Date of Award

12-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Miller, Richard

Committee Member

Ochterbeck, Jay

Abstract

The optimization of the energy consumption in household refrigerators should consider the influence of the gasket which determines the heat transfer and air infiltration rate. In this research project, engineering methods are developed to evaluate the heat leakage due to the gasket and air infiltration in domestic refrigerators. In the first study, experimental and numerical approaches are applied to evaluate the gasket heat transfer based on the “Reverse Heat Load Method”. The main objective is to find the effective heat leakage with the dimensions of energy leakage per gasket length per temperature difference (W/m.K). An insulated cubic box with a 216,000 〖cm〗^3 interior enclosure (60cm x 60cm x 60cm) was designed to accept a matching set of adjoining refrigerator door and wall cuts placed inside the cavity. The door and walls are surrounded by thick insulation material so that only the gasket region is exposed to the ambient environment. A heat source was placed inside the center of the box to create a desired temperature difference between the interior and the ambient. Thermocouples measured the interior and ambient temperatures while six heat flux sensors, mounted on the exposed gasket region, measured the heat flux exiting the box through this region. Two restrictions were imposed with the heat flux sensors to evaluate the heat leakage purely experimentally. The heat flux sensors did not offer sufficient resolution to fully resolve the surface heat flux distribution, and they were incapable of directly measuring the heat flux leaving through the gasket due to its complex geometry. Therefore, Computational Fluid Dynamics (CFD) simulations were necessary to complete the heat flux profile between the experimental data points recorded by the sensor). Accordingly, a two dimensional (2D) simulation was performed to provide a shape profile of the heat flux leaving the gasket region which may be used to fit the experimental data using a “Least Mean Square Error” approach. The estimated heat loss at the gasket region with the original gasket installed on the sample refrigerator was 0.20 W/m.K. Extensive testing with other gaskets showed that their design and materials influenced the heat loss of the refrigerator. The second study developed a methodology to identify the leaks, to estimate the air infiltration rate, and to calculate the energy loss associated with air leaks in domestic refrigerators. The water drain tube was determined to be the primary air leak source due to the presence of the evaporator fan inside the freezer compartment. In addition, many other leaks with unknown sizes were found through bubble tests about the cabinet. Two identical refrigerators were employed to evaluate the impact of the air loads. One refrigerator remained with its original conditions and the other unit was completely sealed so that there existed a single inlet (water drain tube) and a single outlet (a drilled hole). The intact refrigerator was used to measure the normal operating conditions with respect to the ambient environment (e.g. pressure and temperature differences) to mimic these conditions in the sealed unit. The sealed unit had a hole drilled into the cabinet and the water drain tube remained open to the ambient. The size of the drilled hole was adjusted until the same pressure difference was achieved on the new unit at the same temperature difference. A flow meter measured the air flow through the hole and thermocouples measured the ambient and interior temperatures simultaneously. The energy leakage due to the air infiltration was calculated using the first law of thermodynamics based on two temperatures and mass flow rates at the inlet and outlet. The actual air infiltration rate was measured and the effective heat transfer rate due to the air infiltration rate was calculated 4.4 Watts. Modeling shows that refrigerators are not under steady state operation. They “breathe” drawing air in during cooling and forcing air out during warming between compressor cycles. A hypothetical perfectly sealed unit is shown to produce forces upwards of 350 lbf on the fresh food door due to this effect alone.

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