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.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

An Experimental Investigation of Condensation Heat Transfer Coefficients and Pressure Drops of Refrigerants Inside Multiport Mini-channel Tubes

2017 ◽  
Vol 25 (02) ◽  
pp. 1750013 ◽  
Author(s):  
Pham-Quang Vu ◽  
Kwang-Il Choi ◽  
Jong-Taek Oh ◽  
Honggi Cho
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients

The condensation heat transfer coefficients and pressure drops of R410A and R22 flowing inside a horizontal aluminum multiport mini-channel tube having 18 channels are investigated. Experimental data are presented for the range of vapor quality from 0.1 to 0.9, mass flux from 50 to 500[Formula: see text]kg/m2s, heat flux from 3 to 15[Formula: see text]kW/m2 and the saturation temperature at 48[Formula: see text]C. The pressure drop across the test section was directly measured by a differential pressure transducer. At a small scale, the noncircular cross-sections can enhance the effect of the surface tension. The average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux. Under the same test conditions, the heat transfer coefficients of R22 are higher than those for R410A, the pressure drops for R410A are 7–19% lower than those of R22. The lower pressure drop of R410A has an important advantage as an alternative working fluid for R22 in air-conditioning and heat pump systems.

scholarly journals A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7705
Author(s):  
Anas F. A. Elbarghthi ◽  
Mohammad Yousef Hdaib ◽  
Václav Dvořák
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Working Fluid ◽  
Convection Coefficient ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Cold Fluid ◽  
Cold Stream

Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.

Experimental Characterization of Heat Transfer and Pressure Drop Inside a Tubular Evaporator Utilizing Advanced Microgrooved Surfaces

2012 ◽  
Vol 4 (4) ◽  
Author(s):  
Vibhash Jha ◽  
Serguei Dessiatoun ◽  
Michael Ohadi ◽  
Ebrahim Al Hajri
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Rate ◽  
Performance Enhancement ◽  
Water Flow Rate ◽  
Working Fluid ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Diverse Range ◽  
Heat Transfer Coefficients

Performance enhancement of heat exchangers with a focus in optimum weight/volume and the amount of working fluid in circulation is of significance to a diverse range of industries. This paper presents heat transfer and pressure drop characteristics of a compact tubular evaporator which utilizes a manifold force-fed microchannel design. A microgrooved structure with an aspect ratio of 3:1 (channel width of 100 μm and channel height of 300 μm) forms the channels used on the refrigerant side and minichannels of 1 mm depth were used on the water side. The system was tested using R134a as the refrigerant with a refrigerant flow rate of 6 to 22 g/s and water flow rate of 150 to 640 ml/s. Overall heat transfer coefficients of more than 10,000 W/m2 K were obtained with modest values of pressure drop. The present results indicate a significant enhancement in thermal performance when compared to the state-of-the-art technologies in the same application area.

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.

Surface Roughness Effects on Flow Boiling in Microchannels

2009 ◽  
Author(s):  
Benjamin J. Jones ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Pressure Drop ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cut Surface

The influence of surface roughness on flow boiling heat transfer and pressure drop in microchannels is experimentally explored. The microchannel heat sink employed in the study consists of 10 parallel, 25.4 mm long channels with nominal dimensions of 500 μm × 500 μm. The channels were produced by saw-cutting. Two of the test piece surfaces were roughened to varying degrees with electrical discharge machining (EDM). The roughness average, Ra, varied from 1.4 μm for the as-fabricated, saw-cut surface to 3.9 and 6.7 μm for the two roughened EDM surfaces. Deionized water was used as the working fluid. Experiments indicate that the surface roughness has little influence on boiling incipience and only a minor impact on saturated boiling heat transfer coefficients at lower heat fluxes. For wall heat fluxes above 1500 kW/m2, the two EDM surfaces (3.9 and 6.7 μm) have similar heat transfer coefficients that were 20 to 35% higher than those measured for the saw cut surface (1.4 μm). Analysis of the pressure drop measurements indicates that only the roughest surface (6.7 μm) has an adverse effect on the two-phase pressure drop.

Evaporation and Condensation Heat Transfer and Pressure Drop in Horizontal, 12.7-mm Microfin Tubes With Refrigerant 22

1990 ◽  
Vol 112 (4) ◽  
pp. 1041-1047 ◽  
Author(s):  
L. M. Schlager ◽  
M. B. Pate ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Smooth Tube ◽  
Working Fluid ◽  
Test Apparatus ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation And Condensation ◽  
Microfin Tubes ◽  
The Heat Transfer Coefficient

Using R-22 as the working fluid, a series of tests was performed to determine the evaporation and condensation performance of three 12.7-mm o.d. tubes having many small, spiral inner fins. The tubes, referred to as microfin tubes, had a 11.7-mm maximum i.d., 60 or 70 fins with heights ranging from 0.15 to 0.30 mm, and spiral angles from 15 to 25 deg. A smooth tube was also tested to establish a basis of comparison. The test apparatus had a straight, horizontal test section with a length of 3.67 m and was heated or cooled by water circulated in a surrounding annulus. Nominal evaporation conditions were 0 to 5°C (0.5 to 0.6 MPa) with inlet and outlet qualities of 15 and 85 percent, respectively; condensation conditions were 39 to 42°C (1.5 to 1.6 MPa) with inlet and outlet qualities of 85 and 10 percent, respectively. Mass flux varied from 75 to 400 kg/m2·s. The average heat transfer coefficients in the microfin tubes, based on a nominal equivalent smooth tube area, were 1.6 to 2.2 times larger for evaporation and 1.5 to 2.0 times larger for condensation than those in the smooth tube. The pressure drop increased, but by a smaller factor than the heat transfer coefficient.

Experimental results for endwall and pin fin heat transfer coefficients

2002 ◽  
Author(s):  
Massimiliano Rizzi ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients
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