Date on Master's Thesis/Doctoral Dissertation

1-2020

Document Type

Master's Thesis

Degree Name

M.S.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, MS

Committee Chair

Brehob, Ellen

Committee Co-Chair (if applicable)

Kelecy, Andrea

Committee Member

Kelecy, Andrea

Committee Member

Berson, R. Eric

Author's Keywords

Heat transfer; heat flux sensors; heat leak; calorimetry; refrigeration

Abstract

Heat leak into household refrigerated cabinets is a key driver affecting energy consumption and efficiency of the cooling system. Additionally, knowledge of heat transfer coefficients of internal surfaces is valuable in the development of cabinet and system level performance simulations. Several studies have examined heat leak of refrigeration units using heat flux sensors (HFS); however, no such studies have used heat flux measurements to derive convective heat transfer coefficients of the refrigerated unit walls. The goal of this study is to evaluate the use of HFS to quantify heat leak into a 490-liter freezer and determine the wall convective heat transfer coefficients. Cabinet heat leak was measured using thermopile heat flux transducers adhered to the interior walls of a household freezer. The expected heat leak was calculated from an evaporator energy balance with temperature and pressure measurements of refrigerant and compared to HFS measurements. Convective heat transfer coefficients were based on Newton’s law of cooling using measured inner surface and air temperatures. This investigation determined that for the 12 HFS used, the HFS underpredict heat flux by an average of 7% in a one-dimensional validation system. When mounted to the internal walls of the freezer, HFS underpredicted heat leak by approximately 16% when considering gasket heat leak, edge effects, evaporator fan watts and sensor underprediction. Convective heat transfer coefficients were calculated using the average and local heat flux value for a wall and the air and wall temperatures. The average heat transfer coefficient values of the walls were between 8.9 and 14.6 W/m2K. The local convection coefficients were between 6.0 and 17.5 W/m2K. The results showed that HFS are not a reliable method of determining heat transfer coefficients due to their sensitivity to variation in wall and free stream temperatures.

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