A study was conducted to determine if nichrome resistance heating wire or stainless steel immersion heater is better for use to heat water in a boiler container. These two heaters were designed to provide power about 150W. 

Introduction

The aim of this analysis is to find which of the two conducting elements-Nichrome electric resistance heating wire or stainless steel is the best for using for boiling water. The goal is to get a product that a user could purchase that will enable them to boil the most of water quantity. 

Procedure

Information collected

The common material for immersion heaters was stainless steel. Nichrome is also a common heating material that is used in the applications including toasters and hair dryers.  

These materials were selected as possible raw materials for using as heating elements. Information on the physical and thermal characteristics of the materials was collected. The basic concepts of heat transfer given by Frank Incropera and David P. DeWitt were utilized for equation references for temperature distributions and heat conduction study to the surrounding water. 

Assumptions and Limitations

The major assumption is that the heat transfer is conducted in ideal conditions and the measurements will not be adjusted for losses that have occurred. Since the study is comparing outcomes and not finding the specific values, it is not a significant issue. The heating materials were also considered to be uniform throughout the heater. Some heaters use steel or copper for heating however it is not considered in this analysis. The thermal conductivity also varies with the increasing temperature, but here it is assumed constant. This data was for temperature between 0oC to 100oC. 

Variables:

Design variables:  Nichrome resistance heating wire or stainless steel material, radius, extent of heater exposed to water or air, power supply, size of tube.

State variables:Thermal conductivity, water temperature, current, voltage, resistivity, density, specific heat, cost, length, magnitude of water, heat supplied 

Heating materials: Nichrome and stainless steel were the significant variables.

The radius, still a variable was decided on what is available to purchase. The analysis must be enabled to find a useful heating material and designing one that doesn’t waste work. It was decided that the study would be for a heater completely submerged in the water. For maximum heat production, power supply was kept at the constant value of 144W that is the highest power rating for considered generator. 

Constraints: The highest resistivity provided by water is 30 ohms, highest current is 3A and voltage is 48 V,initial water temperature is 20oC, highest water temperature is its boiling temperature, time given for heating is 1 hour, maximum magnitude of water is 500 mL.  

Merit: Temperature distribution of water at specific time intervals, wire temperature context to time, boiling heat transfer rate, and water evaporation rate.  

Analysis:

Temperature decreases with increase in radius. Although, this reduction is less than one degree for bothNichrome resistance heating wire and Stainless steel. Therefore, these are good conductors and one cannot be selected over another on the base of this factor.  

Without any external heat transfer, Nichrome wire will become much hotter than Stainless steel. It seems Nichrome is a better option for the required heating element. Although, stainless steel also could become very hot, hence more factors should be evaluated.

In this study heating element was considered as a center point. It shows the water temperature increases adequately and confirms that water boiling is feasible with both of the heating elements as the power supply is same. It does also not help in deciding which element is better.

The water boiling behavior of Nichrome resistance heating wire and stainless steel is helpful in understanding the various kinds of boiling occurring under the various temperature limits. In 1930, Nukiyama evaluated these dissimilar regimes. It was performed by passing current through Nichrome wire in the saturated water. Upon exceeding the heat flux in the wire, it burned out. But since, Nichrome is cheaper and easily replaceable; it is popularly used, although in the sense of reliability of product, Stainless steel is an ideal heating element.  

The ultimate results from the water evaporation rate make it clear that the stainless steel immersion heater is an ideal choice.

Conclusion:

Minor difference in the temperature distributions from stainless steel and nichrome resistance heating wire is noticed. It leads to a conclusion that one of the heating elements is an acceptable option. Nichrome wire is an attractive choice for its cheaper rate and easier installation in the bottom of boiler to increase the area covered with water. Although, the burnout risk in this wire is a serious limitation. It appears to describe that stainless steel immersion heaters are an ideal choice. The boiling heat transfer rates and water evaporation rates persuade to prefer the stainless steel wire for immersion heater that is costlier but provides better performance.