Enhancement of the performance of the vapour compression plant

The enhancement of the evaporation heat transfer coefficient is important for the design and operation of horizontal tube spray film evaporators. The water spray on a horizontal tube bundle is numerically studied in steady state conditions. The objective of the present work is to numerically study the effect of the tube configuration and the operating conditions on the evaporation heat transfer coefficient. In addition, the enhancement of the evaporation rate ratio by constructing a water collector around the bottom-heated tube is also numerically studied. In order to evaluate the evaporation rate ratio and the heat transfer coefficient of the falling liquid film on the horizontal tube bundle, the nondimensional governing equations of the mass, momentum and energy of the created liquid film around the hot tube surface are solved numerically using the finite difference method. The results show that the evaporation rate ratio is mainly increased by increasing both the surface temperature and the tube's outer diameter. The evaporation rate ratio enhances by decreasing the chamber pressure and inlet liquid subcooling. The falling distance has little influence on the evaporation rate ratio. Moreover, constructing a water collector around the bottom-heated tube enhances the evaporation rate ratio. The increase in the evaporation rate ratio increases by higher heat flux and also by larger the gap between the collector and the tube surface.

The objective of the present research is to experimentally study the effect of the tube configuration and also the effect of the operating conditions on the evaporation rate of the horizontal tube bundle. An experimental test loop was installed and the water spray on a horizontal tube bundle with three nozzles of fan-jet flat nozzle type. The results show that evaporation rate and Nusselt number are increased by increasing the tube surface temperature, increasing the tube's outer diameter, decreasing the evaporation pressure and decreasing the inlet liquid sub-cooling. The falling distance has little influence on the evaporation rate. Constructing water collector around the bottom-heated tubes enhances the evaporation rate. Also, increasing the gap between the water collector and the outer tube surface, from 0.0 to 4.0 mm, results in increasing the evaporation rate. An empirical correlation has been deduced describing the relation between the average heat transfer coefficient and the affecting operating parameters.

Dynamic characteristics of refrigerant evaporation temperature in air-water heat source heat pump

A mechanical vapor recompression heat pump driven by a centrifugal fan is designed together with falling-film evaporation. Based on theoretical analysis, experimental research is applied to study the fan type of MVR. Choosing water as the experimental medium, the operation characteristic of MVR applied to low evaporation is examined. Practically, the pressure difference of the unit is likely to keep stable while its evaporation pressure goes up. After the system performance is tested and analyzed, it shows that the total evaporation water and total input energy increase as its evaporation pressure grows. Further, some calculation is done and the result indicates that its SMER and COP decrease while the evaporation pressure rises. The reason of this phenomenon is: the leakage loss of the fan inside goes up and its displacement efficiency reduces as the evaporation temperature and pressure is high; finally, it brings forth the drop of the systems adiabatic efficiency. Finally, the trend of average input work for compressed vapor is compared in three different terms. The trend of average input work by calculation is the same as that in theory; that is to say, both of them descend when the evaporation pressure ascends. Because of displacement efficiency, the trend of average input work by measure is different from that in theory; that is to say, the average input work by measure grows slightly when the evaporation pressure goes up.

The pressure drops and the friction factor of the air flowing up and down through a horizontal tube bundle with falling film water are investigated in this work, and the effects of air velocity, water spray density and air flow direction are studied. The experiment is conducted on a 13-row horizontal tube bundle with a tube diameter of 38 mm and a total of 33 tubes. The experimental data covers an air velocity range of 2.5~6.4 m/s, a water spray density range of 0.056~0.111 kg/(m·s), an air temperature of 20 °C, an air relative humidity of 60% and a spray water temperature of 30 °C. The pressure drop has a positive relationship with the spray density and air velocity, and the counter flow has a slightly larger pressure loss compared with the cocurrent flow. The proportions of the pressure drop caused by the friction between the air and spray water to the total pressure are observed to increase with the spray density and decrease with the air velocity for both counter and cocurrent flow. These proportions for the two flow patterns are approximately 10~30% for counter flow and 10~25% for cocurrent flow, respectively. Based on experimental data, prediction correlations of the friction factors through horizontal falling film tube bundles are proposed, and the prediction deviation for almost all experimental data is within ±5%.

Performance study on a mechanical vapor compression evaporation system driven by Roots compressor

Effects of nozzle configuration on a shell-and-tube spray evaporator with liquid catcher

Convection–condensation heat transfer characteristics of air/water vapor mixtures with ash particles along horizontal tube bundles

Experiments were conducted to obtain row-by-row heat transfer data during condensation of downward-flowing zeotropic refrigerant mixture HCFC-123/HFC-134a on a 3 × 75 (columns × rows) staggered bundle of horizontal low-finned tubes. The vapor temperature and the HFC-134a mass fraction at the tube bundle inlet were maintained at about 50°C and nine percent, respectively. The refrigerant mass velocity ranged from 9 to 34 kg/m2 s, and the condensation temperature difference from 3 to 12 K. The measured distribution of the vapor mass fraction in the tube bundle agreed fairly well with that of the equilibrium vapor mass fraction. The vapor phase mass transfer coefficient was obtained from the heat transfer data by subtracting the thermal resistance of the condensate film. The heat transfer coefficient and the mass transfer coefficient decreased significantly with decreasing mass velocity. These values first increased with the row number up to the third (or second) row, then decreased monotonically with further increasing row number, and then increased again at the last row. The mass transfer coefficient increased with condensation temperature difference, which was due to the effect of suction associated with condensation. On the basis of the analogy between heat and mass transfer, a dimensionless correlation of the mass transfer coefficient for the 4th to 14th rows was developed.

Experimental measurements for condensation of downward-flowing R123/R134a in a staggered bundle of horizontal low-finned tubes with four fin geometries

Hydrodynamics and thermal performance of turbulent falling films through horizontal tube bundles

Two-phase ejector enhanced carbon dioxide transcritical heat pump for cold climate

Shell-side two-phase pressure drop and evaporation temperature drop on falling film evaporation in a rotated square bundle

Spray evaporation heat transfer of R-141b on a horizontal tube bundle

Thermal analysis of heat transfer performance in a horizontal tube bundle