Evaporator designs for achieving high cooling performance at high superheats

Abstract

An evaporator includes plates disposed in pairs in first and second groups, along spaced tanks. Dimples extend from the interior portions in the first group, and interior fins are disposed against the interior portions of the second group. The dimples enhance the distribution of liquid refrigerant in the passageways and the thermal energy exchange between ambient air and an upstream, low vapor quality flow of fluid passing between upstream and downstream side edges, of the first group of plates. The evaporator also eliminates the tonal noise or whistle under certain transient operating conditions.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to a heat exchanger for use in a vehicle climate control system. More specifically, the invention relates to an evaporator for transferring heat between a cross-flow of air through the evaporator and a refrigerant circulating within the evaporator. [0003] 2. Description of the Related Art [0004] Various evaporator designs exist in the art that incorporate components for promoting heat exchange between a refrigerant fluid flowing within tubes and air flowing through fins that are disposed on the exterior surfaces of the tubes. The tubes typically incorporate features that force the refrigerant entering the evaporator to flow in a number of passes before it exits the evaporator. The evaporators often also include specific modifications to the interior surfaces of the tubes, which increase the surface area available for heat exchange between the ambient air and the fluid. For example, some evapor...

AI Technical Summary

Benefits of technology

[0007] The invention provides a laminate-type evaporator having first and second tanks and fabricated from a plurality of plates. Each plate has upstream and downstream side edges with an interior portion recessed relative thereto. The plates are disposed in pairs with the side edges of each pair in abutting engagement with one another and the interior portions defining a passageway between each pair. The pairs are spaced along the tanks in first and second groups, and the passageways are in fluid communication with the tanks for permitting a fluid to flow between the tanks through the passageways. A thermal energy exchange occurs between the fluid and a cross-flow of air through the first and second groups from the upstream to downstream side edges. Dimples extend from the interior portions into the passageways of the first group. Interior fins are disposed against the interior portions and extend to the upstream and downstream side edges, which enhances the thermal energy exchange between the fluid and the cross-flow of air between the upstream and downstream side edges of the second group of plates.

[0008] Disposing dimples on the first group of plates enhances the thermal energy exchange between the air and a first flow of the fluid passing from the upstream to downstream side edges of the first group of plates. The fins on the second group of plates enhance thermal energy exchange between the air and a second flow of fluid passing from the upstream to downstream side edges of the second group of plates independently and separately from the first flow of fluid.

[0009] The subject invention overcomes the limitations of the art by providing an evaporator which utilizes tubes having interior fins in combination with a separate, distinct group of tubes having interior surfaces upon which dimples are formed. The interior fins are utilized in those tubes which define the final refrigerant passes of the evaporator. Doing so reduces refrigerant side thermal resistance by providing increased refrigerant side surface area to compensate for the decrease in the refrigerant side heat transfer coefficient that often occurs in the last passes of evaporators, especially in those operating at high outlet superheats. Additionally, providing interior fins in the final refrigerant passes also improves the thermal contact between the air fins and the tubes, because the tubes in this region of the evaporator have no dimples. Thus, in the final evaporator passes, a higher overall heat transfer coefficient is achieved resulting from reduced thermal resistance on the refrigerant side and in the conduction path from the air fins to the tube. Tubes having dimples formed on the interior surfaces are utilized in the initial refrigerant passes on the upstream airside of the evaporator where high refrigerant side surface area is not critical to initiate heat exchange, because of the prevailing high refrigerant side heat transfer coefficients associated with low to medium vapor quality two-phase flow. Providing interior fins in the final refrigerant passes also eliminates the tonal noise or whistle originating in the evaporator under certain transient operating conditions. This is because high velocity refrigerant vapor flow over the dimples in the last passes is the cause of a phenomenon called acoustic resonance, which is perceptible as whistling. Combining different surface enhancements by providing them only where they are truly necessary reduces total evaporator mass, decreases manufacturing costs, eliminates transient whistling noise, and improves heat exchange efficiency and temperature uniformity and stability.

Problems solved by technology

While interior fins and “bumped” or “dimpled” surfaces increase heat exchange within the evaporator, limiting use of one or the other of the fins or dimples throughout all of the tubes in an evaporator is not necessarily the optimum way to maximize heat exchange.

This reduces cooling capacity and causes the temperature distribution of the discharge air to become more non-uniform.

Another problem with dimpled evaporators is that under certain transient vehicle operating conditions, vapor flowing over the dimples gives rise to a pure tone noise or “whistle” emanating from the evaporator.

Images