and decoupled phase transitions, large change in electrical resistivity in the vicinity of the martensitic phase transformation, and large magnetocaloric effects in selected compounds. The experimental results have been discussed in detail considering the intrinsic properties of the materials.

Committee: Dr Mahmud Khan (Advisor); Dr. Khalid F. Eid (Committee Member); Dr. Herbert Jaeger (Committee Member) Subjects: Physics

Master of Science (MS), Ohio University, 1990, Mechanical Engineering (Engineering)

Experimental study of evaporative heat transfer for a non-azeotropic refrigerant blend at low temperature

Committee: Roy Lawrence (Advisor) Subjects: Engineering, Mechanical

Master of Science (MS), Ohio University, 1989, Mechanical Engineering (Engineering)

Simulation of a storage freezer operating with a binary nonazeotropic refrigerant blend Part I. Equation of state cycle selection compressor model and air-cooled condenser model

Committee: Roy Lawrence (Advisor) Subjects: Engineering, Mechanical

Master of Science (MS), Ohio University, 1995, Mechanical Engineering (Engineering)

A FORTRAN 77 simulation of a low temperature storage freezer utilizing a non-azeotropic refrigerant blend

Committee: Roy Lawrence (Advisor) Subjects: Engineering, Mechanical

Master of Science, Miami University, 2011, Computational Science and Engineering

In this study, a finite volume, steady-state evaporator model that includes rectangular minichannel and microchannel tubes with louvered fins and headers was developed and validated. The model provides the user with the option of selecting from several published correlations when calculating the air-side and refrigerant-side heat transfer and pressure drop within the control volume. The model was then used to compare the thermal-hydraulic performance of experimental ternary refrigerant mixtures to more traditional refrigerants—namely, R-125/R-32/R-161 (34%/15%/51%) versus R-22 and R-125/R-143a/R-161(45%/40%/15%) versus R-404a. The numerical model was also used to study the effects of header-induced maldistribution on evaporator performance by comparing the predicted cooling capacity and refrigerant-side pressure drop to a distribution rating parameter (Φ) defined by Bowers et al. (2010). It was shown that as the distribution of quality between tubes becomes more uniform (i.e. Φ → 1), the cooling capacity and refrigerant-side pressure drop both approach their maximum values.

Committee: Andrew Sommers PhD (Advisor); Amit Shukla PhD (Committee Member); Kumar Singh PhD (Committee Member); Douglas Coffin PhD (Committee Member) Subjects: Mechanical Engineering