Parallel flow evaporator with variable channel insertion depth

Abstract

In a parallel flow heat exchanger having an inlet manifold connected to a plurality of parallel channels, the degree of insertion depth of the parallel channels into the inlet manifold is variable so as to adjust the impedance to the refrigerant flow into the individual channels. The degree of insertion depth is progressively reduced toward a downstream end of the manifold for the individual channels or for the channel sections. The diameter of the inlet manifold is locally increased or its cross-section area altered in order to accommodate the flow of refrigerant around the tube insertions. Similar technique is applied to the outlet manifold as well to further balance hydraulic resistances.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates generally to air conditioning and refrigeration systems and, more particularly, to parallel flow evaporators thereof. [0002] A definition of a so-called parallel flow heat exchanger is widely used in the air conditioning and refrigeration industry now and designates a heat exchanger with a plurality of parallel passages, among which refrigerant is distributed and flown in the orientation generally substantially perpendicular to the refrigerant flow direction in the inlet and outlet manifolds. This definition is well adapted within the technical community and will be used throughout the text. [0003] Refrigerant maldistribution in refrigerant system evaporators is a well-known phenomenon. It causes significant evaporator and overall system performance degradation over a wide range of operating conditions. Maldistribution of refrigerant may occur due to differences in flow impedances within evaporator channels, non-uniform airfl...

AI Technical Summary

Benefits of technology

[0008] Briefly, in accordance with one aspect of the invention, the insertion depth of the individual parallel channels into the inlet manifold is varied so as to obtain a more uniform refrigerant distribution to the individual channels by way of the differential pressure drop that is created by the variable insertion depth. In this way, a two-phase refrigerant mixture is more uniformly distributed among the channels.

Problems solved by technology

It causes significant evaporator and overall system performance degradation over a wide range of operating conditions.

Maldistribution of refrigerant may occur due to differences in flow impedances within evaporator channels, non-uniform airflow distribution over external heat transfer surfaces improper heat exchanger orientation or poor manifold and distribution system design.

Attempts to eliminate or reduce the effects of this phenomenon on the performance of parallel flow evaporators have been made with little or no success.

The primary reasons for such failures have generally been related to complexity and inefficiency of the proposed technique or prohibitively high cost of the solution.

The evaporator applications, although promising greater benefits and rewards, are more challenging and problematic.

Refrigerant maldistribution is one of the primary concerns and obstacles for the implementation of this technology in the evaporator applications.

As known, refrigerant maldistribution in parallel flow heat exchangers occurs because of unequal pressure drop inside the channels and in the inlet and outlet manifolds, as well as poor manifold and distribution system design.

Furthermore, the recent trend of the heat exchanger performance enhancement promoted miniaturization of its channels (so-called minichannels and microchannels), which in turn negatively impacted refrigerant distribution.

Since it is extremely difficult to control all these factors, many of the previous attempts to manage refrigerant distribution, especially in parallel flow evaporators, have failed.

If, on the other hand, the velocity of the two-phase flow entering the manifold is low, there is not enough momentum to carry the liquid phase along the header.

Also, the liquid and vapor phases in the inlet manifold can be separated by the gravity forces, causing similar maldistribution consequences.

In either case, maldistribution phenomenon quickly surfaces and manifests itself in evaporator and overall system performance degradation.

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