Boiling heat transfer is known for high heat fluxes at relatively small temperature differences. However, over the decades, technological innovations have demanded further augmentation in heat fluxes associated with boiling. Among the various active and passive methods, use of ultrasonic waves in boiling liquid has emerged as a proven technique for the required heat transfer improvement as demonstrated by a number of researchers. The present article reviews the application of ultrasonic waves in enhancing the heat transfer in various regimes of pool boiling. It has been found that the use of ultrasonic field is more promising in case of sub-cooled boiling as compared to saturated condition. Along with ultrasonic field of lower frequency and higher power, the usage of various passive techniques of surface improvement such as micro channel, surface topology, nano coatings etc. leads to further augmentation of heat transfer. Also, the relative placement of heating surface in ultrasonic wave field must be considered inevitably while designing an ultrasonic field assisted pool boiling system. It requires further investigations to conduct more parametric studies such as effect of pressure along with the usage of ultrasonic waves during sub- cooled boiling. Also during ultrasonic assisted pool boiling, various nano fluids can be tested for improving the heat transfer characteristics particularly in the saturated nucleate boiling regime.
In this paper, emission and performance characteristics of diesel fuel-engine was investigated using blending of diesel with bio diesel under steady state. Rape-seed oil was used as biodiesel and blended in diesel with different proportions of 10%, 20% and 30% by volume. The engine used in experiment was single cylinder 4-stroke diesel fuel-engine having water cooling system. Result shows that BTE decreases with more addition of bio-diesel in % fraction. For 10% blend, BTE of engine is almost same compared to diesel. The emission characteristics were remarkably improved by increasing volume fraction of rape seed oil except NOx emission. NOx emission was found maximum for 30% diesel-bio diesel blend.
In present article, engine performance and emission characteristics were investigated with various blends of cotton-seed bio diesel and diesel. Reason to choose cotton seed bio diesel is its thermophysical properties which is identical with diesel. It also consists of higher oxygen content which directly improves combustion efficiency of the engine. Four Stroke, Single cylinder, diesel engine was tested under various blends consist of 5%, 10%, 15% and 20% (by Vol) of cotton seed biodiesel. Experimental results found no significant variation in brake thermal efficiency up to 10% biodiesel blend then it found to be dropped gradually. Brake thermal efficiency decreased by 12% at 20% biodiesel blend. CO & HC emissions exhibited decreasing trends with percentage increase in biodiesel concentration. Increase in NOx emission was insignificant up to 10% biodiesel blend. It can be further noted that 10% biodiesel diesel blend shows optimized performance and emission results.
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