The modeling equations for the temperature distribution and temperature polarization profiles in a laminar concurrent‐flow parallel‐plate direct‐contact membrane distillation (DCMD) module were developed theoretically. The analytical solutions for such conjugated Graetz problems in DCMD systems were obtained using the variable separation method with an orthogonal expansion technique extended in power series. A description of the average Nusselt number variations and temperature distributions of both the hot and cold feed streams is given. The feed velocity effect on the temperature profiles and average Nusselt number was examined and is reported by employing the computed eigenvalues and the relevant constants. The analytical results show that the initial saline temperature effect on the hot feed stream regarding the pure water productivity is more significant than that of the hot and cold feed stream velocity variations.

Abstract:A new device for inserting an absorber plate to divide a flat-plate channel into two subchannels to conduct double-pass wire mesh packed operations was developed. The proposed wire mesh packed device improves the heat transfer efficiency substantially as compared that to flat-plate single-pass and double-pass operations using the same working dimensions, and the improvement of device performance was investigated experimentally and theoretically. Good agreement between the theoretical prediction and the measured values from the experimental results was achieved. Considerable heat transfer improvement was obtained employing wire mesh packed double-pass operations under the absorber plate with external recycle. The influences of recycle ratio on the heat transfer efficiency and the power consumption increase were also discussed.

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