CONDENSATION HEAT TRANSFER OF R-134a IN A HELICAL PIPE

Alternative refrigerant R-134a is considered to be ozone-friendly and apotential candidate for replacing the refrigerant R-12 in refrigeration and air-conditioningapplications. This paper presents an experimental investigation on condensation heat transfer of thealternative refrigerant R-134a flowing inside a helicoidal pipe with the cooling water flowingthrough the annular helicoidal passage in a counter-flow direction. The heat transfer experimentswere performed for R-134a mass flow flux ranging from 100 to 420 kg/m^2 s with the superheat of theinlet vapor of 2. 8℃ and 8.3℃, respectively. The average Nusselt numbers were experimentallydetermined for a helicoidal pipe with the helix axis of vertical direction. In addition, theobtained experimental results were compared with the results for R-134a condensation in straight andhelicoidal pipes available in the open literature.

EXPERIMENTAL STUDY OF CONDENSATION HEAT TRANSFER CHA- RACTERISTICS OF HORIZONTAL TUBE BUNDLES IN VACUUM STATES

TO develop an excellent heat transfer element under the vacuum condition, experiments about the heat transfer performance of horizontal tube bundles of different materials under various vacuum conditions were carried out, including the stainless steel tube, the brass tube, the Ni-based implanted steel tube and the ion implanted brass tube. The relative trends show that the condensation heat transfer coefficient and the overall heat transfer coefficient of bundles of four materials all increase with the vacuum degree, especially, those of the Ni-based implanted steel tube and the ion implanted brass tube. Under a high vacuum condition （0.07 MPa）, the condensation heat transfer coefficient of the Ni-based implanted steel tube bundle is about 1.4 times of that of the stainless steel tube bundle, the condensation heat transfer coefficient of the ion implanted brass tube bundle is found to be about 1.3 times of that of the common brass tube bundle. Therefore, according to the condensation heat transfer characteristics studied under high vacuum conditions, it is believed that a dropwise condensation is partly achieved on the surface of these two implanted tube bundles, and the ion implantation is shown to be an effective method to achieve the dropwise condensation. Based on this study, it is believed that the Ni-based steel tube may replace the brass tube, which is more expensive as a heat transfer component.

Experimental Study on Condensation Heat Transfer Characteristics inside an Inclined Wave-Finned Flat Tube of Direct Air-Cooling System

In this paper,the condensation heat transfer characteristics of parallel flow and counter flow inside an inclined wave-finned flat tube is investigated experimentally.The condensation heat transfer coefficients are analyzed based on the experimental results.Results of experiments show that condensation heat transfer coefficient decreases as the temperature difference Δt=ts-tw increases and mass flow rate decreases.The parallel flow has a similar development with the counter flow,and the condensation heat transfer coefficient of counter flow is less than that of parallel flow under the same air cooling conditions.In addition,condensation heat transfer coefficient correlations are also obtained under experimental ranges.The calculations agree well with the measured data and the agreement is seen to be within ±4% for the parallel flow and ±5% for the counter flow.

Review of the LNG intermediate fluid vaporizer and its heat transfer characteristics

The intermediate fluid vaporizer (IFV), different from other liquefied natural gas (LNG) vaporizers, has many advantages and has shown a great potential for future applications. In this present paper, studies of IFV and its heat transfer characteristics in the LNG vaporization unit E2 are systematically reviewed. The research methods involved include theoretical analysis, experimental investigation, numerical simulation, and process simulation. First, relevant studies on the overall calculation and system design of IFV are summarized, including the structural innovation design, the thermal calculation model, and the selection of different intermediate fluids. Moreover, studies on the fluid flow and heat transfer behaviors of the supercritical LNG inside the tubes and the condensation heat transfer of the intermediate fluid outside the tubes are summarized. In the thermal calculations of the IFV, the selections of the existing heat transfer correlations about the intermediate fluids are inconsistent in different studies, and there lacks the accuracy evaluation of those correlations or comparison with experimental data. Furthermore, corresponding experiments or numerical simulations on the cryogenic condensation heat transfer outside the tubes in the IFV need to be further improved, compared to those in the refrigeration and air-conditioning temperature range. Therefore, suggestions for further studies of IFV are provided as well.