Heat Transfer and Pressure Drop During Condensation of Ammonia in Microchannels

2012 ◽  
Author(s):  
Brian M. Fronk ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Process ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Process Data ◽  
Improve Energy Efficiency ◽  
Tube Heat Exchanger ◽  
Component Size

An experimental investigation of condensation heat transfer and pressure drop of ammonia flowing through a single, circular, microchannel (D = 1.435 mm) was conducted. The use of ammonia in thermal systems is attractive due to its high latent heat, favorable transport properties, zero ozone depletion (ODP), and zero global warming potential (GWP). At the same time, microchannel condensers are also being adopted to increase heat transfer performance to reduce component size and improve energy efficiency. While there is a growing body of research on condensation of conventional refrigerants (i.e., R134a, R404A, etc.) in microchannels, there are few data on condensation of ammonia at the microscale. Ammonia has significantly different fluid properties than synthetic HFC and HCFC refrigerants. For example, at Tsat = 60°C, ammonia has a surface tension 3.2 times and an enthalpy of vaporization 7.2 times greater than those of R134a. Thus, models validated with data for synthetic refrigerants may not predict condensation of ammonia with sufficient accuracy. The test section consisted of a stainless steel tube-in-tube heat exchanger with ammonia flowing through a microchannel inner tube and cooling water flowing through the annulus in counterflow. A high flow rate of water was maintained to provide an approximately isothermal heat sink and to ensure the condensation thermal resistance dominated the heat transfer process. Data were obtained at mass fluxes of 75 and 150 kg m−2 s−1, multiple saturation temperatures, and in small quality increments (Δx∼15–25%) from 0 to 1. Trends in heat transfer coefficients and pressure drops are discussed and the results are used to assess the applicability of models developed for both macro and microscale geometries for predicting the condensation of ammonia.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

Experimental Study on Forced Convection Heat Transfer Inside Horizontal Tubes in an Absorption/Compression Heat Pump

2002 ◽  
Vol 124 (5) ◽  
pp. 975-978 ◽  
Author(s):  
Li Yong and ◽  
K. Sumathy
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Forced Convection ◽  
Experimental Results ◽  
Working Fluid ◽  
Large Temperature ◽  
Absorption Process ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients

Quasi-local absorption heat transfer coefficients and pressure drop inside a horizontal tube absorber have been investigated experimentally, with R-22/DMA as the working pair. The absorber is a counterflow coaxial tube-in-tube heat-exchanger with the working fluid flowing in the inner tube while the water moves through the annulus. A large temperature gliding has been experienced during the absorption process. Experimental results show that the heat transfer coefficient of the forced convective vapor absorption process is higher compared to the vertical falling film absorption. A qualitative study is made to analyze the effect of mass flux, vapor quality and solution concentration on pressure drop and heat transfer coefficients. On the basis of the experimental results, a new correlation is proposed whereby the two-phase heat transfer is taken as a product of the forced convection of the absorption and the combined effect of heat and mass transfer at the interface. The correlation is found to predict the experimental data almost within 30 percent.

Flow Pattern, Heat Transfer and Pressure Drop Behaviors of Micro-Channel Flow Boiling

2018 ◽  
Author(s):  
Sira Saisorn ◽  
Pochai Srithumkhant ◽  
Pakorn Wongpromma ◽  
Maturose Suchatawat ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Flow Boiling ◽  
Flow Direction ◽  
Saturation Pressure ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Stainless Steel Tube

Two-phase flow of R-134a with high confinement number was experimentally carried out in this study. Flow boiling conditions for different orientations were controlled to take place in a stainless steel tube having a diameter of 0.5 mm. Based on a saturation pressure of 8 bar, a heat flux range of 2–26 kW/m2, and a mass flux range of 610–815 kg/m2s, a constant surface heat flux condition was controlled by applied DC power supply on the test section. The flow behaviors were described based on flow pattern and pressure drop data while heat transfer mechanisms were explained by using heat transfer coefficient data. In this work, nucleate boiling was observed, and the importance of the change in the flow direction was neglected, corresponding to the confinement number of around 1.7.

Evaporation of Ammonia in a Smooth Horizontal Tube: Heat Transfer Measurements and Predictions

1999 ◽  
Vol 121 (1) ◽  
pp. 89-101 ◽  
Author(s):  
O. Zu¨rcher ◽  
J. R. Thome ◽  
D. Favrat
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Two Phase

Experimental test results for flow boiling of pure ammonia inside horizontal tubes were obtained for a plain stainless steel tube. Tests were run at a nominal saturation temperature of 4°C, nine mass velocities from 20–140 kg/m2 s, vapor qualities from 1–99 percent and heat fluxes from 5–58 kW/m2. Two-phase flow observations showed that the current test data covered the following regimes: fully stratified, stratified-wavy, intermittent, annular, and annular with partial dryout. The Kattan-Thome-Favrat flow boiling model accurately predicted the local heat transfer coefficients measured in all these flow regimes with only two small modifications to their flow map (to extend its application to G < 100 kg/m2 s). Their flow boiling model was also successfully compared to the earlier ammonia flow boiling data of Chaddock and Buzzard (1986). The Gungor-Winterton (1987) correlation instead gave very poor accuracy for ammonia.

Local Heat Transfer and Pressure Drop for Finned-Tube Heat Exchangers Using Oval Tubes and Vortex Generators

2001 ◽  
Author(s):  
James E. O’Brien ◽  
Manohar S. Sohal ◽  
Philip C. Wallstedt
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Single Channel ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Conduction Model ◽  
Number Range ◽  
Tube Heat Exchanger ◽  
Oval Tube ◽  
Tube Geometry

Abstract This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with an elliptical tube and one or two a delta-winglet pairs. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficients were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over a Reynolds number range based on duct height of 670–6300. Pressure drop measurements have also been obtained for similar elliptical-tube and winglet geometries using a separate single-channel, multiple-tube-row pressure-drop apparatus. The pressure-drop apparatus includes four tube rows in a staggered array. Comparisons of heat transfer and pressure drop results for the elliptical tube versus a circular tube with and without winglets are provided. Mean heat transfer results indicated that the addition of the single winglet pair to the oval-tube geometry yielded significant heat transfer enhancement, averaging 38% higher than the oval-tube, no-winglet case. The corresponding increase in friction factor associated with the addition of the single winglet pair to the oval-tube geometry was very modest, less than 10% at ReDh = 500 and less than 5% at ReDh = 5000.

scholarly journals Ice slurry flow and heat transfer during flow through tubes of rectangular and slit cross-sections

2014 ◽  
Vol 35 (3) ◽  
pp. 171-190
Author(s):  
Beata Niezgoda-Żelasko ◽  
Jerzy Żelasko
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cross Sections ◽  
Heat Transfer Process ◽  
Solid Particles ◽  
Ice Slurry ◽  
Slurry Flow ◽  
Transfer Coefficients ◽  
Laminar And Turbulent Flow ◽  
Flow Through

Abstract The paper presents the results of experimental research of pressure drop and heat transfer coefficients of ice slurry during its flow through tubes of rectangular and slit cross-sections. Moreover, the work discusses the influence of solid particles, type of motion and cross-section on the changes in the pressure drop and heat transfer coefficient. The analysis presented in the paper allows for identification of the criterial relations used to calculate the Fanning factor and the Nusselt number for laminar and turbulent flow, taking into account elements such as phase change, which accompanies the heat transfer process. Ice slurry flow is treated as a generalized flow of a non-Newtonian fluid.

Internal, Shellside Heat Transfer and Pressure Drop Characteristics for a Shell and Tube Heat Exchanger

1985 ◽  
Vol 107 (2) ◽  
pp. 345-353 ◽  
Author(s):  
E. M. Sparrow ◽  
J. A. Perez
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Thermal Loading ◽  
Compartment Pressure ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
Shell And Tube

Per-tube heat transfer coefficients and per-compartment and intracompartment pressure drops were measured on the shell side of a shell and tube heat exchanger. The main focus of the work was to determine the response of these quantities to variations in the size of the baffle window; the Reynolds number was also varied parametrically. The pressure measurements showed that the fluid flow is fully developed downstream of the first compartment of the heat exchanger and that the per-compartment pressure drop is constant in the fully developed regime. Within a compartment, the pressure drop in the upstream half is much larger than that in the downstream half. The per-tube heat transfer coefficients vary substantially within a given compartment (on the order of a factor of two), giving rise to a nonuniform thermal loading of the tubes. Row-average and compartment-average heat transfer coefficients were also evaluated. The lowest row-average coefficients were those for the first and last rows in a compartment, while the highest coefficient is that for the row just upstream of the baffle edge. It was demonstrated that the per-tube heat transfer coefficients are streamwise periodic for a module consisting of two consecutive compartments.

scholarly journals Condensation Heat Transfer of R-407C in Helical Coiled Tube Heat Exchanger

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1157
Author(s):  
Hamad Mohammad AlHajeri ◽  
Abdulrahman Almutairi ◽  
Mohamad Hamad Al-Hajeri ◽  
Abdulrahman Alenezi ◽  
Rashed ALajmi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
The Relationship

The results of an experimental study to evaluate the characteristics of R-407C thermofluid during condensation in a helically coiled copper tube heat exchanger are presented. The effects of saturation temperature (Tsat), and mass and heat fluxes of refrigerant R-407C on thermal performance and pressure drop were determined. The relationship between the refrigerant wall subcooling and heat transfer coefficients was also investigated. This paper reports the effect of the temperature of the water used as cooling medium on the heat transfer rate of condensing R-407C. The study was conducted with mass flux of R-407C in the range of 100–450 kg/m2s, mass flux of the coolant water in the range of 500–5000 kg/m2s and Tsat of 31 °C, 35 °C, and 39 °C. Compared with a straight smooth tube, the use of the helical coiled (helicoidal) tube increased the condensation rate with a corresponding pressure drop that depended on the value of Tsat of the refrigerant and temperature of the coolant.

Sign in / Sign up

Export Citation Format

Share Document