Study On Calculation Method Of Ammonia-Water Absorber Area With Heat And Mass Transfer Process

Ammonia-water absorption refrigeration cycle can effectively make use of waste heat, thus, it’s a kind of environmentally friendly refrigeration method. However, huge volume and large metal consumption make the use of absorption refrigeration cycle limited. Absorber area has a large proportion in the total area needed in the absorption cycle and thus has a great impact on the system. In the absorber design part, the decision of absorber area may affect the metal consumption and covered area, thus, we should pay more attention on the area design. The log mean temperature method, which is short for LMTD method, is always used for determining the area, but it may not be reasonable because it’s suitable for pure heat transfer process and has no consideration for heat brought by mass transfer. In this paper, a correction temperature method was raised based on the LMTD method. Combined with the numerical result and the experimental data, finally, we check whether the correction temperature difference method is rational. This work mainly contains 4 aspects as follows:1. Combining the LMTD method mentioned in the Design Manual of Refrigeration and Engineering with the heat and mass transfer analysis to deduce the correction temperature difference method. The vertical tube falling film absorption process is simplified to a two-dimensional model, taking the heat flux into element heat balance equation, through a series of simplifying assumptions, finally we come to the correction method which has a form close to the LMTD formula. The correction formula contains a coefficient C when compared to the LMTD formula, where C has relation to the mass transfer coefficient, mass flow both in the solution side and the cooling water side, and the heat released on the boundary.2. Analysis on coupled heat and mass transfer absorption cycle with a single, vertical tube. A simplified physical model is created through a series control equations which are listed by some assumptions. Simplify the control equations and use numerical method to solve them. Using Matlab to make the program. According to data, analyzing the effect inlet solution temperature, cooling water temperature, absorption pressure and inlet solution concentration have on the film thickness, final concentration, solution velocity and temperature. Images show that higher inlet solution temperature, cooling water temperature, inlet solution concentration, higher the solution velocity and temperature, while lower the film thickness and final concentration. However, when absorption pressure is higher, the 4 parameters will all raise.3. Experimental study on ammonia water falling film absorption cycle. Making corresponding changes on the test bench which has already exits. Completing the absorption experiments by controlling the cooling water temperature twice. According to the experimental data, pick up 8 groups of experiments which has relatively accurate data. In the 8 groups of experiments, the inlet temperature of cooling water, inlet temperature of solution, absorption pressure and inlet concentration are different Through images of different dilute solution temperature, namely T\, the inlet solution temperature, T3, the concentrated solution temperature, namely,T4 in different experimental conditions, analyzing the effects 4 parameters have on the absorption process. Results show that, lower inlet temperature of cooling water, inlet temperature of solution, inlet solution concentration with higher absorption pressure, greater reaction happened in the absorption process.4. Making data analysis and making comparison between different influences different temperature difference method have on absorber design. Combined with the LMTD method, correction method, numerical method and experiment data, listing the corresponding average temperature difference and area obtained by different method in different experimental conditions. Comparing them with the actual absorber area, we can see that the correction method numerical is more convenient than the numerical method and is closer to the actual area than the results get by LMTD method.