Microscale heat or heat and mass transfer system

Abstract

Microscale, monolithic heat or heat and mass transfer systems: a plurality of shims (102, 104) assembled between two outer plates (110, 111) that, when combined, form discrete but integrated heat and mass transfer system components that make up a microscale, monolithic absorption cooling and / or heating system, or other heat or heat and mass transfer system. The shims generally include a plurality of microchannels (702), voids, fluid passages, and other features for transferring fluids between defined components throughout the system, and into and out of the system to and from heating and cooling sources and sinks as needed. Generally, two distinct shim types are used and combined together as a plurality of shim pairs to enable thermal contact between the fluids flowing within the microchannels in each shim pair, each shim in each shim pair comprising slightly different microchannel and fluid passage arrangements as compared to each other.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 61 / 085,192, filed Jul. 31, 2008, and entitled “Thermally Activated Cooling System”, which is incorporated by reference as if set forth herein in its entirety.TECHNICAL FIELD[0002]The present system relates generally to microscale heat transfer systems or heat and mass transfer systems, and more particularly to monolithic or integrated microscale heat or heat and mass transfer systems or apparatuses comprising a plurality of shims or layers, each shim including a plurality of microchannels for performing heat and / or mass exchange functions.BACKGROUND[0003]Traditionally, vapor-compression systems have been used in various heating and cooling applications, such as residential and commercial air conditioners, chillers, and heat pumps. These systems generally comprise four basic components—an evaporator, compressor, condenser, and expansion devic...

AI Technical Summary

Benefits of technology

[0015]According to another aspect, for large scale implementation of microscale heat or heat and mass transfer assemblies as described herein, multiple assemblies are connected in series and / or parallel arrangements through external plumbing to form a plurality of connected heat or heat and mass transfer assemblies. According to various aspects, for larger capacities, the shims are subdivided into individual assemblies representing each heat and mass transfer system component of the heat or heat and mass transfer system rather than a monolithic heat or heat and mass transfer assembly, to facilitate flexibility in connections, and largely unconstrained increases in delivered loads.

Problems solved by technology

Traditional vapor-compression systems, however, have several disadvantages.

For example, most vapor-compression systems rely on synthetic refrigerants that have negative environmental impact.

Also, most vapor-compression systems utilize expensive, high-grade electrical energy for power.

Further, vapor-compressions systems are often loud and unreliable due to the use of a compressor, and often employ bulky overall system designs that prohibit small-scale or portable use.

Further, unlike vapor-compression systems that utilize high-grade electrical energy as the input that drives the system, absorption heat pumps typically run on more readily available and low-grade thermal energy, which may be obtained from combustion of bio-fuels and fossil fuels, from largely untapped waste heat sources (e.g., automobile exhaust, excess manufacturing heat, etc.), from solar thermal energy, and other similar energy sources.

Because the compressor of a vapor-compression system is replaced in an absorption heat pump by a combination of a desorber, absorber, liquid solution pump, and recuperative solution heat exchanger, absorption heat pumps are generally more heat and mass exchange intensive than vapor-compression systems, thereby requiring additional heat transfer surface area.

Due to this comparatively larger surface area requirement, absorption heat pumps have typically been relegated to very large commercial and industrial chiller applications, and achieving compact designs while delivering high coefficients of performance (COPs) has been a major challenge.

In fact, these cycles have not been widely implemented primarily because of a lack of practically feasible and compact heat and mass exchange devices.

However, in absorption systems that use the two most common working fluid pairs (i.e., lithium bromide-water and ammonia-water), processes such as absorption and desorption naturally involve coupled heat and mass transfer in binary fluids, leading to complexities and challenges in system design.

For example, the primary configuration employed currently in commercial absorption chillers (i.e., absorption of vapor into solution films falling over tube banks carrying coolant liquid) suffers from high coolant-side resistances and poor wetting of the transfer surface by the liquid film.

Additionally, some prior designs enhance absorption / desorption processes, but fail to reduce single-phase resistance on the other side (i.e., coupling fluid side), thereby requiring large system components, and resulting in high working fluid and coupling fluid pressure drop, which results in high parasitic power consumption and also results in losses in driving temperature differences due to decrease in saturation temperatures brought about by pressure drops within system components.

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