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Beth Neel

Condensation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes

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Abstract

Heat transfer enhancement plays an important role in improving energy efficiency and developing high performance thermal systems. Phase-change heat transfer processes   take place in thermal systems; typically heat transfer enhanced tubes are used in these systems and they are designed to increase heat transfer coefficients in evaporation and condensation. Enhanced heat transfer tubes are widely used in refrigeration and air-conditioning applications in order to reduce cost and create a smaller footprint of the application. A new type of enhanced heat transfer tube has been created using dimples/protrusions and secondary petal arrays has been developed, therefore it is important to investigate the condensation heat transfer characteristics of the Vipertex® 1EHT enhanced surface tube and compare it to other tubes.

Convective condensation heat transfer and pressure loss characteristics were investigated for R410A on the outside of: (i) a smooth tube (outer diameter 12.7 mm); (ii) an external herringbone tube (fin root diameter 12.7 mm); and (iii) the 1EHT tube (outer diameter 12.7 mm) for very low mass fluxes. Data was obtained for values of mass flux ranging from 8 to 50 kg/ (m2 s); at a saturation temperature of 318 K; with an inlet quality of 0.8 and an outlet quality of 0.1. In a comparison of heat transfer at a low mass flux, both the 1EHT tube and the herringbone tube did not perform as well as the smooth tube.

Microfins, roughness and dimples are often incorporated into the inner surface of tubes in order to enhance condensation heat transfer performance. Under many conditions, enhanced surface tubes can recover more energy and provide the opportunity to advance the design of many heat transfer products.

Beth Neel

Condensation and Evaporation Heat Transfer Characteristics in Horizontal Smooth, Herringbone and Enhanced Surface EHT Tubes

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Published in International Journal of Heat and Mass Transfer

Full bibliographic details: International Journal of Heat and Mass Transfer, Vol 85c,  (2015) pp. 281-291

http://www.sciencedirect.com/science/article/pii/S0017931015001337

 

 

Condensation and Evaporation Heat Transfer Characteristics in Horizontal Smooth, Herringbone and Enhanced Surface EHT Tubes

 

Abstract

An experimental investigation was performed to evaluate convective condensation and evaporation of R22, R32 and R410A inside a smooth tube (inner diameter 11.43 mm), a herringbone tube (fin root diameter 11.43 mm) and a newly developed enhanced surface EHT tube (inner diameter 11.5 mm) at low mass fluxes. The inner surface of the EHT tube is enhanced by dimple/protrusion and secondary petal arrays. For condensation, the heat transfer coefficient of the herringbone tube is 2.0 to 3.0 times larger than a smooth tube and the EHT tube is 1.3 to 1.95 times that of the smooth tube. The heat transfer enhancement ratios of the herringbone tube and the EHT tube are larger than their respective inner surface area ratios. Mass flux has a non-monotonic relation with the condensation heat transfer coefficient in the herringbone microfin tubes; this was especially evident for R32 and R410A. For evaporation, the EHT tube provides the best evaporation heat transfer performance for all the three refrigerants; this is mainly due to the heat transfer enhancement produced from the larger number of nucleation sites, increased interfacial turbulence, boundary layer disruption, flow separation and secondary flow generation caused by the dimple and petal arrays. The evaporation heat transfer coefficient of the herringbone tube is only slightly higher than that of the smooth tube. Overall, the EHT tube provides increased heat transfer enhancement for both condensation and evaporation.

Beth Neel

Comparison of Tubeside Condensation and Evaporation Characteristics of Smooth and Enhanced Heat Transfer 1EHT Tubes

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This has been recently published in Applied Thermal Engineering:

https://www.sciencedirect.com/science/article/abs/pii/S1359431115000915

 

Comparison of Tubeside Condensation and Evaporation Characteristics of Smooth and Enhanced Heat Transfer 1EHT Tubes

David J. Kukulka, Rick Smith, Wei Li

 

Results are presented here from an experimental investigation that was performed to evaluate the inside condensation and evaporation heat transfer of R410A, R22 and R32 that took place in a 12.7 mm (0.5 in) O.D. horizontal copper tube at low mass fluxes. Tubes considered in this evaluation consisted of a smooth tube (inner diameter 11.43 mm) and a newly developed enhanced surface Vipertex® 1EHT tube. Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in a variety of heat transfer applications. Utilization of enhanced heat transfer tubes is often utilized in the development of high performance air conditioning and refrigeration systems. Vipertex® has designed and produced these surfaces through three dimensional material surface modifications which produces flow optimized, enhanced heat transfer tubes that increase heat transfer. Heat transfer enhancement plays an important role in improving energy efficiencies and developing high performance thermal systems. This study details the evaluation of the in-tube evaporation and condensation that takes place in these tubes over a wide range of conditions.

The test apparatus utilized included a straight horizontal test section with an active length heated by water circulated in the surrounding annulus. Constant heat flux was maintained and refrigerant quality varied. In-tube evaporation measurements of R22, R32 and R410A are reported for evaporation at 10 OC with mass flow rates in the range of 15 to 40 kg/h. Single phase measurements are reported for mass flow rates from 15 kg/h to 80 kg/h. Condensation tests were conducted at a saturation temperature of 47OC, with an inlet quality of 0.8 and an outlet quality of 0.1. In a comparison to smooth tubes, the average heat transfer coefficients for the Vipertex® 1EHT tube exceeded those of a smooth tube. Average evaporation and condensation heat transfer coefficients for R22, R32 and R410A in the 1EHT tube are approximately two times greater than those of a smooth tube.

Enhanced heat transfer tubes are important options to be considered in the design of high efficiency systems. A wide variety of industrial processes involve the transfer of heat energy during phase change. Many of those processes employ old technology; this makes those processes ideal candidates for a redesign using enhanced surfaces that would produce improved process performance. Vipertex® 1EHT enhanced tubes recover more energy and provide an opportunity to advance the design of many heat transfer products.

 

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