Mohd. Kaleem Khan

Bio: Mohd. Kaleem Khan is an academic researcher from Indian Institute of Technology Patna. The author has contributed to research in topics: Heat transfer & Heat flux. The author has an hindex of 17, co-authored 60 publications receiving 1120 citations. Previous affiliations of Mohd. Kaleem Khan include Indian Institute of Technology Roorkee & Thapar University.

Performance enhancement of solar collectors—A review

Abstract: Given rapid depletion of conventional energy sources and environmental degradation caused by their over exploitation, the renewable energy sources are believed to be the future. Technologies utilizing renewable energy sources differ significantly from one another, not only with regard to technical and economic aspects but also in relation to their reliability, maturity, and operational experience in utility scale conditions. Technologies used to harness solar energy have emerged as the most promising and mature since solar energy is abundant, freely available, and it has commercial potential too. This paper presents a review of advancements made in the field of solar thermal technology with a focus on techniques employed for its performance enhancement. It also covers the description of different types of solar collectors to facilitate the systematic understanding of solar thermal technology and the novel modifications realized in each category of solar collectors have been highlighted to promote the use of solar energy in routine activities. Performance enhancement techniques such as geometrical modifications on the absorber plate, use of solar selective coatings and nanofluids have been given a special attention.

A comparative study of flow boiling heat transfer in three different configurations of microchannels

Abstract: In this work, an experimental investigation has been made to compare the flow boiling characteristics of deionized water in three different configurations of microchannels. The investigated channel configurations are uniform cross-section, diverging cross-section and segmented finned microchannels. In each configuration, an array consisting of twelve numbers of microchannels with rectangular cross-section has been fabricated on a copper block with footprint area of 25.7 × 12.02 mm2. Experiments have been conducted with subcooled liquid state at the entry with coolant mass and heat fluxes vary in the range 100–350 kg/m2 s and 10–350 kW/m2, respectively. Depending upon the heat flux and coolant flow rate different regimes of two phase boiling have been observed. The comparison of three configurations has been made in terms of heat transfer coefficient, pressure drop characteristics and affinity towards backflow or flow reversal in the channels. Bubbles dynamics and their role in flow reversal and flow instability have been discussed for all three types of channels. For entire operating conditions, segmented finned channels demonstrate the highest heat transfer coefficient with negligible higher pressure drop compared to other two configurations of channels. The performance of diverging cross-section channels is better than the uniform cross-section channels. However, they underperform compared with segmented finned channels. At higher heat flux, bubble clogging and flow reversal problem is worst in uniform cross-section channels. The problem is partially solved in diverging cross-section channels. Segmented channels completely relieve the problem of bubble clogging allowing smooth and easy passage of growing bubbles. Moreover flow reversal is not observed in segmented channels for entire operating range of heat flux and coolant mass flux.

A review on the clad failure studies

Abstract: In this paper, an attempt has been made to systematically organize the research investigations conducted on clad tube failure, so far. Before presenting the review on the clad failure studies, an introduction to different clad materials has been added, in which the effect of alloying elements on the material properties have been presented. The literature on clad failure has been broadly categorized under the headings LOCA and RIA. The failure mechanisms like creep, corrosion and pellet–clad interaction have been discussed in details. Each subsection of the review has been provided with summary table, in which the studies are arranged in the chronological order. A small section on acceptance criteria for ECCS has also been included. The last section of the review has been dedicated to the core-degradation phenomena.

Flow characteristics of refrigerants flowing through capillary tubes : A review

Abstract: A comprehensive review of the literature on the flow of various refrigerants through the capillary tubes of different geometries viz. straight and coiled and flow configurations viz. adiabatic and diabatic, has been discussed in this paper. The paper presents in chronological order the experimental and numerical investigations systematically under different categories. Flow aspects like effect of coiling and effect of oil in the refrigerants on the mass flow rate through the capillary tube have been discussed. Furthermore, the phenomenon of metastability and the correlations to predict the underpressure of vaporization have also been discussed. The paper provides key information about the range of input parameters viz. tube diameter, tube length, surface roughness, coil pitch and coil diameter, inlet subcooling and condensing pressure or temperature. Other information includes type of refrigerants used, correlations proposed and methodology adopted in the analysis of flow through the capillary tubes of different geometries operating under adiabatic and diabatic flow conditions. It has been found from the review of the literature that there is a lot more to investigate for the flow of various refrigerants through different capillary tube geometries.

Pool boiling heat transfer enhancement with segmented finned microchannels structured surface

Abstract: An experimental investigation has been carried out to investigate pool boiling heat transfer characteristics of segmented finned (SF) microchannels structured surface and compare its performance with that of uniform cross-section (UCS) microchannels structured surface and plane surface. All three surfaces have been fabricated on individual copper block with a foot print area of 10 × 10 mm2. Pool boiling experiments have been performed with these surfaces in atmospheric pressure condition using deionized water. Experiments have been performed for applied effective heat flux range of 0–200 W/cm2. Both the structured surfaces show better heat transfer performance compared to plane surface. It has been observed that SF structured surface shows a heat transfer improvement up to a factor of 3 times the heat transfer coefficient in plane surface whereas uniform UCS structured surface shows the improvement by a factor of 2 times the heat transfer coefficient in plane surface. Thus segmented finned microchannels structured configuration shows better heat transfer performance compared to other two surfaces. The reason behind the heat transfer improvement in SF configuration might be due to more number of active nucleation sites, better rewetting phenomenon and favorable bubble growth and release mechanism.

The growth of vapor bubbles in superheated liquids. report no. 26-6

Abstract: The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.

Review of High-Temperature Central Receiver Designs for Concentrating Solar Power

Abstract: This paper reviews central receiver designs for concentrating solar power applications with high-temperature power cycles Desired features include low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids that can withstand temperatures >650 °C, high solar absorptance, and low radiative and convective heat losses leading to a thermal efficiency >90% Different receiver designs are categorized and evaluated in this paper: (1) gas receivers, (2) liquid receivers, and (3) solid particle receivers For each design, the following information is provided: general principle and review of previous modeling and testing activities, expected outlet temperature and thermal efficiency, benefits, perceived challenges, and research needs Emerging receiver designs that can enable higher thermal-to-electric efficiencies (50% or higher) using advanced power cycles such as supercritical CO 2 closed-loop Brayton cycles include direct heating of CO 2 in tubular receiver designs (external or cavity) that can withstand high internal fluid pressures (~20 MPa) and temperatures (~700 °C) Indirect heating of other fluids and materials that can be stored at high temperatures such as advanced molten salts, liquid metals, or solid particles are also being pursued, but challenges include stability, heat loss, and the need for high-temperature heat exchangers

Applications of nanofluids in solar energy: A review of recent advances

Abstract: Solar energy systems (SESs) are considered as one of the most important alternatives to conventional fossil fuels, due to its ability to convert solar energy directly into heat and electricity without any negative environmental impact such as greenhouse gas emissions. Utilizing nanofluid as a potential heat transfer fluid with superior thermophysical properties is an effective method to enhance the thermal performance of solar energy systems. The purpose of this review paper is the investigation of the recent advances in the nanofluids’ applications in solar energy systems, i.e., solar collectors (SCs), photovoltaic/thermal (PV/T) systems, solar thermoelectric devices, solar water heaters, solar-geothermal combined cooling heating and power system (CCHP), evaporative cooling for greenhouses, and water desalination.

Towards hybrid nanofluids: Preparation, thermophysical properties, applications, and challenges

Abstract: The objective of compiling this study is to seek the attention of young scholars and experts working in the field of heat transfer by discussing the applications and challenges of hybrid nanofluids with a concise discussion on its history, synthesis techniques, thermophysical properties, research gaps, future directions, current status, and the leading groups, organizations, and countries around the world. Applications in different fields like solar energy, heat pipes, automotive industry, manufacturing industry, heat exchangers, cooling of electronic equipment's etc. have been reviewed and discussed in this study. Nanofluids are part of these inventions that possess the ability of uprising the field of heat transfer, but instead of its superior thermal, electrical, and optical properties, advancement in the form of hybrid nanofluids and a numerous study conducted around the world, investigators and manufacturers are still facing the problem of practicing nanofluids in heat transfer devices used commercially and even in an individual's life. This problem works like a magnet, capturing the attention of research societies working around the world by inspiring them to take control and lead this field to the destination of domestic and commercial implementation. With the help of this article, authors endeavored to identify some important work orientations and existing problems that interrupted its performance and implementation for the convenience of captivated scholars. The most recent research work has improved the thermophysical properties of nanofluids by introducing hybrid nanofluids, working on preparation techniques, and by adding the surfactants to improve its stability but still need a lot of attention for the development of correlations/models that can predict the thermophysical properties and heat transfer characteristics, to make it cost-effective, improve its stability, and finally its implementation.