Results from a study that evaluated the performance of 2EHT tubes has just been published in a heat transfer journal.
Title:Experimental study on condensation and evaporation ﬂow inside horizontal three dimensional enhanced tubes
Journal title: International Communications in Heat and Mass Transfer Journal. Volume 80, Page 30-40, 2017.
Experimental investigations of tube side condensation and evaporation in two 3-D enhanced heat transfer (2EHT) tubes were compared to the performance of a smooth surface copper tube. The equivalent outer diameter of all the tubes was 12.7 mm with an inner diameter of 11.5 mm. Both the inner and outer surfaces of the 2EHT tubes are enhanced by longitudinal grooves with a background pattern made up by an array of dimples/embossments. Experimental runs were performed using R410A as the working ﬂuid, over the quality range of 0.2–0.9. For evaporation, the heat transfer coefﬁcient ratio (compares the heat transfer coefﬁcient of the enhanced tube to that of a smooth tube) of the 2EHT tubes is 1.11–1.43 (with an enhanced surface area ratio of 1.03) for mass ﬂux rate that ranges from 80 to 200 kg/m s. For condensation, the heat transfer coefﬁcient ratio range is 1.1– 1.16 (with an enhanced surface area ratio of 1.03) for mass ﬂux that ranges from 80 to 260 kg/m s. Frictional pressure drop values for the 2EHT tubes are very similar to each other. Heat transfer enhancement in the 2EHT tubes is mainly due to the dimples and grooves in the inner surface that create an increased surface area and interfacial turbulence; producing higher heat ﬂux from wall to working ﬂuid, ﬂow separation, and secondary ﬂows. A comparison was performed to evaluate the enhancement effect of the 2EHT tubes using a deﬁned performance factor and this indicates that the 2EHT tubes provides a better heat transfer coefﬁcient under evaporation conditions.
Recent results on the condensation and evaporation on the outside of the Vipertex 1EHT has been published in Applied Thermal Engineering, doi:10.1016/j.applthermaleng.2016.03.036.
Results are presented here from an experimental investigation that evaluated the outside condensation and evaporation heat transfer that took place on a 12.7 mm (0.5 in.) OD horizontal copper tube. Evaporation conditions include a mass flux that ranged from 10 to 40 kg/m2 s; with an inlet quality of 0.1 (±0.05); outlet quality of 0.8 (±0.05); and a nominal evaporation temperature of 279 K. Average evaporation heat transfer coefficients for R22 and R410A on the 1EHT tube are in the range of one to four times greater than those of a smooth tube.
The following research paper has recently been published in Applied Thermal Engineering detailing experimental and numeric results of the Vipertex 1EHT tube.
Volume 101, 25 May 2016, Pages 38–46
Single phase heat transfer and pressure drop analysis of a dimpled
Ming Li, Tariq S. Khan, Ebrahim Al-Hajri
Department of Mechanical Engineering, The Petroleum Institute, Abu Dhabi, United Arab Emirates
Zahid H. Ayub
Isotherm Inc., Arlington, USA
A non-dimensional performance evaluation criterion (PEC) was used to assess the thermal-hydraulic performance of heat transfer enhancement achieved with the Vipertex 1EHT enhanced tube. Based on the experimental data, Nusselt number and friction factor estimation correlations were proposed for the enhanced tube. Simulations were carried out to obtain heat transfer and pressure drop characteristics of smooth and enhanced tubes, using commercial Fluent.
Flow visualization of flows near a heat transfer tube and evaporation heat transfer results of Vipertex 1EHT tubes are compared to Smooth Tubes have been presented at ECCE10 (10th European Congress of Chemical Engineering).
Visualizations of Pool Boiling in Water for a 1EHT Tube – Vectors indicating Flow Speed of Particles
The evaporation heat transfer coefficient enhancement ratio (for the range considered for flows using R410a), for the 1EHT tube is approximately 1.4
The results of a joint research project between Shell Oil and Rigidized Metals has recently been published in the Journal of Enhanced Heat Transfer. Heat Transfer advantages of the 1EHT tube for crude fouling conditions are discussed.
Shell Global Solutions (US) Inc.
Ridigized Metals Corp.
Shell India Markets Pvt. Ltd.
The evaluation shows that depending on the applied constraints, different benefits can be obtained using Vipertex tubes, inculding: – a heat duty increase of up to 19%, an 18-30% reduced flow rate to achieve the same heat duties, or a change in the geometry to achieve a 8-9% increase in heat transfer at the same pumping power.
Published and Presented at HEFAT2015 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, pp.803-812
An experimental investigation was performed to evaluate condensation and evaporation heat transfer on the outside of a smooth tube, herringbone micro fin tube and the Vipertex 1EHT enhanced heat transfer tube as a function of mass flux. Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in two phase heat transfer applications. Utilization of enhanced heat transfer tubes is an effective enhancement method that is utilized in the development of high performance thermal systems. Vipertex™ enhanced surfaces have been designed and produced through material surface modifications, creating flow optimized heat transfer tubes that increase heat transfer. Heat transfer processes that involve phase-change processes are typically efficient modes of heat transfer; however current energy demands and the desire to increase efficiencies of systems have prompted the development of enhanced heat transfer surfaces that can be used in processes involving evaporation and condensation.
Surface enhancement of the 1EHT tube is accomplished through the use of a primary dimple enhancement coupled with a secondary background pattern made up of petal arrays. Enhancement of the herringbone is accomplished through the use of microfins. Convective condensation heat transfer and pressure loss characteristics were investigated using 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 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. For these conditions, both the 1EHT tube, and the herringbone tube did not perform as well as the smooth tube. This was an unexpected result.
Additionally the study also included a determination of the evaporation heat transfer coefficients using R410A on the outside of the same three tubes. The nominal evaporation temperature was 279 K; for a mass flux that ranged from 10 to 40 kg/m2 s; with an inlet quality of 0.1 and the outlet quality of 0.8. Excellent heat transfer performance is demonstrated by the 1EHT tube showing an enhancement ratio of approximately 1.4. Evaporation heat transfer coefficient enhancement values for the herringbone tube ranges from 1.5 to 2.2. For the considered conditions, both the herringbone and 1EHT tubes have higher pressure drops than smooth tubes.
Microfins, surface roughness and three dimensional enhanced surfaces are often incorporated on the surface of tubes in order to enhance 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. Enhanced heat transfer tubes are widely used in refrigeration and air-conditioning applications in order to reduce cost and create a smaller application footprint. A new type of enhanced heat transfer tube has been created using dimples/protrusions with secondary petal arrays; therefore it is important to investigate the heat transfer characteristics of the new Vipertex 1EHT enhanced surface tube and compare it to other tubes.
A General Correlation for Condensation Heat Transfer in Micro-Fin for Herringbone and Dimple-Texture Tubes
An experimental investigation was performed to evaluate the condensation characteristics inside smooth, herringbone and dimple-texture (Vipertex 1EHT) tubes with the same outer diameter (12.7 mm) using R22 and R410a refrigerants, for a mass flux range from 81 to 178.5 kg/m²s. The condensation saturation temperature is 47℃; with an inlet quality of 0.8 and an outlet vapor quality of 0.2. Results indicate that the condensation heat transfer coefficient of the herringbone tube was approximately 3 times that of the smooth tube for R22 and a factor of 2.3 for R410a. Multipliers for the dimple tube heat transfer coefficient is approximately 2 times that of a smooth tube for R22 and 1.8 for R410a. Four previously reported correlations are used to compare heat transfer coefficient measurements in the plain tube; while a new equation is proposed to predict the heat transfer coefficient in the herringbone tube.
Keywords: dimple enhanced tube, Herringbone tube, Condensation, Heat Transfer Coefficient, Correlation.
Evaporation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes
An experiment investigation was performed using R410A in order to determine the single-phase and evaporation heat transfer coefficients on the outside of (i) a smooth tube; (ii) herringbone tube; and (iii) the newly developed Vipertex enhanced surface 1EHT tube; all with the same external diameter (12.7 mm). The nominal evaporation temperature is 279 K, with inlet and outlet qualities of 0.1 and 0.8. Mass fluxes ranged from 10 to 40 kg/m²s. Results suggest that the 1EHT tube has excellent heat transfer performance but a higher pressure drop when compared to a smooth tube. Evaporation heat transfer coefficient for the 1EHT is lower than the herringbone tube and the pressure drop is almost the same.
Keywords: enhanced surface heat transfer tube, herringbone tube, evaporation, pressure drop, heat transfer
Condensation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes
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.
Keywords: enhanced surface tube, condensation, heat transfer
- 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
DOI information: 10.1016/j.ijheatmasstransfer.2015.01.115
Condensation and evaporation heat transfer characteristics in horizontal smooth, herringbone and enhanced surface EHT tubes
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.
Keywords: Herringbone tube, condensation, evaporation, heat transfer enhancement