## 1 Introduction
It was discovered that raising the hot-side temperature, lowering the cold-side temperature, and raising the cold-side flow rate might raise the permeate flux. [PERSON] et al. [43] and [PERSON] et al. [44] looked into how feed temperature, rate affected temperature polarization. It was shown that the temperature polarization rises with increasing feed temperature and decreasing feed and permeate rates. At very low flow rates, the conduction resistance of the membrane dominates, limiting the heat transmission at the membrane contact, which has an impact on the efficiency of the process. [PERSON] et al. [45] and [PERSON] et al. [46] investigated the effect of flow rate on permeate flux on the permeate side, and discovered that increasing the flow rate could increase the heat transfer coefficient and decrease the thermal boundary layer, resulting in a decrease in temperature polarization coefficient. It was indicated that the effect of the feed side was greater than the permeate side in terms of flow rate. For membrane distillation, growing the flow rate of the feed increases the permeate flux but also increases the possibility of membrane wetting. Furthermore, the rise in flow rate may increase the energy consumption of the liquid transport system and the operating cost. Therefore, it is necessary to select the appropriate flow rate to optimize the whole membrane distillation system. Temperature has also been shown by [PERSON] et al. [47] to be a crucial operational component that must be carefully taken into account when designing a DCMD process. To calculate the temperature polarization coefficient on the DCMD membrane, a DCMD model was created. Under various operating circumstances, localized permeate fluxes were obtained. When the flow rate was 3 L/min, the feed temperature was 60 \({}^{\circ}\)C, and the permeation temperature was 20 \({}^{\circ}\)C, it was discovered that the temperature polarization coefficient was at its highest, 0.8. When the feed temperature is 70 \({}^{\circ}\)C and the permeate side temperature is 30 \({}^{\circ}\)C, at a flow rate of 1.5 L/min, the temperature polarization coefficient is 0.66. However, when other conditions remain unchanged, the temperature of the permeate side increased to 70 \({}^{\circ}\)C, and the temperature polarization coefficient reduced to 0.47. It has been demonstrated that the temperature polarization coefficient in DCMD is substantially determined by the internal coefficient of mass transfer of the membranes used. Additionally, [PERSON] [25] noted that a key factor affecting DCMD performance is the membrane material's thermal conductivity. While this was going on, [PERSON] et al. [48] carried out experimental and theoretical research to look into the impact of hydrophobic hollow fiber membranes' thermal conductivity on permeate flux. When the feed temperature is 80 \({}^{\circ}\)C and the distillate temperature is 20 \({}^{\circ}\)C, the hydrophilic layer's thermal conductivity ranges from 0.2 to 1.4 W/mK, and vapor flux increases significantly from 31.4 to 78.5 kg/m\({}^{2}\)h. Embedding MWCNTs containing graphite particles into the hydrophilic layer of hollow fibers increases its thermal conductivity. With the addition of MWCNTs, the thermal conductivity is twice as high as that before it was added. The obtained thermal conductivity is still rather modest; it was found that by maintaining the distillate and feed temperatures at 15 \({}^{\circ}\)C and 80 \({}^{\circ}\)C, the thermal conductivity enhanced with the inclusion of nanomaterials, causing a considerable shift in steam vapor flux to 1.6 times the initial steam vapor flux of 40 kg/m\({}^{2}\)h.  
Because the productiveness of the DCMD process is impacted by many operational parameters, researchers are also working on the sensitivity of DCMD productivity to different parameters. To identify the most crucial operating factors, [PERSON] et al. [49] also carried out a theoretical investigation on the sensitivity of DCMD to different factors using the simulate approach.