1EHT Tube Research Articles

Condensation Flow and Heat Transfer Characteristics of R410A in Micro-Fin Tubes and Three-Dimensional Surface Enhanced Tubes

Condensation heat transfer characteristics (using R410A as the working fluid) were studied experimentally to evaluate the heat transfer performance in copper and stainless-steel heat transfer tubes (smooth and enhanced). Experiments were carried out for a mass flux that varied from 250 to 450 kg m−2 s−1, at a saturation temperature of 318 K. Single-phase heat balance verification found that the heat loss is less than 6%, and the deviation between single-phase experimental results and various prediction correlations is less than 15%. Additionally, tube side condensation flow patterns were observed and recorded. Experimental results found that the enhancement ratio of the condensation heat transfer coefficient (enhanced tube/smooth tube) of the three-dimensional surface (1EHT) tube is in the range of 1.15~1.90, while the ratio of the micro-fin (HX) tube is in the range of 1.18~1.80. Heat transfer performance is affected by material conductivity, with the thermal conductivity of the smooth tube slightly affecting the heat transfer performance; larger heat transfer enhancements are produced in the enhanced tubes. At a low mass flow rates and vapor qualities, the flow pattern is a stratified wavy flow, while at higher mass flow rates and vapor qualities, the flow pattern is an annular flow (with the area in the enhanced tube being larger than the area of a smooth tube). Flow patterns in the smooth tube are consistent with the predicted values shown in previously reported flow pattern maps. A flow pattern diagram for condensation heat transfer in enhanced tubes is presented as part of this study. The condensation heat transfer coefficient increases with an increase in mass flow. When the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient increases. Heat transfer values at lower mass velocities increase slightly with increasing mass flux values; however, at higher mass flux rates the heat transfer increase is larger than that at low mass flux values. Finally, tubes produced from high thermal conductivity materials produce larger heat transfer performance gains than the gains found in smooth tubes; small diameter tubes produce larger gains than larger diameter tubes.

An Experimental Investigation to Determine the Effect of Tube Material on the Tubeside Heat Transfer Performance of the Enhanced 1EHT Three Dimensional Heat Transfer Tube

Condensation heat transfer characteristics were experimentally investigated over a wide range of operating conditions in order to determine the heat transfer performance inside horizontal, smooth and enhanced heat transfer tubes; using R410A in tubes produced of copper and stainless steel. Experimental data was verified and results were compared to the performance measured in a smooth tube. Results indicate that the condensation heat transfer coefficient (HTC) enhancement ratio is in the range from 1.15 to 2.05 for the 1EHT tube and for the HX tube it ranged from 1.18 to 1.69. Smooth tube heat transfer performance was slightly affected by the thermal conductivity of the tube; however, larger enhancements are found in the enhanced tubes.Heat transfer coefficients increase with an increase of mass velocities. When the mass flux increases, the liquid flow becomes more turbulent and the liquid film becomes thinner; this reduces the thermal resistance and enhances the heat transfer. Heat transfer performance for low mass velocities rise slowly, showing only a small difference in magnitude. Performance increase is larger at high mass flux rates than that those found at low mass fluxes. The influence of thermal conductivity on the condensation heat transfer of the enhanced horizontal tubes was discussed. Better heat transfer performance occurs in tubes produced of a higher thermal conductivity material (copper) or in tubes with a smaller diameter.

R410A flow condensation inside two dimensional micro-fin tubes and three dimensional dimple tubes

Condensation heat transfer characteristics were experimentally investigated inside two dimensional helix micro fin (HX) tubes, three-dimensional dimple (1EHT) tubes and smooth (ST) tubes; while using R410A, for a variety of operating conditions and tube parameters. Tubes evaluated had a length of 2 m, with outer diameters of 9.52 and 12.7 mm; tube materials included copper and stainless steel. Experimental procedure was verified using a single-phase heat balance; with a comparison of results (enhanced tubes to smooth tube) being performed. The condensation experiments were performed at a saturated temperature of 35–45 °C; for the vapor quality range from 0.1 to 0.9; with mass fluxes that ranged from 70 to 450 kg m−2 s−1. Additionally, the effect of various parameters (mass flux, mean vapor quality, saturation temperature, tube thermal conductivity, tube diameter, and surface structure) on the tube side condensation heat transfer was evaluated.For the test conditions considered here the HTC enhancement ratio is in the range from 1.15 to 2.05 for the 1EHT tube and for the HX tube it ranged from 1.18 to 1.69; while the performance factor (PF takes into account the pressure drop) is 1.02–1.57 (1EHT) and 1.23–1.78 (HX). Heat transfer performance of the smooth tube was determined to be slightly affected by the thermal conductivity of the tube; however, for enhanced tubes there is a more dramatic increase in the HTC for an increase of thermal conductivity. Additionally, better heat transfer performance is demonstrated for smaller diameter tubes. Finally, the enhancement effect of the experimental parameters on the enhanced tubes was quantified through the use of a newly introduced evaluation factor.

Shell-Side Flow Condensation Heat Transfer on Three-Dimensional Enhanced Surface

Abstract An experimental investigation of shell-side flow condensation was performed on three-dimensional surface enhanced tubes, including a herringbone micro-fin tube and a newly developed 1-EHT tube. An equivalent plain tube was also tested for performance comparison. All the test tubes had similar geometry parameters, i.e., inner diameter 11.43 mm and outer diameter 12.7 mm. The outer shell diameter was 24.5 mm with a wall thickness of 0.6 mm. Tests were conducted using R410A as the working fluid at a dew point of 45 °C. The mass flux range of 10–55 kg/(m2 · s) with an inlet quality of 0.8 and an outlet quality of 0.1. Experimental results showed that the plain tube exhibited a better condensation heat transfer performance. Moreover, the mass flux had a significant influence on the heat transfer coefficient for shell-side condensation. A new prediction model based on the Cavallini’s equation was developed to predict the condensing coefficient where the mean absolute error is less than 4%.

Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the External Surface of Tubes in the Annulus of a Tube-in-Tube Heat Exchanger

An experimental study was carried out to explore the heat transfer characteristics on the outside of smooth and enhanced tubes, during evaporation and condensation of R134A in the annulus of a tube-in-tube heat exchanger. The three-dimensional enhanced surface tube consisted of primary enhancement patterns and secondary patterns; results were compared to the performance of an equivalent smooth tube. The equivalent external diameter of the inside horizontal copper tubes used in this study was 19.05 mm, while the outer tube varied in size, allowing a comparison of heat transfer for different annulus dimensions. Tests were conducted with a fixed inlet/outlet vapor quality and a constant saturation temperature for varied mass velocities in the range of 30 to 100 kg/(m2∙s). For condensation, the ratio of heat transfer coefficient enhancement (enhanced tube/ smooth tube) was up to 1.78; this can be attributed to the turbulence increase, as well as liquid film re-distribution, produced from the dimples. Furthermore, the condensation heat transfer coefficient increased rapidly with increasing mass flux. For flow boiling in the annulus between the 1EHT tube and outer tube, the heat transfer coefficient during boiling was 11–36% higher when compared to the smooth tube at xave = 0.35, while the performance of the 1EHT tube was not as good as the smooth tube at xave = 0.5. The heat transfer deterioration can be explained by decreased effective nucleate flow boiling heat transfer area and the flow pattern transition between a slug/wavy-stratified flow to wavy-stratified flow.

Experimental Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the Outside of Enhanced Surface Tubes with Different Outer Diameters

An experimental investigation was performed, and results are presented here for an evaporation and condensation heat transfer study that took place using enhanced heat transfer (1EHT) tubes of different outside diameters. Results were compared to the performance of a smooth surface copper tube. The equivalent outer diameter of the horizontal copper tubes considered were 12.7 mm (0.5 in) and 19.05 mm (0.75 in). The test apparatus included a straight horizontal test section with an active length heated by water. Constant heat flux was maintained and refrigerant quality varied.Experimental runs were performed using R410A and R134a as the working ?uids. Experimental condensation results are presented for a fixed inlet/outlet vapor quality and fixed saturation temperature, while mass flux varied; producing a heat transfer coef?cient increase (compared to smooth tube) in the range 54 to 64 %, with a frictional pressure drop increase for the 1EHT tubes in the range of 8 to 31 %. Unexpected evaporation results were found at higher mass flows; producing a decrease (compared to smooth tubes) of the heat transfer coef?cient for 1EHT tubes in the range of 100 – 220 %; with an increase of frictional pressure drop values for the 1EHT tubes in the range 5 to 17 %.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 and many of those processes employ old technology. These processes are ideal candidates for a redesign that could achieve improved process performance. Vipertex 1EHT enhanced tubes recover more energy and provide an opportunity to advance the design of many heat transfer products.

Condensation and Evaporation Heat Transfer Characteristics of Low Mass Fluxes in Horizontal Smooth Tube and Three-Dimensional Enhanced Tubes

Abstract An experimental investigation of condensation and evaporation heat transfer characteristics was performed in 15.88-mm-OD and 12.7-mm-OD smooth and three-dimensional enhanced tubes (1EHT, 3EHT) using R134A and R410A as the working fluid. The enhanced surface of the 1EHT tube is made up of dimples and a series of petal arrays; while the 3EHT tube is made up of rectangular cavities. Evaluations are performed at a saturation temperature of 45 °C, over the quality range of 0.8–0.2 for condensation; while for evaporation the saturation temperature was 6 °C and the quality ranged from 0.2 to 0.8. For condensation, the enhancement ratio (enhanced tube/smooth tube) of the heat transfer coefficients was 1.42–1.95 for the mass flux ranging from 80 to 200 kg/m2s; while for evaporation, the heat transfer enhancement ratio is 1.05–1.42 for values of mass flux that range from 50 to 180 kg/m2s. Furthermore, the 1EHT tube provides the best condensation and evaporation heat transfer performance, for both working fluids at the mass flux considered. This performance is due to the dimples in the enhanced surface that produce interface turbulence; additionally, the increased surface roughness causes additional disturbances and secondary flows near the boundary, producing higher heat fluxes. The main objective of this study was to evaluate the heat transfer enhancement of two enhanced tubes when using R134A and R410A as a function of mass flux, saturation temperature, and tube diameter. As a result of this study, it was determined that the heat transfer coefficient decreases with an increase in saturation temperature and tube diameter.

Flow boiling in horizontal annuli outside horizontal smooth, herringbone and three-dimensional enhanced tubes

Heat transfer and pressure drop measurements of R410A saturated flow boiling in horizontal annuli were performed at a saturation temperature of 6 °C over the mass flux range of 8–107 kg/(m2 s). The inner tubes with the same inside diameter of 12.70 mm contain a smooth tube, a herringbone micro-fin tube and a 1EHT tube (a dimpled tube enhanced by petal-shaped background patterns). In this study, the test section is a typical double-tube type heat exchanger and the emphasis is focused on the effects of mass flux, vapor quality, annular width and surface structures on the annulus-side heat transfer. Wilson plot method was adopted to ensure the correction factor of water-side coefficient of 1EHT tube. For flow boiling tests in annuli with an annular gap of 6.35 mm, both the evaporating coefficient and pressure drop increase as the mass velocity increases. Better thermal performance was seen at a outlet vapor quality of 0.6. In this case, the heat transfer rate ratio of enhanced annulus to smooth annulus is 1.7–2.5 for the herringbone micro-fin tube and 1.4–1.7 for the 1EHT tube, respectively. When the annular spacing decreases, heat transfer deterioration will worsen accompanied with a sudden drop in boiling heat-transfer coefficient. Besides, a comparison of flow boiling characteristics of annulus-side and tube-side heat transfer was made. The annulus-side heat transfer coefficient is much larger than that of tube-side case.

Evaporation heat transfer characteristics of R410A inside horizontal three-dimensional enhanced tubes

An experimental investigation was conducted for flow boiling inside three horizontal stainless-steel tubes with a series of newly-developed three-dimensional enhanced surfaces. Both the inner and outer surfaces of the 1EHT tubes were composed of dimples in different sizes and depths, and with an array of rectangular cavities for the 3EHT tube. These enhanced tubes have the same outer and inner diameters of 9.52 mm and of 8.32 mm, respectively. The evaporation experiments were performed using R410A as the working fluid at a constant saturation temperature of 279 K. The mass fluxes varied from 160 to 390 kg/m2s, with inlet and outlet vapor qualities of 0.2 and 0.8, respectively. As the mass velocity increased, the heat transfer coefficient and pressure drop penalty increased accordingly. Experimental results showed that the pressure drop of the 1EHT-1 tube is larger than those of the 1EHT-2 and 3EHT tubes, while the 1EHT-2 tube has the highest evaporation heat transfer coefficient.

Condensation heat transfer of R410A on outside of horizontal smooth and three-dimensional enhanced tubes

Experimental investigations of flow condensation on the outside surface of one smooth tube and two enhanced surface tubes with the same outer diameter of 12.7 mm were conducted. The refrigerant flowed in an annular space between the test tube and the outer tube. The newly developed 2EHT three-dimensional surfaces have multiple enhancement patterns made up of staggered petal arrays and parallel wavy channels. Tests were performed using refrigerant R410A over a mass flux range of 75–250 kg m−2 s−1, at average saturation temperatures ranging from 35 to 45 °C. For the smooth tube, the external heat transfer coefficient decreases first and then flattens out gradually at low mass fluxes. Relative significance of inertia force might be the major reason. New prediction correlations for smooth tubes based on the Nusselt's theory were presented, having all data points within ± 4% error band. The effects of saturation temperature, mass flux and vapor quality on heat transfer coefficients for all the tested tubes were analyzed. In addition, the condensation heat transfer coefficient ratio of the 2EHT-2 tube to a smooth tube is only 0.86–0.94 for mass fluxes ranging from 100 to 250 kg m−2 s−1. This phenomenon can be explained by the retention of condensate and surface tension effects. New correlations for film condensation in the annular channel outside the 2EHT tubes were also developed, showing a good agreement with experimental data.

Condensation heat transfer in horizontal three dimensional two-layer two-side enhanced tubes

Condensation heat transfer characteristics of near-azeotropic refrigerant R410A inside the horizontal copper and stainless steel EHT series tubes were measured. All three dimensional two-layer two-side enhanced tubes have deep-textured surface structures composed of petal-shaped background patterns and dimpled protrusions or boat-shaped cavities. Tests were conducted at an average saturation temperature of 45 °C; over a mass flux range of 100–450 kg/(m2·s); with an inlet quality of 0.8 and outlet quality of 0.2. Condensation heat transfer coefficient of the copper 1EHT1 tube is about 39–47% higher than that of a stainless steel one, showing a beneficial effect of high thermal conductivity material. Effects of saturation temperature and tube diameter on the copper 1EHT tubes were also discussed. Compared with a smooth tube, the heat transfer enhancement ratio of these stainless steel EHT tubes is up to 1.19. As expected, the 1EHT1 tube exhibits the highest condensation heat transfer coefficient due to its larger dimpled protrusions. In addition, the heat transfer performance of 1EHT2 and 3EHT tubes are similar. An explanation could be the condensate retention in boat-shaped cavities on the bottom of the 3EHT tube.

Local convective condensation heat transfer in horizontal double-layer three-dimensional dimple-grooved tubes

An experimental study on local condensation heat transfer characteristics in two three-dimensional double-layer dimple-grooved tubes (2EHT tubes) and a smooth tube is performed using refrigerant of R410A. The smooth tube has an outer diameter of 12.7 mm and inner diameter of 11.07 mm. The 2EHT tubes have a nominal outer diameter of 12.7 mm and wall thickness of 0.8 mm. The enhanced surface areas of two 2EHT tubes are 1.02 and 1.03 times of the smooth tube, respectively. The present experiments are conducted to measure the local wall temperature when the mass flux ranges from 65 kg/(m2·s) to 210 kg/(m2·s), heat flux ranges from 10 kW/m2 to 35 kW/m2 and vapor quality ranges from 0.9 to 0.1. The saturation temperature is maintained at 40 °C. 248 experimental HTC data points are obtained and compared with six correlations. The results show that the measured local HTCs increase with increasing mass fluxes and decrease with increasing heat fluxes, and that the present correlations have a good predictability with smooth tube but cannot predict the HTC of 2EHT tubes. The proposed condensation correlation for 2EHT tubes is validated, and it predicts all experimental points within an error band of ±30%, and 94.25% of all test points within an error band of ±20%.

Investigation on flow condensation of refrigerant in annulus of smooth and enhanced tube-in-tube heat exchanger

An experimental investigation of R22 and R410A condensation outside a horizontal smooth tube, a herringbone tube and a newly developed 3D enhanced heat transfer (1EHT) dimple tube has been conducted. The herringbone tube has a fin root diameter of 11.43 mm, a helical angle of 21.3 °, 48 fins with a fin height of 0.262 mm and an apex angle of 36 °; the 1EHT tube has an inner diameter of 11.5 mm with a dimple enhancement; while the smooth tube has an inner diameter of 11.43 mm; and all the tubes have an outer diameter of 12.7 mm. Experiments were performed for a constant saturation temperature of 45°C; with a constant inlet vapor quality of 0.8 and a constant outlet vapor quality of 0.1; for a mass flux ranging from 5 kg/(m2 s) to 250 kg/(m2 s). In addition, annular side condensation experiments were performed using an outer shell tube with outer diameters of 17 mm and 25.4 mm. Heat transfer performance varied with mass flux. At a low mass flux the enhanced dimple tube had the smallest heat transfer coefficient; while at higher values of mass flux, the smooth tube had the smallest heat transfer coefficient. Finally, the effect of average vapor quality on the heat transfer coefficient was also investigated. Characteristic analysis was performed in order to account for the various phenomena found in this series of experiments. Annular side heat transfer performance combined with pressure drop measurements reveal that the herringbone tube generally had a better heat transfer performance than the other tubes, and can be a good choice for use in annular side condensation applications.

Convective condensation in three enhanced tubes with different surface modifications

An experimental investigation took place in order to determine the convective condensation characteristics of R410A in: two enhanced heat transfer tubes with novel surface modifications; a micro-fin tube and a plain tube. Conditions included: mass flux values ranging from 70 to 330 kg m−2 s−1; saturation temperature is fixed at 313 K; with an inlet quality of 0.9 and outlet quality of 0.2. All tubes evaluated have an outer diameter of 9.52 mm; the heat transfer surface of the 1EHT tube consists of dimples and petal arrays; and the 4EHT tube is produced using trapezoidal dimples in a grid-like arrangement. The experimental results were analyzed using available flow pattern maps. Results indicate that several flow regimes are involved over the range of conditions, including stratified wavy, intermittent and annular. The micro-fin tube exhibits the best enhanced performance with heat transfer coefficients 1.8–2.2 times higher than those of the plain tube; while the 1EHT tube produces a heat transfer coefficient that is 1.4–1.65 times larger than those of the plain tube. Enhancement of the 1EHT tube is achieved by: disruption of the boundary layer; secondary fluid flow generation; fluid mixing caused by a transverse fluid transport; increased fluid turbulence; and increased heat transfer area. When considering enhanced tube frictional pressure drop, the 1EHT tube produces the largest pressure drop and the 4EHT tube is the smallest. Finally, a performance factor comparison was performed in order to evaluate the enhancement effect of the enhanced tubes. This analysis details the superior performance of the 1EHT tube under condensation conditions.

Local flow boiling heat transfer characteristics in three-dimensional enhanced tubes

Experimental study on local flow boiling heat transfer characteristics in two three-dimensional dimple-grooved tubes (2EHT) and an equivalent smooth tube was performed. All the three test copper tubes have the same inner diameter of 11.07 mm and outer diameter of 12.7 mm. The working fluid was the near-azeotropic mixture, R410A. All test runs were conducted in a 2 m long horizontal tube-in-tube heat exchanger. Constant evaporation temperature was maintained at 10 °C when heat flux ranged from 32.6 kW/m2 to 37 kW/m2. Refrigerant quality varied from inlet 0.1 to outlet 0.9 and mass flux was controlled from 70 kg/(m2 s) to 150 kg/(m2 s). The enhanced surface areas of two 2EHT tubes are 1.02 and 1.03 times of the smooth tube, respectively. The local HTC results of saturate flow boiling were presented and compared with the existing correlations. Wall temperature was measured and critical heat flux effect on the tube-side evaporation was discussed. Local wall temperature results showed that the 2EHT tubes produce a better saturate evaporation at a relatively lower wall superheat. HTC increases with increasing heat flux when heat flux is smaller than CHF and decreases when heat flux is larger than CHF. Based on the local thermal properties, a new flow boiling heat transfer correlation for these 2EHT tubes is derived. The new correlation can predict all the experimental heat transfer coefficients within an error band of ±30% and 96.89% of test data within an error band of ±20%.

Experimental study on condensation and evaporation flow inside horizontal three dimensional enhanced tubes

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 12.7mm with an inner diameter of 11.5mm. 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 200kg/m2s. 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 260kg/m2s. 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.

Comparison of Heat Exchanger Designs Using Vipertex 1eht Enhanced Heat Transfer Tubes

A numeric study was performed that compares the performance of heat exchangers using the Vipertex 1EHT enhanced heat transfer tubes to the performance of heat exchangers that use smooth surface tubes. Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in all heat transfer applications. Surface enhancement of the 1EHT tube is accomplished through the use of the primary dimple enhancement and the secondary background pattern made up of petal arrays. Utilization of enhanced heat transfer tubes is an effective method that is utilized in the development of high performance thermal systems. Vipertex™ enhanced surfaces, have been designed and produced through material surface modifications that produce flow optimized heat transfer tubes that increase heat transfer. Current energy demands and the desire to increase efficiencies of systems have prompted the development of enhanced heat transfer surfaces. Enhanced heat transfer tubes are widely used in many areas (refrigeration, air-conditioning, petro-chemical, chemical, etc.) in order to reduce cost and create a smaller application footprint. A new type of enhanced heat transfer tube has been created; therefore it is important to investigate relevant heat exchanger designs using the Vipertex 1EHT enhanced surface tube in industrial applications and compare that performance to other tubes. Results include design characteristics and performance predictions using the design simulations produced using HTRI Exchanger Suite (2016). Performance for all cases considered using the 1EHT tube predicted over performance when compared to a smooth tube design. Vipertex 1EHT tubes produced higher performance and more efficient designs.

Comparison of condensation and evaporation heat transfer on the outside of smooth and enhanced 1EHT tubes

Results are presented here from an experimental investigation that evaluated the outside condensation and evaporation heat transfer that took place on a 12.7mm (0.5in.) OD horizontal copper tube. Evaporation conditions include a mass flux that ranged from 10 to 40kg/m2s; with an inlet quality of 0.1 (±0.05); outlet quality of 0.8 (±0.05); and a nominal evaporation temperature of 279K. Condensation conditions considered here include mass flux values that varied from 5 to 50kg/m2s; at a saturation temperature of 318K; with an inlet quality of 0.8 (±0.05); and outlet quality of 0.1 (±0.05). For enhanced tubes, there are limited heat transfer predicting procedures available (within the degree of confidence necessary to perform analysis) since any work that has been done is limited to specific geometry and operating conditions that have been based upon tests from which the predicting procedures have been derived. Therefore, in this study, smooth tubes were compared to the newly developed Vipertex™ 1EHT enhanced surface tube. 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. Condensation heat transfer performance on the outside of a 1EHT tube is less than a smooth tube due to the pattern/drainage characteristics of that model of tube for the flow conditions considered.Three dimensional enhanced surfaces can be 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 a variety of industries in order to reduce cost and create applications that use a smaller footprint. Vipertex 1EHT tubes are a new type of enhanced heat transfer tube that uses multiple enhancement patterns; a primary pattern made up of dimples/protrusions with a secondary pattern that is an array of petals. Since this design is unique and unlike other tubes it is important to investigate the heat transfer characteristics of this novel enhanced heat transfer tube and compare it to other tubes.

Experimental Investigation to Evaluate the Evaporation and Condensation Heat Transfer Coefficients on the Outside of Vipertex Enhanced Performance 1EHT Tubes

Experimental Investigation to Evaluate the Evaporation and Condensation Heat Transfer Coefficients on the Outside of Vipertex Enhanced Performance 1EHT Tubes

Comparison of tubeside condensation and evaporation characteristics of smooth and enhanced heat transfer 1EHT tubes

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 °C with mass flow rates in the range of 15–40 kg h−1. Single phase measurements are reported for mass flow rates from 15 kg h−1 to 80 kg h−1. Condensation tests were conducted at a saturation temperature of 47 °C, 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.