119. Gravity flooded evaporators have greater heat transfer capability than dry expansion evaporators of the same size and surface area because:

a. They are completely filled with liquid

b. more of the heat transfer surface is wetted.

c. vapor is flowing at a higher velocity

d. there is more evaporator surface.

b. More of the heat transfer surface is wetted 7-1

120. The gravity flooded evaporator, in some applications, can have a higher recirculation ratio than forced liquid overfeed systems because of

a. the accumulator.

b. pumped flow

c. no expansion valve.

d. thermosiphon action.

d. thermosiphon action. 7-4

121. Oil should be drained from a gravity flooded ammonia system evap

a. at the low point in the evap

b. at the highest point in the evap

c. to prevent increased heat transfer

d. gravity flooded systems do not require manual oil draining

a. at the low point in the evap 7-2

123. Excess oil in the lowside of a gravity flooded ammonia refrigerant system accumulates

a. in the suction accumulator

b. below the refrigerant

c. near the top of the refrigerant level.

d. excess oil does not accumulate in the lowside of a gravity flooded ammonia system

b. Below the refrigerant 7-7

124. Excess oil in the lowside of a gravity flooded halocarbon refrigerant system accumulates

a. in the suction accumulator

b. below the refrigerant

c. near the top of the refrigerant level.

d. excess oil does not accumulate in the lowside of a gravity flooded ammonia system

c. near the top of the refrigerant level 7-7

125. Why is there more space in the top of the surge drum than is needed for the operation of the evap?

a. to allow surplus refrigerant to accumulate so convection can circulate the refrigerant

b. the space is needed to reduce the velocity of the vapor for liquid separation.

c. the area allows the vapor to become slightly superheated

d. to allow laminar flow of refrigerant to occur.

b. the space is needed to reduce the velocity of the vapor for liquid separation. 7-2

126. When can a separation header be eliminated from a gravity flooded chiller?

a. separation headers are not required

b. Separation headers can be eliminated from a gravity flooded chiller when a suction line accumulator is used.

c. Separation headers can be eliminated from a gravity flooded chiller in small systems

d. Separation headers can be eliminated from a gravity flooded chiller when the shell is oversized

d. Separation headers can be eliminated from a gravity flooded chiller when the shell is oversized 7-6

127. What determines the selection of a gravity flooded vs dry expansion systems?

a. required operating temp

b. economics based on an analysis by a design engineer

c. system size

d. airflow requirements

b. economics based on an analysis by a design engineer 7-2

128. What causes liquid circulation through a gravity flooded evaporator?

a. the difference in refrigerant densities between the surge drum and the evap heat transfer surfaces

b. a pump

c. the higher pressure in the surge drum forces the refrigerant downward and into the evaporator

d. superheat

a. the difference in refrigerant densities between the surge drum and the evap heat transfer surfaces 7-4

129. What happens to un-evaporated liquid that circulates through a gravity flooded evaporator?

a. it returns to the evaporator through the defrost bypass line.

b. the liquid is pumped back to the receiver.

c. the receiver is isolated and the liquid is returned to the evaporator feed line.

d. the liquid flows to the surge drum and is returned to the evaporator.

d. the liquid flows to the surge drum and is returned to the evaporator. 7-2, 4

130. A gravity flooded shell and tube product chiller

a. usually has refrigerant in the shell

b. usually has the refrigerant in the tubes

c. has refrigerant in the shell and the tubes

d. is more efficient with the refrigerant in the tubes

a. usually has refrigerant in the shell 7-6

131. As the load decreases on a gravity flooded evaporator, the amount of liquid in the heat exchange circuits

a. does not change

b. increases

c. decreases

d. decreases by 1/2

b. increases 7-10, 11

132. Having a DX evaporator and a gravity flooded evap of the same size and surface area, why is capacity better for a gravity flooded evap than in a dry expansion evap?

a. Gravity flooded evaps are made from larger tubing than dry expansion evaps

b. gravity flooded evaps have greater wetted refrigerant surfaces.

c. gravity flooded evaps have more fins per inch

d.gravity flooded evaps operate at lower temps

b. gravity flooded evaps have greater wetted refrigerant surfaces. 7-2

133. What are the two main components used in a gravity flooded evap design not employed in a typical dry expansion evap system?

a. two speed fans and water defrost

b. a thermostatic expansion valve and a low temp cutout

c. a surge vessel and liquid level control device

d. fan shutters and 24v control

c. a surge vessel and liquid level control device 7-2

134. The vapor leaving the surge drum on a gravity flooded evap operating at design conditions is

a. called wet suction

b. superheated.

c. subcooled

d. saturated

d. saturated 7-2

135. Where should oil be drained from in a halocarbon gravity flooded system?

a. the bottom of the receiver

b. the bottom of the low pressure accumulator

c. the return line from the evap to the surge drum

d. oil is skimmed off the surface of the liquid

d. oil is skimmed off the surface of the liquid 7-7

136. What controls the recirc ratio on a grav flooded evap?

a. the setting of the hand exp valve

b. the boiling action within the evap

c. the back pressure regulator

d. gravity flooded evaps do not have recirc ratios.

b. the boiling action within the evap 7-4

137. What is the maximum recirc ratio for a gravity flooded evap referenced in the text?

a. 3:1

b. 4:1

c. 16:1

d. Gravity flooded evaps do not have recirc ratios

c. 16:1 7-4

138. What happens to flash gas in a gravity flooded evap system?

a. it goes directly to the evap

b. it goes through the surge drum to the compressor

c. there is no flash gas in a gravity flooded evap system

d. it is used to power the pmper drum

b. it goes through the surge drum to the compressor 7-4

139. In regard to oil accumulation in the evaps:

a. oil should be removed because it interferes with the ability of the refrigerant to exchange heat at the surface of the evap tube.

b. oil is desirable in the evap because it has a better heat transfer co-efficient

c. oil accumulation in the evap improves defrost characteristics.

d. oil normally does not accumulate in the evaps

a. oil should be removed because it interferes with the ability of the refrigerant to exchange heat at the surface of the evap tube. 7-7

140. How much superheat is found at the outlet of a surge drum of a properly operating gravity flooded system?

a. 5F per pound of refrigerant

b. 5C per pound of refrigerant

c. 10F

d. there is generally no superheat

d. there is generally no superheat 7-2

141. Which evap type would see a greater liquid refrigerant flow rate for the same refrigeration capacity?

a. dry exp under heavy heat load

b. gravity flooded under heavy heat load

c. dry exp under light heat load

d. gravity flooded under light heat load.

b. gravity flooded under heavy heat load 7-4

142. Oil return from an R-22 system low temp vessel is:

a. easy because oil vaporizes

b. drained from the bottom of the unit

c. recovered by special features in the low side vessels

d. recovered by gravity flow.

c. recovered by special features in the low side vessels. 7-7

143. What would be a service problem if ammonia type intercoolers are used in an R-22 system?

a. oil must be drained from the bottom on a regular basis.

b. oil might accumulate in the intercooler since there are no skimmer ports in an ammonia intercooler

c. Oil will return to the compressor wit no problem

d. there will be no service problems if they are the same pressure rating.

b. oil might accumulate in the intercooler since there are no skimmer ports in an ammonia intercooler 7-7