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Three-dimensional invisible finned-tube is a kind of high-efficiency enhanced tube which is widely used at present. In order to study and analyze advantages and disadvantages of heat transfer and flow performance of the three-dimensional invisible finned-tube, other enhanced tube heat exchangers are introduced and compared through experiments. After analysis and research, it is found that the total heat transfer coefficient K is not the only indexes for evaluating the performance of the heat exchanger, and the resistance is also one of the indexes. According to the evaluation standard of the comprehensive performance of the heat exchanger, the comprehensive performance factor η of the tube side and shell side of the three-dimensional invisible finned-tube heat exchanger is better than that of the other enhanced tube heat exchanger, and the enhanced tube standard is reached under certain conditions, which shows that the three-dimensional invisible finned-tube heat exchanger has excellent performance. The analysis results in this paper have certain guiding significance for engineering design and application of three-dimensional invisible finned-tube heat exchanger.

A numerical research is conducted to investigate air side heat transfer and pressure drop performance of twisted oval tube bundles with in line layout in cross flow. The effects of five geometric parameters (the ratio of outer major axis to outer minor axis (A/B), twist pitch length (S), transverse tube pitch (St), longitudinal tube pitch (Sl) and number of longitudinal tube rows (Z)) on the air side heat transfer and pressure drop performance are examined in the range of Reynolds number (Re) from 500 to 23,000. The velocity field and temperature field are repeated periodically every S/2 along the length of the twisted oval tube, which reveals that the twisted oval tube is a streamlined tube that is independent of the angle of attack. Twisted oval tube bundles perform excellent heat transfer performance compared with other tube bundles (circular tube bundle with the same tube layout as the twisted oval tube bundle, elliptic tube bundle with staggered manner, spirally corrugated tube bundle with in line layout) in cross flow. And the staggered tube layout is beneficial to enhance heat transfer performance compared with in line tube layout. Correlations for Nusselt number (Nu) and Euler number (Eu) from this paper are presented.

An experimental research on air side heat transfer and pressure drop performance of twisted oval tube bundle with staggered layout in cross flow is conducted. The comprehensive performance of present twisted oval tube bundle is larger than that of round tube bundle with the same layout by 25.5–33.3% during the experimental range of Remax (7500–18,000). The economic operation Remax among the experimental range is from 7500 to 13,000 for present twist oval tube bundle in cross flow. The correlations for Nusselt number and Euler number deduced from this paper are well compatible with experimental data, which could provide a theoretical reference of twisted oval tube bundle for industrial applications.

A set of experiments to research the heat transfer and pressure drop performance of H type fin and tube bundles with in line layouts are conducted. The effects of different geometry parameters including fin width, fin height, fin pitch, transverse tube pitch, longitudinal tube pitch and Reynolds number on heat transfer and pressure drop characteristics are discussed. The correlations of Nusselt number and Euler number deduced by multiple regressions from this paper are well compatible with experimental data, which could provide a theoretical reference of H type finned tubes for industrial applications related to air or gas heat exchangers.

A single cylinder rotary compressor was applied in the refrigerant injection air-source heat pump to improve the heating performance in cold regions. In this study, the performance of an R410A single cylinder rotary compressor vapor injection (SCRCVI) system was measured and analyzed by varying the compressor frequency f and injection pressure Pinj at the ambient temperature Tod=–10°C.The experimental results indicated that an optimum injection pressure to gain the maximum COPh (coefficient of performance) existed in the SCRCVI cycle. However, the maximum COPh of the SCRCVI system decreased as the increase of the frequency, and the maximum COPh was even lower than that of the CSVC system at high compressor frequency. Therefore, in view of the energy saving and emission reduction, the SCRCVI system should be switched to single stage compression system when the heating capacity demand could be satisfied at high compressor frequency f. Compared to the conventional single-stage vapor compression (CSVC) system, refrigerant injection could enhance the heating capacities and COPh by 28.2% and 7.91%, respectively. The average total mass flow rate of the SCRCVI system was 24.68% higher than that of the CSVC system. As the SCRCVI system worked at the optimum injection pressure, the variation trends of the different system parameters were investigated in detail. These trends were reliably used to optimize the refrigerant injection system design and the control strategy. The parameter of (Pinj–Ps) could be adopted as the signals to control the opening of the upper stage electronic expansion valve EEV1.

Applying the refrigerant injection technology to air-source heat pump had been proved to be an effective access to acquire a better performance in the cold regions. In this paper, the test-bed of R410A single-cylinder rotary compressor vapor injection (SCRCVI) system with flash tank was built and measured by changing the compressor frequency f and injection pressure Pinj under various ambient temperatures. The experimental results indicated that the effect of refrigerant injection became stronger as the ambient temperature decreased. So the SCRCVI showed a superior heating performance at lower ambient temperature, and the conventional single-stage vapor compression (CSVC) system would exhibit higher COPh, while the ambient temperature was beyond the critical value. Compared with the CSVC system, the Qh and COPh were improved by 9.1 ~ 29.5 and 5.35 ~ 7.89%, respectively, under the ambient temperature Tod = − 10 °C. The injection pressure ratio Rp under different operating conditions was varied in the range between 0.2 and 0.22. Specifically, the trend in variation of Rp was reliably used to optimize the refrigerant injection system design and the control strategy.

The longitudinal flow heat exchanger possesses lots of merits but it exhibits poor heat transfer coefficient at low Re condition, which makes it difficult to be applied in the high viscosity fluid area. In this paper, a heat transfer augment solution for lubricating oil flowing on shell side of a novel longitudinal flow twisted trifoliate tube oil cooler was proposed. Experiments were conducted to comparatively investigate the thermal–hydraulic performance of a twisted trifoliate tube oil cooler and a conventional segmental baffle oil cooler. The tube side study demonstrates that the Nu and f of the twisted trifoliate tube are 17.5–75.8% and 16.9–62.9% larger than that of the smooth circular tube. The shell side study shows that at the same oil mass flow rate, the shell side heat transfer coefficient of the twisted trifoliate tube oil cooler is 66.3–148.9% higher than that of the conventional segmental baffle oil cooler with pressure drop increased by 31.6–65.2%. Furthermore, the shell side performance evaluation criterion h/ΔP of the twisted trifoliate tube oil cooler is 1.46 times larger than that of the conventional segmental baffle oil cooler on average. The possible mechanisms responsible for the heat transfer enhancement are analyzed. In addition, the predictive correlations of tube side and shell side of the twisted trifoliate tube bundles for Nu and f are deduced based on the experimental data. Results from current research could provide useful correlations and beneficial guidance for design and application of the longitudinal flow heat exchanger in low Re ranging of 40–250.

This paper presents an experimental investigation of heat transfer enhancement in an evaporative condenser, where the tubes are remodeled with round, elliptical and twist types. The result shows that the heat transfer coefficients of the elliptical and the twisted tubes are higher than that of the round one of 10.2%-18.0% and 14.6%-28.9%, respectively. And then the evaporative-cooled chiller is introduced to a demonstration project to replace the initial water-cooled one. The tests for cold source system with the evaporative-cooled chiller show that the energy-conservation rate is 16.3% and the water-conservation rate is 39.7%, better than that of cold source system with the water-cooled chiller.

The lubrication oil cooler is widely used in many industries. The lubrication oil is usually operated in a laminar state with Reynolds number less than 1000 due to its high viscosity characteristic. It is hard to augment the heat transfer performance of high viscosity fluids without obvious pressure drop. A lot of researches have been conducted on the shell-side heat transfer and fluid flow characteristics of twisted oval tube heat exchangers. However, the previous study mainly focused on the high Reynolds number regime and the correlations obtained are not suitable for low Reynolds flow. In the present paper, a novel self-supported shell-and-tube oil cooler with twisted oval tube bundles (OCTT) is designed. Experiments are conducted to investigate the shell-side heat transfer and pressure drop of OCTT compared to the conventional shell-and-tube oil cooler with round tube bundles (OCRT) in low Reynolds number flow. The experimental results indicate that at identical oil volume flow rate, the shell-side pressure drop of OCTT is lower than that of OCRT. Furthermore the shell-side heat transfer coefficient per unit pressure drop of OCTT is larger than OCRT. The empirical equations for Nusselt number and friction coefficient of OCTT in low Reynolds number ranging of 50–600 are also deduced from the experimental data, which could provide a beneficial guidance for the design of OCTT.