[CMCET 330] - Mechanical Systems (Chp. 1)

Latent heat

Latent heat is the release or storage of heat associated with change in phase of a substance, without a change in the substance's temperature. It is the "hidden" quantity of heat absorbed or released when a material changes phase without a change in temperature.

Power

Power is defined as the measure of energy consumed over a period of time. When energy is extracted, converted into a useful form, and used in an application, power is the result. The unit used to define power in the customary system is Btu per hour (Btu/hr). For brevity, it is sometimes written as Btu/hr (or MBH for thousand Btu per hour and MMBH for million Btu per hour). The amount of energy used to fuel a furnace at its maximum firing capacity (usually for a period of one hour) is its input power rating (e.g., the power rating of an appliance that can deliver 100 000 Btu in an hour is 100 MBH).

What is Specific heat (c)

Specific heat (c) is defined scientifically as the amount of heat that must be added or removed from one pound of substance to change its temperature by one degree. The unit of specific heat in the engineering system is Btu per pound per degree temperature change (Btu/lb °F) or Joules per pound per degree temperature change (J/kg °C).

What is specific heat capacity

Specific heat capacity (C) is defined as the amount of heat required to change the temperature of a specific volume of substance one degree. The property of specific heat capacity of a substance is measured in Btu per cubic foot per degree temperature change (Btu/ft3 °F).

Absolute zero = ____________ degrees F

-459.67

Quantity of heat (Q)

is measured in British thermal units and joules. In scientific terms, the British thermal unit (Btu) is defined as the amount of heat required to raise the temperature of 1 lb (0.45 kg) of water from 59.5°F (15.3°C) to 60.5°F (15.8°C) at constant pressure of standard atmosphere pressure.

The ________________________ of a space is a measure of the combined effects of the temperatures of surfaces within that space

mean radiant temperature (MRT)

This __________________ heating process involves adding heat to air without changing its moisture content

sensible

Heat

the agitation or motion of atoms and molecules. It is thermal energy in motion. Heat always flows from a substance at a higher temperature to the substance at a lower temperature, raising the temperature of the lower temperature substance and lowering the temperature of the higher temperature substance.

Sensible heat

the heat associated with change in temperature of a substance. It appears that the addition or removal of heat from a substance changes its temperature in proportion to the heat added or removed; that is, as heat is added to a substance its temperature typically increases, and when heat is removed the temperature of the substance typically decreases. This phenomenon is referred to as sensible heating . It is "sensible" because it can be observed by the sense of touch.

The human body is constantly generating heat through metabolic activity. The average adult, when sleeping, generates about _________ Btu/hr (73 W) and about ___________ Btu/hr (120 W) when awake but sedentary

250, 400

Water freezes at _______, and boils at ________ degrees F

32, 212

ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy, specifies combinations of indoor space environmental and personal factors that will produce thermal environmental conditions where _________________% of the occupants do not express dissatisfaction with the room conditions;

80%

1 Joule =

= 0.00095 Btu = 0.239 calories (c)

1 kilocalorie (C) =

= 1000 calories

1 Btu =

= 1055 joules (J) = 0.293 watt-hour (W-hr) = 252 calories (c) = 0.252 kilocalories (C)

1 watt-hour (W-hr) =

= 3.413 Btu

Temperature (T)

the measure of the average kinetic energy associated with the chaotic microscopic motion of atoms and molecules within a substance. It is the measure of the intensity of the heat.

The term_______________________is used to describe the effect of the combination of low temperature and air movement in outdoor environments

wind chill factor

_______________________________ is the temperature of the air/water-vapor mixture when it is fully saturated (100% relative humidity).

Dew point (or saturation) temperature (DPT)

______________________________ is the temperature of the mixture of air and moisture at rest. It is measured with a common thermometer

Dry bulb temperature (DBT)

_____________________is the quantity of heat contained in air under specific psychrometric conditions

Enthalpy (h)

_____________ is the release or storage of heat associated with change in phase of a substance, without a change in the substance's temperature

Latent heat

______________ is defined as the amount of heat required to raise the temperature of 1 lb (0.45 kg) of water from 59.5°F (15.3°C) to 60.5°F (15.8°C) at constant pressure of standard atmosphere pressure

Mass Density

_____________ is defined scientifically as the amount of heat that must be added or removed from one pound of substance to change its temperature by one degree

Specific heat (c)

_________________________ is the ratio of water vapor to the total mass of moist air (including water vapor and dry air)

Specific humidity

__________________________ is a ratio of unit volume of dry air per unit weight of dry air, expressed in cubic feet of air per pound of dry air (ft3 /lb) or cubic meters of air per kilogram of dry air (m3 /kg). It is the inverse of density

Specific volume (v)

______________ is the measure of the average kinetic energy associated with the chaotic microscopic motion of atoms and molecules within a substance

Temperature

______________________ is the ratio of the mass of water vapor to the total volume of the sample.

Absolute humidity (or water vapor density)

By definition, thermal comfort is a condition of mind that expresses satisfaction with the thermal environment; it requires subjective evaluation. Defined by. _____________________________

ASHRAE Standard 55-2004

_________________ air, is air found in the atmosphere, is a mixture of several constituent gases, water vapor, and contaminants such as dust, pollen, and smoke. It consists of nitrogen, oxygen, and other trace gases

Atmospheric

________________ is defined as the amount of heat required to raise the temperature of 1 lb (0.45 kg) of water from 59.5°F (15.3°C) to 60.5°F (15.8°C) at constant pressure of standard atmosphere pressure

British thermal unit (BTU)

____________________________is the ratio of the mass of water vapor (Mw) to the mass of dry air (Ma) contained in a sample of air: W = Mw/Ma.

Humidity ratio (W)

A __________________________ is a graphical representation of the thermodynamic properties of moist air.

Psychrometric chart

______ is the study of the thermodynamic properties of gas-water vapor mixtures under varying temperatures and pressures.

Psychrometrics

____________________________ can be thought of as a ratio of moisture present in the air to the maximum amount of moisture it could hold at the same temperature and pressure (when fully saturated).

Relative humidity (RH)

______________air, is air that contains the maximum amount of moisture it can hold at that temperature.

Saturated

_______________ is the heat associated with change in temperature of a substance. Not change in state.

Sensible heat

What is mass density (p)

The mass per unit volume. Density is expressed in units of pounds per cubic foot (lb/ft3) or kilograms per cubic meter (kg/m3).

(True or false) The rate of air movement has a significant bearing on the sensation of freshness and thermal comfort.

True

(True or false) Thermal comfort means different things to different people because individuals have different thermal preferences and sensitivities.

True

____________________________ is the temperature measured by a thermometer with a wetted cloth sock covering its bulb as fast-moving air passes across it.

Wet bulb temperature (WBT)

thermometer

an instrument that measures the temperature of a body or substance in a quantitative way

• With a decrease in air pressure, density of air _________________. Similarly, with an increase in air pressure, density __________________. • As the temperature of air decreases, density of air _____________________. Likewise, as the temperature of air increases, air density_______________.

decreases, increases, decreases, increases