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The paper’s primary goal is to investigate mass and heat transfer processes in reactive nanofluid particles. Within Buongiorno’s model, three chemical reactions are discussed. The main subject is on the nanoparticle fractions at the boundary. The characteristics of $Nt$ and $Nb$ with regard to the nanoparticle fraction have been found to be passively rather than actively controlled at the boundary. To put it another way, these qualities naturally develop and are controlled by the circumstances at the boundary or interface where the nanoparticles interact with the surrounding medium. They are not the result of active manipulation or outside forces. The system of partial differential equations was converted into ordinary differential equations using similarity transformations. To solve the system of ODEs, they combined the shooting method with a numerical technique known as RK-Fehlberg. The study examines various physical parameters and their effects using graphs. The paper also contains a table showing how different parameters affect the regional Nusselt and Sherwood numbers. This enables a deeper comprehension of the impact that these variables have on the heat and mass transfer within the reactive nanofluid particles. Core findings: Examining three chemical reactions involving nanofluids has led to the study’s key discoveries. Additionally, it looks into how specific physical variables may affect the Nusselt and Sherwood numbers.

To bridge the structure gap, electrochemical reactions can be studied in flow cells with nm-sized catalyst particles deposited or fabricated on the cell walls. The understanding of the role of mass transport in such cells is now limited. To clarify the likely effects in this field, we analyze the simplest reaction scheme including intermediate desorption, readsorption, and subsequent reaction and show how the net rate of the formation of intermediate can be influenced by its diffusion in the liquid phase. With certain approximations, we derive analytical results describing reaction and diffusion near catalyst particles and in more remote regions in the simplest 1D case and more complex 2D and 3D situations.

The electrochemical formation of single silver needles from aqueous silver sulfate was studied under both potentiostatic and galvanostatic conditions utilizing different quasi-2D cells. Under potentiostatic conditions, four (I–IV) stages of growth were distinguished. Stage III involved single needle growth under a quasi-steady-state (q-ss) regime in which, at the millimeter scale, the tip profile remained almost unchanged. Fast growing needles exhibited a truncated quasi-conical tip, and slow growing ones approached prolate hemispheroids. At stage III, the almost constant q-ss silver deposition rate was evaluated from the tip front displacement (dL_z/dt) perpendicularly to the tangential plane of the tip. For the cathode to anode potential difference in the range -1.00 ≤ E_c-a ≤ -0.22 V, values of (dL_z/dt) in the range 0.08–2.0 μm s^-1 were obtained. At the needle stem, the q-ss radial silver deposition rate (dL_x/dt) was about two orders of magnitude lower than (dL_z/dt). The transition from stage III to IV was characterized by tip thickening, i.e. a change in the tip q-conical profile to that of a prolate hemispheroid, and eventual tip splitting. Scanning electron micrographs at the micrometer scale of single silver needle tips from potentiostatic runs showed either a defined crystallography or an irregular topography covered by a large number of tiny crystals. In contrast, stems were always faceted. This difference indicated that surface relaxation processes following silver ion mass transport and discharge played a relevant role in the needle growth mode. At stage III, the growth regime is described utilizing a dual diffusion (D) and migration (M) model consisting of a DM direct contribution that becomes dominant at the needle stem, and a space charge (SC)-assisted DM contribution that operates at the tip apex. This explanation is consistent with the local cathodic current density values, the concentration ratio of silver clusters at the stem and tip apex surface, and the distinct kinetic behavior of needles produced from potentiostatic and galvanostatic runs. The complex link between mass transport phenomena of silver ions from the binary solution side, the silver ion discharge at the interface and the surface relaxation of silver adatoms and clusters at the metal lattice shed new light on the aspects of single silver needle formation.

Flow visualization in reciprocating flow inside branching tubes was performed to investigate the mechanism of axial gas exchange in the human lung system. A bronchial tube model is employed which is geometrically similar to the average human lung system. Water is used as the working fluid. The ranges of Reynolds and Womersley numbers in the present study correspond to those of normal human respiration and HFV (high frequency ventilation), respectively. It is revealed that the axial gas exchange phenomenon occurring in the human lung system is governed by a "trap-and-release" mechanism caused by the formation-and-destruction of the separation regions, which are formed on the wall of the parent tube and or daughter tubes, depending on the direction of the reciprocating flow.

Increasingly biological sciences are being built on a quantitative foundation, based upon our ability to accurately determine the temporal and spatial variations in the concentration of key molecules. It is this quantitative analytical data that provides the testable basis for building hypotheses about biological systems. Although many, diverse analytical techniques have been used to collect quantitative data these are often destructive of the system being analysed. Biosensors by contrast promise the ability to measure selected molecules continuously and in real-time with good spatial resolution. They use specific molecular recognition at the surface of a transducer such that an electrical signal is generated in proportion to the concentration of the target analyte. Many different molecular recognition reagents have been exploited in this respect and include enzymes, binding proteins and nucleic acids, whilst electrochemical, optical and mass sensitive signal transduction devices have been used to generate the electrical signal (typically a voltage or current).

Using biosensors in vivo presents additional challenges over and above simply relating signal to concentration. Biocompatibility is an ever-present issue and includes both the effect of the biological matrix on the sensor as well as sensor components on the biology. In this chapter a review of the different sensing modes is presented and their potential applicability to the monitoring of cells, tissue and tissue constructs is presented.

The replacement of the "flat biology" of the Petri dish with three-dimensional (3D) cell cultures has shown to narrow the gap between cell behaviours and function in vitro and at the physiological settings. A fundamental challenge to realise the potential of the 3D cell culture is the design and application of "smart" bioreactor systems. These systems should provide homogenous mass transport into the internal volume of the cultured cell constructs as well as to efficiently propagate physical and mechanical stimuli. Herein, we describe the design principles of various bioreactors, starting with the conventional spinner flasks, the rotary wall vessels and up to the latest perfusion vessels. In particular, the key role of perfusion bioreactors in regenerating the dynamic 3D cell microenvironment is demonstrated by providing a few successful examples of engineering thick functional tissues, such as the cardiac muscle tissue. In closing this chapter, we envision future innovations in bioreactors.