Development and Analysis of Micro-Channel Heat Exchangers for Natural Gas Cooling

Author(s):  
S. Menon ◽  
H. Ganti ◽  
H. Wang ◽  
C. Hagen

Abundant availability and potential for lower CO2 emissions are drivers for increased utilization of natural gas in automotive engines for transportation applications. However scarce refueling resources for on-road vehicles impose an infrastructure limited barrier on natural gas use in transportation. A novel ‘bimodal’ engine which can operate in a compressor mode has been developed that allows on-board refueling of natural gas where available without the need for any supplemental device. Engine compression of natural gas however results in considerable heating of the gas which is undesirable from a system stand-point. Micro-channel heat exchangers have been developed to absorb heat from the natural gas using engine coolant and compressed air. This work presents the design and development of the micro-channel heat exchangers as well as a preliminary analysis of system performance. Design methodology for the heat exchanger was based on trade-off studies that correlated system performance with component design. Energy flows through the system are analyzed as a function of engine compression ratio, operating speed, charge flow rate, and ambient air and natural gas conditions. These results are further used to estimate heat transfer co-efficient and effectiveness of the micro-channel heat exchanger. Future work involves developing CFD models of the heat exchanger to obtain a detailed understanding of the conjugate heat transfer and fluid flow processes within the micro-channels.

Author(s):  
Merrill A. Wilson ◽  
Kurt Recknagle ◽  
Kriston Brooks

Typically, ceramic micro-channel devices are used for high temperature heat exchangers, catalytic reactors, electronics cooling, and processing of corrosive streams where the thermomechanical benefits of ceramic materials are desired. These benefits include: high temperature mechanical and corrosion properties and tailorable material properties such as thermal expansion, electrical conductivity and thermal conductivity. In addition, by utilizing Laminated Object Manufacturing (LOM) methods, inexpensive ceramic materials can be layered, featured and laminated in the green state and co-sintered to form monolithic structures amenable to mass production. In cooperation with the DOE and Pacific Northwest National Labs, silicon carbide (SiC) based micro-channel recuperator concepts are being developed and tested. The performance benefits of a high temperature, micro-channel heat exchanger are realized from the improved thermal efficiency of the high temperature cycles and the improved effectiveness of micro-channels for heat transfer. In designing these structures, the heat and mass transfer within the micro-channels are being analyzed with heat transfer models, computational fluid dynamics models and validated with experimental results. As an example, a typical micro-turbine cycle was modified and modeled to incorporate this ceramic recuperator and it was found that the overall thermal efficiency of the micro-turbine could be improved from about 27% to over 40%. Process improvements require technical advantages and cost advantages. These LOM methodologies have been based on well-proven industry standard processes where labor, throughput and capital estimates have been tested. Following these cost models and validation at the prototype scale, cost estimates were obtained. For the micro-turbine example, cost estimates indicate that the high-temperature SiC recuperator would cost about $200 per kWe. The development of these heat exchangers is multi-faceted and this paper focuses on the design optimization of a layered micro-channel heat exchanger, its performance testing, and fabrication development through LOM methodologies.


Author(s):  
Ian W. Jentz ◽  
Mark H. Anderson

Abstract The Homogenized Heat Exchanger Thermohydraulic (HHXT) modeling environment has been developed to provide thermodynamic modeling of printed circuit heat exchangers (PCHEs). This finite element approach solves solid conduction and fluid thermohydraulics simultaneously, without the need to mesh the minuscule micro-channels of a PCHE. The model handles PCHE features such as headers, solid side walls, and channel inlet and outlet regions, in addition to the micro-channel core. The HHXT model resolves PCHE thermohydraulics using simple model definitions and minimum computational overhead, making it an ideal design tool. This work introduces the thermohydraulic model at the core of HHXT. The homogenization approach used in the model occupies a medium between simplified linear analyses of heat transfer within a PCHE and the brute force of a fully resolved finite element, or computational fluid dynamics, model. An example problem modeling an experimental PCHE is presented. The ability of the HHXT model to simulate fluid flow through a directional varying micro-channel core of two heat-exchanging streams is demonstrated. The HHXT model is being distributed for free within the research community.


1999 ◽  
Author(s):  
Linan Jiang ◽  
Yuelin Wang ◽  
Man Wong ◽  
Yitshak Zohar

Abstract A micro-system consisting of micro-channels with integrated temperature sensors was successfully designed and fabricated for the study of heat-transfer properties of fluid flow in micro-domains. Surface micro-machining technology was used to construct the micro-channels with dimensions of about 40μm × 1.4μm × 4000μm. Polysilicon thermistors, 4μm × 4μm × 0.4μm in size were suspended across the channels and directly exposed to the fluid for local temperature measurements. The micro-channels and the micro-sensors were calibrated prior to the heat-transfer studies. Experimental results of temperature distributions along a micro-channel are presented. The integrated micro-system performance was analyzed to provide a framework for the interpretation of the experimental data, and the various heat-transfer mechanisms are subsequently discussed.


Author(s):  
Mesbah G. Khan ◽  
Amir Fartaj

In past few years, narrow diameter flow passages (≤3 mm) have attracted huge research attentions due to their several advantageous features over conventional tubes (≥6 mm) especially from the view points of higher heat transfer, lesser weight, and smaller device size. Several classifications of narrow channels, based on sizes, are proposed in the open literature from mini to meso and micro (3 mm to 100 μm). The meso- and micro-channels have not yet entered into the HVAC and automotive heat exchanger industries to the expected potentials to take the above-mentioned advantages. The reasons may be the limited availability of experimental data on pressure drop and heat transfer and the lack of consolidated design correlations as compared to what is established for compact heat exchangers. While a number of studies available on standalone single straight channels, works on multi-channel slab similar to those used as typical thermal heat exchanger core elements are inadequate, especially the research on multichannel serpentine slab are limited in the open literature. The 50% ethylene glycol and water mixture is widely used in heat exchanger industry as a heat transfer fluid. Studies of pressure drop and heat transfer on this commercially important fluid using narrow tube multi-channel slab is scarce and the availability of experimental data is rare in the open literature. Conducting research on various shapes of meso- and micro-channel heat exchanger cores using a variety working fluids are a definite needs as recommended and consistently urged in ongoing research publications in this promising area. Under present long-term project, an automated dynamic single-phase experimental infrastructure has been developed to carryout the fluid flow and heat transfer research in meso- and micro-channel test specimens and prototype microchannel heat exchanger using a variety of working fluids in air-to-liquid crossflow orientation. In the series, experiments have been conducted on 50% ethylene glycol and water solution in a serpentine meso-channel slab having 68 individual channels of 1 mm hydraulic diameter to obtain the heat transfer data and the general pressure drop nature of the test fluid. Current paper presents the heat transfer characteristics of ethylene glycol-water mixture and the Reynolds number effects on pressure drop, heat transfer rate, test specimen NTU and effectiveness, overall thermal resistance, and the Nusselt number.


2018 ◽  
Vol 941 ◽  
pp. 2148-2153
Author(s):  
James Allen Zess ◽  
Martin Dressler

Micro-channel heat exchangers (MCHXs) manufactured by Zess & Lin Industries provide highly effective heat transfer and are used in a growing number of critical applications. MCHXs consist of stainless steel or high temperature Nickel-based alloy plates with micro channels that are chemically etched or machined into each plate. These traditional extractive manufacturing methods of chemical etching and machining used in manufacturing MCHX plates are difficult and costly as a large percentage of expensive alloy is lost during manufacturing.


Author(s):  
Merrill A. Wilson ◽  
Charles Lewinsohn ◽  
James Cutts ◽  
Valery Ponyavin

It has been proposed that compact ceramic heat exchangers can be used for high temperature, corrosive applications. This paper discusses the design development of a micro-channel heat exchanger for the decomposition of sulfuric acid as part of the hydrogen producing sulfur iodine thermo-chemical cycle. Corrosion studies of candidate materials indicate that ceramic materials have superior corrosion and creep resistance under these high temperature, high acid concentration environments. This compact heat exchanger utilizes micro-channels to enhance the heat transfer while maintaining low pressure drops within the system. Through modular stacking of these micro-channel networks, a "shell and plate" configuration enables the processing of commercial-scale processes. The ceramic materials provide for long-life applications. The design of the micro-channel features captures the enhanced heat transfer characteristics at the micro-scale; the modular assembly permits the integration into macro-scale processes. As a case study, the thermal performance and the economics were investigated to determine the feasibility of this compact heat exchanger for the hydrogen producing sulfur iodine thermo-chemical cycle. The results of this design effort with its associated performance goals and development status will be reported.


Author(s):  
Kevin W. Kelly ◽  
Andrew McCandless ◽  
Christoffe Marques ◽  
Ryan A. Turner ◽  
Shariar Motakef

The performance of a micro-channel gas-liquid cross flow heat exchanger, manufactured by the LIGA technique is presented. Large heat transfer coefficients are achieved on the gas side by achieving gas-flow passage dimensions as low as 300 microns. Cross flow heat exchanger panels have been produced as large as 20 cm by 15 cm. These panels can be arranged in a variety of ways to produce heat exchangers capable of handling large thermal loads. Experimental results have shown that these heat exchangers are approximately one order of magnitude better, in terms of heat transfer per unit volume, than the commercially available tube-fin heat exchangers with characteristic cross flow channel dimensions that are typically three times larger.


2016 ◽  
Author(s):  
Yibin Deng ◽  
Shyam Menon ◽  
Zoe Lavrich ◽  
Hailei Wang ◽  
Christopher Hagen

Micro-channel heat exchangers offer potential for a highly compact solution in heat transfer applications that have space limitations. Mobile applications such as automotive vehicles are one such area. This work presents the design, modeling, simulation and testing of a two-region micro-channel heat exchanger, employing both engine coolant and R134a, for use in an engine that compresses natural gas for on-board refueling at pressures up to 250 bar. The novel design of the micro-channel heat exchanger is presented. Numerical simulations were performed using ANSYS Fluent utilizing extrapolation techniques to estimate the pressure drop as a function of flow rate and symmetry methods to investigate heat transfer. Pressure drop was determined experimentally, and heat transfer was investigated through system tests employing the novel engine. Experimental results showed good comparison with corresponding numerical simulations which demonstrated the validity of the applied extrapolation and symmetry methods, enabling considerable reduction in computational cost. The pressure drop, flow distribution, and heat transfer characteristics of the heat exchanger are discussed.


Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1853 ◽  
Author(s):  
Pavel Neuberger ◽  
Radomír Adamovský

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m2 and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m2·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m2/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters.


Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.


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