###### Abstract  
Determination of blood viscosity requires consistent measurement of blood flow rates, which leads to measurement errors and presents several issues when there are continuous changes in hematocrit changes. Instead of blood viscosity, a coflowing channel as a pressure sensor is adopted to quantify the dynamic flow of blood. Information on blood (i.e., hematocrit, flow rate, and viscosity) is not provided in advance. Using a discrete circuit model for the coflowing streams, the analytical expressions for four properties (i.e., pressure, shear stress, and two types of work) are then derived to quantify the flow of the test fluid. The analytical expressions are validated through numerical simulations. To demonstrate the method, the four properties are obtained using the present method by varying the flow patterns (i.e., constant flow rate or sinusoidal flow rate) as well as test fluids (i.e., glycerin solutions and blood). Thereafter, the present method is applied to quantify the dynamic flows of RBC aggregation-enhanced blood with a peristaltic pump, where any information regarding the blood is not specific. The experimental results indicate that the present method can quantify dynamic blood flow consistently, where hematocrit changes continuously over time. c 2021 11 7260. [[https://doi.org/10.3390/app11167260](https://doi.org/10.3390/app11167260)]([https://doi.org/10.3390/app11167260](https://doi.org/10.3390/app11167260))  
**Citation**: [PERSON] Quantitative Monitoring of Dynamic Blood Flows Using Codlowing Laminar Streams in a Sensorless Approach. _Appl. Sci._**2021**, _11_, 7260. [[https://doi.org/10.3390/app11167260](https://doi.org/10.3390/app11167260)]([https://doi.org/10.3390/app11167260](https://doi.org/10.3390/app11167260))  
Academic Editors: [PERSON], [PERSON] and [PERSON]  
Received: 5 July 2021  
Accepted: 5 August 2021  
Submitted: 6 August 2021  
**Publisher's Note**: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. of diffracted light for measuring the velocity of oil bubbles or gas bubbles [32]. [PERSON] et al. demonstrated small displacement of a Bragg grating on a soft wall for determining the flow rate of water [33]. [PERSON] et al. suggested a cantilever-based optofluidic sensor for measuring the flow rate of water [34]. [PERSON] et al. reported a microcantilever sensor for quantifying the flow rate of water in a paper microfluidic system [35]. [PERSON] et al. reported fluorescence photobleaching for determining velocity as well as the viscosity of PEG or sucrose [36]. [PERSON] et al. suggested a microwave-microfluidic resonator for detecting the flow rate of the culture medium (DMEM) [37]. [PERSON] et al. introduced multiple thermistors for measuring the mass flow rate of water and isopropyl alcohol (IPA) [38]. [PERSON] et al. introduced a check valve for a photo-responsive hydrogel (pNIPPAM) for controlling the flow rate of water [39]. [PERSON] et al. demonstrated that the flow rate of suspension blood (RBCs in 1\(\times\) PBS, hematocrit [Hct] = 10-20%) could be quantified with the micro-PIV technique [40]. The blood flow rate obtained with micro-PIV is varied significantly depending on the hematocrit [41]. For example, when aggregation-enhanced blood is circulated in an in vitro loop, the hematocrit of blood is varied continuously over time [30]. When a driving syringe is installed horizontally or vertically, the hematocrit also tends to increase or decrease with time [42]. For this reason, the micro-PIV technique does not provide an accurate flow rate of blood if (1) the hematocrit of blood varies over time or (2) information regarding hematocrit is not available. According to the working principle of blood viscosity, the flow rate of blood should be obtained in advance or controlled. While measuring the blood viscosity, inaccurate information on the blood flow rate results in large measurement errors.