DEVELOPMENT OF AN IMPROVED WHOLE BODY HEAT TRANSFER MODEL FOR DETERMINING TIME OF DEATH IN FORENSIC SCIENCE
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Date
2018-01-01
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Department
Mechanical Engineering
Program
Engineering, Mechanical
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Distribution Rights granted to UMBC by the author.
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Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan thorugh a local library, pending author/copyright holder's permission.
This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
Abstract
Estimating time of death is important for forensic science as it allows detectives to test an alibi to convict someone of a crime. The most commonly used method to estimate time of death consists of taking a temperature measurement at a body site and using a simple formula to calculate postmortem interval. Unfortunately, these formulas yield much error in the time of death estimation based on the one-size-fits-all approach. The goal of this research is to develop a whole body heat transfer model to improve the accuracy of estimating postmortem interval. A simulation of the steady state temperature profile of a realistic body model before death was conducted first. The thermal resistance of the clothing layer covering the body was estimated via an indirect method of adjusting the thermal conductivity of the clothing layer to ensure that the body had reached thermal equilibrium with its environment. Then, a transient simulation was conducted for a 24 hour time frame for which the body was lying on cement floor with or without carpet. In this study, we focused on temperature decays at the center of the head and center of the internal organs region. For practicality, a formula for the dimensionless temperature was proposed using a combination of two exponential functions with two time constants. The adjustable parameters in the formula were determined via curve fitting analysis with an R2 value over 0.999, leading to a fitting error of 2 minutes. The shorter time constant in the formula represents the initial temperature plateau duration, while the longer time constant relates to the measurement window before the temperature at the site approaches the environmental temperature. At the brain location, the plateau duration is approximately 1 hour, while the measurement window is approximately 10 hours. At the internal organs location, postmortem position and environmental temperature have significant effects on the cooling rate since they determine the thermal resistances of the clothing and that of floor materials. Due to the thermal resistance of the clothing layer and conduction resistance of carpet and cement on the floor, the cooling rate at the internal organs site is much smaller than that of the brain site, leading to a longer measurement window at the internal organs site varying from 19 hours to 40 hours. The slowest postmortem dimensionless temperature decay occurs in a 15�C environment with the body lying on cement floor with carpet, resulting in a measurement window of approximately 40 hours. Whereas, the fastest dimensionless temperature decay occurs when the air temperature is the highest at 30�C with the body lying on cement floor alone. In conclusion, the developed whole body heat transfer model greatly improves accuracy of modeling heat exchange between a body and its environment and the obtained formula of the dimensionless temperature can be used by detective at the scene to calculate the postmortem interval.