Conceptual Design, Visualization And Heat Transfer Analysis Of Multiple Parallel-Pass Condensers

Heat exchanger includes condenser, evaporator, heater core, etc. Heat exchanger technology has wide applications in HVAC and powertrain cooling industry covers automotive, power energy, food process, etc. Global challenges on conservation of non-renewable energy and the ever-increasing awareness on environmental protection demand thermal scientists and engineers to accelerate technology innovation in pursuit of lighter, greener, more compact and effective heat exchangers. Aluminum microchennel tube fined heat exchanger, or, microchannel heat exchanger is one of the achievements from the demand. Introduction of Aluminum material replaced the traditional heavy and spacious copper and makes the current heat exchanger more efficient. Microchannel tube parallel flow condenser , or , PF condenser, is the pioneer of this transition.During the past two decades, considerable attentions have been paid to the fundamental and application researches in two-phase flow and heat transfer of microchannel tube condenser technology. The pioneering researchers have laid a solid foundation for automotive industry to completely embrace microchannel condenser technology because of its merits in thermal performance, structural robustness, compactness and weight reduction, as well as corrosion resistance in comparison to traditional tube and fin heat exchanger technology. The successful application of microchannel heat exchanger in automotive industry also opens up a new frontier and creates a positive momentum for other industries, such as residential and commercial HVAC industries, to quickly move into the position of adapting and improving the microchannel heat exchanger technology.This paper describes and analyzes a novel design of multiple parallel-pass (MPP) microchannel tube condenser and its applications to automotive A/C systems. A flow distributor concept is introduced in MPP condenser in order to enable parallel flow arrangement in adjacent flow paths. Visual observation and two phase flow heat transfer analysis were conducted through an automotive HVAC system simulation testing. The purpose of this innovative concept is to explore a new heat transfer enhancement method in order to provide a condenser with better performance and higher efficiency.Multiple parallel-pass (MPP) condenser, a variant of microchannel heat exchangers, is basically constructed in such a way that one or several baffles in the header tubes of a condenser are turned into flow distributors. The flow distributors alter in-series refrigerant flow arrangement into parallel flow between two adjacent passes. Throughout analysis of two-phase flow and heat transfer processes in MPP condenser, the authors developed a two-phase zone augmentation technique that can be employed to enhance condensation heat transfer and reduce pressure drop, which provides a design method for enabling a lighter and more compact condenser for automotive application.Test samples for both MPP condenser and baseline PF condenser with same overall dimensional size, total tubes number, fin profile but different flow path arrangement, different tube number arrangement for each pass, different distribution hole sizes and different numbers of hole placement, etc. are used. Experiments in both visualization and performance tests are carried out to evaluate the two phase flow and heat transfer mechanism of MPP condenser by referencing a same-sized parallel flow (PF) condenser. Visual observation by using a high-speed camera indicates that a more uniform refrigerant two-phase mixture entering the downstream cooling pass can be achieved in MPP condenser because superheat vapor through a pass-through hole on flow distributor directly injects into the separated liquid–vapor zone in a header tube. From heat transfer enhancement stand point of view, it can significantly improve heat transfer.Test results also shown that under the same overall dimensional size, total tubes number, fin profile, heat transfer performance, refrigerant mass flow and pressure drop have been impacted by different flow path arrangement, different tube number arrangement for each pass, different distribution hole sizes and different numbers of hole placement, etc.In addition, analytical and test results show MPP condenser, being designed to enlarge two-phase condensing zone, is able to improve cooling performance as high as 9.6% while its refrigerant mass flow increases as high as 13.34% when comparing to a benchmark PF condenser for 4 passes MPP condenser and to improve cooling performance as high as 5.5% while its refrigerant mass flow increases as high as 8% when comparing to a benchmark PF condenser for 6 passes MPP condenser.It needs to be realized that the MPP condenser performance optimization will become complicated if under the same overall dimensional size, total tubes number, fin profile, but different flow path arrangement, different tube number arrangement for each pass, different distribution hole sizes and different numbers of hole placement, etc.